U.S. Department of the Interior

U.S. Fish and Wildlife Service

Pacific Remote Islands Marine National Monument

Palmyra Atoll National Wildlife Refuge

300 Ala Moana Boulevard, Suite 5-231

Box 50167

Honolulu, HI 96850

http://www.fws.gov

May 2011
FINAL ENVIRONMENTAL IMPACT STATEMENT

Palmyra Atoll National Wildlife Refuge Rat Eradication Project

U.S. Department of the Interior

Fish and Wildlife Service

Prepared by: 

Pacific Region

Portland, Oregon

May 2011
 

Palmyra Atoll National Wildlife Refuge Rat Eradication Project – FINAL Environmental Impact Statement -- May 2011 

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Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement i

Executive Summary

The U.S. Fish and Wildlife Service (Service) is proposing to restore and protect the native 

species and habitats of Palmyra Atoll National Wildlife Refuge by eradicating all nonnative rats 

(Rattus rattus) from the atoll through the successful delivery of a lethal dose of toxicant to every 

rodent on the island in a manner that minimizes harm to the ecosystem while still maintaining a 

high probability of success. This Final Environmental Impact Statement (FEIS or Final EIS) is 

the final analysis for this action and identifies the preferred alternative (Alternative C) as the 

option that would achieve the desired outcomes with the least harm to the environment.

Modifications (greater than a few words) to the DEIS are italicized in the Final EIS.

Eradicating rats from Palmyra is expected to result in obvious, empirically tested biodiversity 

benefits for seabirds, plants, terrestrial invertebrates, and other components of the atoll‟s 

terrestrial ecosystem. Eradicating rats will eliminate mammalian predation on existing seabird 

species breeding at the atoll and allow the recolonization of indigenous seabirds such as 

Audubon‟s shearwater, Christmas Island shearwater, wedge-tailed shearwater, Phoenix petrel, 

white-throated storm-petrel, Bulwer‟s petrel, blue noddy, and gray-backed tern that cannot 

reproduce on islands invaded by rats. The benefits of rat eradication will be greatest for nesting 

species. However, migratory shorebirds will also benefit, especially the bristle-thighed curlew. 

Predation around the world by introduced predators, such as dogs, cats, pigs and rats, is an 

important source of mortality for wintering curlews during the molt-induced flightless period. By 

removing the threat of rats, Palmyra‟s remnant native forest will be given the opportunity to 

recover to its natural species composition, structure, and function. Rats would be eliminated as 

an agent that prevents native tree recruitment by herbivory of seeds and seedlings. Ecological 

disruption by nonnative rats affects ecological function of the entire ecosystem, disrupting 

community relationships and biogeochemical cycles. The benefit of this conservation action is 

significant from a regional perspective because Palmyra is the only moist tropical atoll 

ecosystem in the Central Pacific with strong protections, as well as the only moist tropical atoll 

ecosystem in this region that is not experiencing exploitation of both marine and terrestrial 

natural resources by burgeoning human populations. From the regional perspective, removing 

rats from Palmyra will help prevent the loss of the Central Pacific moist tropical island ecotype.

Nationally, the eradication of black rats at Palmyra Atoll supports the Service‟s priority to 

facilitate ecological adaptation in the face of accelerating global climate change removing a nonclimate change ecosystem stressor in the relatively pristine Palmyra ecosystem. 

Palmyra Atoll National Wildlife Refuge is located in the Northern Line Islands, approximately 

1,000 miles south of Honolulu, Hawai`i, in the Central Pacific Ocean. The Refuge was 

established in 2001 to protect, restore, and enhance migratory birds, coral reefs, and threatened 

and endangered species in their natural setting and is managed in coordination with The Nature 

Conservancy who owns the largest island in the atoll and manages a preserve and research 

station there. Palmyra Atoll consists of approximately 25 small, heavily vegetated islets 

surrounding 3 central lagoons. Habitats consist of 618 acres of land and 15,512 acres of lagoons 

and shallow reefs. The Refuge‟s boundary extends seaward 12 nautical miles, encompassing 

515,232 acres. Palmyra‟s terrestrial habitats support one of the largest remaining tropical coastal 
 

Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement ii

strand forests in the U.S. Pacific Islands. A diverse land crab fauna including the coconut crab, 

ecologically intact predator-dominated fish assemblages, and large seabird populations are 

important resources of this Refuge. 

The original configuration of the atoll was significantly modified by the U.S. Navy during World 

War II. A network of roadways connecting the major islets and the construction of a north-south 

causeway altered natural water circulation. Invasive species are having negative impacts on 

Palmyra Atoll‟s native forests, fauna, and habitats. The major impacts on Palmyra are associated 

with World War II-era atoll restructuring and invasive species introductions that include plants 

(coconut palm, Cocos nucifera), insects (several ant species, mosquitoes, scale insects), and 

mammals (black rats, Rattus rattus). The black rat causes degradation of nearly all aspects of the 

atoll‟s terrestrial ecosystem from breeding seabird populations to the native Pisonia forest 

ecotype. Rats prey directly upon native seabirds and their eggs at Palmyra and are likely 

preventing the recolonization of eight additional seabird species indigenous to the area. Rats also 

prey on native land crabs and directly compete with them for food resources. Rats foraging on 

coconuts create habitat for invasive mosquitoes and disperse the seeds of invasive plants. These 

introduced rats are modifying the terrestrial ecosystem of this important atoll by limiting the 

reproduction, recruitment, and establishment of several native tree species through seed and 

seedling predation that is significantly more intense than seed and seedling predation by native 

land crabs. Furthermore, the coconut palm, an invasive tree, already dominates 45 percent of 

Palmyra‟s forests. The dominance of the coconut palm is likely aided by rat-related recruitment 

and limitation of native tree species, and the palm‟s ability to resist rat-related limitations to 

recruitment relative to that of native tree species. Left unchecked, the combined effects of rats 

and coconut palms could continue to alter forest structure and prevent the recovery of Palmyra‟s 

native forest. All of these impacts in turn affect the relationship between land and marine 

resources, and compromise the Service‟s ability to achieve Refuge purposes.

The National Wildlife Refuge System Administration Act of 1966 (Refuge Administration Act), 

as amended, requires all lands within the National Wildlife Refuge System to be managed in 

accordance with achieving the purposes for which a refuge was established. For Palmyra, the 

eradication of introduced rats would aid in achieving the following Refuge purposes. 

Perpetuate a functioning atoll ecosystem with natural diversity and abundance of fauna 

and flora.

Preserve, restore, and enhance all terrestrial species of animals and plants that are 

endangered or threatened with becoming endangered.

Provide for conservation of migratory bird resources at the Refuge.

Removing rats from Palmyra is the first step in a series of restoration efforts designed to restore 

the atoll to its pre-World War II status. Rat eradication is the first step in the process because the 

eradication of rodents is feasible and relatively quickly accomplished; and their removal would 

provide the framework to initiate the palm removal and native forest propagation stage of the 

restoration process, and allow extirpated breeding seabirds to recolonize the atoll.

We announced a Notice of Intent to prepare an Environmental Impact Statement on January 14, 

2010. The action alternatives were developed to focus on the primary issues identified by 
 

Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement iii

resource specialists within the Service, national and international experts in island rodent 

eradication, public comments received after the Notice of Intent to prepare an EIS was released, 

and government regulatory agencies that have a stake in the decision-making process. In order to 

be retained for consideration, an alternative had to: 1) have a high likelihood of success, 2) have 

an acceptably low probability for adverse effects on the populations of non-target species and the 

environment, and 3) be permitted under regulations governing the Refuge. The potential impacts 

of a No Action Alternative and the three “action” alternatives were assessed in the Draft 

Environmental Impact Statement (DEIS) and where appropriate, mitigation measures were 

identified to avoid the potential effect or reduce its intensity on non-target organisms. The DEIS 

was released for a 45-day public comment period from February 25, 2011 to April 11, 2011. 

Comments were received from 21 individuals, agencies, or organizations. The Service reviewed 

and considered all comments and determined whether or not they were substantive and 

warranted further analysis and documentation. Modifications (greater than a few words) to the 

DEIS are italicized in the Final EIS. Responses to those comments are included in Appendix M

and helped inform the final analysis in this FEIS. The Service has identified Alternative C as the 

Preferred Alternative.

The 4 alternatives are: 

Alternative A: No Action 

Alternative B: Aerial broadcast of brodifacoum 

Alternative C: Aerial broadcast of brodifacoum, with proactive mitigation of risk for 

vulnerable shorebird taxa – Preferred Alternative

Alternative D: Bait stations with brodifacoum, with canopy baiting

Alternatives C, the Preferred Alternative entails aerial bait broadcast that would be accomplished 

by applying bait pellets containing the anticoagulant rodenticide brodifacoum (0.0025% active 

ingredient) from a helicopter using a specialized bait bucket. The bucket would broadcast bait in 

at the appropriate rate in a directional manner to deliver the material to all potential rat territories 

within a short operational period. Special measures to prevent the bait from entering the water 

include hand broadcast of narrow strands and tiny islands and baiting the canopy trees that 

overhang the water using bait packets installed by hand. Alternative C – our Preferred 

Alternative – proposes additional management of migratory birds in an effort to minimize the 

risk of exposure to the toxicant.

There would be some negative effects to migratory birds associated with the eradication 

program. However, the Preferred Alternative includes several measures to minimize these 

effects. Shorebirds would be the most vulnerable to direct and secondary poisoning during the 

eradication, so the eradication is scheduled to occur during the summer nesting season, when 

the number of migratory shorebirds is at its lowest (June-July). Not all shorebirds migrate to the 

nesting grounds in the Arctic and we plan to capture as many of the remaining shorebirds as 

possible and hold them under direct, constant veterinary care during the period when they would 
 

Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement iv

be vulnerable to primary or secondary poisoning. Regular surveys of the island would be 

conducted and all carcasses that could potentially be a source of secondary poisoning would be 

removed. Color and size were considered when selecting the bait formulation to minimize the 

attractiveness of the bait to birds and minimize the time toxicant is available to birds. To 

minimize exposure potential to seabirds bait would be hand broadcast along the narrow 

causeways where the majority of the boobies nest, and this bait would not be distributed within 

reach of birds sitting in the nest. Areas known to host concentrations of shorebirds roosting 

would be baited using bait stations to further restrict bait availability.

The action alternative that involves bait stations as the primary bait delivery method (Alternative 

D) would require that bait stations containing bait pellets containing the anticoagulant 

rodenticide brodifacoum (0.0025% active ingredient) be placed throughout the entire atoll and 

maintained until all rats were removed (or two years). Bait stations are box-like enclosures with 

small entryways designed to be attractive to rodents, but difficult to navigate for other species 

such as birds and land crabs. Bait stations reduce the risk of rodenticide exposure in non-target 

species by making bait more difficult to access and reducing the total amount of bait introduced 

into the ecosystem. The bait station design for Palmyra would need to effectively exclude land 

crabs, including the large coconut crab, and shorebirds while allowing easy access for rats. 

Within this document, we provide a quantitative and qualitative assessment of the environmental 

consequences of all the alternatives. The potential significance of the environmental 

consequences (or “impacts”) of each action alternative and the no action alternative are discussed 

on a case-by-case basis for each environmental issue considered. The issues analyzed in this 

document include:

Impacts to physical resources

o Water resources

o Geology and soil

Impacts to biological resources

o Impacts to species vulnerable to toxicant use

o Impacts to species vulnerable to disturbance

o Indirect effects to biological resources

Impacts to the social and economic environment

o Impacts to refuge visitors and recreation

o Impacts to historical and cultural resources

Cumulative impacts

Irreversible or irretrievable commitment of resources

Relationship of short-term uses to long-term productivity
 

Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement v

Within the section on impacts to biological resources, we provide a quantitative assessment of 

the risk to the shorebird species found at Palmyra that would be incurred from the three action 

alternatives. Four species of shorebirds are expected to be common at Palmyra during the 

operational window (June through July): bristle-thighed curlew, Pacific golden-plover, 

wandering tattler, and ruddy turnstone. None of these species nest at Palmyra. The population 

densities of shorebirds at Palmyra (and on other tropical Pacific islands) are significantly lower 

during the summer breeding season (June through August) when breeding individuals are at their

northern breeding grounds. Some individuals of all four of the shorebirds mentioned above

would likely be present during the eradication, and could potentially be exposed to rodenticide 

through several pathways including: 

Feeding directly on bait pellet

Feeding on prey items that have consumed the bait or contaminated prey (e.g., land crabs, 

hermit crabs, rat carcasses)

Alternative C – Preferred Alternative includes measures to reduce risk to shorebirds that may be 

present during the operational period including the capture and captive holding of birds for a 

month until the availability of the toxicant in the environment was substantially diminished.

We also assess the risk to, or the impact on Palmyra‟s native biota that would be incurred from 

the no action alternative. The no action alternative would allow rat-related disturbance of 

Palmyra‟s migratory bird populations, land crab populations, and native forest system would 

continue. Furthermore, other efforts to restore Palmyra‟s terrestrial ecosystem would be hindered

by such impacts.

The FEIS includes a working-draft biosecurity plan to prevent re-infestation of nonnative rats 

and a draft monitoring plan to assess efficacy of the operation and the ecological effects, both 

beneficial and deleterious of an eradication operation at Palmyra. These appendices continue to 

evolve and are considered “working” documents. The FEIS also includes the results of numerous 

scientific investigations conducted at Palmyra to develop appropriate eradication methods and 

quantify ecological risk, the supplemental registered label for brodifacoum 25W, and the 

comments received during review period and the Service‟s response to those comments. A 

Record of Decision on this project shall be signed no sooner than 30 days after this document is 

noticed in the Federal Register. 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- A

1 Table of Contents

2

Executive Summary....................................................................................................................... i

1 Purpose and Need ................................................................................................................. 1

1.1 Introduction............................................................................................................................................1

1.2 Purpose of This Document...............................................................................................................1

1.2.1 Description of Palmyra Atoll......................................................................................................1

1.3 Purpose of the Proposed Action.....................................................................................................4

1.4 Need for Action......................................................................................................................................4

1.4.1 Background: The Problem of Introduced Rats on Islands...........................................6

1.4.2 Summary of Rat Impacts on the Palmyra Ecosystem.................................................. 10

1.5 Authority and Responsibility to Act ......................................................................................... 11

1.6 Scope of the Proposed Action....................................................................................................... 12

1.7 Environmental Issues Identified................................................................................................. 13

2 Alternatives.......................................................................................................................... 14

2.1 Introduction......................................................................................................................................... 14

2.1.1 Integrated Pest Management (IPM) .................................................................................... 15

2.2 Alternative A: No Action................................................................................................................ 16

2.3 Alternatives Considered and Dismissed from Detailed Analysis................................. 16

2.3.1 Rat Removal with the Goal of “Control”........................................................................... 16

2.3.2 Use of Disease ................................................................................................................................. 17

2.3.3 Trapping........................................................................................................................................... 17

2.3.4 Biological Control......................................................................................................................... 17

2.3.5 Fertility Control ............................................................................................................................ 17

2.3.6 Aerial Broadcast or Bait Stations with Diphacinone and Diphacinone-50 Bait 

Products........................................................................................................................................................... 18

2.3.7 Bait Broadcast Using Brodifacoum-25W at the Maximum Application Rate 

Allowed by the 2010 Product Use Label ........................................................................................... 25

2.3.8 Hand Broadcast of Brodifacoum-25W................................................................................ 25

2.3.9 Use of Other Toxicants............................................................................................................... 26

2.4 Features Common to All Action Alternatives....................................................................... 26

2.4.1 Introduction .................................................................................................................................... 26

2.4.2 Adaptive Management............................................................................................................... 27

2.4.3 Project Support Operations..................................................................................................... 27

2.4.4 Rodenticide...................................................................................................................................... 27

2.4.5 Protecting Cultural Resources................................................................................................ 27

2.4.6 Monitoring Eradication Efficacy and Ecosystem Response...................................... 28

2.4.7 Reducing Wildlife Disturbance .............................................................................................. 30

2.4.8 Public Information....................................................................................................................... 30

2.4.9 Timing Considerations............................................................................................................... 30

2.4.10 Equipment and Materials......................................................................................................... 31

2.4.11 Post-Bait Application Rodent Detection and Rodent Reintroduction Prevention 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- B

and Response................................................................................................................................................. 32

2.4.12 Aerial Broadcast Alternatives................................................................................................. 33

2.4.13 Applying Bait to the Forest Canopy..................................................................................... 33

2.5 Pre-Eradication Rodenticide Studies........................................................................................ 33

2.5.1 An Analysis of the Eradication Success of Brodifacoum-25W (Alternatives B, 

C, and D): an Anticoagulant Rodenticide Registered Under FIFRA .................................. 33

2.5.2 Preliminary Eradication Trials Conducted at Palmyra Atoll .................................. 37

2.5.3 Actions Taken to Develop the Action Alternatives Presented in 

this Document............................................................................................................................................... 47

2.6 Alternative B: Aerial Broadcast of Brodifacoum-25W.................................................... 48

2.6.1 Rationale........................................................................................................................................... 48

2.6.2 Summary of Bait Delivery Methods..................................................................................... 49

2.6.3 Timing and Weather ................................................................................................................... 49

2.6.4 Bait Application Plan.................................................................................................................. 49

2.7 Alternative C: Aerial Broadcast of Brodifacoum, with Proactive Mitigation of 

Risk for Vulnerable Shorebird Taxa – Preferred Alternative ....................................................... 60

2.7.1 Rationale........................................................................................................................................... 60

2.7.2 Taxa .................................................................................................................................................... 60

2.7.3 Proportion of Population that Would be Captured ...................................................... 61

2.7.4 Capture Method(s)....................................................................................................................... 62

2.7.5 Retain Captured Birds in On-Island Captive-Holding Facility or Transfer to 

Off-Island Location.................................................................................................................................... 62

2.7.6 Captive Bird Care ........................................................................................................................ 62

2.7.7 Aspects of Captive-Holding Facility..................................................................................... 62

2.7.8 Length of Time Held ................................................................................................................... 63

2.8 Alternative D: Bait Stations with Canopy Baiting of Brodifacoum-25W................ 63

2.8.1 Rationale........................................................................................................................................... 63

2.8.2 Summary of Bait Delivery Methods..................................................................................... 63

2.8.3 Monitoring for Eradication Success..................................................................................... 64

2.8.4 Timing/timing Considerations................................................................................................ 64

2.9 Effort and Estimated Costs............................................................................................................. 65

2.9.1 Aerial Bait Broadcast – Helicopter Flight Time............................................................. 65

2.9.2 Bait Stations and Canopy Baiting ......................................................................................... 65

3 Affected Environment ........................................................................................................ 68

3.1 Introduction......................................................................................................................................... 68

3.2 General Description of Palmyra ................................................................................................. 68

3.2.1 Geographical Setting................................................................................................................... 68

3.2.2 Size and Topography .................................................................................................................. 68

3.2.3 Climate .............................................................................................................................................. 69

3.2.4 Physical Resources....................................................................................................................... 71

3.2.5 Biological Resources.................................................................................................................... 72

3.2.6 Terrestrial Wildlife of Palmyra.............................................................................................. 81

3.2.7 Intertidal and Nearshore Ecosystems.................................................................................. 85

3.2.8 Terrestrial Vegetation ................................................................................................................ 90
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- C

3.2.9 Social and Economic Environment....................................................................................... 94

4 Environmental Consequences............................................................................................ 98

4.1 Purpose and Structure of Environmental Consequences................................................ 98

4.2 Environmental Issues Addressed ............................................................................................... 99

4.2.1 Scope for Environmental Issue............................................................................................... 99

4.2.2 Issues.................................................................................................................................................. 99

4.2.3 Aspects of Environment Excluded from Detailed Analysis (with Rationale)..100

4.3 Consequences: Physical Resources..........................................................................................100

4.3.1 Water Resources.........................................................................................................................100

4.3.2 Geology and Soils........................................................................................................................103

4.4 Consequences: Biological Resources.......................................................................................104

4.4.1 Introduction ..................................................................................................................................104

4.4.2 Assessing Significance of Impacts to Biological Resources......................................104

4.4.3 Impacts of Alternative A (No Action) on Biological Resources.............................108

4.4.4 Impacts of Action Alternatives (B, C, and D) on Biological Resources..............112

4.4.5 Indirect Impacts to Biological Resources.........................................................................157

4.5 Impacts to the Social and Economic Environment ..........................................................157

4.5.1 Eradication Personnel ..............................................................................................................157

4.5.2 Refuge Visitors and Recreation............................................................................................158

4.5.3 Historical and Cultural Resources......................................................................................159

4.6 Consequences: Cumulative Impacts.......................................................................................159

4.6.1 Assessing Cumulative Impacts.............................................................................................159

4.7 Irreversible and Irretrievable Impacts..................................................................................163

4.7.1 Alternative A – No Action.......................................................................................................163

4.7.2 Alternative B.................................................................................................................................164

4.7.3 Alternative C– Preferred Alternative ..................................................................................164

4.7.4 Alternative D.................................................................................................................................164

4.8 Short-term Uses and Long-term Productivity....................................................................164

5 Consultation and Coordination ....................................................................................... 165

5.1 Introduction.......................................................................................................................................165

5.2 Regulatory Framework.................................................................................................................165

5.3 Agency Scoping and Review.......................................................................................................166

5.4 Public Participation........................................................................................................................166

5.5 Preparers and Primary Contributors....................................................................................171

1

6 Literature Cited................................................................................................172

2

3

4

5

6

7

8
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- D

Appendices

Appendix A. Palmyra Atoll rainforest restoration project: rat eradication monitoring plan 

for all aerial broadcast alternatives (Working-draft)

Appendix B. Palmyra Atoll biosecurity plan: prevention of rodent incursion (Workingdraft)

Appendix C. Palmyra Atoll rat eradication assessment trip report 2004

Appendix D. Progress in Palmyra Atoll restoration: rat eradication trial 2005

Appendix E. Palmyra Atoll rat eradication: biomarker validation of an effective bait 

application rate, 19 June to 5 July, 2008

Appendix F. The ecotoxicology and palatability of two rodenticide bait products: fieldbased assessment at Palmyra Atoll

Appendix G. Palmyra Atoll rainforest restoration project: rat genetic sampling, detection 

method testing, and canopy bait testing

Appendix H. Summary of risks & potential mitigation options for bristle-thighed curlews 

(Numenius tahitiensis) at Palmyra Atoll during a rat eradication campaign

Appendix I. Hermit crab predation by bristle-thighed curlews

Appendix J.

Appendix K.

Appendix L

Appendix M

Palmyra food web

Draft operational details: Palmyra Atoll Rat Eradication– Alternative C 

(Preferred Alternative)

Brodifacoum-25w Conservation Label & Supplemental Labeling For 

Brodifacoum-25w Conservation To Control And Eradicate Black Rats

On Palmyra Atoll. U.S. EPA Registration No. 56228-36

Comments Received on Draft EIS and FWS Responses To Comments
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- E

List of Tables

Number Title Page

2.1 Known rat eradication attempts worldwide using diphacinone bait products. 21-22

2.2 LD50 values for Rattus sp. exposed to brodifacoum and diphacinone. 23

2.3 The composition of Brodifacoum-25W Conservation 34

2.4 Mean concentration of toxicant (ppm) within excrement samples from crabs 

that consumed 25W or D-50 bait pellets ad lib for 7 days

45

2.5 A record of bait broadcast-based rat eradications and studies to inform such 

rat eradications on tropical islands that have environmental factors that are 

similar to those found in Palmyra‟s eradication environment: climate, plant 

community, and land crab community. 

54

2.6 The minimum effort required to achieve the primary operational objectives 

for all three action alternatives.

66

2.7

2.8

Comparative summary of actions by alternative 

Budget Estimates for Treatment Options

67

67

3.1 Palmyra Atoll historical rainfall data in inches (1977 – 2009) 71

3.2 Breeding seabirds of Palmyra Atoll 74

3.3 Crab abundance survey results, Palmyra Atoll (Howald et al. 2004). Units 

represent #/hectare estimates

83

4.1 Acute toxicity of brodifacoum to shorebirds and seabirds at Palmyra Atoll. 117-119

4.2 Impacts of Alternative B on biological resources 137

4.3 Impacts of Alternative C on biological resources 147

4.4

4.5

Estimated populations of migratory birds at Palmyra Atoll and estimated 

take.

Impacts of Alternative D on biological resources

148

156
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- F

List of Figures

Title Page

2.1. Daily bait consumption estimates for the first “A” and second “B” bait 

applications on Home, Portsmouth, and Whippoorwill Islands. Mean bait 

consumption was measured by observing bait pellet removal from fixed 25 x 1 m 

plots: Home = 22 plots, Portsmouth = 7 plots, Whippoorwill = 18 plots. Error bars 

represent ± 1 standard error of the sample mean.

42

2.2. Mean concentration of brodifacoum (N=3 per day) and diphacinone (N=3 per 

day) found in surface samples of sandy soil and organic humus soil over four 

exposure periods. Samples were taken directly beneath bait pellets (or remains of 

pellets) on day 2 and day 7. Samples taken on days 28, 36, and 50 were taken 

directly beneath where a pellet had rested for 7 days. 

44

2.3. Comparison of the concentration (ppm) of brodifacoum in crab excrement and 

tissue over time to the concentration (ppm) of diphacinone in crab excrement

45

2.4. Onboard TracMap GPS used by a helicopter pilot to monitor and guide the aerial 

bait broadcast at Rat Island, 2008. 

50

2.5. Results from the bait consumption study conducted on Whippoorwill Island 

during the 2005 trail rat eradication at Palmyra (Buckelew et al. 2005). The 

vertical bars represent 99% confidence intervals for the mean consumption 

estimates, and show that in order to maintain bait availability for four days, the 

sowage rate should be between 60 and 90 kg/ha.

53

2.6. Bait broadcast application plan for eradicating rats from Palmyra Atoll. The 

treatment is scheduled for 2 days, and each day is divided into 6 sequential 

segments, with each segment representing a stand-alone area that would not need 

to be re-baited if the baiting operation is temporarily suspended (for up to 3 days). 

Different bait application methods (color coded in the figure) would be used to 

minimize bait spread into the marine environment.

56

2.7. Alternative C – Preferred Alternative -Placement of bait stations during the rat 

eradication at Palmyra Atoll.

59

2.8 The location of bristle-thighed curlew and Pacific golden-plover roosting sites 

(capture sites) and a possible location for the captive-holding facility on Cooper 

Island, Palmyra Atoll. For scale, the runway is one mile long.

62

2.9. Bait station transects spaced 50 m apart to allow for a 50 m x 25 m bait station 

grid at Palmyra Atoll. 

64

3.1. A map of the prominent forest types at Palmyra. The coconut palm canopy (dark 

green) is frequently used by rats and covers roughly 45 % of Palmyra‟s land area.

70
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- G

List of Acronyms

AM Adaptive Management

APHIS Animal and Plant Health Inspection Service

BTCU Bristle-thighed curlews

CEQ Council on Environmental Quality

CITES Convention on International Trade of Endangered Species

CSIRO Commonwealth Scientific and Industrial Research Organization

CWA Clean Water Act

DEIS Draft Environmental Impact Statement

EIS Environmental Impact Statement

EPA U.S. Environmental Protection Agency

ESA Endangered Species Act

FEIS

FIFRA

Final Environmental Impact Statement

Federal Insecticide, Fungicide, and Rodenticide Act

FWS U.S. Fish and Wildlife Service

GECI Island Conservation and Ecology Group, C.A. (Grupo de Ecología y 

Conservación de islas, A.C.)

GIS Geographic Information System

GPS Global Positioning System

IC Island Conservation

IPM Integrated Pest Management

ITCZ Inter-tropical Convergence Zone

IUCN International Union for Conservation of Nature

MBTA Migratory Bird Treaty Act

MMPA Marine Mammal Protection Act

NEPA National Environmental Policy Act

NHPA National Historic Preservation Act

NMFS National Marine Fisheries Service

NOAA National Oceanic and Atmospheric Administration

NOEL No Observed Effect Level

NPDES National Pollutant Discharge Elimination System

NWR National Wildlife Refuge

NWRSAA National Wildlife Refuge System Administration Act

OHA Office of Hawaiian Affairs

PARC Palmyra Atoll Research Consortium

PGPL Pacific golden-plovers

PIFSC Pacific Islands Fisheries Science Center

POBSP Pacific Ocean Biological Science Project

PPE Personal Protective Equipment

TNC The Nature Conservancy
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- H

USCG U.S. Coast Guard

USDA

USFWS

U.S. Department of Agriculture

U.S. Fish and Wildlife Service

EPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

UXO Unexploded Ordnances

WS USDA Wildlife Services

WWII World War II

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Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 1

1 1 Purpose and Need

2

3 1.1 Introduction

4 The United States Fish and Wildlife Service (“FWS” or “the Service”) proposes to undertake the 

5 following actions on Palmyra Atoll, managed as a nature preserve and as the Palmyra Atoll 

6 National Wildlife Refuge (“Refuge” or “Palmyra”) within the Pacific Remote Islands Marine 

7 National Monument:

8 Eradication of the nonnative black rat (Rattus rattus); and

9

10 Development of a prevention and emergency response plan for responding to 

11 reintroduction of rats, other nonnative rodents, and other nonnative animals to the atoll.

12

13 In accordance with the National Environmental Policy Act of 1969 as amended (NEPA) (42 

14 U.S.C. 4321 et seq.,), and the Council on Environmental Quality (CEQ) regulations for 

15 implementing NEPA (40 CFR 1500 et seq.), Federal agencies must consider the environmental 

16 impacts of actions – projects, programs, policies, or plans that are implemented, funded,

17 permitted, or controlled by a Federal agency or agencies – they propose to undertake. 

18 Specifically, Federal agencies must consider the environmental impacts of a reasonable range of 

19 alternatives for implementing an action and make the public aware of the environmental impacts 

20 of each of the alternatives presented. If adverse environmental impacts are identified, NEPA 

21 requires an agency to show evidence of its efforts to reduce these adverse impacts through 

22 mitigation. An environmental analysis, such as this Final Environmental Impact Statement 

23 (FEIS), documents that an agency has considered and addressed these impacts.

24

25 In the Draft Environmental Impact Statement (DEIS or Draft EIS), the Service solicited public 

26 involvement and assessed whether implementation of any of the alternatives would have a 

27 significant effect on the quality of the human environment. This Final (FEIS or Final EIS))

28 identifies the Preferred Alternative (Alternative C) and will be used by the Service to inform the 

29 public and constitutes our final assessment of effects on the quality of the human environment.

30 Modifications (greater than a few words) to the Draft EIS are italicized in the Final EIS.

31

32 1.2 Purpose of This Document

33 This Final EIS evaluates the environmental effects of proposed black rat eradication on the 

34 natural and cultural resources of Palmyra. It is part of the Service‟s decision making process in 

35 accordance with NEPA, as amended, and implementing regulations.

36

37 1.2.1 Description of Palmyra Atoll 

38 Located in the Northern Line Islands, approximately 1,000 miles south of Honolulu, Hawai`i, 

39 Palmyra Atoll is an incorporated territory of the United States in the Central Pacific Ocean. The 

40 atoll originally consisted of approximately 54 small, heavily vegetated islets surrounding 3 

41 central lagoons. Many of these islets were modified or joined during U.S. Navy occupation in 

42 World War II. On January 18, 2001, Secretary‟s Order 3224 established the area as the Palmyra 

43 Atoll National Wildlife Refuge to protect, restore, and enhance migratory birds, coral reefs, and 

44 threatened and endangered species in their natural setting. The Refuge now includes 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 2

1 approximately 446.25 acres (180.57 ha) of emergent land, approximately 503,963 acres (203,946

2 ha) of submerged lands and associated waters, including roughly 16,094 acres (6,515 ha) of coral 

3 reef habitat (Federal Register 2001).
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 3
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 4

1 Palmyra Atoll is currently owned and managed by the Service, The Nature Conservancy (TNC), 

2 and the Cooper family. The majority of the islands, waters, and the coral reef surrounding 

3 Palmyra up to 12 nautical miles to sea are owned and managed by the FWS as the Refuge for the 

4 “conservation and management of native species of wildlife and fish and their habitats” (Federal 

5 Register 2001). In 2000, TNC purchased Palmyra from the Fullard-Leo family to protect its 

6 waters and lands. Now TNC owns Cooper and Menge islands (TNC 2005) and cooperatively 

7 manages the atoll with FWS. The Cooper family has retained ownership of Home Island. 

8

9 Prior to 2001, Palmyra was a privately owned atoll with a history of military and other 

10 government use. In 2009, Presidential Proclamation 8336 included Palmyra Atoll NWR and its 

11 surrounding waters out to 50 nautical miles in the Pacific Remote Islands Marine National 

12 Monument.

13

14 Palmyra Atoll represents a globally important biodiversity center and conservation opportunity. 

15 It is the only fully protected moist tropical forest ecosystem in the Central Pacific. The atoll is 

16 replete with dense seabird colonies, a globally imperiled forest ecotype, native terrestrial flora 

17 and fauna, and relatively pristine predator-dominated coral reef communities. Palmyra‟s six 

18 species of land crabs make up one of the largest, richest, and most robust populations in the 

19 Central Pacific region. Notwithstanding the protective status, multiple pressures continue to 

20 threaten the native biota. Chief among these threats are an introduced, invasive rodent species –

21 the black rat (Rattus rattus). 

22

23 1.3 Purpose of the Proposed Action

24 The purpose of the proposed action is to aid the protection and restoration of the native species 

25 and habitats of Palmyra Atoll by eradicating all nonnative rats from the atoll by ensuring the 

26 successful delivery of a lethal dose of toxicant to every rodent on the island in a manner that 

27 minimizes harm to the ecosystem while still maintaining a high probability of success.

28

29 1.4 Need for Action

30 Palmyra is an important center of biodiversity and species abundance in the Central Pacific 

31 region. The atoll is the only seabird nesting habitat within 450,000 square miles of ocean and is 

32 an important marine feeding ground for seabirds. It is home to one of the largest red-footed 

33 booby populations in the world, ranking in global importance behind the Galapagos Islands 

34 (Flint 1992). Numerous shorebirds and other migrants forage and rest at Palmyra. The atoll 

35 supports one of the last remaining stands of Pisonia forest communities in the world and is home 

36 for a vibrant and diverse land crab assemblage, including the world‟s largest land invertebrate: 

37 the coconut crab. In the surrounding waters, the Refuge coral reefs are home to five times as 

38 many coral species as the Florida Keys and three times as any as Hawai`i and the Caribbean, 

39 ranking it as one of the most diverse and spectacular coral reef systems in the world. 

40

41 No baseline record of Palmyra‟s terrestrial ecosystem prior to the 19th century exists. It is 

42 possible, however, that Polynesian voyagers altered Palmyra‟s environment prior to European 

43 exploration of the Pacific by introducing coconuts (Cocos nucifera). During World War II the 

44 original configuration of the atoll was significantly modified by the U.S. Navy when a network 

45 of roadways connecting the major islets and the construction of a north-south causeway altered 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 5

1 natural water circulation. The pace of anthropogenic impacts accelerated during and after World 

2 War II with introductions of additional plants, terrestrial arthropods, and mammals. Rats were 

3 likely introduced to the atoll during this period. The introduced rats are now severely degrading 

4 the terrestrial ecosystem of this important atoll by limiting the reproduction, recruitment, and 

5 establishment of several native tree species. Furthermore, the coconut palm, an invasive tree, 

6 already dominates 45 percent of Palmyra's forests. The spread of coconut palm is believed to be 

7 aided by rat-related recruitment and limitation of other tree species. Left unchecked, the 

8 combined effects of rats and coconut palms drastically alter forest structure. Introduced rats on 

9 islands are also known to prey heavily on seabirds, which is likely preventing eight seabird 

10 species from successfully nesting on the atoll. The rats also prey on native land crabs and 

11 directly compete with them for limited food resources. All of these impacts in turn affect the 

12 relationship between land and marine resources, and compromise the Service's ability to achieve 

13 Refuge purposes. 

14

15 Rats have likely contributed to the extirpation of as many as eight seabird species from Palmyra: 

16 Audubon‟s shearwater (Puffinus lherminieri), Christmas Island shearwater (Puffinus nativitatis) 

17 wedge-tailed shearwater (Puffinus pacificus), Phoenix petrel (Pterodroma alba), white-throated 

18 storm-petrel (Nesofregetta fuliginosa), Bulwer‟s petrel (Bulweria bulwerii), blue noddy 

19 (Procelsterna cerulea), and gray-backed tern (Onychoprion lunatus). These are species that are 

20 known to not coexist with introduced predators of the size of rats or larger (Flint 1999). While no 

21 historical or paleontological records are found for Palmyra, there is evidence of the Pacific 

22 faunal assemblages prior to the introduction mammalian predators such as rats in Hawai`i, the 

23 Cook Islands, Easter Island, the Marquesas, Tonga, the Pitcairn Group, and the Northern 

24 Marianas. These studies document that islands with introduced mammals including rats have lost 

25 large components of their original seabird fauna. The global patterns of seabird distributions we 

26 observe today are not natural (Steadman 1995). (Jones et al. 2008) found that rats depress many 

27 similar bird taxa and that rats are likely preventing them from nesting at Palmyra. Many seabird 

28 species are found regionally, but are not breeding at Palmyra. Species known to nest at adjacent 

29 rat-free islands or islands in the Line archipelago (Kiritimati Island, Republic of Kiribati) 

30 typically nest on the ground, and some (the shearwaters and petrels) characteristically leave eggs 

31 and chicks unattended in nesting burrows. Black rats would effectively prevent the 

32 establishment, or reestablishment of breeding populations of any of these species (Norman 

33 1975).

34

35 Small, oceanic islands have simplified seed dispersal systems that generally lack mammalian 

36 vectors and are vulnerable to disruption by invasive species (Drake et al. 2002). Rats can disrupt 

37 seed dispersal mutualisms by depositing seeds in microhabitats that are ill-suited for germination 

38 or subsequent growth. Native crab species prey on seeds as well, although they only eat the 

39 fleshy pulp, leaving the seed coat intact, allowing the seed to germinate. Rats are able to 

40 consume the fleshy pulp and chew through the seed coat killing the existing seed and preventing 

41 germination and recruitment of native plants. It is possible that rats can also indirectly reduce 

42 plant fitness by reducing the effectiveness or numbers of native dispersers through competition 

43 and predation (Wegmann 2009). As there is no mention of rodents in accounts of Palmyra‟s biota 

44 prior to World War II (Rock 1916, Christophersen 1927, Rock 1929), it is theorized black rats 

45 (Rattus rattus) were introduced to Palmyra during U.S. military operations in the 1940s. 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 6

1 There is good evidence that the introduction of black rats and possible introduction and recorded 

2 cultivation of coconuts limits the reproduction, recruitment, and establishment of several native 

3 tree species at Palmyra. The introduction of both coconuts and rats led to a change in plant4 animal interactions and canopy dynamics that favor coconut establishment over that of native 

5 tree species. The coconut palm, an invasive tree dominating 45 percent of Palmyra‟s forests 

6 (Wegmann 2005) is possibly aided by rat-related recruitment limitation of other tree species. 

7 Furthermore, tree-nesting seabirds exhibit a strong preference for native tree canopy over 

8 coconut canopy as nesting habitat (Young et al. 2010).

9

10 Most of Palmyra‟s ten native tree species are locally rare and show limited or no recruitment 

11 (Wegmann 2009). In order to initiate the restoration of Palmyra‟s rainforest and protect the 

12 species found there in, it is desirable to eradicate rats. Left unchecked, the combined effects of 

13 rats and coconuts could lead to an invasion-caused meltdown (Simberloff and B. Von Holle 

14 1999) of native forest structure and a transition to a coconut monoculture. The seabird 

15 communities at Palmyra show preference to nesting in native forests as opposed to stands of 

16 coconuts. Sea birds are a critical link between the marine and terrestrial environments, a 

17 relationship clearly seen at Palmyra. These bird species are known to feed over thousands of 

18 square kilometers of ocean but are dependent on small isolated islands for safe breeding. 

19 Foraging in the pelagic environment, sea birds transport critical marine nutrients back to the 

20 atoll, depositing nutrients in the form of guano as they roost and breed in native forests. This 

21 influx of nutrients fuels the growth of native forests. Introduced rats have been shown to have 

22 detrimental impacts on ground nesting sea birds, preying on eggs and chicks. The detrimental 

23 impacts of rat on native forest recruitment and breeding sea birds, negatively affects the crucial 

24 link and nutrient cycling between marine and terrestrial environments, resulting in a break down 

25 in community and ecosystem functioning. To restore Palmyra‟s forest to a natural state where 

26 crabs encourage native tree recruitment through dispersal without recruitment-limiting seed 

27 predation, rats must be completely removed from the atoll.

28

29 This project to implement eradication of black rats at Palmyra Atoll is consistent with the 

30 Service‟s 2010 Rising to the Urgent Challenge: Strategic Plan for Responding to Accelerating 

31 Climate Change (FWS 2010c). This project identifies a number of objectives that will move us 

32 toward the priority of Adaptation – to plan and deliver management actions to help reduce the 

33 impacts of climate change on fish, wildlife, and their habitats. Rat eradication will facilitate 

34 system resilience by reducing a non-climate-change ecosystem stressor. It will promote habitat 

35 connectivity and improve genetic resources by adding to the total area of safe habitats for 

36 vulnerable species. It will restore key ecological processes such as seed dispersal and nutrient 

37 cycling, and reduce nonnative pests and pathogens.

38 

39 1.4.1 Background: The Problem of Introduced Rats on Islands

40 The Importance of Island Ecosystems

41 It is widely accepted that the natural world is currently facing a particularly high rate of species 

42 extinction (Raup 1988); most recent extinctions can be directly attributed to human activity 

43 (Diamond 1989); and that for ethical, cultural, aesthetic, and economic reasons, this current rate 

44 of extinction is cause for considerable concern (Ehrlich 1988, Ledec and Goodland 1988). One 

45 of the major worldwide causes of anthropogenic extinctions is the introduction of nonnative 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 7

1 species. Introduced species are responsible for 39 percent of all recorded animal extinctions since 

2 1600 for which a cause could be attributed (World Conservation Monitoring Center 1992).

3

4 Island ecosystems are key areas for conservation of global biological diversity. While islands 

5 make up only about 3 percent of the earth‟s surface, they are home to 15 – 20 percent of all plant, 

6 reptile, and bird species (Whittaker 1998). Small population sizes and limited habitat availability 

7 make species endemic to islands especially vulnerable to extinction and their adaptation to 

8 isolated environments makes them especially vulnerable to aggressive introduced species 

9 (Diamond 1985, Diamond 1989, Olson 1989). Of the 484 recorded animal species extinctions 

10 since 1600, 75 percent were species endemic to islands (World Conservation Monitoring Center 

11 1992). 

12

13 Islands are high-value targets for conserving biodiversity because a large percentage of their 

14 biota consists of endemic species and subspecies with small populations, which makes them 

15 particularly extinction-prone. In addition, islands are crucial habitat for animals such as seabirds 

16 and turtles, which feed over thousands of square kilometers of ocean but are dependent on small 

17 isolated islands for safe breeding. Protection of these animals at their island breeding sites may 

18 be easier and more cost-effective than protecting them from threats at sea (such as plastics 

19 pollution and accidental or deliberate entanglement in fishing tackle), which could affect them 

20 anywhere along their travels (Wilcox and Donlan 2007). Finally, many smaller islands are 

21 sparsely inhabited or uninhabited by humans, keeping the socioeconomic costs of protection 

22 relatively low.

23

24 Impacts of Rats on Island Ecosystems

25 The impacts from invasive predatory mammals are one of the leading causes of species 

26 extinction on islands (Blackburn et al. 2004, Duncan and Blackburn 2007). Rats living in close 

27 association, or commensally, with humans ( Norway rat, Rattus norvegicus; black rat, R. rattus; 

28 and Polynesian rat, R. exulans) have been introduced to about 90 percent of the world‟s islands 

29 and have a pronounced effect on island ecosystems (Towns et al. 2006). In addition, the 

30 extinction of many island species of mammal, bird, reptile, and invertebrate have been attributed 

31 to the impacts of invasive rats (Andrews 1909, Daniel and Williams 1984, Meads et al. 1984, 

32 Atkinson 1985, Tomich 1986, Hutton et al. 2007), and estimates of 40 – 60 percent of all 

33 recorded bird and reptile extinctions globally were directly attributable to invasive rats (Atkinson 

34 1985) (Island Conservation analysis of World Conservation Monitoring Centre data). 

35

36 Even if species are not extirpated, rats can have negative direct and indirect effects on native 

37 species and ecosystem functions. For example, a comparisons of rat-infested and rat-free islands, 

38 and pre- and post-rat eradication experiments have shown that rats depressed the population size 

39 and recruitment of birds (Campbell 1991, Thibault 1995, Jouventin et al. 2003), reptiles 

40 (Whitaker 1973, Bullock 1986, Towns 1991, Cree et al. 1995), plants (Pye et al. 1999), and 

41 terrestrial invertebrates (Bremner et al. 1984, Campbell et al. 1984). In particular, rats have 

42 significant impacts on seabirds, preying upon eggs, chicks, and adults and causing population 

43 declines, with the most severe impacts on burrow-nesting seabirds (Atkinson 1985, Towns et al. 

44 2006, Jones et al. 2008). The introduction of rats on Midway Atoll during 1943 decreased 

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 8

1 seabird populations there and caused the extinction of the Laysan rail and Laysan finch (Fisher 

2 and Baldwin 1946).

3

4 In addition to preying on seabirds, introduced rats feed opportunistically on plants, and alter the 

5 flora communities of island ecosystems (Campbell and Atkinson 2002); in some cases degrading 

6 the quality of nesting habitat for birds that depend on the vegetation. On Tiritiri Matangi Island, 

7 New Zealand, ripe fruits, seeds, and understory vegetation underwent significant increases after 

8 rats were eradicated from the island, indicating the rats‟ previous impacts on the vegetation 

9 (Graham and Veitch 2002).

10

11 Rats are documented to affect the abundance and age structure of intertidal invertebrates directly 

12 (Navarrete and Castilla 1993), indirectly affect species richness and abundance of a range of 

13 invertebrates (Towns et al. 2009), and contribute to the decline of endemic land snails in Hawai`i 

14 (Hadfield et al. 1993), Japan (Chiba 2010), and American Samoa (Cowie 2001).

15

16 There is also increasing evidence that rats alter key ecosystem properties. For example, total soil 

17 carbon, nitrogen, phosphorous, mineral nitrogen, marine-derived nitrogen, and pH are lower on 

18 rat-invaded islands relative to rat-free islands (Fukami et al. 2006). In rocky intertidal habitats, 

19 invasive rats affected invertebrate and marine algal abundance, changing intertidal community 

20 structure from an algae-dominated system to an invertebrate dominated system (Kurle et al. 

21 2008). Such changes led to indirect negative effects of rats causing a reduction in seabird 

22 populations and predation by rats often drives seabird colonies to near-extirpation (Moller 1983, 

23 Atkinson 1985, McChesney and Tershy 1998). This predation further leads to the loss of seabird24 derived nutrients on islands (Fukami et al. 2006). Where rats co-exist with other predators (such 

25 as cats or predatory birds) the collective direct effect of introduced predators on seabirds is 

26 greater than the sum of the individual impacts because rats also act as a food resource to higher 

27 level predators when seabirds are absent from the islands (Moors and Atkinson 1984, Atkinson 

28 1985).

29

30 Given the widespread successful colonization of rats on islands and their effect on native species, 

31 rats are identified as key species for eradication (Howald et al. 2007) by many managers of 

32 island wildlife.

33

34 Eradication of Rodents from Islands

35 The first successful rodent eradication was in 1951 on Rouzic Island in France (Lorvelec and 

36 Pascal 2005). Through the 1970s and 1980s, New Zealand biologists developed the methodology 

37 for systematic rodent eradication techniques and successfully eradicated rats from several small 

38 islands (Moors 1985, Thomas and Taylor 2002). Building on these successes, and with the 

39 application of new strategies and research to monitor the campaigns, rats were eradicated from 

40 increasingly larger islands culminating in Campbell Island in 2002 (11,300 ha), the largest island 

41 to date from which rats have been completed eradicated (Taylor and Thomas 1989, Taylor and 

42 Thomas 1993, Cromarty et al. 2002, Morris 2002, Clout and Russell 2006). The successful 

43 eradication of rats on Midway Atoll in the 1990s has had significant positive impacts on small 

44 nesting seabirds such as Bonin petrels and storm-petrels (Rauzon 2007).
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 9

1 As of this writing, more than 332 successful rodent eradications have been completed on 284 

2 islands in 18 countries, totaling over 47,628 ha (Howald et al. 2007). The fundamental 

3 methodology that all but one of these eradications used was the delivery of bait containing a 

4 rodenticide into every potential rodent territory on the island. Bait was typically delivered during 

5 a time of year when rats were relatively food deprived, as indicated by annual resource6 dependent population declines. Depending on island topography and size, climate, native species 

7 assemblages, operational logistics and other factors, these eradication projects applied bait using 

8 either bait stations, broadcast, or both. Bait stations were typically laid out on a grid pattern. Bait 

9 broadcast could be delivered by hand or by using spreaders suspended under a helicopter 

10 (Howald et al. 2007).

11

12 Benefits of Rat Eradication Worldwide

13 The global conservation benefits of these rat eradications include increases in abundance and 

14 population parameters of a variety of taxa including seabirds, landbirds, reptiles, mammals, and 

15 plants, as well as overall ecosystem recovery. Owing to the well-documented effect of rats on 

16 seabirds (Jones et al. 2008), removal of rats almost automatically provides protection for existing 

17 seabird colonies. In Western Mexico, the eradication of black rats from 5 islands resulted in the 

18 protection of 46 seabird populations (Aguirre-Muñoz et al. 2008). Direct benefits to breeding 

19 seabirds have also been reported, including an increase in nest site occupancy, nesting attempts, 

20 hatching success, and reduced nest depredation (Jouventin et al. 2003, Whitworth et al. 2005, 

21 Smith et al. 2006, Amaral et al. 2010). At Midway Atoll National Wildlife Refuge, Bonin petrel 

22 populations increased from fewer than 5,000 nesting pairs in the 1980s to over 135,000 pairs in 

23 2008 subsequent to eradication of rats in 1997 (Pyle and Pyle 2009, FWS 2010a) Change in 

24 productivity was the most commonly reported demographic response in bird populations after rat 

25 eradication in a review by Lavers et al. (2010). They found that productivity increased by 25.3 

26 percent in 112 studies of 87 species. Increases in native land birds after rat eradication have also 

27 been reported. In New Zealand, the abundance of 4 species of native landbirds increased between 

28 10 and 178 percent during the 3 years after rat eradication (Graham and Veitch 2002), and 

29 endemic species have even recolonized islands after local extirpation by rats (Barker et al. 2005, 

30 Ortiz-Catedral et al. 2009). Also in New Zealand, rodent eradication has been used to restore 

31 endemic and native reptile populations. By 1998, rodents had been removed from 25 islands 

32 providing measurable or potential benefits for Tuatara (Sphenodon sp.), 2 species of Naultinus

33 geckos, 6 species of Hoplodactylus geckos, 5 species of Cyclodina skinks, and 7 species of 

34 Oligosoma skinks (Towns 1994, Cree et al. 1995, Towns et al. 2007). Island-dwelling mammals 

35 have also benefited from rodent eradication, including an endemic deer mouse in California 

36 (Howald et al. 2010) and 2 species of shrew in France (Pascal et al. 2005). At the ecosystem37 level, indigenous forest restoration has been documented as a result of substantial increase in the 

38 number of shrub and tree seedlings after Norway rat eradication (Allen et al. 1994). 

39

40 In addition to direct biological diversity benefits, rat eradications have been carried out to create 

41 rat-free refuges for native and endemic fauna and flora that are at risk from rat impacts elsewhere 

42 in their range. By 2003, rodents had been eradicated from more than 90 offshore islands in New 

43 Zealand, allowing for the translocation of native birds, reptiles, amphibians, and invertebrates to 

44 these predator-free refuges (Towns and Broome 2003). 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 10

1

2 1.4.2 Summary of Rat Impacts on the Palmyra Ecosystem

3 Invasive species are having negative impacts on Palmyra Atoll‟s native forests, fauna, and 

4 habitats. The major impacts on Palmyra are associated with World War II-era atoll restructuring 

5 and invasive species introductions that included plants (coconut palm, Cocos nucifera), insects 

6 (several ant species, mosquitoes, scale insects), and mammals (black rats). The black rat causes 

7 degradation of nearly all aspects of the atoll‟s ecosystems, from breeding seabirds to the native 

8 Pisonia ecosystem. Rats compete for food with land crabs, prevent nesting of at least eight 

9 seabird species, provide habitat for invasive mosquitoes, and spread the seeds of invasive flora 

10 throughout the atoll. 

11

12 Throughout the last 200 years, since Polynesian and Western discovery, Palmyra has 

13 experienced major habitat manipulation and numerous plant and animal invasions, including the 

14 introduction of black rats. The black rat is a common invader of island ecosystems throughout 

15 the world (Campbell and Atkinson 2002, Towns et al. 2006). This species is known to prey on 

16 seabird eggs and chicks, diminishing reproduction and changing population dynamics (Jones et 

17 al. 2008). Comparisons to similar islands nearby (Flint et al. 1996, Spennemann 1998, Rauzon 

18 and Wegmann 2004), and the composition of the seabird community observed in the immediate 

19 region, indicate that rats are likely the primary limiting factor preventing at minimum eight 

20 seabird species from successfully nesting on the atoll: Audubon‟s shearwater (Puffinus 

21 lherminieri), Christmas Island shearwater (Puffinus nativitatis) wedge-tailed shearwater 

22 (Puffinus pacificus), Phoenix petrel (Pterodroma alba), white-throated storm-petrel 

23 (Nesofregetta fuliginosa), Bulwer‟s petrel (Bulweria bulwerii), blue noddy (Procelsterna 

24 cerulea), and gray-backed tern (Onychoprion lunatus). 

25

26 Rats prey on native land crabs and directly compete with them for food resources (Wegmann 

27 2009). Rats also limit the reproduction, recruitment, and establishment of several native tree 

28 species. Small, oceanic islands have simplified seed dispersal systems that generally lack 

29 mammalian vectors (Carlquist 1967), and thus are vulnerable to disruption by invasive species 

30 (Drake et al. 2002). Invasive animal species can disrupt seed dispersal mutualisms (Bond 1994, 

31 Compton and McCormack 1999) by depositing seeds in microhabitats that are ill-suited for 

32 germination or subsequent growth (Zettler et al. 2001, Traveset and Richardson 2006), and by 

33 destroying the seed coat of native seeds, preventing germination and propagation. In many island 

34 systems, both land crabs and introduced rats are known seed dispersers (Fall et al. 1971, Lee 

35 1985, O'Dowd and Lake 1991, Sherman 2002, Lindquist and Carroll 2004, Fall et al. 2007). 

36 Where land crabs aid in dispersal of native seeds, subsequently increasing recruitment of native 

37 tree species, rats have a detrimental effect, killing seeds before they germinates. Furthermore, the 

38 coconut palm, an invasive tree dominating 45 percent of Palmyra‟s forested area, is aided by rat39 related recruitment limitation of other tree species. In Palmyra rats have been shown to 

40 preferentially prey on native seeds and seedlings, allowing for the spread of coconut palms 

41 throughout the atoll. If left unchecked, the combined effects of rats and coconut palms could lead 

42 to an invasive meltdown of native forest structures forcing the transition to a forest community 

43 dominated by a single invasive tree – namely, the coconut palm (Wegmann 2009, Young et al. 

44 2010).
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 11

1 Benefits of Rat Eradication to the Palmyra Ecosystem

2 Removing rats from Palmyra is the first step in a series of restoration efforts designed to restore 

3 the atoll to its pre-World War II status. Rat eradication is the first step in the process because the 

4 eradication of rodents is relatively simple and fast; their removal will slow the spread of invasive 

5 coconut palms, allow extirpated breeding seabirds to recolonize the atoll, and provide the 

6 framework to initiate the palm removal stage of the restoration process. Additionally, rats out7 compete native fauna for resources and provide habitat for other invasive species to invade 

8 Palmyra. By removing rats, we are removing non-climate-related impacts to the species and 

9 habitats and enhancing the resistance of the ecosystem to global perturbations from accelerating 

10 climate change.

11

12 Eradicating rats from Palmyra is expected to result in obvious, empirically tested biodiversity 

13 benefits for seabirds, plants, terrestrial invertebrates, and other components of the atoll‟s 

14 terrestrial ecosystem. By removing the threat of rats, Palmyra‟s remnant native forest and the 

15 extant and likely extirpated seabird species will be given the opportunity to recover. The benefit 

16 of this conservation action is significant from a regional perspective because Palmyra is the only 

17 moist tropical atoll ecosystem in the Central Pacific that is entirely protected, as well as the only 

18 atoll ecosystem in this region that is not experiencing exploitation of both marine and terrestrial 

19 natural resources by burgeoning human populations. From the regional perspective, removing 

20 rats from Palmyra will help prevent the loss of the Central Pacific moist tropical island ecotype 

21 and improve the adaptability of the system to global climate threats.

22

23 1.5 Authority and Responsibility to Act

24 The eradication of nonnative rats from Palmyra Atoll is authorized and in many cases mandated 

25 by several Federal laws requiring FWS resource managers to conserve and restore wildlife and 

26 habitats under their jurisdiction.

27

28 The U.S. Fish and Wildlife Service‟s mission is to work with others to “conserve, protect and 

29 enhance fish, wildlife, and plants and their habitats for the continuing benefit of the American 

30 people.” The threat that introduced species pose to habitat and native wildlife makes addressing 

31 their impacts one of the Service‟s top management priorities. Lessening or eliminating the 

32 impacts of introduced species on Palmyra is essential to the Service‟s management strategy for 

33 the island.

34

35 The Fish and Wildlife Act of 1956 (16 U.S.C. 742a-742j, not including 742 d-l, 70 Stat. 1119), 

36 as amended, gives general guidance requiring the Secretary of the Interior to take steps "required 

37 for the development, management, advancement, conservation, and protection of fish and 

38 wildlife resources."

39

40 The National Wildlife Refuge System Administration Act of 1966 (Refuge Administration 

41 Act), as amended (16 U.S.C. 668dd-ee), established the unifying mission of the National 

42 Wildlife Refuge System “to administer a national network of lands and waters for the 

43 conservation, management, and where appropriate, restoration of the fish, wildlife, and plant 

44 resources and their habitats within the United States for the benefit of present and future 

45 generations of Americans.” Among other mandates, the Refuge Administration Act requires the 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 12

1 Service to provide for the conservation of fish, wildlife, and plants, and their habitats within the 

2 System; and to ensure that the biological integrity, diversity, and environmental health of the 

3 System are maintained. The National Wildlife Refuge System Improvement Act of 1997, which 

4 amended the Refuge Administration Act, serves as an “Organic Act” for the Refuge System and 

5 provides comprehensive legislation on how the Refuge System should be managed and used by 

6 the public. The act clearly establishes that wildlife conservation is the singular Refuge System 

7 mission, provides guidance to the Secretary of the Interior for management of the System, 

8 provides a mechanism for refuge planning, and gives refuge managers uniform direction and 

9 procedures for making decisions regarding wildlife conservation and uses of the System.

10

11 The Endangered Species Act of 1973 (ESA) (16 U.S.C. 1531-1544, 87 Stat. 884), as amended, 

12 directs the Service to conserve ecosystems upon which threatened and endangered species 

13 depend.

14

15 The FWS policy for maintaining biological integrity and diversity and environmental health

16 (601 Fish and Wildlife Manual 3, 2001), directs Refuges to “prevent the introduction of invasive 

17 species, detect and control populations of invasive species, and provide for restoration of native 

18 species and habitat conditions in invaded ecosystems.” Furthermore, 601 FW 3 further directs 

19 refuge managers to “develop integrated pest management strategies that incorporate the most 

20 effective combination of mechanical, chemical, biological, and cultural controls while 

21 considering the effects on environmental health.”

22

23 Presidential Executive Order 13112 on Invasive Species (February 3, 1999): Section 2(a)(2), on 

24 Federal agency duties, states: “Each Federal agency whose actions may affect the status of 

25 invasive species shall, to the extent practicable and permitted by law, subject to the availability 

26 of appropriations, and within Administration budgetary limits, use relevant programs and 

27 authorities to: (i) prevent the introduction of invasive species; (ii) detect and respond rapidly to 

28 and control populations of such species in a cost-effective and environmentally sound manner; 

29 (iii) monitor invasive species populations accurately and reliably; (iv) provide for restoration of 

30 native species and habitat conditions in ecosystems that have been invaded; (v) conduct research 

31 on invasive species and develop technologies to prevent introduction and provide for 

32 environmentally sound control of invasive species; and (vi) promote public education on 

33 invasive species and the means to address them.”

34

35 Executive Order 13112 defines “invasive species” as “an alien species [a species that is not 

36 native with respect to a particular ecosystem] whose introduction does or is likely to cause 

37 economic or environmental harm or harm to human health.”

38

39 1.6 Scope of the Proposed Action

40 This Final EIS has been developed in accordance with the National Environmental Policy Act. 

41 Its purpose is to inform decision makers and the public of the likely environmental consequences 

42 of the action alternatives. This FEIS identifies, documents, and evaluates the effects of the 

43 proposed action: to aid the protection and restoration of the native species and habitats of 

44 Palmyra Atoll, U.S.A. by removing nonnative rats from the atoll that harm populations of native 

45 trees, nesting seabirds, and land crabs. 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 13

1 The FEIS is composed of four alternatives. The alternatives are described in Chapter 2. 

2 Other actions that may occur in the future as a result of any of the various actions being 

3 implemented will not be analyzed in detail in this document. The potential implications of the 

4 various alternatives in relation to future actions will be discussed in the Cumulative Impacts 

5 sections of the Environmental Consequences section (Chapter 4). Comments received during a 

6 45-day public comment period are in Appendix M, along with Service responses to the 

7 substantive comments.

8

9 An interdisciplinary team of environmental scientists and other specialists has analyzed the 

10 proposed action in light of existing conditions and has identified relevant effects associated with 

11 implementing the Proposed Action compared to the No Action alternative. 

12

13 1.7 Environmental Issues Identified

14 Section 1501.7 of the CEQ guidelines for NEPA requires that agencies implement a scoping 

15 process to determine the range of issues to be addressed in an environmental impacts analysis, as 

16 well as identify the major environmental issues related to the proposed action that need to be 

17 analyzed in the environmental consequences section. The scoping process included research in 

18 published and unpublished literature, consultations with experts on the ecology of Palmyra, in 

19 nonnative species eradication, with relevant government agencies, and with the public through an 

20 open comment period. More details on the Service‟s scoping process conducted for this Final

21 EIS is described in Chapter 5. During the scoping process, the Service identified the major 

22 environmental issues, or “impact topics,” that are described below. These issues guided the 

23 development of the alternatives, and the scope and content of the environmental impacts analysis 

24 found in Chapter 4.

25

26 Physical Resources

27 Subtopic: Impacts to water resources

28 Because the proposed action includes the delivery of a toxicant into the Palmyra environment, 

29 the potential impacts of the toxicant to local water quality was identified as an important 

30 environmental issue.

31

32 Subtopic: Impacts to geology and soils

33 Because the proposed action includes delivery of a toxicant into the Palmyra environment, the 

34 potential for transfer and persistence of the toxicant in soils was identified as an important 

35 environmental issue.

36

37 Biological Resources

38 Subtopic: Nontarget impacts from toxicant use

39 Rat eradication would include the use of a toxicant that is lethal to rats and other nontarget

40 species. Toxicants should only be used in the environment if the behavior of that toxicant can be 

41 predicted with some accuracy. The effect of the toxicant to species other than rats and the 

42 persistence of the toxicant in the environment are important environmental issues that must be 

43 analyzed further because animals other than rats, including birds, could ingest the toxicant 

44 through primary or secondary pathways.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 14

1

2 Subtopic: Disturbance to sensitive species

3 Similar to most other oceanic islands, Palmyra provides crucial habitat for species such as 

4 seabirds and marine turtles that are especially sensitive to disturbance. The risk of disturbance to 

5 sensitive species from the proposed action is an important environmental issue particularly 

6 because of Palmyra‟s importance as a breeding and overwintering environment for seabirds and 

7 shorebirds.

8

9 Social and Economic Environment

10 Sub-topic: Impacts to Refuge visitors and recreation

11 Due to its remote location and difficulty to access, there are very few visitors to Palmyra. FWS 

12 manages the limited visitation to protect the Refuge‟s sensitive biological resources and to 

13 enhance species‟ survival throughout their entire range. However, the biological resources found 

14 on or near Palmyra are important for wildlife enthusiasts who do visit the nearshore waters 

15 around Palmyra. Recreational boaters use the marine region surrounding the atoll for wildlife16 dependent recreational wildlife observation through snorkeling and scuba diving, as well as 

17 recreational fishing. Finally, a small number of FWS and TNC personnel, contractors, and 

18 visiting researchers reside at the atoll throughout the year.

19

20 Subtopic: Impacts to historical and cultural resources

21 The effect of the action on historical structures and artifacts at Palmyra is an important 

22 environmental issue.

23

24 2 Alternatives

25

26 2.1 Introduction

27 As part of the analytical process mandated by NEPA, section 102(2)(E) requires all Federal 

28 agencies to “study, develop, and describe appropriate alternatives to recommended courses of 

29 action in any proposal which involves unresolved conflicts concerning alternative uses of 

30 available resources.” Based upon the existing site conditions, need for action and constraints and 

31 concerns identified during the initial scoping process, four alternatives were identified: three 

32 action alternatives (Alternatives B-D), and the No Action Alternative (Alternative A). The No 

33 Action Alternative is included in NEPA analysis to provide a benchmark with which to compare 

34 the magnitude of environmental effects of the action alternatives. The No Action Alternative 

35 describes the Service‟s current management regime on Palmyra Atoll with regard to the rat 

36 population and its impacts to the island ecosystem. The Service has identified Alternative C as 

37 the Preferred Alternative for the Final EIS.

38

39 The action alternatives were developed to focus on the primary issues identified by resource 

40 specialists within the Service, experts in island rodent eradication, and government regulatory 

41 agencies that have a stake in the decision making process. All individuals, agencies, and 

42 organizations that provided substantive input regarding the proposed action are listed in Chapter 

43 5. In order to be retained for consideration, an alternative had to: 1) have a high likelihood of 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 15

1 success, 2) have an acceptably low probability for adverse effects on the populations of nontarget

2 species and the environment, and 3) be permitted under regulations governing the Refuge. The 

3 alternatives are:

4 Alternative A: No Action 

5

6 Alternative B: Aerial broadcast of brodifacoum 

7

8 Alternative C: Aerial broadcast of brodifacoum, with proactive mitigation of risk for 

9 vulnerable shorebird taxa

10

11 Alternative D: Bait stations with brodifacoum, with canopy baiting

12

13 2.1.1 Integrated Pest Management (IPM)

14

15 In accordance with the Interior Departmental Manual policy, 517 DM 1 and FWS Manual policy, 

16 569 FW 1, an integrated pest management (IPM) approach would be used, where practicable, to 

17 eradicate, control, or contain pest and invasive species (herein collectively referred to as pests) 

18 on refuge lands. Integrated Pest Management would involve using methods based upon 

19 effectiveness, cost, and minimal ecological disruption, which considers minimum potential 

20 effects to nontarget species and the refuge environment. Pesticides may be used where physical, 

21 cultural, and biological methods or combinations thereof, are impractical or incapable of 

22 providing adequate control, eradication, or containment. If a pesticide would be needed on refuge 

23 lands, the most specific (selective) chemical available for the target species would be used unless 

24 considerations of persistence or other environmental and/or biotic hazards would preclude it. In 

25 accordance with 517 DM 1, pesticide usage would be further restricted because only pesticides 

26 registered with the U.S. Environmental Protection Agency (USEPA or EPA) in full compliance 

27 with the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and as provided in 

28 regulations, orders, or permits issued by EPA may be applied on lands and waters under refuge 

29 jurisdiction.

30

31 Environmental harm by pest species would refer to a biologically substantial decrease in 

32 environmental quality as indicated by a variety of potential factors including declines in native 

33 species populations or communities, degraded habitat quality or long-term habitat loss, and/or 

34 altered ecological processes. Environmental harm may be a result of direct effects of pests on 

35 native species including preying and feeding on them; causing or vectoring diseases; preventing 

36 them from reproducing or killing their young; outcompeting them for food, nutrients, light, nest 

37 sites or other vital resources; or hybridizing with them so frequently that within a few 

38 generations, few if any truly native individuals remain. Environmental harm can also be the 

39 result of an indirect effect of pest species. For example, decreased waterfowl use may result from 

40 invasive plant infestations reducing the availability and/or abundance of native wetland plants 

41 that provide forage during the winter. 

42

43 Environmental harm may involve detrimental changes in ecological processes. For example, 

44 extirpation of seabird populations on islands by introduced rodents reduces the rate of nutrient 

45 flow in the form of guano from the pelagic zone to the island and surrounding reefs. This change 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 16

1 in nutrient regime in turn, favors different coral reef species and modifies communities. 

2 Environmental harm may also cause or be associated with economic losses and damage to 

3 human, plant, and animal health. For example, invasions by fire-promoting grasses that alter 

4 entire plant and animal communities, eliminating or sharply reducing populations of many native 

5 plant and animal species can also greatly increase fire-fighting costs.

6

7 A number of action alternatives that were evaluated as part of using the IPM approach and 

8 subsequently dismissed from detailed consideration are also described, and a rationale for their 

9 dismissal is given (Section 2.3).

10

11 2.2 Alternative A: No Action

12 Analysis of the no action alternative is required under NEPA. Under the no action alternative, the 

13 island‟s rat population would not be subject to any targeted management actions. Rat 

14 management currently consists of trapping rats for human health and safety around human use 

15 areas on Cooper Island, including the TNC galley and camp area, workshop, and laboratory. 

16 There are currently no other activities taking place at Palmyra with respect to rat control. Other 

17 ongoing invasive species management programs at Palmyra would continue based on previous 

18 agency decisions. Furthermore, any other related programs or projects decided and implemented 

19 under different authority, now or in the future, would also continue. 

20

21 Taking no action to address the effects of rats would be contrary to the purposes of the Refuge. 

22 It would also be contrary to the mission of the National Wildlife Refuge System, which is to 

23 administer a national network of lands and waters for the conservation, management, and where 

24 appropriate, restoration of the fish, wildlife, and plant resources and their habitats within the 

25 United States for the benefit of present and future generations of Americans. Furthermore, taking 

26 no action would be contrary to the FWS policy on maintaining the biological integrity, diversity, 

27 and environmental health of the National Wildlife Refuge System.

28

29 2.3 Alternatives Considered and Dismissed from Detailed Analysis

30

31 2.3.1 Rat Removal with the Goal of “Control”

32 The net conservation gain achieved by successful rat control (i.e., reducing and maintaining rat 

33 populations at extremely low levels) compared to complete eradication could be similar. 

34 However, the risks to nontarget wildlife from control operations are greater than the risks from 

35 an eradication operation due to the indefinite timeline for which a control operation must be 

36 continued. Long-term bait presence and repeated disturbances from control operations puts 

37 nontarget wildlife at constant risk. In addition, should scheduled control operations be 

38 interrupted, rats could quickly reproduce and rapidly repopulate the island, thereby achieving 

39 former population sizes and requiring an intensification of control operations once more. The 

40 constant maintenance of an ecologically beneficial rat control program (i.e. control of island41 wide rat populations to levels low enough to eliminate them as an ecosystem threat) would be far 

42 less cost-effective, increase personnel safety risks, and would not result in the permanent 

43 conservation benefits of entire-island eradication. It is thus disqualified from detailed 

44 consideration.

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 17

1 2.3.2 Use of Disease

2 While there is ongoing research focused on the development of taxon-specific diseases that can 

3 control populations of nonnative species (such as by the Australian agency Commonwealth 

4 Scientific and Industrial Research Organization (CSIRO), 

5 www.cse.csiro.au/research/rodents/publications.htm), there are no pathogens with proven 

6 efficacy at eradicating rodents (Howald et al. 2007). Even a highly lethal rat-specific pathogen 

7 would be ineffective at eradicating rats from Palmyra because if the rat population rapidly 

8 declined, transmission rates of the introduced pathogen would also decline so as to be ineffective 

9 in eradicating the few remaining individuals. Furthermore, the introduction of novel pathogens 

10 into the environment carries tremendous potential risks to nontarget species. Therefore, the use 

11 of pathogens is disqualified from detailed consideration.

12

13 2.3.3 Trapping

14 This alternative would call for the use of live traps and/or lethal (“snap”) traps to eradicate rats. 

15 This action would be highly unlikely to succeed at Palmyra. The use of live traps and/or lethal 

16 traps to remove rats from an area is a strong selection agent in favor of rats that are “trap-shy”. 

17 Thus, after extensive trapping the only rats that would remain would be those that are 

18 behaviorally less likely to enter a trap, and these rats would be very difficult to remove without 

19 the introduction of alternate methods such as toxicants. The high densities of land crabs found at 

20 Palmyra also make effective trapping almost impossible due to interference from crabs being 

21 captured as soon as the traps are set. The use of snap traps at Palmyra would result in high 

22 mortality of land crabs. Furthermore, the widespread use of traps is not feasible because of the 

23 extensive effort and considerable personnel risk required to set and monitor traps. Therefore, this 

24 alternative is disqualified from detailed consideration.

25

26 2.3.4 Biological Control

27 The introduction of predators on rats, such as snakes and cats, was dismissed because biological 

28 control most often only reduces, rather than fully eliminates the target species and thus fails to 

29 achieve the desired ecological benefit gained through complete rat removal. There is no known 

30 effective biological control agent for rats on islands, and some forms of biological control would 

31 result in unreasonable damage to the environment. The introduction of cats to islands in order to 

32 control introduced rodents has been attempted numerous times since European explorers began 

33 crossing the Atlantic and Pacific Oceans. The introduction of a rodent predator, such as cats, 

34 generally results in a greater combined effect on birds than if one or the other were present alone. 

35 When seabirds are present, cats have been shown to prey heavily on seabirds (Atkinson 1985), 

36 consuming fewer rodents during these times. When seabirds leave the islands following the end 

37 of the breeding season, cats switch prey to rodents, which allow the islands cat population to 

38 remain stable at a higher level than if no rodents were present on the island (Atkinson 1985, 

39 Courchamp et al. 1999, 2000).Thus, birds are affected not only by rodents but also the larger 

40 number of cats that are sustained by rodent presence on the island. Introduction of another 

41 species onto an island can have severe and permanent consequences to the ecosystem (Quammen 

42 1996). Therefore, this alternative is disqualified from detailed consideration.

43

44 2.3.5 Fertility Control

45 Fertility control has been used with limited success as a method of pest management in a few 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 18

1 species. Experimental sterilization methods have included chemicals and proteins delivered by 

2 vaccine, and genetically-modified viral pathogens. However, the effectiveness of these 

3 experimental techniques in the wild, and their impacts to nontarget animals are unknown. Aerial 

4 application of rodenticide is a more practical, effective, and a safer method to eradicate rats than 

5 repeated baiting of uncertain oral contraceptives on a remote island across seasons or capturing, 

6 vaccinating, and releasing every member of a single gender of the Palmyra rat population. This 

7 lack of data and tools disqualifies the use of fertility control from detailed consideration (Tobin 

8 and Fall 2005).

9

10 2.3.6 Aerial Broadcast or Bait Stations with Diphacinone and Diphacinone-50 Bait 

11 Products 

12

13 Aerial broadcast and bait station alternatives employing the Diphacinone-50 bait product (the 

14 only other bait product besides Brodifacoum-25W Conservation and Brodifacoum-25D 

15 Conservation registered with the USEPA for conservation-based rodent eradications on islands) 

16 were considered in the development of this Final EIS, but not put forward as Action Alternatives. 

17 Factors considered in this decision include: 

18 1) the multi-agency/organization collaborative report (the Feasibility Study, Appendix 

19 C), which evaluated causes of an initial failed eradication attempt at Palmyra in 2002-2004; 

20 2) field and laboratory trials conducted in 2004-2010 (Appendices C through G); 

21 3) reported results of Diphacinone-50 laboratory and field studies, such as relative 

22 toxicity and efficacy of the product (including palatability); 

23 4) exceptional biological conditions of Palmyra Atoll, including the inordinately dense 

24 population of land crabs, their extreme ability to penetrate enclosures, and their voracious 

25 consumption (which influences application rates needed); and 

26 5) relative financial costs.

27

28 The collaborative report from 2004 which followed the failed Palmyra rat eradication effort (the 

29 Feasibility Study, Appendix C) examined the feasibility of broadcast treatment with a product

30 equivalent to Diphacinone-50 but, at that time, diphacinone – although effective at rat control

31 under different conditions – had not been proven to be an effective tool for rat eradication from 

32 tropical islands, or for broadcast-based eradications in general. The 2005 field trial at Palmyra 

33 followed the recommendations of the 2004 Feasibility Study (Appendix D and C, respectively). In 

34 2005, the investigators elected not to trial a diphacinone broadcast product because of a) the 

35 significantly greater application rates, relative to brodifacoum, necessary for testing to ensure 

36 availability of bait, for a long enough period, to all rats; b) a limited number of discrete islets at 

37 Palmyra for adequate sample sites; and c) limits on funding available to conduct tests in the 

38 unconventional Palmyra ecosystem.

39

40 Ultimately, while Diphacinone-50 was included in the palatability and environmental fate 

41 studies conducted at Palmyra in 2010 (Appendix F) (Alifano and Wegmann 2010), the service 

42 does not have enough information on the efficacy of Diphacinone-50 within Palmyra‟s rat 

43 eradication environment to proceed with this bait product employed in a broadcast or bait 

44 station-based Action Alternative. Additional and expensive field trials would be required to 

45 evaluate the viability of this product for meeting a high probability of eradicating rats from the 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 19

1 extreme conditions at Palmyra Atoll; however, they may not remove uncertainties. Furthermore, 

2 incurring the added expense, with continued uncertainty, is not practical for the Palmyra 

3 eradication because there is sufficient documentation on the success of brodifacoum.

4 A total of 12 successful island rodent eradications have been reported using diphacinone as the 

5 primary toxicant (Table 2.1) (Howald et al. 2007, Island Conservation unpubl. data). One 

6 additional successful eradication, on Nonsuch Island in Bermuda, also used diphacinone but as 

7 a supplement to warfarin which was the primary toxicant used. Of the 12 successful eradications

8 using diphacinone as the primary toxicant, 3 used hand broadcast as the primary delivery 

9 technique, 8 used bait stations as the primary delivery technique, and 1 used aerial broadcast. 

10 Fifteen eradications using diphacinone are reported to have been unsuccessful: Lehua Island in 

11 Hawaii (Dunlevy and Swift 2011) ; Mukojima, Torishima, and Higashijima Islands in Japan 

12 (Hashimoto 2010) using aerial methods; and 9 Islands in Alaska, Congo Cay in U.S. Virgin 

13 Islands, and Nishijima in Japan (Pierce 2003, Hall et al. 2006). Although diphacinone has less 

14 of a record of success for island rodent eradication in comparison to brodifacoum, some success 

15 has been achieved. And, it is often a preferred rodenticide because of the reduced environmental 

16 risk to nontarget species in comparison to brodifacoum (Fisher et al. 2003, Eason and Ogilvie 

17 2009). Additional successful island rodent eradications would be needed to adequately 

18 demonstrate that diphacinone could be a substitute for other proven anticoagulants in efficacy 

19 and cost-efficiency, particularly for large scale and complex eradication projects, such as at 

20 Palmyra. Based on available data and historical failure to remove rats from Palmyra, no 

21 conclusions of Diphacinone-50„s reasonable likelihood of success could be made to meet the 

22 purpose and need of this project.

23

24 Toxicological Properties of the Rodenticides (relative toxicity and efficacy) 

25 The physiological action of diphacinone on target organisms is the same as for brodifacoum: 

26 diphacinone interferes with the blood‟s clotting ability and causes profuse bleeding. However, 

27 diphacinone and other first-generation anticoagulants have a reduced affinity for the enzyme 

28 that produces vitamin K-dependent clotting agents (in comparison to brodifacoum and other 

29 second-generation anticoagulants,) resulting in a slower depletion time of these clotting agents 

30 in the bloodstream (Eason and Ogilvie 2009). Also, diphacinone is more actively metabolized 

31 and excreted by rats than brodifacoum. In one trial, after a single dose of diphacinone, 80 

32 percent of the toxicant was eliminated in feces and urine within 8 days (Yu et al. 1982).

33

34 As a result of these properties, diphacinone requires multiple exposures to ensure a lethal dose is 

35 obtained. Although diphacinone can be lethally toxic to some rats when administered in a single, 

36 large dose, it is relatively more potent in small doses administered over several days (Buckle and 

37 Smith 1994, Timm 1994). Single lethal doses of 1.93 - 43.3 mg/kg have been reported for 

38 laboratory rats, but doses of less than 1 mg/kg over 5 successive days are more effective (Hone 

39 and Mulligan 1982, Jackson and Ashton 1992). Laboratory studies demonstrate that both single40 dose and multiple-dose LD50 values for rats exposed to diphacinone are higher than for 

41 brodifacoum (Table 2.6) and, that for mortality to occur, diphacinone generally must be ingested 

42 regularly over a period of days (Buckle and Smith 1994, Erickson and Urban 2004). Jackson

43 and Ashton (1992) reported LD50 values over a 5-day period of 0.21 and 0.35 mg/kg/day in 

44 domestic and wild Norway rats respectively. Tobin (1992) demonstrated that for mortality to 

45 occur, black (R. rattus) and Polynesian rats (R. exulans) required a mean of 8.6 mg/kg (11.8 -
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 20

1 28.4 g of pellet), and Norway rats required a mean of 10 mg/kg (34.6 g pellet) ingested over an 

2 average of 6 to 7 days, with a range of between 4 and 12 days. From laboratory bioassays 

3 against wild-caught black and Polynesian rats in Hawai`i, Swift (1998) found Ramik® Green 

4 [Diphacinone-50] was effective at very low amounts and for half the exposure time generally 

5 recommended for diphacinone. She concluded minimum exposure times and bait amounts of 7 

6 days and 37.5 grams (15 commercial-sized pellets) for R. rattus and 6 days and 30.0 g (12 

7 commercial-sized pellets) for R. exulans (90% mortality) should be sufficient to effectively 

8 control wild rats in Hawaiian ecosystems with Ramik® Green [Diphacinone-50]. After 

9 considering these studies, we concluded that, to ensure 100 percent mortality to the rat 

10 population at Palmyra Atoll (eradication rather than control), if Diphacinone-50 bait was used, 

11 it would need to be consistently available and consumed by some rats for up to 12 days.

12

13 The primary advantage of diphacinone as a rodenticide for conservation purposes is the low risk 

14 it poses to nontarget organisms in comparison to second generation anticoagulants.

15 Diphacinone has comparatively low persistence in animal tissues, which makes toxicity to 

16 nontarget birds through primary and secondary exposure less likely than for brodifacoum (but 

17 does not eliminate the risk) (Fisher 2009). Furthermore, laboratory trials have indicated that 

18 diphacinone has low toxicity to birds when compared with brodifacoum (Erickson and Urban 

19 2004, Eisemann and Swift 2006). However, recent research suggests that the toxicity of 

20 diphacinone to some birds may be considerably higher than previously thought (Rattner et al. 

21 2010 (submitted)), although the overall toxicity of diphacinone still remains low compared with 

22 brodifacoum. From the perspective of nontarget risk, particularly for birds, diphacinone is the 

23 optimum choice. However, the choice would be risky when gauged with overall baiting efficacy

24 on Palmyra. The long exposure to diphacinone necessary to achieve rat mortality ultimately 

25 decreases the probability that all rats would consume enough bait, given the conditions at the 

26 atoll. For example, the availability of other, natural food items and competition with other 

27 consumers (e.g., land crabs) both could decrease the probability of all rats consuming enough 

28 bait. Competition with other consumers also would potentially leave some rat territories with 

29 inadequate access to bait. All of these factors increase the risk of eradication failure.

30

31 Diphacinone-50 is a cereal bait product, available in 1-2 g pellets, with an added fish flavor. 

32 The bait contains 50 ppm diphacinone. Pellets are dyed dark green, which has been shown to 

33 make them less attractive to some birds and reptiles (Pank 1976, Tershy et al. 1992, Tershy and 

34 Breese 1994). The Diphacinone-50 bait product is identical to commercially available Ramik® 

35 Green bait products. Diphacinone-50 has been tested for rodent eradication with equivocal 

36 results in the Aleutian Islands of Alaska (Table 2.1). Rats were reportedly eradicated from some 

37 but not all trial islets (mostly < 0.5 ha in size) during a bait station trial eradication near Adak 

38 Island (Dunlevy and Spitler 2008). However, successful eradication has been achieved with bait 

39 station application of Diphacinone-50 elsewhere.

40

41 While diphacinone has been tested or used with favorable results in a number of landscape-scale 

42 rodent control efforts (Dunlevy et al. 2000, Spurr et al. 2003a, Spurr et al. 2003b), the success of 

43 these control efforts does not provide assurance that Diphacinone-50 would be successful as a 

44 tool for rodent eradication when competition for bait between the target species and nontarget

45 consumers is high (such as at Palmyra).The goal of a rodent control operation is to reduce a 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 21

1 rodent population to an acceptably small size and maintain low density populations, whereas the 

2 goal of an eradication operation is to permanently remove every rodent. This is a critical 

3 fundamental difference when assessing the relative merits of different bait products; a bait 

4 product that is available for use, attractive to rodents, but has an uncertain efficacy may be an 

5 excellent tool for a control operation but not for a broadcast eradication operation at this time. 

6

7

8 Table 2.1. Known rat eradication attempts worldwide using diphacinone bait products. 

Island Name Country Species Area 

(ha)

Year Primary 

Delivery

Rodenticide Outcome Reference

Kalkun Cay, 

USVI

USA R. rattus 1.4 1982 hand 

broadcast

diphacinone successful Parkes and 

Fisher 2011

Dog Cay, USVI USA R. rattus 4.8 1983 hand 

broadcast

diphacinone successful Parkes and 

Fisher 2011

Steven Cay, 

USVI

USA R. rattus 0.8 1983 hand 

broadcast

diphacinone successful Parkes and 

Fisher 2011

Nonsuch, 

Bermuda

UK R. norvegicus 

R. rattus

5.8 <1985 bait stations warfarin, 

diphacinone

successful Wingate 1985

Buck Island 

Reef National 

Monument, 

USVI

USA R. rattus 80 2000 bait stations diphacinone successful Witmer et al. 

2007

San Jorge East, 

Gulf of Mexico

MEX R. rattus 5 2000 bait stations diphacinone successful Donlan et al. 

2003

Mokoli`i, Hawaii USA R.rattus 1.5 2002 bait stations, 

traps

diphacinone successful Smith et al. 

2006a

Congo Cay, 

USVI

USA R. rattus 10.6 2003 bait stations diphacinone failed Pierce 2003

Cormorant (Bay 

of Islands, 

Alaska)

USA R. norvegicus 2.1 2003 bait stations, 

spot baiting

diphacinone failed Dunlevy & 

Scharf 2007

Dutchcap Cay, 

USVI

USA R. norvegicus 

R. rattus

12.9 2003 bait stations diphacinone successful Pierce 2003

Green (Bay of 

Islands, Alaska)

USA R. norvegicus 22.4 2003 bait stations, 

spot baiting

diphacinone failed Dunlevy & 

Scharf 2007

Saba Cay, USVI USA R. norvegicus 

R. rattus

12.3 2003 bait stations diphacinone successful Pierce 2003

South (Bay of 

Islands, Alaska)

USA R. norvegicus 11.4 2003 bait stations, 

spot baiting

diphacinone failed Dunlevy & 

Scharf 2007

Aureola (Bay of 

Islands, Alaska)

USA R. norvegicus 0.3 2004 bait stations diphacinone failed Dunlevy & 

Scharf 2007

Black (Bay of 

Islands, Alaska)

USA R. norvegicus 1 2004 bait staitions diphacinone failed Dunlevy & 

Scharf 2007

Bubba (Bay of 

Islands, Alaska)

USA R. norvegicus 0.5 2004 bait stations diphacinone successful? Dunlevy & 

Scharf 2007

Camoflage (Bay 

of Islands, 

Alaska)

USA R. norvegicus 4.3 2004 bait stations diphacinone failed Dunlevy & 

Scharf 2007

Channel (Bay of 

Islands, Alaska)

USA R. norvegicus 2.9 2004 bait stations diphacinone successful? Dunlevy & 

Scharf 2007

Duh (Bay of 

Islands, Alaska)

USA R. norvegicus 0.1 2004 bait stations diphacinone failed Dunlevy & 

Scharf 2007

Earl (Bay of 

Islands, Alaska)

USA R. norvegicus 6.4 2004 bait stations diphacinone failed Dunlevy & 

Scharf 2007

Ina (Bay of 

Islands, Alaska)

USA R. norvegicus 4.5 2004 bait stations diphacinone failed Dunlevy & 

Scharf 2007

North Rocks 

(Bay of Islands, 

Alaska)

USA R. norvegicus 0.7 2004 bait stations diphacinone successful? Dunlevy & 

Scharf 2007

Sweet (Bay of 

Islands, Alaska)

USA R. norvegicus 0.5 2004 bait stations diphacinone successful? Dunlevy & 

Scharf 2007
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 22

Buck Island 

NWR, USVI

USA R. norvegicus 

R. rattus

16.8 2005 bait stations diphacinone successful Pierce 2007

Capella Island, 

USVI

USA R. norvegicus 

R. rattus

8.8 2005 bait stations diphacinone successful Pierce 2005

Canna Island UK R. norvegicus 1130 2006 bait stations diphacinone successful Bell et al. in 

press

Nishijima, 

Ogasawara

JPN R. rattus 49 2007 bait stations diphacinone failed Hashimoto 2010

Higashijima, 

Ogasawara

JPN R. rattus 28 2008 aerial diphacinone failed Hashimoto 2010

Lehua, Hawaii USA R.rattus 117 2008 aerial diphacinone failed Dunlevy & Swift 

2011

Mokapu, Hawaii USA R. rattus 4 2008 aerial diphacinone successful FWS 2008b

Mukojima, 

Ogasawara

JPN R. rattus 268 2008 aerial diphacinone failed Hashimoto 2010

Torishima JPN R. rattus 11 2008 aerial diphacinone failed Hashimoto 2010

Cocos (Guam) USA R. exulans 33.6 2009 hand 

broadcast, 

some bait 

stations with 

brodifacoum 

trapping

diphacinone pending Parkes and 

Fisher 2011

Egmont Cay JPN R. rattus 112 2009 bait stations, 

hand 

broadcast

diphacinone pending Parkes and 

Fisher 2011

Tea Island, 

Falkland 

Islands

UK R. norvegicus 320 2009 hand 

broadcast

diphacinone pending Poncet 2009

Anijima JAP R. rattus 785 2010 aerial diphacinone pending Harrison 2010

Higashijima, 

Ogasawara

JPN R. rattus 28 2010 aerial diphacinone pending Harrison 2010

Mukojima, 

Ogasawara

JPN R. rattus 268 2010 aerial diphacinone pending Harrison 2010

Nishijima, 

Ogasawara

JPN R. rattus 49 2010 aerial diphacinone pending Harrison 2010

Otoutojima JPN R. rattus 530 2010 aerial diphacinone pending Harrison 2010

Torishima JPN R. rattus 11 2010 aerial diphacinone pending Harrison 2010

1 Country codes: UK = United Kingdom, MEX = Mexico, USA = United States of America, JPN = Japan.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 23

1 Table 2.2. LD50 values for Rattus sp. exposed to brodifacoum and diphacinone. 

2

3 Data from Hone and Mulligan (1982); Buckle (1994); Erickson and Urban (2004)

4

5 Brodifacoum has a higher success rate for rat eradication than diphacinone likely, in part, 

6 because brodifacoum has a higher toxicity (less bait would need to be consumed to achieve 

7 mortality; in some cases, one feeding of brodifacoum bait would be lethal) (see Section 2.5.1 of 

8 this document). It is expected that some rats on the island would consume only a little bait due to 

9 the natural variation in the population with some rats preferring natural foods vs. the presented 

10 bait. Thus, there would be a greater probability of eradication success using brodifacoum. In 

11 addition, higher toxicity may be more important for aerial broadcast because of the relatively

12 short duration of bait availability, compared to a bait station approach where bait can be made 

13 available for long periods of time. Rodent eradications using brodifacoum have been successful 

14 using either 1 or 2 broadcast applications. For diphacinone, the few successful eradications 

15 using broadcast application indicates that a strategy for aerial application has not been 

16 extensively tested and proven. Given that diphacinone is physiologically more effective with 

17 repeated doses and that diphacinone bait was consistently available for long time periods in 

18 successful eradications using bait stations, broadcast application of Diphacinone-50 would 

19 require either multiple applications (>2) or significantly higher application rates (if only 1-2 

20 applications) to ensure availability for a longer period of time. For this reason, an eradication 

21 effort on Palmyra using brodifacoum and broadcast techniques would be more cost-effective and 

22 more effort-efficient (Table 2.8), with a higher probability of success than a diphacinone 

23 broadcast. Diphacinone broadcast would require a higher application rate and more frequent 

Species LD5 0 mg/kg LD5 0 mg/kg

brodifacoum diphacinone

Laboratory rat 0.41 (0.35 – 0.50) 2.5 (1.3 - 3.4)

0.56 (0.47 – 0.66) 2.1 (1.5 – 2.9)

7.0 (5.2 – 9.5)

5-day dose @ 0.21/day=1.05

1.9

Norway rat (wild) 5-day dose @ 0.35/day=1.75

Rat (unspecified) 3.0 (< 1 over 5 days)

Norway rat 10 (40% mortality)

Black rat 8.6 (90% mortality)

Polynesian rat 8.6 (90% mortality)

Rat (unspecified) 0.39

Norway rat 0.3 3

Norway rat-male 0.4 (0.35-0.46)

Norway rat-female 0.49 (0.43-0.56)

Norway rat-male 0.42 (0.37-0.48)

Norway rat-female 0.56 (0.46 – 0.73)

Norway rat-male 0.98 (0.78 – 1.2)

Norway rat-female 1.3 (1.0 – 1.6)

Norway rat-male 0.81 (0.7 – 0.95)

Norway rat-female 1.0 (0.4 – 2.1)

Norway rat 0.22-0.27

Black rat 0.65-0.73
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 24

1 applications to make bait consistently available for long time period, resulting in an overall 

2 higher volume of pesticide introduced into the environment. Diphacinone, delivered by aerial 

3 broadcast, has been reported to be successful in removing rats from only a single island and has 

4 failed on 4 islands (Table 2.1).The multiple-feed requirement of diphacinone and its measured 

5 acceptance rates (palatability) (Pitt et al. 2010) cannot be ruled out as possible contributors to 

6 operational failure for aerial applications. With respect to Lehua Island, Hawai`i, where aerial 

7 broadcast of diphacinone in 2009 was unsuccessful in eradicating rats, Parkes and Fisher 

8 (2011) conclude that diagnosis of the cause of failure at Lehua is difficult while recognizing 

9 there is some cause for caution on the use of diphacinone as an eradication tool. In comparison, 

10 brodifacoum, delivered by aerial-broadcast, hand-broadcast, or a combination of both, has been 

11 used successfully for rodent eradication on at least 75 occasions (Howald et al. 2007) with one 

12 or two bait applications. It is acknowledged that there have been failures with the use of 

13 brodifacoum, some causes of which are unknown, others due to operational deficiencies, or 

14 reintroductions. 

15

16 Bait palatability is another important factor affecting the likelihood of successful rat eradication. 

17 In a laboratory setting, Pitt et al. (2010) found that the Ramik® Green (Diphacinone-50) 

18 product they tested had lower average consumption and lower percent acceptance rate than the 

19 second generation anticoagulant products tested, including brodifacoum. The diphacinone 

20 product did not meet a minimum threshold of at least 80% mortality in two-choice tests after 7 

21 days of exposure. The result was attributed to low product toxicity, limited exposure times, and 

22 low palatability compared to the other products tested (Pitt et al. 2010).The lower acceptance 

23 rate directly affected efficacy and fewer animals succumbed to the diphacinone product under 

24 test conditions as compared to other products. If the animals do not eat the bait product, efficacy 

25 will be compromised. For field uses, such as what is proposed on Palmyra, if a bait product fails 

26 basic laboratory acceptance and efficacy trials (regardless of toxicant), the acceptance of the 

27 product under field conditions is questionable, and potentially risks the success of the 

28 eradication effort.

29

30 At Palmyra, however, the products Brodifacoum-25W and Diphacinone-50 have both been 

31 shown to be preferred when presented to rats along with naturally available food items

32 (Appendix F). Brodifacoum-25 bait products have been used to successfully eradicate rats on at 

33 least 5 islands and have shown favorable results in at least 3 other eradication trials. The bait 

34 product Diphacinone-50 was reported to be successfully used on Mokapu Island, Hawai`i by 

35 aerial broadcast. Diphacinone-50 has shown equivocal results in bait station eradication trials 

36 in the Aleutian Islands, Alaska, but was successfully used to remove rats from Buck Island, USVI 

37 (Witmer et al. 2007).

38

39 From an operational perspective, the essential difference between Diphacinone-50 and 

40 Brodifacoum-25W for eradicating rats from Palmyra is that the quantity of Diphacinone-50 

41 would need to remain relatively high across a period of up to 12 days (potentially per 

42 application), while a brodifacoum operation would require only that bait be available long 

43 enough for each rat to receive a single-dose, about 4 days per application. With a brodifacoum 

44 operation, because of brodifacoum‟s toxicity, a rat that ingests bait on day one will likely not 

45 need to ingest bait again (brodifacoum has a high binding affinity in the liver and is metabolized 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 25

1 slowly). However, with a diphacinone operation, bait needs to be available to all rats and 

2 consumed almost exclusively for up to12 days; this requires that 1) the bait is highly attractive to 

3 rats to ensure that they consistently prefer bait above natural food items, 2) that sufficient bait is 

4 available daily to ensure rats frequently encounter bait within their environment, and 3) that the 

5 consistent bait loss in the environment to other rats, crabs, and other animals, and degradation 

6 by invertebrate, microbial, and other environmental action, does not diminish the amount of bait 

7 available to a level at which sufficient bait is no longer available to rats. For these reasons, it 

8 was determined that aerial use of Diphacinone-50 would require three times the bait for 

9 Palmyra, at more cost, than aerial use of Brodifacoum-25W. Relative costs of treatment options 

10 are outlined in Table 2.8.

11

12 As outlined in this section and discussed in detail in the Environmental Consequences section 

13 (Chapter 4), the use of diphacinone is acknowledged here to impart a considerably lower risk to 

14 nontarget species than does brodifacoum. However, the product‟s variable results in laboratory 

15 and field acceptance studies and efficacy trials, combined with varying degrees of success in 

16 island eradication efforts, questions a successful use of Diphacinone-50 on Palmyra at this time. 

17 Additional and expensive trials may increase the understanding of the product in Palmyra‟s 

18 extreme conditions; however, they may not remove uncertainties. A failed eradication attempt 

19 with lower nontarget risk would provide no conservation returns at great expense since rats 

20 would quickly re-establish throughout the atoll (Appendix D).When considering other important 

21 factors, such as the demonstrated eradication success of Brodifacoum-25W in comparison to 

22 Diphacinone-50, the technology for distributing the toxicant effectively when feasibility was 

23 considered in 2004 and trialed in 2005, and the probability of administering toxic levels to all 

24 rats, Brodifacoum-25W was concluded to be more desirable at this time when coupled with 

25 mitigation strategies to minimize the risks to nontarget species at the atoll. Subsequently, the use 

26 of Diphacinone-50 for Palmyra at this time was considered and dismissed.

27

28 2.3.7 Bait Broadcast Using Brodifacoum-25W at the Maximum Application Rate Allowed 

29 by the 2010 Product Use Label

30 The 2008 Bait Broadcast Application Rate Assessment (Appendix E) conducted at Palmyra 

31 (Wegmann 2008) showed that the current bait sowage rate maximum for Brodifacoum-25W is 

32 not sufficient to expose all rats to bait, and thus would not achieve eradication success. A 

33 supplemental label for this product for use on Palmyra was approved April 15, 2011.

34

35 2.3.8 Hand Broadcast of Brodifacoum-25W

36 Applying Brodifacoum-25W by hand rather than via aerial application was considered but 

37 rejected as a viable action alternative because of the following factors:

38 There are several islands at Palmyra where unexploded ordinance from WWII U.S. 

39 military activities still persist. Such areas would have to be surveyed by qualified 

40 technicians and found ordinance would have to be removed. 

41

42 Palmyra‟s dense vegetation would limit the distance between hand baiting transects to 15 

43 feet. Based on the effort required to broadcast bait by hand to the ground and coconut 

44 palm canopy during the 2005 trial eradication (19.5 person-hours/ha) (Buckelew et al. 

45 2005), it would take a 20-person team 243 days to complete each of the two bait 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 26

1 applications. While some efficiencies could be expected with a larger operation (the 2005 

2 trial islands were baited by teams of 4-5 people), the effort required for a hand broadcast 

3 eradication at Palmyra would be monumental. 

4

5 The risk to nontarget species during a hand broadcast operation would not be decreased 

6 from that incurred during an aerial broadcast operation.

7

8 2.3.9 Use of Other Toxicants

9 The use of other rodenticides registered with the EPA was dismissed from further consideration 

10 for one or more of the following reasons: 1) greater toxicity to other refuge wildlife such as 

11 terrestrial arthropods; 2) lack of proven effectiveness in island rat eradications; 3) potential for 

12 development of bait shyness in the rat population; and 4) the lack of an effective antidote in case 

13 of human exposure. Each of these issues and the associated rodenticides are discussed below.

14

15 Most documented island-wide rodent eradication programs (226, 68 percent) have used second16 generation anticoagulants, including brodifacoum (Howald et al. 2007). Twenty-nine have used 

17 first-generation anticoagulants such as diphacinone. Nine additional eradications have used non18 anticoagulant toxicants including zinc phosphide, strychnine, and cholecalciferol. Acute 

19 rodenticides, such as zinc phosphide and strychnine, have the ability to kill rats quickly after a 

20 single feeding. However, because poisoning symptoms appear rapidly, the acute rodenticides can 

21 induce learned bait avoidance if animals consume a sub-lethal dose. Studies with zinc phosphide 

22 have demonstrated that rodents associate toxicity symptoms with bait they had consumed earlier 

23 if the onset of symptoms occurs as long as 6 to 7 hours after consumption (Lund 1988). Thus, 

24 any individual that consumes a sub-lethal dose is likely to avoid the bait in the future (Record 

25 and Marsh 1988). Also, acute rodenticides are often extremely toxic to humans and effective 

26 antidotes are not always available. The combination of these factors disqualifies the acute 

27 rodenticides from detailed consideration.

28

29 Cholecalciferol, which is classified as a “subacute” rodenticide, has the ability to kill rats more 

30 quickly than the anticoagulant rodenticides, but most often more slowly than the acute 

31 rodenticides. Cholecalciferol has a lower level of toxicity to birds. It has been used successfully 

32 to eradicate rats from very small islands (Donlan et al. 2003). These characteristics give 

33 cholecalciferol potential as a candidate toxicant for eradications, but it has not been extensively 

34 tested for eradication efficacy (Howald et al. 2007) or impacts to nontarget species. Thus, its use 

35 at Palmyra would be largely experimental in nature. The presence of unique taxa at Palmyra, and 

36 the need for a high probability of conducting a successful eradication on the first attempt, 

37 disqualifies cholecalciferol from detailed consideration. Additionally, no EPA labeled 

38 cholecalciferol bait product is currently available for rodent eradication or control activities.

39

40 2.4 Features Common to All Action Alternatives

41

42 2.4.1 Introduction

43

44 The purpose of eradicating rats from Palmyra Atoll is to restore and protect historic seabird 

45 colonies, to conserve, protect and enhance habitat for all native wildlife species, and to restore 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 27

1 the biotic integrity of the island. The overarching goal of successfully eradicating rodents is 

2 dependent upon ensuring the delivery of a lethal dose of toxicant to every rodent on the island in 

3 a manner that minimizes harm to the ecosystem while still maintaining a high probability of 

4 success. 

5

6 2.4.2 Adaptive Management

7 Based upon 522 DM 1 (Adaptive Management Implementation policy), refuge staff shall use 

8 adaptive management (AM) for conserving, protecting, and, where appropriate, restoring lands 

9 and resources. Within 43 CFR 46.30, AM is defined as a system of management practices based 

10 upon clearly identified outcomes, where monitoring evaluates whether management actions are 

11 achieving desired results (objectives). The recently published DOI Adaptive Management 

12 Technical Guide also defines AM as a decision process that “promotes flexible decision making 

13 that can be adjusted in the face of uncertainties as outcomes from management actions and other 

14 events become better understood.” Adaptive Management accounts for the fact that complete 

15 knowledge about fish, wildlife, plants, habitats, and the ecological processes supporting them 

16 may be lacking. The role of natural variability contributing to ecological resilience also is 

17 recognized as an important principle for AM. It is not a “trial and error” process, but rather AM 

18 emphasizes learning while doing based upon available scientific information and best 

19 professional judgment considering site-specific biotic and abiotic factors on refuge lands. 

20

21 2.4.3 Project Support Operations

22 Equipment and supplies for all action alternatives would be transported to Palmyra via a 

23 chartered ocean-going vessel. The vessel tender would require that the vessel be inspected for 

24 rodents and declared free of rodents no more than 2 days prior to departure from the port of call 

25 to Palmyra Atoll. All equipment and supplies loaded onto the vessel would be inspected for 

26 stowaway rodents and other biosecurity hazards, such as propagules from invasive plants and 

27 invasive insects. Project personnel would either fly to Palmyra on a chartered airplane departing 

28 from Honolulu, HI, or ride with the equipment and supplies aboard the chartered vessel. Small 

29 quantities of equipment and supplies would be transported via airplane; all such equipment and 

30 supplies would be inspected for rodents and other pest species prior to departure from Honolulu.

31

32 2.4.4 Rodenticide 

33 Pressed-grain bait pellets that are between 0.04 – 0.1 oz (1 – 5 g) containing a rodenticide will be 

34 applied at a rate that is expected to successfully eradicate rats from the treatment area according 

35 to EPA -approved pesticide label instructions, which define the legally allowable uses and 

36 restrictions of the specific pesticide under the FIFRA. All bait application activities will be 

37 conducted under the supervision of a Pesticide Applicator holding a commercial pesticide 

38 applicator (State of Hawai`i Category 2 (Forest Pest Control)) certification.

39

40 2.4.5 Protecting Cultural Resources

41 Project personnel would exercise caution in general in order to avoid disturbing cultural or 

42 historical resources at Palmyra. Personnel would be briefed on the identification of 

43 archaeological and historical resources that may be present on the island. Personnel would not 

44 dig into the ground or alter the physical environment except at discrete locations for the 

45 installation of bait stations.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 28

1 2.4.6 Monitoring Eradication Efficacy and Ecosystem Response

2 Rats at Palmyra would be monitored to determine the effectiveness of the eradication action. Rat 

3 presence/absence at Palmyra would be monitored for 2 years from the onset of the eradication 

4 operation to confirm eradication success. 

5

6 Resistance to rodenticide exposure is a potential concern; however, it has been 7 years since 

7 rodenticide was made available to rats at Palmyra, and because of this, if there were rats in the 

8 population that were resistant, it is likely that this trait would not have been selected for and is no 

9 longer present in the population (Bailey and Eason 2000, Pitt 2010). The survival of one ship rat 

10 (from a sample of 48) for 21 days during a study evaluating the „resistance‟ of rats at Palmyra to 

11 brodifacoum (Appendix C) generated concern that that there may be other rats on Palmyra that 

12 have similar or greater level of „resistance‟. In evaluating the risks of resistance posed as a 

13 result of 2 years of intensive use and then 3 years of localized use of brodifacoum at Palmyra, it 

14 is instructive to review literature from studies completed elsewhere. Literature reveals that 

15 resistance in three commensal rodents (R. norvegicus, R. rattus and Mus musculus) is widely 

16 documented for first-generation anticoagulants such as warfarin, and cases of resistance have 

17 been observed for two of the three commonly used second-generation anticoagulants 

18 (diphenacoum and bromadiolone). While some instance of increased tolerance to brodifacoum 

19 have been noted, resistance has never been encountered in black rats or in any of the world‟s 

20 most important pest species (Lund 1984). A study completed in New Zealand also found no 

21 evidence of anticoagulant resistance in rats living in areas with a history of 2-5 years of use of

22 brodifacoum (Bailey et al. 2005). Confidence can also be taken from the number of successful 

23 rodent eradications completed on islands or in areas with an extensive history of brodifacoum 

24 use (e.g. Tawharanui Regional Park; and Motuhora, Rangitoto, and Motutapu islands (all in 

25 NZ)). 

26

27 Resistance to rodenticide exposure is always a concern. However, the lack of evidence for 

28 resistance to brodifacoum in other eradication scenarios, even in situations where brodifacoum 

29 had been used for sustained periods of longer than the 6 years, suggest that the risk to the 

30 proposed rat eradication on Palmyra is negligible. 

31

32 For Alternatives B and C that employ aerial bait-broadcast as the primary rodenticide delivery 

33 method, rodent detection devices such as traps, flavored chew blocks, tracking tunnels, and 

34 motion-sensing cameras would be deployed in a post bait application efficacy monitoring 

35 program that would attempt to detect remnant rodents on islands where “mop up” response 

36 baiting is feasible. Also, radio collars would be deployed on rats captured on Cooper Island prior 

37 to the bait application. The collared rats would be monitored prior to the bait application to 

38 confirm vitality and then after bait application to confirm mortality. 

39

40 For Action Alternative D that employs bait-stations as the primary rodenticide delivery method, 

41 eradication efficacy would be measured by the record of station activity and by rat chew blocks 

42 and tracking tunnels associated with the stations. 

43

44 Passive observation by field station staff, visiting scientists, and Service personnel would be a 

45 very effective post-eradication efficacy monitoring measure. Due to the aseasonal abundance of 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 29

1 natural food resources at Palmyra, a remnant rat population should become readily detectible 

2 within 1 year of the eradication effort.

3

4 For aerial broadcast alternatives, 4-6 weeks after the second bait application, a small team would 

5 return to Palmyra to establish rat detection stations throughout the atoll. Every station would 

6 have a corrugated plastic indicator block, and tracking tunnels and motion-sensing camera traps 

7 will be spaced intermittently throughout the detection station network. The stations would be 

8 checked and serviced every 3 days over a 15-day period. If rat signs are encountered on an 

9 isolated land mass that is small enough to effectively retreat by hand, the monitoring team would 

10 consult with the project management team about conducting a follow-up bait application on this 

11 land mass. Detection stations that are placed in the camp area would be monitored and serviced 

12 by trained TNC station staff according to this schedule: once per week for 6 months following 

13 the eradication, once per month after 6 months. At 1 year and 2 years after the eradication, a 

14 monitoring team would return to Palmyra and re-establish the rat detection stations. During these 

15 monitoring efforts, live traps would be added to the detection station network, and stations would 

16 be monitored and serviced every 3 days for 15 days.

17

18 As part of the atoll‟s biosecurity program, all station staff would be trained in the detection of rat 

19 sign. If signs are observed, indicator blocks would be placed in the surrounding area and any 

20 blocks with potential rat chew marks would be sent to rodent identification experts for 

21 verification. 

22

23 Please refer to the eradication monitoring plan presented in Appendix A for a more detailed 

24 description of the monitoring activities that would surround the rat eradication.

25

26 In addition to the above biosecurity plan, the Service would work with others to conduct 

27 biological monitoring both before and after rat eradication in order to detect any positive or 

28 negative changes to native biodiversity and ecosystem functioning. Monitoring activities would 

29 largely consist of repeated measures on native taxa including birds, reptiles, invertebrates, and 

30 plants, and would continue for 5 years post-eradication. Supplemental monitoring activities that 

31 require animal handling or alteration of the physical environment may be conducted as well. If 

32 required, these supplemental activities may be subject to additional Refuge Special Use

33 permitting.

34

35 The timing of the eradication prior to the arrival or after the departure of migratory shorebirds 

36 would be the most effective strategy to minimize the risk of short-term rodenticide exposure in a 

37 bait broadcast scenario. The Service and its partners would actively monitor the resident 

38 shorebird populations by searching known roosting sites for dead or moribund individuals during 

39 and directly after the bait application for a period of 2 months. The long-term risk of rodenticide 

40 exposure to nontarget shorebirds is low given the low rates of toxicant migration into the soil and 

41 the quick decline in toxicant residues in crab tissues post bait application (USDA 2006, Alifano 

42 and Wegmann 2010); however, regular and opportunistic monitoring of the shorebird 

43 populations would continue throughout the year as part of the Service‟s resource management 

44 for the Refuge. All sick or moribund shorebirds found during and directly after the eradication 

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 30

1 may be captured and treated with vitamin K, an antidote to anticoagulant rodenticides, as 

2 directed by a veterinarian.

3

4 2.4.7 Reducing Wildlife Disturbance

5 Before eradication operations begin, personnel would be briefed on strategies and techniques for 

6 minimizing wildlife disturbance. These techniques would be implemented during actual 

7 eradication operations. Requirements would include:

8 Moving slowly and deliberately to avoid frightening birds.

9

10 Traveling carefully by foot and avoiding sensitive areas when possible to reduce 

11 unnecessary impacts.

12

13 All staff would be shown a map detailing areas with sensitive wildlife.

14

15 2.4.8 Public Information

16 Access by the general public onto Palmyra is restricted but the waters surrounding the islands 

17 provide diving and snorkeling opportunities. In addition, TNC also conducts occasional visits to 

18 the atoll with philanthropic donors and administers an innovative research consortium. Visitors 

19 or scientists with an interest in Palmyra would be directly informed about eradication activities 

20 and timing and all research activities would be adjusted to accommodate the eradication project. 

21 Palmyra Atoll would be closed to all non-essential access during eradication efforts.

22

23 With a bait-broadcast approach, public access to the Refuge would be suspended during the 

24 operational period of the eradication action. With a bait-station approach, public access to the 

25 refuge would be suspended for the first 2 months of the eradication period. Permitted researchers 

26 and noncritical FWS and TNC staff would not be present at Palmyra during the eradication 

27 implementation period.

28

29 All Service-approved island users, including Service personnel, researchers and technicians, 

30 contractors, and volunteers would be given written materials stating that rodent bait containing a 

31 rodenticide is currently in use, or was recently used, for a rodent eradication. The material would 

32 describe its appearance and provide guidelines to avoid unintended human interaction or 

33 interference with rodenticide. 

34

35 Approved pesticide warning signs would be placed along the coastline at typical island access 

36 points and would remain in place until bait pellets are no longer found on the atoll after the bait 

37 application has been completed. Signs would be posted in English informing any individuals 

38 about the presence of and risks associated with rodenticide. Adequate signage would be installed 

39 to ensure that even unauthorized visitors to the island are aware of the temporary presence of a 

40 toxicant.

41

42 2.4.9 Timing Considerations

43 The seasonal timing for the action alternatives would be an important factor for both the 

44 likelihood of conducting a successful eradication and the risk of negative impacts to the 

45 biological resources of Palmyra. For most rodent eradications on temperate or subarctic and 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 31

1 subantarctic islands, the likelihood of success is influenced by three seasonally dependent 

2 factors: 1) the demographic patterns of the local rat population; 2) the availability of alternative 

3 food sources for rats; and 3) local weather conditions and seasonal patterns that would affect the 

4 feasibility of conducting operations. Furthermore, the risk of negative impacts to biological 

5 resources depends on the seasonal breeding and migratory patterns of animals other than rats that 

6 may be vulnerable to rodenticide exposure, and to disturbance caused by the bait application 

7 process. 

8

9 Wet, tropical islands and atolls like Palmyra are characterized by aseasonal, productive 

10 environments that provide rats with year-round access to food resources. Because of this, rat 

11 reproduction on wet tropical islands does not adhere to the seasonal patterns observed in 

12 temperate regions (Storer 1962). For the Palmyra rat eradication, the time period for bait 

13 application under the preferred alternative would be determined by the seasonality in the local 

14 abundance of migratory shorebirds that are at risk of exposure to the applied rodenticide.

15

16 Seasonal Patterns of Native Wildlife

17 Effects of the operational activities associated with rat eradication (e.g., exposure to toxicants, 

18 helicopter operations) on the native wildlife could be reduced by avoiding seasons in which large 

19 numbers of animals, such as migratory shorebirds, are present. Palmyra‟s shorebird populations 

20 reach an annual low during the months of June and July, while the birds are at breeding grounds 

21 in North America. A more detailed description of shorebird residency patterns at Palmyra is 

22 given in Chapter 3.

23

24 Weather Consideration

25 Palmyra is within the Intertropical Convergence Zone (ITCZ), a wet, warm climatic region that 

26 encircles the Earth near the equator. Palmyra‟s weather is aseasonal, with regular precipitation 

27 year-round and very little fluctuation in temperature and humidity. The aerial bait broadcast 

28 action alternatives (Alternatives B and C) are designed with the assumption that 1 week of 

29 contingency time may be required to wait out weather conditions such as heavy rainfall that 

30 preclude bait application. 

31

32 2.4.10 Equipment and Materials

33 Bait Design Requirements

34 The grain-based matrix of the bait pellets would be attractive as a food item only to granivorous 

35 and opportunistic omnivorous animals. Insectivores such as some landbirds, most shorebirds, and 

36 some reptiles, would not intentionally consume pellets as food. There would likely be 

37 unintentional consumption. Seabird species that reside at or visit Palmyra would also not 

38 intentionally consume pellets as food. Additionally, pellets would be dyed blue, which has been 

39 shown to make them less attractive to birds (Pank 1976, Tershy et al. 1992, Tershy and Breese 

40 1994) (H. Gellerman unpubl. data).

41

42 Aerial Broadcast Equipment

43 Aerial bait broadcast would be conducted using a single primary-rotor/single tail-rotor 

44 helicopter. Helicopter models considered for use in the operations would include the Bell 206B 

45 Jet Ranger, Bell 206L4 Long Ranger, MD500, or other small- to medium-sized aircraft. 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 32

1 Bait would be applied from a specialized bait bucket, known as a hopper, and slung beneath the 

2 helicopter. The hopper would be composed of a bait storage compartment, a remotely triggered 

3 adjustable gate to regulate bait flow out of the storage compartment, and a motor-driven, 

4 broadcast spinner that can be turned on (to broadcast bait over a wide swath) and off (to dribble 

5 bate in narrow swaths) remotely and independently of the outflow gate. The broadcast device 

6 would include a deflector that can be installed when directional (rather than 360°) broadcast is 

7 necessary, such as along the coastline.

8

9 Bait Stations

10 Bait stations are box-like enclosures with small entryways designed to be attractive to rodents, 

11 but difficult to navigate for other species such as birds and crabs. Bait stations reduce the risk of 

12 rodenticide exposure in nontarget species by making bait more difficult to access and reducing 

13 the total amount of bait introduced into the ecosystem. The bait station design for Palmyra would

14 need to effectively exclude land crabs, including the large coconut crab, and shorebirds while 

15 allowing easy access for rats. U.S. Department of Agriculture-Animal and Plant Health 

16 Inspection Service-Wildlife Services (USDA-APHIS-WS) has developed a bait station that 

17 meets these criteria (Dunlevy personal comm.); this station design would be deployed at Palmyra 

18 during the rat eradication.

19

20 2.4.11 Post-Bait Application Rodent Detection and Rodent Reintroduction Prevention and 

21 Response 

22

23 The conservation and socioeconomic benefits of eradicating rats from Palmyra would only be 

24 fully realized if it is successful and any rodent reinvasion is prevented. Rat detection response 

25 and pest reinvasion mitigation or biosecurity plans are critical components of successful 

26 eradication campaigns. A quantity of bait (not to exceed 2000 lbs/ 907 kg) would be stored on27 island. The Service would appropriately secure, label, and store all bait left at Palmyra in a dry 

28 location, ready for use should residual or incursion rats be detected.

29

30 If rat sign were encountered or a rat sighting occurred, rat detection devices (e.g., indicator 

31 blocks, live traps, and tracking tunnels) would be established in the area surrounding the sign or 

32 sighting and on adjacent islands. Confirmed rat presence would initiate a rat removal response

33 to eradicate a residual population or an incursion (See Appendix B), The area surrounding the 

34 confirmed rat detection would be treated with rodenticide applied by hand broadcast or bait 

35 station, or by live trapping, or by a combination of the three control methods. The area would be 

36 monitored. 

37

38 The risk of rat reintroduction is high because Palmyra Atoll is a remote Refuge and scientific 

39 research station that is maintained through periodic shipments of supplies including consumable 

40 and bulk goods, as well as personnel via regular airplane and annual barge service from 

41 Honolulu. Occasional visiting research and recreational vessels from all areas of the Pacific also 

42 come to Palmyra. 

43

44

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 33

1 To mitigate for post eradication rodent reinvasion risk, a biosecurity plan that was drafted by the 

2 U.S. Geological Survey (Hathaway and Robert 2010) and amended by the Service and TNC and 

3 is currently in effect (See Appendix B). 

4

5 2.4.12 Aerial Broadcast Alternatives

6 For the aerial broadcast alternatives, helicopter operations would be staged on Cooper Island. 

7 Helicopters would fly to designated staging areas where personnel would refill the bait hopper, 

8 refuel the helicopter(s), and conduct other necessary maintenance. The staging area would be 

9 adequately stocked with bait, fuel, Personal Protective Equipment, and other supplies and 

10 equipment to support the helicopters and project personnel during the bait application process. 

11 The camp area would be excluded from the aerial broadcast and would be treated by hand12 broadcast and placement of bait stations. All inland standing bodies of water and the runway will 

13 be excluded from the aerial bait application.

14

15 2.4.13 Applying Bait to the Forest Canopy

16 Previous studies have found that rats frequent the forest canopy at Palmyra (Appendix C) and 

17 spend more time in the crowns of coconut palm trees than in the crowns of other tree species 

18 comprising the forest‟s canopy (Wegmann et al. 2007). Removal of the coconut palms was 

19 considered in early planning (2005-2008) as a way to reduce available rat habitat. However, 

20 while this action would reduce rat habitat, it would also greatly hinder personnel movement on 

21 the ground for rat eradication because of successional plant growing in the resulting light gaps 

22 (Wegmann 2009), and would remove a large component of the only crab-free habitat within 

23 Palmyra's terrestrial environment (the forest canopy). Bait applied to coconut crowns would not 

24 be available to land crabs that would compete with rats for bait, but would be available only to 

25 rats. Therefore, the application of bait to coconut palm crowns became a consideration in all of 

26 the action alternatives. 

27

28 2.5 Pre-Eradication Rodenticide Studies

29

30 2.5.1 An Analysis of the Eradication Success of Brodifacoum-25W (Alternatives B, C, and 

31 D): an Anticoagulant Rodenticide Registered Under FIFRA

32

33 Brodifacoum (3-[3-(4‟–bromobiphenyl-4-yl)-1,2,3,4-tetrahydro-1-naphthyl]-4 hydroxycoumarin) 

34 is an anticoagulant rodenticide used for the eradication and control of rodents. Brodifacoum25W 

35 Conservation (registrant: Animal and Plant Health Inspection Service (APHIS), USDA; 

36 registration number is 56228-36; manufactured Bell Laboratories, Madison, WI)) is an 

37 anticoagulant rodenticide registered under FIFRA for use in the United States and its territories 

38 for conservation purposes eradicating rodents from islands. Anticoagulant rodenticides are the 

39 most widely used toxicant for control of small mammals worldwide (Eason et al. 2002, Hoare 

40 and Hare 2006a, Howald et al. 2007). They act by inhibiting the synthesis of vitamin K41 dependent clotting agents in the liver, interfering with the blood‟s ability to form clots and 

42 causing sites of even minor tissue damage to bleed continuously (Hadler and Shadbolt 1975, 

43 Eason and Ogilvie 2009). Mortality from anticoagulant rodenticides is caused by internal 

44 hemorrhaging, typically within 3-10 days of initial consumption (Buckle and Smith 1994, 

45 Howald et al. 2007, Eason and Ogilvie 2009)
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 34

1 .Anticoagulants are classified as first or second-generation according to their toxicity (Eason et 

2 al. 2002). The term “first generation anticoagulants” was introduced to contrast anticoagulants 

3 that were not effective against rodents with genetic resistance to them with anticoagulants that

4 could kill resistant individuals (Dubock and Kaukeinen 1978). The chemistries that became

5 known as “second-generation anticoagulants” – a term apparently first used in print by Marsh 

6 et al. (1980) – were developed through a search for rodenticides (Hadler and Shadbolt 1975)

7 that would be effective against individual commensal rodents that are resistant to warfarin, 

8 pindone, diphacinone, chlorophacinone, and other first-generation anticoagulants. See also 

9 Jackson and Ashton (1992). Why the second generation anticoagulants can kill warfarin10 resistant individuals (greater affinity for the “Vitamin-K receptor”) was fully characterized after 

11 the compounds were put into use as rodenticides. The so-called “single-feeding” effect 

12 attributed to brodifacoum (Dubock and Kaukeinen 1978), and other second-generation 

13 anticoagulants results from this greater affinity, but is dependent upon the amount of the 

14 compound that is ingested on the first day of exposure to it. The amount of anticoagulant 

15 ingested on the first day of exposure is determined by the rodent‟s willingness to consider the 

16 bait as a food item; the concentration of the rodenticide in the bait; the palatability of the bait to 

17 the rodent; and, in a control situation, the amount of bait available to the rodent. The last of 

18 these is an issue on Palmyra due to documented competition for bait with other terrestrial 

19 animals, chiefly crabs.

20

21 First-generation anticoagulants generally appear to be most effective at achieving mortality in 

22 rodents when consumed over several consecutive days, although a single high dose may be toxic 

23 to some animals (Eason and Ogilvie 2009). Second-generation anticoagulants are more toxic 

24 than first-generation, with lower LD50 values (median lethal dose, or the amount required to kill 

25 50 percent of a test population), and are typically „single feed‟ poisons in high enough 

26 concentrations (Hone and Mulligan 1982, Eason and Ogilvie 2009). The generally lower toxicity 

27 of first-generation anticoagulants compared to second-generation anticoagulants is attributed to a 

28 poorer ability to bind to sites in the liver. Second-generation anticoagulants have a greater 

29 binding affinity than first-generation anticoagulants, which increases the rate of metabolism by 

30 10; therefore, requiring only one feeding to be effectively kill a rat (Parmar et al. 1987). In order

31 for either toxicant to be lethal, levels in the liver must reach a toxic threshold and this level can 

32 vary widely between species and even between individuals within a species. However, any 

33 rodenticide can be effectively used to eradicate an entire rodent population where there are no 

34 resistant individuals, if all individuals within the population consume enough bait over an 

35 appropriate amount of time. 

36

37 Table 2.3. The composition of Brodifacoum-25W 

Bait product 

name

Bait pellet size 

(g ± 1SD) Active ingredient Inert ingredients Optimal 

environmental 

conditions Rodenticide 

name

Concn

(ppm) Description Concn(%)

Brodifacoum-25W 1.55 – 2.31 Brodifacoum 25 Sweet, cereal 

flavor 99.9975 Wet climates1

Note: 1 38 (Wegmann 2008, Alifano and Wegmann 2010)

39
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 35

1 Brodifacoum-25W is designed to be highly attractive to rodents, such that island rodents are 

2 more likely to choose the bait over natural food sources. The predominant inactive ingredients in 

3 these bait products are non-germinating grains (either sterile or crushed) (Table 2.3).

4

5 Brodifacoum-25W is a “restricted use pesticide” according to the EPA-approved pesticide label 

6 developed for each product under FIFRA:

7 The product may only be used on islands or vessels [marine is implied].

8

9 The product may only be used for the control or eradication of invasive rodents.

10

11 The product are only available for sale to 3 Federal government agencies: US Department 

12 of Agriculture (Animal and Plant Health Inspection Service and Wildlife Services), U.S. 

13 Fish and Wildlife Service, and U.S. National Park Service; although these agencies can 

14 make the bait available to other agencies or private parties under their oversight.

15

16 The product may only be applied by Certified Pesticide Applicators (a certification 

17 generally provided by the State or Territory in which the bait is to be applied) or persons 

18 under their direct supervision.

19

20 Brodifacoum-25W Bait Product

21 Brodifacoum is the most frequently used rodenticide for rodent eradication from islands. Of the 

22 278 successful island rodent eradication events worldwide (where the toxicant applied was 

23 known), 197 (71 percent) used brodifacoum as the primary rodenticide (Howald et al. 2007, 

24 Island Conservation unpubl. data). On 47 percent of successful eradications bait stations were the 

25 primary technique used to deliver brodifacoum; on 29 percent, aerial broadcast was the primary 

26 technique; on 21 percent, hand-broadcast was the primary technique; and on 17 percent, a 

27 combination of all three techniques and/or the use of traps were used. The most commonly used 

28 technique was aerial broadcast supplemented with hand-broadcast (14 or 7 percent) (Howald et 

29 al. 2007, Island Conservation unpubl. data).

30

31 Brodifacoum is highly toxic to rats and requires the consumption of no more than a few bait 

32 pellets (weighing 2g each) during a single feeding event, or during several feeding events, to 

33 result in mortality (Erickson and Urban 2004, Eason and Ogilvie 2009). The LD50 dose has been 

34 achieved in Norway rats (Rattus norvegicus) ingesting 1.5 g (0.052 oz) of brodifacoum bait in a 

35 single feeding (0.3 mg/kg at 50 ppm brodifacoum) (Buckle and Smith 1994), but within and 

36 between Rattus species variations do occur. The toxicity of brodifacoum to rats makes it 

37 desirable as a tool for rat eradication because it reduces the need to make bait consistently 

38 available to rats for an extended period of time.

39

40 Brodifacoum-25W is an unwaxed cereal bait product with 25 ppm brodifacoum, available in 

41 0.05 – 0.1 oz (1.5-3 g) pellets with a sweet, grain flavor. The product is manufactured 

42 specifically for conservation purposes; Brodifacoum-25W is for use in wet climates and is 

43 designed to break down slowly (≤ 14 days) after exposure to moisture, including both dew and 

44 rainfall, making this bait product suitable for use in Palmyra‟s humid wet environment. 

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 36

1 Compressed cereal bait products containing brodifacoum at a concentration of 25 ppm (Bell 

2 Laboratories, Madison, WI) have been used to successfully eradicate rats from at least 5 islands 

3 using aerial broadcast as the primary technique (Samaniego-Herrera et al. 2009, Buckelew et al. 

4 2010, Howald et al. 2010), and from one island using hand-broadcast (Hall et al. 2006). In 

5 addition, the bait product has been tested for efficacy and palatability under laboratory conditions 

6 prior to their use in eradication operations. 

7

8 To successfully eradicate rats from an island, every rodent must be exposed to a sufficient 

9 quantity of rodenticide, by either consuming bait or by eating other animals that have consumed 

10 bait, to acquire a lethal dose of brodifacoum. A bait trial must similarly demonstrate that 100 

11 percent of the rodents in the trial area were lethally exposed to bait. Compressed cereal bait 

12 products containing brodifacoum at a concentration of 25 ppm (Bell Labs, Madison, WI) have 

13 also been tested with favorable results in at least 3 field sites: the Aleutian Islands in Alaska 

14 (Buckelew et al. 2008), Palmyra Atoll in the equatorial Pacific (Buckelew et al. 2005), and 

15 Pohnpei, Micronesia in the western Pacific (Wegmann et al. 2007). 

16

17 During field trials, Brodifacoum-25W was shown to be palatable to rats in comparison to 

18 naturally-available food sources (Buckelew et al. 2005, Buckelew et al. 2008, Alifano and 

19 Wegmann 2010). The palatability of Brodifacoum-25W to rats makes it a desirable tool for rat 

20 eradication because it increases the probability that every rat on the island will consume the bait.

21

22 While high toxicity and high palatability are desirable bait characteristics from the perspective of 

23 successfully eradicating rats, these same characteristics can be undesirable from the perspective 

24 of minimizing nontarget impacts (Hoare and Hare 2006a). Brodifacoum is highly toxic to many 

25 bird species (Erickson and Urban 2004), and can be toxic to secondary consumers that prey on 

26 primary bait consumers (Rammell et al. 1984, Dowding et al. 1999, Stone et al. 1999). 

27 Furthermore, because brodifacoum can persist in the body tissues of vertebrate and invertebrate 

28 species, potential nontarget impacts from brodifacoum through secondary exposure of predators, 

29 has been shown to be extended beyond the period of time that bait pellets themselves are 

30 available in the environment (Eason et al. 2002, Fisher et al. 2004). The pellets are manufactured 

31 with a grain base to be attractive as a food item to rodents, but the pellets are also likely 

32 attractive to other granivorous, opportunistic, and omnivorous animals. Other species such as 

33 insectivores (some landbirds, shorebirds, reptiles), frugivores (e.g., fruit-eating pigeons), and 

34 piscivores (e.g., fish-eating seabirds) would be highly unlikely to identify the pellets as a food 

35 item, would not be as attracted to the pellets as food, and thus would be unlikely to intentionally 

36 consume them. Additionally, pellets would be dyed blue to act as a deterrent; this technique has 

37 been shown to make pellets less attractive to some birds and reptiles (Pank 1976, Tershy et al. 

38 1992, Tershy and Breese 1994). Despite these efforts, mortality in individual nontarget birds 

39 during several rat eradication operations has been attributed to brodifacoum bait products that 

40 were used for the eradications (Eason and Spurr 1995, Eason et al. 2002, Buckelew et al. 2010).

41

42 In an effort to reduce risks to wildlife and people, but allow rodenticide products to remain 

43 available, the EPA recently limited the use of brodifacoum and nine other rodenticides. The 

44 EPA‟s registration of Brodifacoum-25W explicitly exempted its use for island rodent 

45 eradications (U.S. Environmental Protection Agency 2008). The New Zealand Department of 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 37

1 Conservation, the world‟s leader in island pest eradications, identifies brodifacoum as the 

2 preferred toxicant for island rodent eradication (Eason and Ogilvie 2009). These explicit 

3 exemptions are logical in light of the fact that island rodent eradication operations are 

4 fundamentally different from rodent control operations. Rodent eradications are primarily 

5 attempted on islands with minimal human use or isolated land masses that provide a finite area; 

6 the intent of an eradication is the complete removal of rodents, where experts can ensure that 

7 every rodent will receive a lethal dose of the toxicant. Control efforts on the other hand, are 

8 primarily used on the mainland, for agricultural purposes, or on large islands that are heavily 

9 used; the intent of a control effort is to keep the rodent population as small as possible in the 

10 treatment area because it is impossible to ensure that every rodent will receive a lethal dose of 

11 the toxicant. The potential risks of using brodifacoum for eradication can be avoided or reduced 

12 more effectively on an isolated island, with a finite time period of bait availability, than for 

13 rodent control operations on mainland or larger-island sites where rodenticide is chronically 

14 available in the environment. The generally high cost and logistical complexity of conducting a 

15 whole-island rodent eradication necessitate techniques and tools that maximize the probability of 

16 successful eradication on the first attempt.

17

18 2.5.2 Preliminary Eradication Trials Conducted at Palmyra Atoll

19 Prior to project implementation, the Service and partners from Island Conservation (IC) 

20 conducted trials at Palmyra as part of the detailed operational planning process, including a 

21 determination of a successful bait application rate for aerial broadcast, as well as the 

22 development and design of bait stations and canopy baiting techniques. All studies have focused 

23 on the need to maximize the probability of eradication success while minimizing the risk of 

24 harming nontarget individuals through exposure to rodenticide (as described above).

25

26 2004 Rat Eradication Feasibility Study (see Appendix C for the Full Report)

27 In August 2004, a team of nine people with representatives from Island Conservation (IC), 

28 USDA-National Wildlife Research Center, USDA-Wildlife Services, FWS-Ecological Services, 

29 FWS- Refuges, and the Department of Conservation New Zealand visited the atoll for 8 days to 

30 investigate the previous, failed eradication attempt in 2001-2002 and to develop strategies for a 

31 subsequent eradication program. Two IC staff and one FWS representative remained on the atoll 

32 for an additional month to complete the planned research. The main goals of this expedition were 

33 to:

34 Assess the previous effort to eradicate rats from Palmyra Atoll, both to learn why it was 

35 not successful, and what experiences from that effort could be used to develop methods 

36 for a follow up rat eradication.

37

38 Conduct site-specific research needed to develop a plan for successful rat eradication.

39

40 Palmyra‟s high rainfall and aseasonal environment were recognized as obstacles to successful rat 

41 eradication. They make it difficult for bait to maintain its palatability and attractiveness to all rats 

42 for longer than 1 - 2 weeks post-delivery. In addition, abundant land crabs compete with rats for 

43 bait and make it difficult to ensure that enough bait is available to all rats for an adequate time 

44 period of 4 days (Wegmann 2008).

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 38

1 Results from a study of rat home range size and habitat use, conducted during the 2004 site visit, 

2 indicated that the bait station spacing of 50 x 50 m used in the previous rat eradication attempt at 

3 Palmyra may have been insufficient to deliver bait into every rat‟s ranging territory. This is due 

4 to the fact that the rats at Palmyra live in a three-dimensional habitat, using resources and habitat 

5 that includes the coconut palm canopy. For future eradication projects, it was recommended that 

6 a 25 m grid for the placement of bait stations would be needed to increase the proportion of rats 

7 coming into contact with bait stations, but that alone might not be adequate to intercept all rats. 

8

9 The site assessment indicated that a bait broadcast treatment would require an application rate of 

10 60 - 80 kg/ha to ensure that enough bait was available on the ground for 4 days to overcome 

11 competition from land crabs that are attracted to and consume the bait. Land crabs are not 

12 negatively affected by the anticoagulant rodenticides. This study was unable to precisely 

13 determine an effective broadcast application rate because of the high density of crabs and a lack 

14 of enough placebo bait with which to complete the studies.

15

16 To test the efficacy of several bait station designs, the team ran 35 separate lab trials with a total 

17 crab exposure time of 41,175 hours. Three bait stations were evaluated: pipe stations, bucket 

18 stations, and box stations. Of the three, only the pipe station was accessed by crabs, and coconut 

19 crabs (Birgus latro) were the only species that entered the station and consumed bait. The bucket 

20 stations excluded all crab entries across each taxonomic group, although coconut crabs easily 

21 accessed the top of the bucket station. The box station also excluded all crab entries across each 

22 taxonomic group; coconut crabs were able to climb the PVC pipe that supported the box and 

23 reach the delivery device, but were unable to access the secured bait inside the box. Hermit crabs 

24 (Coenobita spp.) were able to climb the support pipe for both the pipe and box stations, but were 

25 unable to access bait as the platforms on both stations precluded entry. Only large adult hermit 

26 crabs were observed climbing the PVC pipe supporting the box station. Both adult and larger 

27 sub-adult hermit crabs were able to climb the half-inch diameter pipe supporting the bait station. 

28 In several instances, sub-adult hermit crabs were observed clinging to the shell of adult crabs as 

29 they climbed, and were therefore capable of reaching higher on the stations than if climbing 

30 unaided. Land crabs (Cardisoma spp.) were not observed making any entry attempts into any of 

31 the bait stations during the lab trials. It is possible that land crabs would have a greater effect to 

32 eradication efforts if broadcast methodologies were incorporated. However, given the small 

33 number of stations available for use in this study, and the short duration of testing, field 

34 evaluations provided limited information on crab exclusion and rat accessibility. In 3 nights of 

35 field use, only a single bucket station received a rat visit. All stations in the field trial were free 

36 of any indication of crab entries.

37

38 The group also conducted a study to determine if Palmyra‟s rat population includes individuals 

39 that were resistant to brodifacoum due to previous, chronic baiting efforts. Seven rats died with a 

40 single dose at the LD50 level for black rats. Furthermore, 28 of 29 rats died within 2 weeks of the 

41 initial dose. These results indicate that there may be a relatively small portion of the population 

42 that is resistant to the effects of brodifacoum. The length of time between the initial dose and 

43 death of at least one rat supports the notion that a small portion of the population may be 

44 resistant to effects of brodifacoum. This conclusion is further supported by the lack of 

45 hemorrhaging observed during the necropsy of the rat that persisted 21days after the initial dose; 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 39

1 this rat received 4 times the LD50 for its body weight and did not show obvious signs of 

2 hemorrhaging. 

3

4 Finally, the 2004 feasibility study identified non-resident migratory shorebirds as being at risk of 

5 either primary or secondary exposure to the rodenticide. The species of concern include the 

6 bristle-thighed curlew (Numenius tahitiensis), and the Pacific golden-plover (Pluvialis fulva). 

7 Both species overwinter on the atoll, with some individual juvenile birds present throughout the 

8 year. The most effective mitigation strategy is to time the eradication when the minimum number 

9 of birds is present on the atoll. 

10

11 2005 Trial Hand Broadcast Eradications (see Appendix D for the Full Report)

12 In July 2005, a team of six FWS, IC, and New Zealand Department of Conservation personnel 

13 returned to Palmyra to test trial rat eradication broadcast methodologies discussed in the 2004 

14 feasibility assessment. The main goals of this expedition were to:

15 Evaluate the palatability and efficacy of the newly formulated bait (Brodifacoum-25W 

16 bait, containing 25 ppm brodifacoum, Bell Laboratories, Inc.) on the local rat population 

17 under laboratory and field conditions.

18

19 Conduct a broadcast trial rat eradication using Brodifacoum-25W bait.

20

21 Evaluate rodenticide exposure risks to nontarget species.

22

23 The group conducted trial eradications on 5 small islets at Palmyra, totaling 4.08 ha.

24 Each island was treated with a hand broadcast on the ground using PI-25 (the prototype of 

25 Brodifacoum-25W), and by slingshot, pole or hand broadcast into every coconut palm tree on 

26 each island. At the time of the study there were no examples of broadcast eradications using 

27 diphacinone so products using that toxicant were not included in the study design.

28

29 The team developed a bait application rate that ensured bait availability to all potential rat 

30 territories in the study area for a minimum period of 4 days. A calibration trial indicated that 

31 between 54–80.4 lb/acre (60 - 90 kg/ha) would be required to successfully treat all rats; however, 

32 due to uncertainty in the data the team initially applied bait at a high application rate on the first 

33 treated island, and reduced the application rate for subsequent islands based on bait uptake 

34 monitoring. The bait was broadcast at 84.8 lb/acre (95 kg/ha; Whippoorwill Island), 75.9 lb/acre 

35 (85 kg/ha; Home Island), 71.4 lb/acre (80 kg/ha; Fern Island), 62.5 lb/acre (70 kg/ha; Bunker 

36 Island), and 54lb/acre (60 kg/ha; Little East Island). The team then monitored bait uptake and the 

37 effect on the local rat population.

38

39 The team determined that bait applications of 80 kg/ha or less would be inadequate to ensure that 

40 bait would be available in every potential rat territory for at least 4 days on islands with a high 

41 abundance of land crabs and hermit crabs that consume the bait (but are not negatively affected 

42 by the rodenticide). The bait consumption study indicated that an application rate of 85 - 95 

43 kg/ha would be adequate to overcome competition from land crabs, with 99.9 percent bait 

44 removed from the islands by 7 days post-broadcast. Direct (radio collared rats and live traps) and 

45 indirect (wax chew blocks) monitoring of efficacy indicated that these application rates were 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 40

1 successful in eradicating rats from all the treated islets. 

2

3 A small juvenile, weanling rat was detected live 8 days after the broadcast on the 95 kg/ha 

4 treated island but was found moribund on day 10. The discovery of a live weanling rat strongly 

5 suggests that a second bait application is necessary to ensure bait is available to all weanling rats 

6 that would not have left the nest while bait would be available from the first application. For the 

7 rat eradication to have a high probability of succeeding by broadcast with PI-25, it was 

8 recommended by the team that bait be applied twice at 90 kg/ha, 10 - 14 days apart, to overcome 

9 competition by the abundant land crabs and hermit crabs, and to ensure enough bait is available 

10 to the entire rat population for a minimum of 4 days.

11

12 To evaluate the risk of rodenticide exposure to nontarget species, the team monitored the local 

13 shorebird population before and after the bait applications, and sampled land crabs for 

14 brodifacoum residues on days 2, 6, 10, 21 and 56 post-broadcast. Of the 4 shorebird species that 

15 are common to Palmyra, bristle-thighed curlew, wandering tattler, Pacific golden-plover , and the 

16 ruddy turnstone, the curlew and plovers were believed to be at the greatest risk of primary and 

17 secondary exposure to the rodenticide due to foraging habits that could lead them to directly 

18 consume bait, or feed on hermit crabs that consumed bait. The frequency of detection of these 

19 shorebirds was consistently higher post broadcast and was likely due to migratory influx. No 

20 dead or moribund birds were detected in the treated areas. 

21

22 2008 Bait Broadcast Application Rate Assessment (see Appendix E for the Full Report)

23 The main goals of this expedition were to:

24 Test the maximum bait application rate stipulated by the bait product label against 

25 Palmyra‟s challenging eradication environment.

26

27 Test an application rate that is greater than what is currently allowed by the bait product 

28 label yet lower than the rates tested during the 2005 trial eradications.

29

30 Measure rat carcass longevity (assess risk of rodenticide exposure for nontarget species).

31

32 Measure invertebrate and reptile (gecko) exposure to Brodifacoum-25W in a bait 

33 broadcast scenario.

34

35 From June 19 to July 5, 2008, non-toxic (placebo) Brodifacoum-25W Biomarker bait (produced 

36 by Bell Laboratories) was hand-broadcast to the ground and forest canopy on 3 islands at 

37 Palmyra Atoll: Home Island (1.7 ha), Whippoorwill Island (1.9 ha), and Portsmouth Island (0.8 

38 ha). Rats were eradicated from Home and Whippoorwill Islands during trial broadcast-based 

39 eradications in 2005 (Buckelew et al. 2005), but have since re-established at densities that 

40 matched those found prior to the 2005 trial eradications (Wegmann and Middleton 2008). 

41

42 The biomarker bait used in this study contained pyranine, a non-toxic hydrophilic, pH-sensitive 

43 fluorescent dye. Pyranine is non-toxic, odorless and tasteless, and is fluorescent green when 

44 exposed to UV light. While biomarkers are commonly used in wildlife management studies (Fry 

45 and Dunbar 2007), the use of pyranine as a biomarker agent within an eradication scenario is a 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 41

1 relatively new convention (Towns and Broome 2003, Greene and Dilks 2004, Griffiths et al. 

2 2008). 

3

4 Bait was broadcast to the ground and forest canopy at the label-specified maximum application 

5 rate (18 kg/ha followed by 9 kg/ha 5 days later) on Whippoorwill and Portsmouth Islands, and at 

6 more than twice the maximum label application rate (36 kg/ha followed by 36 kg/ha 5 days later) 

7 on Home Island. Bait was hand-broadcast by a 6-person baiting line in which broadcasters were 

8 spaced 5 m apart. Bait consumption data were collected to describe the amount of bait consumed 

9 by both target and nontarget species: Whippoorwill (18 plots), Home (22 plots), and Portsmouth 

10 (7 plots). Bait consumption plots were 25 m long x 1 m wide. 

11

12 Hagaruma live catch rat traps were placed 10 m from each other along transects traveling the 

13 length of each island. Captured rats were brought to a central processing location at each study 

14 site. Rats were first inspected for external signs of biomarker using handheld UV flashlights. If a 

15 rat showed external any signs of biomarker (paws, anus, tail, mouth), it was euthanized and 

16 inspected for internal signs. Rats without external signs were marked with a permanent marker 

17 on the proximal-dorsal section of their tails and released at their point of capture.

18

19 Both of the bait application rates tested in this study failed to expose 100 percent of rats from 

20 each sample population. On Whippoorwill and Portsmouth Islands (treated with 18 kg/ha + 9 

21 kg/ha), 32 percent (29/91) and 3 percent (1/31), respectively, of the rats sampled showed no 

22 external or internal signs of biomarker. On Home Island (treated with 36 kg/ha + 36 kg/ha), 5 

23 percent (1/21) of captured rats showed no signs of biomarker. 

24

25 Lower application rates (9 kg/ha and 18 kg/ha) resulted in rapid bait consumption. Following the 

26 9 kg/ha application on Whippoorwill, only 2 of 180 pellets (4.6 g of 414 g of bait) remained in 

27 18 bait consumption plots 24 hours after the bait application; the 2 remaining pellets were 

28 consumed by day 2 (Figure 2.1), and bait was not observed elsewhere on the island. Bait 

29 consumption on Portsmouth showed a similar trend, as nearly all of the 9 kg/ha application was 

30 consumed within 24 hrs, and all pellets within bait consumption plots were consumed within 3 

31 days. The 18 kg/ha baiting regimes on Portsmouth and Whippoorwill resulted in more bait 

32 remaining after the initial 24 hours; however 100 percent bait consumption occurred in all plots 

33 on both islands within 3 days of the bait application. The 36 kg/ha bait applications at the Home 

34 study site resulted in 60 percent bait consumption within 24 hours, and small amounts of bait 

35 persisting until day 4 after the first and second applications. 

36
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 42

1

2 Figure 2.1. Daily bait consumption estimates for the first “A” and second “B” bait applications on Home, 

3 Portsmouth, and Whippoorwill Islands. Mean bait consumption was measured by observing bait pellet 

4 removal from fixed 25 x 1 m plots: Home = 22 plots, Portsmouth = 7 plots, Whippoorwill = 18 plots. Error 

5 bars represent ± 1 standard error of the sample mean.

6

7 At Palmyra, the bait consumption trends and rat bait-exposure ratios suggest that high bait 

8 application rates are needed for bait broadcast campaigns to succeed on crab rich islands. Even 

9 with 2 bait applications of 36 kg/ha – 3 times more bait than is typically applied to temperate 

10 islands (Veitch and Clout 2002, Towns and Broome 2003) – the operation failed to expose 100 

11 percent of the rat population. Furthermore, an increase in bait consumption was observed during 

12 the second application at Home Island, and this happened in the absence of rats (n = 17) removed 

13 from the population during the sampling session that followed the first bait application. This 

14 suggests that at Palmyra, crab-related bait consumption prevents repeat bait applications more 

15 than 5 days apart from having a cumulative effect on the amount of bait made available to target 

16 rodents. To be effective, the bait application rate for the second broadcast should be high enough 

17 to overcome competition for bait by land crabs. 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 43

1

2 Also, for the 2 sites treated at 18 kg/ha + 9 kg/ha, bait consumption was greater at the study site 

3 with the highest crab index of abundance value – Whippoorwill Island. Across the 3 study sites, 

4 bait consumption was greatest at the site treated with the highest bait application rate – Home 

5 Island. These results suggest that crab abundance has a positive correlation with bait 

6 consumption, as does the bait application rate. Therefore, increased bait application rates are 

7 needed to overcome crab-related bait consumption; however, this is not a linear function because 

8 an increase in bait application rate leads to an increase in bait consumption – to an unspecified 

9 asymptote. 

10

11 To successfully eradicate rats from Palmyra Atoll using a bait broadcast technique, an 

12 application rate greater than 36 kg/ha (shown to be unsuccessful in this study) is required. The 

13 2005 trial eradications demonstrated that rats can be eradicated from islands with high land crab 

14 densities when bait is broadcast at rates from 85kg/ha to 95 kg/ha. The findings of the 2008 

15 biomarker study, in concert with the results from the 2005 trial eradication, indicate that a 

16 Palmyra-specific amendment, under FIFRA, to the existing bait product label that permits bait 

17 application rates as high as 90 kg/ha (specific to Palmyra Atoll) will be needed to conduct a 

18 successful bait broadcast-based eradication at Palmyra Atoll.

19

20 2010 Bait Palatability and Ecotoxicology Studies (see Appendix F for the Full Report)

21 From April 29 to May 28, 2010, two IC personnel visited Palmyra Atoll to assess the fate, 

22 palatability, and environmental impacts associated with the broadcast application of two 

23 rodenticide products: Diphacinone-50 (50 ppm Diphacinone), and Brodifacoum-25W (25 ppm 

24 brodifacoum). The main components of this study were:

25 Measure the concentration of toxicant found in the surface soil (≥ 2 cm) after exposure to 

26 bait pellets for time periods that would be expected during a real broadcast-based 

27 eradication.

28

29 Assess the concentration of rodenticide residue in the tissue of hermit crabs (Coenobita 

30 spp.) and excrement from land crabs (Cardisoma carnifex) in a simulated bait broadcast 

31 setting.

32

33 Assess the palatability, for rats and land crabs, of the two bait products currently 

34 approved for use to eradicate rats at Palmyra Atoll.

35

36 Conduct site-specific research needed to inform the development of operational plans for 

37 a successful rat eradication.

38

39 Palmyra consists of 618 acres 250 of emergent land (fragmented into 25 islands), 16 of which 

40 were used during these studies. Rats were live-captured on the following islands: Strawn, 

41 Cooper, Aviation, Quail, Whippoorwill and Bunker, Eastern, Portsmouth, Barren, the South 

42 Island Complex, Paradise, Home, Sand, Fern, Lost, and the North-South Causeway (Figure 2.1). 

43 Soil samples were obtained from Lost Island and Cooper Island. All land crabs were collected 

44 haphazardly from Cooper Island and Strawn Island. Hermit crabs were collected from 

45 Whippoorwill Island.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 44

1

2 Analysis of the soil samples, collected from the plots in the study that looked at rodenticide 

3 leaching from pellets placed on the ground into the surface soil, found low amounts of 

4 rodenticide in sandy and organic soil regardless of the exposure period (2, 7, 28, 36, and 50 

5 days). The concentrations of brodifacoum found in sandy soil samples were similar across all 

6 sample periods (DF=3 F=1.59 P= 0.26), and diphacinone was not detected in sandy soil samples, 

7 regardless of the exposure period. In organic soil, we found no difference in the brodifacoum 

8 concentration (DF= 3 F= 0.33 P=0.80) or diphacinone concentration (DF= 3 F= 2.67 P= 0.11) 

9 between exposure periods. 

10

11 Out of 48 samples (not including controls), only two contained a toxicant concentration that was 

12 high enough to quantify. The rest of the samples yielded a zero value (toxicant not detected) or a 

13 „trace‟ value (toxicant detected but < method detection limit) (Figure 2.2). This study suggests 

14 that only minimal amounts of both rodenticides (from either Diphacinone-50 or Brodifacoum15 25W bait) remain in the surface soil after the maximum period of exposure (the time a bait pellet 

16 would be expected to be in contact with the soil) that would be experienced during a broadcast 

17 bait application at Palmyra. 

Day

0 10 20 30 40 50 60

Toxicant Concentration (ppm)

0.0

0.2

0.4

0.6

0.8

1.0

Brodifcaoum in Sandy Soil

Diphacinone in Sandy Soil

Brodifacoum in Organic Soil

Diphacinone in Organic Soil

18

19 Figure 2.2. Mean concentration of brodifacoum (N=3 per day) and diphacinone (N=3 per day) found in 

20 surface samples of sandy soil and organic humus soil over four exposure periods. Samples were taken 

21 directly beneath bait pellets (or remains of pellets) on day 2 and day 7. Samples taken on days 28, 36, and 

22 50 were taken directly beneath where a pellet had rested for 7 days. 

23

24 The mean concentration of toxicant residue within crab excrement varied by exposure period for 

25 both rodenticides (Table 2.4). Toxicants were most concentrated within crab excrement during 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 45

1 the first two sampling periods. Both brodifacoum and diphacinone were actively consumed 

2 during these periods, until the bait products were removed from crab diets on day 7. A reduction 

3 in the toxicant concentration in sampled excrement was observed between day 6 and day 10 

4 (Figure 2.3).

5

6

7 Table 2.4. Mean concentration of toxicant (ppm) within excrement samples from crabs 

8 that consumed 25W or D-50 bait pellets ad lib for 7 days.

Analyte Day 2 concentration ± (1SD) Day 6 Day 10 Day 23

Brodifacoum (ppm) 2.8 (1.2) 2.6 (1.3) 1.0 (0.7) 0.25 (0.3)

Diphacinone (ppm) 8.4 (2.9) 8.9 (8.4) 2.5 (0) 2.5 (0)

9

10

11

Sample Day

0 10 20 30 40 50 60

Toxicant Concentration (ppm)

0

5

10

15

20

Brodifacoum - excrement

Diphacinone - excrement

Brodifacoum - crab tissue

12

13 Figure 2.3. Comparison of the concentration (ppm) of brodifacoum in crab excrement and tissue over time 

14 to the concentration (ppm) of diphacinone in crab excrement. The concentration of brodifacoum in crab 

15 tissue was determined by the National Wildlife Research Center Analytical Lab (USDA 2006) after a trial 

16 broadcast eradication in 2005. Crabs consumed rodenticide until day 7, and subsequently fed on natural 

17 food items. Positive “trace” results were included as 1⁄2 the reporting limit (0.1 for brodifacoum and 2.5 for 

18 diphacinone). 

19

20 Palatability trials were run using 68 rats. While both bait products were consumed when 

21 challenged against naturally available food items (solid coconut endosperm, coconut meristem, 

22 and Pandanus mesocarp), neither bait product was found to be significantly more palatable than 

23 the other.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 46

1

2 2010 Genetic Sampling, Rat Detection, and Canopy Baiting Studies (see Appendix G for the 

3 Full Report)

4 Primary Objectives:

5 Collect genetic samples from the R. rattus population at Palmyra Atoll.

6

7 Measure the baseline detection success of three devices: chew blocks, tracking 

8 tunnels, and live traps.

9

10 Construct and deploy bait stations in a variety of environments to measure 

11 variability in bait removal rates, crab interference, structural integrity of the 

12 stations, and overall attractiveness to rats.

13

14 Determine the degradation rates and effects of weathering and decay for different 

15 types of canopy bait designs, and measure the persistence of canopy baits in the 

16 crowns of coconut palms.

17

18 Document rats consuming pellets and canopy baits in the crowns of coconut 

19 palms; determine which type of bola material is preferred by rats.

20

21 Field-test three canopy bait launching devices and establish the situations in 

22 which each performs best.

23

24 Monitor placebo bait pellets in the marine environment to determine degradation 

25 rates of the matrix under varying conditions.

26

27 Quantify the degradation rate of rat carcasses in areas with high shorebird 

28 densities, and photograph any avian species interested in consuming the carcasses.

29

30 A team of three people conducted several studies at Palmyra Atoll from September 22, 2010 

31 until October 17, 2010. Rodent live-trapping confirmed that rats were present on all landmasses 

32 visited, with the exception of Dudley Island where no rats were detected. Captured rats (304 

33 total) ranged from juvenile to adult (24 g to 227 g), indicating that breeding had recently taken 

34 place. Chew blocks were slightly more successful at detecting rats in comparison to live traps, 

35 but needed frequent replacement, as the hard candy interior lasted less than 24 hours due to rats, 

36 crabs, ants, rain, and humidity. Tracking tunnels were unsuccessful at detecting rat presence until 

37 coconut bait was placed inside as an added incentive. Bait station performance, pellet removal 

38 rate, and station resistance to crab-related interference varied widely depending on the location 

39 of the station. 

40

41 Surgitube, a tubular gauze dressing, was the most effective material for canopy bait (“bola”) 

42 construction. It was easy for rats to chew through, retained pellets during high-velocity launches, 

43 and prevented inside bait from molding. Three launching devices were tested, the HyperDog 

44 slingshot, the Big Shot pole-mounted sling shot, and the Squall 250 air cannon. Each device 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 47

1 performed best within specific conditions, and it was evident that a combination of methods may 

2 be required for fast and accurate canopy baiting. Once in the palm canopy, bolas were typically 

3 consumed within 24 hours.

4

5 Placebo bait pellets placed in the marine environment degraded completely within 48 hours, 

6 disappearing faster on the intertidal ocean-facing side of the atoll (within 24 hours). Rat 

7 carcasses placed in locations frequented by shorebirds and typified by low crab densities (North 

8 Beach and along the runway), degraded due to consumption by invertebrates and environmental 

9 decay within 72 hours; carcass feeding by shorebirds was not observed in the images captured by 

10 motion sensing cameras that were monitoring the rat carcasses.

11

12

13 2.5.3 Actions Taken to Develop the Action Alternatives Presented in this Document

14

15 Alternative B: Aerial Broadcast of Brodifacoum 

16 2004

17 Bait weathering study

18 Toxicant efficacy (field) study

19 2005

20 Bait weathering study

21 Trial eradication

22 Bait palatability study

23 Measurement of toxicant residue in crab tissue

24 2008

25 Bait application rate study

26 Nontarget species bait exposure pathways study

27 2010

28 Toxicant bioavailability study

29 Measurement of toxicant integration into soil 

30 Bait palatability study

31 Canopy bait design and testing

32 Bait station design and testing

33 Bait fate in the marine environment study

34 Rat detection device testing

35 Eradication monitoring plan

36

37 Alternative C: Aerial Broadcast of Brodifacoum, with Proactive Mitigation of Risk 

38 for Vulnerable Shorebird Taxa

39 2004

40 Bait weathering study

41 Toxicant efficacy (field) study

42 2005

43 Bait weathering study
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 48

1 Bait palatability study

2 Toxicant residue in crab tissue

3 2008

4 Bait application rate study

5 Nontarget species bait exposure pathways study

6 2010

7 Toxicant bioavailability study

8 Measurement of toxicant integration into soil 

9 Bait palatability study

10 Canopy bait design and testing

11 Bait station design and testing

12 Bait fate in the marine environment study

13 Rat detection device testing

14 Eradication monitoring plan

15 Testing of shorebird capture methods

16

17 Alternative D: Bait Stations with Brodifacoum, with Canopy Baiting

18 2004

19 Bait weathering study

20 Toxicant efficacy (field) study

21 2005

22 Bait weathering study

23 2008

24 Nontarget species bait exposure pathways study

25 2010

26 Toxicant bioavailability study

27 Measurement of toxicant integration into soil 

28 Bait palatability study

29 Canopy bait design and testing

30 Bait station design and testing

31 Rat detection device testing

32

33

34 2.6 Alternative B: Aerial Broadcast of Brodifacoum-25W 

35

36 2.6.1 Rationale

37 Brodifacoum is the most extensively used rodenticide for rodent eradication from islands. Of the 

38 332 successfully reported island rodent eradication efforts worldwide as of 2007, 71 percent used 

39 brodifacoum as the primary rodenticide (Howald et al. 2007). The specific product Brodifacoum40 25 has been used successfully on four islands, all using aerial broadcast as the primary technique. 

41 Three of these islands were treated with Brodifacoum-25D (especially formulated for dry 

42 environments), and one was treated with Brodifacoum-25W (especially formulated for wet 

43 environments). While every project is unique, and techniques have varied substantially between 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 49

1 projects, many of the basic parameters for success using brodifacoum are now well-established 

2 within the conservation world. Brodifacoum is highly acutely toxic to rats; this classification 

3 describes a chemical that has a high level of acute toxicity and the ability to cause harmful local

4 and systemic effects after a single exposure.

5

6 Brodifacoum-25W has also been tested with favorable results in 2 similar tropical study sites: 

7 Palmyra Atoll in the equatorial Pacific (Buckelew et al. 2005), and Pohnpei, Micronesia in the 

8 western Pacific (Wegmann et al. 2007). 

9

10 2.6.2 Summary of Bait Delivery Methods

11 Brodifacoum-25W bait would be systematically applied to all land areas above the mean high 

12 tide mark. Draft operational details for Alternative C (Preferred Alternative) are presented in 

13 Appendix K and include elements such as eradication techniques, team members and roles, 

14 communications, timing, health and safety, monitoring, bird mitigation, and logistics. Many 

15 lessons learned from the Rat Island, Alaska eradication project (Salmon and Paul 2010); such as 

16 minimizing risks to nontarget species while maintaining a high probability of eradication 

17 success, comprehensive logistical planning, structured communications, recording keeping, and 

18 documentation of impacts; have been taken into consideration and incorporated.

19

20 For areas at Palmyra that cannot be baited by helicopter, such as sections of land that are too 

21 narrow to avoid bait spread into the marine environment, personnel would broadcast bait by 

22 hand, including placing bait in the coconut palm canopy by hand. Coconut palm crowns that 

23 overhang the mean high tide mark will be baited by hand. Personnel would also install bait 

24 stations in limited circumstances around the research station and wharf areas, on the support 

25 vessel, and at select shorebird roosting sites that are thought to be rat-free. 

26

27 2.6.3 Timing and Weather

28 Aerial broadcast operations would be conducted in June and July, and would coincide with the 

29 seasonal low in populations of migratory shorebirds. Aerial broadcast operations would be 

30 conducted when weather conditions are favorable for flight operations.

31

32 2.6.4 Bait Application Plan

33 Bait broadcast by helicopter would consist of multiple low-altitude overflights of Palmyra. 

34 The baiting regime would follow methods based on successful island rodent eradications 

35 elsewhere in the U.S. and globally (Howald et al. 2007); in which overlapping flight swaths are 

36 flown across the interior island area, and overlapping swaths with a deflector attached to the 

37 hopper (to prevent bait spread into the marine environment) are flown around the coastal 

38 perimeter. The width of a flight swath would be determined beforehand in calibration trials, and 

39 would likely range between 33 – 131 feet (10 - 40 m). 

40

41 Each flight swath would overlap the previous one by approximately 50 percent to ensure no gaps 

in bait coverage. The precision of bait application to the island would be guided by a TracMap®42

43 GPS guidance system that shows baiting coverage and cautions the pilot against baiting outside 

44 predetermined areas (Figure 2.4). 

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 50

1

2 Figure 2.4. Onboard TracMap GPS used by a helicopter pilot to 

3 monitor and guide the aerial bait broadcast at Rat Island, 2008.

4

5 The bait would be applied according to a flight plan that would take into account:

6 1. The need to apply bait evenly, according to label rates, and without gaps in coverage or 

7 excessive overlap.

8 2. Current and forecasted weather conditions.

9 3. The need to avoid bait broadcast into the marine environment.

10 4. The need to minimize disturbance to native wildlife.

11 5. The need to minimize the substantial costs associated with helicopter flight time.

12

13 The helicopter would fly: 

14 1. At a speed ranging from 25 - 50 knots (29 - 58 mph or 46 - 93 km/hr).

15 2. At an average altitude of approximately 164 ft (50 m) above the ground.

16 3. With the bait hopper on a long-line 49 - 66 ft (15-20 m) slung below the helicopter.

17

18 Concurrent to the aerial bait application, four or five personnel trained in GPS-guided hand19 broadcast baiting (Wegmann et al. 2009) would treat land areas that are too narrow for aerial 

20 treatment. During each bait application, emergent land areas suitable for aerial broadcast would 

21 be subject to at least one pass with the bait hopper, and likely two.

22

23 In order to ensure eradication success, it would be necessary to conduct a second bait 

24 application, 7 - 14 days after the first, to minimize the likelihood of competitively inferior adult 

25 rats or juvenile rats surviving the initial broadcast because they were not given an opportunity to 

26 feed on bait. For each aerial bait application there would likely be no more than 3 consecutive 

27 days of aerial baiting followed by up to 7 days of placing bait in overhanging palms. Bait would 

28 be applied according to the limitations set by the EPA‟s pesticide regulations under FIFRA. 

29

30
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 51

1 Bait Sowage Rate

2 With Alternative B, Brodifacoum-25W bait would be applied to Palmyra‟s emergent land area. 

3 For each day of aerial broadcast baiting (2-3 days/application), baiting would follow a section4 by-section plan so that an unexpected halt to baiting operations would result in a minimized 

5 unbaited edge for the previously baited sections. Two bait applications would be conducted; the 

6 second would follow the first by 7 to14 days, and would be at a lesser application rate to account 

7 for the reduction in bait consumers – rats that died from rodenticide exposure following the first 

8 bait application. The bait application will be as uniform as is possible given current bait 

9 application technology at a target rate not expected to exceed 80.4 lb/acre (90 kg/ha) or lower 

10 than 53.6 lb/acre (60 kg/ha).

11

12 Justification for the Bait Sowage Rates Proposed in Alternative B

13 Sowage rates for broadcast-based rodent eradications are driven by the need to have bait on the 

14 ground for multiple nights, and in adequate density and distribution to ensure that all rats have 

15 access to enough bait to ensure 100 percent removal of the target population. The factors and 

16 considerations leading to the determination of bait sowage rates for Alternative B are:

17

18 1. The registration of anticoagulant baits with the EPA were based, in part, on laboratory 

19 efficacy studies that are 3-day choice trials, with a minimum of 90 percent mortality as 

20 the target threshold for registration purposes (Schneider and Hitch 1982). In 1998, the 

21 EPA switched to 24-hour choice test trials for the registration of second generation 

22 anticoagulants; these trials do not result in 100 percent mortality of the test population (P. 

23 Martin, pers. comm.). Furthermore, recent laboratory studies where R. rattus were 

24 provided brodifacoum bait (in a no-choice scenario) for a 3-day exposure period did not 

25 result in 100 percent mortality of the sample rats (Pitt et al. 2010). This demonstrates that 

26 a 1 - 3 day exposure period is inadequate to ensure 100 percent mortality of rats when 

27 using brodifacoum. As such, 1- 3 days is an inappropriate benchmark for calibrating 

28 baiting rates for eradications on islands where 100 percent mortality of the target 

29 population is the defined goal. In Alternative B, the sowage rates selected will, according 

30 to the best available information, provide 4 days of bait availability for every rat. 

31 2. Rats on islands compete with other species in their environment for access to food

32 resources. Once bait is placed on the island, biotic (molds, microbes, and insects) and 

33 abiotic (moisture, temperature fluctuations) factors begin to degrade the bait. This 

34 competition for, and subsequent degradation of bait over time, could lead to low bait 

35 availability to rats, and ultimately to failure of the eradication. That bait rates are directly 

36 correlated with the density of rats is intuitively logical; however, it does not account for 

37 competition for the bait by other species that are attracted to the highly nutritious and 

38 energy-rich bait matrix. The broadcast bait sowage rates presented here are not directly 

39 correlated with rat densities at Palmyra, and will by necessity be more than is strictly 

40 needed to expose every rat to a lethal dose. 

41 3. Rats are noted for their neophobic behavior toward new or novel food items, including 

42 bait products that contain rodenticide (Galef and Clark 1971).To counter this bait needs 

43 to be available to all rats in the target population for a long enough period so that all rats 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 52

1 will repeatedly encounter bait, identify it as a food resource, and choose to consume it 

2 over the available natural foods that they normally seek out. It takes time for rats to 

3 overcome their wariness over new food resources, such as bait pellets broadcast into their 

4 environment. 

5 4. The bait application must account for the variation in individual vulnerability due to age, 

6 behavior, body size or mass, food supply, and range size (Cromarty et al. 2002). On any 

7 given night, any given rat may choose not to forage because of the availability of cached 

8 food, or behavior that may limit their time devoted to foraging such as (but not limited to) 

9 defending territories, constructing and maintaining nests, reproductive behavior, or caring 

10 for young. Thus, bait availability must be long enough to account for the real possibility 

11 that individual rats will not consume bait directly after the bait application.

12 The bait application rate for Alternative B is based on the results of several bait availability 

13 studies conducted at Palmyra (Section 2.4.4), and real and trial rat eradications conducted on 

14 island ecosystems that are similar to that at Palmyra (Table 2.3). “Bait availability” is defined as 

15 the time period in which rats would have direct access to bait pellets broadcast on the ground. 

16 The 2005 trial eradication conducted at Palmyra found that with bait sowage rates as high as 80.4 

17 lb/acre (90 kg/ha), bait is available to rats for a maximum of 7 days and is only uniformly 

18 available for 4 days (Figure 2.5). 

19

20 Bait consumption by land crabs (counted at 300 crabs/ha) is the primary factor determining bait 

21 availability. In order to ensure that rats have access to bait for 4 days, Alternative B would 

22 require bait application rates that exceed the maximum bait application rate specified by the bait 

23 product‟s FIFRA registration. Alternative B is being considered concurrently with an effort to 

24 acquire a FIFRA registration specifically for Palmyra that would allow for bait application rates 

25 that carry a high probability of eradication success that can overcome the limitations at Palmyra. 

26 The proposed broadcast alternative will knowingly expose crabs, ants, cockroaches, etc. to bait; 

27 however, these organisms are not target species and are not expected to be harmed by the 

28 exposure. Additionally, FIFRA only limits pesticide applications where nontarget species are 

29 unreasonably adversely affected by the toxicant. That is not the case for invertebrates because 

30 brodifacoum is not known to cause adverse effects to invertebrates (see FIFRA Code Section 2). 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 53

1

2 Figure 2.5. Results from the bait consumption study conducted on Whippoorwill Island during the 2005 

3 trail rat eradication at Palmyra (Buckelew et al. 2005). The vertical bars represent 99% confidence 

4 intervals for the mean consumption estimates, and show that in order to maintain bait availability for 

5 4days, the sowage rate should be between 60 and 90 kg/ha.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 54

1 Table 2.5. A record of bait broadcast-studies at Palmyra and rat eradications in similar environments to those found in Palmyra‟s 

2 eradication environment: in terms of climate, plant community, and land crab densities to inform such rat eradications on tropical 

3 islands. 

Island Context Method Sowage 

rate 

(kg/ha)

Rodenticide Target 

species

Project 

year

Eradication 

result

Source

Whippoorwill Island, 

Palmyra Atoll

Trial 

eradication

Hand broadcast 

w/canopy baiting 95 Brodifacoum R. rattus 2005 Successful Buckelew et al. 2005

Bunker Island, 

Palmyra Atoll

Trial 

eradication

Hand broadcast 

w/canopy baiting 70 Brodifacoum R. rattus 2005 Successful Buckelew et al. 2005

Little East Island, 

Palmyra Atoll

Trial 

eradication

Hand broadcast 

w/canopy baiting 60 Brodifacoum R. rattus 2005 Successful Buckelew et al. 2005

Fern Island, Palmyra 

Atoll

Trial 

eradication

Hand broadcast 

w/canopy baiting 80 Brodifacoum R. rattus 2005 Successful Buckelew et al. 2005

Home Island, 

Palmyra Atoll

Trial 

eradication

Hand broadcast 

w/canopy baiting 85 Brodifacoum R. rattus 2005 Successful Buckelew et al. 2005

Dekehtik Island, 

Pohnpei, FSM

Trial 

eradication

Hand broadcast 

w/canopy baiting 50 Brodifacoum R. exulans 2007 Failed Wegmann et al 2008

Pein Mal Island, 

Pohnpei, FSM

Trial 

eradication

Hand broadcast 

w/canopy baiting 50 Brodifacoum R. rattus 2007 Successful Wegmann et al 2008

Whippoorwill Island, 

Palmyra Atoll

Biomarker 

study

Hand broadcast 

w/canopy baiting 18 + 9 Brodifacoum R. rattus 2008 Failed Wegmann et al 2008

Portsmouth Island, 

Palmyra Atoll

Biomarker 

study

Hand broadcast 

w/canopy baiting 18 + 9 Brodifacoum R. rattus 2008 Failed Wegmann et al 2008

Home Island, 

Palmyra Atoll

Biomarker 

study

Hand broadcast 

w/canopy baiting 36 + 36 Brodifacoum R. rattus 2008 Failed Wegmann et al 2008

Fanna Island, Palau Eradication Hand broadcast 25 + 25 Brodifacoum R. exulans 2009 Failed Isechal 2009

Henderson Island, 

UK OST Eradication Aerial broadcast 60 + 601 Brodifacoum R. exulans 2011 Pending (Brooke et al. 2010)

1 4 Brooke et al. (2010) recommend two applications at 60 kg/ha for the areas of the island with the highest land crab density; the rest of the island, with markedly 

5 lower land crab density, will be treated with lower application rates.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 55

1 A sowage rate range (53.6 lb/acre to 80.4 lb/acre) was selected for Alternative B because bait 

2 efficacy studies have shown that “standard” application rates would not expose all individual rats 

3 within the target population (Wegmann 2008), while “higher” bait application rates (53.6 lb/acre 

4 to 84.8 lb/acre) carry a high probability of eradication success (Buckelew et al. 2005). 

5 Admittedly, there is a substantial information gap between the boundaries of the tested bait 

6 sowage rates (32 lb/acre – 53.6 lb/acre); however, bait consumption studies conducted at 

7 Palmyra show that even at high bait sowage rates (84.8 lb/acre), bait is uniformly available to 

8 rats for only 4 days and essentially not available 7 days after application (Buckelew et al. 2005). 

9 Limitations to bait availability are due primarily to the abundance of land crabs that consume 

10 large quantities of bait at Palmyra. Because land crabs travel great distances in short periods of 

11 time (Wegmann 2009), it is not possible to predict areas of low crab density and treat such 

12 locations with “lower” bait application rates. During the 2005 trial eradication, rats were 

13 successfully removed from the study site with the highest crab density using 84.8 lb/ha; after 

14 subsequent analysis of the results from bait consumption studies and rat exposure studies 

15 (biomarker studies) conducted at Palmyra. The Service believes that an application rate between 

16 53.6 lb/acre and 80.4 lb/acre will successfully remove rats from the atoll while creating a 

17 relatively short window of bait availability for nontarget species (Buckelew et al. 2005, USDA 

18 2006, Alifano and Wegmann 2010).

19

20 Palmyra‟s tropical rat eradication environment is vastly different from the environment(s) in 

21 which current bait product label specifications and general rat eradication models were 

22 developed (Wegmann 2008), and it has been well documented that rodent eradications on 

23 tropical islands require special consideration (Varnham 2010). In considering what is 

24 appropriate for rat eradication at Palmyra, we must shift our baseline from the model based on 

25 rat eradications in temperate regions to that of one based on the nuances of moist tropical island 

26 ecosystems. Two applications at 25 kg/ha (brodifacoum) spaced ten days apart failed to eradicate 

27 R. exulans from Fanna Island in Palau (tropical, high density of land crabs) (Isechal 2009), and a 

28 single hand broadcast application of 50 kg/ha (brodifacoum) augmented by canopy baiting failed 

29 to eradicate R. exulans from Dekehtik Island in Pohnpei State, FSM (tropical, high density of 

30 land crabs) (Wegmann et al. 2007). The sowage rates employed in both cases would be 

31 considered “high” compared to sowage rates used for rat eradications in temperate climates, yet 

32 they failed to eradicate the targeted rat populations. Because of the risk of missing rats in areas of 

33 high crab density, the Royal Society for the Protection of Birds (RSPB) has selected 60 kg/ha 

34 (brodifacoum) as the sowage rate for specified areas in an upcoming eradication on Henderson 

35 Island. 

36

37 The sowage rates proposed for Alternative B are “high” when compared to sowage rates 

38 typically used on temperate islands, or even tropical islands with low land crab density; however, 

39 when compared to sowage rates selected for eradication projects on islands that share Palmyra‟s 

40 eradication environment (land crab rich, fast rate of bait degradation) (Table 2.5), the sowage 

41 rates proposed here are not extraordinary.

42

43 Avoiding Bait Drift into the Marine Environment

44 To avoid spreading bait into the marine environment, bait would be applied with application 

45 methods that are tailored to the width of the treated area; see Figure 2.6 for an example of how 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 56

1 different bait application methods could be employed to minimize bait drift into the marine 

2 environment. 

3

4 In between the first and second bait applications, the crowns of palms that overhang the lagoon 

5 and the ocean-facing shoreline would be baited by hand. As a precautionary measure, bait 

6 stations containing a second generation anticoagulant rodenticide product would be placed 

7 around the research station, the wharf, and at select shorebird roosting sites. 

8

9

10

11

12 Figure 2.6. Bait broadcast application plan for eradicating rats from Palmyra Atoll. The treatment is 

13 scheduled for 2 days, and each day is divided into 6 sequential segments, with each segment representing 

14 a stand-alone area that would not need to be re-baited if the baiting operation is temporarily suspended 

15 (for up to 3 days). Different bait application methods (color coded in the figure) would be used to 

16 minimize bait spread into the marine environment.

17

18

19 Before the bait application process initiates calibration between the pilot, helicopter, and hopper 

20 would be conducted to ensure consistency and accuracy of the bait application using a placebo 

21 bait broadcast. The calibration would occur over a test site off-island in atmospheric conditions 

22 similar to those at Palmyra. A non-toxic version of Brodifacoum-25W bait would be used for the 

23 calibration.

24
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 57

1 To ensure complete and uniform application:

2 The actual application path would be monitored onboard the helicopter using an onboard 

3 global positioning system (GPS), a navigation bar, and a computer to precisely guide, 

4 track, and document the application in order to avoid gaps and prevent unintended 

5 overlaps in application coverage.

6

7 The application rate would be calculated using the known rate of bait flow from the 

8 hopper, the helicopter‟s reported velocity, and overlaps in the bait swath reported by the 

9 helicopter‟s onboard GPS tracking system.

10

11 The application rate would also be monitored in plots established on Cooper Island.

12

13 Adjustments in bait flow rates, helicopter speed, and flight lines would be made as 

14 necessary to meet the optimal application rate, while staying within the bait application 

15 limits legally required by the bait product‟s FIFRA registration.

16

17 Preventing Bait Drift into the Marine Environment

18 Every reasonable effort would be made to minimize the risk of bait drift into the marine 

19 ecosystem. A broadcast directional bucket would be attached to the hopper for treatment of 

20 shoreline areas (Figure 2.6). With this bucket configuration, there is a shunt inside the hopper 

21 that directs bait to just one side of the spinner, which results in bait being slung to one side of the 

22 bucket – the effective bait swath from the directional bucket is approximately 1⁄2 the width of the 

23 swath from the standard bucket. The directional bucket will be used to apply bait inland from the 

24 mean high tide line, broadcasting bait within approximately 120° of the onshore side of the 

25 helicopter, to minimize the risk of bait drift into the ocean in the opposite direction or seaward 

26 side. Observer teams would be on-the-ground to monitor proper operation of hopper and shunt 

27 and would move into treatment areas immediately after application to assess bait application rate 

28 and any accidental drift in the marine environment (Appendix A).

29

30 Coconut palms growing along the shoreline commonly hang over the high tide line. To prevent 

31 bait drift from vegetation, overhanging palms would be baited by hand rather than with the 

32 helicopter and bait hopper. Following each aerial bait application, the crowns of palms that 

33 overhang the lagoon-facing and ocean-facing shoreline would be baited at a rate not to exceed 

34 3.5 oz of bait (100 g) for every stand-alone palm or every third interconnected palm; the number 

35 of overhanging palms was recently estimated to be 3,546 (Alifano and Wegmann 2010). 

36

37 Coverage of Baiting Gaps

38 Unoccupied structures (from World War II-era operations on the atoll), which are potential rat 

39 habitat, may not receive the optimal bait coverage with helicopter broadcast alone. All identified 

40 structures would be hand-baited directly after or directly before the aerial broadcast over the 

41 adjacent land area. 

42

43 In cases where it is evident or suspected that any land area did not receive full coverage, there 

44 would be supplemental systematic broadcast, either by foot, helicopter, or combination of the 

45 above. All personnel who would participate in hand broadcast baiting would be trained in 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 58

1 systematic, Geographic Information System (GIS)-guided hand-broadcast bait application 

2 methods prior to the actual bait application (Wegmann 2009).

3

4 Bait stations would be placed around the research station and camp area, the wharf, and several 

5 shorebird roosting sites that are thought to be rat and crab-free (Figure 2.7). Bait stations would 

6 be loaded with a second generation anticoagulant bait product registered by the EPA and used in 

7 accordance with FIFRA. All stations would be checked regularly and bait would be replenished 

8 every 2 weeks for at least 45 days. Tamper-resistant bait stations would be purchased for use in 

9 and around areas of human habitation. For uninhabited areas of the atoll, crab-resistant bait 

10 stations would be constructed with off-the-shelf materials (Appendix G.) and placed at shorebird 

11 roost sites.

12

13 All personnel who handle bait would meet or exceed all requirements for personal protective 

14 equipment (PPE) required by the EPA. All bait application activities (aerial broadcast, hand 

15 broadcast, and bait station filling) would be conducted by or under the supervision of pesticide 

16 applicators licensed by EPA.

17
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 59

1

Figure 2.7. Alternative C 

– Preferred Alternative - Placement of bait stations during the rat eradication at Palmyra Atoll.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 60

1 2.7 Alternative C: Aerial Broadcast of Brodifacoum, with Proactive 

2 Mitigation of Risk for Vulnerable Shorebird Taxa – Preferred Alternative

3

4 2.7.1 Rationale

5 The operational components of Alternative C would be identical to Alternative B, except that 

6 Alternative C, as the Preferred Alternative, includes the implementation of a shorebird risk 

7 abatement effort. Shorebird mitigation is a measure intended to reduce adverse impacts to 

8 vulnerable shorebird species. This effort is in addition to the timing of the bait broadcast and 

9 would occur during the period of year that has the lowest numbers of shorebirds present at 

10 Palmyra. We would capture and hold “at risk” birds prior to and during the period when they 

11 would be at risk of lethal exposure to rodenticide. 

12

13 Regardless of the bait application method (broadcast or bait station) employed to eradicate rats 

14 from Palmyra, shorebirds, and in particular bristle-thighed curlews (BTCU) and Pacific golden15 plovers (PGPL), are at risk of exposure to rodenticide. The first attempt to eradicate rats from 

16 Palmyra – a bait station operation that used both brodifacoum and bromethalin (Howald et al. 

17 2004), resulted in the death of at least one BTCU. Some BTCU and PGPL mortality was 

18 recorded directly after a brodifacoum bait hand broadcast eradication effort in the Phoenix 

19 Islands (Pierce et al. 2008), and PGPL were observed consuming non-toxic “placebo” bait pellets 

20 at Wake Atoll (Wegmann et al. 2009). 

21

22 Both BTCU and PGPL are seasonal migrants that overwinter on islands in the tropical Pacific 

23 Ocean and spend summers at breeding grounds in Alaska. The number of BTCU and PGPL 

24 present at Palmyra decreases significantly during the months of June and July; however, some 

25 juveniles or non-breeding adults (149 - 182 BTCU, 34-62 PGPL; FWS unpublished data) remain 

26 at Palmyra throughout the summer. An aerial broadcast of brodifacoum bait, as proposed in 

27 Alternatives B and C, would create a scenario of high exposure risk for individuals of both 

28 shorebird species for a short period of time – approximately 34 days (USDA 2006, Alifano and 

29 Wegmann 2010). Shorebird exposure risk from rodenticides is discussed in greater detail in 

30 Chapter 4. 

31

32 The capture and captive holding of shorebirds would be a safeguard against negative impacts to 

33 individuals resulting from exposure to, and mortality from, brodifacoum bait during and directly 

34 after the eradication. However, bringing individuals into captivity, holding them for the required 

35 period, and re-releasing them onto the island, also presents risks of injury, deterioration in body 

36 condition, mortality of individuals, behavioral changes, and disease outbreak in the captive37 holding facility. 

38

39 2.7.2 Taxa 

40 The bristle-thighed curlew (BTCU) and Pacific golden-plover (PGPL) are the most numerous 

41 shorebirds at Palmyra, and the species that are most likely to be put at risk by a rat eradication at 

42 Palmyra. 

43

44 The BTCU is a medium-sized curlew with a wingspan of approximately 40-44 cm and blue-gray 

45 legs. During the breeding season, BTCUs are found in the remote mountainous regions of 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 61

1 western Alaska in the Andreafsky Wilderness Area north of the Yukon River mouth and on the 

2 central Seward Peninsula (McCaffery and G. Pelota Jr. 1986, Kessel 1989, Gill et al. 1990, 

3 Marks et al. 2002). During the non-breeding season this species is found on remote Pacific 

4 Ocean islands and atolls (Marks et al. 1990) including the Hawaiian Islands (U.S.), U.S. Minor 

5 Outlying Islands, Northern Mariana Islands (to U.S.), Federated States of Micronesia, Marshall 

6 Islands, Nauru, Kiribati, Tuvalu, Tokelau (to New Zealand), Fiji, Tonga, Niue (to New Zealand), 

7 Samoa, American Samoa, Cook Islands, and French Polynesia, also reaching the Solomon 

8 Islands, Norfolk Island (to Australia), Kermadec Islands (New Zealand), Pitcairn Islands (to UK) 

9 (notably Oeno) and Easter Island (Vilina et al. 1992, Brooke 1995). Sub-adults may remain in 

10 the Pacific until they are nearly 3 years old (Collar et al. 1992). Site fidelity on both the breeding 

11 and wintering grounds is high with many birds returning to the same location on an island for 

12 multiple years (Marks and Redmond 1996).

13

14 Based on comprehensive surveys of the known breeding range on the Seward Peninsula, the 

15 global population size is estimated at approximately 3,200 breeding pairs (6,400 breeding birds;

16 via a statistically valid sampling regime last assessed in 2000-2001, L. Tibbitts pers. comm.).The 

17 total number of bristle-thighed curlews, including non-breeding adults and subadults is 

18 estimated at 10,000 (Morrison et al 2006). Population trends are unknown (Marks et al. 2002). 

19

20 The Pacific golden-plover is a medium-sized plover with gray-black legs (Johnson and Connors 

21 1996). During the breeding season, this species frequents the arctic and subarctic tundra of 

22 Russia and western Alaska, nesting along the Chukchi and Bering Sea coasts, inland throughout 

23 the entire Seward Peninsula, and much of the Yukon-Kuskokwim region (Petersen et al. 1991, 

24 Connors et al. 1993, Johnson and Connors 1996). This species winters over a considerable 

25 portion of the Earth's surface. It is known to occupy upland and coastal habitats in the Hawaiian 

26 Islands, U.S. Minor Outlying Islands (including Johnston, Wake, and Palmyra Atolls) eastern 

27 central Japan, Polynesia, Micronesia, Melanesia, New Zealand, and Australia. Its wintering 

28 range further extends to Indonesia, Philippines, southern China, Southeast Asia, Bangladesh, 

29 Nepal, India, Sri Lanka, Pakistan, Iran, Bahrain, Ethiopia, and Somalia (Jones 1995, Johnson and 

30 Connors 1996, Johnson et al. 2004). Data are few about breeding site fidelity for this species in 

31 Alaska and Russia. Recent studies have shown individuals of this species will return year after 

32 year to the same breeding site (Johnson et al. 1993, Underhill et al. 1993). Studies on wintering 

33 populations in O`ahu, Hawai`i, show high rates of site fidelity at wintering grounds as well 

34 (Johnson et al. 1981, Johnson et al. 1989). 

35

36 The global population estimate for PGPL is between 166,000 and 216,000 (Delany and Scott 

37 2002). There is a consensus that the overall population trend is decreasing for the PGPL 

38 (Bamford et al. 2008, BirdLife International 2010). One study conducted between 1986 and 

39 1995, showed a 72 percent decline in numbers at wintering sites in Australia. (Harris 1995). 

40

41 2.7.3 Proportion of Population that Would be Captured

42 Personnel would attempt to capture 100 percent, or as many as is possible, of the BTCU and 

43 PGPL remaining at Palmyra after breeding birds had left the atoll for their summer breeding 

44 grounds in Alaska and just prior to the implementation of the eradication. 

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 62

1 2.7.4 Capture Method(s)

2 Effective, safe capture methods for BTCU and PGPL at Palmyra Atoll are currently under 

3 development; however, shorebird experts maintain that it would be very difficult to capture 

4 BTCU (Gill 2010). When the lagoon flat habitat is flooded during high-tide cycles both species 

5 congregate on the runway, North Beach on Cooper Island, and Strawn Beach on Strawn Island 

6 (Figure 2.8). Single capture devices, such as pole-nets and soft-snares may be used, as well as 

7 multiple-capture devices, such as mist nets and net guns or walk-in traps. Because of anticipated 

8 shyness caused by trial capture events (successful or not), large-scale testing of capture methods 

9 would not be possible prior to the main capture event. 

10

11 2.7.5 Retain Captured Birds in On-Island Captive-Holding Facility or Transfer to Off12 Island Location

13 Captured BTCU and PGPL would be banded and immediately transferred to a captive-holding 

14 facility established in the camp and research station area of Cooper Island. A wildlife 

15 veterinarian would be present for the entirety of the capture and holding process and would 

16 supervise the design of the captive-holding facility and manage the care of captured birds. All 

17 personnel involved in the capture and care of BTCU and PGPL would have significant, prior 

18 experience with wild bird capture, bird banding, and wild bird care.

19

20

21 Figure 2.8. The location of bristle-thighed curlew and Pacific golden-plover roosting sites (capture sites) 

22 and a possible location for the captive-holding facility on Cooper Island, Palmyra Atoll. For scale, the 

23 runway is 1 mile long.

24

25 2.7.6 Captive Bird Care

26 A wildlife veterinarian and aviculturist familiar with captive care of shorebirds would be present 

27 for, and involved in, all bird capture and care scenarios. The veterinarian would regulate the diets 

28 of the captive birds, and, if necessary, modify their captive environment to reduce stress and the 

29 likelihood of stress-related illnesses. 

30

31 2.7.7 Aspects of Captive-Holding Facility

32 The captive-holding facility would be located on a cement slab (approximately 50 m x 30m) on 

33 Cooper Island near the camp area. Shaded, rat- and crab-proof pens would be constructed at this 

Captive-holding facility

North Beach

Strawn Beach
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 63

1 location. Each pen would hold up to 20 birds, and birds would be segregated by species. Birds 

2 would be fed an appropriate diet, and fresh water would be provided ad-libitum during the 

3 captive period. The pens would be designed with flooring material appropriate to maintain foot 

4 health for the birds and cleaned daily. The condition of each bird would be monitored throughout 

5 the captive-holding period. 

6

7 2.7.8 Length of Time Held

8 As previously stated, capturing and holding wild animals to avoid the risk of exposure to 

9 rodenticide carries inherent risk of injury, illness, or death for the captured birds. Efforts would 

10 be made to minimize the potential for harm caused by the holding process, but harm would still 

11 be expected. Minimizing efforts include that BTCU and PGPL would be kept in captivity only as 

12 long as is needed to avoid risk of mortality from exposure to rodenticide. The birds would be 

13 released after the risk of primary exposure to rodenticide through direct bait consumption has 

14 been eliminated – determined to be when bait pellets are no longer available to ground-based 

15 foragers, and after the risk of secondary exposure has decreased to a negligible level. This 

16 negligible level is determined as when rat carcasses have been consumed by invertebrates, and 

17 when invertebrates consumed by BTCU and PGPL have brodifacoum residue levels that have 

18 dropped below the risk-causing threshold. Bait pellets would not be available for primary 

19 consumption beyond 7 days post-bait application (Buckelew et al. 2005, Wegmann and 

20 Middleton 2008), and brodifacoum residue concentrations in hermit crabs (prey for BTCU) fall 

21 below 100 ppb 20 days after the second bait application. To minimize the exposure of BTCU and 

22 PGPL residing at Palmyra during the rat eradication, birds would be captured and held until a 

23 point at which their release would not incur a risk of harmful exposure to residual rodenticide. 

24

25 2.8 Alternative D: Bait Stations with Canopy Baiting of Brodifacoum-25W

26

27 2.8.1 Rationale

28 Bait station operations, in contrast to aerial bait broadcast operations, mechanically limit the 

29 probability that nontarget species would come into direct contact with rodenticide, and thus 

30 reduce the risk of mortality for nontarget individuals. 

31

32 2.8.2 Summary of Bait Delivery Methods

33 Bait stations armed with Brodifacoum-25W bait pellets would be placed on a 50 m x 25 m grid 

34 consisting of 7 - 8 stations per hectare (Figure 2.9). Palmyra has 250 hectares of emergent land, 

35 requiring 1,862 bait stations to completely cover the atoll. To account for bait station attrition 

36 during the operation, an additional 20 percent of the total number of bait stations would be 

37 purchased and brought to the atoll. Tamper-resistant bait stations would be purchased for use in 

38 and around areas of human habitation. For uninhabited areas of the atoll, crab-resistant bait 

39 stations would be constructed with off-the-shelf materials (Appendix G.) and placed along the 

40 grid.

41
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 64

1

2 Figure 2.9. Bait station transects spaced 50 m apart to allow for a 50 m x 25 m bait station grid at Palmyra 

3 Atoll. The total length of all transects is 46,323 m. 

4

5 For the first 6 weeks of the operation, each station would be checked every 2 days. During this 

6 time, bait would be continuously maintained in every station. Bait that has become moldy would 

7 be removed from the stations and replaced with fresh bait. 

8

9 Rats at Palmyra have unusually small home ranges; female rat home range sizes have been 

measured at less than 400 m210 . To account for the small home range size, and to eliminate the 

11 possibility of “missing” rats that primarily forage in the forest canopy, bait would be applied to 

12 every third coconut palm crown (n = 26,666 palm trees) 4 times. 

13

14 Management of the bait station operation detailed in Alternative D would be adaptive. If the bait 

15 station design selected for the operation proved ineffective in the long-term at excluding land 

16 crabs and/or shorebirds, or limited access to less than 100 percent of the rat population, 

17 modifications to station design would be made on-site. Additionally, there are two islands (Quail 

18 and Barren) that are known to have unsecured unexploded ordinance residual from WWII. A bait 

19 station operation would require that all transects and paths on these two islands be cleared by 

20 qualified personnel. Modification to the baiting plan would be made to address higher or lower 

21 than expected rates of bait removal from stations. 

22

23 2.8.3 Monitoring for Eradication Success

24 For the duration of the bait station eradication described here, the bait stations would act as 

25 indicators of rat presence. To detect station-shy rats, chew-blocks would be associated with bait 

26 stations that showed little or no rat activity. Bait stations would be maintained until rat presence 

27 was not detected for 6 months, and then eradication success would be confirmed 2 years after the 

28 stations were deactivated. 

29

30 2.8.4 Timing/timing Considerations

31 Similar to bait broadcast eradications, bait station operations entail significant rodenticide 

32 exposure risk for nontarget species, usually through secondary pathways or direct exposure due 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 65

1 to bait station malfunction or human error. Because of this, the bait station operation would 

2 begin during the months of June and July when the carcasses of rats that succumb to 

3 brodifacoum toxicity are most prevalent, and “at risk” nontarget species bristle-thighed curlew 

4 and Pacific golden-plover) are least abundant at Palmyra. Some movement of brodifacoum from 

5 bait stations to the environment through the rats and insects that feed on the bait would continue 

6 for the full 2 year period of baiting, however.

7

8 2.9 Effort and Estimated Costs

9

10 2.9.1 Aerial Bait Broadcast – Helicopter Flight Time

11 Based on past aerial broadcast eradications (e.g., Rat Island, Alaska), it is estimated that bait can 

12 be applied by helicopter at a rate of 800 kg/hr. For an aerial broadcast of Brodifacoum-25W, 56 

13 hours of flight time would be needed to complete both bait applications. The total personnel time 

14 for a Brodifacoum-25W broadcast application eradication (Alternative B) would be 616 person15 days, or 684 person days if active shorebird mitigation occurred (Alternative C). 

16

17 2.9.2 Bait Stations and Canopy Baiting

18 Palmyra‟s emergent land area is covered with dense forest; transects would be cut and 

19 maintained to allow for easy access to the bait stations. The total length of transect required for a 

20 50 m x 25 m grid is 50,659 yards (46.32 km). We estimate that transects can be cut at the rate of 

21 546 yards/person-day (500m/person-day), and maintained at the rate of 5,468 yards/person-day 

22 (5,000 m/person-day). Vegetation grows quickly in Palmyra‟s warm, moist climate; transects 

23 would need dedicated maintenance every 3 months. We estimate the total effort for cutting and 

24 maintaining (for the 2-year duration of the project) bait station transects at Palmyra to be 173 

25 person-days (93 person-days for the initial cutting, 10 person-days for each of 8 transect 

26 maintenance sessions). 

27

28 We estimate that one person can travel to, inspect, and resupply approximately 100 bait stations 

29 in a day. To restock 1,862 stations every other day for the first 6 weeks, a minimum of 20 people 

30 are required. After the first 6 weeks, a team of five would be able to cycle through all of the 

31 stations on a 2-week rotation. 

32

33 We estimate that the rate at which palm crowns can be baited is 100 crowns/person-day. The 

34 total baiting effort is 267 person-days for each eradication action period, or 868 person-days. 

35

36 The total effort for a bait station eradication with transect cutting and maintenance, and canopy 

37 baiting is estimated at 2,476 person-days. The effort (measured in person-days) that would be 

38 required to complete the major components of the action alternatives is presented in Table 2.4.

39

40 Cost estimates (Table 2.8) were calculated based upon 2008 market research and the effort 

41 estimates in Table 2.6. Because maintaining bait stations would not require highly skilled 

42 expertise, personnel costs are calculated at the technician level (based on the Federal General 

43 pay Schedule “GS” 7) for implementing bait stations. Aerial broadcast treatments would require 

44 more expertise and knowledge, and are calculated at the GS13 level. 

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 66

1 Table 2.6. The Minimum Effort Required to Achieve the Primary Operational Objective

2 for All Three Action Alternatives.

Alternatives

Included

Eradication Action 

Periodaction period

People Required Number of Days Effort (in PersonDays)

(Prep for Aerial broadcast)

B, C 0 – 2 months 4 7 28

(Prep for shorebird capture)

 C 0 – 2 months 2 34 68

(Post-bait application environmental and nontarget monitoring – 25W)

B, C 0 – 2 months 4 32 128

(Aerial broadcast – 25W)

B, C 0 – 2 months 20 23 460

(Transect cutting and maintenance)

4 – 0 months 10 9.3 93

0 – 24 months 5 16 80

 D Total 173

(Bait stations)

0 - 6 weeks 20 40 800

6 weeks - 6 months 5 12 175

6 - 12 months 5 46 230

1 - 2 years 5 46 230

 D Total 1,435

(Canopy baiting)

0 - 6 weeks 10 27 267

6 weeks – 6 months 5 54 267

6 - 12 months 5 54 267

 D 1 - 2 years 5 54 267

Total 868

Action Alternative Estimated Total 

Effort (PersonDaystotal effort 

(person-days)

B - Aerial broadcast of brodifacoum 616

C - Aerial broadcast of brodifacoum with proactive shorebird mitigation 684

D - Bait stations with brodifacoum and canopy baiting 2,476

3

4
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 67

1 Table 2.7 Comparative Summary of Actions by Alternative

2

Action attribute Alternative B: 

Aerial broadcast of 

brodifacoum 

Alternative C: 

Aerial broadcast of 

brodifacoum with proactive 

bird mitigation

Alternative D: 

Bait station with hand 

broadcast of 

brodifacoum

Primary bait 

delivery method

Aerial broadcast Aerial broadcast Bait station

Secondary bait 

delivery methods

Hand broadcast; bait 

stations

Hand broadcast; bait stations Canopy Baiting

Toxicant type Brodifacoum Brodifacoum Brodifacoum

Actions to minimize 

risk to shorebirds

Seasonal timing Seasonal timing

Capture of “at risk” shorebirds

Seasonal timing

Bait stations

Actions to minimize 

risk to reptiles

Minimizing bait drift into 

the marine environment

Minimizing bait drift into the 

marine environment

Seasonal timing June-July June-July June-July

3

4

Table 2.8 Budget Estimates for Treatment Options

Bait Stations 

(diphacinone or 

brodifacoum)

Diphacinone 

(aerial, hand 

broadcast, and 

bait stations)

Brodifacoum 

(aerial, hand 

broadcast, and 

bait stations)

Bait $ 118,000 $ 710,800 $ 240,300 

Transporting bait to Palmyra and boat charter $ 174,400 $ 366,300 $ 366,300 

Equipment purchase and shipment $ 5,800 $ 60,800 $ 60,800 

Communications $ 26,400 $ 19,000 $ 19,000 

Environmental samples $ 31,000 $ 31,000 $ 31,000 

Helicopter calibration and operations -- $ 412,000 $ 333,000 

Travel and on-site logistics for implementation $ 1,065,400 $ 70,400 $ 70,400 

Demobilization $ 30,500 $ 25,800 $ 25,800 

Safety $ 20,300 $ 6,800 $ 6,800 

Supplies $ 83,700 $ 27,000 $ 27,000 

Salaries* $ 396,000 $ 186,000 $ 186,000 

Total $1,951,500 $1,915,900 $1,366,400

* Salaries for bait station treatments calculated at GS7 level for 2,476 person-days. Salaries for aerial 

treatments calculated at GS 13 level for 684 person-days (which includes proactive shorebird mitigation).
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 68

1 3 Affected Environment

2 3.1 Introduction

Palmyra Atoll National Wildlife Refuge (Palmyra) located approximately at 6° N and 162 3

° W in 

4 the Line Islands – Central Pacific, represents a globally important conservation stronghold. In 

5 2001, after a history of military and private ownership, most of Palmyra Atoll and the 

6 surrounding coral reef were designated as a National Wildlife Refuge (NWR) by the Secretary of 

7 the Interior. In addition, The Nature Conservancy owns Cooper and Menge Islands, and the 

8 Cooper family owns 1.7 ha Home Island. The U.S. Fish and Wildlife Service (FWS or Service) 

9 and The Nature Conservancy (TNC) co-manage Palmyra‟s emergent land area, while the FWS 

10 retains sole management over marine resources extending 12 nautical miles out from the islands. 

11 In 2009, Palmyra Atoll National Wildlife Refuge and its surrounding waters out to 50 nautical 

12 miles from shore were included within the Pacific Remote Islands Marine National Monument 

13 (The White House 2009). The National Oceanic and Atmospheric Administration (NOAA) 

14 provides consultation to the FWS for management planning in the monument and the Service 

15 provides consultation to the NOAA, who retains primary responsibility for fisheries issues in 

16 monument areas from 12 to 50 nmi.

17

18 Palmyra is the only fully protected moist tropical forest ecosystem in the Central Pacific, yet 

19 native biota are currently threatened by an introduced, invasive rodent – the black rat. Palmyra is 

20 a breeding ground for 10 seabird species; however, predation by rats on eggs and chicks has 

21 likely led to the extirpation of 8 additional species. Palmyra‟s land crab community is one of the 

22 largest, if not the richest and most robust populations in the Central Pacific region. Palmyra is 

23 home to six land crab species (excluding the intertidal family Ocypodidae that includes fiddler 

24 and ghost crabs). Four of these land crab species occur in high densities at the atoll, with roughly 

25 300 crabs per hectare. 

26

27 Palmyra‟s high rainfall and complex vegetation structure make it very different from the other 

28 seabird colonies protected in the U.S. Pacific Islands. The wet Pisonia equatorial forest 

29 ecosystem found at Palmyra is a globally imperiled ecosystem, due to predation of seeds and 

30 seedling and by black rats and competition from introduced coconut palms. Since their 

31 introduction to Palmyra, black rats have affected migratory shorebird and seabird populations, as 

32 well as reptile, invertebrate, and plant communities. 

33

34 3.2 General Description of Palmyra

35

36 3.2.1 Geographical Setting

37 Palmyra Atoll is one of the northernmost land masses in the Line Island chain, located 

38 approximately 1,000 mi (1,609 km) southwest of Hawai`i at 5° 53 ́ N latitude, 162° 05 ́ W 

39 longitude. Palmyra is in very close proximity to the Inter-Tropical Convergence Zone (ITCZ). 

40

41 3.2.2 Size and Topography

42 Palmyra is a coral atoll with 618 acres (250 ha) of land area that is currently distributed between 

43 25 islands(Collen et al. 2009). The atoll is approximately 7.5 mi (12 km) long (Collen et al. 

44 2009). The atoll is shaped like a horseshoe and was originally composed of 54 small islands. 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 69

1 During the early 1940s the U.S. Navy increased the land area of the atoll by dredging, filling, 

2 and construction of islands runways, and causeways. The outer islands were connected, by roads 

3 and fill, into a ring and a channel was dredged. None of Palmyra‟s natural emergent land areas 

4 exceed 6.5 ft (2 m) above sea level, while dredge-fill islands reach 15 ft in elevation. The islands 

5 vary in size from approximately 0.24 to 242 acres (0.1 to 97.9 ha). The atoll has three lagoons, 

6 the eastern lagoon was separated from the central and western lagoons by the creation of a 

7 causeway. Palmyra is surrounded by an extensive reef flat on all sides with wide shallow reef 

8 flats and broad submerged reef terraces on the western and eastern ends (Collen et al. 2009). 

9

10 3.2.3 Climate

11 Palmyra is considered to be a wet atoll with high humidity, typically greater than 90 percent, and 

12 warm temperatures, between 75-81°F (24-27 °C) (Hathaway et al. 2009). The climate at Palmyra 

13 is generally wet and humid, and predominantly governed by the proximity of the ITCZ 

14 (Anderson 2007). The ITCZ is characterized by moderate to strong convection currents that are 

15 interspersed with the doldrums, resulting in areas of flat calm winds and frequent torrential rains 

16 coupled with thunder and lightning (Anderson 2007). Doldrums are formed when trade winds 

17 from the northern and southern hemispheres meet, creating weather patterns with light winds and 

18 plentiful rains (Clark 2008). Precipitation patterns at Palmyra are largely governed by the 

19 strength and location of the doldrums (Barkley 1962). 

20

21 Palmyra has a high annual precipitation rate averaging 175 inches (444.5 cm) per year (FWS 

22 2001). The average annual wind speed is 8 knots (Sadler 1959). In an El Niňo year, Palmyra 

23 experiences periods of reduced rainfall, increased temperatures, and other climactic anomalies 

24 that are the direct result of the ITCZ shifting east, and creating warm ocean surface temperatures 

25 and weak trade winds (Burns 2002). Palmyra receives rainfall regularly throughout the year 

26 without a specific rainy season (see Table 3.1), creating a high resource environment. Due to an 

27 abundance of food available throughout the year rats are able to thrive and reproduce in all 

28 months of the year without a seasonal breeding period.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 70

1

2 Figure 3.1. A map of the prominent forest types at Palmyra Atoll. The coconut palm canopy (dark green) 

3 is frequently used by rats and covers roughly 45 percent of Palmyra‟s land area.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 71

1 Table 3.1. Palmyra Atoll Historical Rainfall Data in Inches (1977 – 2009) 

1977 1978 1979 1980 2001 2002 2003 2004 2005 2006 2007 2008 2009 AVG

Jan 28.5 18.9 17.3 15.9 8.83 14.0 17.8 19.0 11.7 16.9 15.3

Feb 9.05 9.8 11.6 17.6 21.43 25.6 9.9 12.3 7.4 23.7 13.5

Mar 12.8 6.3 15.7 13.0 11.6 19.6 24.7 8.9 11.5 15.4 5.2 12.0

Apr 12.8 6.9 14.8 17.4 9.2 7.5 19.9 12.8 6.3 8.3 6.2 10.2

May 8.5 3.5 11.8 11.3 15.1 13.0 25.2 17.1 19.4 11.4 16.4 12.7

Jun 9.8 9.8 26.6 12.7 20.8 15.3 22.5 7.2 15.0 9.6 9.8 13.3

Jul 8.26 14.76 17.0 16.1 9.6 23.3 20.1 19.4 16.1 18.5 14.8

Aug 14.8 4.3 12.8 19.0 22.3 20.5 27.0 16.9 9.8 12.7 9.1 14.1

Sept 3.9 7.9 12.2 9.1 10.8 7.4 8.4 7.1 13.2 3.0 8.7 7.5 7.6

Oct 9.8 6.3 16.1 12.1 14.1 16.4 18.5 15.6 17.3 9.4 22.0 17.5 13.5

Nov 14.7 11.2 17.7 11.2 19.9 17.2 16.6 10.8 18.3 5.7 17.5 20.0 13.9

Dec 23.6 11.8 19.3 17.1 35.2 34.4 21.0 19.4 25.6 17.6 9.3 22.7 19.8

Total 131.3 119.4 199.3 203.8 180.1 235.1 185.00 148.3 150.0 173.4 160.6

2 Source: Palmyra Atoll NWR Daily Weather Record

3

4 3.2.4 Physical Resources

5

6 Water Resources

7 Although Palmyra receives a high amount of rainfall, porous soil prevents the formation of 

8 freshwater wetlands (Scott 1993, FWS 2001). Due to the porous carbonate soils characteristic of 

9 the atoll, surface runoff is nearly nonexistent at Palmyra. Little to no information is available 

10 about groundwater at Palmyra because no significant groundwater sources are on any of the 

11 islands. Groundwater is most likely present as a saturated zone on the atoll. A 1998 report on the 

12 contaminants of Palmyra reported that the surface water table is typically found at depths of 

13 approximately 2-4 ft (0.6 – 1.2 m) below the ground surface and is greatly influenced by the tide 

14 (Environmental Chemical Corporation 1998).

15

16 Limited direct sources of water pollution at Palmyra are from small boats. Submerged waste and 

17 debris remains from World War II activities. It is unknown if these environmental contaminants 

18 had or continue to have an effect on water quality.

19

20 Military activities during World War II included construction of a north-south causeway between 

21 the East and Center Lagoons, construction of a smaller causeway and two islands in Center 

22 Lagoon, and dredging of a seaplane runway, and an entrance channel through the perimeter reef 

23 southwest of West Lagoon (Dawson 1959). Altered and reduced water circulation in West and 

24 Center Lagoons has been reported since the 1950s. Additionally, a decrease in water circulation 

25 in East Lagoon is reducing coral reef life and increasing temperature regimes in all 3 lagoons. 

26 Altered water circulation in the lagoons has caused an increase in coral bleaching, heightened 

27 predation by coral-eating sea stars, and increased lagoon shoreline erosion (Miller et al. 2008). 

28 Several breaks in the perimeter of the East Lagoon have allowed a minimal amount of mixing 

29 with the ocean at high tide. Continued high temperature and turbidity levels in all lagoons has 

30 dramatically slowed marine ecosystem recovery in the lagoons (Miller et al. 2008). Outside of 

31 the lagoon habitats, waters surrounding Palmyra Atoll are generally well mixed and clear with 

32 light transmission levels greater than 80 percent (Pacific Island Fisheries Science Center 2004). 

33

34 There is significant evidence of weak but consistent upwelling along Palmyra Atoll‟s southern 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 72

1 side and its connection to high biomass measured with bioacoustics. Poor water circulation 

2 within Palmyra‟s back reef areas causes variations in water temperature (Brainard et al. 2005). 

3

4 Geology and Soils

5 Palmyra Atoll is one of only 12 seamounts or undersea mountains in the Central Pacific ocean 

6 that rise in excess of 16,405 ft (5,000 m) from the sea floor to form an atoll (Keating 1992). 

7 Palmyra was formed by a combination of carbonate coral reef growth along the side of an 

8 ancient volcano, coupled with erosion and subsidence of the basalt layer (Smith et al. 2006). 

9 Through a multibeam mapping process, Smith et al. (2006) identified a group of pinnacles on the 

10 south and west flanks and a flat-topped volcanic cone with a summit depth of 3,661 ft (1,160 m). 

11

12 Almost all islands at Palmyra have a thin layer of soil and organic material over a limestone 

13 base. The soil found under the organic plant layer is brown, sandy soil that ranges in thickness 

14 from 4-12 in. The uppermost layer is approximately 4-in thick and is composed of dark gray and 

15 very dark gray brown, silty sand. The second layer is composed of pinkish white fine to very fine 

16 sand, intermixed with coralline gravel and cobbles (Aronson and Anderson 2000). Some of the 

17 soils at Palmyra are calcium phosphate with hard pans (Christophersen 1927). The organic 

18 matter and acidity of the soil varies throughout the atoll and few data are available for specific 

19 islands (FWS 2001). The two main types of soil found at Palmyra vary based on the type of 

20 vegetation found in that area. In the Pisonia grandis forests, the main soil type is highly 

21 phosphatic and composed almost entirely of organic matter (Christophersen 1927). In the 

22 coconut forests the soils are sandy and nonphosphatic with medium to low organic matter 

23 (Christophersen 1927).

24

25 Air Quality

26 Air quality at Palmyra is generally excellent. Sources of emissions on the atoll are minimal and 

27 include two diesel powered generators generating electrical power, a 25-ft diesel-powered boat 

28 for offshore activities, four smaller boats, two tractors, two pickup trucks, a front end loader, a 

29 compactor/roller, a waste incinerator, and several gasoline-operated garden tools. There is no 

30 record of natural- or human-initiated wildfires at Palmyra Atoll. Currently, airplane flights to 

31 Palmyra are determined on an as-needed basis for the purposes of transporting staff, scientists, 

32 visitors, and restocking perishable foods. Flights are typically more frequent during the summer 

33 than in winter months, with an average of two flights occurring per month in the summer and 

34 two flights total in the winter months between December and March. 

35

36 3.2.5 Biological Resources

37

38 Introduction

39 No terrestrial mammals are native to Palmyra Atoll, but a variety of native birds, lizards, 

40 arthropods, and crabs, as well as several nonnative plants, vertebrate and invertebrate species 

41 have been inventoried to date. Palmyra Atoll‟s native flora and fauna have been altered due to 

42 World War II-era atoll restructuring and introductions of nonnative species, notably coconut 

43 palms, ants, scale insects, and black rats. Nevertheless, Palmyra is an important center of 

44 biological diversity and species abundance in the Central Pacific region. Now protected within 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 73

1 the FWS‟s National Wildlife Refuge System, a national monument, and as a Nature Conservancy 

2 Preserve; Palmyra sharply contrasts with other moist Central Pacific island groups where the 

3 degradation of terrestrial and marine ecosystems keeps pace with increased human population 

4 and the resultant anthropogenic resource use. The continued presence of black rats at Palmyra 

5 Atoll hinders recruitment for extant indigenous species, may preclude the reestablishment of 

6 extirpated species of seabirds, and may thwart nesting attempts by endangered green turtles 

7 (Chelonia mydas) and hawksbill turtles (Eretmochelys imbricata). 

8

9 Palmyra is a breeding site for seabird species, but predation by rats on eggs and chicks has likely 

10 led to reduced breeding success of these species and the extirpation of 8 additional species 

11 (Table 3.2). Due to the absence of predation pressure by an established human population, 

12 Palmyra‟s land crab community is among the richest and most robust in the Central Pacific 

13 region. Palmyra is home to six species of terrestrial crabs (excluding the intertidal family 

14 Ocypodidae), four of which are super abundant (Table 3.3).

15

16 Birds at Palmyra

17 Systematic observations of all bird species found at Palmyra were first made during visits of 

18 scientists from the Pacific Ocean Biological Sciences Project between 1964 and 1965. On 

19 subsequent visits starting in 1987 Service staff or visiting scientists made additional estimates of 

20 population sizes for all birds seen. Ten species of seabirds breed at Palmyra, and it is home to 

21 one of the largest colonies of red-footed boobies in the world. Additional seabird species have 

22 been documented foraging in the waters surrounding the islands of Palmyra, several of which 

23 would likely breed there if no rats were present. These including the wedge-tailed shearwater, 

24 Christmas Island shearwater, Audubon‟s shearwater, Bulwer‟s petrel, and blue noddies have 

25 been documented visiting land at Palmyra Atoll.

26
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 74

1 Table 3.2. Breeding seabirds of Palmyra Atoll

Family Common Name Scientific Name Status IUCN-list

Procellariidae Audubon‟s shearwater Puffinus lherminieri Believed extirpated Least Concern

wedge-tailed shearwater Puffinus pacificus Extirpated Least Concern

Phoenix petrel Pterodroma alba Believed extirpated Endangered*

Christmas Island shearwater Puffinus nativitatis Believed extirpated Least Concern

Bulwer‟s petrel Bulweria bulwerii Believed extirpated Least Concern

Hydrobatidae Polynesian storm-petrel Nesofregetta fuliginosa Believed extirpated Endangered*

Laridae black noddy Anous minutus Breeding Least Concern

blue noddy Procelsterna cerulea Believed extirpated Least Concern

brown noddy Anous stolidus Breeding Least Concern

sooty tern Onychoprion fuscatus Breeding Least Concern

gray-backed tern Onychoprion lunatus Believed extirpated Least Concern

white tern Gygis alba Breeding Least Concern

Fregatidae great frigatebird Fregata minor Breeding Least Concern

lesser frigatebird Fregata ariel Resident Least Concern

Phaethontidae white-tailed tropicbird Phaethon lepturus Breeding Least Concern

red-tailed tropicbird Phaethon rubricauda Breeding Least Concern

Sulidae red-footed booby Sula sula Breeding Least Concern

brown booby Sula leucogaster Breeding Least Concern

masked booby Sula dactylatra Breeding Least Concern

2 * = Declining population trend

3

4 Palmyra is the only undisturbed site left for seabirds within the Northern Line Islands that prefer 

5 P. grandis trees as nesting habitat (Flint 1999). Seabirds are marine foragers and travel long 

6 distances to feed (e.g., red-footed boobies will travel over 200 km per day), returning to Palmyra

7 to rest and breed (Young et al. 2010). In addition to their important role as seed dispersal agents 

8 for P. grandis, seabirds are important drivers in the ecosystem because they bring marine9 derived nutrients (guano) to the islands. To a lesser extent, seabirds provide nutrients used 

10 throughout the food chain, in the form of feathers, regurgitated fish, addled eggs, and bird 

11 carcasses.

12

13 The distribution, population, status and trends, ecology, and conservation concerns for these 

14 seabird species can be found in the Regional Seabird Conservation Plan, Pacific Region (FWS 

15 2005). The greatest local and global threats to the seabirds found at Palmyra include; introduced 

16 black rats and other invasive species, fishery interactions, contaminants, marine debris, and 

17 climate change. 

18

19 Black rats may be responsible for the current absence of burrow-nesting seabird species at 

20 Palmyra. Species such as wedge-tailed shearwaters, Audubon‟s shearwaters, and Polynesian 

21 storm-petrels have been observed offshore (Depkin 2002) and (J. Smith; M. McKown; E. Flint, 

22 FWS; L. Ballance; and R. Pitman oral communication 2008) or collected on the atoll (i.e., 

23 Smithsonian Institute; USNM 496523; petrel specimen from 2008 - Matthew McKown) in the 

24 past. Pre-World War II accounts of Palmyra‟s terrestrial ecology focused on botanical aspects, 

25 supplying little information about the avian fauna, and no record of these species breeding at 

26 Palmyra (Rock 1916).
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 75

1

2 Palmyra also supports overwintering populations of shorebirds, including bristle-thighed 

3 curlews, Pacific golden-plovers, wandering tattlers, ruddy turnstones, and sanderlings. The 

4 bristle-thighed curlew and Pacific golden-plover are designated by the FWS Shorebird 

5 Conservation plans as species of high conservation concern in National and Regional Shorebird 

6 Plans, including the U.S. Pacific Islands Regional Shorebird Conservation Plan (Engilis Jr. and 

7 Naughton 2004). The bristle-thighed curlew has also been designated as a Bird of Conservation 

8 Concern by the FWS at the regional and national scale (FWS 2008a) due to limited breeding and 

9 non-breeding distributions, low relative abundance, and threats during the non-breeding season. 

10 Both of these species overwinter at Palmyra Atoll, with low numbers of juvenile or non-breeding 

11 birds also present through the summer months.

12

13 There are currently no records of breeding land birds at Palmyra Atoll. Two nonnative bird 

14 species are known to have been introduced to Palmyra Atoll. The myna (Acridotheres tristis) has 

15 been reported as introduced but has since been extirpated (Fefer 1987). Domestic chickens 

16 (Gallus gallus) were also reported (Flint 1992), but are no longer present.

17

18 Seabirds

19 Palmyra Atoll NWR is the only seabird nesting habitat within 450,000 square miles of ocean and 

20 is an important marine feeding ground for seabirds (Flint 1992). Located on the boundary 

21 between the North Equatorial Countercurrent and other ocean currents in the vicinity, several 

22 species of nesting seabirds regularly visit the atoll. No long-term monitoring time series for 

23 seabird populations exist due to the previous irregularity of visits, the aseasonality of seabird 

24 breeding at Palmyra, and the high inter-annual variability of seabird population size and breeding 

25 success in low latitude colonies. 

26

27 Pacific Ocean Biological Science Project (POBSP) staff did not find any masked boobies 

28 breeding in 1964 or 1965, nor did Fefer in 1987, though both groups observed a few individuals 

29 at the site. The masked booby has more recently been reported on Whippoorwill, Portsmouth, 

30 Holei, Tanager, and the Fighter Causeway (Flint 1999, Depkin 2002). In 2010 Meyer reported 

31 nests from small islands in the Milky Way, North and South fighter strips, the East-West 

32 Causeway, Paradise Spit, and the North-South Causeway. The masked boobies found in this area 

33 are believed to be of the subspecies S. dactylatra personata because adults do not have black 

34 colored eyes (Depkin 2002). Two adult birds were observed roosting by Fefer (1987) and 13 

35 masked boobies were seen by Flint in 1992. Nest inventories by Flint (1992) indicate that the 

36 nest sites of the species are usually solitary and clutch size is two eggs. Depkin (2002) estimated 

37 that approximately 35 pairs of masked boobies inhabit Palmyra. Nineteen active nests were 

38 found on the East-West Causeway during a count in April 2010.

39

40 The largest concentration of brown boobies has been observed on the East-West Causeway (Flint 

41 1992, Depkin 2002). They are also found on Ainsley, Dudley, Leslie, North-South causeway, 

42 North and South fighter strips, Paradise Spit, Whippoorwill, and The Milky Way. These birds 

43 nest and roost on the ground and typically forage in pelagic waters off Palmyra Atoll. The global 

44 population of brown boobies is approximately 221,000 – 275,000 pairs (FWS 2005). The POBSP 

45 staff documented breeding and estimated 600 birds in the fall of 1964. Early counts by Fefer 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 76

1 (1987) documented 600 birds and 286 nests at Palmyra. Approximately 60 percent of the nests 

2 observed on this visit contained eggs and most were located underneath Tournefortia and 

3 Scaevola shrubs. A total of 253 brown boobies were seen by Flint (1992), including two 

4 identified as male Sula leucogaster brewsteri. This subspecies has a gray head as opposed to 

5 brown head and throat prominent in the remainder of the population (Flint 1992). This 

6 subspecies native to the Eastern Tropical Pacific is still seen in small numbers every year at 

7 Palmyra. The highest recent population estimate for brown boobies at Palmyra Atoll is 371 pairs 

8 (Depkin 2002). Depkin banded a total of 379 chicks between early September 2001 and late 

9 August 2002. In September 2009 there were 302 active nests counted on the East-West 

10 Causeway. During this sampling period, the hatch rate was 44 percent and a recruitment rate was 

11 97 percent. Typically, pairs of brown boobies lay two eggs with only one surviving chick due to 

12 siblicide (FWS 2005).

13

14 Palmyra supports the second or third largest colony of nesting red-footed boobies (Sula sula) in 

15 the world with current total population estimates around 6,250 pairs (FWS 2005). During the 

16 POBSP, 25,000 red-footed boobies were reported from Palmyra Atoll in March 1965 (Clapp, 

17 unpublished). Sixty-five hundred birds and 2,100 nests were counted in 1987 (Fefer), and 8,880 

18 birds were seen in the 1992 FWS survey (Flint). In 2002, Depkin documented 929 nests with 

19 eggs and 1,243 nests with chicks in three index plots. Their most common nesting and roosting 

20 sites is in tree heliotrope (Tournefortia argentea) along the water‟s edge and nests were most 

21 frequently lined with Primrose Willow (Ludwigia octivalvis). Due to the high number of nests 

22 and varied stages of nesting activity, it has been suggested that nesting of the red-footed boobies 

23 occurs year round at Palmyra (Fefer 1987, Depkin 2002). Surveys conducted prior in 1992 

24 showed important colonies of red-footed boobies in Pisonia forests on Eastern, Holei, Bird, and 

25 Papala Islands (Flint 1992). 

26

27 Clapp (1966, unpublished) called the great frigatebird a fairly common resident and estimated 

28 200 birds were present at Palmyra in April of 1964. The great frigatebird is widespread in the 

29 tropical Pacific, Indian, and Atlantic oceans. Their plumage is not waterproof and these birds are 

30 considered the most aerial of all seabirds (Berger 1981). This species is also notorious for being 

31 kleptoparasitic: they dive in pursuit of other seabirds to force them to forfeit their catch. In 1987, 

32 a total of 200 birds and 65 nest sites were recorded on Eastern Island, Lost Island, and Papala 

33 Island (Fefer 1987). During a survey in December of 2001, Depkin recorded 307 individuals, 

34 suggesting that the potential breeding population is probably over 200 pairs. Primary nesting 

35 habitat for the great frigatebird is within the Pisonia forest (Fefer 1987, Redmond 1990, Depkin 

36 2002); however, 34 great frigatebird nests were recorded in Tournefortia on 3 islands near 

37 Whippoorwill Island (Flint 1992). An accurate measurement of the reproductive success for the 

38 great frigatebird population at Palmyra has been difficult to determine due to the great height of 

39 most of their nest sites in the Pisonia forest (Depkin 2002). In recent years this species has also 

40 used trees on the North-South Causeway and Bunker Island for nest sites.

41

42 On drier islands of the tropical Pacific, brown noddies nest primarily on open ground or under 

43 vegetation. At Palmyra, brown noddy nests are more common in the interior and were only 

44 found in Pisonia, Tournefortia, and Cocos canopies (Fefer 1987). Brown noddies and white45 tailed tropicbirds are the only species at Palmyra known to use Cocos for nesting (Depkin 2002)
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 77

1 and are most common on Eastern, Sand, Leslie, Dudley, and the South Fighter Strip. Females lay 

2 a single egg per clutch, and chicks vary in color from solid black to solid white (Berger 1981). 

3 Clapp (1966) estimated 2000 brown noddies inhabiting Palmyra in March of 1965. More recent 

4 estimates of the brown noddy population have ranged from 400 (Fefer 1987, Depkin 2002) to 

5 564 birds (Flint 1992). 

6

7 Palmyra shelters the largest nesting colony of black noddies in the central Pacific (FWS 2001). 

8 The black noddy can be differentiated from the brown noddy by their smaller size, darker color, 

9 and longer, thinner bill. This species also tends to be less pelagic, feeding in flocks over near10 shore waters (Pratt et al. 1987). It is not uncommon for black noddy pairs to lay a second egg 

11 while still tending to the first chick (FWS 2005). Clapp (1966) provides an estimate of 8000 

12 birds for November 1964. A crude estimate of 3,500 birds and 1,100 nests was made on Sand 

13 Island in a survey conducted by Fefer in 1987. During the 1992 FWS survey (Flint 1992), 6,498 

14 black noddies were recorded, and the following year Marks (1993) estimated approximately 

15 20,000 black noddies at Palmyra. A survey in December 2001 found approximately 1,350 black 

16 noddies concentrated in two colonies on Eastern Island (Depkin 2002). 

17

18 White terns are most common in Pisonia and Tournefortia areas, but small numbers have been 

19 observed in other habitats throughout the atoll as well. POBSP scientists estimated as many as 

20 200 birds. In 1987, approximately 500 birds were common residents of the atoll (Fefer 1987). 

21 Depkin (2002) suggested that the white tern breeding population at Palmyra was minimal. 

22 Researchers throughout the Pacific Islands have found that this species does not build nests, but 

23 lays elliptical eggs in any suitable depression (FWS 2005). 

24

25 The sooty tern, commonly found throughout the tropical Pacific Ocean, is an abundant resident 

26 of Palmyra. This species spend most of its time at sea, only coming to land to breed. Clapp 

27 (1966) suggests there were as many as 750,000 birds. An estimated 260,000 birds and 126,000 

28 nests were reported in 1987 (Fefer 1987). Flint (1992) estimated the number of eggs on the 

29 ground to be around 219,000. A survey the following year estimated that a total of 750,000 sooty 

30 tern nests occur at Palmyra (Marks 1993). The most recent seabird survey found 69,867 pairs or 

31 139,734 birds (Depkin 2002). Evidence suggests that sooty terns may have two breeding seasons 

32 at Palmyra. This may be a result of nest site limitations or high nest failure rate due to 

33 anthropogenic activities (Depkin 2002). Irregular breeding seasonality and periodic large-scale 

34 failure may also be attributed to conditions at sea on the foraging grounds. All studies found that 

35 the highest population of the tern colonies was located on the runway on Cooper Island. Thus, 

36 airplane arrivals and departures have historically had a negative effect on sooty tern colonies at 

37 Palmyra (King 1973). In hopes of luring the terns away from the runway, areas on the range 

38 marker on Strawn Island were cleared as possible nesting sites. Depkin estimated there were 

39 40,611 eggs on the North Fighter Strip during the 2001-2002 survey (Depkin 2002). Egg 

40 predation by rats has also been a significant threat to the population in the past (Fefer 1987) and 

41 is still regularly observed by island residents. 

42

43 Scientists from POBSP observed as many as five White-tailed Tropicbirds during their visits but 

44 never found a nest. In 1992, two adult White-tailed Tropicbirds were seen together in a Pisonia

45 grove on Holei Island. Redmond (1990) reported several White-tailed Tropicbirds flying above 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 78

1 the canopy on Eastern Island and Fefer (1987) counted six throughout Palmyra. No nests were 

2 found on these visits. Adult White-tailed Tropicbirds were seen monthly from August 2001 

3 through September 2002, with the highest numbers spotted above the Pisonia forests of Eastern 

4 and Holei Islands. Three nest sites were discovered on Eastern and another nest was found on 

5 Holei. All nests were in natural cavities in Pisonia trees, and nest height ranged from less than 15 

6 to over 50 ft above ground (Depkin 2002). Nests have also been found on Lost and Paradise 

7 Islands and in coconut palm crowns and epiphytic bird‟s nest ferns in 2009 and 2010 (H. Young 

8 pers. comm.). 

9

10 The red-tailed tropicbird tends to avoid land during nonbreeding periods (FWS 2005). 

11 Considered a rare resident by POBSP scientists, they found only one nest in April of 1964. Fefer 

12 (1987) reported a nest, which also contained a feathered chick, under heavy growth of 

13 Tournefortia. Fifteen red-tailed tropicbirds were observed by Flint at three islands in the atoll. 

14 Ten out of a total of 14 nests found were located on Ainsley Island, possibly due to lack of rats 

15 on this portion of the atoll. All nests contained eggs except for one, which sheltered a down16 covered chick (Flint 1992). Between August 2001 and August 2002, Depkin banded a total of 

17 261 red-tailed tropicbirds (128 chicks and 133 adults). The sites were located on causeways and 

18 could indicate a growing population, dominated by young individuals. It has also been suggested 

19 that because nest sites are typically under dense groundcover, earlier surveys underestimated the 

20 true population due to poor detection of nests (Depkin 2002). The increases also followed an 

21 attempted eradication of rats in 2001 that reduced the density of rats and most likely the 

22 incidence of egg predation. Nesting activity, although concentrated in the late winter and early 

23 spring, was reported year round. The reported hatch rate for red-tailed tropicbirds is 

24 approximately 57 percent, with a fledgling success for this period of approximately 45 percent

25 (Depkin 2002). In May of 2010 Refuge manager Meyer banded 100 adult red-tailed tropicbirds 

26 and handled 131 birds, 28 of which had been previously banded. She also banded 23 red-tailed 

27 tropicbird chicks. 

28

29 During the months of August 2001, September 2001, March 2002, and May 2002, May 2009, 

30 September 2009, June 2010, and November 2010. Wedge-tailed shearwaters were heard 

31 vocalizing over Cooper Island (Flint pers. comm.). In May 2002, 3 dark morph wedge-tailed 

32 shearwaters were found dead along the shoreline on North Beach and another dark morph was 

33 discovered in the West Lagoon (Depkin 2002). This dark color phase of the species is the most 

34 often observed type at sea in the waters around Palmyra Atoll. In 2005, a pair of wedge-tailed 

35 shearwaters attempted to nest on Cooper Island; the nest failed and the adults disappeared soon 

36 thereafter (Wegmann pers. comm. 2005). In 2009 and 2010 five wedge-tailed shearwaters were 

37 found on Cooper Island. These birds were attracted to the lights of the research station. The birds 

38 were captured, held overnight and released the following morning. These incidences are the only 

39 reported occurrences for this species at Palmyra Atoll. The Audubon‟s Shearwater, or tropical 

40 Shearwater as it has recently been renamed, has also been sighted at the atoll (Depkin 2002).

41

42 Other uncommon seabirds at Palmyra include the lesser frigatebird, red-billed tropicbird, 

43 Franklin‟s gull, laughing gull (Depkin 2002, Clapp 1966 unpubl. data), and the black tern 

44 (Chlidonas niger) (Wegmann pers. comm. 2008).

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 79

1 Shorebirds

2 The Pacific Islands function as an essential migratory habitat for maintaining global shorebird 

3 populations. The rocky shoreline and extensive sand flats that are exposed at Palmyra during low 

4 tide are important foraging areas for several wintering migratory shorebirds. Four shorebird 

5 species winter full-time at Palmyra; however, other species have been known to occur in small 

6 numbers. All of the shorebird species using Palmyra Atoll demonstrate a pattern of greater 

7 abundance during the winter months with very few or no individuals remaining throughout the 

8 summer when adult birds return to the breeding grounds in the Arctic.

9

10 Palmyra‟s tidal flats, beaches, and runway are important foraging and roosting habitat for bristle11 thighed curlews that migrate between Alaska and the Central and South Pacific (Marks 1993). 

12 These are among the most numerous shorebirds at Palmyra. Between 1987 and 1992, shorebird 

13 surveys estimated more than 200 wintering curlews during each visit (Fefer 1987, Flint 1992). In 

14 the 1992 survey, four of the curlews observed at Palmyra had color bands from Alaskan breeding 

15 locations (Flint 1992). A December 2001 survey resulted in a total count of 84 wintering birds 

16 (Depkin 2002). An April 2010 all-atoll count yielded sightings of 266 bristle-thighed curlews at 

17 Palmyra Atoll. The highest weekly runway index counts occurred during the last week of May 

18 and from late August to early October, possibly because many birds were passing through 

19 Palmyra on their way further North or South during migration. During the 2000-2002 rat 

20 eradication attempts, several curlews were caught in traps while attempting to consume bait. In 

21 addition, there was one reported curlew death caused by internal bleeding from the ingestion of 

22 rodent bait containing the anticoagulant rodenticide brodifacoum. Because no rodenticide was 

23 found in the gizzard of the curlew, it has been suggested that the curlew died of secondary 

24 poisoning after preying on terrestrial invertebrates that had been exposed to brodifacoum 

25 (Depkin 2002). 

26

27 Redmond (1990) suggested that curlew distribution within Palmyra varies regularly with the tide. 

28 At high tide most curlews are concentrated in open areas such as the airstrip and shoreline. At 

29 low tide, when the tidal sand flats are exposed, the curlews flocked to this habitat to forage on 

30 invertebrates (Redmond 1990). This species undergoes a molt-induced flightless period in 

31 autumn, and therefore, are more susceptible to predatory attacks in those months (Marks 1993). 

32 With a global population of approximately 10,000 individuals, the FWS has designated the 

33 bristle-thighed curlew as a Bird of Conservation Concern (FWS 2008), and it was also ranked as 

34 Vulnerable by the IUCN (Engilis Jr. and Naughton 2004). 

35

36 Pacific golden-plovers prefer to forage in open spaces such as low vegetation fields, roadsides, 

37 sandy beaches, or mudflats. Although these plovers do not nest in the tropical Pacific, they may 

38 return to the same winter foraging island each year (Pratt et al. 1987). This species has been 

39 sighted regularly on the shoreline of Palmyra and in open, grassy areas near the camp. Direct 

40 counts in 1987 (Fefer) and 1992 (Flint) estimated a total wintering population at 75 and 144 

41 plovers, respectively. Approximately 100 individuals were counted in December 2001 (Depkin 

42 2002). Between September 2008 and July 2010 the highest index counts on the runway at high 

43 tide on May 21, 2010 (79 birds) and the lowest counts were on June 13, 21, and 27, 2009 (0 

44 birds). This shows temporal patterns of Pacific golden-plover presence at Palmyra the U.S. 

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 80

1 Pacific Islands Regional Shorebird Conservation Plan (2004) identified the plover as a species of 

2 high conservation concern. 

3

4 Wandering tattlers have been seen in abundance along Palmyra‟s shoreline. The U.S. Pacific 

5 Islands Regional Shorebird Conservation Plan (2004) estimated that the total world population of 

6 wandering tattlers ranges from 10,000- 25,000 individuals. Fefer (1987) recorded 104 wintering 

7 wandering tattlers during a visit in 1987, and in 1992 Flint observed 126 wintering individuals. 

8 A survey in December 2001 reported 44 individuals at the atoll (Depkin 2002). Index counts on 

9 the runway ranged from nine birds in November 2009 and May 2010, and zero birds on 24 

10 different counts over a 2-year period. The runway index count may not be as useful a tool for 

11 monitoring wandering tattler numbers as it is for other shorebird species, due to their more 

12 shoreline-oriented behavior.

13

14 The ruddy turnstone is common throughout the Pacific Islands; however, the wintering 

15 population in this region is small compared to the global total (Engilis Jr. and Naughton 2004). 

16 POBSP observers estimated 300 individuals in November 1964. Fefer (1987) reported 112 ruddy 

17 turnstones at Palmyra, mostly along the sand beaches and shoreline habitat of the atoll. Seventy18 seven individuals were counted in the 1992 FWS visit (Flint 1992), and an August 2002 survey 

19 found 39 turnstones at Palmyra (Depkin 2002). These birds tend to flock in larger groups than 

20 the plovers or tattlers (Flint 1992). 

21

22 The U.S. Pacific Islands Regional Shorebird Conservation Plan (2004) designated sanderlings as 

23 a species of “limited importance” in the Pacific Islands since the vast majority of these 

24 shorebirds winter in other parts of the globe. POBSP records indicate 5 birds were seen in 

25 November 1964. Sanderlings have been seen on the north beach of Cooper-Menge, Bird and 

26 Papala Island. Two sanderlings were observed in 1987 (Fefer), and 2 individuals were observed 

27 in November 2001(Depkin 2002). This species is an uncommon migrant to the atoll. 

28

29 During the fall, infrequent sightings have been recorded for the following shorebirds: sharp30 tailed sandpiper (Calidris acuminata), lesser yellowlegs (Tringa flavipes), semipalmated plover 

31 (Charadrius semipalmatus), buff-breasted sandpiper (Tryngites subruficollis), solitary sandpiper 

32 (Tringa solitaria), pectoral sandpiper (Calidris melanotos), and short-billed dowitcher 

33 (Limnodromus griseus).

34

35 Uncommon visitors recorded at Palmyra

36 Nonnative cattle egrets (Bubulcus ibis) were observed several times at Palmyra Atoll. Fefer 

37 (1987) saw one egret, and Flint (1992) reported five individuals roosting in a Tournefortia tree 

38 on the Cooper Island runway. Additionally, two sightings of individual egrets were documented 

39 in September 2002 (Depkin 2002). POBSP scientists sighted two American wigeons (Anas 

40 americana) and one Eurasian wigeon (Anas penelope) in November 1964. Two northern

41 shovelers (Anas clypeata) were seen in a brackish pond on Holei Island and in the mudflats on 

42 Cooper Island during the 1992 FWS survey (Flint 1992). Depkin (2002) also reported a single 

43 shoveler in November 2001 at the east end of the runway. In 1987, a banded northern pintail 

44 (Anas acuta) that had been banded 82 days before in Utah was captured (Fefer 1987). Three 

45 Pintails were seen flying over Barren Island with a group of curlews in September 2002, and six 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 81

1 individuals were observed on the runway in October 2002 (Depkin 2002). In addition to three 

2 green-winged teals (Anas crecca) sighted in April 1964, two individuals were seen at the east 

3 end and north side of the runway in November 2001 (Depkin 2002). A single lesser scaup 

4 (Aythya affinis) was reported on three separate occasions along the north side of the runway 

5 during November 2001 (Depkin 2002). A brief sighting of a bobolink (Dolichonyx oryzivorus) 

6 occurred in October 2001, the first recording of this species at Palmyra (Depkin 2002). An 

7 unidentified snipe was briefly observed in November 2010 (M. Naughton pers. comm.) A small 

8 population of crested mynas (Acridotheres cristatellus) was introduced to the atoll in 1950 but 

9 has subsequently been extirpated (Fefer 1987). 

10

11 Special legal protection for birds at Palmyra

12 No bird species at Palmyra are listed under the Endangered Species Act (ESA) of 1973. All of 

13 the birds listed above are protected under the Migratory Bird Treaty Act (MBTA) of 1918, which 

14 prohibits the take of migratory birds without a permit. Additionally, the bristle-thighed curlew 

15 and Pacific golden-plover are designated as species of high conservation concern in National and 

16 Regional Shorebird Plans, as well as in the U.S. Pacific Islands Regional Shorebird Conservation 

17 Plan (Engilis Jr. and Naughton 2004). The bristle-thighed curlewhas also designated as a Bird of 

18 Conservation Concern by the FWS at the regional and national scale (FWS 2008a) due to limited 

19 breeding and nonbreeding distributions, low relative abundance, and threats during non-breeding 

20 season. Both of these species overwinter at Palmyra Atoll, with some juvenile and non-breeding 

21 birds remaining at Palmyra during the summer breeding season.

22

23 3.2.6 Terrestrial Wildlife of Palmyra

24 Invertebrates

25 Palmyra Atoll supports six species of native terrestrial crabs (Table 3.3), including the coconut 

26 crab (Birgus latro), two species of hermit crabs, two species of land crabs, and the brown tree 

27 climbing crab (Geograpsis crinipes). These crabs play an important role in breaking down 

28 organic matter and mixing soils, as well as dispersing seeds (Wiens 1962, Wegmann 2009). The 

29 existing literature for all terrestrial crab species found at Palmyra Atoll is limited, but there is 

30 slightly more information available for the coconut crab than the other crab species.

31

32 The coconut crab, the world‟s largest terrestrial arthropod, occurs on islands across the tropical 

33 Indo-Pacific region (Reyne 1939, Lavery et al. 1996). The coconut crab digs shallow burrows for 

34 mating and molting and frequently maintains several burrows within a territory. The species is 

35 omnivorous and will scavenge carcasses, climb trees to access food or escape, and can live up to 

36 70 years. Because it is highly sought after for human consumption, it is rare on all inhabited 

37 islands and considered an imperiled species. Rock (1916) noted that the coconut crab “abounds 

38 in great numbers” and went on to note that the species eats their “brother crab”. 

39

40 Over the past several years, coconut crab populations throughout its range have declined due to 

41 overharvesting and habitat modification or destruction in many regions, and the species has 

42 become regionally extinct on Mauritius (Wells et al. 1983). Although progress toward 

43 sustainable use has been made in several countries, this species maintains an International Union 

44 for Conservation of Nature (IUCN) listing of „Data Deficient‟, and information on natural 

45 populations remains sparse (Eldredge 1996).
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 82

1

2 At present, the coconut crab is the least abundant land crab at Palmyra Atoll, and coconut crab 

3 harvesting is prohibited (Howald et al. 2004). Limited quantitative data from four islands 

4 indicate variability in coconut crab densities at Palmyra Atoll (Buckelew et al. 2005). Qualitative 

5 accounts of differences in coconut crab densities around the atoll suggest that few islands 

6 currently support dense populations of this species. It is likely that black rats directly (through 

7 predation) and indirectly (through competition for food resources) adversely affect Palmyra‟s 

8 coconut crab population. Coconut crabs may also modify their activity patterns from nocturnal to 

9 diurnal in reaction to rat-related pressures. It is unknown to what extent coconut crabs are 

10 affected by rats at Palmyra, but evidence of predation (coconut crab carapace pieces in rat 

11 husking stations) has been observed (Wegmann and Fisher pers. comm. 2008), and there is 

12 considerable diet overlap between rats and land crabs (Wegmann 2009). 

13

14 Palmyra hosts 2 species of hermit crabs at Palmyra. The most abundant crab species is the red 

15 hermit crab (Coenobita perlatus), followed by the purple hermit crab (C. brevimanus) (Buckelew 

16 et al. 2005). These crabs use a gastropod shell (or other covering) to protect their unarmored 

17 abdomen and to prevent desiccation. Hermit crabs are omnivorous scavengers and are generally 

18 nocturnal; however, they are active diurnally in humid regions such as Palmyra Atoll. Rock 

19 (1916) reported sightings of “multitudes” of hermit crabs climbing the trees and eating T. 

20 argentea flowers, as well as its conspecifics. 

21

22 Two species of land crab, the orange land crab (Cardisoma carnifex) and purple land crab 

23 (Cardisoma rotundum) are found at Palmyra. Cardisomid crabs construct well defined, deep 

24 burrows that go below the water table. They are primarily herbivorous, but will also scavenge 

25 dead animals. The brown tree climbing crab (Geograpsis carinipes) also has been recorded at 

26 Palmyra Atoll, though at much lower densities than the five crab species mentioned above.

27

28 Most terrestrial crabs are crepuscular or nocturnal to avoid desiccation, however, at Palmyra the 

29 aforementioned species are also active during the daytime (Wegmann pers. comm. 2008). 

30 Buckelew et al. (2005) found red hermit crabs to be the most abundant crab species at Palmyra 

31 Atoll (Table 3.3), no preference across vegetation types for any crab species, and that there was a 

32 general avoidance of open areas. Little is known about what might be affecting crab populations 

33 at Palmyra. Potential limiting factors include predation and competition for food resources by 

34 rats and limited access to suitable shells (for hermit crabs and juvenile coconut crabs).

35

36 Table 3.3. Crab abundance survey results, Palmyra Atoll (Howald et al. 2004). Units represent 

37 #/hectare estimates

Crab species Mean # of crabs per hectare Standard dev. Mass (g)2

Birgus latro 7 3811000

Coenobita brevimanus 46 8 50

Coenobita perlatus 182 80 50

Cardisoma carnifex 33 8 300

Cardisoma rotundum 28 5 300

1 38 Large variance probably due to low probability of encounter and patchy distribution.

2 39 Approximate adult mass
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 83

1 Palmyra Atoll supports a few native and many accidentally introduced nonnative invertebrates 

2 (Handler et al. 2007). Little is known about the native invertebrates and their distributions and 

3 abundance across the atoll. In 2003, a terrestrial survey collected 115 arthropod taxa at Palmyra 

4 Atoll; most species were nonnative accidental introductions (Handler et al. 2007). The most 

5 detrimental nonnative insects include several ant species, a scale species, and mealy bugs. The 

6 most extensive invasive invertebrate distribution data available are included in P. grandis 

7 censuses (Nonner 2007) and an informal survey of the distribution of whiteflies (Aleyrodidea), 

8 scale (Pulvinaria urbicola), mealy bugs (Pseudococcidae), and aphids (Aphidoidea). In the latter 

9 survey, it was found that only 9 percent of plant species surveyed were not infested, and most 

10 observed plants harbored white flies (67 percent). In addition, 40 percent of plant species 

11 harbored mealy bugs while 28 percent harbored scale, and 18 percent harbored aphids (Freeman 

12 2006). Additional studies have been undertaken to collect more data on the distribution and 

13 abundance of insects in general; however, these data have not yet been analyzed (Young et al. 

14 2010).

15

16 Reptiles

17 Two species of marine turtles, the ESA-listed (Endangered) hawksbill turtle (Eretmochelys 

18 imbricata) and the ESA-listed (Threatened) green turtle (Chelonia mydas), are found at Palmyra 

19 Atoll with green turtles being the more common species (Fefer 1987) (Sterling pers. comm. 

20 2008). Both species of turtles are known to forage in the nearshore waters and lagoons of 

21 Palmyra, and nesting has been documented at least twice for green turtles (Fefer 1987, Depkin 

22 2002). Scientists from the FWS, American Museum of Natural History, and recently USGS have 

23 conducted surveys targeting both species abundance, and distribution in the eastern lagoons 

24 where turtles are most prevalent. Green turtles typically nest on sandy beach habitats, but may be 

25 prevented from nesting and laying eggs at Palmyra Atoll. One hypothesis for the lack of nesting 

26 may be the extreme abundance of coconut palms close to the beach where turtles might 

27 otherwise attempt to dig nesting pits (Suchanek et al. 2007). Additionally, turtle hatchlings are 

28 vulnerable to predation by rats as rats have been documented eating turtle eggs and hatchlings 

29 (Caut et al. 2008).

30

31 The ranges of at least 3 other species of marine turtles (all listed under the ESA) encompass the 

32 waters of Palmyra including the loggerhead turtle (Caretta caretta), the olive ridleyOlive Ridley 

33 (Lepidochelys olivacea), and the leatherback (Dermochelys coriacea) but have not been 

34 documented near shore.

35

36 Three terrestrial reptile species presently occur at Palmyra. These include an undescribed native 

37 gecko species (Lepidodactylus n. sp.), the potentially nonnative mourning gecko (Lepidodactylus 

38 lugubris) (a parthenogenic species represented on the atoll by many different clone types, of 

39 which there may be both native and nonnative clone types), and an introduced house gecko 

40 (Hemidactylus frenatus). The house gecko is suspected of transferring parasites to at least the 

41 mourning gecko (Fisher unpubl. data). Current studies are underway to investigate the 

42 distribution and habitat use of all three gecko species in order to gather baseline information and 

43 consider nonnative species eradication (Fisher and Hathaway 2007). One nonnative amphibian, 

44 the marine toad (Bufo marinus), was historically present at Palmyra Atoll but has not been 

45 observed since 2002 (Barclay pers. comm. 2008). 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 84

1 Nonnative Animals

2 Nonnative species have the potential to be invasive, which is defined by Executive Order 13112 

3 as a species whose introduction has or may cause harm to environmental or human health 

4 (National Invasive Species Council 2008). Invasive species are known to be important factors in 

5 the decline of unique natural communities, threatened and endangered species, and ecological 

6 processes (Vitousek 1990, Veitch and Clout 2002, Engilis Jr. and Naughton 2004). Palmyra 

7 Atoll is home to a variety of nonnative invasive species, including plants, arthropods, and black 

8 rats.

9

10 The first invasive species to reach Palmyra Atoll are unknown, but likely arrived with early 

11 movement through the area by Polynesians over 1,500 years ago. It is widely held, though not 

12 proven, that the first introduction of coconut palms came to Palmyra from Polynesian movement, 

13 and it is clear that additional plantings have been made over the years. Coconut palms now 

14 dominate Palmyra‟s forest community, and often occur in monotypic stands that limit the 

15 recruitment potential for native tree species (Wegmann 2009). There are several other invasive 

16 plant species warranting investigation and prioritization for control and eradication, including 

17 Koa Haole (Leucaena leucocephala) and Pothos (Epipremnum pinnatum) (Hathaway et al. 

18 2009).

19

20 Rats are well known to have severe effects on the ecosystems they invade, and there is extensive 

21 literature on the negative impacts of these mammals on Pacific Islands (Veitch and Clout 2002, 

22 Engilis Jr. and Naughton 2004, Howald et al. 2004, Buckelew et al. 2005, FWS 2005, Jones et al. 

23 2008, Towns et al. 2009). They are thought to be responsible for the lack of burrow-nesting 

24 seabirds breeding at Palmyra Atoll, such as shearwater and petrel species that are often observed 

25 offshore (Depkin 2002) (J. Smith, M. McKown, E. Flint, L. Ballance, and R. Pitman pers. comm. 

26 2008). Rats have been observed preying upon the ground nesting breeders at Palmyra, 

27 particularly sooty ternsTerns (Fefer 1987) (Wegmann pers. comm. 2008). While nesting events 

28 for green turtles have rarely been documented at Palmyra, it is worth mentioning that rats have 

29 been documented killing and consuming turtle hatchlings elsewhere (Caut et al. 2008). 

30 Furthermore, black rats at Palmyra have been observed attacking hermit crabs, and land crab 

31 carapace pieces are commonly found in rat husking stations (A. Wegmann and R. Fisher pers. 

32 comm. 2008). Aside from their impacts on the native fauna of Palmyra rats also affect the native 

33 flora by limiting native tree recruitment through seed and seedling predation (Wegmann 2009). 

34 Rats are also known to carry parasites, and recent studies have found that the parasites that 

35 accompanied rats to Palmyra use geckos as paratenic hosts (Lafferty et al. 2010)

36

37 Radio telemetry data comparing movements of rats that were live-trapped both in the crowns of 

38 coconut palms and on the ground, found that rats at Palmyra function in a 3 dimensional 

39 environment, and regularly move between the forest canopy and the ground. The planar home 

ranges of rats at Palmyra are small, between 475 ft2and 11,482 ft2(145m2and 3500m240 ), n = 20) 

41 (Howald et al. 2004).

42

43 The Nature Conservancy, in conjunction with the U.S. Department of Agriculture‟s Wildlife 

44 Services, and the FWS initiated a rat eradication project at Palmyra Atoll in 2001. This 

45 eradication project was an attempt to restore Palmyra Atoll‟s terrestrial ecosystem. It was 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 85

1 suspended in August 2003 after it became apparent that rats could not be eradicated at Palmyra 

2 Atoll through the methods in use at the time. 

3

4 Various species of nonnative arthropods including scale insects, mealy bugs, ants, mud daubers, 

5 and mosquitoes are all present at Palmyra Atoll, and their effects are poorly understood. Ten 

6 species of nonnative ants have been recorded at Palmyra Atoll (Handler et al. 2007), 3 of which 

7 are considered highly invasive: the big-headed, crazy, and ghost ants (Pheidole megacephala, 

8 Paratrechina longicornis, and Tapinoma melanocephalum, respectively) (Pacific Invasive Ant 

9 Group 2004). It has been hypothesized that scale infestations were exacerbated by tending ant 

10 species, contributing to the recent decline of the P. grandis canopy area (Handler et al. 2007). 

11 The Big-headed ant is known to displace most native invertebrate fauna through aggressive 

12 behavior (Wetterer 2007). There have also been several noteworthy decreases in the abundance 

13 of vertebrates where the Big-headed ant is extremely abundant. 

14

15 Wasps and mosquitoes are also prolific at Palmyra. Mosquitoes are of particular concern because 

16 they are potential vectors for a variety of human and wildlife diseases. Two of the mosquito 

17 species found at Palmyra, recently identified by Handler et al. (2007) are clearly threats. The 

18 Asian Tiger mosquito (Aedes albopictus) has a wide host range including humans and birds and 

19 is a known carrier of dengue, avian malaria, and West Nile Virus (Kyle and Harris 2008). The 

20 southern house mosquito (Culex quinquefasciatus) is a potential vector for avian diseases 

21 including avian malaria, avian pox, and West Nile Virus (C. van Riper III et al. 2002, LaDeau et 

22 al. 2008). Rats prey on coconuts, leaving behind the excavated shell to be filled by rain water, 

23 creating prime habitat for mosquitoes to lay their eggs.

24

25 Other nonnative animal species include house geckos, which also may be responsible for 

26 transmitting parasites and out-competing native geckos. House geckos are currently only found 

27 in association with buildings and other structures around the camp area. 

28

29 3.2.7 Intertidal and Nearshore Ecosystems

30

31 Marine Wildlife

32 Corals 

33 Extensive coral reef flats surround Palmyra, spanning 47 km2 within the 10 fathom contour 

34 around the atoll (NMFS 2005). Palmyra Atoll supports three times as many coral species as 

35 found in Hawai`i, five times as the Florida Keys, and three times the species reported for the 

36 entire Caribbean (Maragos 2000). The coral fauna at Palmyra is even more diverse than other 

37 Line Islands, except for nearby Kingman Reef (Maragos 2006). Palmyra‟s specific location 

38 within the Equatorial Countercurrent may allow transportation of coral larvae from the highly 

39 diverse western Pacific region (Brainard et al. 2005). As a result, Palmyra likely functions as a 

40 coral larval source, dispersing species to atolls and reef islands in the central Pacific (Brainard et 

41 al. 2005). 

42

43 The species composition and condition of coral reefs at Palmyra vary depending on the location 

44 within the atoll and have undergone drastic changes over time. The first significant survey of 

45 coral reefs at Palmyra was conducted by Maragos in 1987, when he noted evidence of reef 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 86

1 damage from the negative impacts of previous military dredging and filling activities at Palmyra. 

2 Several important genera, especially Acropora, Pavona, and Pocillopora showed obvious signs 

3 of stress along the western reef (Maragos 1993).

4

5 Further impairment occurred in the mid-1990‟s, when the largest global coral bleaching and 

6 mortality event ever recorded damaged 16 percent of coral reefs around the world (Goldberg and 

7 Wilkinson 2004). Previously thriving Acropora staghorn coral thickets observed off Palmyra‟s 

8 broad western reef terraces in 1987 (Maragos 1988) degenerated into rubble deposits by 1998 

9 (Brainard et al. 2005). The distribution of large Porites heads and numerous Pocillopora coral 

10 heads present on the terrace suggest that this collapse was due to mass coral bleaching rather 

11 than wave action. Bleaching was likely caused by warm ocean waters passing over the reef as a 

12 result of an El Niňo Southern Oscillation (ENSO) event. Degraded water circulation and 

13 increased temperature regimes due to earlier military activities were compounding factors 

14 contributing to the drastic collapse. Southern reefs down drift from the dredged channel also 

15 showed signs of sick or bleached corals, possibly due to turbid, warm water from the lagoons 

16 (Maragos et al. 2004). Corals along the north face of the terrace appeared unaffected by the 

17 event. 

18

19 In 2002, rapid coral recolonization following the massive bleaching event of 1998 occurred on 

20 ocean facing reefs. Although not as abundant as 1987, corals off the broad western reef terrace 

21 appeared healthy and diverse (Maragos et al. 2004). Large colonies of Porites (6 – 12 ft or 2 – 4 

22 m in diameter) were more dominant than Pocillopora, which was the most abundant coral at this 

23 location in 1998 and 2000. Coral abundance and diversity were dramatically higher off 

24 southeastern ocean facing reefs than earlier surveys, with coverage exceeding 50 percent at most 

25 sites (Maragos et al. 2004). All recent shifts indicate a slow ecosystem recovery process after the 

26 previous bleaching event (Maragos 2006).

27

28 In the southeastern reef pools, Coral Gardens has over 25 species of Acropora including rare 

29 species and species absent elsewhere at the atoll. No one genus accounted for more than 18 

30 percent of the corals. Eighteen or more genera of coral faunal species were documented with the 

31 highest richness on the eastern and northern reef sites (Maragos 2006). While the most recent 

32 survey in March 2006 documented similar species richness as the 2004 survey, overall coral 

33 cover at this site has been declining over recent years. This may be due to lagoon water flowing 

34 out of a break in the islands surrounding the East Lagoon, bringing heated, sediment laden water 

35 into the Coral Gardens, thus stressing and killing corals there. 

36

37 Despite the current health of Palmyra‟s coral reefs, one potential for devastation recently became 

38 apparent. In 1991, a long line fishing vessel wrecked on the western shelf of Palmyra, and was 

39 first examined by Maragos in 2004. Initial inspection of the wreck revealed low numbers of the 

40 corallimorph Rhodactis howesii, a cnidarian that can damage and overgrow benthic organisms, 

41 thus rendering it competitively superior to some coral species (den Hartog 1980). 

42 Corallimorpharians possess elongated marginal tentacles that allow them to kill scleractinian 

43 corals (Chadwick 1987, Williams 1991) and has several modes of clonal replication, allowing 

44 them to rapidly monopolize space on tropical coral reefs (den Hartog 1980, Langmead and 

45 Chadwick-Furman 1999). This corallimorph may be stimulated by substances dissolving from 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 87

1 the wreckage such as iron, an essential trace element for primary producers on coral reefs 

2 (Entsch et al. 1983, Maragos 2004). In 2005 R. howesii cover expanded, and by 2006 the 

3 population increased dramatically. High densities were documented at the wreck site that 

4 decreased with distance from the shipwreck, while R. howesii was rare or absent in other parts of 

the atoll (Maragos 2004, Work et al. 2008). R. howesii still occupies over 2 km2 5 of reef habitat, 

6 smothers thousands of corals, and is the largest corallimorph invasion of a reef known to date 

7 (Work et al. 2008). Given its ability to rapidly reproduce, R. howesii may continue to expand 

8 across Palmyra‟s western reef even if the shipwreck is removed. Management of the 

9 phenomenon may include manual removal or chemical sterilization of the benthos, however the 

10 efficacy of these methods is unknown (Work et al. 2008).

11

12 Fishes

13 Coral reefs like those at Palmyra Atoll can sustain inverted biomass pyramids, a phenomenon in 

14 which up to 85 percent of the fish biomass is composed of apex predators (Friedlander and 

15 DeMartini 2002, Sandin et al. 2008). Fish species diversity at Palmyra Atoll is higher than other 

16 remote Pacific refuges, consisting of 418 species (The White House 2009). Piscivore biomass is 

17 dominated by several species of sharks (gray reef shark (Carcharhinus amblyrhynchos), black tip 

18 reef shark (C. melanopterus), and white tip reef shark (Triaenodon obesus) (DeMartini et al. 

19 2008). Shark abundance was fairly consistent between years, although a predominance of 

20 juvenile gray reef sharks (85 percent were less than 150 cm) may be indicative of fishing 

21 pressure (Brainard et al. 2005). Several giant hammerhead sharks (Sphyrna mokarran) have been 

22 observed at Palmyra (Pacific Island Fisheries Science Center 2004). Quite a few species of 

23 snappers are present, the most common are twinspot snapper (Lutjanus bohar), humpback 

24 snapper (L. gibbus), smalltooth jobfish (Aphareus furca), and onespot snapper (L. monostigma). 

25 giant trevally (Caranx ignobilis), bluefin trevally (C. melampygus), and black jacks (C. lugubris) 

26 were the most numerous of the jacks reported. Sixteen species of grouper were observed in 2004, 

27 with peacock grouper (Cephalopholis argus) the most abundant. Smaller numbers of the flagtail 

28 grouper (C. urodeta) and the camouflage grouper (Epinephelus polyphekadion) were also 

29 reported (Brainard et al. 2005). Combined, these large fishes account for 56 percent of the fish 

30 biomass at Palmyra (Stevenson et al. 2007).

31

32 Other marine fishes observed in the coral reef surrounding Palmyra include butterfly fish 

33 (Chaetodontidae), damselfish (Pomacentridae), parrotfish (Scaridae), wrasse (Labridae), and 

34 surgeonfish (Acanthuridae) or tangs (FWS 2001). Manta rays (Manta birostris), eagle rays 

35 (Myliobatidae), and bonefish (Albulidae) are frequently sighted in the lagoons. Palmyra also 

36 hosts one of the largest lightly fished (catch and release) round-jaw bonefish (Albula 

37 glossodonta) populations in the Pacific, being studied by participants of the Palmyra Bonefish 

38 Conservation Research Program (Ault 2008).

39

40 Turtles

41 2 species of turtles have been observed foraging at Palmyra Atoll: the hawksbill, and the more 

42 common green turtle (Fefer 1987). Large numbers of turtle sightings during survey periods 

43 indicates that Palmyra is a significant marine chelonian foraging area. Hawksbill turtles are 

44 typically found feeding in the vicinity of rock or reef habitats in shallow tropical waters with 

45 little turbidity (Witzell 1983). Hawksbill turtles are specialist sponge carnivores, selecting just a 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 88

1 few genera of sponges for their principal diet (Vicente 1994). This feeding strategy is unique, as 

2 few vertebrates are capable of digesting sponges without being injured by the sponges' silicate 

3 spicules (needles). Green turtles of nearshore habitats in the Hawaiian Islands feed on benthic 

4 algae of the following genera: Codium, Amansia, Pterocladia, Ulva, Gelidium, and Caulerpa 

5 (NMFS 1998). In 2009 the Eastern-Pacific green turtle, which is distinguished by its darker 

6 color, was found in the waters surrounding Palmyra (Meyer pers. Comm.)

7

8 Green turtles often nest on wide sandy beaches and nesting has been documented at least twice at 

9 Palmyra, primarily on the northwestern side of Cooper Island (Fefer 1987, Depkin 2002).

10 However, the close proximity and great abundance of coconut palms on the beaches of Palmyra 

11 may deter green turtles from digging nesting pits. Predators of green turtles typically raid nests 

12 closest to the vegetation line, rarely destroying nests at low or mid-beach position (Fowler 1979). 

13 The outer islands of the refuge are less conducive to marine turtle nesting activity due to the 

14 narrow area, lack of sand during high tide, and continuous beach erosion exacerbated by World 

15 War II era alterations. 

16

17 Marine mammals

18 Marine mammals of two orders, Cetacea and Pinnipedia have been observed in the pelagic

19 waters surrounding Palmyra. The most commonly sighted cetaceans are bottlenose dolphins 

20 (Tursiops truncatus) (Fefer 1987, Yuen 1991), spinner dolphins (Stenella longirostris), and 

21 melon-headed whales (Peponocephala electra) (Brainard et al. 2005). Palmyra‟s surrounding 

22 waters also support populations of short-finned pilot whales (Globicephala melas) and false 

23 killer whales (Pseudorca crassidens) (Brainard et al. 2005). A possible recently re-discovered 

24 species of tropical beaked whale Mesoplodon hotaula was described from two specimens 

25 stranded at Palmyra and one at Christmas Island (Dalebout et al. 2007) and in 2010 killer whales 

26 (Orcinus orca), were also observed (A. Meyer, personal comm). Cetaceans have not been known 

27 to enter Palmyra‟s lagoons. Although protected under the Marine Mammal Protection Act, none 

28 of the cetaceans mentioned here are listed under the ESA or otherwise considered threatened.

29

30 Two sightings of Hawaiian monk seals (Monachus schauinslandi), ESA-listed as Endangered, 

31 have occurred at Palmyra decades ago (Redmond 1990, Westlake and Gilmartin 1990). These 

32 sightings are considered vagrant animals, as Palmyra is well outside of their known range 

33 (Gilmartin and Forcada 2002). 

34

35 All marine mammals are federally protected under the Marine Mammal Protection Act (MMPA) 

36 of 1972.

37

38 Algae

39 Alga contribute to the health of coral reef ecosystems, providing trophic resources for grazers 

40 and herbivorous fish, and bioconstruction of calcified reef (Gattuso et al. 1998), as well as 

41 contributing to coral reef productivity (Rowan 1998). Transfer of nutrients from algae to coral 

42 occurs when fish or invertebrates forage on primary producers and excrete on the coral reef 

43 (Birkeland and Grosenbaugh 1985). Lyngbya, blue-green algae, was the most common algal 

44 species originally observed by Dawson (1959) on the broad reef-flats of the northern and 

45 southern portions of the atoll. Lyngbya tolerates high temperatures, turbidity, low salinity, and 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 89

1 high organic content caused by restricted circulation, allowing its abundance on reef-flats 

2 (Dawson 1959). In 2006, 19 genera of algae were observed, compared to the 10 genera identified 

3 only 2 years prior (Pacific Island Fisheries Science Center 2006). Caulerpa and other 

4 Chlorophyta species are known to be an important food source for turtles (Bjorndal 1985). 

5 Macroalgal blooms usually associated with anthropogenic inputs of nutrients to coastal waters 

6 are absent at Kingman and Palmyra, which suggests that grazing activity, of an intact herbivore 

7 community, on unpopulated reefs may control macroalgal abundance even at high inorganic 

8 nutrient concentrations (Sandin et al. 2008).

9

10 Marine invertebrates

11 Noncoral marine invertebrates were rarely examined throughout the reef habitat at Palmyra 

12 Atoll. The first large-scale quantitative assessment of benthic fauna was conducted in 2008 by 

13 the Coral Reef Ecosystem Division of NOAA at the NOAA Pacific Islands Fisheries Science 

14 Center (PIFSC). Research divers conducted belt-transect surveys and counted common 

15 invertebrate components of the reef habitats within the phyla Cnidaria, Echinodermata, 

16 Mollusca, and Arthropoda. Marine invertebrate fauna included several species of anemones 

17 (Heteractis, Stichodactyla, Phymanthus), sea urchins, sea cucumbers, sea stars, Spondylid

18 oysters, pearl oysters, Tridacnid clams (giant clams), Charonia (Triton's trumpet) and Lambis

19 (spider conch), octopuses, hermit crabs, lobsters, and large crabs (Brainard et al. 2008). The most 

20 common macroinvertebrates observed during 2006 surveys were Trapezid crabs and hermit 

21 crabs, which were mostly associated with Pocillopora corals. Echinoderms were rare during 

22 surveys in 2006 (Pacific Island Fisheries Science Center 2006).

23

24 Fluted giant clams (Tridacna squamosa) and maxima clam (T. maxima) are the two giant clam 

25 species present at the atoll. Surveys in 2004 found that giant clams were not abundant at 

26 Palmyra, except on the shallow sheltered “coral gardens” reef (Pacific Island Fisheries Science 

27 Center 2004), and giant clams were recorded from only five sites in 2006 (Pacific Island 

28 Fisheries Science Center 2006). Throughout their adult lives, these species are firmly attached to 

29 coral reefs by byssal threads (Munro 1985), however, recruitment is poorly understood. Very 

30 little is known about source areas for larvae and whether some reefs act as stepping stones for 

31 species dispersal (Wells 1995). Like the coral reef, giant clams harbor enormous numbers of 

32 primary producing dinoflagellates, zooxanthellae (Symbiodinium microadriaticum). Giant clams 

33 benefit from a highly efficient internal food source, allowing them to grow faster and larger than 

34 other bivalves (Heslinga and Fitt 1987). Populations of these clams have been declining on other 

35 Pacific Islands over the years. Giant clams have been harvested in such numbers for their meat, 

36 that they have been listed in Appendix II of the Convention on International Trade of 

37 Endangered Species (CITES)(Wells 1985, FWS 2001) in an attempt to control their international 

38 movement. 

39

40 Threatened and Endangered Marine Species

41 Many species that are threatened, endangered, and depleted at a global level thrive at Palmyra 

42 Atoll, including green and hawksbill turtles (ESA listed), black-lipped pearl oysters (Pinctada 

43 margaritifera) (CITES listed), maxima clams (CITES listed), reef sharks, groupers (CITES 

44 listed), humphead (ESA species of concern) or Napoleon wrasse (Cheilinus undulates) (CITES 

45 listed), green bumphead parrotfish (Bolbometopon muricatum) (ESA species of concern and 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 90

1 candidate species), and various cetaceans. In addition, 21 of the 82 species of corals currently 

2 under petition for ESA listing by NOAA occur at Palmyra (Kenyon et al. 2011).

3

4 Worldwide populations of the green turtle have seriously declined as a direct result of 

5 overharvesting of turtles and eggs over the last centuries (Parsons 1962). In 1978, the green turtle 

6 was listed as threatened under the Endangered Species Act (ESA 1973). Additional protective 

7 regulations are enforced throughout all areas within U.S. jurisdiction in an effort to conserve and 

8 restore marine turtle populations to their former levels of abundance. Inclusion of green turtles 

9 into CITES made it illegal to trade any products made from this species in the U.S. and 130 other 

10 countries. Since 2001, the Hawai`i-based long-line fishing industry has undergone a series of 

11 regulatory changes to protect marine turtles and the short-tailed albatross (Phoebastria albatrus) 

12 (NMFS 2001). 

13

14 Palmyra Atoll National Wildlife Refuge has been noted as a significant habitat for the threatened 

15 green turtle. Turtle hatchlings are also vulnerable to predation by rats (Caut et al. 2008), 

16 therefore successful rat eradication may expand the nesting habitat for threatened green turtles. 

17

18 The hawksbill turtle is listed as an endangered species throughout its range by the International 

19 Union for the Conservation of Nature and Natural Resources and the Endangered Species Act of 

20 1973. Despite protective legislation, international trade in hawksbill shells, meat, and eggs

21 continues unabated in many countries and poses a significant threat to the survival of the species. 

22 More than one million hawksbill turtles have been killed for their shells since 1970 and illegal 

23 international trade continues to be the primary threat to the species. 

24

25 3.2.8 Terrestrial Vegetation

26 Records of collections and descriptions of the vascular flora of Palmyra Atoll date as far back as 

27 1873 (Streets 1877, Rock 1916, Dawson 1959, Herbst 1987, Depkin 2002, Freeman 2006). The 

28 most recent surveys, completed by Herbst in 1987 and 1992 (and subsequent identification of 

29 two additional species sent to him in 2002), provide a vascular plant species list and a brief 

30 description of the primary plant associations. These were later updated by Wegmann (2005) and 

31 Freeman (2006). According to Herbst (1987. 1992), three main vegetation associations, 

32 including P. grandis forest, Scaevola-Tournefortia (coastal strand forest), and coconut palm 

33 forest, were observed on the islands. Other minor vegetation types occurred, but were so small 

34 that they would not be plotted on a conventional vegetation map (Herbst 1992). 

35

36 As early as 1862, coconut palms and food plants were being introduced to the atoll (report from 

37 Zenas Bent while he was under commission by King Kamehameha IV to take possession of 

38 Palmyra under the Hawaiian flag) (Rock 1916). Following Rock‟s 1916 account describing 15 

39 species of vascular plants, including coconut palms, many additional species were added to the 

40 list of both native and nonnative species. Some of the species added to the list were likely present 

41 when Rock visited in 1913, but were not encountered or not recognized at the time. The native 

42 Beach gardenia (Guettarda speciosa) was collected on the atoll in 1949, but several other species 

43 were not recorded until much later. These species include mareer (Cordia subcordata), mago

44 (Hernandia sonora), and sea poison tree (Barringtonia asiatica) (Herbst 1987, 1992), and it has 

45 been assumed that they arrived at Palmyra relatively recently without human intervention. While 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 91

1 unlikely to give a complete pre-historic snapshot of the flora of Palmyra, ongoing 

2 paleoecological collecting and analyzing fossil pollen may help resolve some of the uncertainties 

3 surrounding which species have been present over time. The practice of introducing and 

4 cultivating plants for food and as ornamentals continued until recently (Freeman 2006), however, 

5 the list of unintentional introductions is also large. Some introduced plant species were unable to 

6 persist, but many have naturalized. The total vascular flora identified in past and current records 

7 at Palmyra Atoll includes 129 species. Twenty-five are considered native and two of these may 

8 now be extirpated; 48 were cultivated ornamentals or food plants; and 56 were adventives or 

9 naturalized plants (Herbst 1992, Freeman 2006). Freeman (2006) suggests that in 2006, 78 

10 vascular plant species were still present. Twenty-five of these were considered native species, 

11 while 53 species are considered nonnative. One subspecies of native grass, Lepturus repens var. 

12 palmyrensis, is considered endemic to Palmyra. 

13

14 Dominant Vegetation Types

15 Palmyra‟s aseasonal climate, with high precipitation and warm temperatures, supports dense 

16 assemblages of native and nonnative trees, shrubs, and herbaceous understory plants. A forest 

17 map based on 2001 satellite imagery (Wegmann 2005) estimated that a large portion of the atoll 

18 (approximately 43 percent) is dominated by the potentially nonnative coconut palm (C. nucifera) 

19 followed by beach naupaka (Scaevola sericea) and T. argentea (~29.5 percent) and P. grandis 

20 (~12 percent). Other vegetation types include broadleaf forests dominated by potentially 

21 nonnative Bengal almond (Terminalia catappa, ~6.2 percent), native sea hibiscus (Hibiscus 

22 tiliaceus, ~0.5 percent), and monodominant stands of native Pandanus fischerianus. Understory 

23 plant assemblages include L. repens grassland, P. scolopendria stands, and bare ground 

24 (Wegmann 2005). Natural temporal succession within these communities has been shaped by 

25 biophysical interactions and natural disturbance regimes from strong winds and cyclones, 

26 precipitation, seabird derived nutrients, and land crab-driven herbivory, seed dispersal, and seed 

27 predation. 

28

29 Pisonia grandis forest

30 Pisonia grandis (Nyctaginaceae) is a large fast growing tree with soft wood reaching heights up 

31 to 25 m at Palmyra (Herbst 1992). The distribution of P. grandis is limited to small remote 

32 islands in the Indian and Pacific Oceans (Airy-Shaw 1952), and was described in the 1890s as 

33 one of the most conspicuous forest types on coral atolls visited by the U.S. Fisheries 

34 Commission cruises (Fosberg 1994). It is now declining in much of its range due to human 

35 activities (Walker 1991), Pisonia trees primarily reproduce vegetatively, though the species does 

36 have sticky seeds that are dispersed long distances through adhesion to seabird feathers (Burger 

37 2005). 

38

39 There is little genetic differentiation between P. grandis individuals across the species‟ Pacific 

40 range. This suggests that bird dispersal was effective enough at mixing P. grandis genes between 

41 isolated islands throughout the Pacific (Walker 1991). The factors influencing the pattern of 

42 distribution and growth of P. grandis preclude a simple explanation. For instance, P. grandis is 

43 found on both very wet and very dry atolls, as well as with and without guano inputs. Walker 

44 (1991) suggests that multiple contributing factors include: low dispersal frequency, guano 

45 effects, precipitation patterns, competition, insect grazing, genetic variation, and mycorrhizal 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 92

1 associations. He points out that P. grandis would likely be dispersed widely by seabirds through 

2 uncharacteristic dispersal events, such as cyclone scatter of seabirds. However, islands in 

3 relatively close proximity to each another, P. grandis may be present at some islands but not 

4 others. While it has been suggested that P. grandis requires guano for growth, its distribution 

5 shows that this is not necessarily the case provided the soil contains adequate nutrients (Wiens 

6 1962, Spicer and Newberry 1979). P. grandis have very shallow root systems, adapted for using 

7 near surface water, as a results of these adaptations, P. grandis is found at both the wettest (e.g., 

8 approximately 4,500 mm/yr at Palmyra Atoll) and very driest islands (e.g., 70 mm/yr at Vago 

9 Island) (Walker 1991). 

10

11 The Pisonia population at Palmyra Atoll suffered severe losses of most of the mature individuals 

12 between 2002 and 2005 possibly due to an unexplained population explosion of the nonnative 

13 scale insect Pulvenaria urbicola (Nonner and Woodward 2006). Several management options 

14 were evaluated including systemic application of the insecticide imidicloprid to specimen trees 

15 and control of ant species suspected of facilitating scale survival. Results were equivocal from all 

16 these experiments but there is currently good regeneration occurring in the Pisonia forest.

17

18 Coastal strand forest or Scaevola-Tournefortia

19 Native S. sericea and T. argentea are the dominant species of the coastal strand vegetation type. 

20 S. sericea is more dominant on lagoon borders, and T. argentea dominates on the ocean edges 

21 (Herbst 1992). Both are considered widespread, halophytic, pioneer species, and they can be 

22 found in monotypic stands, or co-dominant and mixed forest (Niering 1963, Kepler and Kepler 

23 1994). These species are generally not dense enough to prohibit ground cover and appear to have 

24 no substrate preference (Fosberg 1957). This vegetation type, specifically T. argentea, is heavily 

25 used by red-footed boobies for roosting and nesting, and is comparable to P. grandis in native 

26 bird use overall (Young pers. comm. 2008). T. argentea is less abundant across the Pacific than it 

27 was formerly (Kepler and Kepler 1994). Kepler and Kepler (1994) report that most mature T. 

28 argentea trees occur at the T. argentea - P. grandis interface but die off as P. grandis expands. 

29 Geckos have been observed drinking the nectar from T. argentea flowers, and Rock (1916) 

30 reported that crabs feed on the flowers. Herbst (1992) noted that S. sericea is the dominant 

31 species on Barren Island with only a few C. nucifera and T. argentea present. Barren Island is 

32 the most recently formed island in the atoll and often disturbed by storms. The dominance of S. 

33 sericea on this island suggests that it represents a very early successional stage. Usinger and La 

34 Rivers (1953) reported that both S. sericea and T. argentea at Arno Atoll have their own distinct 

35 insect populations.

36

37 Pandanus fischerianus

38 Fosberg (1957) observed small groves of dense native P. fischerianus scattered throughout 

39 Palmyra Atoll. There were records or collections of P. fischerianus from 20 islands in 2006.

40

41 Lepturus repens var. palmyrensis

42 One of the other native but minor vegetation types occurring at Palmyra includes small patches 

43 of native grasslands. This grassland is composed of Palmyra‟s only endemic species Lepturus 

44 repens var. Palmyrensis (Herbst 1992). It is closely related to the taxa found on Malden and 

45 Christmas Islands as well as Pokak and Wake Atolls (Herbst 1992).
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 93

1

2 Cocos nucifera

3 The occurrence of the possibly nonnative coconut palm at Palmyra is likely the result of early 

4 introduction by Polynesian explorers. Subsequent expansions of this species through plantings 

5 occurred prior to and during military occupation and continued until at least 1957 (Dawson 

6 1959). While this species could have arrived on its own via drift dispersal (Harries 1992), it is 

7 clear that its distribution is augmented by human movement. In addition, C. nucifera has 

8 displayed invasive behavior at Palmyra, increasing from approximately 9,600 coconut palms in 

9 1886 to approximately 2 million currently (Rock 1916, Wegmann 2009). C. nucifera is now the 

10 dominant forest type at Palmyra. It rapidly colonizes canopy gaps opened in other forest types 

11 (Herbst 1992, Freeman 2006), and ongoing research by Hillary Young of Stanford University 

12 indicates that coconut palms outcompete native species for nutrients. In addition, Young found 

13 that the large nuts and fronds cause physical damage to native species when they fall, allowing 

14 for further expansion of already established coconut palm groves. Data collected recently 

15 regarding coconut palm grove habitat by native animal species is still being analyzed. However, 

16 it seems clear that few seabirds use coconut palms for roosting and even fewer for nesting 

17 (Young et al. 2010). The C. nucifera forest provides abundant food and habitat for nonnative 

18 black rats (Howald et al. 2004, Wegmann et al. 2007) and the fruits are used as a food source by 

19 the atoll‟s land crab community (Wegmann 2009). Abundant evidence demonstrating elevated 

20 native seed predation in C. nucifera dominated sites relative to other forest types further suggests 

21 significant cascading effects of C. nucifera forest dominance throughout the larger Palmyra Atoll 

22 system (Young et al. 2010).

23

24 Terminalia catappa

25 The history of T. catappa or Tropical Almond at Palmyra is unknown, but it is generally 

26 regarded as a nonnative invasive species. Dawson (1959) describes T. catappa and other species 

27 as being purposely introduced through original plantings on Menge Island. It is the dominant tree 

28 in several groves on Cooper Island, particularly near the TNC camp, but it apparently has not yet 

29 spread in large numbers to other islands. T. catappa should be considered for control plans 

30 similar to the plans suggested for coconut palms. At minimum it should be monitored to examine 

31 how quickly it is expanding in distribution.

32

33 Hibiscus tiliaceaus

34 The history of hibiscus (H. tiliaceaus) at Palmyra is also unknown, but it is also regarded by 

35 some as a nonnative invasive species. Dawson (1959) describes this and other species as being 

36 purposely introduced through original plantings on Menge Island. Small, very dense, monotypic 

37 hibiscus groves are scattered on several islands in the atoll. In addition, there is a nearly 

38 impenetrable hibiscus swamp in the central portion of Pelican Island and another smaller 

39 hibiscus swamp on Home Island. The rate of spread of hibiscus is unknown; expansion should be 

40 monitored and control plans considered.

41

42 Miscellaneous species

43 In addition to the aforementioned vascular plants, two species of terrestrial algae, three mosses, 

44 eight lichens, and four fungi species have been identified at Palmyra Atoll (Rock 1916, Dawson 

45 1959, Herbst 1992).
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 94

1 3.2.9 Social and Economic Environment

2

3 Ownership, Management, Major Stakeholders

4 Ownership

5 Palmyra Atoll is currently owned and managed by the U.S. Fish and Wildlife Service, The 

6 Nature Conservancy, and the Cooper family. The majority of the islands, waters, and the coral 

7 reef surrounding Palmyra up to 12 nautical miles to sea is owned and managed by the FWS as a 

8 National Wildlife Refuge for the “conservation and management of native species of wildlife and 

9 fish and their habitats” (Federal Register 2001). Palmyra Atoll NWR was established on January 

10 18, 2001, by Secretary‟s Order 3224; it includes approximately 446.25 acres (180.57 ha) of 

11 emergent land, approximately 503,963 acres (203,946 ha) of submerged lands and associated 

12 waters, including roughly 16,094 acres (6,515 ha) of coral reef habitat (Federal Register 2001). 

13 The Nature Conservancy purchased Palmyra from the Fullard-Leo family in 2000 to protect its 

14 waters and lands. TNC now owns Cooper and Menge Island (TNC 2005). The Cooper family has 

15 retained ownership of Home Island. The atoll is an incorporated territory of the United States. 

16 The Nature Conservancy operates a research station on Cooper Island that supports the Palmyra 

17 Atoll Research Consortium or “PARC” (http://www.palmyraresearch.org/). PARC is not a land 

18 owning entity.

19

20 The FWS manages the Refuge for the “conservation and management of native species of 

21 wildlife and fish and their habitats. Wildlife species identified as endangered or threatened will 

22 receive management priority, with a special emphasis on stewardship of endangered and 

23 threatened turtles, migratory seabirds that forage in the refuge waters, the coral reef, and pelagic 

24 wildlife. Management actions will include protection of the refuge waters and wildlife from 

25 commercial fishing activities” (Federal Register 2001). 

26

27 Access

28 Public access to Palmyra Atoll is largely self-limiting due to the very high expense of flying to 

29 such a remote destination. TNC owns and operates the only airplane runway at Palmyra (Cooper 

30 Island) and travel to the atoll by boat is a 5-7 day voyage from Honolulu, Hawai`i. The public 

31 may gain access to the refuge in four ways: 1) working for, contracting with, or volunteering for 

32 TNC or FWS; 2) conducting scientific research via FWS Special Use Permits; 3) invitation 

33 through TNC, FWS, or PARC; or 4) by private recreational sailboat or motorboat. With prior 

34 approval by the FWS, privately owned vessels are permitted access to the Palmyra Atoll NWR 

35 for up to 7 days to observe and enjoy the natural resources of the Refuge. A maximum of two 

36 vessels are allowed at one time and up to six yachts may visit in a month. Private vessels must 

37 have U.S. Coast Guard (USCG) approved holding tanks for sewage and an appropriate and 

38 current USCG inspection certificate. Access to Cooper Island must be arranged and secured 

39 through TNC (FWS 2010e). 

40

41 Historical and Cultural Resources and Values

42 Palmyra has undergone a series of private ownership turnovers and is one of the few wet atolls 

43 that was not permanently occupied or claimed by any Pacific Island culture (Maragos et al. 

44 1999). Palmyra received its official name when Capt. Sawle landed his American vessel, 

45 Palmyra, on the atoll on November 7, 1802. In 1859, Dr. G.P. Judd of the American brig 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 95

1 Josephine, claimed possession of the atoll for the United States and the American Guano 

2 Company. In 1862, Kamehameha IV commissioned Hawaiian citizens, Captain Zenas Bent and 

3 Mr. Johnson Wilkinson to perform a formal ceremony taking possession of the atoll from the 

4 U.S. and the American Guano Company. Captain Bent sold his portion to Wilkinson in 1866 for 

5 $500, and his wife inherited the atoll following his death. The heirs of Mrs. Wilkinson sold 

6 Palmyra to the Pacific Navigation Company for a single dollar and “other valuable 

7 considerations” in 1885 (U.S. Supreme Court 1947). When the United States annexed the 

8 Hawaiian Islands in 1898, Palmyra Atoll was specifically included as part of the Hawaiian 

9 Territory. After a series of private ownerships, Hawai`i Circuit Court Judge Henry E. Cooper 

10 bought Palmyra in 1911 for $750, hoping to find an allegedly buried pirate treasure. The Fullard11 Leo family of Honolulu purchased Palmyra (except Home Island) for $15,000 from Judge 

12 Cooper in 1922 (Aronson and Anderson 2000). 

13

14 In 1939, the Fullard-Leo family received notice that the U.S. government was reclaiming 

15 Palmyra Atoll (U.S. Supreme Court 1947). Beginning in 1939, Palmyra was heavily used as a 

16 naval base until the end of World War II. Approximately 6,000 military personnel were stationed 

17 on the atoll for several years. Military activities included road construction along the perimeter, 

18 causeway construction between the lagoons, dredging a 200-foot wide channel through the 

19 western reef, enlarging Cooper Island to build an airstrip and port along the island‟s southern 

20 shore, dredging of a sea plane runway, and the creation of two fighter plane air strips. The U.S. 

21 Coast Guard also had operations at Palmyra during this time. After years of court battles with the 

22 Navy, the Fullard-Leo family was awarded valid title by the U.S. Supreme Court and the Navy 

23 abandoned the atoll in 1945. In 1947, the Federal Aviation Administration leased the atoll, 

24 stationing 970 personnel and their families on the atoll for 3 years (Aronson and Anderson 

2000). In 1959 Hawai`i became the 50th 25 State of the United States of America. Palmyra was 

26 specifically excluded from statehood and became the only completely privately owned U.S. 

27 insular area. Executive Order No. 10967 (dated October 10, 1961) stated that the Secretary of the 

28 Interior was responsible for the civil administration and executive and legislative authority of 

29 Palmyra.

30

31 In 2000, TNC purchased Palmyra from the Fullard-Leo family in an effort to help preserve its 

32 natural resources. Further protection was granted in January 2001 when the lagoons and 

33 surrounding waters within the 12 nm U.S. territorial seas were transferred via Secretarial Order 

34 from the Office of Insular Affairs to the FWS and designated as a National Wildlife Refuge. In 

35 March 2003, TNC sold a portion of the emergent lands to the FWS (Davis 2003). In 2007, TNC 

36 sold another 3 parcels to the FWS (Lyons pers. Comm.).

37

38 Several World War II military structures remain at Palmyra, including a basketball court, water 

39 cistern, bunkers, a collapsed building, a Quonset hut, a drainage ditch, a hospital, and several 

40 “pill-boxes” and supporting structures for gun batteries. Some of these structures are decaying 

41 due to vegetation growth, harsh climate conditions, and wave action (Aronson and Anderson 

42 2000, FWS 2001). 

43

44 The Office of Hawaiian Affairs (OHA) has indicated that the Hawaiian people are interested in 

45 cultural resources that may be found at Palmyra. Because Palmyra was once claimed by the 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 96

1 Hawaiian Kingdom, OHA believes the atoll has cultural importance to native Hawaiians. No 

2 sufficient documentation has shown that customary or traditional Hawaiian practices (such as 

3 fishing) occurred on the atoll (FWS 2001). 

4

5 Human environment

6 Since purchasing the atoll in 2000, TNC has organized approximately four to six visitor trips to 

7 Palmyra each year (Lyons pers. comm.). Visitors participate in catch-and-release bonefishing, 

8 offshore blue-water recreational fishing, nature walks, kayaking, SCUBA diving, and other 

9 activities deemed compatible with the Refuge (Depkin 2002). TNC guests and staff are allowed 

10 three weekly catches of tuna, ono, or mahi for local consumption.

11

12 In 2004, TNC partnered with 10 academic institutions and government agencies in the 

13 establishment of the Palmyra Atoll Research Consortium. In 2005 a new research station facility 

14 was constructed on Cooper Island (TNC 2005). The station includes 16 small residential 

15 cottages, a galley, shower house, bathrooms, and a research laboratory. The station is capable of 

16 housing and supporting 25 staff and researchers at one time. Fresh water is supplied through a 

17 refurbished 100,000-gallon fresh water catchment tank. The station relies on an environmentally 

18 friendly septic system, which uses a multi-stage system to flush sewage through tanks before 

19 reaching a leach field. Nutrients are absorbed by native sedges and the remaining water irrigates 

20 a grassy area (Lyons pers. comm.). Electric power is generated and transmitted by 2,500 kv 

21 diesel generators on Cooper Island, but there are plans for the station to switch to solar power. A 

22 satellite dish was installed in 2006 to supply the station with internet connectivity and web-based 

23 telephones. Pre-existing infrastructure in use on Cooper Island includes a seaplane ramp, a 

24 crushed-coral runway, and concrete bunkers (Howald et al. 2004). 

25

26 Currently, between five to six permanent and temporary TNC employees are stationed at 

27 Palmyra to manage conservation and research activities and support visitors and PARC 

28 researchers. Staff positions include a field station manager, a galley manager, one to two galley 

29 assistants, a maintenance manager, a boat captain and a chief of marine operations. These 

30 employees work in 3-month cycles. At least one FWS employee, a Refuge Manager or assistant, 

31 is stationed at Palmyra.

32

33 Recreational and aesthetic uses

34 The Conceptual Management Plan for Palmyra Atoll National Wildlife Refuge established five 

35 Interim Compatible Determinations for recreational uses at Palmyra Atoll NWR. 

36

37

38 Environmental education

39 Members of the public are permitted to visit the Refuge to participate in environmental 

40 education, interpretive hikes, motorboat and kayak outings, and wildlife photography. Up to 30 

41 participants at any one time are allowed to participate in Refuge environmental education and 

42 interpretive programs, including hikers and kayakers. A minimum of one approved guide for 

43 each group of hikers and kayakers is required. Groups of hikers or kayakers may not exceed 10 

44 individuals. 

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 97

1 Wildlife observation through diving and snorkeling

2 Up to 12 visitors at any one time are allowed to participate in recreational diving and snorkeling 

3 programs. Two groups of up to four divers or snorkelers are allowed per boat in the lagoon, 

4 channel, or ocean reef sites at any given time. An additional four snorkelers are permitted to use 

5 the third small skiff near the lagoon or channel area for diving and snorkeling. 

6

7 Bonefishing

8 Recreational bonefishing is conducted at Palmyra on a catch-and-release basis with artificial flies 

9 and barbless hooks. A total of eight anglers are allowed in the lagoons at one time, with no more 

10 than two fishing outings permitted per day and must be accompanied by a FWS-approved guide. 

11 Catch rates are monitored through daily logs and tagging studies in order to assure sustainable 

12 fishery conditions. 

13

14 Blue water (offshore) fishing

15 The offshore sport fishing program at Palmyra allows visitors access to pelagic game-fish, 

16 including tuna (ahi), wahoo (ono), and mahi-mahi. Fishing is limited to eight people per trip, one 

17 trip per day. Fishing logs are required for each trip. Only pelagic species are permitted for on18 atoll consumption and only 150 lbs of pelagic fish maybe be taken each week from the waters 

19 surrounding the atoll. No bottom fish or reef fish are allowed to be targeted for consumption and 

20 any that are accidentally caught are to be immediately released. Jacks can be fished on a catch21 and-release basis; none are permitted to be consumed or retained for any reason. An independent 

22 scientific research and monitoring program is required for jacks in order to form a basis for 

23 determining whether the jack catch-and-release program should be retained, scaled back, or 

24 cancelled. Boat captains and crews are required to be trained on the scope, restrictions, and 

25 associated rationale for the sportfishing program. 

26

27 Sailing and motor boating

28 With prior approval by the FWS, privately owned vessels are permitted to access the atoll for up 

29 to 7 days to see and enjoy the natural resources of the refuge. A maximum of two vessels are 

30 allowed at one time and up to six yachts may visit monthly. Private vessels must have U.S. Coast 

31 Guard (USCG) approved holding tanks for sewage and an appropriate and current USCG 

32 inspection certificate. 

33

34 Unexploded ordnance (UXO)

35 One safety issue at Palmyra is unexploded ordnance (UXO). UXO is explosive weaponry that 

36 did not explode when deployed, and subsequently poses a risk of detonation. During World War 

37 II, Palmyra was used by the U. S. Navy and Coast Guard as a Naval Air Station. Later in 1962, 

38 the U.S. Department of Defense used the atoll for an instrumentation site during high altitude 

39 atomic weapon tests over Johnston Island. In an effort to improve atoll safety, the Defense 

40 Environmental Restoration Program conducted a site survey of UXO at Palmyra in 1995. Survey 

41 results indicated that Whippoorwill Island, Barren Island, Quail Island, and Cooper Island (in 

42 total, 40 percent of the atoll‟s emergent land area; 107 ha) contained UXO (Donaldson 

43 Enterprises 1995). In 2002, a cooperative team of the U.S. Army, Navy, and Coast Guard joined 

44 forces to dispose of UXOs at Palmyra. The team cleared out a storage magazine containing 

45 corroded and raw explosives, as well as other UXO that were exposed on the atoll. All of the 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 98

1 removed UXO was taken to an environmentally safe location for proper disposal (Sekerak 2002). 

2 However, not all of Palmyra‟s land area has been surveyed for UXO, and it is likely that UXO is

3 still present on the islands mentioned above, and on other islands as well.

4

5

6 4 Environmental Consequences

7

8 4.1 Purpose and Structure of Environmental Consequences

9 Chapter 4 analyzes the environmental consequences of the alternatives as presented in Chapter 2. 

10 For comparative purposes, Chapter 4 also includes a similar analysis of the consequences of 

11 taking no action to address the problems associated with the presence of nonnative black rats 

12 (Rattus rattus) at Palmyra Atoll. The purpose of the impact analyses in this chapter is to identify 

13 and compare the risks associated with the identified alternatives including the no action 

14 alternative. Additionally, this chapter will discuss the risks associated with the toxicity of, and 

15 exposure to brodifacoum and the potential disturbance to the ecosystem associated with the 

16 implementation of each alternative. The cumulative assessment of the environmental 

17 consequences of each alternative will inform the decision-making process and allow decision 

18 makers to identify the alternative that will accomplish our eradication goals, while decreasing the 

19 probability of causing harm to nontarget species and other environmental factors, and eradication 

20 personnel.

21

22 The concept of significance, according to the Council on Environmental Quality (CEQ) 

23 regulations (40 CFR 1508.27), is composed of both the context in which an action will occur and 

24 the intensity of that action on the aspect of the environment being analyzed. “Context” is the 

25 setting within which an effect is analyzed, such as a particular locality, the affected region, or 

26 society as a whole. “Intensity” is a measure of the severity of an effect. Determining the intensity 

27 of an effect requires consideration of the appropriate context of that effect, as well as a number 

28 of other considerations, including the following:

29 Impacts may be both beneficial and adverse. A significant effect may exist even if on 

30 balance the overall effect of that action will be beneficial.

31 The degree to which an action affects public health or safety.

32 Unique characteristics of the geographic area (e.g., historical or cultural significance, 

33 specially protected lands, ecologically critical areas).

34 The degree to which the impacts of an action are likely to be highly controversial. The 

35 courts have since elaborated on this consideration, stating that controversy would be in 

36 the form of “substantial dispute” as to “the size, nature or effect of the major Federal 

37 action rather than to the existence of opposition to a use [e.g., eradication of mice], the 

38 effect of which is relatively undisputed” (Hanly v. Kleindienst, 471 F.2d 823, 830 [2nd 

39 Cir. 1972]).

40 The degree to which the possible impacts of an action are highly uncertain, or involve 

41 unique or unknown risks.

42 The degree to which an action may 1) establish a precedent for future actions with 

43 significant effects; and/or 2) represents a decision in principle about a future 

44 consideration.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 99

1 Whether an action is related to other actions with individually insignificant but 

2 cumulatively significant impacts. Significance exists if it is reasonable to anticipate a 

3 cumulatively significant effect on the environment.

4 The degree to which an action may adversely affect properties listed in or eligible for 

5 listing in the National Register of Historic Places, or may cause loss or destruction of 

6 significant scientific, cultural, or historical resources.

7 The degree to which an action may adversely affect an endangered or threatened species 

8 or critical habitat as listed under the ESA.

9 Whether the action threatens a violation of Federal, State, or local law or requirements 

10 imposed for the protection of the environment.

11

12 4.2 Environmental Issues Addressed

13

14 4.2.1 Scope for Environmental Issue

15 The FWS compiled a list of major environmental issues, or impact topics that warranted specific 

16 consideration in this analysis. The compilation of this list of issues was informed by a scoping 

17 process that included informal discussions with representatives from numerous government 

18 agencies, private groups and individuals with relevant expertise or a stake in Palmyra Atoll, and 

19 solicitation of public comments.

20

21 In the analysis below, the potential significance of the environmental consequences (or 

22 “impacts”) of each action alternative and the no action alternative will be discussed on a case-by23 case basis for each environmental issue considered.

24

25 4.2.2 Issues

26 The issues analyzed in this document include:

27 Impacts to physical resources

28 o Water resources

29 o Geology and soil

30 Impacts to biological resources

31 o Impacts to species vulnerable to toxicant use

32 o Impacts to species vulnerable to disturbance

33 o Indirect effects to biological resources

34 Impacts to the social and economic environment

35 o Impacts to refuge visitors and recreation

36 o Impacts to historical and cultural resources

37 Cumulative impacts

38 Irreversible or irretrievable commitment of resources

39 Relationship of short-term uses to long-term productivity

40

41 Brief descriptions of many of these topics can be found in Section 1.7.

42
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 100

1 4.2.3 Aspects of Environment Excluded from Detailed Analysis (with Rationale)

2 4.2.3.1 Air quality

3 Impacts of the action alternatives on air quality at Palmyra Atoll will not be analyzed in detail 

4 because no activities are proposed that would represent a measurable change from the 

5 background levels of air pollution caused by use of machinery. The brief, localized helicopter 

6 operations that would occur as part of Alternatives B and C would have no more than a 

7 negligible contribution to local or regional changes in air quality. Additionally, the transportation 

8 of personnel to and from Palmyra during the eradication window will be coordinated with TNC 

9 and FWS to minimize the number of flights. The power generators that supply the research 

10 station with electricity would not experience increased use due to any of the action alternatives.

11

12 4.2.3.2 Marine mammals

13 Potential impacts of rat eradication activities to cetaceans (whales, dolphins, and their close 

14 relatives) in the waters surrounding Palmyra will not be analyzed in this Environmental Impact 

15 Statement (EIS) other than to establish a significance threshold under the Marine Mammal 

16 Protection Act (MMPA). The likelihood of cetacean exposure to brodifacoum would be 

17 negligible, and cetaceans would have to consume extremely large quantities of this toxicant to 

18 experience lethal or even sub-lethal effects because of their extremely large size. The only point 

19 of concern to cetaceans would be from small boat traffic around the atoll. With all action 

20 alternatives, such traffic would be limited to the lagoons inside of the barrier reef; cetaceans are 

21 not known to enter Palmyra‟s lagoons. The majority of the activities described in the action 

22 alternatives would be aerial or terrestrial, and the likelihood of these activities having measurable 

23 impacts on cetaceans would be negligible as well.

24

25 4.2.3.3 Environmental justice

26 The impacts of the action alternatives on environmental justice, mandated by Executive Order 

27 12898 of 1994 identifies and addresses the potential for disproportionate placement of adverse 

28 environmental, economic, social, or health impacts on minority and low-income populations, 

29 will not be analyzed in detail because no minority or low-income populations would be affected 

30 by any of the action alternatives.

31

32 4.3 Consequences: Physical Resources

33

34 4.3.1 Water Resources

35 Significant impacts to water quality are analyzed for the identified action alternatives with 

36 respect to potentially adverse physical and biological impacts from the use of rodenticide with 

37 each of the alternatives. Water quality at Palmyra is regulated by the U.S. Environmental 

38 Protection Agency (EPA), which requires that Federal waters meet minimal criteria for a number 

39 of designated uses.

40

41 While the Federal Clean Water Act (CWA) prohibits the discharge of “pollutants” into waters of 

42 the United States, in 2007, the EPA clarified its interpretation of the term “pollutant” to exclude 

43 pesticides that may unavoidably enter the water through bait drift while being applied to control 

44 pests that occur “over, including near” water bodies (71 CFR 227 pp. 68483-68492). This ruling 

45 was vacated by the 6th Circuit Court of Appeals in 2009. Subsequently, the EPA was granted a 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 101

1 stay until April 9, 2011 to allow time for the EPA to develop guidelines for permits and the 

2 permitting process. We will fully comply with all CWA National Pollutant Discharge 

3 Elimination System (NPDES) permitting required by the EPA pending the 2011 announcement.

4 On March 3, 2011, the EPA requested an extension on CWA permit requirement for pesticide 

5 discharges, and on March 28, 2011, the U.S. Court of Appeals for the Sixth Circuit granted 

6 EPA's request for an extension of the deadline for when permits will be required for pesticide 

7 discharges into U.S. waters from April 9, 2011 to October 31, 2011.

8

9 Rats at Palmyra are frequently found on and near the shoreline. For this reason, it is essential that 

10 rodenticide is made accessible to rats all the way down to the high tide mark to ensure the 

11 exposure of all rats throughout entire atoll. Even though maximum effort will be taken to prevent 

12 bait drift into the marine environment, permitting for aerial pesticide use around the littoral zone 

13 will be sought to comply with EPA‟s new CWA guidelines for aerial pesticide applications over 

14 waters of the United States.

15

16 4.3.1.1 Analysis framework for water resources

17 Alternative A: No Action

18 Rats at Palmyra Atoll do not currently affect the quality or quantity of potable water or marine 

19 water resources; however, rats are a vector for Leptospirosis potable water stores could become 

20 contaminated with Leptospirosis, a bacterial zoonotic disease caused by spirochaetes of 

21 the genus Leptospira that affects humans and a wide range of animals, including mammals, 

22 birds, amphibians, and reptiles. Rats pass the disease to humans by urinating directly into potable 

23 water supplies. Even though rats at Palmyra are not known to carry the bacterium that causes 

24 Leptospirosis, their very presence incurs a significant risk by ensuring the presence of a vector 

25 for infecting humans and wildlife.

26

27 Alternative B: Aerial Broadcast with Brodifacoum

28 There could be accidental bait drift or into the nearshore marine waters surrounding Palmyra 

29 during aerial bait application operations. However, the bait application techniques described 

30 would include mitigation measures that minimize unintentional bait drift into water bodies .To 

31 minimize unintentional bait drift into the water, we would use an internal deflector fit to the bait 

32 hopper to direct the bait flow away from the water body. Furthermore, a tarp would be secured 

33 over roof of the potable water catchment to prevent bait from entering the drinking water supply.

34 After each bait application, all pellets will be cleared from the tarp.

35

36 If bait were to unintentionally drift into a body of water at the full application rate, it would be 

37 very unlikely to contribute to detectable levels of brodifacoum in the water column. The low 

38 water solubility (U.S. Environmental Protection Agency 1998) and strong chemical affinity of 

39 brodifacoum to the grain matrix of the bait pellets prohibits the rodenticide from entering aquatic 

40 environments via runoff. Hypothetically, even if brodifacoum had greater water solubility, and 

41 bait was broadcast at the rate of 16 lb/ac (18 kg/ha) into water only 3.3 ft (1 m) deep, the 

42 resultant brodifacoum concentration in the water – about 0.04 parts per billion – would still be 

43 nearly 1000 times less than the measured LC50 value for trout (0.04 parts per million) (Syngenta 

44 Crop Protection Inc. 2003). Empson and Miskelly (1999) investigated the impacts on reef fish 

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 102

1 during a rat eradication on Kapiti Island, NZ. They found no evidence that reef fish were 

2 negatively affected. 

3

4 Environmental testing during rodent eradications and eradication trials in the California Current 

5 marine system and elsewhere have failed to detect brodifacoum in any water samples taken after 

6 bait application (Buckelew et al. 2008, Island Conservation unpubl. data). These studies, 

7 however, involve bait application rates that were several times lower than what is proposed for a

8 Palmyra application, and results may also differ.

9

10 Water supplies for personnel at Palmyra will be protected during bait application activities to 

11 prevent the entry of pellets into the water catchment. In summary, it is estimated that aerial 

12 application of brodifacoum bait pellets will result in a negligible risk to the marine water column 

13 or the drinking water supply.

14

15 Alternative C: Aerial Broadcast with Brodifacoum and Protective Bird Mitigation

16 It is likely that there will be accidental drift of some bait pellets into the nearshore marine waters 

17 surrounding Palmyra during aerial bait application operations. However, the bait application 

18 techniques described would include mitigation measures that minimize unintentional bait drift 

19 into water bodies. To minimize unintentional bait drift into the water, we would use an internal 

20 deflector fit to the bait hopper to direct the bait flow away from the water body. Furthermore, a 

21 tarp would be secured over roof of the potable water catchment to prevent bait from entering the 

22 drinking water supply. After each bait application, all pellets will be cleared from the tarp.

23

24 If bait were to unintentionally drift into a body of water at the full application rate, it would be 

25 very unlikely to contribute to detectable levels of brodifacoum in the water column. The low 

26 water solubility (U.S. Environmental Protection Agency 1998) and strong chemical affinity of 

27 brodifacoum to the grain matrix of the bait pellets prohibits the rodenticide from entering aquatic 

28 environments via run-off. Hypothetically, even if brodifacoum had greater water solubility, and 

29 bait was broadcast at the rate of 16 lb/ac (18 kg/ha) into water only 3.3 ft (1 m) deep, the 

30 resultant brodifacoum concentration in the water – about 0.04 parts per billion – would still be 

31 nearly 1000 times less than the measured LC50 value for trout (0.04 parts per million) (Syngenta 

32 Crop Protection Inc. 2003). Empson and Miskelly (1999) investigated the impacts on reef fish 

33 during a rat eradication on Kapiti Island, NZ. They found no evidence that reef fish were 

34 negatively affected. Environmental testing during rodent eradications and eradication trials in 

35 the California Current marine system and elsewhere have failed to detect brodifacoum in any 

36 water samples taken after bait application (Buckelew et al. 2008, Island Conservation unpubl. 

37 data). These studies, however, involve bait application rates that were several times lower than 

38 what is proposed for a Palmyra application, and results may also differ.

39

40 Water supplies for personnel at Palmyra will be protected during bait application activities to 

41 prevent the entry of pellets into the water catchment. In summary, it is estimated that aerial 

42 application of brodifacoum bait pellets will result in a negligible risk to the marine water column 

43 or the drinking water supply.

44

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 103

1 Alternative D: Bait Station Delivery of Brodifacoum

2 The use of bait stations will eliminate any threats to water quality by eliminating the potential for 

3 accidental delivery of bait into bodies of water. However, the use of bait stations would not 

4 preclude the risk of contaminating potable water stores with brodifacoum. Rats and terrestrial 

5 invertebrates would have ready access to bait via the bait stations for the entire duration of the 

6 operation. A rat or terrestrial invertebrate that recently fed on bait from a bait station could fall 

7 into and thus contaminate a potable water store. To prevent such contamination from happening, 

8 all potable water stores would be maintained as rodent and invertebrate free structures for the 

9 duration of the eradication operation.

10

11 4.3.2 Geology and Soils

12 4.3.2.1 Analysis framework for geology and soils

13 The major issues of concern for the geology and soil resources of Palmyra are: 1) permanent 

14 damage to carbonate rock formations, 2) increases in soil erosion, and 3) contamination of soils.

15

16 Alternative A: No Action

17 Under the Alternative A, the no action alternative, rats would remain on the atoll and would 

18 continue to disturb the soil layer by burrowing and scavenging for food resources. However, 

19 there are three land crab species that burrow in the soil, and it is assumed that rat burrowing 

20 activity would not cause more disturbances to the soil layer than does crab burrowing. Rats 

21 would not have a measurable effect on rock formations or contribute additional contamination to 

22 soils.

23

24 Alternative B: Aerial Broadcast with Brodifacoum

25 The activities in Alternative B would not have a noticeable effect on soil erosion, rock 

26 formations, or soil contamination. The installation and maintenance of bait stations in limited 

27 circumstances may cause highly localized, minor disturbance to soil and rock. If bait pellets were 

28 to remain in contact with soil for the maximum expected period of 7 days, the extremely low 

29 concentration of brodifacoum in the bait pellets (25 ppm) would not lead to major or lasting soil 

30 integration of brodifacoum into the soil (Alifano and Wegmann 2010) (Appendix F). In 

31 environmental monitoring after the brodifacoum-based rat eradication on Anacapa Island, all soil 

32 samples collected except one tested negative for brodifacoum residue (Howald et al. 2010). 

33

34 Alternative C: Aerial Broadcast with Brodifacoum and Protective Bird Mitigation

35 The activities in Alternative C would not have a noticeable effect on soil erosion, rock 

36 formations, or soil contamination. The installation and maintenance of bait stations in limited 

37 circumstances may cause highly localized, minor disturbance to soil and rock. If bait pellets were 

38 to remain in contact with soil for the maximum expected period of 7 days, the extremely low 

39 concentration of brodifacoum in the bait pellets (25 ppm) would not lead to major or lasting 

40 integration of brodifacoum into the soil (Alifano and Wegmann 2010) (Appendix F). In 

41 environmental monitoring after the brodifacoum-based rat eradication on Anacapa Island, all soil 

42 samples collected except one tested negative for brodifacoum residue (Howald et al. 2010). 

43

44 Alternative D: Bait Station Delivery of Brodifacoum

45 Each bait station would be secured to the ground with the use of metal or plastic anchors placed 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 104

1 into the soil or bedrock; stakes will have negligible long-term impacts to the soil and will be 

2 removed once the bait station operation is completed. The bait stations would be durable enough 

3 to stay in place for 2 years and prevent crabs from entering or destroying them, but they would 

4 be removed at the end of the treatment period and not a permanent fixture on the atoll. Because 

5 bait would be retained in bait stations, there would be little risk of brodifacoum integration into 

6 soil through direct contact between soil and bait pellets. 

7

8 4.4 Consequences: Biological Resources

9

10 4.4.1 Introduction

11 In order for this project to be considered a restoration success, the long-term benefits of rat 

12 eradication must outweigh any potential ecosystem costs associated with the implementation of 

13 the project. The eradication of rats is expected to have benefits for a number of animals and 

14 plants that are presently negatively affected by rats. However, it is also critical to identify the 

15 potential biological impacts of the actual eradication operation, including mortality and injury to 

16 nontarget species as a result of ingestion of rodenticide or disturbance from project operations. 

17 Furthermore, it is important to identify any biological resources that are currently dependent on 

18 nonnative rats in some way and may be negatively affected once rats are removed. This 

19 document‟s analysis of impacts to biological resources will identify both the benefits (positive 

20 effects) and the costs (negative effects) of rat eradication. 

21

22 While the impacts of each alternative can be analyzed with relative confidence over the short 

23 term, it is more difficult to accurately predict specific long-term responses to rat eradication. The 

24 overall determination of the ecosystem response to rat eradication at Palmyra includes too many 

25 variables to analyze within the scope of this document; however, data from other island rat 

26 eradications can be used to predict long-term ecosystem responses. Whenever possible, these 

27 data will be used in the analysis sections below to help determine long-term effects.

28

29 The No Action Alternative will be analyzed for the impacts to biological resources from the 

30 continued presence of rats at Palmyra. Additionally, analysis of the three action alternatives will 

31 include toxicant exposure pathways, toxicant risk, exposure risk, disturbance risk, and the extent 

32 of risk from either the toxicant or disturbance to biological resources. Finally, cumulative 

33 impacts will be analyzed by identifying all of the past, present, and future projects that will likely 

34 contribute to the overall effect of the action alternatives, and determine the extent of the impact 

35 to the biota at Palmyra from the combined effects of every identified project.

36

37 4.4.2 Assessing Significance of Impacts to Biological Resources

38 As described in Section 4.1, the concept of significance is shaped by both the context of an 

39 action and the intensity of the action‟s effects. Although we are assuming that this project will 

40 put individuals of a few nontarget species at risk, we will still use the significance value to 

41 determine which species are most at risk from the action alternatives. In the case of the action 

42 alternatives analyzed here, the actions have a very limited, site-specific context. However, many 

43 of the species that use Palmyra have large ranges or interact, at a population level, with other 

44 individuals that may be spread out over an area much larger than Palmyra. Therefore, the most 

45 appropriate context within which to consider impacts to biological resources is at the population 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 105

1 level rather than the individual level. The intensity of effects is dependent on a multitude of 

2 variables that are different for each taxon. This analysis will focus on additional legal protection 

3 (ESA listing and MMPA listing) as the primary defining criterion for determining the intensity of 

4 an effect to a species. In other words, impacts to species that have been assigned specific legal 

5 protection under the ESA or MMPA will be considered on an individual level and as “more 

6 intense” than similar impacts to unlisted species.

7

8 For all biological resources analyzed, except those identified in the “special considerations” 

9 sections below, the potential for significance will be determined using the following guidelines:

10 Is there a high likelihood that the population of a species will experience noticeable 

11 changes that will be measurable throughout its range?

12

13 Is there a high likelihood that impacts to species at Palmyra will be measurable elsewhere 

14 in the region?

15

16 4.4.2.1 Special significance considerations for Endangered Species Act (ESA)-listed species

17 There are five species that are likely to occur at or near Palmyra that are on the Federal 

18 Endangered Species list as a threatened, endangered, or a candidate species. Listed species 

19 include the threatened green turtle (Chelonia mydas), the endangered hawksbill turtle 

20 (Eretmochelys imbricata), the endangered Hawaiian monk seal (Monachus schauinslandi), and 

21 two species of concern: the bumphead parrotfish (Bolbometopon muricatum), and the humphead 

22 wrasse (Cheilinus undulates). The bumphead parrotfish has been designated a candidate species. 

23 Listing under ESA provides a context for impacts analysis which lowers the threshold of 

24 significance. This analysis will identify any ESA-listed species and any ESA-designated critical 

25 habitat that may be affected by the preferred alternative. The significance of these impacts will 

26 be determined separately, but the ESA-listed status of the species affected will be given special 

27 weight.

28

29 For green turtle, the significance threshold for effects will be set at an action that causes 

30 the significant potential for mortality of one or more individuals.

31

32 For hawksbill turtle, the significance threshold for effects will be set at an action that is 

33 likely to cause the mortality of one or more individuals.

34

35 For Hawaiian monk seal, significance threshold for effects will be set at an action that is 

36 likely to cause the mortality of one or more individuals.

37

38 For bumphead parrotfish, the significance threshold for effects will be set at an action 

39 that is likely to cause the mortality of one or more individuals.

40

41 For humphead wrasse, the significance threshold for effects will be set at an action that is 

42 likely to cause the mortality of one or more individuals.

43

44 The ESA regulations also oblige Federal agencies to ensure that the actions they take are not 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 106

1 likely to “jeopardize the continued existence of a listed species or result in the destruction or 

2 adverse modification of designated critical habitat” (ESA Section 7(a) 2 1973). If a Federal 

3 action is likely to adversely affect an ESA-listed species or its designated critical habitat, the 

4 action agency must initiate a formal process of consultation with either the FWS or National 

5 Marine Fisheries Service (NMFS) (depending on the species) to estimate the likely type and 

6 amount of take of the listed species and determine whether or not the action will put the affected 

7 species in jeopardy of extinction. If a non-jeopardy determination is made the action must 

8 include reasonable measures to avoid and minimize this take, which may then be authorized 

9 under section 7(a) (2) of the ESA. The Service will comply with all ESA requirements and 

10 conduct an informal Section 7 Consultation for any case deemed necessary by the FWS.

11

12 4.4.2.2 Special significance considerations for listed marine mammals under the Marine 

13 Mammal Protection Act (MMPA)

14 Listing under MMPA provides a context for impacts analysis that lowers the threshold of 

15 significance. The MMPA regulations generally prohibit the killing, injury, or disturbance of 

16 marine mammals, but permits can be granted allowing exceptions to this prohibition for actions 

17 that may affect a marine mammal if the affect is incidental rather than the intention of the action. 

18 This analysis will identify the potential for impacts to marine mammals that may require 

19 additional permits under MMPA.

20

21 The Marine Mammal Protection Act (MMPA) listed species that are found near or around 

22 Palmyra will be given special significance thresholds to minimize negative impacts to listed 

23 marine mammals. Therefore, the significance threshold for impacts to marine mammals will be 

24 set at an action that causes the mortality of an individual animal. The MMPA prohibits “take” of 

25 marine mammals, which is defined as “to harass, hunt, capture, or kill, or attempt to harass, 

26 hunt, capture, or kill any marine mammal” (16 U.S.C. 1362 Sec. 3(13)). Further, the term 

27 “harassment” is defined as “any act of pursuit, torment, or annoyance which – (i) has the 

28 potential to injure a marine mammal or marine mammal stock in the wild; or (ii) has the 

29 potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption 

30 of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, 

31 feeding, or sheltering” (16 U.S.C. 1362 Sec. 3(18)(A)). The acts described in the subparagraphs 

32 (A)(i) and (A)(ii) are also referred to as Level A and Level B harassment, respectively (16 U.S.C. 

33 1362 Sec. 3(18)(C) and Sec. 3(18)(D). Disturbance will not alone constitute a significant affect 

34 in this analysis, but other potential circumstances (including the analysis of cumulative impacts) 

35 may nevertheless contribute to an overall determination of significant impacts.

36

37  For the Hawaiian monk seal, the significance threshold will be set according to the 

38 MMPA‟s definition of Level A Harassment: “any act which injures or has the significant 

39 potential to injure a marine mammal or marine mammal stock in the wild” (MMPA 

40 515.18(A)).

41

42  For the false killer whale (Pseudorca crassidens), the significance threshold will be set 

43 according to the MMPA‟s definition of Level A Harassment: “any act which injures or has 

44 the significant potential to injure a marine mammal or marine mammal stock in the wild” 

45 (MMPA 515.18(A)).
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 107

1

2  For the short-finned pilot whale (Globicephala macrorhynchus), the significance threshold 

3 will be set according to the MMPA‟s definition of Level A Harassment: “any act which 

4 injures or has the significant potential to injure a marine mammal or marine mammal stock in 

5 the wild” (MMPA 515.18(A)).

6

7  For the spinner dolphin (Stenella longirostris), the significance threshold will be set 

8 according to the MMPA‟s definition of Level A Harassment: “any act which injures or has 

9 the significant potential to injure a marine mammal or marine mammal stock in the wild” 

10 (MMPA 515.18(A)).

11

12  For the bottlenose dolphin (Tursiops truncatus), the significance threshold will be set 

13 according to the MMPA‟s definition of Level A Harassment: “any act which injures or has 

14 the significant potential to injure a marine mammal or marine mammal stock in the wild” 

15 (MMPA 515.18(A)).

16

17  For the melon-headed whale (Peponocephala electra), the significance threshold will be 

18 set according to the MMPA‟s definition of Level A Harassment: “any act which injures or 

19 has the significant potential to injure a marine mammal or marine mammal stock in the wild” 

20 (MMPA 515.18(A)).

21

22  For the killer whale (Orcinus orca), the significance threshold will be set according to the 

23 MMPA‟s definition of Level A Harassment: “any act which injures or has the significant 

24 potential to injure a marine mammal or marine mammal stock in the wild” (MMPA 

25 515.18(A)).

26

27  For the tropical beaked whale (Mesoplodon hotaula), the significance threshold will be set 

28 according to the MMPA‟s definition of Level A Harassment: “any act which injures or has 

29 the significant potential to injure a marine mammal or marine mammal stock in the wild” 

30 (MMPA 515.18(A)).

31

32 4.4.2.3 Special significance considerations for birds listed under the Migratory Bird Treaty 

33 Act (MBTA)

34 Listing under the Migratory Bird Treaty Act (MBTA) provides a context for impacts analysis 

35 which lowers the threshold of significance for this analysis. Take under the MBTA includes the 

36 unlawful pursuit, hunt, take, capture, or kill, of any migratory bird, nest, or egg of any such bird. 

37 MBTA listed species that are found near or around Palmyra will be given special significance 

38 thresholds. All of the birds found at Palmyra Atoll are protected under the MBTA. Therefore, the 

39 significance threshold for impacts to birds will be set at an action that causes the mortality of an 

40 individual animal. 

41

42 Under certain circumstances where the goal is eradicating or controlling invasive species, the 

43 FWS will provide practitioners with a Special Purpose Permit under the MBTA that allows for 

44 the take of listed individuals for “projects where the applicant demonstrates expected benefits to 

45 migratory birds. These projects support the Service‟s bird conservation mandate and mission and 

46 are consistent with the Administration‟s emphasis on control of invasive species” (FWS 2010b). 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 108

1 The Service will comply fully with all MBTA requirements including obtaining a special 

2 purpose permit, prior to the implementation of any of the three action alternatives.

3

4 4.4.3 Impacts of Alternative A (No Action) on Biological Resources

5 4.4.3.1 Introduction

6 If no action is taken towards the removal of nonnative black rats from Palmyra, the impacts that 

7 rats have on the atoll‟s biological resources would continue. This section summarizes the known 

8 and suspected impacts from black rats on Palmyra‟s biological resources. 

9

10 The most pronounced effect of introduced rodents on atoll ecosystems is the extirpation and 

11 extinction of endemic species. Introduced rats (Rattus sp.) are responsible for an estimated 40-60 

12 percent of all bird and reptile extinctions (Atkinson 1985), Island Conservation analysis of World 

13 Conservation Monitoring Centre data), and have caused the extinction of endemic mammals, 

14 birds, and invertebrates on islands throughout the world‟s oceans (Andrews 1909, Daniel and 

15 Williams 1984, Meads et al. 1984, Atkinson 1985, Tomich 1986, Hutton et al. 2007).

16

17 Rat Impacts to Biological Resources

18 Impacts on terrestrial reptiles

19 Rats alter the floral component of the landscape, which directly affects the suitable habitat for 

20 reptiles. Additionally, rats are known to consume reptile eggs, insects, and other invertebrates 

21 that many reptiles rely on as a primary food source. Rats at Palmyra are thought to prey on native 

22 geckos, and overlap of rat and native gecko diets could limit food resources for native geckos. 

23 Additionally, rats are the obligate host of a parasitic nematode that is often found in geckos at 

24 Palmyra (Lafferty et al. 2010). The persistence of rats on the atoll will likely continue to have a 

25 negative effect on terrestrial reptile species.

26

27 Impacts on green turtles

28 While successful nesting attempts by green turtles have not been recorded at Palmyra, rats could 

29 have a negative impact on green turtle reproductive success if nesting attempts were successful 

30 (Caut et al. 2008). 

31

32 Impacts on hawksbill turtles

33 While successful nesting attempts by hawksbill turtles have not been recorded at Palmyra, rats 

34 could have a negative impact on hawksbill turtle reproductive success if nesting attempts were 

35 successful (Caut et al. 2008). 

36

37 Impacts on shorebirds

38 Rats often compete with shorebirds for food resources and may prey upon small-bodied species 

39 (Dowding and Murphy 2001). The following is a discussion of the impacts that rats likely have 

40 on the six most common shorebird species found at Palmyra.

41

42 bristle-thighed curlew

43 The bristle-thighed curlew‟s diet likely overlaps with the rat‟s diet in both the 

44 intertidal zone and forested habitat, which may result in resource competition. 

45 Curlews and rats both forage for invertebrates; however, we are uncertain if these 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 109

1 resources are limited and if there is true competition between curlews and rats. 

2 Additionally, predation by rats on curlews is possible (Marks et al. 2002) as curlews 

3 experience a period of flightlessness while molting, but there is no direct evidence of 

4 this occurring at Palmyra. 

5

6 Pacific golden-plover

7 The Pacific golden-plover‟s diet probably overlaps with that of rats; however, 

8 plovers are known to thrive in other locations where multiple mammalian predators 

9 are present. For example, plovers overwinter on the island of O`ahu, Hawai`i, where 

10 feral cats, rats, and mongooses are abundant.

11

12 ruddy turnstone and wandering tattler 

13 Ruddy turnstones and wandering tattlers may have dietary overlap with rats at 

14 Palmyra; however, the rat-related impacts to these species are thought to be minimal.

15

16 pectoral sandpiper

17 Pectoral sandpipers are rare at Palmyra, however, there is thought to be a slight dietary 

18 overlap with rats.

19

20 sanderling

21 Sanderlings are rare at Palmyra, however, there is thought to be a slight dietary 

22 overlap with rats. Additionally, sanderlings are small enough to be vulnerable to 

23 predation by rats, but there is no direct evidence of this occurring at Palmyra.

24

25 Impacts on breeding seabirds

26 Rats are known to prey on or cause disturbance to breeding seabirds, resulting in failed breeding 

27 attempts and higher susceptibility to predation by other species (Tomkins 1985, Jouventin et 

28 al. 2003). Smaller seabird species and species that nest on the ground and in burrows are also 

29 likely to suffer from predation by rats of eggs, chicks, and adults (Atkinson 1985, Towns et al. 

30 2006). Predation by rats often drives seabird colonies to near-extirpation (Moller 1983, 

31 Atkinson 1985, McChesney and Tershy 1998), resulting in the loss of seabird-derived 

32 nutrients on islands (Fukami et al. 2006). By reducing seabird populations, rats alter key 

33 ecosystem properties; for example, total soil carbon, nitrogen, phosphorous, mineral nitrogen, 

34 marine-derived nitrogen and pH are lower on rat-invaded islands relative to rat-free islands 

35 (Fukami et al. 2006). The following is a breakdown of the impacts that rats have on the 15 

36 seabird species found at Palmyra.

37

38 masked booby, brown booby, and red-footed booby

39 Rats are thought to have little impact on the three tropical booby species: masked, 

40 brown, and red-footed (Hilton and Cuthbert 2010).

41

42 lesser frigatebird and great frigatebird

43 There are no known impacts from rats to lesser or great frigatebirds.

44

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 110

1 red-tailed tropicbird 

2 Prior to the first rat eradication attempt in 2000, three thorough seabird surveys 

3 indicated that red-tailed tropicbird nesting was rare at Palmyra and primarily restricted 

4 to a single islet in the atoll that was likely too small to sustain a regular presence of 

5 rats (Fefer 1987, Clapp unpubl. data, Flint 1992). Nest numbers and distribution of 

6 red-tailed tropicbirds increased dramatically (from 14 nests in 1992 to 128 in 2002) 

7 immediately following the reduction in rat numbers in 2001. Predation by rats of red8 tailed tropicbird eggs could negatively affect the productivity of this species at 

9 Palmyra.

10

11 white-tailed tropicbird 

12 At Palmyra, white-tailed tropicbird nests are most often located in tree cavities and are 

13 difficult to observe, so little is known about the vulnerability of this species to 

14 predation by rats. However, it is likely that rat impacts on white-tailed tropicbirds are 

15 similar to rat impacts on red-tailed tropicbirds.

16

17 sooty tern 

18 Rats prey on sooty Tern eggs and chicks (Feare 1979), and sooty tern egg fragments 

19 are regularly observed in rat husking stations at Palmyra (Fefer 1987, FWS unpubl. 

20 data). Rats are regularly observed by FWS staff taking and eating sooty Tern eggs at 

21 Palmyra.

22

23 black noddy and brown noddy 

24 Rats likely prey on black and brown noddy eggs and chicks at Palmyra (Kepler 1967, 

25 Norman 1975); however there is no documentation of egg or chick predation at 

26 Palmyra.

27

28 white tern 

29 Rats likely prey on white tern eggs and chicks (Kepler 1967, Norman 1975); however, 

30 there is no documentation of egg or chick predation at Palmyra. 

31

32 Regionally present seabirds that are absent or uncommon at Palmyra

33 Rats have likely contributed to the extirpation of the following seabird species from 

34 Palmyra. These species fall into a category of seabirds that cannot coexist with 

35 introduced predators of the size of rats or larger (Flint 1999). While no historical or 

36 paleontological records exist for Palmyra itself there is evidence from studies of the 

37 faunal assemblages prior to the introduction of mammalian predators such as rats in 

38 Hawai`i, the Cook Islands, Easter Island, the Marquesas, Tonga, the Pitcairn Group, and 

39 the Northern Marianas that islands with introduced mammals, including rats, have lost 

40 large components of their original seabird fauna. The global patterns of seabird 

41 distributions we observe today are not natural (Steadman 1995). Jones et al. (2008)

42 found that rats depress many similar bird taxa and that rats are likely preventing them 

43 from nesting at Palmyra. The following is a list of seabird species that are found 

44 regionally, but are not breeding at Palmyra. All of the below listed species nest at 

45 adjacent islands in the Line archipelago that do not have rats or have rat-free refugia on 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 111

1 islets in the lagoon (Kiritimati Island). These species typically nest on the ground, and 

2 some (the shearwaters and petrels) characteristically leave eggs and chicks unattended 

3 in nesting burrows; black rats would effectively prevent the establishment, or 

4 reestablishment of breeding populations of any of these species (Norman 1975).

5

6 wedge-tailed shearwater (– unsuccessfully attempted to breed at Palmyra in 2005 

7 (Wegmann pers. comm.)

8 Bulwer's petrel (Bulweria bulwerii ) – sighted offshore

9 Christmas Island shearwater (Puffinus nativitatis) – sighted offshore

10 Audubon‟s shearwater (Puffinus lherminieri) – sighted offshore

11 Polynesian storm-petrel (Nesofregetta fuliginosa) – regional breeding species

12 Phoenix petrel (Pterodroma alba) – regional breeding species

13 gray-backed tern (Onychoprion lunatus) – sighted flying over Cooper Island in 

14 2005 (Wegmann pers. comm.)

15 blue noddy (Procelsterna cerulea) – a pair was sighted at Palmyra (on Barren 

16 Island) in 2010

17

18 Impacts on Uncommon Visitors

19 laughing Gull (Leucophaeus atricilla) and Franklin's gull (Leucophaeus pipixcan)

20 These gulls are rare visitors to Palmyra and do not breed there. There is no expected 

21 effect to these species of continued presence of rats at Palmyra.

22

23 Northern shoveler (Anas clypeata) and Northern pintail (Anas acuta)

24 Ducks are very rare visitors that do not breed at Palmyra and there are no known 

25 impacts from rats to adult ducks.

26

27 Impacts on fish

28 Rats are not known to affect fish species at Palmyra.

29

30 Impacts on invertebrates

31 Rats negatively affect the abundance and age structure of intertidal invertebrates through 

32 predation (Navarrete and Castilla 1993). Terrestrial crabs have been known to shift from 

33 nocturnal behavior to diurnal behavior in the presence of introduced rats, and with the removal of 

34 rats, crabs have been known to return to their nocturnal nature (Burggren and McMahon 1988). 

35 This shift in behavior is likely the result of competition for food and other resources between 

36 crabs and rats. Furthermore, rats have been documented preying on crabs at Palmyra, (Wegmann 

37 2009). Rats are not known to negatively affect coral species or other aquatic invertebrates. 

38 However, rats may be responsible for an increase in the mosquito population at Palmyra by 

39 creating an abundance of mosquito breeding habitat in water-filled coconut husks. Mosquitoes 

40 carry avian malaria, dengue, and other wildlife and human diseases. 

41

42 Rat impacts to vegetation

43 Introduced rats feed opportunistically on plants, and alter the floral communities of ecosystems 

44 in which they are introduced (Campbell and Atkinson 2002, Wegmann 2009). At Palmyra, rats 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 112

1 alter patterns of tree seedling recruitment by increasing the frequency of predation on tree seeds 

2 and seedlings, and by shifting tree seed dispersal from an interaction driven by land crabs to a 

3 directed dispersal model driven by rats; rats deposit seeds in microhabitats (husking stations) that 

4 are ill-suited for germination or subsequent growth. Furthermore, rats surpass crabs in the 

5 frequency of herbivore-seedling interactions, and rat impacts on seedling survival may be 

6 responsible for the structure of the atoll‟s current, alien species-dominated forest community 

7 (Wegmann 2009). 

8

9 4.4.4 Impacts of Action Alternatives (B, C, and D) on Biological Resources

10 4.4.4.1 Impacts to Biological Resources vulnerable to toxicant use

11

12 Analysis Framework for Impacts from Toxicant Use

13 The risk of impacts from brodifacoum or any other rodenticide to individual animals is 

14 determined by two factors (Erickson and Urban 2004):

15 The toxicity of the compound to that individual; and

16

17 The likelihood that exposure to the compound will result in harm to that individual.

18

19 The three action alternatives differ in both factors in terms of the individual animals‟ likelihood 

20 of exposure to the toxicant. 

21

22 Toxicity

23 Toxicity to birds and mammals – The toxicity of a particular compound to an individual animal is 

24 often expressed in a value known as the “LD50” – the dosage (D) of a toxicant that is lethal (L) to 

25 50 percent of animals in a laboratory test. The EPA has compiled laboratory data for 

26 brodifacoum LD50 values for a number of species. However, due to the difficulty and expense of 

27 obtaining extensive laboratory data, the LD50 values for many species, including most species at 

28 Palmyra, remain unknown for brodifacoum. Besides lethal toxicity, there are other physiological 

29 effects from ingestion of anticoagulants. Erickson and Urban (2004) report that individual birds 

30 and mammals that are exposed to anticoagulants and survive may nevertheless experience 

31 internal hemorrhaging, external bleeding, and other physical symptoms of anticoagulant toxicity.

32

33 The EPA has determined that the toxicity of brodifacoum to all birds, and mammals in general is 

34 high and only requires one dose to be lethal (Erickson and Urban 2004). Furthermore, animals 

35 that have a large body mass, such as pinnipeds or cetaceans, would generally need to ingest more 

36 of the compound in order to reach an LD50 threshold.

37

38 While the concentration of brodifacoum in bait pellets would be consistent, the number of bait 

39 pellets that individual animals would consume would vary considerably and unpredictably. 

40 Furthermore, predators and scavengers can also be exposed to a toxicant through secondary or 

41 tertiary pathways by consuming organisms that were previously exposed to the toxicant. It is 

42 difficult to predict the amount of toxicant that would be present in these prey animals, and 

43 difficult to predict how much a particular predator or scavenger would need to consume to reach 

44 a toxic threshold. 

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 113

1 In addition to the following quantitative assessment of the acute toxicity of brodifacoum to 

2 shorebirds that overwinter at Palmyra, risk to nontarget species will be estimated using the 

3 organism‟s risk of exposure. However, the large body mass of animals, such as cetaceans, would 

4 likely reduce the risk of toxic effects and will also be taken into account. 

5

6 Potential impacts to migratory shorebirds present at Palmyra during the operational window

7 Biology and Status

8 Four species of shorebirds are expected to be common at Palmyra during the operational window 

9 (June through July): bristle-thighed curlew, Pacific golden-plover, wandering tattler, and ruddy 

10 turnstone. None of these species nest at Palmyra. Populations at Palmyra have an annual range 

11 from 84 – 266 individuals for curlews, 75 – 144 for Pacific golden-plovers, 44 – 126 for 

12 wandering tattlers, and 39 – 112 for ruddy turnstones (Fefer 1987, Flint 1992, Depkin 2002, 

13 FWS 2010d). The population densities‟ of shorebirds at Palmyra (and on other tropical Pacific 

14 islands) are significantly lower during the summer breeding season - June through August 

15 (Engilis Jr. and Naughton 2004, FWS 2010d). The Risk Analyses for each alternative consider 

16 the populations present during the corresponding period of risk (ie. June-July for Alternatives B 

17 and C and over two years for Alternative D.)

18

19 Bristle-thighed curlews forage on intertidal and terrestrial invertebrates, Pacific golden-plovers 

20 feed on terrestrial insects and intertidal invertebrates, wandering tattlers feed on intertidal 

21 invertebrates and mollusks, and ruddy turnstones feed on marine invertebrates in the intertidal 

22 zone. Other shorebird species, all intertidal foragers, have been observed at Palmyra, but are not 

23 expected to be present in significant numbers during the operational window for Alternatives B 

24 and C, or during the highest activity period for Alternative D: sharp-tailed sandpiper, lesser 

25 yellowlegs, semipalmated plover, buff-breasted sandpiper, solitary sandpiper, pectoral sandpiper, 

26 and short-billed dowitcher.

27

28 Potential Brodifacoum Exposure Pathways for Palmyra Shorebirds

29 Bristle-thighed curlews, Pacific golden-plovers, wandering tattlers, and ruddy turnstones are 

30 likely to be present during the operational window at Palmyra and could potentially be exposed 

31 to the rodenticide through several pathways including: 

32 1. Feeding directly on bait pellets (Pierce et al. 2008)

33

34 2. Feeding on prey items that have consumed the bait and/or contaminated prey (e.g., 

35 land crabs, hermit crabs, rat carcasses)

36

37 This quantitative risk assessment evaluates the degree of the toxicological risk to shorebirds via 

38 primary and secondary pathways. Tertiary and further pathways of exposure are possible, and 

39 multiple, repeated exposures via the exposure pathways are possible, but will not be evaluated in 

40 this analysis here as the likelihood of mortality from either single feeding exposure event(s) will 

41 lead to measurable impacts due to the high toxicity of brodifacoum to birds. The toxicological 

42 risk is impossible to precisely and accurately quantify because of the lack of species-specific 

43 toxicity data for the shorebirds found at Palmyra. However, using data from surrogate bird 

44 species (mallard duck, one of the most sensitive species measured), and statistical probability, we 

45 can predict the rough toxicological risk to these four shorebird species from exposure to 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 114

1 rodenticide at Palmyra during and after the rat eradication. This analysis used data from the 

2 literature, and data collected during field trials at Palmyra in 2005 (Buckelew et al. 2005, USDA 

3 2006). A conservative approach to the secondary exposure risk assessment was taken, by using 

4 the mean and maximum brodifacoum residue values found in tissues, i.e., a worst case 

5 toxicological assessment. The likely impact or measurable endpoint of exposure is mortality 

6 because of the very high toxicity of brodifacoum to birds. 

7

8 This analysis quantifies the toxicological risk using the LD50 (Lethal Dose that will kill 50% of 

9 the sample population), LC50 (Lethal Concentration that will kill 50% of the sample population), 

10 and NOEL (No Observed Effects Level) data from other species which can be extrapolated to 

11 roughly predict the likely consequence of brodifacoum exposure to shorebirds at Palmyra. The 

12 NOEL is used here as a point of reference and demonstrates the level above which physiological 

13 effects of anticoagulant exposure has been measured in birds. 

14

15 Toxicological Risk from Direct Consumption of Bait Pellets Containing Brodifacoum 

16 (Primary, Nontarget Exposure)

17 Table 4.1 indicates that all shorebirds are at a high risk of primary poisoning through 

18 consumption of relatively few bait pellets. There is a high likelihood that shorebirds that identify 

19 bait pellets as a potential food source will find more than enough to exceed the LD50 within 4- 7 

20 days of each bait broadcast application, until land crabs, hermit crabs and rats remove bait pellets 

21 from the environment. It is expected that there will be some small areas of the island will have 

22 residual bait that may not be consumed by rats, land crabs, or other invertebrates within 7 days of 

23 the operation. In these areas, bait will likely degrade within 2 weeks due to molds, microbial 

24 action, and consumption by small invertebrates such as ants (Howald et al. 2004, Buckelew et al. 

25 2005), reducing the primary exposure risk. Bait will mold exceedingly rapidly in Palmyra‟s 

26 warm, humid environment. 

27

28 With the initial high availability of bait pellets after each broadcast event, mortality of individual 

29 birds will be the likely outcome of exposure. To minimize/reduce exposure potential to 

30 shorebirds, bait pellets will only be broadcast into Palmyra‟s vegetated environment, and 

31 directional baiting will be used to prevent bait drift into the intertidal and nearshore marine 

32 environment where many shorebirds show preferential, but not exclusive, foraging. Further, the 

33 color of the bait (blue), and timing of the operation (during the breeding season when the least 

34 number of shorebirds are present at Palmyra) would reduce (but not eliminate) the risk of 

35 primary exposure to the populations. For shorebirds present at Palmyra during the operational 

36 window, the risk of primary poisoning is very high.

37

38 The bumphead parrotfish, Bolbometopon muricatum, has been designated as a candidate 

39 species under ESA. Bumphead parrotfish are the largest of the parrotfish attaining 120cm in 

40 length, are in decline throughout most of their geographic range, but are abundant at Palmyra. 

41 The fish are found on the terrace and fore reefs outside the atoll where coral is abundant, and

42 they are not found on the lagoon flats. No bait is expected to reach terrace or forereef areas. If 

43 bait accidentally reached these areas, it is unlikely the fish would be exposed to it, as the 

44 bumphead parrotfish is a benthic corallivore, feeding solely on corals. The bumphead parrotfish 

45 should not be at risk of primary or secondary exposure to the toxicant.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 115

1 Potential Impacts from Indirect Ingestion of Brodifacoum through Prey Items 

2 (Secondary Nontarget Exposure)

3

4 Hermit and land crabs 

5 Wegmann et al. (2008) confirmed that both land crabs and hermit crabs will be attracted to and 

6 consume bait that is broadcast into Palmyra‟s terrestrial environment. The crabs will compete 

7 directly with rats to gain access to bait pellets, thus to maximize the probability of eradication of 

8 rats, enough bait has to be broadcast to account for both rat and crab consumption. The 

9 consumption of bait pellets, and primarily poisoned rats and potentially birds, by hermit and land 

10 crabs will result in accumulation of brodifacoum residue in the tissues of crabs. For the purpose 

11 of this analysis, we used the residue levels from the hepatopancreas of land crabs of the genus 

12 Cardisoma (a worst case scenario) and brodifacoum body burden in hermit crabs of the genus 

13 Coenobita (Table 4.1). The data indicate that the residue levels in the crabs decline rapidly to 

14 near non-detectable levels within 2 months of the broadcast which suggests that the 

15 accumulation of residues is a function of contaminated prey items, and either retention time 

16 and/or metabolism of the rodenticide is quick. For the purpose of this analysis, the mean and 

17 maximum detected residues in hepatopancreas and hermit crab body burden were used to 

18 evaluate toxicological risk. We translated this risk into equivalent numbers of crabs needed to 

19 cause a high likelihood of poisoning.

20

21 The data (Table 4.1) indicates that crabs will accumulate enough brodifacoum residues to present 

22 a high secondary exposure risk within 10 days of the bait broadcast through single and repeated 

23 exposures. Relatively few crabs will need to be consumed to reach an LD50, less than one crab 

24 hepatopancreas or hermit crab will exceed the NOEL, and a physiological response will be 

25 theoretically measurable. However, because of the high toxicity of brodifacoum to birds, and the 

26 possibility of repeated exposure via hermit crabs, and possibly land crabs, this analysis concludes 

27 that the shorebirds that are present at Palmyra within 10 days of the broadcast application, and 

28 are attracted to and consume either land crabs or hermit crabs, are at a very high risk of 

29 secondary poisoning, with a high likelihood of mortality. The risk of exposure and poisoning to 

30 shorebirds returning to Palmyra at, and after 2 months of the broadcast application are at risk of 

31 exposure to a low level of brodifacoum residue, and are at a relatively low risk of secondary 

32 poisoning via consumption of hermit and land crabs. 

33

34 Filter feeders (mussels)

35 Shorebirds at Palmyra are not likely at risk of exposure to brodifacoum via mussels or other filter 

36 feeders because of the mitigation measures to prevent the broadcast of the bait into the marine 

37 environment (directional baiting), the insolubility of brodifacoum, and the low availability of 

38 mussels and filter feeders as prey items relative to the high abundance of fiddler crabs, land crabs 

39 and hermit crabs that may be preferred prey items for some shorebirds at Palmyra. However, as a 

40 conservative approach, this analysis evaluated the potential toxicological risk using data from the 

41 literature for mussel tissue (Table 4.1). 

42

43 Table 4.1 indicates that there is a theoretical secondary poisoning risk if enough mussel tissue (or 

44 tissue from comparable filter feeders) is consumed by individual shorebirds. However, because 

45 of the reasons outlined above, the relatively low availability of mussel (or other filter feeders) at 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 116

1 Palmyra, and the high abundance of alternative prey (crabs), the consequence of this exposure 

2 pathway is believed to be relatively low for shorebirds. 

3

4 Fish liver

5 The shorebirds at Palmyra are not known to prey on fish, but could be exposed to brodifacoum 

6 via fish if any fish were to consume a lethal dose from errant bait pellets, and subsequently wash 

7 up on shore for shorebirds to scavenge. While some fish in the nearshore environment at Palmyra 

8 are known to consume bait pellets (see Appendix F), the likelihood of this exposure pathway is 

9 very small as precautions are in place to minimize risk of bait drift into the marine environment, 

10 and minimizes this exposure pathway.

11

12 Should inadvertent bait pellets drift into the marine environment, and fish consume the bait 

13 pellets, and any dead or dying fish wash up on shore, shorebirds may be exposed to brodifacoum 

14 via a fish liver pathway. The data from the risk assessment (Table 4.1) suggest that a significant 

15 amount of fish liver tissue would need to be consumed to reach an LD50/LC50. However, while 

16 theoretically possible, the amount of liver to be consumed is greater than what could be 

17 realistically consumed during a single feeding). This analysis concludes that the risk to 

18 shorebirds via this pathway is very low.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 117

1 Table 4.1 Acute toxicity of brodifacoum to shorebirds and seabirds at Palmyra Atoll. 

Species

Estimated # of grams of pellets consumed Estimated # of pellets consumed Estimated grams of mussels consumed Estimated grams of fish liver consumed

LD50

LD50

probabilistic 

(0.11mg/kg)*

LD50

probabilistic 

(0.56mg/kg)* LC50

NOE

L LD50

LD50

probabilistic 

(0.11mg/kg)*

LD50

probabilistic 

(0.56mg/kg)* LC50 NOEL LD50

LD50

probabilistic 

(0.11mg/kg)*

LD50

probabilistic 

(0.56mg/kg)* LC50 NOEL LD50

LD50

probabilistic 

(0.11mg/kg)*

LD50

probabilistic 

(0.56mg/kg)* LC50

NOE

L

Bristlethighed 

curlew 5.1 2.2 11.0 14.1 0.0 2.5 1.1 5.5 7.1 0.0 310.7 131.5 669.3 860.5 1.2 3185.0 1347.5 6860.0

8820.

0 12.3

Pacific 

goldenplover 1.4 0.6 2.9 3.7 0.0 0.7 0.3 1.5 1.9 0.0 82.4 34.9 177.6 228.3 0.3 845.0 357.5 1820.02340.

0 3.3

Wandering 

tattler & 

ruddy 

turnstone 1.1 0.5 2.5 3.2 0.0 0.6 0.2 1.2 1.6 0.0 69.8 29.5 150.2 193.2 0.3 715.0 302.5 1540.0

1980.

0 2.8

Masked 

Booby 16.9 7.1 36.4 46.7 0.1 8.4 3.6 18.2 23.4 0.0

Red-footed 

Booby 8.9 3.8 19.2 24.7 0.0 4.5 1.9 9.6 12.3 0.0

Brown 

Booby 11.0 4.7 23.7 30.5 0.0 5.5 2.3 11.9 15.3 0.0

Red-footed 

Booby 8.9 3.8 19.2 24.7 0.0 4.5 1.9 9.6 12.3 0.0

Great 

Frigatebird 9.6 4.1 20.7 26.6 0.0 4.8 2.0 10.3 13.3 0.0

Lesser 

Frigatebird 7.8 3.3 16.8 21.6 0.0 3.9 1.7 8.4 10.8 0.0

Red-tailed 

Tropicbird 7.1 3.0 15.3 19.7 0.0 3.6 1.5 7.7 9.9 0.0

White-tailed 

Tropicbird 3.0 1.3 6.5 8.3 0.0 1.5 0.6 3.2 4.1 0.0

Brown 

Noddy 1.8 0.8 3.9 5.0 0.0 0.9 0.4 1.9 2.5 0.0

Black 

Noddy 0.9 0.4 2.0 2.6 0.0 0.5 0.2 1.0 1.3 0.0

Sooty Tern 2.2 0.9 4.7 6.0 0.0 1.1 0.5 2.3 3.0 0.0

White Tern 1.1 0.4 2.3 2.9 0.0 0.5 0.2 1.1 1.5 0.0

*Acute probabilistic LD50 for 95% of bird species with unknown sensitivity to brodifacoum: 0.11mg/kg (95% confidence) and 0.56mg/kg (50% confidence). From 

Howald et. al (1999).

**Crab hepatopancreas sampling on Day 10 included one outlying value of 1.19 mg/kg brodifacoum, which explains the lower LD50 for day 10 compared to Day 6.

***Based on average crab weight from 2005 Cardisoma tissue brodifacoum residue analyses data (USDA 2006).

 Average strawberry hermit crab weight was estimated at ~85 grams (range: 56-140g based on non-published 'internet' data)

†Day 56 for hermit crab tissue analyses only had one sample with Brodifacoum levels above MLOD
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 118

Table 4.1 (Continued: Acute toxicity of brodifacoum to shorebirds summering at Palmyra Atoll).

Species 

& 

Samplin

g Day

Using MEAN brodifacoum ppm reported in tissue analysis

Estimated grams of hepatopancreas consumed Estimated # of crabs consumed** * Estimated grams of hermit crab consumed Estimated # of hermit crabs consumed****

LD50

LD50

probabilistic 

(0.11mg/kg)*

LD50

probabilistic 

(0.56mg/kg)* LC50

NOE

L LD50

LD50

probabilistic 

(0.11mg/kg)*

LD50

probabilistic 

(0.56mg/kg)* LC50

NOE

L LD50

LD50

probabilistic 

(0.11mg/kg)*

LD50

probabilistic 

(0.56mg/kg)* LC50

NOE

L LD50

LD50

probabilistic 

(0.11mg/kg)*

LD50

probabilistic 

(0.56mg/kg)* LC50

NO

EL

Curlew

Sampling 

day 2 76.7 32.4 165.1 212.3 0.3 3.7 1.6 8.0 10.3 0.0 245.8 104.0 529.3 680.6 0.9 2.9 1.2 6.2 33.0 0.0

Sampling 

day 6 475.6 201.2 1024.3 1317.0 1.8 23.0 9.7 49.6 63.8 0.9 390.7 165.3 841.4 1081.8 1.5 4.6 1.9 9.9 52.4 0.1

Sampling 

day 10** 432.7 183.1 931.9 1198.2 1.7 21.0 8.9 45.1 58.0 0.1 964.9 408.2 2078.2 2671.9 3.7 11.4 4.8 24.4 129.4 0.2

Sampling 

day 56 12536.3 5303.8 27001.2

34715.

9 48.2 607.1 256.8 1307.6 1681.2 2.3 29627.9† 12534.9† 63814† 82046.5† 114.0 348.6† 147.5† 750.8† 3973.2†

5.5

†

Pacific golden-plover

Sampling 

day 2 20.3 8.6 43.8 56.3 0.1 1.0 0.4 2.1 2.7 0.0 65.2 27.6 140.4 180.6 0.3 3.2 1.3 6.8 8.7 0.0

Sampling 

day 6 126.2 53.4 271.8 349.4 0.5 6.1 2.6 13.2 16.9 0.0 103.6 43.8 223.2 287.0 0.4 5.0 2.1 10.8 13.9 0.0

Sampling 

day 10** 114.8 48.6 247.2 319.9 0.4 5.6 2.4 12.0 15.4 0.0 256.0 108.3 551.3 708.9 1.0 12.4 5.2 26.7 34.3 0.0

Sampling 

day 56 3326.0 1407.1 7163.6 9210.3 12.8 161.0 68.1 346.9 446.0 0.6 7860.5† 3325.6† 16930.2† 21767.4† 30.2† 380.7† 161.1† 819.9† 1054.1†

1.5

†

Wandering tattler & ruddy turnstone

Tattler & Ruddy Turnstone

Sampling 

day 2 17.2 7.3 37.1 47.7 0.1 0.8 0.4 1.8 2.3 0.0 55.2 23.3 118.8 152.8 0.2 2.7 1.1 5.8 7.4 0.0

Sampling 

day 6 106.8 45.2 230.0 295.7 0.4 5.2 2.2 11.1 14.3 0.0 87.7 37.1 188.9 242.9 0.3 4.2 1.8 9.1 11.8 0.0

Sampling 

day 10** 97.1 41.1 209.2 269.0 0.4 4.7 2.0 10.1 13.0 0.0 216.6 91.6 466.5 599.8 0.8 10.5 4.4 22.6 29.0 0.0

Sampling 

day 56 2814.3 1190.7 6061.5 7793.4 10.8 136.3 57.7 293.5 377.4 0.5 6651.2† 2814† 14325.6† 18418.6† 25.6† 322.1† 136.3† 693.7† 891.9†

1.2

†

1 *Acute probabilistic LD50 for 95% of bird species with unknown sensitivity to brodifacoum: 0.11mg/kg (95% confidence) and 0.56mg/kg (50% confidence). From Howald et. al (1999).

2 **Crab hepatopancreas sampling on Day 10 included one outlying value of 1.19 mg/kg brodifacoum, which explains the lower LD50 for day 10 compared to Day 6.

3 ***Based on average crab weight from 2005 Cardisoma tissue brodifacoum residue analyses data (USDA 2006).

4  Average strawberry hermit crab weight was estimated at ~85 grams (range: 56-140g based on non-published 'internet' data)

5 †Day 56 for hermit crab tissue analyses only had one sample with Brodifacoum levels above MLOD

6

7

8

9

10

11

12

13

14
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 119

1

2

3 Table 4.1 (Continued: Acute toxicity of brodifacoum to shorebirds summering at Palmyra Atoll). 

Species & 

Sampling 

Day

Using MAX brodifacoum ppm reported in tissue analyses

Estimated grams of crab hepatopancreas 

consumed Estimated # of crabs consumed** * Estimated grams of hermit crab consumed Estimated# of hermit crabs consumed**** 

LD50

LD50

probabilistic 

(0.11mg/kg)

*

LD50

probabilistic 

(0.56mg/kg)

* LC50 NOEL LD50

LD50

probabilistic 

(0.11mg/kg)

*

LD50

probabilistic 

(0.56mg/kg)

* LC50 NOEL LD50

LD50

probabilistic 

(0.11mg/kg)

*

LD50

probabilistic 

(0.56mg/kg)

* LC50

NOE

L LD50

LD50

probabilistic 

(0.11mg/kg)

*

LD50

probabilistic 

(0.56mg/kg)

* LC50 NOEL

Curlew

Sampling day 2 33.4 14.1 71.8 92.4 0.1 1.6 0.7 3.5 4.5 0.0 158.9 67.2 342.1 439.9 0.6 1.9 0.8 4.0 21.3 0.0

Sampling day 6 75.8 32.1 163.3 210.0 0.3 3.7 1.6 7.9 10.2 0.0 229.1 96.9 493.5 634.5 0.9 2.7 1.1 5.8 30.7 0.0

Sampling day 

10** 107.1 45.3 230.6 296.5 0.4 5.2 2.2 11.2 14.4 0.0 315.3 133.4 679.2 873.3 1.2 3.7 1.6 8.0 42.3 0.1

Sampling day 

56

5137.

1 2173.4 11064.5

14225.

8 19.8

248.

8 105.2 535.8

688.

9 1.0

29627

.9† 12534.9† 63814†

82046.5

† 114.0

348.6

† 147.5† 750.8†

3973.2

† 5.5†

Pacific golden-plover

Sampling day 2 8.8 3.7 19.1 24.5 0.0 0.4 0.2 0.9 1.2 0.0 42.1 17.8 90.8 116.7 0.2 2.0 0.9 4.4 5.7 0.0

Sampling day 6 20.1 8.5 43.3 55.7 0.1 1.0 0.4 2.1 2.7 0.0 60.8 25.7 130.9 168.3 0.2 2.9 1.3 6.3 8.2 0.0

Sampling day 

10** 28.4 12.0 61.2 78.7 0.1 1.4 0.6 3.0 3.8 0.0 83.7 35.4 180.2 231.7 0.3 4.1 1.7 8.7 11.2 0.0

Sampling day 

56

1362.

9 576.6 2935.5 3774.2 5.2 66.0 27.9 142.2

182.

8 0.3

7860.

5† 3325.6† 16930.2†

21767.4

† 30.2†

380.7

† 161.1† 819.9†

1054.1

† 1.5†

Wandering tattler & ruddy 

Turnstone

Sampling day 2 7.5 3.2 16.1 20.7 0.0 0.4 0.2 0.8 1.0 0.0 35.7 15.1 76.8 98.8 0.1 1.7 0.7 3.7 4.8 0.0

Sampling day 6 17.0 7.2 36.7 47.1 0.1 0.8 0.3 1.8 2.3 0.0 51.4 21.8 110.8 142.4 0.2 2.5 1.1 5.4 6.9 0.0

Sampling day 

10** 24.0 10.2 51.8 66.6 0.1 1.2 0.5 2.5 3.2 0.0 70.8 30.0 152.5 196.0 0.3 3.4 1.5 7.4 9.5 0.0

Sampling day 

56

1153.

2 487.9 2483.9 3193.5 4.4 55.8 23.6 120.3

154.

7 0.2

6651.

2† 2814† 14325.6†

18418.6

† 25.6†

322.1

† 136.3† 693.7† 891.9† 1.2†

4 *Acute probabilistic LD50 for 95% of bird species with unknown sensitivity to brodifacoum: 0.11mg/kg (95% confidence) and 0.56mg/kg (50% confidence). From Howald et. al (1999).

5 **Crab hepatopancreas sampling on Day 10 included one outlying value of 1.19 mg/kg brodifacoum, which explains the lower LD50 for day 10 compared to Day 6.

6 ***Based on average crab weight from 2005 Cardisoma tissue brodifacoum residue analyses data (USDA 2006).

7  Average strawberry hermit crab weight was estimated at ~85 grams (range: 56-140g based on non-published 'internet' data)

8 †Day 56 for hermit crab tissue analyses only had one sample with Brodifacoum levels above MLOD

9

10

11
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 120

1 Bristle-thighed curlew rodenticide risk: from Chris Gill‟s 2010 Summary of Risks and 

2 Potential Mitigation Options for Bristle-thighed curlews at Palmyra Atoll during a Rat 

3 Eradiation Campaign (See Appendix H for full report):

4 During the upcoming rat eradication, bristle-thighed curlews (BTCU) are expected to be at the 

5 greatest risk of mortality from rodenticide exposure at Palmyra Atoll. BTCUs are at risk of 

6 primary and secondary exposure to the rodenticide contained in the bait that will be deployed to 

7 eradicate rats from Palmyra. In May, breeding BTCUs depart their wintering grounds (such as 

8 Palmyra) for summer breeding grounds in Alaska. This migratory behavior creates a seasonal 

9 low in Palmyra‟s BTCU population. The proposed rat eradication action will take advantage of 

10 this seasonal low to minimize the risk of harming individual BTCUs.

11

12 BTCUs have a fairly small global population with approximately 3,200 breeding pairs and about 

13 10,000 individuals (Marrison et al. 2006). Researchers also believe that BTCU numbers are 

14 slowly declining with an estimated population growth rate (λ) of 0.994 (appendix H). 

15 Furthermore, BTCUs winter on remote Pacific Islands, which are continually affected from 

16 anthropogenic activities and mammalian predators that disturb wintering grounds and consume 

17 ground-nesting seabird eggs that are a major source of nutrition for BTCUs in preparation for 

18 spring migration. Moreover, approximately 50 percent of the adult BTCU population becomes 

19 flightless for an estimated 92 days during a prebasic molt period that is typically between August 

20 and December. Researchers believe that “disturbance or mortalities on the wintering grounds 

21 could have a significant effect on the total (BTCU) population size” (Gill 2010). Fortunately, the 

22 maximum estimated number of individuals that would likely remain at Palmyra through the 

23 summer breeding season is 182 (based on 2010 all-atoll count data, USFWS unpublished data), 

24 which is less than two percent of the entire BTCU global population. 

25

26 By using a population size of 10,000, modelers were able to calculate the deterministic 

27 population growth rate for the BTCU with a potential mortality rate of 80 percent for the 

28 Palmyra population during the time of the rat eradication. Model outputs indicated that impacts 

29 to the global BTCU population would only result in minor decreases in the population growth 

30 rate with diminishing impacts on the projected future population. Furthermore, with the current 

31 parameter estimates, “there is no risk of extinction over the next 50 years under any scenario” 

32 (Gill 2010). 

33

34 Researchers believe that the benefits of rat eradication at Palmyra outweigh the potential, small 

35 affect to the global BTCU population. “Removal of rats from Palmyra would have a positive 

36 effect on the population” since it is believed that BTCUs are being negatively affected by 

37 introduced mammalian predators, including rats, on their wintering grounds (Marks et al. 2002,

38 (Gill 2010). “Other researchers have suggested that the high density of introduced rats preying

39 on eggs and nestlings greatly reduces nest success and fledging rates of sooty terns at Palmyra; 

40 therefore, removing rats from the Atoll may also indirectly benefit BTCUs by increasing the 

41 breeding population of sooty terns, and thus egg production at Palmyra” (Gill 2010). 

42

43

44

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 121

1 Potential Impacts to Breeding Seabirds Present at Palmyra during the Operational Window

2 Biology and Status

3 Ten species of seabirds breed at Palmyra: black and brown noddies, sooty and white terns, great 

4 frigatebirds, white- and red-tailed tropicbirds, and red-footed, masked and brown boobies. One 

5 additional species (lesser frigatebird) is present, but does not breed. These equatorial nesting 

6 seabirds can nest during any season and there is high inter-annual variability in the number of 

7 birds present and nesting during any given month. Seabirds are abundant at Palmyra year8 round. All 11 species, with the possible exception of sooty terns, are expected to be common at 

9 Palmyra during the operational window (June-July). 

10

11 All of these seabirds forage in the marine environment and their diets are predominantly marine 

12 fish and invertebrates. A small number of birds forage within the lagoon at Palmyra but the 

13 overwhelming majority forage away from the atoll in the pelagic ocean environment.

14

15 Potential Brodifacoum Exposure Pathways for Palmyra Seabirds

16 Given their diet and foraging habits, it is extremely unlikely that any of the breeding seabirds 

17 will ingest contaminated prey or deliberately ingest bait pellets. However, it is possible that 

18 birds could accidentally ingest toxicant during nest maintenance or preening. Great and lesser 

19 frigatebirds are known to prey opportunistically upon small chicks of other seabird species at the 

20 colony. This is an insignificant component of their diet, and these two frigatebird species are the 

21 only breeding seabird on Palmyra known to derive any food items from the terrestrial 

22 environment. We do not anticipate that small seabird chicks will ingest any bait pellets, but the 

23 remote possibility exists that either of the frigatebird species would consume a small shorebird 

24 (e.g., a ruddy turnstone) that is contaminated (and therefore its ability to evade predators 

25 compromised). 

26

27 Toxicological Risk from Direct Consumption of Bait Pellets Containing Brodifacoum 

28 (Primary, Nontarget Exposure)

29 Even though the risk of ingestion is extremely low, Table 4.1 indicates that, ingestion of 

30 relatively few bait pellets poses a high risk of primary poisoning for all but the largest seabirds. 

31 To minimize/reduce exposure potential to seabirds, bait pellets will be hand broadcast along the 

32 causeways where the majority of the boobies nest, and this bait will not be distributed within 

33 reach of birds sitting in the nest. 

34

35 Potential Impacts from Indirect Ingestion of Brodifacoum through Prey Items 

36 (Secondary Nontarget Exposure)

37 Most seabirds will be foraging for fish and invertebrates at sea, away from the atoll. A few birds 

38 might forage within the lagoon. The potential for fish to be exposed will be minimized by hand 

39 baiting hear the shoreline and using an internal deflector system in the bait hopper to prevent 

40 bait from being broadcast in the water.; thus, it is unlikely that measurable amounts of 

41 brodifacoum will be incorporated into the lagoon food chain and then indirectly affect foraging 

42 seabirds. 

43

44 Frigatebirds could possibly become secondarily poisoned by consuming a compromised and 

45 contaminated shorebird, but this is unlikely.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 122

1 Toxicity to reptiles and amphibians

2 Little is known about the effect that brodifacoum has on turtles. Rodenticide toxicity experiments 

3 have not been conducted in turtle species and therefore the LD50 values are unknown for both 

4 species of turtle present in the waters surrounding Palmyra. However, an initial assessment from 

5 preliminary findings of a USDA National Wildlife Research Center (NWRC) turtle-anticoagulant 

6 hazards study indicates ornate wood turtles (Rhinoclemmys pulcherrima) were not negatively 

7 affected by brodifacoum consumption. Turtles that were fed high brodifacoum doses received 1.6 

8 mg/kg of brodifacoum, and none died or showed signs of ill health when euthanized one week 

9 later. The turtle with the highest liver residue level (2.02 ppm) weighed 319 g, which means that 

10 it received about 0.5 mg (500 ppm) of brodifacoum. Since a Brodifacoum-25W pellet contains 25 

11 ppm, the turtle essentially received the equivalent of 20 pellets (G. Witmer APHIS USDA, pers. 

12 comm). Adult green turtles weigh on average 325 lbs. (147 kg) (NOAA Fisheries Service 2011a), 

13 thus, using similar metrics, one adult green turtle would have to consume approximately 9,200 

14 pellets or 40.5 lbs. (18.4kg) of pellets to receive a comparable exposure to that the ornate wood 

15 turtle received (which did not cause death or signs of ill health). Adult hawksbill turtles weigh on 

16 average 125 lbs. (57kg) (NOAA Fisheries Service 2011b), thus one turtle would have to consume 

17 approximately 3,500 pellets or 15.4 lbs. (7.0kg) of pellets to receive a comparable exposure to 

18 that the ornate wood turtle received.

19

20 No published studies have been identified on the laboratory testing of anticoagulants to reptiles. 

21 Major references listing the LD50 values for anticoagulants (Timm 1994, Tasheva 1995) do not 

22 list any values for reptiles. Brooks et al. (1998) found that warfarin (a first generation 

23 coagulant) was lethal to brown tree snakes (Boiga irregularis) when orally administered in 

24 ethanol (but not propylene glycol) at 40 mg/kg, but elicited no signs of discomfort or internal 

25 hemorrhaging upon necropsy. In the same study, diphacinone delivered orally to brown tree 

26 snakes was consistently lethal at dosages of 40 – 80 mg/kg, but snakes displayed no apparent 

27 clinical signs prior to death or evidence of internal hemorrhaging upon necropsy. Gopher snakes 

28 (Pituophis catenifer) fed with mice poisoned with lethal quantities of the anticoagulants Prolin® 

29 (0.05% warfarin, 0.05 % sulfaquinoxaline), Diphacin®, and warfarin showed no observable 

30 behavioral or physiological reaction (Brock 1965). Snakes fed brodifacoum-killed house mice 

31 (R. Marsh pers. comm.), and lizards (Uta sp.) force-fed 50 ppm brodifacoum (Tershy et al. 1992, 

32 Tershy unpubl. data) survived for at least several weeks. 

33

34 Similarly, no published studies are found on the toxicity of brodifacoum to reptiles. Brodifacoum 

35 inhibits vitamin K dependent pathways in mammals and birds. Because reptiles are 

36 poikilothermic (cold-blooded), their blood chemistry and physiology is different from that of 

37 mammals and birds (homoeothermic or warm-blooded animals) (Merton 1987), and blood 

38 coagulation mechanisms in reptiles are slower than those of mammals (Frost et al. 1999, 

39 Kubalek et al. 2002). Reptiles have an active extrinsic clotting pathway (Spurling 1981) but, for 

40 example in spectacled caimans (Caiman crocodilus) several factors (Factors V, VIII, IX, and XI, 

41 and possibly XII) in the Vitamin K dependent (intrinsic) clotting pathway are missing in the 

42 blood (Arocha-Pinango et al. 1982). In the puff adder (Bitis arietans), other clotting activation 

43 factors, such as prothrombin, α2-antiplasmin (fibrinogen system) and kallikrein (kallikrein 

44 system) have significantly reduced activity when compared with humans (Frost et al. 1999).

45 Bait consumption has been recorded in several reptile species in the wild where no evidence of 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 123

1 mortality was found. There are reports of larger skinks consuming baits containing brodifacoum 

2 during island rat and rabbit eradication efforts in the Seychelles, however, no observed mortality 

3 was detected (Wright‟s skinks Mabuya wrightii (Thorsen et al. 2000), Seychelles skinks 

4 Trachylepis seychellensis (Merton et al. 2002)). In brodifacoum baiting operations on two South 

5 Pacific islands two species, Duvaucel‟s gecko (Hoplodactylus duvaucelii) (Christmas 1995) and 

6 common gecko H. maculatus (Hoare and Hare 2006b), showed some evidence of having 

7 consumed brodifacoum baits in bait boxes. Wedding (2007) tracked visitation rates of shore 

8 skinks (Oligosoma smithi) to brodifacoum bait stations in Tawharanui, New Zealand and found 

9 rates reached 81 percent. One skink was observed consuming bait directly; of the 802 skinks 

10 captured in brodifacoum controlled areas, none showed clinical or behavioral signs of ill health 

11 (Wedding 2007). 

12

13 In a laboratory, McCann‟s skinks (Oligosoma maccanni) were offered two types of cereal-based 

14 bait with no alternative food. Skinks preferred dry pindone bait (a first-generation 

15 anticoagulant) to dry non-toxic RS5 bait (which is commonly infused with sodium 

16 monofluoroacetate (1080)). When bait was offered wet, both bait palatability increased and was 

17 similar. Both baits offered were infused with a green dye (Bayer V200) and the dye was detected 

18 in fecal pellets in 55 percent of skinks fed RS5 and in 97 percent of skinks fed pindone. However, 

19 relatively little bait was consumed over the 2-day trials (mean pindone = 0.020g; mean RS5 = 

20 0.012g), and toxin ingestion levels were far below probable lethal doses for this species 

21 (Freeman et al. 1996). In another study, captive rainbow skinks (Lampropholis delicata) were 

22 fed brodifacoum loaded mealworms and none showed signs of ill health, although this may be 

23 attributed to low toxin concentrations (mean = 0.118 ug/g) (Wedding 2007). Marshall and 

24 Jewell (2007) tested free-ranging skinks palatability to three bait types that are commonly used 

25 in pest mammal control programs (RS5 cereal baits, carrot and FeraCol® paste). All bait types 

26 were presented in non-toxic form and were sampled by both species of skink (grand skink 

27 Oligosoma grande and Otago skink O. otagense) (Marshall and Jewell 2007). However, Booth et 

28 al. (2004) found that spotted skinks (Oligosoma lineoocellatum) did not consume any non-toxic 

29 paste or cereal blocks offered in trials to test for the palatability of FeraCol®.

30

31 Reports of reptile mortality associated with brodifacoum bait consumption are uncommon. In 

32 two separate observations, single dead moko skinks (Oligosoma moco) were found near baiting 

33 stations at two locations in New Zealand. On analysis, one skink had a brodifacoum residue 

34 (probably whole body) of 0.82 μg/g, while analysis of stomach contents in the second lizard 

35 showed consumption of 19 μg/g of pindone. Necropsy of the second skink found blood clots 

36 ventral and caudal to the heart (Tocher 2008) (though clotting signs are not normally associated 

37 with anticoagulant effects). A single Northland green gecko (Naultinus grayii) was found dead 

38 after pindone baiting operations near Boundary Stream, New Zealand, and contained 0.52 μg/g 

39 pindone residues. This level of pindone was similar to the concentration found in the baits 

40 (Tocher 2008). During a two month-long rabbit eradication program on Round Island, 

41 Mauritius, using Talon 20P® pelleted baits (20 ppm brodifacoum), Merton (1987) noted that out 

42 of several species of skinks and geckos, only Telfair‟s skinks (Leiolopisma telfairii) routinely 

43 consumed bait pellets. After three weeks of bait exposure, dead Telfairs‟s skinks began to be 

44 found, with increasing mortality for a further five weeks, when lizard mortality abruptly ceased. 

45 In all, over 100 dead Telfair‟s skinks (out of an estimated 5000 individuals) were found, 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 124

1 primarily during the hottest parts of the day and on the hottest days. However, because of the 

2 subsequent eradication of invasive rabbits, populations of Telfair‟s skink (and other endemic 

3 species) on Round Island expanded rapidly following anticoagulant baiting and skinks are now 

4 being translocated to other islands which were part of the species‟ historic range (ARKive.org 

5 2011). Analysis of bulked livers (n = 10) from intoxicated Telfair‟s skinks yielded brodifacoum 

6 residues of 0.6 mg/kg, but only one lizard showed signs of internal hemorrhaging. Merton (1987)

7 speculated that since dead lizards were only found during the hottest portion of the day, 

8 anticoagulant intoxication may have interfered with thermoregulatory mechanisms rather than 

9 inhibition of blood coagulation. The extent of the mortality may also have been due to the overly 

10 long exposure time.

11

12 During a rat eradication campaign in the Montebello Islands Conservation Park, Australia,

13 bungarras (Varanus gouldii) were observed scavenging dead or dying rats poisoned with Talon 

14 G® (50ppm brodifacoum) to the extent that some rat droppings contained the green dye from the

15 bait, but no dead or moribund bungarras were found, and the following year, bungarra tracks 

16 were plentiful (Burbridge 2004). During a rat eradication campaign on Seymour Island in the 

17 Galapagos Islands, 6 of 134 Galapagos land iguanas (Conolophus subcristatus) were found 

18 dead 2-3 months after the bait application at least one of which was directly attributable to bait 

19 consumption (Harper pers. comm.). On Isabel Island, México, brown iguanas (Ctenosaura 

20 pectinata) were observed eating rodent bait pellets directly and 19 were found dead after an 

21 aerial bait application of brodifacoum bait in 2009 (M. Rodriguez Malagón pers. comm.). 

22

23 In 1986, plans to eradicate rats from Monito Island, Puerto Rico, were stopped owing to 

24 concerns over the potential mortality of Sphaerodactylus macrolepsis from 0.005 percent 

25 brodifacoum (Talon-G®) deduced from a laboratory experiment (García 1994, Gaa 1986 in 

26 García et al. 2002). A rat eradication campaign was eventually implemented on Monito Island 

27 (García et al. 2002), but in order to address the earlier concern, a second captive experiment 

28 was conducted in 1994 to test the effect of the second-generation anticoagulant 0.005 percent 

29 bromadiolone (Maki® mini blocks) on a surrogate species, the Mona Island gecko 

30 Sphaerodactylus monensis (justification for using bromadiolone in the test and brodifacoum in 

31 the actual Monito island eradication is described in García et al. 2002). No mortality or change 

32 in behavior was observed. Prior to the Monito program, successful rat eradications had also 

33 been achieved on Cayo Ratones (Puerto Rico), and Steven Cay (U.S. Virgin Islands), with no 

34 apparent effect on nontarget reptiles including native Sphaerodactylus species. 

35 Researchers have estimated the LD50 of brodifacoum for species with unknown LD50 values to be 

36 0.56 mg/kg with a confidence level of 95 percent (Howald et al. 1999). For this reason, we 

37 assume the toxicity risk level for brodifacoum to be very high for terrestrial reptiles. However, 

38 there have been no indications of adverse population-level effects to reptiles or amphibians as a 

39 result of rodent eradications that used brodifacoum. On Anacapa Island, for example, 

40 monitoring of slender salamanders (Batrachoseps sp.) showed no changes in the population 

41 after rats were eradicated using brodifacoum (Island Conservation unpubl. data). In many cases, 

42 the removal of non-native rodents from the ecosystem has led to a large increase in native reptile 

43 and amphibian populations (Towns 1991, Newman 1994, North et al. 1994, Towns 1994, Eason 

44 and Spurr 1995, Towns et al. 2001, NMFS 2005, Parrish 2005, Daltry 2006). At Palmyra, the 

45 expected bait availability period is 4-7seven days (Buckelew et al. 2005). Therefore, the 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 125

1 probability of exposure will be high for 4-7days after the bait is applied, and the concentration 

2 of toxicant that reptiles could be exposed to via primary or secondary pathways will decrease 

3 quickly (USDA 2006, Alifano and Wegmann 2010). Although lethal toxicity in reptiles at

4 Palmyra is possible, little impact to species at the population-level is expected and population 

5 increases are expected.

6

7 Toxicity to invertebrates

8 Arthropods are not thought to be susceptible to brodifacoum (Booth et al. 2001). Soft-bodied 

9 invertebrates such as mollusks may be affected, but the evidence for this is still inconclusive 

10 (Booth et al. 2001) and recent field studies suggest that at least some species of terrestrial 

11 mollusks are not affected by brodifacoum (Brooke et al. 2010). Furthermore, post-application 

12 sampling in the Anacapa Island rat eradication only detected minimal levels of brodifacoum 

13 residue in five out of ten of the intertidal invertebrates tested (Howald et al. 2010). 

14

15 Invertebrates may also function as short-term intermediate carriers of brodifacoum that could be 

16 ingested by their predators. Land crabs have been documented to retain brodifacoum in their 

17 system for up to 56 days (USDA 2006).

18

19 Toxicity to plants

20 Plants are not known to be susceptible to toxic effects of brodifacoum.

21

22 Toxicant Exposure

23 Exposures to toxicants are primarily dependent on 2 factors:

24 Food habits, behavior patterns, and other specific characteristics that increase or decrease 

25 an animal‟s exposure to the toxicant; and

26

27 The availability of the toxicant in the local environment.

28

29 In the form used for rodent control, or eradication, brodifacoum can only effectively be delivered 

30 through oral ingestion; animals can either ingest the toxicant by consuming bait (known as 

31 “primary exposure”), by preying on or scavenging animals that previously consumed bait 

32 (known as “secondary exposure”), or by ingesting soil that contains bait fragments or other 

33 organic particles to which the toxicant has adhered. Brodifacoum molecules adhere strongly to 

34 the bait pellet grains, and are unlikely to be leached away by moisture. Once the pellets 

35 disintegrate into particles that are too small for most foraging animals to consume, the toxicant is 

36 essentially unavailable for direct consumption. Eventually, even the sub-measurable 

37 concentrations of toxicant remaining from a fully disintegrated pellet would break down into 

38 non-toxic compounds including carbon dioxide and water with no toxic intermediate compounds 

39 (U.S. National Park Service 2000).

40

41 Primary exposure

42 Herbivorous and omnivorous species are much more likely to consume bait (primary exposure) 

43 than carnivorous species (including insectivores and piscivores) because the bait is composed 

44 primarily of grain. It is unlikely that the carnivorous, piscivores, or insectivorous at Palmyra 

45 would intentionally consume bait pellets as food. 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 126

1

2 There is no direct information on shorebird soil consumption at Palmyra; however, we can 

3 assume that a small percentage (for example, less than 0.03% of the atoll‟s 618 acres of land 

4 would come into direct contact with a bait pellet if 0.4 inch x 1 inch bait pellets were applied at 

5 80.4 lb/acre) of the topsoil at Palmyra will contain low concentrations (Alifano and Wegmann 

6 2010)of brodifacoum for less than 1year beyond the eradication action; brodifacoum has a 

7 reported half-life of 157 days when in soil (World Health Organization 1995). Early studies of 

8 sediment consumption in shorebirds estimated between 10 – 60 percent of the contents in the 

9 digestive system were sand; no apparent correlation with feeding habits were found (Reeder 

10 1951). More recently, Beyer et al. (1994) found that the diet of four species of sandpiper: stilt 

11 sandpiper (Calidris himantopus), semipalmated sandpiper (Calidris pusilla), least sandpiper 

12 (Calidris minutilla), and western sandpiper (Calidris mauri) contained on average 7 – 30 percent 

13 sediment in their digestive track. Black-bellied plovers (Pluvialis squatarola) and willets (Tringa 

14 semipalmata) consumed 29 percent and 3 percent sediment, respectively (Hui and Beyer 1998). 

15 Feeding habits of these species differ; black-bellied plovers have short bills and primarily peck at 

16 food, while willets have long bills and probe into the soil with their bills open. Mathot et al. 

17 (2010) found that the stomach contents of western sandpipers (Calidris mauri) contained more 

18 than 75 percent sediment, while the stomach contents of dunlins (Calidris alpina) contained 

19 more than 40 percent sediment. Dunlins probe with an open bill and western sandpipers forage

20 by pecking or probing. Therefore, measureable amounts of sediment can be consumed by 

21 shorebirds while foraging for sediment-dwelling prey, and some correlation may be exist 

22 between feeding strategy and the amount of soil consumed while foraging. While it is possible 

23 that shorebirds at Palmyra will consume brodifacoum bound to organic particles within the soil 

24 that they are feeding, it is unlikely that this will be a high-risk pathway of exposure due to the 

25 following reasons: 1) Shorebirds primarily forage in the intertidal zone and on emergent lagoon 

26 flats; with the broadcast alternatives (Alternatives B and C) measures will be taken to minimize 

27 the amount of bait that will land in the intertidal and marine environments, and the bait station 

28 alternative (Alternative D) would all but eliminate bait from entering the intertidal and marine 

29 environments; 2) Brodifacoum concentrations in sandy and humus topsoil are low during and 

30 directly after a bait broadcast (Alternatives B and C), and quickly decline to trace or undetectable 

31 levels (Alifano and Wegmann 2010, Appendix F). 

32

33 Secondary exposure

34 Rats and other animals that directly consume bait can also transfer some of the toxicant in their 

35 systems to predators or scavengers (secondary exposure). Different organisms show considerable 

36 variation in the amount of time that they retain toxicants in their bodies. For vertebrates that 

37 experience sub-lethal dosing, brodifacoum can be retained in the liver for many months. 

38 Specifically, brodifacoum concentrations in the livers of rats that experienced sub-lethal dosing 

39 took 350 days to reduced by 50 percent (Erickson and Urban 2004). Brodifacoum retention times 

40 for birds have not yet been determined. For invertebrates, the exact mechanisms of brodifacoum 

41 retention are unclear but the general understanding is that most invertebrates only retain 

42 brodifacoum briefly in their digestive system and body tissues (Booth et al. 2001). A recent 

43 study of brodifacoum in crab tissue at Palmyra indicated that crabs retain more of the toxicant in 

44 the hepatopancreas than in the claw meat, and all of the samples had negligible quantities of 

45 brodifacoum in their tissues by day 56 of the study (USDA 2006).
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 127

1

2 In a toxicant-based rat eradication scenario, rats that die from rodenticide exposure could 

3 become a secondary pathway of exposure for nontarget species (Salmon and Paul 2010). To 

4 determine the timeframe within which this exposure pathway presents a risk to nontarget species, 

5 87 rats were captured and euthanized during the 2008 biomarker study and placed at their point 

6 of capture and monitored. Seventy-five percent of the sample rats were completely consumed 

7 within 24 hours, and the carcasses that were not completely consumed were mostly reduced to 

8 small pieces: teeth, tails, and skull fragments (Wegmann et al. 2008).

9

10 Land crabs are capable scavengers and will readily consume carrion and may consume rats that 

11 have been sub-lethally exposed to brodifacoum. Cox and Smith (1990) suggest that sub-lethal 

12 dosing in may alter thigmotactic behavior in rats, which in turn may alter exposure of secondary 

13 consumers to rodenticide residues in rat tissue. Aside from crabs, rats have no other terrestrial 

14 predators at Palmyra, and crabs are the primary scavengers of rat carcasses. Land crabs appear 

15 to have no ill effect from primary or secondary exposure to brodifacoum; therefore, it is unlikely 

16 that nontarget species will be harmed by direct consumption of sub-lethally exposed rats, or rat 

17 carcasses.

18

19 At Palmyra, only a few species are at risk of exposure to the applied rodenticide through a 

20 secondary pathway. Rats may be at risk of secondary exposure by consuming crabs and other 

21 invertebrates like cockroaches, dead shorebirds, and other rats that had all previously consumed 

22 bait. Crabs (hermit crabs, land crabs, and coconut crabs) may be at risk of secondary exposure to 

23 rodenticide through the consumption of crabs and other invertebrates, dead shorebirds, and dead 

24 or dying rats that had all previously consumed bait. Shorebirds, primarily the bristle-thighed 

25 curlew and Pacific golden-plover, may be at risk of secondary exposure to rodenticide through 

26 the consumption of invertebrates that had previously consumed bait; bristle-thighed curlews are

27 the only shorebird species at Palmyra that are known to occasionally feed on terrestrial hermit 

28 crabs (see Appendix I Hermit Crab Predation by Bristle-thighed Curlews). Shorebirds showed no 

29 interest in rat carcasses during a rat carcass degradation study conducted at Palmyra in 2010 

30 (Alifano and Wegmann 2010). The two gecko species at Palmyra may be at risk of secondary 

31 exposure to rodenticide through the consumption of invertebrates that had previously consumed 

32 bait; however, none of the 50 geckos sampled during the 2008 biomarker study showed any sign 

33 of primary or secondary exposure to bait (Wegmann et al. 2008). 

34

35 4.4.4.2 Analysis framework for impacts from disturbance

36

37 Helicopter Operations

38 The operation of low-flying aircraft throughout Palmyra would likely result in disturbance to 

39 wildlife from sound, the sudden appearance of an aircraft, or a combination of both (Efroymson 

40 et al. 2001). Wildlife could be exposed to noise that exceed background levels. Due to the 

41 relatively low altitude at which helicopters would fly (50-100 feet above the canopy), the 

42 majority of the helicopter noise would be focused in a narrow cone directly underneath the 

43 aircraft, reducing the area of disturbance for each helicopter pass (Richardson et al. 1995). 

44 Animals on land would likely be exposed to higher-decibel noise than animals in the water; 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 128

1 however, researchers at Grupo de Ecología y Conservación de Islas, A.C (GECI) assessed the 

2 impact helicopter operations on breeding boobies on Isla Isabel (Mexico) and found no 

3 significant effect to the birds (GECI 2009). Also, rotor wash from helicopters landing or 

4 hovering near nesting white terns, black noddies, or brown noddies could cause disturbance to 

5 individual birds, eggs, or chicks; however, of these three species, only white terns, would be 

6 nesting near any of the designated helicopter landing zones. All helicopter landing zones would 

7 be surveyed for nesting seabird nesting activity prior to the commencement of helicopter 

8 operations. If nests were found close to pre-determined landing zones, alternate landing zones 

9 would be sought out. We do not anticipate that helicopter operations in association with the 

10 action Alternatives B and C would cause more than a nominal disturbance to wildlife at Palmyra. 

11

12 Personnel Activities

13 Additional wildlife disturbance could result from personnel traveling by foot across the atoll 

14 (e.g., when hand-broadcasting bait, tending bait stations, and surveying for nontarget mortality), 

15 or traveling in small boats in the nearshore waters. Personnel associated with the rat eradication 

16 action would be based at Palmyra for approximately one month under Alternative B, two months 

17 under Alternative C, and for up to 2 years under Alternative D. Following eradication, there will 

18 be several monitoring visits to the atoll for at least 2 years post eradication. There are personnel 

19 at Palmyra conducting ongoing research, monitoring, and other management activities year20 round, but rat eradication will increase the number of personnel on the atoll and the extent of 

21 affect. Most current monitoring activities take place in discrete and limited areas of the atoll, 

22 whereas rat eradication operations will require personnel to travel throughout the atoll. Personnel 

23 would be briefed on techniques to reduce wildlife disturbance, but minor disturbance events will 

24 likely still occur. Personnel will also be briefed on biosecurity practices and will adhere to 

25 biosecurity protocols to prevent the spread of invasive plants and animals (invertebrates) around 

26 the atoll.

27

28 4.4.4.3 Methods for impacts analysis to biological resources

29

30 Impact Indices

31 The following impacts analysis identifies the level of risk from the perspective of bait 

32 availability (the amount of time bait will be available through either primary or secondary 

33 exposure pathways), toxicant exposure (the number of exposure pathways available to individual 

34 species based on feeding ecology and toxicant fate), toxicant risk (the toxicity of the toxicant to 

35 different species based on toxicological properties), disturbance risk (the sensitivity to 

36 disturbance and the amount of disturbance risk that individuals may be exposed to during 

37 operations), extent of the risk (the number of individuals that may be affected by eradication 

38 operations and the influence that this could have global or regional breeding populations), and 

39 the duration of the risk (the period of time that individuals will be exposed to toxicant or 

40 disturbance risks). The following indices illustrate the methodology employed to analyze the 

41 impacts to each of the identified species for the three action alternatives:

Bait availability 42

o Short: Bait or rat carcasses with toxicant residue available for up to 36 days 43

o Medium: Bait in crab excrement or animal tissue available for 37-90 days 44

o Long: Toxicant persistent anywhere in the environment for more than 90 days 45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 129

Risk of mortality from toxicant use 1

o None: No toxicological sensitivity 2

o Low: Minor toxicological sensitivity 3

o Medium: Moderate toxicological sensitivity 4

o High: Severe toxicological sensitivity 5

Toxicant exposure risk level 6

o None: No exposure pathway 7

o Low: Possible exposure pathway 8

o Medium: One exposure pathway 9

o High: Multiple exposure pathways 10

Disturbance risk 11

o None: No disturbance pathway 12

o Low: Low sensitivity to disturbance 13

o Medium: Moderate sensitivity to disturbance 14

o High: Severe sensitivity to disturbance 15

Extent of toxicant/disturbance risk within a population 16

o Individuals: Few individuals affected 17

o Island population: Many individuals affected with no affect to the global or 18

regional breeding population 19

o Global or regional population: Many individuals affected with impacts on the 20

global or regional breeding population 21

Duration of the Risk (Toxicant or Disturbance) 22

o Short: Impacts for up to 2 months 23

o Medium: Impacts for more than 2 months and up to 6 months 24

o Long: Impacts for more than 6 months 25

26

27 4.4.4.4 Impacts of Alternative B on biological resources

28

29 Impacts on Birds

30 Generally, birds that primarily eat plant matter such as seeds and fruits would initially be at high 

31 risk for primary exposure to brodifacoum. Predators and scavengers would in some cases be at 

32 high risk of secondary exposure to brodifacoum. Animals that feed on rats, rat carcasses, or large 

33 ground-dwelling invertebrates such as land crabs would initially be at high risk of secondary 

34 exposure to brodifacoum. Birds that have a broad, omnivorous diet would initially be at high risk 

35 for both primary and secondary exposure.

36

37 The risk of exposure (either primary or secondary) in initially high-risk animals (terrestrial 

38 herbivores, many predators and scavengers, and omnivores) would begin to decline rapidly 

39 within 30 days of the final bait application session as the rat population declines, bait pellets are 

40 consumed or disintegrated, and bait becomes less available to invertebrate consumers. The risk 

41 of exposure in these initially high-risk animals would generally be low within 30 days of the 

42 final bait application and negligible within a few months thereafter. 

43

44 On the other hand, birds foraging in the intertidal zone would be at lower risk for primary 

45 exposure because pellets that drift into the water would disintegrate and become unavailable 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 130

1 within a few hours. Similarly, birds that forage primarily in the intertidal zone and specialize in 

2 intertidal invertebrates would initially be at a low risk of secondary exposure. Also, birds that 

3 feed primarily on flying insects and “micro-invertebrates” would be at an initial, lower risk of 

4 secondary exposure due to the low likelihood that these classes of invertebrates would be 

5 carrying brodifacoum in their systems; this risk would steadily decline to negligible within a few 

6 months. The likelihood of exposure in intertidal specialists would decline even more rapidly, 

7 becoming negligible within 30 days of the final bait application.

8

9 The following is a breakdown of the direct toxicant and disturbance impacts to each of the 

10 identified bird species that migrate to, breed at, and overwinter at Palmyra. Additionally, we 

11 have quantified the number of individuals per species that are likely to be adversely affected by 

12 Alternative B (we have assumed the worst case scenario and consider any individuals that may 

13 be present on the atoll during the eradication operations to be vulnerable to adverse impacts from 

14 the action alternative). The take numbers for action Alternative B are from runway and all-atoll 

15 shorebird counts conducted during the season (June-July) when breeding adults should be at their 

16 breeding grounds in Alaska, or from Depkin (2002).

17

18 Bristle-thighed curlew

19 Toxicant Risk

20 Bristle-thighed curlews could be exposed to brodifacoum through both primary and secondary 

21 exposure pathways. Generally, curlews forage in the intertidal zone for aquatic invertebrates and 

22 seabird eggs, and have been observed ignoring placebo (non-toxic) bait pellets when they are 

23 placed in the vicinity of more typical prey items – fiddler crabs (see Appendix F). Additionally, 

24 curlews are known to eat small fruit and insects in the forested areas of the atoll, and to a limited 

25 extent prey on terrestrial hermit crabs (see Appendix I). The primary exposure pathway is limited 

26 to curlews that forage in the forests and directly consume bait; whereas, the secondary exposure 

27 pathways include consumption of intertidal invertebrate species, hermit crabs, roaches, and other 

28 terrestrial invertebrates. The bait availability will be for the short-term, the mortality risk is high, 

29 and the exposure risk is high because of the range of toxicant exposure pathways. The duration 

30 of the risk will likely be for the medium-term due to the retention time of the toxicant in the 

31 tissue of species that provide a secondary exposure pathway to curlews. The extent of the affect 

32 will be to the entire atoll population.

33

34 Disturbance Risk

35 Bristle-thighed curlews could be exposed to disturbances from both ground and air operations, 

36 which will likely cause curlews to flush the area to an alternate site on the atoll. The impacts 

37 associated with disturbance risks for this alternative are low, the duration of the disturbance will 

38 be for the short-term, and the extent of the affect will be to the entire atoll population. 

39

40 As many as 182 individuals are likely to be exposed to impacts from Alternative B.

41

42 Pacific golden-plover

43 Toxicant Risk

44 Pacific golden-plovers could be exposed to brodifacoum through both primary and secondary 

45 exposure pathways. Generally, plovers forage in the intertidal zone for aquatic invertebrates and 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 131

1 insects. Additionally, plovers are known to eat insects in the forested and grassland areas of the 

2 atoll. The primary exposure pathway is limited to plovers that forage in the forests and consume 

3 rodenticide; whereas, the secondary exposure pathways include consumption of hermit crabs, 

4 roaches, other terrestrial invertebrates, and possibly intertidal invertebrate species. The bait 

5 availability is for the short-term, the mortality risk is high, and the exposure risk is high because 

6 of the range of toxicant exposure pathways. The duration of the risk will likely be for the 

7 medium-term due to the retention time of the toxicant in the tissue of species that provide a 

8 secondary exposure pathway to plovers. The extent of the affect will be to the entire atoll 

9 population.

10

11 Disturbance Risk

12 Pacific golden-plovers could be exposed to disturbances from both ground and air operations, 

13 which will likely cause plovers to flush the area to an alternate site on the atoll. The impacts 

14 associated with disturbance risks for this alternative are low, the duration of the disturbance will 

15 be for the short-term, and the extent of the affect will be to the entire atoll population.

16

17 As many as 62 individuals are likely to be exposed to impacts from Alternative B.

18

19 Ruddy turnstone

20 Toxicant Risk

21 Ruddy turnstones could be exposed to brodifacoum through both primary and secondary 

22 exposure pathways. Generally, turnstones forage in the intertidal zone for aquatic invertebrates. 

23 Additionally, turnstones eat terrestrial insects and feed on carrion when available. The primary 

24 exposure pathway is limited to turnstones that forage in the forests that consume rodenticide; 

25 whereas, the secondary exposure pathways include consumption of intertidal and terrestrial 

26 invertebrate species, carrion, and other terrestrial invertebrates that have consumed the toxicant. 

27 The bait availability will be for the short-term, the mortality risk is high, and the exposure risk is 

28 high because of the range of toxicant exposure pathways. The duration of the risk will likely be 

29 for the medium-term due to the retention time of the toxicant in the tissue of species that provide 

30 a secondary exposure pathway to turnstones, and the extent of the affect will be to the entire atoll 

31 population.

32 Disturbance Risk

33 Ruddy turnstones could be exposed to disturbances from both ground and air operations, which 

34 will likely cause turnstones to flush the area to an alternate site on the atoll. The impacts 

35 associated with disturbance risks for this alternative are low, the duration of the disturbance will 

36 be for the short-term, and the extent of the affect will be to the entire atoll population.

37

38 As many as 35 individuals are likely to be exposed to impacts from Alternative B.

39

40 Wandering tattler

41 Toxicant Risk

42 Wandering tattlers would only be exposed to brodifacoum through secondary exposure 

43 pathways. Generally, tattlers forage in the intertidal zone for aquatic invertebrates at Palmyra. 

44 Tattlers feed on aquatic insects, mollusks, crustaceans, and small fish. The bait availability will 

45 be for the short-term, the mortality risk is high, and the exposure risk is moderate because of 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 132

1 limited exposure to the rodenticide. The duration of the risk will likely be for the short-term due 

2 to the retention time of the toxicant in the tissue of species that provide a secondary exposure 

3 pathway to tattlers. The extent of the affect will be to individuals because of the moderate

4 exposure risk.

5 Disturbance Risk

6 Wandering tattlers could be exposed to disturbances from both ground and air operations, which 

7 will likely cause tattlers to flush the area to an alternate site on the atoll. The impacts associated 

8 with disturbance risks for this alternative are low, the duration of the disturbance will be for the 

9 short-term, and the extent of the affect will be to the entire atoll population.

10

11 As many as 48 individuals are likely to be exposed to impacts from Alternative B.

12

13 Sanderling and pectoral sandpiper

14 Toxicant Risk

15 Sanderlings and pectoral sandpipers would only be exposed to brodifacoum through secondary 

16 exposure pathways. Generally, these species forage in the intertidal zone for aquatic 

17 invertebrates. The bait availability will be for the short-term, the mortality risk is high, and the 

18 exposure risk is low because of limited exposure to the rodenticide. The duration of the risk will 

19 likely be for the medium-term due to the retention time of the toxicant in the tissue of species 

20 that provide a secondary exposure pathway to these species. The extent of the affect will only be 

21 to a few individuals because the atoll populations of both sanderlings and pectoral sandpipers are 

22 relatively low at Palmyra and the exposure risk is low.

23

24 Disturbance Risk

25 Sanderlings and pectoral sandpipers could be exposed to disturbances from both ground and air 

26 operations, which will likely cause sanderlings and pectoral sandpipers to flush the area to an 

27 alternate site on the atoll. The impacts associated with disturbance risks for this alternative are 

28 low, the duration of the disturbance will be for the short-term, and the extent of the affect will be 

29 to the entire atoll population.

30

31 As many as five sanderling individuals are likely to be exposed to impacts from 

32 Alternative B.

33

34 As many as eight pectoral sandpiper individuals are likely to be exposed to 

35 impacts from Alternative B.

36

37 Laughing and Franklin‟s gull

38 Toxicant Risk

39 Laughing and Franklin‟s gulls could be exposed to brodifacoum through both primary and 

40 secondary exposure pathways. Generally, gulls are omnivorous and are often found foraging in 

41 the intertidal zone for aquatic and terrestrial invertebrates, eating seeds and plants, or feeding on

42 carrion. The primary exposure pathway is significant because gulls are known to consume bait 

43 pellets. Additionally, the secondary exposure pathways include consumption of intertidal and 

44 terrestrial invertebrate species, carrion, and other terrestrial invertebrates that have consumed the 

45 toxicant. The bait availability would be for the short-term, the mortality risk is high, and the 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 133

1 exposure risk is high because of the range of toxicant exposure pathways. The duration of the 

2 risk will likely be for the medium-term due to the retention time of the toxicant in the tissue of 

3 species that provide a secondary exposure pathway to gulls. The extent of the affect will be to 

4 individuals because gulls are very infrequent visitors of Palmyra.

5

6 Disturbance Risk

7 Franklin‟s and laughing gulls could be exposed to disturbances from both ground and air 

8 operations, which will likely cause gulls to flush the area to an alternate site on the atoll. The 

9 impacts associated with disturbance risks for this alternative are low, the duration of the 

10 disturbance will be for the short-term, and the extent of the affect will be to the entire atoll 

11 population.

12 As many as one laughing gull individual is likely to be exposed to impacts from 

13 Alternative B.

14

15 As many as nine Franklin‟s gull individuals are likely to be exposed to impacts 

16 from Alternative B.

17

18 Northern shoveler and northern pintail

19 Toxicant Risk

20 Northern shovelers and northern pintail ducks could be exposed to brodifacoum through both 

21 primary and secondary exposure pathways. Generally, ducks forage in small, inland ponds for 

22 aquatic invertebrates, eat terrestrial insects, and consume plants and seeds. Ducks are susceptible 

23 to primary exposure of the bait because they are granivorous and would likely be attracted to the 

24 grain matrix within the bait pellet. The secondary exposure pathways include consumption of 

25 intertidal and terrestrial invertebrate species that have consumed the toxicant. The bait 

26 availability would be for the short-term, the mortality risk is high, and the exposure risk is 

27 medium because of the range of toxicant exposure pathways. The duration of the risk will likely 

28 be for the medium-term due to the retention time of the toxicant in the tissue of species that 

29 provide a secondary exposure pathway to ducks. We expect that less than ten individuals will be 

30 impacted by the eradication because ducks are highly infrequent visitors to Palmyra.

31

32 Disturbance Risk

33 Northern shovelers and pintail ducks could be exposed to disturbances from both ground and air 

34 operations, which will likely cause ducks to flush the area to an alternate site on the atoll. The 

35 impacts associated with disturbance risks for this alternative are low, the duration of the 

36 disturbance will be for the short-term, and the extent of the affect will be on the individual level.

37

38 As many as six northern pintail individuals are likely to be exposed to impacts 

39 from Alternative B.

40

41 As many as two northern shoveler individuals are likely to be exposed to impacts 

42 from Alternative B.

43
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 134

1 Breeding seabirds (masked booby, brown booby, red-footed booby, great frigatebird, 

2 sooty tern, white tern, red-tailed tropicbird, white-tailed tropicbird, black noddy, and 

3 brown noddy) 

4 Toxicant Risk

5 The breeding seabirds at Palmyra are at extremely low risk of toxicant exposure because they 

6 rarely if ever feed on anything other than marine organisms. We would minimize the potential of 

7 exposure of groun- nesting boobies to toxicant by hand-baiting the causeways where most brown 

8 and masked boobies nest and bait will not be distributed within reach of birds sitting in the nest. 

9 We would minimize the potential for fish to be exposed to the toxicant by hand baiting near the 

10 shoreline and using an internal deflector system in the bait hopper to prevent bait from being 

11 broadcast into bodies of water; therefore, the extent of the effect is insignificant and does not 

12 require further scrutiny. Young boobies of all three species at Palmyra engage in manipulative 

13 play with sticks and small objects. They don‟t ingest the objects but could be exposed to very 

14 small amounts by holding the pellets in their bills. 

15

16 Disturbance Risk

17 Breeding seabirds are at a greater risk from disturbance because they will be attending nests and 

18 caring for young. The majority of the disturbance will come from both ground and air operations, 

19 which would cause individuals to flush from roosts and nests leaving eggs and chicks vulnerable 

20 to predation or injury. Additionally, there is a risk of breeding disturbance from the listed 

21 disturbance impacts; however, there will be limited aerial operations directly above ground 

22 breeding masked or brown booby colonies. The risk level from disturbance from aerial 

23 operations would be low. This is supported from research conducted by GECI on disturbance 

24 affect to booby populations on Isla Isabel from helicopter operations, which found little to no 

25 effect on booby colonies from helicopter operations (GECI 2009). Additionally, ground 

26 operations will be minimal near breeding colonies and will result in low disturbance impacts. 

27 The duration for the disturbance affect is for the short-term and the extent is to the entire atoll 

28 population.

29 100,000 – 200,000 individuals are likely to be exposed to impacts from 

30 Alternative B.

31

32 Non-breeding seabirds (lesser frigatebird) 

33 Toxicant Risk

34 Lesser frigatebirds are at a no risk of toxicant exposure because they rarely if ever feed on 

35 anything other than marine fish. We would mitigate impacts to fish by hand baiting near the 

36 shoreline and using a deflector to prevent bait from entering the waterways; therefore, the extent 

37 of the affect is insignificant and does not require further scrutiny. 

38

39 Disturbance Risk

40 Lesser frigatebirds could be exposed to disturbances from both ground and air operations, which 

41 will likely cause them to flush the area to an alternate site on the atoll. The impacts associated 

42 with disturbance risks for this alternative are low, the duration of the disturbance will be for the 

43 short-term, and the extent of the affect will be on the individual level.

44

45 20 individuals are likely to be exposed to impacts from Alternative B.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 135

1

2 Impacts on Reptiles

3 Geckoes (native Lepidodactylus sp) and nonnative mourning gecko (Lepidodactylus 

4 lugubris))

5 Toxicant Risk

6 Geckoes are at risk of secondary exposure to rodenticide through the consumption of terrestrial 

7 invertebrates; however, there is a gap in the literature on the toxicity of anticoagulant 

8 rodenticides to reptiles. Additionally, even less is known about either the native or nonnative 

9 geckoes at Palmyra. Therefore, this assessment is likely deficient at examining all of the 

10 potential toxicant exposure pathways, as well as, the fate of individuals that consume bait 

11 through secondary pathways. The bait availability would be for the short-term, the mortality risk 

12 is high, and the exposure risk is medium. The duration of the risk is for the medium-term, and 

13 the extent is to the entire atoll population.

14

15 Disturbance Risk

16 Geckoes are at a negligible risk of disturbance from both ground and air operations because they 

17 are fairly elusive and have many alternative areas to retreat to during eradication operations; 

18 therefore, they are only vulnerable for the short-term and only to a few individuals.

19

20 Hawksbill turtle and green turtle

21 Toxicant Risk

22 Turtles may face a primary risk of exposure to the toxicant through eating bait directly as it 

23 drops through the water column. These turtles‟ common foraging behaviors make exposure 

24 unlikely, but juvenile green turtles in particular are known to be comparatively opportunistic 

25 feeders, and marine turtles have been documented ingesting marine debris elsewhere (Carr 

26 1987, Meylan 1988, NOAA Fisheries pers. comm., Bjorndal et al. 1994, Coyne 1994, Bugoni et 

27 al. 2001). Mitigation measures to reduce bait drift into waterways will be employed to reduce the 

28 exposure risk to turtles, including hand-baiting narrow strips of land and portions of the coconut 

29 palm canopy than cannot be safely and effectively baited by air, and using a deflector to control 

30 the direction of the bait flow from the hopper. Even if bait pellets enter the water at the full 

31 application rate, they will only be ingestible by turtles for a few hours prior to embedding in the 

32 sediment and breaking down to tiny fragments (Empson and Miskelly 1999). Thus, the duration 

33 of risk to turtles is for the very short term. The extent of risk is only to a few individuals. The risk 

34 of turtle mortality, given the low likelihood of exposure to the toxicant, is unknown but suspected 

35 to be low.

36

37 Disturbance Risk

38 Turtles could be exposed to disturbances from boat operations, which will likely cause turtles to 

39 flee from the immediate area. However, boat operations in association with the rat eradication 

40 would not exceed normal levels of boat use during the research season, and no negative impact 

41 to turtles has been associated with boat activities during the research season (A. Meyer pers. 

42 comm.). The impacts associated with disturbance risks for this alternative are low, the duration 

43 of the disturbance will be for the short-term, and the extent of the affect will be on the individual 

44 level.

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 136

1 Impacts on Fish

2 Fish (black-spotted sergeant (Abudefduf sordidus), stripe belly puffer (Arothron 

3 hispidus), camouflage grouper (Epinephelus polyphekadion), bohar (Lutjanus bohar), 

4 black tail snapper (Lutjanus fulvus), dusky farmerfish (Stegastes nigricans), and bonefish 

5 (Albula vulpes))

6 Toxicant Risk

7 Some fish species face both a primary and secondary risk of exposure to the toxicant through the 

8 consumption of aquatic invertebrates and by eating bait directly as it drops through the water 

9 column - species analyzed here either consumed or mouthed placebo bait during field trials at 

10 Palmyra Atoll in May 2010 (Alifano and Wegmann 2010) (see Appendix F). Little is known 

11 about the effect that brodifacoum has on fish; therefore, for the purposes of this analysis we are 

12 considering the mortality risk from brodifacoum to be high. Additionally, mitigation measures to 

13 reduce bait drift into waterways will be employed to further reduce the exposure risk to fish 

14 including hand baiting narrow strips of land and portions of the coconut palm canopy than 

15 cannot be safely and effectively baited by air, and using a deflector to control the direction of the 

16 bait flow from the hopper. The duration of risk is for the very short-term because bait pellets will 

17 only be available for a few hours prior to embedding in the sediment and breaking down to tiny 

18 fragments. The extent of risk is only to a few individuals.

19

20 Disturbance Risk

21 Fish could be exposed to disturbances from boat operations, which likely will cause fish to flush 

22 the immediate area. The impacts associated with disturbance risks for this alternative are low, the 

23 duration of the disturbance will be for the short-term, and the extent of the effect will be on the 

24 island population level.

25

26 Impacts on Invertebrates

27 Terrestrial crabs

28 Toxicant Risk

29 Terrestrial crabs are at both a primary and secondary risk of exposure to the brodifacoum bait 

30 from the consumption of bait pellets, carrion, invertebrates, or crab excrement. The exposure risk 

31 is high; however, crabs show not adverse response to ad-lib consumption of bait (Alifano and 

32 Wegmann 2010). We anticipate no risk of mortality to the island population for the short-term.

33

34 Disturbance Risk

35 Disturbance risks to terrestrial crabs include minor impacts from ground operations, as well as a 

36 disruption of their typical foraging base by providing an alternative food source through the bait 

37 pellets. The duration of this disturbance would only be for the short-term, but the extent will be 

38 to the entire atoll population. 

39

40 Impacts on Vegetation

41 Toxicant Risk

42 Vegetation is at a negligible risk of toxicant impacts because brodifacoum lacks any herbicidal 

43 properties; therefore, the extent of the affect is insignificant and does not require further scrutiny.

44
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 137

1 Disturbance Risk

2 Vegetation is at a minor risk of disturbance by trampling from ground operations with the 

3 greatest threat from the introduction or dispersal of nonnative invasive plant species. The risk of 

4 spreading invasive plant species will be minimized by integrating biosecurity measures into the 

5 daily eradication operations. The duration of the affect will be for the very short-term.

6

Impacts Table for Alternative B: Biological Resources

Table 4.2. Impacts of Alternative B on Biological Resources 

Species

Bait 

availability1

Risk 

mortality -

toxicant 

use2

Toxicant 

exposure 

risk level3

Disturbance 

risk4

Extent of risk within a 

population5 Duration of risk6

toxicant disturbance toxicant disturbance

Bristle-thighed 

curlew Short High High Low Island Island Medium Short

Pacific Goldenplover Short High High Low Island Island Medium Short

Ruddy turnstone Short High High Low Island Island Medium Short

Wandering 

tattler Short High Moderate Low Individ. Island Short Short

Sanderling & 

pectoral 

sandpiper

Short High Low Low Individ. Island Medium Short

Laughing & 

Franklin‟s gull Short High High Low Individ. Island Medium Short

Northern 

shoveler & 

pintail duck

Short High Medium Low Individ. Individ. Medium Short

Breeding 

seabirds7 Low Low Low Low None Island None Short

Non-breeding 

seabirds8 Low Low Low Low None Individ. None Short

Geckoes9

Short High Medium None Island Individ. Medium Short

Turtles10 Low Low Low Low Individ. Individ. Short Short

Fish11 Short High Low Low Individ. Island Short Short

Terrestrial crabs Short None High Low Island Island Short Short

Vegetation None None None Low None Island None Short

1None: No toxicological sensitivity; Short: Bait or rats with toxicant residue available for up to 36 days; Medium: Bait in crab 

excrement or animal tissue available for 37-90 days; Long: Toxicant persistent anywhere in the environment for more than 90 

days. 

2None: No toxicological sensitivity; Low: Minor toxicological sensitivity; Medium: Moderate toxicological sensitivity; 

High: Severe toxicological sensitivity. 3None: No exposure pathway; Low: Possible exposure pathway; Medium: One exposure 

pathway; High: Multiple exposure pathways. 4None: No disturbance pathway; Low: Low sensitivity to disturbance; Medium: 

Moderate sensitivity to disturbance; High: Severe sensitivity to disturbance. 5Individual (Individ.): Few individuals affected; 

Island population (Island): Many individuals affected with no affect to the global or regional breeding population; Global or 

regional population (Global): Many individuals affected with impacts on the global or regional breeding population. 6Short: 

Impacts for up to 2 months; Medium: Impacts for more than 2 months and up to 6 months; Long: Impacts for more than 6 

months. 7Breeding seabirds includes: masked booby, brown booby, red-footed booby, great frigatebird, sooty tern, white tern, 

red-tailed tropicbird, white-tailed tropicbirds, black noddy, and brown noddy. 8lesser frigatebird. 9Native (Lepidodactylus n. sp) 

and nonnative mourning gecko. 10hawksbill turtle and green turtle. 11black-spotted sergeant, stripe belly puffer, camouflage 

grouper, bohar, black tail snapper, dusky farmerfish, and bonefish.

7

8
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 138

1 4.4.4.5 Impacts of Alternative C- Preferred Alternative on biological resources

2

3 Impacts on Birds

4 Generally, birds that primarily eat plant matter such as seeds and fruits would initially be at high 

5 risk for primary exposure to brodifacoum. Predators and scavengers would in some cases be at 

6 high risk of secondary exposure to brodifacoum. Animals that feed on rats, rat carcasses, or large 

7 ground-dwelling invertebrates such as land crabs would initially be at high risk of secondary

8 exposure to brodifacoum. Birds that have a broad, omnivorous diet would initially be at high risk 

9 for both primary and secondary exposure.

10

11 The risk of exposure (either primary or secondary) in initially high-risk animals (terrestrial 

12 herbivores, many predators and scavengers, and omnivores) would begin to decline rapidly 

13 within 30 days of the final bait application session as the rat population declines, bait pellets are 

14 consumed or disintegrated, and bait becomes less available to invertebrate consumers. The risk 

15 of exposure in these initially high-risk animals would generally be low within 30 days of the 

16 final bait application and negligible within a few months thereafter. 

17

18 On the other hand, birds foraging in the intertidal zone would be at lower risk for primary 

19 exposure because pellets that drift into the water would disintegrate and become unavailable 

20 within a few hours. Similarly, birds that forage primarily in the intertidal zone and specialize in 

21 intertidal invertebrates would initially be at a low risk of secondary exposure. Also, birds that 

22 feed primarily on flying insects and “micro-invertebrates” would be at an initial, lower risk of 

23 secondary exposure due to the low likelihood that these classes of invertebrates would be 

24 carrying brodifacoum in their systems; this risk would steadily decline to negligible within a few 

25 months. The likelihood of exposure in intertidal specialists would decline even more rapidly, 

26 becoming negligible within 30 days of the final bait application.

27

28 The successful eradication would result in important benefits for migratory birds. Rats have 

29 likely contributed to the extirpation of as many as eight seabird species from Palmyra: 

30 Audubon‟s shearwater, Christmas Island shearwater, wedge-tailed shearwater, Phoenix petrel, 

31 white-throated storm-petrel, Bulwer‟s petrel, blue noddy, and gray-backed tern. While no 

32 historical or paleontological records were found for these species nesting at Palmyra, they do 

33 breed regionally at rat-free islands in the Line archipelago, such as Kiritimati Island in the 

34 Republic of Kiribati and Jarvis Island National Wildlife Refuges. Black rats would effectively 

35 prevent the establishment, or reestablishment of breeding populations of any of these species 

36 (Norman 1975). When rats are eradicated from Palmyra Atoll, we expect the number of nesting 

37 seabirds and reproductive success of these seabirds to increase. We also anticipate that several 

38 of the aforementioned ground nesting shearwaters, petrels and terns will reestablish colonies at 

39 Palmyra. The benefits of rat eradication will be greatest for nesting species. However, migratory 

40 shorebirds will also benefit, especially the bristle-thighed curlew. Predation by introduced 

41 predators, such as dogs, cats, pigs and rats, is an important source of mortality elsewhere for 

42 wintering curlews during the molt-induced flightless period (Marks et al. 1990, Marks et al. 

43 2002). Eradication of rats will eliminate this source of mortality at Palmyra. 

44

45 There is expected to be some negative effects to migratory birds associated with the eradication 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 139

1 program. However, the Preferred Alternative includes several measures intended to minimize 

2 these effects. Shorebirds will be the most vulnerable to direct and secondary poisoning during 

3 the eradication, so the eradication is scheduled to occur during the summer nesting season, 

4 when the number of migratory shorebirds is at its lowest (June-July). Not all shorebirds migrate 

5 to the nesting grounds and we plan to capture as many of the remaining shorebirds as possible 

6 and hold them under direct, constant veterinary care during the period when they would be 

7 vulnerable to primary or secondary poisoning. Regular surveys of the island will be conducted 

8 and all carcasses that could potentially be a source of secondary poisoning will be removed. 

9 Color and size were considered when selecting the bait formulation to minimize the 

10 attractiveness of the bait to birds and minimize the time toxicant is available to birds. To 

11 minimize exposure potential to seabirds bait will be hand broadcast along the narrow causeways 

12 where the majority of the boobies nest, and this bait will not be distributed within reach of birds 

13 sitting in the nest. Areas known to host concentrations of shorebirds roosting will be baited using 

14 bait stations to further restrict bait availability.

15

16 The following is a breakdown of the direct toxicant and disturbance impacts to each of the 

17 identified bird species that migrate to, breed at, and overwinter at Palmyra. Additionally, we 

18 have quantified the number of individuals per species that are likely to be adversely affected by 

19 Alternative C (we have assumed the worst case scenario and consider any individuals that may 

20 be present on the atoll during the eradication operations to be vulnerable to adverse impacts from 

21 the action alternative). The take numbers for Action Alternative C are from runway and all-atoll 

22 shorebird counts conducted during the season (June-July) when breeding adults should be at their 

23 breeding grounds in Alaska, or from Depkin (2002).

24

25 Bristle-thighed curlew

26 Toxicant Risk

27 Bristle-thighed curlews could be exposed to brodifacoum through both primary and secondary 

28 exposure pathways. Generally, curlews forage in the intertidal zone for aquatic invertebrates and 

29 seabird eggs, and have been observed ignoring placebo (non-toxic) bait pellets when they are 

30 placed in the vicinity of more typical prey items – fiddler crabs (see Appendix F). Additionally, 

31 curlews are known to eat small fruit and insects in the forested areas of the atoll, and to a limited 

32 extent, prey on terrestrial hermit crabs (see Appendix I). The primary exposure pathway is 

33 limited to curlew‟s who forage in the forests and directly consume bait; whereas, the secondary 

34 exposure pathways include consumption of intertidal invertebrate species, hermit crabs, roaches, 

35 and other terrestrial invertebrates. The bait availability will be for the short-term, the mortality 

36 risk is high, and the exposure risk is high because of the range of toxicant exposure pathways.

37 The duration of the risk will likely be for the medium-term due to the retention time of the 

38 toxicant in the tissue of species that provide a secondary exposure pathway to curlews. The 

39 extent of the affect will be to the individuals that remain on the atoll after the captive hold and to 

40 those who could not be captured.

41

42 Disturbance Risk

43 Bristle-thighed curlews who remain at Palmyra during the aerial broadcast could be exposed to 

44 disturbances from both ground and air operations, which will likely cause curlews to flush the 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 140

1 area to an alternate site on the atoll. The impacts associated with disturbance risks for individuals 

2 that remain at Palmyra are low, the duration of the disturbance will be for the short-term, and the 

3 extent of the affect will be to the entire atoll population. The curlews that will be captured and 

4 held during the time that the bait is available in the environment will experience disturbance 

5 impacts from being captured, as well as, while they are in captivity. Curlews could experience 

6 increased stress, injury, risk of disease, and potential mortality from captive care operations. The 

7 risk level is high and will last for the medium-term to ensure that released birds will not be 

8 exposed to harmful concentrations of the toxicant (see Section 4.4.1.2.1). Captured individuals 

9 are at a high risk from disturbance impacts.

10

11 As many as 182 individuals could be exposed to impacts from Alternative C

12

13 Pacific golden-plover

14 Toxicant Risk

15 Pacific golden-plovers could be exposed to brodifacoum through both primary and secondary 

16 exposure pathways. Generally, plovers forage in the intertidal zone for aquatic invertebrates and 

17 insects. Additionally, plovers are known to eat insects in the forested areas of the atoll. The 

18 primary exposure pathway is limited to plovers that forage in the forests and consume 

19 rodenticide; whereas, the secondary exposure pathways include consumption of terrestrial 

20 invertebrates. The bait availability would be for the short-term, the mortality risk is high, and the 

21 exposure risk is high because of the range of toxicant exposure pathways, and the duration of the 

22 risk will likely be for the medium-term due to the retention time of the toxicant in the tissue of 

23 species that provide a secondary exposure pathway to plovers. The extent of the toxicant risk will 

24 be to the individuals that remain on the atoll after the captive hold, which is intended to mitigate 

25 the impacts to plovers from toxicant exposure.

26

27 Disturbance Risk

28 Pacific golden-plovers that remain at Palmyra during the aerial broadcast could be exposed to 

29 disturbances from both ground and air operations, which will likely cause plovers to flush the 

30 area to an alternate site on the atoll. The impacts associated with disturbance risks for individuals 

31 that remain at Palmyra are low, the duration of the disturbance will be for the short-term, and the 

32 extent of the affect will be to the entire atoll population. The plovers that will be captured and 

33 held during the time that the bait is available in the environment will experience disturbance 

34 impacts from being captured, as well as, while they are in captivity. Plovers could experience 

35 increased stress, injury, risk of disease, and potential mortality from captive operations. The risk 

36 level is high and will last for the medium-term to ensure that there will be no residual toxicant on 

37 the atoll. Captured individuals are at a high risk from disturbance impacts. 

38

39 As many as 62 individuals could be exposed to impacts from Alternative C.

40

41 Ruddy turnstone

42 Toxicant Risk

43 Ruddy turnstones could be exposed to brodifacoum through both primary and secondary 

44 exposure pathways. Generally, turnstones forage in the intertidal zone for aquatic invertebrates. 

45 Additionally, turnstones eat terrestrial insects and feed on carrion when available. The primary 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 141

1 exposure pathway is limited to turnstones who forage in the forests that consume rodenticide; 

2 whereas, the secondary exposure pathways include consumption of intertidal and terrestrial 

3 invertebrate species, carrion, and other terrestrial invertebrates that have consumed the toxicant. 

4 The bait availability would be for the short-term, the mortality risk is high, and the exposure risk 

5 is high because of the range of toxicant exposure pathways. The duration of the risk will likely 

6 be for the medium-term due to the retention time of the toxicant in the tissue of species that 

7 provide a secondary exposure pathway to turnstones. The extent of the affect will be to the entire 

8 atoll population.

9

10 Disturbance Risk

11 Ruddy turnstones could be exposed to disturbances from both ground and air operations, which 

12 will likely cause turnstones to flush the area to an alternate site on the atoll. The impacts 

13 associated with disturbance risks for this alternative are low, the duration of the disturbance will 

14 be for the short-term, and the extent of the affect will be to the entire atoll population.

15

16 As many as 35 individuals could be exposed to impacts from Alternative C.

17

18 Wandering tattler

19 Toxicant Risk

20 We expect that wandering tattlers would only be exposed to brodifacoum through secondary 

21 exposure pathways. Generally, tattlers forage in the intertidal zone for aquatic invertebrates at 

22 Palmyra. Tattlers feed on aquatic insects, mollusks, crustaceans, and small fish. The bait 

23 availability would be for the short-term, the mortality risk is high, and the exposure risk is 

24 moderate because of limited exposure to the rodenticide. The duration of the risk will likely be 

25 for the short-term due to the retention time of the toxicant in the tissue of species that provide a 

26 secondary exposure pathway to tattlers. The extent of the affect will be to individuals only 

27 because of the moderate exposure risk.

28

29 Disturbance Risk

30 Wandering tattlers could be exposed to disturbances from both ground and air operations, which 

31 will likely cause tattlers to flush the area to an alternative site on the atoll. The impacts 

32 associated with disturbance risks for this alternative are low, the duration of the disturbance will 

33 be for the short-term, and the extent of the affect will be to the entire atoll population.

34 As many as 48 individuals could be exposed to impacts from Alternative C.

35

36 Sanderling and pectoral sandpiper

37 Toxicant Risk

38 Sanderlings and pectoral sandpipers would only be exposed to brodifacoum through secondary 

39 exposure pathways. Generally, these species forage in the intertidal zone for aquatic 

40 invertebrates. The bait availability would be for the short-term, the mortality risk is high, and the 

41 exposure risk is low because of limited exposure to the rodenticide. The duration of the risk will 

42 likely be for the medium-term due to the retention time of the toxicant in the tissue of species 

43 that provide a secondary exposure pathway to tattlers. The extent of the affect will only be to a 

44 few individuals because the atoll populations of both sanderlings and pectoral sandpipers are 

45 relatively low at Palmyra.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 142

1 Disturbance Risk

2 Sanderlings and pectoral sandpipers could be exposed to disturbances from both ground and air 

3 operations, which will likely cause them to flush the area to an alternate site on the atoll. The 

4 impacts associated with disturbance risks for this alternative are low, the duration of the 

5 disturbance will be for the short-term, and the extent of the affect will be to the entire atoll 

6 population.

7 As many as five sanderling individuals are likely to be exposed to impacts from 

8 Alternative C.

9

10 As many as eight pectoral sandpiper individuals are likely to be exposed to 

11 impacts from Alternative C.

12

13 Laughing and Franklin‟s gull

14 Toxicant Risk

15 Laughing and Franklin‟s gulls could be exposed to brodifacoum through both primary and 

16 secondary exposure pathways. Generally, gulls are omnivorous and are often found foraging in 

17 the intertidal zone for aquatic and terrestrial invertebrates, eating seeds and plants, or feeding on 

18 carrion. The primary exposure pathway is significant because gulls are known to consume bait 

19 pellets. Additionally, the secondary exposure pathways include consumption of intertidal and 

20 terrestrial invertebrate species, carrion, and other terrestrial invertebrates that have consumed the 

21 toxicant. The bait availability would be for the short-term, the mortality risk is high, and the 

22 exposure risk is high because of the range of toxicant exposure pathways. The duration of the 

23 risk will likely be for the medium-term due to the retention time of the toxicant in the tissue of 

24 species that provide a secondary exposure pathway to gulls. The extent of the affect will be to 

25 individuals because gulls are very infrequent visitors of Palmyra.

26

27 Disturbance Risk

28 Franklin‟s and laughing gulls could be exposed to disturbances from both ground and air 

29 operations, which will likely cause gulls to flush the area to an alternative site on the atoll. The 

30 impacts associated with disturbance risks for this alternative are low, the duration of the 

31 disturbance will be for the short-term, and the extent of the affect will be to the entire atoll 

32 population.

33 One laughing gull individual may be exposed to impacts from Alternative C.

34

35 As many as nine Franklin‟s gull individuals may be exposed to impacts from 

36 Alternative C.

37

38 Northern shoveler and northern pintail 

39 Toxicant Risk

40 Northern shovelers and northern pintail ducks could be exposed to brodifacoum through both 

41 primary and secondary exposure pathways. Generally, ducks forage in small, inland ponds for 

42 aquatic invertebrates, eat terrestrial insects, and consume plants and seeds. Ducks are susceptible 

43 to primary exposure of the bait because they are granivorous and would likely be attracted to the 

44 grain matrix within the bait pellet. The secondary exposure pathways include consumption of 

45 intertidal and terrestrial invertebrate species that have consumed the toxicant. The bait 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 143

1 availability would be for the short-term, the mortality risk is high, and the exposure risk is 

2 medium because of the range of toxicant exposure pathways. The duration of the risk will likely 

3 be for the medium-term due to the retention time of the toxicant in the tissue of species that 

4 provide a secondary exposure pathway to ducks. We expect that fewer than ten individuals will 

5 be affected by the eradication because ducks are highly infrequent visitors to Palmyra.

6

7 Disturbance Risk

8 Northern shovelers and pintail ducks could be exposed to disturbances from both ground and air 

9 operations, which will likely cause ducks to flush the area to an alternate site on the atoll. The 

10 impacts associated with disturbance risks for this alternative are low, the duration of the 

11 disturbance will be for the short-term, and the extent of the affect will be on the individual level.

12 As many as six northern pintail individuals may be exposed to impacts from 

13 Alternative C.

14

15 As many as two northern shoveler individuals may be exposed to impacts from 

16 Alternative C.

17

18 Breeding seabirds (masked booby, brown booby, red-footed booby, great frigatebird, 

19 sooty tern, white tern, red-tailed tropicbird, white-tailed tropicbird, black noddy, and 

20 brown noddy)

21 Toxicant Risk

22 The breeding seabirds at Palmyra are at extremely low risk of toxicant exposure because they 

23 rarely if ever feed on anything other than marine organisms. The primary exposure pathway 

24 would be the accidental ingestion of toxicant during nest maintenance or preening. The risk of 

25 this type of exposure is extremely low, and even lower for species that do not build nests (sooty 

26 tern and white tern). We would minimize the potential of exposure of ground nesting boobies to 

27 toxicant by hand baiting the causeways where most brown and masked boobies nest and this bait 

28 will not be distributed within reach of birds sitting in the nest. We would minimize the potential 

29 for fish to be exposed to the toxicant by hand baiting near the shoreline and using an internal 

30 deflector system in the bait hopper to prevent bait from being broadcast into bodies of water; 

31 therefore, the extent of the affect is insignificant and does not require further scrutiny.

32

33 Disturbance Risk

34 Breeding seabirds are at a greater risk from disturbance because they will be attending nests and 

35 caring for young. The majority of the disturbance will come from both ground and air operations, 

36 which would cause individuals to flush from roosts and nests leaving eggs and chicks vulnerable 

37 to predation or injury. Additionally, there is a risk of breeding disturbance from the listed 

38 disturbance impacts; however, there will be limited aerial operations directly above ground 

39 breeding masked or brown booby colonies. The risk level from disturbance from aerial 

40 operations would be low. This is supported from research conducted by GECI on disturbance 

41 affect to booby populations on Isla Isabel from helicopter operations, which found little to no 

42 effect on booby colonies from helicopter operations (GECI 2009). Additionally, ground 

43 operations will be minimal near breeding colonies and will result in low disturbance impacts. 

44 The duration for the disturbance affect is for the short-term and the extent is to the entire atoll 

45 population.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 144

1 100,000 – 200,000 individuals are likely to be exposed to impacts from 

2 Alternative C.

3

4 Non-breeding seabirds (lesser frigatebird) 

5 Toxicant Risk

6 Lesser frigatebirds are at extremely low risk of toxicant exposure because they rarely if ever feed 

7 on anything other than marine organisms. We would minimize the potential for fish to be 

8 exposed to the toxicant by hand baiting near the shoreline and using an internal deflector system 

9 in the bait hopper to prevent bait from being broadcast into bodies of water; therefore, the extent 

10 of the affect is insignificant and does not require further scrutiny.

11

12 Disturbance Risk

13 Lesser frigatebirds could be exposed to disturbances from both ground and air operations, which 

14 will likely cause them to flush the area to an alternate site on the atoll. The impacts associated 

15 with disturbance risks for this alternative are low, the duration of the disturbance will be for the 

16 short-term, and the extent of the affect will be on the individual level.

17

18 20 individuals are likely to be exposed to impacts from Alternative C.

19

20 Impacts on Reptiles

21 Geckoes (native and nonnative)

22 Toxicant Risk

23 Geckoes are at risk of secondary exposure to rodenticide through the consumption of terrestrial 

24 invertebrates; however, there is a gap in the literature on the toxicity of anticoagulant 

25 rodenticides to reptiles. Additionally, even less is known about either the native or nonnative 

26 geckoes at Palmyra. Therefore, this assessment is likely deficient at examining all of the 

27 potential toxicant exposure pathways, as well as, the fate of individuals that consume bait 

28 through secondary pathways. The bait availability would be for the short-term, the mortality risk 

29 is high, and the exposure risk is medium. The duration of the risk is for the medium-term, and 

30 the extent is to the entire atoll population.

31

32 Disturbance Risk

33 Geckoes are at a negligible risk of disturbance from both ground and air operations because they 

34 are fairly elusive and have many alternative areas to retreat to during eradication operations; 

35 therefore, they are only vulnerable for the short-term and only to a few individuals.

36

37 Hawksbill turtle and green turtle

38 Toxicant Risk

39 Turtles may face a primary risk of exposure to the toxicant through eating bait directly as it 

40 drops through the water column. These turtles‟ common foraging behaviors make exposure 

41 unlikely, but juvenile green turtles in particular are known to be comparatively opportunistic 

42 feeders, and marine turtles have been documented ingesting marine debris elsewhere (Carr 

43 1987, Meylan 1988, NOAA Fisheries pers. comm., Bjorndal et al. 1994, Coyne 1994, Bugoni et 

44 al. 2001). Mitigation measures to reduce bait drift into waterways will be employed to reduce the 

45 exposure risk to turtles, including hand baiting narrow strips of land and portions of the coconut 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 145

1 palm canopy than cannot be safely and effectively baited by air, and using a deflector to control 

2 the direction of the bait flow from the hopper. Even if bait pellets enter the water at the full 

3 application rate, they will only be ingestible by turtles for a few hours prior to embedding in the 

4 sediment and breaking down to tiny fragments (Empson and Miskelly 1999). Thus, the duration 

5 of risk to turtles is for the very short term. The extent of risk is only to a few individuals. The risk 

6 of turtle mortality, given the low likelihood of exposure to the toxicant, is unknown but suspected 

7 to be low.

8

9 Disturbance Risk

10 Turtles could be exposed to disturbances from boat operations, which will likely cause turtles to 

11 flee from the immediate area. However, boat operations in association with the rat eradication 

12 would not exceed normal levels of boat use during the research season, and no negative impact 

13 to turtles has been associated with boat activities during the research season (A. Meyer pers. 

14 comm.). The impacts associated with disturbance risks for this alternative are low, the duration 

15 of the disturbance will be for the short-term, and the extent of the affect will be on the individual 

16 level.

17

18 Impacts on Fish

19 Fish (black-spotted sergeant, stripe belly puffer, camouflage grouper, bohar, black tail snapper, 

20 dusky farmerfish, and bonefish)

21 Toxicant Risk

22 Some fish species face both a primary and secondary risk of exposure to the toxicant through the 

23 consumption of aquatic invertebrates and by eating bait directly as it drops through the water 

24 column - species analyzed here either consumed or mouthed placebo bait during field trials at 

25 Palmyra Atoll in May 2010 (Alifano and Wegmann 2010) (see Appendix F). Little is known 

26 about the effect that brodifacoum has on fish; therefore, for the purposes of this analysis we are 

27 considering the mortality risk from brodifacoum to be high. Additionally, mitigation measures to 

28 reduce bait drift into waterways will be employed to further reduce the exposure risk to fish 

29 including hand baiting narrow strips of land and portions of the coconut palm canopy than 

30 cannot be safely and effectively baited by air, and using a deflector to control the direction of the 

31 bait flow from the hopper. The duration of risk is for the very short-term because bait pellets will 

32 only be available for a few hours prior to embedding in the sediment and breaking down to tiny 

33 fragments. The extent of risk is only to a few individuals.

34

35 Disturbance Risk

36 Fish could be exposed to disturbances from boat operations, which likely will cause fish to flush 

37 the immediate area. The impacts associated with disturbance risks for this alternative are low, the 

38 duration of the disturbance will be for the short-term, and the extent of the affect will be on the 

39 island population level.

40

41 Impacts on Invertebrates

42 Terrestrial crabs

43 Toxicant Risk

44 Terrestrial crabs are at both a primary and secondary risk of exposure to the brodifacoum bait 

45 from the consumption of bait pellets, carrion, invertebrates, or crab excrement. The exposure risk 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 146

1 is high; however, crabs show not adverse response to ad-lib consumption of bait (Alifano and 

2 Wegmann 2010). We anticipate no risk of mortality to the island population for the short-term.

3

4 Disturbance Risk

5 Disturbance risks to terrestrial crabs include minor impacts from ground operations, as well as a 

6 disruption of their typical foraging base by providing an alternative food source through the bait 

7 pellets. The duration of this disturbance would only be for the short-term, but the extent will be 

8 to the entire atoll population. 

9

10 Impacts on Vegetation

11 Toxicant Risk

12 Vegetation is at a negligible risk

13

14 Disturbance Risk

15 Vegetation is at a minor risk of disturbance by trampling from ground operations with the 

16 greatest threat from the introduction or dispersal of nonnative invasive plant species. The risk of 

17 spreading invasive plant species will be minimized by integrating biosecurity measures into the 

18 daily eradication operations. The duration of the affect will be for the very short-term.

19
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 147

1 Impacts Table for Alternative C: Biological Resources

Table 4.3. Impacts of Alternative C on Biological Resources 

Species

Bait 

availability1

Risk 

mortality -

toxicant 

use2

Toxicant 

exposure 

risk level3

Disturbance 

risk4

Extent of risk within a 

population5 Duration of risk6

toxicant disturbance toxicant disturbance

Bristle-thighed 

curlew Short High High/Low7 Low/ High8

Individ. Island Medium Short

Pacific goldenplover Short High High/

Low7 Low/ High8

Individ. Island Medium Short

Ruddy turnstone Short High High Low Island Island Medium Short

Wandering 

tattler Short High Moderate Low Individ. Island Short Short

Sanderling & 

pectoral 

sandpiper

Short High Low Low Individ. Island Medium Short

Laughing & 

Franklin‟s gull Short High High Low Individ. Island Medium Short

Northern 

shoveler & 

pintail duck

Short High Medium Low Individ. Individ. Medium Short

Breeding 

seabirds9 Low Low Low Low None Island None Short

Non-breeding 

seabirds10 Low Low Low Low None Individ. None Short

Geckoes11 Short High Medium Low Island Individ. Medium Short

Turtles12 Low Low Low Low Individ Individ. Short Short

Fish13 Short High Low Low Individ. Island Short Short

Terrestrial crabs Short None High Low Island Island Short Short

Vegetation None None None Low None Island None Short

1None: No toxicological sensitivity; Short: Bait or rats with toxicant residue available for up to 36 days; Medium: Bait in crab 

excrement or animal tissue available for 37-90 days; Long: Toxicant persistent anywhere in the environment for more than 90 

days. 

2None: No toxicological sensitivity; Low: Minor toxicological sensitivity; Medium: Moderate toxicological sensitivity; 

High: Severe toxicological sensitivity. 3None: No exposure pathway; Low: Possible exposure pathway; Medium: One exposure 

pathway; High: Multiple exposure pathways. 4None: No disturbance pathway; Low: Low sensitivity to disturbance; Medium: 

Moderate sensitivity to disturbance; High: Severe sensitivity to disturbance. 5Individual (Individ.): Few individuals affected; 

Island population (Island): Many individuals affected with no affect to the global or regional breeding population; Global or

regional population (Global): Many individuals affected with impacts on the global or regional breeding population. 6Short: 

Impacts for up to 2 months; Medium: Impacts for more than 2 months and up to 6 months; Long: Impacts for more than 6 

months. 7High toxicant risk for birds left at Palmyra, low toxicant risk for birds captively held. 8 Low disturbance risk for birds 

left at Palmyra, high disturbance risk for birds captively held. 9Breeding seabirds includes: masked booby, brown booby, redfooted booby, great frigatebird, sooty tern, white tern, red-tailed tropicbird, white-tailed tropicbirds, black noddy, and brown 

noddy10lesser frigatebird11. Native (Lepidodactylus n. sp) and nonnative mourning gecko. 12hawksbill turtle and green turtle. 

13black-spotted sergeant, stripe belly puffer, camouflage grouper, bohar, black tail snapper, dusky farmerfish, and bonefish. 

2

3

4

5

6

7
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 148

Table 4.4. Estimated populations of migratory birds at Palmyra Atoll and estimated take.

Common Name Scientific Name Estimated 

Palmyra 

Population

1

Estimated World 

Population

Estimated 

Take by 

Evaluating 

Risk 

Factors

Estimated 

Maximum 

Take

(Assuming 

100%)

Bristle-thighed curlew Numenius tahitiensis 266 10,0002140 182

Pacific golden-plover Pluvialis fulva 144 185,000-250,000245 62

Ruddy turnstone Arenaria interpres 112 450,000-600,000220 35

Wandering tattler Tringa incana 126 10,000-25,000335 48

Sanderling Calidris alba 5 590,00020 5

Pectoral sandpiper Calidris melanotos 8 >500,00030 8

Solitary sandpiper Tringa solitaria 1 150,00020 1

Semipalmated plover Charadrius 

semipalmatus

1 150,00020 1

Sharp-tailed sandpiper Calidris acuminata 3 160,00020 3

Buff-breasted 

sandpiper

Tryngites subruficollis 1 30,00030 1

Lesser yellowlegs Tringa flavipes 1 400,00020 1

Short-billed dowitcher Limnodromus griseus 

caurinus

5 75,00020 1

Cattle egret Bubulcus ibis >6,000,00020 5

Northern pintail Anas acuta 6 >4,000,00020 6

Northern shoveler Anas clypeata 2 >6,000,00020 2

Green-winged teal Anas crecca 

carolinensis

2 >2,000,00020 2

Lesser scaup Aythya affinis 2,950,00020 1

Laughing gull Leucophaeus atricilla 1 817,000-837,00020 1

Franklin's gull Leucophaeus pipixcan 9 470,000-1,490,00020 9

Breeding Seabirds (Assuming 

1%)

Black noddy Anous minutus 6,500 >560,00020 65

Brown noddy Anous stolidus 560 >1,000,00020 6

Sooty tern Onychoprion fuscatus 219,000 >21,000,00020 2,190

5

White tern Gygis alba 500 250,000-1,000,00020 5

Great frigatebird Fregata minor 400 500,000-1,000,0004 0 4

Lesser frigatebird Fregata aerial 20 >400,00040 1

White-tailed tropicbird Phaethon lepturus 10 <400,00040 1

Red-tailed tropicbird Phaethon rubricauda 400 35,000-45,00040 4

Red-footed booby Sula sula 12,500 <600,00040 125

Brown booby Sula leucogaster 740 440,000-550,00040 8

Masked booby Sula dactylatra 70 >200,00040 1

1 Maximum recent count /estimate; 2Wetlands International (2006); 3Morrison et al. (2006); 4

FWS (2005); 5 1 Take of 

2 seabirds is extremely unlikely and the estimated maximum take is assumed to be less than 1% of the individuals 

3 present. The calculated maximums for black noddies, sooty terns, and red-footed boobies are far greater than what is 

4 expected to take even in the worst case scenario. However, high numbers of these species breed at Palmyra so the 

5 calculated estimate (1%) is a large number. If sooty terns are not breeding during the operational window, the 

6 expected maximum take will equal zero. 

7

8
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 149

1 4.4.4.6 Impacts of Alternative D on biological resources

2

3 Impacts on Birds

4 Generally, birds that primarily eat plant matter such as seeds and fruits would initially be at high 

5 risk for primary exposure to brodifacoum. Predators and scavengers would in some cases be at 

6 high risk of secondary exposure to brodifacoum. Animals that feed on rats, rat carcasses, or large 

7 ground-dwelling invertebrates such as beetles would initially be at high risk of secondary 

8 exposure to brodifacoum. Birds that have a broad, omnivorous diet would initially be at high risk 

9 for both primary and secondary exposure.

10

11 Birds foraging in the intertidal zone would be at lower risk for primary exposure because pellets 

12 that enter the water would disintegrate and become unavailable within a few hours. Similarly, 

13 birds that forage primarily in the intertidal zone and specialize in intertidal invertebrates would 

14 only be at an initially low risk of secondary exposure. Also, birds that feed primarily on flying 

15 insects and “micro-invertebrates” would be at an initially low risk of secondary exposure due to 

16 the low likelihood that these classes of invertebrates would be carrying brodifacoum in their 

17 systems. The risk of exposure (secondary) in birds that feed on flying insects and “micro18 invertebrates”, would initially be low, and would steadily decline to negligible within a few 

19 months. The likelihood of exposure in intertidal specialists would decline even more rapidly, 

20 becoming negligible within 30 days of the final bait application.

21

22 The following is a breakdown of the direct toxicant and disturbance impacts to each of the 

23 identified bird species that migrate, breed, and overwinter at Palmyra. Additionally, we have 

24 quantified the number of individuals per species that are likely to be adversely affected by 

25 alternative D (we have assumed the worst case scenario and consider any individuals that may be 

26 present on the atoll during the eradication operations to be vulnerable to adverse impacts from 

27 the action alternative). The take numbers for bait station alternative D are from runway and all28 atoll shorebird counts conducted during winter months when the atoll‟s entire population 

29 (breeders and non-breeders) should be present, and from Depkin (2002):

30

31 Bristle-thighed curlew

32 Toxicant Risk

33 Bristle-thighed curlews could be exposed to brodifacoum through both primary and secondary 

34 exposure pathways. Generally, curlews forage in the intertidal zone for aquatic invertebrates and 

35 seabird eggs, and have been observed ignoring placebo (non-toxic) bait pellets when they are 

36 placed in the vicinity of more typical prey items – fiddler crabs (see Appendix F). Additionally, 

37 curlews are known to eat small fruit and insects in the forested areas of the atoll, and to a limited 

38 extent prey on terrestrial hermit crabs (see Appendix I). The primary exposure pathway is limited 

39 to curlews that forage in the forests and directly consume bait; whereas, the secondary exposure 

40 pathways include consumption of intertidal invertebrate species, hermit crabs, roaches, and other 

41 terrestrial invertebrates. The bait availability will be for the long-term due to the length of time 

42 bait stations will be on the ground, the mortality risk is high, and the exposure risk is low. The 

43 duration of the risk will likely be for the long-term because bait stations will be on the ground for 

44 up to 2 years, and the extent of the effect will be to individuals on the atoll due to the low 

45 exposure risk.
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 150

1 Disturbance Risk

2 Bristle-thighed curlews could be exposed to disturbances from both ground operations and 

3 maintenance of bait station transects, which will likely cause curlews to flush the area to an 

4 alternate site on the atoll and potentially alter their habitat. The impacts associated with 

5 disturbance risks for this alternative are very high, the duration of the disturbance will be for the 

6 long-term, and the extent of the effect will be to the entire atoll population. 

7

8 As many as 226 individuals are likely to be exposed to impacts from Alternative 

9 D.

10

11 Pacific golden-plover

12 Toxicant Risk

13 Pacific golden-plovers could be exposed to brodifacoum through both primary and secondary 

14 exposure pathways; however, with a bait station operation the exposure risk will be much less 

15 than with an aerial broadcast operation. Generally, plovers forage in the intertidal zone for 

16 aquatic invertebrates and insects. Additionally, plovers are known to eat insects in the forested 

17 areas of the atoll. The primary exposure pathway is limited to plovers that forage in the forests 

18 that consume rodenticide pellets that have been removed from bait stations; whereas, the 

19 secondary exposure pathways include consumption of intertidal invertebrate species, roaches, 

20 and other terrestrial invertebrates. The bait availability will be for the long-term due to the length 

21 of time that bait stations will be on the ground, the mortality risk is high, and the exposure risk is 

22 low. The duration of the risk will likely be for the long-term because bait stations will be on the 

23 ground for up to 2 years, and the extent of the effect will be to individuals on the atoll.

24

25 Disturbance Risk

26 Pacific golden-plovers could be exposed to disturbances from both ground operations and 

27 maintenance of bait station transects, which will likely cause plovers to flush the area to an 

28 alternate site on the atoll and potentially alter their habitat. The impacts associated with 

29 disturbance risks for this alternative are very high, the duration of the disturbance will be for the 

30 long-term, and the extent of the effect will be to the entire atoll population.

31

32 As many as 88 individuals are likely to be exposed to impacts from Alternative D.

33

34 Ruddy turnstone

35 Toxicant Risk

36 Ruddy turnstones could be exposed to brodifacoum through both primary and secondary 

37 exposure pathways; however, with a bait station operation the exposure risk will be much less 

38 than with an aerial broadcast operation. Generally, turnstones forage in the intertidal zone for 

39 aquatic invertebrates. Additionally, turnstones eat terrestrial insects and feed on carrion when 

40 available. The primary exposure pathway is limited to turnstones that forage in the forests that 

41 consume rodenticide pellets that have been removed from bait stations; whereas, the secondary 

42 exposure pathways include consumption of intertidal and terrestrial invertebrate species, carrion, 

43 and other terrestrial invertebrates that have consumed the toxicant. The bait availability would be 

44 for the long-term due to the length of time that bait stations would be on the ground, the 

45 mortality risk is high, and the exposure risk is low. The duration of the risk will likely be for the 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 151

1 long-term because bait stations will be on the ground for up to 2 years, and the extent of the 

2 effect will be to individuals on the atoll due to the low exposure risk.

3

4 Disturbance Risk

5 Ruddy turnstones could be exposed to disturbances from both ground operations and 

6 maintenance of bait station transects, which will likely cause turnstones to flush the area to 

7 alternate site on the atoll and potentially alter their habitat. The impacts associated with 

8 disturbance risks for this alternative are very high, the duration of the disturbance will be for the 

9 long-term, and the extent of the affect will be to the entire atoll population.

10

11 As many as 28 individuals are likely to be exposed to impacts from Alternative D.

12

13 Wandering tattler, sanderling, and pectoral sandpiper

14 Toxicant Risk

15 Wandering tattlers, sanderlings, and pectoral sandpipers are at no risk of toxicant exposure 

16 because they rarely if ever feed on anything other than intertidal invertebrates at Palmyra, which 

17 will not be exposed to the rodenticide through a bait station operation. Therefore, the extent of 

18 the effect is insignificant and does not require further scrutiny.

19

20 Disturbance Risk

21 Wandering tattlers, sanderlings, and pectoral sandpipers could be exposed to disturbances from 

22 both ground operations and maintenance of bait station transects, which will likely cause them to 

23 flush the area to an alternate site on the atoll. The impacts associated with disturbance risks for 

24 this alternative are very high, the duration of the disturbance will be for the long-term, and the 

25 extent of the effect will be to the entire atoll population.

26

27 As many as 37 wandering tattler individuals are likely to be exposed to impacts 

28 from Alternative D.

29

30 As many as five sanderling individuals are likely to be exposed to impacts from 

31 Alternative D.

32

33 As many as eight pectoral sandpiper individuals are likely to be exposed to 

34 impacts from Alternative D.

35

36 Laughing and Franklin‟s gull

37 Toxicant Risk

38 Laughing and Franklin‟s gulls could be exposed to brodifacoum through primary and secondary 

39 exposure pathways; however, with a bait station operation the exposure risk will be much less 

40 than with an aerial broadcast operation. Generally, gulls are omnivorous and are often found 

41 foraging in the intertidal zone for aquatic and terrestrial invertebrates, eating seeds and plants, or 

42 feeding on carrion. The secondary exposure pathways include consumption of intertidal and 

43 terrestrial invertebrate species, carrion, and other terrestrial invertebrates that have consumed the 

44 toxicant. The bait availability would be for the long-term due to the length of time that bait 

45 stations will be on the ground, the mortality risk is high, and the exposure risk is low. The 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 152

1 duration of the risk will likely be for the long-term because bait stations will be on the ground for 

2 up to 2 years, and the extent of the effect will be to individuals on the atoll due to the low 

3 exposure risk.

4

5 Disturbance Risk

6 Franklin‟s and laughing gulls could be exposed to disturbances from both ground operations and 

7 maintenance of bait station transects, which will likely cause gulls to flush the area to an 

8 alternate site on the atoll and potentially alter their habitat. The impacts associated with 

9 disturbance risks for this alternative are very high, the duration of the disturbance will be for the 

10 long-term, and the extent of the effect will be to the entire atoll population.

11

12 As many as 10 individuals are likely to be exposed to impacts from Alternative D.

13

14 Northern shoveler and pintail duck

15 Toxicant Risk

16 Northern shovelers and northern pintail ducks could be exposed to brodifacoum through both 

17 primary and secondary exposure pathways. Generally, ducks forage in small, inland ponds for 

18 aquatic invertebrates, eat terrestrial insects, and consume plants and seeds. Ducks are susceptible 

19 to primary exposure of the bait because they are granivorous and would likely be attracted to the 

20 grain matrix within the bait pellet. The secondary exposure pathways include consumption of 

21 intertidal and terrestrial invertebrate species that have consumed the toxicant. With a bait station 

22 operation, it is unlikely that ducks will have access to bait, however it is possible that they could 

23 consume terrestrial invertebrates have consumed bait. The duration of the risk will likely be for 

24 the long-term because bait stations will be on the ground for up to 2 years, and the extent of the 

25 effect will be to individuals on the atoll due to the low exposure risk.

26

27 Disturbance Risk

28 Northern shovelers and pintail ducks could be exposed to disturbances from both ground 

29 operations and maintenance of bait station transects, which will likely cause ducks to flush the 

30 area to an alternate site on the atoll and potentially alter their habitat. The impacts associated 

31 with disturbance risks for this alternative are very high, the duration of the disturbance will be 

32 for the long-term, and the extent of the effect will be to a few individuals.

33

34 As many as 10 individuals are likely to be exposed to impacts from Alternative D.

35

36 Ground-nesting seabirds (brown and masked booby, red-tailed tropicbird, sooty tern)

37 Toxicant Risk

38 Ground nesting seabirds are at no risk of toxicant exposure because they rarely if ever feed on 

39 anything other than fish, which will not be exposed to the rodenticide through a bait station 

40 operation. Therefore, the extent of the effect is insignificant and does not require further scrutiny.

41

42 Disturbance Risk

43 Ground nesting seabirds could be exposed to disturbances from ground operations, breeding 

44 disturbance, and maintenance of bait station transects, which will likely cause seabirds to flush 

45 the area to an alternate site on the atoll leaving eggs and chicks vulnerable to predation, as well 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 153

1 as, potentially altering their habitat. The impacts associated with disturbance risks for this 

2 alternative are very high, the duration of the disturbance will be for the long-term, and the extent 

3 of the effect will be to the entire atoll population.

4

5 100,000 – 150,000 individuals are likely to be exposed to impacts from 

6 Alternative D.

7

8 Tree-nesting seabirds (red-footed booby, white tern, black and brown noddy, great frigatebird)

9 Toxicant Risk

10 Tree nesting seabirds are at no risk of toxicant exposure because they rarely if ever feed on 

11 anything other than fish, which will not be exposed to the rodenticide through a bait station 

12 operation. Therefore, the extent of the affect is insignificant and does not require further scrutiny.

13

14 Disturbance Risk

15 Tree nesting seabirds could be exposed to disturbances from ground operations, breeding 

16 disturbance, and maintenance of bait station transects, which will likely cause seabirds to flush 

17 the area to an alternate site on the atoll leaving eggs and chicks vulnerable to predation, as well 

18 as, potentially altering their habitat. The impacts associated with disturbance risks for this 

19 alternative are very high, the duration of the disturbance will be for the long-term, and the extent 

20 of the effect will be to the entire atoll population.

21

22 20,000-50,000 individuals are likely to be exposed to impacts from Alternative D.

23

24 Lesser frigatebird

25 Toxicant Risk

26 Lesser frigatebirds are at no risk of toxicant exposure because they rarely if ever feed on 

27 anything other than fish, which will not be exposed to the rodenticide through a bait station 

28 operation. Therefore, the extent of the effect is insignificant and does not require further scrutiny.

29

30 Disturbance Risk

31 Lesser frigatebirds could be exposed to disturbances from both ground operations and 

32 maintenance of bait station transects, which will likely cause frigatebirds to flush the area to an 

33 alternate location on the atoll and potentially alter their habitat. The impacts associated with 

34 disturbance risks for this alternative are very high, the duration of the disturbance will be for the 

35 long-term, and the extent of the effect will be to a few individuals.

36

37 20-30 individuals are likely to be exposed to impacts from Alternative D.

38

39 Impacts on Reptiles

40 Geckoes (native and nonnative)

41 Toxicant Risk

42 Geckoes are at risk of secondary exposure to rodenticide through the consumption of terrestrial 

43 invertebrates; however, there is a gap in the literature on the toxicity of anticoagulant 

44 rodenticides to reptiles. Additionally, even less is known about either the native or nonnative 

45 geckoes at Palmyra. Therefore, this assessment is likely deficient at examining all of the 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 154

1 potential toxicant exposure pathways, as well as, the fate of individuals that consume bait 

2 through secondary pathways. The bait availability would be for the long-term due to the length 

3 of time that bait stations will be on the ground, the exposure risk is low, the mortality risk is 

4 high, the duration of the risk is for the long-term, and the extent is to the entire atoll population.

5

6 Disturbance Risk

7 Geckoes could be exposed to disturbances from both ground operations and maintenance of bait 

8 station transects, which will likely alter their habitat. The impacts associated with disturbance 

9 risks for this alternative are high, the duration of the disturbance will be for the long-term, and 

10 the extent of the effect will be to a few individuals.

11

12 Hawksbill turtle and green turtle

13 Toxicant Risk

14 Turtles may face a primary risk of exposure to the toxicant through eating bait directly as it 

15 drops through the water column. These turtles‟ common foraging behaviors make exposure 

16 unlikely, but juvenile green turtles in particular are known to be comparatively opportunistic 

17 feeders, and marine turtles have been documented ingesting marine debris elsewhere (Carr 

18 1987, Meylan 1988, NOAA Fisheries pers. comm., Bjorndal et al. 1994, Coyne 1994, Bugoni et 

19 al. 2001). By limiting the spread of bait to bait stations placed inland of the high tide line, bait 

20 would only enter the marine environment by human error, such as spilling bait while moving 

21 from one bait station transect to the next. Any bait pellets that do enter the water will only be 

22 ingestible by turtles for a few hours prior to embedding in the sediment and breaking down to 

23 tiny fragments (Empson and Miskelly 1999). Thus, the duration of risk to turtles is for the very 

24 short term. The extent of risk is essentially negligible. The risk of turtle mortality, given the 

25 extremely low likelihood of exposure to the toxicant, is unknown but suspected to be negligible.

26

27 Disturbance Risk

28 Turtles could be exposed to disturbances from boat operations, which will likely cause turtles to 

29 flee from the immediate area. However, boat operations in association with the rat eradication 

30 would not exceed normal levels of boat use during the research season, and no negative impact 

31 to turtles has been associated with boat activities during the research season (A. Meyer pers. 

32 comm.). The impacts associated with disturbance risks for this alternative are low, the duration 

33 of the disturbance will be for the short-term, and the extent of the effect will be on the individual 

34 level.

35

36 Impacts Fish

37 Fish (black-spotted sergeant, stripe belly puffer, camouflage grouper, bohar, black tail snapper, 

38 dusky farmerfish, and bonefish)

39 Toxicant Risk

40 Some fish species face both a primary and secondary risk of exposure to the toxicant through the 

41 consumption of aquatic invertebrates and by eating bait directly as it drops through the water 

42 column - species analyzed here either consumed or mouthed placebo bait during field trials at 

43 Palmyra Atoll in May 2010 (Alifano and Wegmann 2010) (see Appendix F). Little is known 

44 about the effect that brodifacoum has on fish; therefore, for the purposes of this analysis we are 

45 considering the mortality risk from brodifacoum to be high. Additionally, by limiting the spread 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 155

1 of bait to bait stations placed inland of the high tide line, bait would only enter the marine 

2 environment by human error, such as spilling bait while moving from one bait station transect to 

3 the next. The duration of risk is for the very short-term because bait pellets will only be available 

4 for a few hours prior to embedding in the sediment and breaking down to tiny fragments. The 

5 extent of the toxicant risk is only to a few individuals.

6

7 Disturbance Risk

8 Fish could be exposed to disturbances from boat operations, which likely will cause fish to flush 

9 the immediate area. The impacts associated with disturbance risks for this alternative are low, the 

10 duration of the disturbance will be for the short-term, and the extent of the effect will be on the 

11 island population level.

12

13 Impacts on Invertebrates

14 Terrestrial crabs

15 Toxicant Risk

16 Terrestrial crabs are at both a primary and secondary risk of exposure to the brodifacoum bait 

17 from the consumption of bait pellets, carrion, invertebrates, or crab excrement. The exposure risk 

18 is medium because crabs would likely attempt to break into bait stations and consume the bait; 

19 however, crabs are not susceptible to the toxicant (Alifano and Wegmann 2010) resulting in no 

20 risk of mortality to individuals for the long-term.

21

22 Disturbance Risk

23 Disturbance risks to terrestrial crabs include minor impacts from ground operations and 

24 maintenance of bait station transects, as well as a disruption of their typical foraging base by 

25 providing an alternative food source through the bait pellets. The disturbance risk will be very 

26 high. The duration will be for the long-term, and the extent will be to the entire atoll population. 

27

28 Impacts on Vegetation

29 Toxicant risk

30 Vegetation is at no risk of toxicant impacts because brodifacoum lacks any herbicidal properties; 

31 therefore, the extent of the affect is insignificant and does not require further scrutiny

32

33 Disturbance Risk

34 Vegetation is at a risk of disturbance from trampling by ground operations and maintenance of 

35 bait station transects (28.5 miles of 1m transect would be established and maintained) with the 

36 greatest threat from the introduction or dispersal of nonnative invasive plant species. The risk of 

37 spreading invasive plant species will be minimized by integrating biosecurity measures into the 

38 daily eradication operations. The disturbance risk is very high; the duration of the affect will be 

39 for the long-term, and will affect the entire atoll community.

40
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 156

1 Impacts Table for Alternative D: Biological Resources

Table 4.5. Impacts of Alternative D on Biological Resources 

Species

Bait 

availability1

Risk 

mortality -

toxicant 

use2

Toxicant 

exposure 

risk level3

Disturbance 

risk4

Extent of risk within a 

population5 Duration of risk

6

toxicant disturbance toxicant disturbance

-thighed curlew Long High Low High Individ. Island Long Long

Pacific goldenplover Long High Low High Individ. Island Long Long

Ruddy turnstone Long High Low High Individ. Island Long Long

Wandering 

tattler None None None High None Island None Long

Sanderling & 

pectoral 

sandpiper

None None None High None Island None Long

Laughing & 

Franklin‟s gull Long High Low High Individ. Island Long Long

Northern 

shoveler & 

pintail duck

None Low Low High Low Individ. None Long

Ground-nesting 

seabirds7 None None None High None Island None Long

Tree-nesting 

seabirds8 None None None High None Island None Long

Lesser 

frigatebird None None None High None Individ. None Long

Geckoes9

Long High Low High Island Individ. Long Long

Turtles10 None None None Low None Individ. None Short

Fish11 None None None Low None Island None Short

Terrestrial crabs Long None Medium High Individ. Island None Long

Vegetation None None None High None Island None Long

1None: No toxicological sensitivity; Short: Bait or rats with toxicant residue available for up to 36 days; Medium: Bait in crab 

excrement or animal tissue available for 37-90 days; Long: Toxicant persistent anywhere in the environment for more than 90 

days. 

2None: No toxicological sensitivity; Low: Minor toxicological sensitivity; Medium: Moderate toxicological sensitivity; 

High: Severe toxicological sensitivity. 3None: No exposure pathway; Low: Possible exposure pathway; Medium: One exposure 

pathway; High: Multiple exposure pathways. 4None: No disturbance pathway; Low: Low sensitivity to disturbance; Medium: 

Moderate sensitivity to disturbance; High: Severe sensitivity to disturbance. 5Individual (Individ.): Few individuals affected; 

Island population (Island): Many individuals affected with no affect to the global or regional breeding population; Global or 

regional population (Global): Many individuals affected with impacts on the global or regional breeding population. 6Short: 

Impacts for up to 2 months; Medium: Impacts for more than 2 months and up to 6 months; Long: Impacts for more than 6 

months. 7Ground-nesting seabirds includes: masked booby, brown booby, red-tailed tropicbird, sooty tern. 8Tree-nesting 

Shorebirds includes: red-footed booby, white tern, black noddy, brown noddy, great frigatebird. 9Native (Lepidodactylus n. sp) 

and nonnative mourning gecko. 10hawksbill turtle and green turtle. 11black-spotted sergeant, stripe belly puffer, camouflage 

grouper, bohar, black tail snapper, dusky farmerfish, and bonefish.

2

3

4
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 157

1 4.4.5 Indirect Impacts to Biological Resources

2 Indirect Impacts or secondary effects are not directly linked to the original action and are 

3 removed from it by distance or time. Indirect effects often include socioeconomic impacts such 

4 as community growth or changes in population patterns as a result of implementation of a 

5 proposed action. Additionally, indirect impacts often far exceed those of direct impacts and 

6 include both positive outcomes and long-term negative impacts. The following is an analysis of 

7 the indirect impacts from each of the three alternatives.

8

9 4.4.5.1 Indirect effects under Alternative A

10 Alternative A, the no action alternative, would leave rats at Palmyra. Rats will continue to impact 

11 the atoll by altering vegetation communities (Wegmann 2009), reduce the breeding success of 

12 seabirds (Norman 1975), and impact important ecosystem processes (Young et al. 2010). 

13 Specifically, rats will continue to depress the recruitment of native tree species through seed and 

14 seedling predation. Furthermore, rats create breeding habitat for invasive mosquitoes that could 

15 be vectors West Nile virus, avian malaria, and dengue. 

16

17 4.4.5.2 Indirect effects under common to all action alternatives

18 The three action alternatives are designed to remove invasive rats from Palmyra. By removing 

19 rats from the atoll, some seabirds should experience higher reproductive success, and seabird 

20 species that are conspicuously absent from the atoll may reestablish. Native vegetation would be 

21 released from rat-related recruitment limitations, which would lead to a long term increase in 

22 preferred nesting habitat for tree-nesting seabirds. Nonnative vegetation could likewise be 

23 released. Vegetation communities would be monitored for responses to rat removal.

24

25 4.5 Impacts to the Social and Economic Environment

26

27 4.5.1 Eradication Personnel

28

29 4.5.1.1 Alternative A – No Action

30 Eradication personnel will not be on the island, and therefore, would experience no impacts. 

31 However, the personnel that maintain and utilize the research station would continue to 

32 experience rat-related loss of food stores, damage to supplies and equipment, and rat-related 

33 degradation of the natural environment.

34

35 4.5.1.2 Alternative B

36 Eradication personnel would experience minor noise impacts from helicopter operations during 

37 the aerial baiting process. This impact would only impact personnel for a very short period of 

38 time and would not be likely to result in any long-term impacts.

39

40 4.5.1.3 Alternative C – Preferred Alternative

41 Eradication personnel would experience minor noise impacts from helicopter operations during 

42 the aerial baiting process. This impact would only impact personnel for a very short period of 

43 time and will not be likely to result in any long-term impacts.

44
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 158

1 4.5.1.4 Alternative D

2 Eradication personnel would be subject to the physical stress of establishing and maintaining an 

3 extensive network of bait stations in difficult working conditions. 

4

5 4.5.2 Refuge Visitors and Recreation

6 The CEQ guidelines at 40 CFR 1508.14 include the human relationship with the natural 

7 environment as a category of potential impacts that must be considered in a National 

8 Environmental Policy Act (NEPA) analysis. This is interpreted to mean that a NEPA analysis 

9 needs to examine the potential effects of an action on any economic and/or social values that are 

10 related to the natural environment.

11

12 4.5.2.1 Analysis framework for refuge visitors and recreation

13 Public access to Palmyra is limited due to the remoteness of the atoll, and is by permit only. This 

14 analysis will examine the likely changes to visitor experience as a result of all the action 

15 alternatives. The Service would consider any major, long-term changes to the visitor experience 

16 to be significant.

17

18 Alternative A – No Action

19 There will be no effect to refuge visitors under the no action alternative. During the eradication 

20 and for 2 years afterwards, signs that inform visitors about the potential risks inherent to 

21 toxicant-based rodent eradication projects would be posted, along with signs that described the 

22 anticipated benefit that would come to Palmyra‟s terrestrial ecosystem due to rat removal.

23

24 Alternative B

25 The area immediately surrounding Palmyra Atoll will be closed to recreational boater access 

26 during aerial bait application operations, which would be a minor short-term inconvenience to 

27 the few refuge visitors that are likely to frequent Palmyra. During the eradication and for 2 years 

28 afterwards, signs that inform visitors about the potential risks inherent to toxicant-based rodent 

29 eradication projects would be posted, along with signs that described the anticipated benefit that 

30 would come to Palmyra‟s terrestrial ecosystem due to rat removal.

31

32 Alternative C – Preferred Alternative

33 The area immediately surrounding Palmyra Atoll will be closed to recreational boater access 

34 during aerial bait application operations, which would be a minor short-term inconvenience to 

35 the few refuge visitors that are likely to frequent Palmyra. During the eradication and for 2 years 

36 afterwards, signs that inform visitors about the potential risks inherent to toxicant-based rodent 

37 eradication projects would be posted, along with signs that described the anticipated benefit that 

38 would come to Palmyra‟s terrestrial ecosystem due to rat removal.

39

40 Alternative D

41 There will be no effect to refuge visitors during the implementation of alternative D. During the 

42 eradication and for 2 years afterwards, signs that inform visitors about the potential risks inherent 

43 to toxicant-based rodent eradication projects would be posted, along with signs that described the 

44 anticipated benefit that would come to Palmyra‟s terrestrial ecosystem due to rat removal.

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 159

1 4.5.3 Historical and Cultural Resources

2 4.5.3.1 Analysis framework for historical and cultural resources

3 The National Historic Preservation Act (NHPA) defines the concept of an “adverse affect” to 

4 historical resources, but the regulations make it clear that “a finding of adverse effect on a 

5 historic property does not necessarily require an EIS under NEPA” (36 CFR 800.8(a)(1)). 

6 Section 106 of the NHPA requires agencies to consult with the appointed regional Historic 

7 Preservation Officer(s) if adverse impacts to historical or cultural resources are possible. This 

8 analysis will describe the potential impacts to historical and cultural resources at Palmyra Atoll 

9 as a reference for consultation with the appropriate Historic Preservation Officers. The majority 

10 of the cultural and historical artifacts are remnants of World War II era activities at Palmyra 

11 including: bunkers, pill boxes, concrete buildings, concrete foundations, bottles, silverware, 

12 barbed wire, and unexploded ordinances. 

13

14 Alternative A – No Action

15 The Service has no evidence that rat activities affect historical and cultural resources on the atoll. 

16 Rats are burrowing animals, a behavior that has the potential to damage buried artifacts, but there 

17 are crab species that burrow on the atoll as well, which makes the preservation of buried artifacts 

18 at Palmyra difficult, whether or not rats are present. Rats may continue to cause damage to the 

19 historical buildings at Palmyra, but this damage would likely be minor and would not likely be 

20 irreversible.

21

22 Alternative B

23 Alternative B would not involve activities that would require soil disruption or any other actions 

24 that would affect the historical or cultural resources at Palmyra.

25

26 Alternative C– Preferred Alternative

27 Alternative C would not involve activities that would require soil disruption or any other actions 

28 that would affect the historical or cultural resources at Palmyra.

29

30 Alternative D

31 Because the bait stations would be placed over the entire atoll, there is high likelihood that some 

32 of the excavations would uncover artifacts related to WWII. Therefore, installing the bait 

33 stations throughout the entire atoll would be considered an undertaking with the potential to 

34 affect a historic property and would require compliance with Section 106 of the National 

35 Historic Preservation Act including identification, evaluation, and assessment of effects for 

36 Alternative D.

37

38 4.6 Consequences: Cumulative Impacts

39

40 4.6.1 Assessing Cumulative Impacts

41 The NEPA regulations require Federal agencies to consider not just the direct and indirect 

42 impacts of an action but also the cumulative impacts to which an action would contribute. 

43 Analyzing cumulative impacts at Palmyra Atoll requires consideration of other, unrelated 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 160

1 impacts that are occurring simultaneously to those resources, impacts that have occurred in the 

2 past, or impacts that are likely to occur in the foreseeable future. The continued presence of rats 

3 is likely affecting many of the species on the atoll and the biogeochemical cycles that those 

4 species drive, but there are no other clear localized impacts known to be occurring today. 

5 Furthermore, there are no foreseeable future human actions on the atoll that are likely to 

6 negatively affect the atoll‟s environment, because the land is being managed in perpetuity as a 

7 National Wildlife Refuge. However, many of the species at Palmyra may still be recovering from 

8 severe past impacts. Also, many of the species that use Palmyra Atoll have large ranges. These 

9 far-ranging populations may have been affected in the past, may be currently experiencing 

10 unrelated impacts, or may be at risk of impacts from foreseeable consequences elsewhere in their 

11 ranges. 

12

13 The following is a breakdown of the past, present, and foreseeable future actions that will likely 

14 contribute to the cumulative impacts associated with the three identified alternatives. Direct and 

15 indirect impacts from each alternative will be analyzed with the following list of activities to 

16 determine the cumulative impacts for the given alternative.

17

18 4.6.1.1 Past actions 

19 Past actions are actions that occurred in the past but have lasting impacts that could contribute to 

20 the impacts associated with the proposed action.

21 Failed rat eradication – In 2002 there was an attempt to eradicate rats from Palmyra with 

22 the use of bait stations and brodifacoum bait. The eradication failed and resulted in the 

23 continued presence of rats; however, the currently proposed eradication would counter 

24 this impact from the previous eradication attempt and would not negatively contribute to 

25 the impacts from the proposed action.

26

27 Military occupation since World War II – Likely introduction of nonnative rats and ants, 

28 both of which have negative impacts on almost all facets of the terrestrial ecosystem.

29

30 Construction of a fish processing facility – A facility was built in the late 1990s with no 

31 lasting impacts that would contribute to the impacts from the proposed action.

32

33 Construction of TNC camp – In the early 2000s a camp was built with no lasting impacts 

34 that would contribute to the impacts from the proposed action.

35

36 TNC camp upgrade – In 2005 TNC updated the camp with no lasting impacts that would 

37 contribute to the impacts from the proposed action.

38

39 4.6.1.2 Current actions 

40 Current actions are actions that are occurring within the same timeframe as the proposed action, 

41 or within the planning and compliance phase of the proposed action, and could contribute to the 

42 impacts from the proposed action.

43
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 161

1  Runway maintenance – The runway at Palmyra Atoll is regularly graded and maintained 

2 by TNC. This process does not have a direct negative impact on native species, and could 

3 be seen as a benefit to shorebirds – the runway is the most commonly used roosting site 

4 for all of Palmyra‟s shorebird species.

5

6  Anthropogenic climate change - The four areas of impact linked to global climate change 

7 that may have the greatest potential effect at Palmyra Atoll are sea level rise, weather 

8 changes, coral bleaching, and oceanic chemical composition change (often called ocean 

9 acidification). Of these, sea level rise is most applicable to this terrestrial analysis. Insert 

10 in line 5, page 148. ....temperature of 0.5 to 1.0 "degrees" C by 2090. Regional 

11 predictions (IPCC 2007) for the North Central Pacific Gyre area are for increases of 

12 surface temperature of 0.5 to 1.0 °C by 2090. More recently, New et al. (2011) indicate 

13 the likelihood of temperature rises of 3 or 4 "degrees" C within this century. Palmyra‟s 

14 terrestrial ecology will be affected by increasing rainfall and it is likely that future 

15 tropical cyclones (typhoons and hurricanes will become more intense, with larger peak 

16 wind speeds and more heavy precipitation associated with ongoing increases of tropical 

17 sea surface temperatures at all sites. Localized variations in subsidence and emergence of 

18 the sea floor and plate-tectonics activity prevent extrapolations in sea level fluctuations 

19 and trends between different regions. Thus, it may not be possible to discuss uniform 

20 changes in sea level on a global scale, or the magnitude of greenhouse gas-forced 

21 changes as these changes may vary regionally (Michener et al. 1997) but it is certain that 

22 sea level will rise and contribute to shoreline erosion and salt water intrusion into 

23 subsurface freshwater aquifers as have already been noted throughout the Pacific (Shae et 

24 al. 2001). Coral bleaching and oceanic chemical composition changes will likely affect 

25 structure and ecosystem services of the coral reef atoll.

26

27  Scientific research - The combination of its location, isolation, rich biological systems, 

28 and lack of persistent human pressures make Palmyra an exceptional and unique location 

29 for a wide range of research pertaining to biodiversity, conservation, natural history, 

30 ecosystem restoration, marine ecosystem dynamics, biogeochemistry, climate dynamics, 

31 and atmospheric processes. Scientists and institutions interested in studying the natural 

32 systems of Palmyra Atoll and its surrounding region have united to form a partnership, 

33 the Palmyra Atoll Research Consortium (PARC). The current research projects that may 

34 contribute to the cumulative impacts of the proposed action include (each project will be 

35 evaluated for impacts separately):

36

37 Biodiversity research - Biodiversity research at Palmyra focuses on the 

38 characterization of compositions, distributions, and interactions in the marine 

39 environment. This effort includes comprehensive biological surveys along with 

40 biophysical, biogeochemical, and ecological analyses designed to understand the 

41 importance of organisms, ranging from microbes to top predators, to ecosystem 

42 function. All of these projects are focused on marine biodiversity and would not 

43 contribute to the cumulative impacts from the proposed action.

44

45
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 162

1 Top predator research – The reefs and lagoons of Palmyra are home to abundant 

2 predator populations proving great opportunities for researchers to study the 

3 importance of predators in the marine environment. These projects aim at 

4 increasing our understanding of the roles that predators play in shaping marine 

5 ecosystems by documenting, in detail, the ecological linkages and dynamics 

6 affected by predators. These projects are focused on marine predators and would 

7 not contribute to the cumulative impacts from the proposed action.

8

9 Lagoon research – Lagoon research at Palmyra Atoll is focused on characterizing 

10 and quantifying the dynamics of lagoon ecosystems in terms of hydrology, 

11 sediment supply and transportation, and biology. The majority of the impacts 

12 from U.S. military occupation stem from lagoon modification and long term 

13 occupation during World War II. These alterations are in the process of breaking 

14 down, which causes sediment to redistribute via natural processes. These projects 

15 would not contribute to the cumulative impacts from the proposed action.

16

17 Conservation research – Conservation research is focused on understanding the 

18 current invasive species problems at Palmyra and instigating mitigation and 

19 restoration efforts, as well as, monitoring ongoing physical and biological changes 

20 to the atoll ecosystem. These projects could positively contribute to the 

21 cumulative impacts of the proposed action and will likely decrease the overall 

22 impacts that invasive species have on the atoll. 

23

24 Climate and biogeography research – Climate and biogeography research will 

25 help explain the changing climate and oceanographic regime in a key region of 

26 the global ocean. It is hoped that the researchers will develop a greater 

27 understanding of the affect that changing ocean temperatures and ocean chemistry 

28 has on atoll ecology and assess the short-term and long-term effects for similar 

29 atoll systems. These projects would not add to the cumulative impacts of the 

30 proposed action.

31

32 Future Actions – actions that are reasonably foreseeable in the future that could contribute to 

33 the cumulative impacts from the proposed action.

34  Invasive palm removal – The FWS and U.S. Geological Survey (USGS) may coordinate 

35 efforts to remove invasive palms (Cocos nucifera) from Palmyra. This action will 

36 positively affect the atoll by removing a prevalent invasive plant and, in doing so, free up 

37 limiting resources (e.g., light and soil nutrients) for native plants. This project could 

38 positively contribute to the cumulative impacts of the proposed action by improving 

39 habitat for native species and contributing to the overall restoration of the atoll.

40

41  Bird translocation project – The FWS may coordinate efforts to translocate two 

42 endangered tropical land birds, the Christmas Island warbler (Acrocephalus 

43 aequinoctialis) and the Tuamotu sandpiper (Prosobonia cancellata), to Palmyra should 

44 the rat eradication be successful. Both species were historically found in the Line Islands 

45 (BirdLife International 2008, IUCN 2010) but have both been severely affected by 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 163

1 invasive predators. Palmyra Atoll will provide predator-free habitat for both birds. This 

2 project could positively contribute to the cumulative impacts of the proposed action by 

3 improving the overall biodiversity of the atoll.

4

5 4.6.1.3 Cumulative impacts under Alternative A – No Action

6 Under the no action alternative, the negative impacts that rats have on Palmyra‟s terrestrial 

7 system would continue in perpetuity. These impacts could be additive to other, unrelated future 

8 impacts on Palmyra‟s resources. The minor impacts that ongoing projects (primarily research 

9 related) would have on the biological, physical, and cultural resources of Palmyra are not likely 

10 to contribute to rat-related impacts. If rats persist at Palmyra, the biological resources of the atoll 

11 would continue to be negatively affected.

12

13 4.6.1.4 Cumulative impacts under Alternative B

14 There would be no major negative impacts to the biological, physical, or cultural resources of 

15 Palmyra Atoll under Alternative B. The minor negative impacts to biological, physical, and 

16 cultural resources as a result of Alternative B would not contribute to the impacts related to any 

17 separate, current or future projects. Similarly, the expected positive impacts of Alternative B to 

18 Palmyra‟s biological resources could contribute to the cumulative, positive impacts from 

19 separate, current or future projects.

20

21 4.6.1.5 Cumulative impacts under Alternative C– Preferred Alternative

22 There would be no major negative impacts to the biological, physical, or cultural resources of 

23 Palmyra Atoll under Alternative C. The minor negative impacts to biological, physical, and 

24 cultural resources as a result of Alternative C would not contribute to the impacts related to any 

25 separate, current or future projects. Similarly, the expected positive impacts of Alternative BC to 

26 Palmyra‟s biological resources could contribute to the cumulative, positive impacts from 

27 separate, current or future projects.

28

29 4.6.1.6 Cumulative impacts under Alternative D

30 There would be no major negative impacts to the biological, physical, or cultural resources of 

31 Palmyra Atoll under Alternative D. The minor negative impacts to biological, physical, and 

32 cultural resources as a result of Alternative D would not contribute to the impacts related to any 

33 separate, current or future projects. Similarly, the expected positive impacts of Alternative BD to 

34 Palmyra‟s biological resources could contribute to the cumulative, positive impacts from 

35 separate, current or future projects.

36

37 4.7 Irreversible and Irretrievable Impacts

38

39 4.7.1 Alternative A – No Action

40 The no action alternative does not require the commitment of any resources that are considered 

41 to be irreversible or irretrievable. The majority of the impacts associated with this alternative will 

42 only result in short term impacts and do not require the use of any non-renewable resources. 

43

44
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 164

1 4.7.2 Alternative B

2 This alternative does not require the commitment of any resources that are considered to be 

3 irreversible or irretrievable except for the use of fuel for the helicopter and boat operations. The 

4 majority of the impacts associated with this alternative will only result in short term impacts and 

5 do not require the use of any non-renewable resources. Furthermore, there will be no 

6 construction or development of any permanent structures, divergence of any waterways, or 

7 extraction of gas or oil resources during the project implementation period.

8

9 Project activities would require a commitment of funds that would then be unavailable for use on 

10 other Service projects. At some point, commitment of funds (for purchase of supplies, payments 

11 to contractors, etc.) would be irreversible; once used, these funds would be irretrievable. Non12 renewable or non-recyclable resources committed to the project (such as helicopter fuel and bait) 

13 would also represent an irreversible or irretrievable commitment of resources.

14

15 4.7.3 Alternative C– Preferred Alternative

16 This alternative does not require the commitment of any resources that are considered to be 

17 irreversible or irretrievable except for the use of fuel for the helicopter and boat operations. The 

18 majority of the impacts associated with this alternative will only result in short term impacts and 

19 do not require the use of any non-renewable resources. Furthermore, there will be no 

20 construction or development of any permanent structures, divergence of any waterways, or 

21 extraction of gas or oil resources during the project implementation period.

22

23 Project activities would require a commitment of funds that would then be unavailable for use on 

24 other Service projects. At some point, commitment of funds (for purchase of supplies, payments 

25 to contractors, etc.) would be irreversible; once used, these funds would be irretrievable. Non26 renewable or non-recyclable resources committed to the project (such as helicopter fuel and bait) 

27 would also represent an irreversible or irretrievable commitment of resources.

28

29 4.7.4 Alternative D

30 This alternative does not require the commitment of any resources that are considered to be 

31 irreversible or irretrievable except for the use of fuel for boat operations. The majority of the 

32 impacts associated with this alternative will only result in short term impacts and do not require 

33 the use of any nonrenewable resources. Furthermore, there will be no construction or 

34 development of any permanent structures.

35

36 Project activities would require a commitment of funds that would then be unavailable for use on 

37 other Service projects. At some point, commitment of funds (for purchase of supplies, payments 

38 to contractors, etc.) would be irreversible; once used, these funds would be irretrievable. Non39 renewable or non-recyclable resources committed to the project (such as bait and bait stations) 

40 would also represent an irreversible or irretrievable commitment of resources.

41

42 4.8 Short-term Uses and Long-term Productivity

43 An important goal of the Service is to maintain the long-term ecological productivity and 

44 integrity of the biological resources on the Refuge. The action alternatives are designed to 

45 contribute to the long-term ecological productivity of Palmyra and would not result in short-term 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 165

1 uses of the resources that would counteract this long-term productivity. Any short-term, negative 

2 impacts to the atolls biological resources would be outweighed by the ecosystem‟s long-term 

3 restoration-based benefits caused by the eradication of rats.

4

5 5 Consultation and Coordination

6

7 5.1 Introduction

8 The NEPA scoping process (40CFR 1501.7) was used to determine the scope of the analysis and 

9 to identify potential issues and opportunities related to the Proposed Action. A summary of the 

10 scoping and public involvement process for the proposed project is as follows:

11 

12 The NEPA scoping process for the eradication of black rats from Palmyra Atoll involved both 

13 internal and external scoping. The internal scoping process included review of the biological, 

14 physical, and social issues associated with eradicating rats from Palmyra Atoll, as well as a 

15 review of the 2001 and 2002 rat eradication project that failed to removal all of the rats from 

16 Palmyra. The Refuge, TNC, PARC, and IC coordinated on scientific experiments to identify the 

17 ecological factors that are affected by the presence of rats, as well as the potential benefits to 

18 ecological services, including species recovery, from rat removal. The external scoping process 

19 involved consultation with cooperative and regulatory agencies that have a specialized expertise 

20 or stake in the outcome of the project, and a 45-day public scoping period prior to preparation of 

21 the Draft EIS. 

22

23 5.2 Regulatory Framework 

24 The following federal laws, proclamations, executive orders are the most relevant to eradicating 

25 rats at Palmyra atoll:

26

27 Antiquities Act (16 U.S.C. § 431, et seq.), provides statutory authority for the establishment of 

28 national monuments and Proclamation 8336, January 6, 2009, establishing Palmyra Atoll as a 

29 part of the Pacific Remote Islands Marine National Monument;

30

31 Clean Water Act of 1972, as amended (33 U.S.C. §1251 et seq.);

32

33 Endangered Species Act of 1973, as amended (16 USC. § 1531 et seq.);

34

35 Executive Order 13186 of 2001 Responsibilities of Federal Agencies to Protect Migratory Birds; 

36

37 Executive Order 13112 of February 3, 1999 - Invasive Species; 

38

39 Federal Insecticide, Fungicide, and Rodenticide Act of 1947, as amended (7 U.S.C. §136 et seq.)

40

41 Fish and Wildlife Act of 1956 (16 U.S.C. § 742f); 

42

43 Fish and Wildlife Improvement Act of 1978 (16 U.S.C. § 742l);

44
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 166

1 Marine Mammal Protection Act of 1972 (16 U.S.C. § 1361 et seq.);

2

3 Migratory Bird Treaty Act of 1918, as amended (16 U.S.C. §§ 703-712, July 3, 1918);

4

5 National Environmental Policy Act of 1969 (42 U.S.C.A. § 4331 et seq.)

6

7 National Historic Preservation Act of 1966, as amended through 2000, (16 U.S.C. § 470 et

8 seq.);

9

10 National Wildlife Refuge System Administration Act of 1966, as amended, (16 U.S.C. §§

11 668dd-ee); and

12

13 Refuge Recreation Act (16 U.S.C. § 460k-3).

14

15 5.3 Agency Scoping and Review

16 A planning and work team consisting of Refuge, TNC, and IC staff held quarterly meetings to 

17 prepare the draft plan. The team involved and consulted with the National Wildlife Research 

18 Center USDA-APHIS, EPA, NMFS, The New Zealand Department of Conservation, and the 

19 Service‟s Ecological Services offices throughout the process and provided drafts of all 

20 documents prepared during the process. Team members met with scientists from the Insecticide 

21 and Rodenticide branch of the registration division of the Office of Pesticide Programs at EPA in 

22 Washington D.C. in April 2010 and with scientists at the National Wildlife Research Center in 

23 Fort Collins, CO in June 2010 to discuss pesticide label issues.

24

25 5.4 Public Participation

26 On January 14, 2010, FWS issued a Federal Register notice of intent to prepare an EIS (FR Doc. 

27 2010-579). The notice stated the Service “intend[s] to prepare an environmental impact 

28 statement to evaluate eradication of nonnative rats on Palmyra Atoll National Wildlife Refuge 

29 (Refuge). We provide this notice to advise the public and other agencies of our intent, and obtain 

30 public comments, suggestions, and information on the scope of issues to consider in the EIS and 

31 the important issues to be considered during NEPA analysis.” This scoping period closed March 

32 1, 2010. Substantive comments were received from three individuals or organizations (Attached 

33 below). All substantive comments were taken into consideration in the preparation of this Final

34 EIS.

35

36 The Draft EIS was made available for review by the public during a 45-day comment period 

37 between February 25 and April 11, 2011 (76 FR 10621). The Service sought public to provide 

38 input on its content. Direct mail was sent to known interested parties. Twenty-one reviewers 

39 provided comments via email and letters. The comments and the Service‟s responses to them are 

40 in Appendix M.

41

42 This Final EIS will be released to the public. Availability of the Final EIS will be advertised in 

43 the Federal Register, by mail to all interested parties who have requested information, and in 

44 local media as appropriate. A Record of Decision on the action will be made no sooner than 30-

45 days after the Federal Register publication. 
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 167

1

2 Comments Received During the Public Scoping Review

3 The following three comments represent the sum total of all comments received during the 

4 public scoping review period. 

5

6 Comment 1:

7

8

9
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 168

1 Comment 2: 

2

3
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 169

1
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 170

1

2

3 Comment 3:

4

5

6

7
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 171

1

2 5.5 Preparers and Primary Contributors

3 Jim Breeden – Assistant Refuge Manager, Palmyra Atoll National Wildlife Refuge, FWS

4 Dr. Beth Flint – Supervisory Wildlife Biologist Pacific, Pacific Reefs National Wildlife 

5 Refuge Complex, FWS

6

7 Dr. Amanda Meyer – Refuge Manager, Palmyra Atoll National Wildlife Refuge, FWS

8 Susan White – Project Leader, Pacific Reefs National Wildlife Refuge Complex, , FWS 

9 Dr. Lee Ann Woodward – Ecotoxicologist, Pacific Reefs National Wildlife Refuge 

10 Complex, FWS

11

12 Mark Fox –Director of External Affairs, The Nature Conservancy

13 Jordan Jokiel – Palmyra Program Director, The Nature Conservancy

14 Evelyn White – Senior Communications Manager, The Nature Conservancy

15

16 Aurora Alifano – Island Restoration Specialist, Island Conservation

17 Amy Carter, Philanthropy & Communications Manager, Island Conservation

18 Dr. Gabrielle Feldman – Environmental Compliance Specialist, Island Conservation

19 Dr. Gregg Howald – North American Regional Director/Ecotoxicologist, Island 

20 Conservation

21 Bradford Keitt, Director of Conservation, Island Conservation

22 Lillie Langlois – Assistant Environmental Compliance Specialist, Island Conservation

23 Jacob Sheppard – Environmental Compliance Specialist, Island Conservation

24 Dr. Alex Wegmann – Palmyra Rat Eradication Project Manager, Island Conservation

25
Palmyra Atoll National Wildlife Refuge Rat Eradication Project - FINAL Environmental Impact Statement, --May 2011---- 172

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1

APPENDIX A

PALMYRA ATOLL RAINFOREST RESTORATION PROJECT: RAT 

ERADICATION MONITORING PLAN FOR ALTERNATIVES B AND C 

(AERIAL BROADCAST OF 25W) [DRAFT]
2
i

PALMYRA ATOLL RAINFOREST RESTORATION PROJECT: RAT 

ERADICATION MONITORING PLAN FOR ALTERNATIVES B AND C 

(AERIAL BROADCAST OF 25W) [DRAFT]

By the US Department of Agriculture, APHIS, Wildlife Services, National Wildlife 

Research Center and Island Conservation

For

The Palmyra Atoll Rainforest Restoration Project Partnership

16 April 2011

Contact: William Pitt, USDA, APHIS, Wildlife Services, National Wildlife Research Center, PO Box 10880, Hilo, HI 96721; 808 

961-4482 ext 22, will.pitt@aphis.usda.gov: John Eisemann, USDA, APHIS, Wildlife Services, National Wildlife Research Center, 

4101 Laporte Avenue, Fort Collins, CO 80521, John.D.Eisemann@aphis.usda.gov.
ii

Contents

1 Introduction...........................................................................................................................................................................................1

1.1 Background ..................................................................................................................................................................................1

1.2 Conservation action..................................................................................................................................................................1

1.3 Scope ...............................................................................................................................................................................................2

2 Monitoring Actions .............................................................................................................................................................................2

2.1 Bait Application Rate Monitoring.......................................................................................................................................2

2.1.1 Terrestrial Environment..............................................................................................................................................3

2.1.2 Lagoon Environment.....................................................................................................................................................3

2.2 Bait Pellet Fate ............................................................................................................................................................................3

2.2.1 Palm Canopy......................................................................................................................................................................3

2.2.2 Ground.................................................................................................................................................................................4

2.2.3 Crab burrows ....................................................................................................................................................................4

2.3 Impacts to Target and Non-Target Organisms (Rats, Fish, Geckos, Crabs, Birds)........................................ 5

2.3.1 Carcass searching and shorebird counts..............................................................................................................5

2.4 Environmental Sampling........................................................................................................................................................6

2.4.1 Water sampling................................................................................................................................................................6

2.5 Efficacy ...........................................................................................................................................................................................7

2.5.1 Direct - Radio Collars.....................................................................................................................................................7

2.5.2 Indirect - Monitoring Stations (Chew Blocks, Tracking Tunnels, Motion-Sensing Cameras)....... 7

3 Tables and Figures ..............................................................................................................................................................................8

4 Citations.................................................................................................................................................................................................15
1

1 Introduction

1.1 Background

Palmyra Atoll (Palmyra), co-managed by the US Fish & Wildlife Service and The Nature 

Conservancy, is an important center of biodiversity and species abundance in the Central 

Pacific region. No baseline record of Palmyra’s terrestrial ecosystem prior to the 19th

century exists; however, it is possible that Polynesian voyagers altered Palmyra’s 

environment prior to European exploration of the Pacific by introducing coconut palms. 

Anthropogenic impacts accelerated during and after WWII with introductions of other 

plants, terrestrial arthropods, and mammals. Rats were likely introduced to the atoll during 

this period. 

Introduced non-native species are a leading cause of extinctions in island communities 

worldwide. Removing rats from Palmyra will result in biodiversity benefits for seabirds, 

plants, terrestrial invertebrates, and other components of the atoll’s terrestrial ecosystem; 

however, the removal process is complicated and could cause short- or even long-term 

damage to some of Palmyra’s animal populations. If the removal of rats from Palmyra does 

cause harm to local individual animals or animal populations, we anticipate that this impact 

will be short-lived and overshadowed by the large restoration benefit achieved through the 

removal of rats.

1.2 Conservation action

In June of 2011, the Palmyra Atoll Rainforest Restoration Project (PARRP) partnership will 

treat the entire atoll with rodenticide to remove the alien rat (Rattus rattus) population. 

The eradication will involve both aerial and ground application of bait containing the 

second generation anticoagulant rodenticide brodifacoum at a concentration of 25 ppm

(Brodifacoum 25 W Conservation Bait registered with the US EPA, sold by USDA - APHIS, 

and manufactured by Bell Labs, Madison WI). All emergent land areas will be treated, and 

measures will be employed to prevent intentional and minimize accidental bait drift into 

the marine environment. 

Bait will be applied to the atoll according to a strategic plan that will minimize the risk of 

bait drift into the marine environment while ensuring that a sufficient amount of bait is 

delivered to every potential rat territory. Two applications of bait over the entire atoll will 

be conducted during the eradication, and each application will employ three methods of 

aerial broadcast baiting (full swath - 40m, directional swath - 20m, and narrow swath - 10 

m), and hand baiting. Bait will be slung into the crowns of coconut palms (Cocos nucifera) 

that overhang near-shore waters as this habitat will not be baited during the aerial 

application, and bait stations will be placed and maintained around the camp area and on 

select small islands that are thought to be rat-free.

The operation is scheduled to coincide with the summer migration of shorebird species 

that are at risk of exposure to the rodenticide. The implementation team will include 4-5 

personnel who are dedicated to monitoring the parameters of the eradication, such as bait 

application rate and bait fait, and environmental factors, such as rodenticide residue in 
2

water and non-target species exposure to the rodenticide. All sampling devices, including 

location markers, such as flagging tape, will be recovered once the monitoring goals have 

been met. 

This conservation action, including the monitoring component, will be a cooperative effort 

by the US Department of Agriculture, US Fish and Wildlife Service, The Nature Conservancy, 

and Island Conservation.

1.3 Scope

This monitoring plan details the ecotoxicology and efficacy monitoring that will be 

undertaken in conjunction with the implementation of the rat removal project at Palmyra. 

The five objectives of the monitoring plan are:

1. Verification of the application rate on the ground and in the coconut palm canopy

2. Document adverse impacts, or lack thereof, to Palmyra’s biota caused by the rat 

removal action.

3. Document long term negative impacts, or lack thereof, to Palmyra’s biota caused by 

the rat removal action

4. Establish clear pathways by which non-target species could be exposed to the 

rodenticide employed to remove rats from Palmyra, and measure rodenticide 

exposure levels for key non-target species

5. Document that the rat removal action has successfully removed all rats from 

Palmyra.

The monitoring actions described in this plan will occur prior to, during, and after the 

implementation of the eradication. This plan builds on prior studies of Palmyra’s 

eradication environment (Howald et al. 2004, Buckelew et al. 2005, USDA-APHIS 2006, 

Wegmann et al. 2008, Alifano and Wegmann 2010, Alifano et al. 2010), rodent eradication 

studies conducted in similar environments (Wegmann et al. 2006, Wegmann et al. 2007, 

Wegmann 2008), and decades of research on the management of invasive species (Witmer 

et al. 2007). The monitoring activities, number of samples that will be collected, and the 

effort (number of personnel) that will be required for each sampling activity are presented 

in Tables 1 and 2.

2 Monitoring Actions

2.1 Bait Application Rate Monitoring
3

2.1.1 Terrestrial Environment

During each bait application, the amount of bait that will be available to ground-foraging 

rats and other consumers will be measured within 30 minutes of the bait landing on the 

ground. The monitoring team will use plastic hoops (“sampling hoops”) that are 91.44 cm 

diameter to quantify the bait application rate on the ground. 

2.1.1.1 Monitoring Procedure

Thirteen areas will be monitored for bait application rate (figure 1). These areas represent 

the four habitat types on the atoll. At least 192 independent measurements will be taken 

during each of the two bait applications across these 13 sampling areas. Each measure will 

consist of counting bait pellets within a sampling hoop. Approximate locations of sampling 

points will be determined by GPS location prior to application. Monitoring will occur 

within 1 hour after bait has been applied to these areas. 

2.1.2 Lagoon Environment

Despite the measure employed to prevent bait drift into the marine environment, a small 

amount of bait may enter near-shore waters due to wind, ricochet off of vegetation, or 

human error. The monitoring team will use sampling hoops placed in the near-shore 

marine environment to measure the amount of bait that accidentally enters the water.

2.1.2.1 Monitoring Procedure

The sampling hoops will be placed at sample sites throughout the atoll. At each sample site

(10sites), five transects of three sampling hoops that run perpendicular to the shoreline 

will be established with 5 m between each transect. The three hoops in each transect will 

be secured at 3m, 6m, and 9m from the high-tide line, which will be identified as the 

highest reach of the last high tide cycle. Each sampling hoop will be secured to weights 

placed on the bottom or stakes driven into the marine sediment. Transects at a minimum 

of five sites will be sampled directly after bait is aerially broadcast onto the adjacent land 

area, and only at low tide or when the sampling hoops are not submerged. To account for 

the chance that the aerial baiting schedule may not coincide with a tide that is low enough 

to allow for sampling, ten sites will be established (Figure 2).

2.2 Bait Pellet Fate

2.2.1 Palm Canopy

An assessment of the presence of bait pellets and pellet fate in coconut palm crowns will 

occur directly after the first and second bait applications. 

2.2.1.1 Monitoring Procedure

Fifteen coconut palms that can be easily accessed with a 40’ extension ladder and located 

on Cooper Island (Figure 3) will be selected prior to the first bait application. Each palm 

will be checked for the presence of bait pellets within four hours of bait being broadcast 

over the surrounding canopy. During this initial assessment, the location of five bait pellets 

(the bait pellets will be found in the tree or placed there if less than five are found) will be 

indicated by using a permanent marker to draw an arrow that points to the pellet on an 
4

adjacent frond. Each of the five study pellets in each study tree will be given a unique, two 

digit identifier (“1-1” will mean that this is pellet 1 in tree 1) and checked daily until the 

pellet disappears or is undetectable. While the pellets remain in the crowns, pellet fate will 

be recorded according to the following bait pellet condition scale:

1. Bait hard, intact, whole

2. Bait hard, intact, partially gone

3. Bait soft, intact, whole

4. Bait soft, intact, partially gone

5. Bait mushy, disintegrated

6. Bait dry, disintegrated 

7. Bait pellet gone

2.2.2 Ground

The fate of bait pellets on the ground will be measured after each of the two bait 

applications. 

2.2.2.1 Monitoring Procedure

PVC sampling hoops will be fixed in place within representative patches of Palmyra’s four 

main terrestrial habitat types: Coconut Palm Forest, Scaevola/Heliotropium shrubland, 

Pisonia forest, and Lepturus meadow (Figure 4). The four study patches will be located on 

Cooper Island. Ten sampling hoops will be placed in each study patch. Directly following 

the treatment of the surrounding area, pellets will be added to or removed from the 

sampling hoops so that the bait density within the hoop equals the target application rate. 

Each sampling hoop within each study patch will be visited every day until all pellets are 

gone from within the hoop; the number of pellets remaining and general pellet condition 

(see the bait pellet condition scale above) will be recorded during each visit. 

2.2.3 Crab burrows

Consumption of bait by land crabs is a well documented occurrence during rodent 

eradication operations. While Land crabs readily consume bait brodifacoum and 

diphacinone (Pain et al. 2000, Tanner et al. 2004, Alifano and Wegmann 2010), and 

presumably other anticoagulant rodenticides do not appear to harm the crabs. However, it 

is possible that Gecarcinid land crabs, such as the Cardisoma species occurring at Palmyra, 

cache bait in their burrows. If bait caching occurs (this behavior has not been 

documented), then such caches may facilitate the eradication effort by acting as bait 

stations, or increase the potential risk of harmful exposure of non-target species to the 

applied rodenticide by creating pockets of bait that are not readily consumed. A bait 

caching study will be conducted prior to the eradication.
5

2.2.3.1 Monitoring Procedure

Prior to the eradication, non-toxic (placebo) 25W bait pellets will be broadcast by hand 

around an area containing shallow Cardisoma sp. burrows. Following the bait application, 

up to 10 burrows will be checked for evidence of bait caching by crabs. If bait caching is 

observed (if pellets are brought into the burrow by the crab(s) and are not directly 

consumed), the fate of the cached pellets will be monitored daily and pellet condition will 

be assessed according the aforementioned bait pellet condition scale.

2.3 Impacts to Target and Non-Target Organisms (Rats, Fish, Geckos, 

Crabs, Birds)

2.3.1 Carcass searching and shorebird counts

The Palmyra rat eradication project has been designed to specifically target rats and avoid 

harm to non-target species; however, with a broadcast bait application, the potential for 

exposing non-target individuals to the applied rodenticide exists. To document harm 

caused to non-target organisms due to exposure to rodenticide, the Monitoring Team will 

conduct directed carcass searches, and will sample terrestrial and marine organisms for 

evidence of exposure. In addition, all carcasses located opportunistically during all 

eradication operations will be collected for necropsy and residue analysis.

2.3.1.1 Directed Searches

Organized searches for dead or moribund target (rat) and non-target individuals (fish, 

geckos, crabs, and birds) will occur during and after the eradication.

2.3.1.1.1 Monitoring Procedure

Starting three days prior to the first bait application and continuing until 30 days after the 

second bait application, organized carcass searches will occur on the runway and on North 

Beach – both are prominent, easily accessed shorebird roosting sites (Figure 5). In addition 

to this search effort, an all atoll shorebird count and carcass search (Figure 6) will occur at 

the following intervals after the first bait application: days 5, 8, 15, and 18. Furthermore, 

all project staff will be instructed on proper collection and tagging protocols should they 

come across a carcass during other project activities – this will allow for opportunistic 

documentation of non-target species response to the eradication action. All dead or 

moribund target and non-target individuals found during and up to 2 months after the 

operation will be properly collected and necropsied, and the resulting samples will be 

labeled for lab-based detection and quantification of rodenticide residue. 

2.3.1.2 Terrestrial Non-Target sampling: hermit crabs, geckos, ants, cockroaches

To further assess non-target species exposure to the applied rodenticide, small samples of 

select terrestrial non-target species will be collected and analyzed for rodenticide residue.

2.3.1.2.1 Monitoring Procedure

A minimum of 5 pooled samples (2-5g per sample) will be collected at four intervals after 

the first bait application: 1-4 days, 11-14 days, day 24, and day 56. In addition, one preeradication sample will be collected for method development. Geckos will be haphazardly 
6

collected at night from the trunks of coconut palms, ants will be collected with guarded bait 

cards (sugar and protein bait placed on 5cm x 5cm paperboard cards that are secured 

inside crab-proof cages that are anchored to the ground), and cockroaches will be 

haphazardly collected at night in and around unused manmade structures, on the trunks of 

coconut palms, and via leaf-litter sifting. All collection will occur on Cooper Island, and all 

specimens will be properly collected, preserved, and labeled for lab-based assessment of 

exposure to rodenticide. 

2.3.1.3 Marine Non-Target sampling: Black-spot Sergeant, fiddler crabs

To further assess non-target species exposure to the applied rodenticide, small samples of 

select marine non-target species will be collected and analyzed for rodenticide residue. 

Because of their foraging strategies, abundance, and, in the case of the fiddler crab, 

foodweb-based connection to target and other non-target species, the Black-Spot Sergeant

(Abudefduf sordidus), and the fiddler crab Uca tetragonon were selected as indicator 

vertebrate and invertebrate marine organisms.

2.3.1.3.1 Monitoring Procedure

Samples comprising three Black-Spot Sergeants will be collected from ten different 

locations before the eradication and 1-2 days after the second bait application. For fiddler 

crabs, a minimum of 5 pooled samples (2-5g per sample), plus one sample for method 

development will be collected prior to the eradication, and at four intervals after the first 

bait application: 1-4 days, 11-14 days, day 24, and day 56. 

2.4 Environmental Sampling

2.4.1 Water sampling

As mentioned, sincere effort will be taken during the eradication to prevent bait drift into 

the near-shore waters. However, it is possible that rodenticide could enter aquatic water 

bodies through accidental, direct spread of pellets into water, or through the flushing of 

land-based sediment during heavy rain events. To assess both marine and inland waters 

for rodenticide residue, the Monitoring Team will collect water samples after each bait 

application and at the end of the operation. 

2.4.1.1 Monitoring Procedure

Within 24 hours of each application and on the last day of the operation (after the second 

application), the monitoring team will collect 12 one-liter water samples (in chemically 

cleaned jars) from 12 sites (Figure 7): 

 3 sites outside lagoon (western terrace)

 6 sites inside adjacent to baited area in deep water

 1 site in the brackish eel pond adjacent to Cooper Island

 1 site in the runway pond

 1 site in a groundwater well on Eastern Island
7

2.5 Efficacy

2.5.1 Direct - Radio Collars

During the eradication, the efficacy of the operation will be assessed by following rats that 

were fitted with radio transmitters prior to the first bait application

2.5.1.1 Monitoring Procedure

Starting the night after the first bait application, the monitoring team will follow 30 rats 

fitted with radio collars. Fifteen rats will be trapped within the camp area (preferably 

inside or around buildings), ten rats will trapped and followed on Aviation Island, and five 

rats will be trapped and followed on Strawn Island. All collared rats will be found every 

other night until mortality is confirmed by observation of the carcass or retrieval of the 

collar. 

2.5.2 Indirect - Monitoring Stations (Chew Blocks, Tracking Tunnels, MotionSensing Cameras)

Following the eradication operation, rat detection stations will be established throughout 

the atoll; the stations will be frequently checked and serviced over a two week period. At 

this time, Rat detection stations will also be established in the camp area and these stations 

will become part of the ongoing biosecurity program. 

2.5.2.1 Monitoring Procedure

Four to six weeks after the second bait application, a small team will return to Palmyra to 

establish rat detection stations throughout the atoll (Figure 8). Every station will have a 

corrugated plastic indicator block, and tracking tunnels and motion sensing camera traps 

will be spaced intermittently throughout the detection station network. The stations will 

be checked and serviced every three days over a fifteen day period. If rat sign is 

encountered on an isolated land mass that is small enough to effectively retreat by hand, 

the monitoring team will consult with the PARRP management team about conducting a 

follow-up bait application on this land mass. 

Detection stations that are placed in the camp area will be monitored and serviced by 

trained TNC station staff according to this schedule: once per week for six months 

following the eradication, once per month after six months. 

At one year and two years after the eradication, a monitoring team will return to Palmyra 

and re-establish the rat detection stations. During these monitoring efforts, live traps will 

be added to the detection station network, and stations will be monitored/serviced every 

three days for fifteen days.

As part of the atoll’s biosecurity program, all station staff will be trained in the detection of 

rat sign. If sign is observed, indicator blocks will be placed in the surrounding area and any 

blocks with potential rat chew marks will be sent to rodent identification experts for 

verification. 
8

3 Tables and Figures
9

Table 1. Sample collection schedule for the Palmyra Atoll Rat Eradication monitoring tasks – the numbers in the cells represent the number of samples that will be 

collected for the given monitoring activity on the given day.

PALMYRA ATOLL RAT ERADICATION DAYS AFTER 1ST BROADCAST

MONITORING ACTIVITIES Pre 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Post TOTAL

Application Rate Ground: Hoops 96 96 96 96 384

Application Rate Lagoon: Hoops 75 75 75 75 300

Bait Fate Ground: Hoops1 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 960

Bait Fate Canopy: Palm Crowns2 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 360

Bait Fate Crab Burrows: Burrows 10 10

Focused Carcass Search: Days (N-Beach, Runway) 6 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 56

Atoll Carcass Search: Samples 1 1 1 1 4

Shorebird Count Runway: Samples 1 1 1 1 4

Shorebird Count Atoll: Samples 1 1 1 1 4

Non-Target Sampling- Geckos: Pooled Samples3 2 2 3 2 3 2 3 5 22

Non-Target Sampling- Ants: Pooled Sample3 2 2 3 2 3 2 3 5 22

Non-Target Sampling- Cockroaches: Pooled Samples3 2 2 3 2 3 2 3 5 22

Non-Target Sampling- Fish: Individuals 30 15 15 60

Non-Target Sampling- Fiddler Crabs3 2 2 3 2 3 2 3 5 22

Non-Target Sampling- Hermit Crabs 3 5 5 10

Environmental Sampling- Water- Outside: 3 3 3 3 12

Environmental Sampling- Water- Inside Lagoon: 6 6 6 6 24

Environmental Sampling- Water- Brackish Eel Pond: 1 1 1 1 4

Environmental Sampling- Water- Runway Pond: 1 1 1 1 4

Environmental Sampling- Water- Fresh Water Well: 1 1 1 1 4

Efficacy Monitoring- Radio Collars- Strawn: Locations 5 5 5 5 5 5 5 5 5 5 5 5 60

Efficacy Monitoring- Radio Collars- Cooper: Locations 15 15 15 15 15 15 15 15 15 15 15 15 175

Efficacy Monitoring- Radio Collars- Aviation: Locations 10 10 10 10 10 10 10 10 10 10 10 10 120

Efficacy Monitoring- Stations- Chew Blocks: Stations 215 215

Efficacy Monitoring- Stations- Tracking Tunnels: Stations 43 43

Efficacy Monitoring- Stations - Camera Traps: Stations 24 24

1 Each hoop should include approximately 15 pellets (if application rate is 90 kg/ha and each pellet weight about 6 grams), consequently, ~600 pellets per app. or 1,200 pellets over both apps.

2 Each palm crown will contain 5 pellets (15 palms x 5 pellets/palmx 2 applications = 150 pellets monitored each day until gone)

3 Each Non-target sample consists of a minimum of 5 individuals (> 10 grams total). 
10

Table 2. Staffing schedule for the Palmyra Atoll rat eradication monitoring tasks – the numbers in the cells represent the number of personnel that will be needed to 

complete the given task on the given day.

PALMYRA ATOLL RAT ERADICAITON DAYS AFTER 1ST BROADCAST

MONITORING ACTIVITIES Pre 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Post

Application Rate Ground: Hoops 4 4

Application Rate Lagoon: Hoops 4 4

Bait Fate Ground: Hoops 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Bait Fate Canopy: Palm Crowns 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

Bait Fate Crab Burrows: Burrows 1

Focused Carcass Search: Days (N-Beach, Runway) 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

Atoll Carcass Search: Samples 12 12 12 12

Shorebird Count Runway: Samples 1 1 1 1

Shorebird Count Atoll: Samples 12 12 12 12

Non-Target Sampling- Geckos: Pooled Samples 2 2 2 2 2 2 2 2 2 2 2

Non-Target Sampling- Ants: Pooled Samples 2 2 2 2 2 2 2 2 2 2 2

Non-Target Sampling- Cockroaches: Pooled Samples 2 2 2 2 2 2 2 2 2 2 2

Non-Target Sampling- Fish: Individuals 2 2 2

Non-Target Sampling- Fiddler Crabs: 2 2 2 2 2 2 2 2 2 2 2

Environmental Sampling- Water- Outside: 2 2 2 2

Environmental Sampling- Water- Inside Lagoon: 2 2 2 2

Environmental Sampling- Water- Brackish Eel Pond: 2 2 2 2

Environmental Sampling- Water- Runway Pond: 2 2 2 2

Environmental Sampling- Water- Fresh Water Well: 2 2 2 2

Efficacy Monitoring- Radio Collars- Strawn: Locations 2 1 1 1 1 1 1 1 1 1 1 1

Efficacy Monitoring- Radio Collars- Cooper: Locations 2 1 1 1 1 1 1 1 1 1 1 1

Efficacy Monitoring- Radio Collars- Aviation: Locations 2 1 1 1 1 1 1 1 1 1 1 1

Efficacy Monitoring- Stations- Chew Blocks: Stations 2

Efficacy Monitoring- Stations- Tracking Tunnels: Stations 2

Efficacy Monitoring- Stations - Camera Traps: Stations 2
11

Figure 1. A map of the thirteen sampling locations that will be used to measure the bait application rate on the ground during each of the two aerial broadcasts that will 

occur during the Palmyra Atoll rat eradication.

Figure 2. A map of the four sampling locations that will be used to measure the fate of bait pellets after each of the two aerial broadcasts that will occur during the 

Palmyra Atoll rat eradication.
12

Figure 3. A map of the three sampling locations that will be used to measure the fate of bait pellets lodged in the crowns of palm trees after each of the two aerial 

broadcasts that will occur during the Palmyra Atoll rat eradication.

Figure 4. A map of the ten sampling locations that will be used to measure the rate at which bait drifts into the near-shore marine environment during each of the two 

aerial broadcasts that will occur during the Palmyra Atoll rat eradication.
13

Figure 5. The locations where daily carcass searching will occur during the Palmyra Atoll rat eradication.

Figure 6. A depiction of the routs followed during an “All-Atoll” shorebird count and carcass search.
14

Figure 7. A map of the twelve sampling locations that will be used to test water for brodifacoum residue after the bait application associated with the Palmyra Atoll rat 

eradication. Circles represent the three sites that are outside of the lagoon. Squares represent the six sampling sites that are inside the lagoon. The star is the brackish 

“Eel Pond” on Cooper Island. The triangle is the “Runway Pond” on Cooper Island. And, the cross is the fresh water well on Eastern Island. 

Figure 8. A map of the approximate locations of rat monitoring stations that will be established four to six weeks after the second bait application. Three detection 

devices will be employed during this monitoring effort: chew blocks, tracking tunnels, and camera traps. The monitoring stations will be activated and monitored for 

two weeks at this time, and then again for two weeks at one year and two years post eradication.
15

4 Citations

Alifano, A. and A. Wegmann. 2010. The ecotoxicology and palatability of two rodenticide 

bait products: field-based assessment at Palmyra Atoll Island Conservation, Santa 

Cruz, California.

Alifano, A., A. Wegmann, M. Pott, and E. Oberg. 2010. Assessment of rat detection and 

rodenticide application methods at palmyra atoll. Island Conservation, Santa Cruz, 

California.

Buckelew, S., G. R. Howald, A. Wegmann, J. Sheppard, J. Curl, P. McClelland, B. Tershy, K. 

Swift, E. Campbell, and B. Flint. 2005. Progress in Palmyra Atoll restoration: rat 

eradication trial, 2005. Island Conservation, Santa Cruz, California.

Howald, G., A. Samaniago, S. Buckelew, P. McClelland, B. Keitt, A. Wegmann, W. C. Pitt, D. S. 

Vice, E. Campbell, K. Swift, and S. Barclay. 2004. Palmyra Atoll rat eradication 

assessment trip report, August 2004. Island Conservation, Santa Cruz, California.

Pain, D. J., M. D. Brooke, J. K. Finnie, and A. Jackson. 2000. Effects of brodifacoum on the land 

crabs of Ascension Island. Journal of Wildlife Management 64:380-387.

Tanner, M., C. Orazio, W. Steiner, and G. LIndsey. 2004. Method for the definitive analysis of 

rat poison diphacinone in exposed coconut crabs. SETAC 4th World Congress / 25th 

Annual Meeting in North America, Society of Environmental Toxicology and 

Chemistry, November 14-18, Portland, OR.

USDA-APHIS. 2006. Analysis of brodifacoum in crab tissues. USDA-APHIS National Wildlife 

Research Center.

Wegmann, A., J. Helm, A. Samaniego, W. Smith, B. Jacobs, D. Drake, J. Smith, M. McKown, A. 

Henry, S. Hathaway, and R. Fisher. 2008. Palmyra Atoll rat eradication: biomarker 

validation of an effective bait application rate, 19 June to 5 July, 2008. Island 

Conservation, Santa Cruz, California.

Wegmann, A., G. Howald, and H. Jones. 2006. Feasibility of rat eradication from Ahnd Atoll, 

Federated States of Micronesia. Project Design Document, Island Conservation.

Wegmann, A., R. Marquez, G. Howald, J. Curl, J. Helm, C. Llewellyn, and P. Shed. 2007. 

Pohnpei rat eradication research and demonstration project: Pohnpei, Federated 

States of Micronesia - 16 January to 7 March 2007. Island Conservation, Santa Cruz, 

USA.

Wegmann, A. S. 2008. Fanna Island rat eradication site visit: technical report - August 2008. 

Island Conservation, Santa Cruz, California.

Witmer, G. W., W. C. Pitt, and K. A. Fagerstone, editors. 2007. Managing vertebrate invasive 

species: proceedings of an international symposium. USDA/APHIS Wildlife Services, 

National Wildlife Research Center, Fort Collins, Colorado, USA, Fort Collins, 

Colorado.
1

APPENDIX B

WORKING DRAFT PALMYRA ATOLL BIOSECURITY PLAN: 

PREVENTION OF RODENT INCURSION AND RODENT 

DETECTION RESPONSE
2
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WORKING DRAFT PALMYRA ATOLL BIOSECURITY 

PLAN: PREVENTION OF RODENT INCURSION AND 

RODENT DETECTION RESPONSE 

PREPARED BY THE NATURE CONSERVANCY*

April 15, 2011

*

Contact: Jordan Jokiel, The Nature Conservancy, 923 Nuuanu Ave., Honolulu, HI 96817, 808-

587-6282
** THIS IS A WORKING DOCUMENT -- DO NOT CITE ** v. 4-15-2011

INTRODUCTION

The conservation and socio-economic benefits of eradicating rats from Palmyra Atoll 

(“Palmyra”) will only be fully realized if rodent reinvasion is prevented. Pest reinvasion 

mitigation or biosecurity plans are critical components of successful eradication campaigns. 

Because The Nature Conservancy (TNC), United States Fish and Wildlife Service (FWS) and 

Palmyra Atoll Research Consortium (PARC) collectively maintain and operate a Nature 

Preserve, a research station, and National Wildlife Refuge there is a steady influx of supplies, 

equipment, and personnel which regularly arrive at Palmyra via airplane and ocean going vessel 

from many ports of call. As such, the risk of rat-reintroduction is high.

To mitigate the risk of a post eradication rodent reinvasion, a biosecurity plan must be put into 

action prior to the eradication and continued indefinitely. The biosecurity measures identified in 

this plan were developed with the guidance of the Department of Conservation (New Zealand), 

The Island Eradication Advisory Group (New Zealand) and a review of the document entitled, 

“Review of Rat Invasion Biology; Implications for Island Biosecurity” (J.C. Russel, D.R. Towns 

and M.N. Clout). 

The three basic units of biosecurity are quarantine, surveillance and contingency response. 

Implementation, oversight and funding responsibility for biosecurity actions for Palmyra are the 

responsibility of TNC and FWS. TNC will be the primary lead for managing biosecurity 

measures in Honolulu and on Cooper Island, and FWS will be the primary lead for actions in the 

Refuge.

Potential pathways for rodent introduction to Palmyra include: airplanes, marine vessels, and 

their associated cargo. Biosecurity measures for each of these pathways are described below.

BIOSECURITY MEASURES

PATHWAY BIOSECURITY MEASURE

PLANE PRE-DEPARTURE QUARANTINE:

• Maintain permanent control devices* in 

Honolulu hangar area. 

• Place detection** and control devices on 

plane 3 days prior to departure to Palmyra. 

Check prior to departure.

• Ensure plane is secured (doors closed) on 

the runway in Honolulu.

POST-ARRIVAL QUARANTINE:

• Ensure plane is secured (doors closed) on 

runway.
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PATHWAY BIOSECURITY MEASURE

• Maintain permanent control devices at 

Palmyra runway area. 

SURVEILLANCE: 

• Place detection and control devices on plane 

3 days prior to departure to Palmyra. Check 

prior to departure.

CONTINGENCY RESPONSE:

• Maintain control and detection devices at a 

density of one device per hectare in a one 

kilometer radius around the runway at 

Palmyra.
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PATHWAY BIOSECURITY MEASURE

CARGO TRANSPORTED ON PLANE PRE-DEPARTURE QUARANTINE:

• Develop a secure, dedicated staging area for 

Palmyra provisioning operations which will 

allow for better inspection, decontamination 

and storage of all Palmyra-bound cargo

• Maintain permanent control and detection 

devices in provisioning area. 

• Visually inspect all cargo, especially 

produce and large equipment before loading 

on plane. 

• Reduce packaging and re-pack in rodentproof containers. 

• Reduce the threat of this pathway by 

producing more food locally at the atoll.

POST ARRIVAL QUARANTINE:

• Visually inspect all cargo as it is being 

unloaded.

SURVEILLANCE:

• Require rodent free certification inspection 

for provisioning staging area once per year

CONTINGENCY RESPONSE:

• Maintain control and detection devices at a 

density of 4 devices per hectare in 200 m 

radius around the portion of the runway 

where the plan stops to load and unload 

passengers and cargo.
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PATHWAY BIOSECURITY MEASURE

VESSELS THAT DOCK AT PALMYRA 

(ANNUAL PROVISIONING SHIP, 

RESEARCH VESSELS, OTHER)

PRE-DEPARTURE QUARANTINE: 

• Maintain permanent control devices* in 

wharf area in Honolulu. 

• Require rodent free certification inspection 

for vessel 2 weeks prior to departing for 

Palmyra.

• Visually inspect interior and exterior of 

vessel for evidence of rodents three days 

prior to departure to Palmyra.

• Deploy rodent control and detection devices 

on vessel one week prior to departure. 

Maintain and check every two days prior to 

and during duration of operation.

POST-ARRIVAL QUARANTINE:

• Ensure vessel is secured when docked at 

Palmyra (minimize physical vectoring 

pathways between vessel and dock)

SURVEILLANCE: 

• Deploy rodent control and detection devices 

on vessel one week prior to departure. 

Maintain and check every two days prior to 

and during duration of stay at Palmyra.

CONTINGENCY RESPONSE:

• Maintain control and detection devices at a 

density of one device per hectare in a one 

kilometer radius around the wharf at 

Palmyra.
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PATHWAY BIOSECURITY MEASURE

VESSELS THAT DOCK AT PALMYRA 

(ANNUAL PROVISIONING SHIP, 

RESEARCH VESSELS, OTHER)

PRE-DEPARTURE QUARANTINE:

• Develop a secure, dedicated staging area for 

Palmyra provisioning operations which will 

allow for better inspection, decontamination 

and storage of all Palmyra-bound cargo.

• Maintain permanent control and detection 

devices in provisioning area. 

• Visually inspect all cargo, especially 

produce and large equipment before loading. 

• Reduce packaging and re-pack in rodentproof containers. 

• Place cargo in shipping containers. 

• Implement rodent control and detection 

measures inside shipping containers.

• Reduce the threat of this pathway by 

producing more food locally at the atoll.

POST ARRIVAL QUARANTINE:

• Visually inspect all cargo as it is being 

unloaded.

SURVEILLANCE:

• Require rodent free certification inspection 

for provisioning staging area once per year.

CONTINGENCY RESPONSE:

Maintain control and detection devices at a density 

of 4 devices per hectare in 200 m radius around the 

wharf. 
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PATHWAY BIOSECURITY MEASURE

VISITING VESSELS (ARRIVAL OF 

VESSEL HAS BEEN COORDIANTED 

AND OPERATION HAS GONE 

THROUGH THE PERMITTING 

PROCESS GOVERNED BY FWS AND 

TNC) 

QUARANTINE:

• Ensure bio-security information is provided 

via the permitting process and on website.

• No visiting vessels are permitted to dock 

(except for emergencies or with prior 

approval and protocols) and must moor at 

designated areas in the lagoon.

• Ensure ship is moored properly.

SURVEILLANCE:

• Implement rat control and detection 

measures on vessel while moored.

CONTINGENCY RESPONSE:

• Maintain control and detection devices at a 

density of 4 devices per hectare in a one 

kilometer radius on the land area adjacent to 

the mooring site.
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PATHWAY BIOSECURITY MEASURE

VISITING VESSELS (UNEXPECTED 

ARRIVAL AND/OR OPERATOR HAS 

NOT GONE THROUGH THE 

PERMITTING PROCESS GOVERNED 

BY FWS AND TNC) 

QUARANTINE:

• Provide bio-security information to visiting 

vessel.

• Assess the likelihood that the vessel may 

harbor rodents before granting access to 

moor in the lagoon.

• No visiting vessels are permitted to dock 

(except for emergencies or with prior 

approval and protocols) and must moor at 

designated areas in the lagoon.

• Ensure ship is moored properly.

SURVEILLANCE:

• Implement rodent control and detection 

measures on vessel while moored.

CONTINGENCY RESPONSE:

• Maintain control and detection devices at a 

density of 4 devices per hectare in a one 

kilometer radius on the land area adjacent to 

the mooring site.
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PATHWAY BIOSECURITY MEASURE

VISITING VESSELS THAT NEED TO 

DOCK FOR EMERGENCY PURPOSES 

QUARANTINE: 

• Assess the likelihood that the vessel may 

harbor rodents before granting access to 

dock.

• Ensure vessel is secured when docked 

(minimize physical vectoring pathways 

between vessel and dock)

SURVEILLANCE:

• Deploy rodent control and detection devices 

on vessel. Maintain and check every two 

days.

• Visually inspect all cargo before it is 

unloaded. 

CONTINGENCY RESPONSE:

• Maintain control and detection devices at a 

density of 4 devices per hectare in a one 

kilometer radius around the wharf.
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PATHWAY BIOSECURITY MEASURE

VESSEL (ATTENDED OR 

UNATTENDED) RUNS AGROUND 

SURVEILLANCE: 

• Inspect vessel and assess the likelihood that 

the vessel may harbor rodents.

CONTINGENCY RESPONSE:

• Deploy rodent control and detection 

measures at a density of eight devices per 

hectare in a one kilometer radius on adjacent 

emergent land.

BIOSECURITY CONSIDERATIONS

BIOSECURITY ISSUE BIOSECURITY MEASURE

Ensure that biosecurity measures continue 

to be maintained and refined as needed by 

all staff and stakeholders in perpetuity. 

Disseminate information describing the importance 

of keeping Palmyra rat free as well as indentifying 

specific measures which reduce the possibility for 

vectoring rodents to Palmyra. Information can be 

disseminated via SUP process, PARC pre-trip 

information packet, PARC meetings, and new 

employee briefings.

Visiting vessels may not take adequate 

steps to reduce likelihood of vectoring 

rodents to Palmyra.

Disseminate information via FWS and TNC permit 

process and websites.
** THIS IS A WORKING DOCUMENT -- DO NOT CITE ** v. 4-15-2011

FWS and TNC may not be trained in 

techniques to readily detect and rapidly 

respond to rodent infestations.

Provide rat detection/rapid response training to 

existing employees, and make such training 

compulsory when staffing pertinent positions.

*Control devices include bait stations, live traps, sticky traps, and snap traps, as well as an 

integrated approach that includes a combination of these devices. 

**Detection devices include, tracking tunnels, and chew blocks, as well as an integrated 

approach that includes a combination of these devices.

RODENT DETECTION RESPONSE 

The conservation and socioeconomic benefits of eradicating rats from Palmyra would only be 

fully realized if it is successful and any rodent reinvasion is prevented. Rat detection response 

and pest reinvasion mitigation or biosecurity plans are critical components of successful 

eradication campaigns. A quantity of a FIFRA registered bait product (not to exceed ≤ 2000 lbs

or 907 kg) would be stored at the PARC field station. TNC and FWS would appropriately secure, 

label, and store all bait left at Palmyra in a dry location, ready for use should rats be detected

after the rat eradication. All use of bait would be in accordance with the bait product’s label.

If rat sign were encountered or a rat sighting occurred, rat detection devices (as described 

above) would be established in the area surrounding the sign or sighting and on adjacent 

islands. Confirmed rat presence would initiate a rat removal response to eradicate a residual 

population or an incursion. The area surrounding the confirmed rat detection would be treated 

with rodenticide applied by hand broadcast or bait station, or by live trapping, or by a 

combination of the three control methods. Detection devices placed in and beyond the treatment 

area would be monitored as frequently as possible during the control period, and until the point 

at which rats have not been detected for 30 consecutive days. Control of the invading or 

residual rat population would be adaptively managed to minimize risk to non target species 

while maximizing the probability of removing all target individuals. 
1 

APPENDIX C 

PALMYRA ATOLL RAT ERADICATION ASSESSMENT TRIP REPORT 

2004 
2 
Page 1 of 61 

PALMYRA ATOLL RAT

ERADICATION ASSESSMENT

TRIP REPORT

AUGUST 2004 

PREPARED BY: 

GREGG HOWALD*

ISLAND CONSERVATION NW, BRITISH COLUMBIA

ARACELI SAMANIEGO

CONSERVACIÓN DE ISLAS, MEXICO

STACEY BUCKELEW

ISLAND CONSERVATION, USA 

PETE MCCLELLAND

NEW ZEALAND DEPARTMENT OF CONSERVATION

BRADFORD KEITT

ISLAND CONSERVATION, USA 

ALEX WEGMANN

UNIVERSITY OF HAWAI`I AND USFWS 

WILLIAM C. PITT

USDA- WILDLIFE SERVICES, NATIONAL WILDLIFE RESEARCH CENTER

DANIEL S. VICE

USDA-WILDLIFE SERVICES, GUAM

EARL CAMPBELL

US FISH AND WILDLIFE SERVICE, ECOLOGICAL SERVICES, HAWAI`I

KATIE SWIFT

US FISH AND WILDLIFE SERVICE, ECOLOGICAL SERVICES, HAWAI`I

STEVE BARCLAY

US FISH AND WILDLIFE SERVICE, REFUGES, HAWAI`I

CORRESPONDENCE: ghowald@islandconservation.org

PHONE: (604) 628-0250
SUMMARY

With funding from Mr. Ian Cumming, we studied the feasibility of rat eradication on 

Palmyra Atoll in August - September 2004. In August 2004, a team of nine people with 

representatives from Island Conservation, three US government agencies (USDA-NWRC, 

USDA-WS, USFWS-ES and USFWS Refuges) and the Department of Conservation New 

Zealand visited the atoll for eight days to initiate detailed research. Two Island Conservation 

staff remained on the atoll for one additional month to complete the planned research. 

The main goals of this expedition were to: 

1) Assess the previous effort to eradicate rats from Palmyra Atoll both to learn why it 

was not successful and what experiences from that effort can be used to develop 

methods for a follow-up rat eradication. 

2) Conduct site-specific research needed to develop a plan for a successful rat 

eradication. 

Research was conducted on-island to answer questions critical to successful rat eradication. 

To determine if all rats would have access to rodenticide bait we asked: 

•Do rats spend multiple days in trees without coming to the ground (will ground baiting 

suffice or must bait be available above ground as well)? 

•What is the two dimensional (planar) movements of rats over a period of several days 

(how does bait need to be spatially distributed)? 

•How much bait needs to be put out given bait loss to weather, land crabs and other 

invertebrates? 

•Because land crabs are the main source of competition for bait, what is their distribution 

and density, and are there effective crab-proof bait station designs? 

To make sure the rodenticide of choice, brodifacoum, was effective against the rats on 

Palmyra, we ran a small toxicity study in the field. Finally, to make sure the eradication could 

be conducted without harming other components of Palmyra’s ecosystem, we identified 

potential non-target species that might require special mitigation. 

Page 2 of 61 
We found that Palmyra’s abundant rainfall and aseasonal environment were obstacles to 

successful rat eradication. They make it difficult to develop a bait that maintains its 

palatability over time and is more attractive to all rats than the abundant natural food 

resources. The abundant landcrabs compete with rats for the bait and make it difficult to 

ensure enough bait is available to all rats for an adequate time period. 

Our rat range data indicate that the standard bait station spacing of 50 x 50 m may have been 

insufficient to get bait into every rat’s ranging territory because the animals live in a threedimensional habitat that includes the forest canopy. We recommend any bait station-based 

efforts require a distribution of stations with a maximum separation of 25 m to increase the 

proportion of rats coming into contact with bait stations, which still might not be adequate 

to intercept all rats. 

Our initial estimates suggest that a broadcast application will require an application of 60-80 

kg/ha to ensure that enough bait is available to the rats on the ground for four days, to 

overcome competition from landcrabs that are attracted to and consume the bait (but are 

not affected by the anticoagulant rodenticide). We were unable to precisely determine an

effective broadcast application rate because of the high density of crabs and limited 

availability of placebo bait. We estimated the rate of bait application required to overcome 

crab consumption using measured crab densities multiplied by the mean and highest rate of 

bait consumption for each species of crab (measured in cage trials). We estimate that for the 

highest density of crabs in coconut palm forests, we would need to apply from as little as

3.34 kg/ha to as much as 47.74 kg/ha to overcome bait loss to crabs. Additional bait would 

be applied to ensure enough bait is available to rats. Further field testing to determine an 

appropriate application rate will be required. 

Our resistance trials demonstrated that there is some tolerance or resistance to brodifacoum 

in the rat population, likely developed after long-term, chronic rat control. The build-up of 

resistance or tolerance may have contributed to the compromised original rat eradication 

effort and may suggest a need for an alternate toxin in addition to brodifacoum in future 

eradication efforts. 

Page 3 of 61 
We tested six different bait types on Palmyra – CI-25, CI-25 Waxed, Ramik (8 g), Ramik (2 

g), Weatherblock XT, and Final Blox. CI-25 proved to be the most palatable bait; however, 

it was unable to endure the wet climate on Palmyra. Ramik (8 g) retained its shape and 

firmness in Palmyra’s climate for long enough, but the bait was not (relative to the other 

bait) palatable to the rats. Weatherblock XT and Final Blox survived well in Palmyra’s 

environment; however, they contain Bitrex, a bittering agent that reduces palatability of the 

bait which may limit the success of the eradication. We identified the characteristics of the 

bait we need to deliver to the rats on Palmyra. We are currently working with Bell 

Laboratories of Madison, WI, to develop a bait for us to further test on Palmyra in 2005. 

We believe that the most effective means to eradicate rats from Palmyra will be the use of 

baits containing brodifacoum and perhaps an additional bait containing a non-anticoagulant 

(such as bromethalin) rodenticide, either aerially broadcast or with an approach combining 

aerial broadcast and bait stations spaced at 25 m intervals. Because of the stringent 

regulatory environment in the US, which makes the approval of an aerial rodenticide 

broadcast a complex process, and the need to assure availability of bait both to rats in the 

canopy and on the forest floor, we believe that the combined use of bait stations (spaced at 

25 m) and aerial broadcast may be the most effective method of eradication, but also the 

most logistically complex and costly. Rats with small territories, which may not encounter 

bait stations during foraging, should encounter the bait broadcast into the canopy and thus 

will not escape bait exposure. Bait station eradication can be implemented at any time 

during the year. Timing of the broadcast could be closely linked to the migratory patterns of 

non-target birds on the island, with little impact on the eradication. 

We identified non-resident migratory shorebirds at risk of both primary and/or secondary 

exposure to the rodenticide. The primary species of concern are the Bristle-thighed Curlew 

Numenius tahitiensis and the Pacific Golden Plover Pluvaialis fulva. Both species are identified 

as species of high conservation concern in the US Pacific Islands Regional Shorebird 

Conservation Plan (2004) and the US Shorebird Conservation Plan (2000). Both species 

overwinter on the atoll, with some individual juvenile birds present throughout the year. 

The most effective mitigation for these species is to conduct the eradication when there are 

the smallest numbers of birds present on the atoll. 

Page 4 of 61 
With $120,000 in funding from the USFWS, we recommend conducting a trial hand 

broadcast (to mimic an aerial application) application into representative habitat to test the 

efficacy, risks and logistics of eradicating rats from Palmyra Atoll coincident with the lowest 

numbers of migratory shorebirds. 

Page 5 of 61 
Table of Contents 

Summary................................................................................................................................................2

Table of Contents ................................................................................................................................6

Introduction..........................................................................................................................................7

Objectives of Site Visit......................................................................................................................10

Constraints..........................................................................................................................................10

Access..............................................................................................................................................10

Infrastructure..................................................................................................................................12

Weather...........................................................................................................................................12

Island Size and Topography.........................................................................................................12

Plants and Animals........................................................................................................................13

Review of Past Eradication Efforts.................................................................................................14

Planning ..........................................................................................................................................15

Communication .............................................................................................................................16

Funding ...........................................................................................................................................16

Eradication Technique..................................................................................................................16

Bait Station Design........................................................................................................................17

Bait Station Spacing.......................................................................................................................18

Bait...................................................................................................................................................19

Conclusions on Past Eradication Efforts.......................................................................................22

Studies Conducted on Pre-Eradication Trip Assessment............................................................23

Evaluate the Arboreal Nature and Planar Movements of Rats on Palmyra Atoll................23

Broadcast Application Rate..........................................................................................................27

Brodifacoum Resistance ...............................................................................................................32

Bait Palatability...............................................................................................................................33

Bait Degradation............................................................................................................................34

Non-Target Species and Mitigation Measures ..........................................................................37

Conclusions from Pre-eradication Studies.....................................................................................38

Management Implications for Future Eradication Efforts..........................................................38

Recommendations .............................................................................................................................39

Acknowledgements............................................................................................................................39

References...........................................................................................................................................40

APPENDIX 1...........................................................................................42 

APPENDIX 2...........................................................................................47 

APPENDIX 3...........................................................................................57

Page 6 of 61 
INTRODUCTION

Island ecosystems, such as Palmyra Atoll, are key areas for conservation because they are 

essential habitat for seabirds, pinnipeds and sea turtles that range over thousands of square 

kilometers of open ocean, but depend on islands for breeding, raising young, and resting. In 

addition, islands tend to be rich in endemic species and are home to 15-20% of all plant, 

reptile and bird species, even though they make up only about 3% of the Earth’s area 

(Whittaker 1998). 

Unfortunately islands have been disproportionately affected by humans. More than 80% of 

all of recorded extinctions (excluding fish) have occurred on islands, and most of these were 

caused, at least in part, by invasive species (Island Conservation analysis of data from IUCN 

Global Red List and World Conservation Monitoring Center 1992). 

One of the most significant invasive species on islands are rats in the genus Rattus. They 

have been introduced onto about 82% of the world’s islands and/or island chains (Atkinson 

1985), where they frequently have a quantifiable negative impact on the distribution and 

abundance of native flora and fauna. This is most pronounced on oceanic islands where 

native species have evolved in the absence of mammalian predators and thus have limited

behavioral, morphological, and life-history defenses against rats (Brown 1997). 

Consequently, rats have been implicated in 40-60% of recorded bird and reptile extinctions 

since 1600 (Groombridge 1992). Fortunately, it is possible to eradicate rats from many 

islands, and in the last 20 years there has been a series of technological innovations in the 

field of rat eradication that have dramatically increased the power of this important 

conservation tool (Figure 1, Galvan et al. 2005). Briefly, rats are eradicated by distributing a 

bait containing a rodenticide, usually brodifacoum, into all rat territories. Bait can be placed 

in bait stations spaced on a grid of 25 x 25 m to 100 x 100 m, or can be broadcast evenly at a 

known density either by hand on small islands or with a helicopter using a bait-spreading 

bucket on larger islands. 

Palmyra Atoll National Wildlife Refuge, located in the Line Islands of the central Pacific 

Ocean, approximately 1760 km south of the main Hawai`ian Islands, likely never supported 

Page 7 of 61 
native mammals because of its remoteness. However, non-native black rats (Rattus rattus) 

were introduced to Palmyra, likely during the US military occupation of the atoll in the 

1940s. The establishment of rats on Palmyra is believed to have had a major negative impact 

on the ecosystem, especially on seabirds, invertebrates, and vegetation. 

Figure 1. Total area, number and maximum island size of global rat eradications per five years (1951-2005). Taylor and 

Thomas (1989) developed a systematic bait station approach which facilitated a dramatic increase in successful 

eradications. The application of aerial broadcast by the early 1990’s allowed much bigger and complex island rat 

eradications (Source: Unpub. data: Island Conservation, IUCN, University of California Santa Cruz, Auckland University)

0.00

5000.00

10000.00

15000.00

20000.00

25000.00

1951 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Total island area (ha)

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

1951 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Number of succesful eradications 

Total Area (ha) per 5 Years

Total Eradications per 5

Years

0

2000

4000

6000

8000

10000

12000

1951 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Island area (ha)

Max island size (ha) per 5

Years

Taylor & Thomas

The Nature Conservancy (TNC), in conjunction with the US Department of Agriculture’s 

Wildlife Services and the US Fish and Wildlife Service initiated a rat eradication on Palmyra 

Atoll in 2001 in an attempt to restore the island ecosystem. However, the eradication effort 

Page 8 of 61 
was suspended in August 2003 after it became apparent that the rats could not be eradicated 

using the methods employed despite the ongoing efforts of island staff and volunteers. 

In the spring 2004, Island Conservation and TNC secured funding from Mr. Ian Cumming 

to conduct a site assessment on Palmyra and develop specific recommendations, techniques 

and options to complete the eradication. In August 2004, a team of nine people with 

experience in island rodent eradication or control (Table 1) visited Palmyra Atoll to gather 

enough information to plan a trial eradication and begin planning eradication of rats from 

Palmyra Atoll. 

Table 1. Eradication assessment team 

Name Organization Expertise

Gregg Howald 

Director, 

Island 

Conservation 

NW 

Ecotoxicology/Eradication/Compliance 

Brad Keitt 

Project 

Director, 

Island 

Conservation 

Avian Ecology/Eradication 

Araceli Samaniego 

Project 

Director, 

Island 

Conservation 

Rodent Ecology/Eradication 

Stacey Buckelew 

Biologist, 

Island 

Conservation 

Island Ecology/Conservation 

Dan Vice USDA-WS, 

Guam Wildlife Biology/Control 

Earl Campbell USFWS-ES, 

Hawai`i Wildlife Biology/Control 

Will Pitt 

USDANWRC, 

Hawai`i 

Wildlife Biology/Control 

Pete McClelland 

New Zealand 

Dept. of 

Conservation 

Island Mgmt/Rodent 

Eradication/Endangered Species Mgmt. 

Alex Wegmann PhD student, 

U. of Hawai`i USFWS Palmyra Refuge Support 

Page 9 of 61 
An initial eight-day site assessment was held to conduct basic studies and define site-specific 

research to be continued by two Island Conservation staff who remained on the island for 

an additional four weeks. 

OBJECTIVES OF SITE VISIT

1. Evaluate the constraints of eradicating rats from Palmyra Atoll. 

2. Review past eradication efforts. 

3. Conduct site-specific research to aid in design of an eradication project, specifically: 

a. Evaluate the arboreal nature of rats and their planar movements, to determine if 

bait application into trees would be necessary. 

b. Determine an effective broadcast application rate that would deliver enough bait 

to the rats. 

c. Evaluate the presence of brodifacoum resistance in the local rat population from 

chronic control during past eradication efforts. 

d. Compare palatability of baits to natural foods and various alternative baits. 

e. Evaluate degradation rates of different types of bait in the Palmyra environment. 

4. Assess presence of and risks to potential non-target species, and develop any necessary 

mitigation measures. 

Field work was conducted from August 7 - September 11, 2004. 

CONSTRAINTS

Access 

Palmyra is approximately 1760 km south of Honolulu, in the Line Islands (Figure 2). 

Visitors to Palmyra can reach the atoll by either charter aircraft or by ship or boat. The atoll 

has a one-mile long coral rubble runway that is maintained by TNC staff. There is no 

regular air service to Palmyra, but TNC and USFWS regularly charter a small Gulfstream II 

twin turbo prop from Air Services Hawai`i, based on the south side of Honolulu 

International Airport. The aircraft can carry a maximum payload of 3300 pounds (both 

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supplies and people). Maximum seating is for 18 persons. The cost for air charter is 

$20,000 for one round trip, typically with no overnight layovers. 

hips and smaller pleasure craft visit the atoll regularly. The deepwater lagoon provides a 

. 

dditional bareboat charters are available from the mainland and Honolulu, and the costs 

0

S

safe, protected anchorage and can accommodate larger tugs and barges for deliveries of 

materials and supplies. TNC hires a tug/barge out of Honolulu to service the atoll yearly

The barge is able to tie up to Cooper Island near the old fish processing plant west of the 

main camp area. The cost of the barge/tug combination is a very expensive $150,000 per 

run. 

A

range from $2800 – $5500 per day, with some boats offering a maximum payload of 500,00

pounds. 

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Infrastructure 

The developed portion of the atoll is on Cooper Island, and is owned and operated by TNC. 

TNC currently operates a full service tent camp capable of supporting 28 persons, with a 

generator for power and a rainwater collection system for drinking and wash water. 

Additional infrastructure includes old copra plantation buildings which provide shelter from 

the rain, a recreation facility, small dock, concrete bunkers, a well-maintained one mile long 

coral rubble runway for small aircraft and large propeller planes such as C-130s, and small 

boats to move personnel and gear between the islets. TNC charges users an access fee to

fund the maintenance of these facilities. 

Staff and guests are housed in groups of two in small weatherports. Two large weatherports 

support the communal kitchen/eating area, and shower/laundry facilities. The old fish plant 

and copra plantation buildings, and some additional weatherports, provide a workshop and 

ample storage space for equipment and supplies. Since the 2004 field work described in this 

report, TNC and a consortium of universities have completed construction of a new field 

research station on Palmyra. 

Two small (about 18’ long), plastic, open runabout boats are available to shuttle gear and 

people between islets as necessary. The shallow lagoon limits access to only a few landing 

points on the islets. 

Weather 

Palmyra lies within the Inter-Tropical Convergence Zone (ITCZ), the band of low pressure 

along the equator formed by the upward convection of warm, moist air from the Earth’s

surface. The climate of Palmyra is characterized by high humidity (>90%), warm 

temperatures (75 – 85 degrees Fahrenheit) with almost daily copious rainfall events 

associated with thunderstorms. Mean annual rainfall on Palmyra is 4.06 m. 

Island Size and Topography 

Palmyra Atoll is comprised of 54 islets encompassing 228 ha, rising to a maximum elevation 

of 2 m. The atoll is well within the size range of successful rat eradications (Figure 1). All of 

the land area can be accessed on foot, however, there are areas of thick vegetation, especially 

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the Scaevola habitat, which precludes access without trail cutting. Although most of the islets 

are not connected, they can be reached by wading or swimming across the narrow channels 

that separate individual islets, or by boat. 

There are potential safety concerns to eradication staff from unexploded ordnance, 

contaminated dump sites, hidden bunkers and marine wildlife (e.g. sharks), which could limit 

the successful implementation of a ground-based operation. Barrier and Quail Islands are 

inaccessible due to unexploded ordnance concerns. All areas of concern should be identified 

prior to implementation of the eradication. 

Plants and Animals 

The aseasonal climate on Palmyra supports dense vegetation of native and non-native trees 

and shrubs. A large portion of the atoll (approximately 48%) lies under a canopy of nonnative coconut palm (Cocos nucifera). Other habitat types include broadleaf forest composed 

of Terminalia catappa, the native Pisonia grandis, and the shrub-like Scaevola sericea and 

Tournefortia argenatea. The Pisonia forest was once regarded as the best example of a pristine 

Pisonia forest in the American Pacific, but the trees are now dying due to stress response 

from introduced scale insects whose populations are inflated due to their symbiotic 

relationship with the introduced ant Pheidole megacephala. The decline of the Pisonia forest has 

caused dramatic changes in the Palmyra ecosystem. 

The terrestrial habitats on Palmyra support 10 species of breeding seabirds. There are no 

breeding landbirds on Palmyra, but the island supports overwintering populations of Bristlethighed Curlews (Numenius tahitiensis) and other shorebird including Wandering Tattlers 

(Heterscelus incanus), Pacific Golden Plovers (Pluvialis fulva) and Ruddy Turnstones (Arenaria 

interpres). The curlew and Pacific Golden Plover are designated by the US and Region 1 

Shorebird Conservation plans as Species of High Conservation Concern because of limited 

breeding and non-breeding distributions, low relative abundance, and a decline in 

populations. 

Palmyra supports a notably diverse assemblage of six landcrab species, including the large 

coconut crab (Birgus latro). The most abundant landcrab is the red hermit crab (Coenobita 

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perlatus). Additional species include the purple hermit crab (Coenobita brevimanus), orange land 

crab (Cardisoma carnifex) and purple land crab (Cardisoma rotundum). These crabs compete 

with rats for access to the bait. 

There are two terrestrial reptile species on Palmyra, an introduced house gecko (Hemidactylus 

frenatus) and a native mourning gecko (Lepidodactylus lugubris). 

Palmyra supports a diverse collection of both native and non-native insects, including 

cockroaches and ants that are known to compete with rats for access to bait. During the 

first eradication attempt, it was noted that ants overwhelmed some bait stations, completely 

consuming the bait present in the stations within 24 hours. 

Two domestic cats and a domestic dog are present as pets on the atoll, as well as one cat that 

is confined to a boat moored in the lagoon. We recommend that the pets be removed from 

the atoll prior to any eradication attempt. These animals would be at risk of exposure to any 

rodenticides used during an eradication effort. 

REVIEW OF PAST ERADICATION EFFORTS

A review of the past eradication efforts was conducted in an attempt to identify why the 

eradication failed, so that some benefit can come from the time, energy and financial 

resources put into that project, and to ensure that any mistakes are not repeated in future 

efforts. This section summarizes the observations made by the crew that visited the island in 

August 2004. The review was designed to identify the processes or systems that failed. 

The three fundamental, and interrelated, parts of a successful rat eradication are: 

1. exhaustive planning, 

2. ongoing and effective communication between and among participants, and 

3. adequate funding to implement the plan, including a contingency for unexpected 

costs or needed modifications to the eradication plan. 

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Planning 

Based on the information that was provided, there appears to have been a lack of detailed 

planning, with only an Environmental Assessment that functioned as a written plan. No 

detailed plan was peer reviewed for potential problems, or shared with all participants to

ensure continuity. Insufficient planning resulted in the use of techniques that proved 

inadequate to eradicate the rats. There was an ineffective management structure, use of 

volunteers and other staff with no expertise in rat eradication, poor communication between 

the involved parties and an inadequate budget to complete the eradication. The lack of a 

monitoring and communication plan led to poor data feedback to management and technical 

support that resulted in the continued use of inappropriate techniques and eventually 

contributing to a failed eradication (Figure 3). 

Figure 3. A conceptual model of constant evaluation needed for a successful eradication 

project. 

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Communication 

Initiating the eradication with an inappropriate approach or technique does not have to 

result in a failed eradication if there are adequately trained staff collecting data and making

observations that are delivered to management and technical support staff, to troubleshoot 

and make modifications to the program as necessary. 

There were many parties involved in the eradication, including USDA-Wildlife Services, US 

Fish and Wildlife Service, The Nature Conservancy management, TNC island managers and 

staff, a range of bait station technicians from previous projects and a series of inexperienced 

volunteers. There was no written communication plan that outlined either individuals’ role 

or lines of communication for various aspects of the eradication. There appears to have

been periodic communication breakdowns between the parties that led to strained relations 

between individuals and reluctance to share data or information. A detailed plan with an 

effective communication structure could have facilitated the relaying of information to 

appropriate support staff, who could have identified and rectified the problems with the 

eradication early and made the necessary changes. 

Funding 

The initial budget submitted to the National Fish and Wildlife Foundation was grossly 

inadequate to complete the project. The project appeared to be supply-driven, i.e., the 

project was constructed within the confines of the available funds. The project relied on the 

use of unpaid, inexperienced volunteer bait station technicians who were unable to identify 

subtle problems. Similarly, there was no contingency to modify the project as unanticipated 

problems arose. 

The attempted eradication should not have been started given the inadequate funding. It is 

extremely important that eradication projects are adequately budgeted, with an appropriate 

contingency to respond to unexpected, unpredictable challenges. If only partial funding can 

be found, the project should be delayed until adequate funding is secured. 

Eradication Technique

Successful eradication of rats from islands requires the use of techniques that: 

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1. Put every individual rat at risk from the proposed technique(s), 

2. Remove/kill rats faster than they can replace themselves (breed), and 

3. Prevent the in-migration by other rats.

Because of Palmyra’s isolation, and the basic quarantine measures for ships and barges that 

regularly visit the atoll, the risk of rats immigrating to Palmyra is very low. Thus, the 

eradication efforts focus on steps 1 and 2. 

The aseasonal, warm, humid climate and abundance of natural foods on Palmyra enable a 

sustained high density of rats that likely breed year round. Rats are capable of producing and 

weaning a litter every month. Thus, any technique that is used on Palmyra requires that the 

eradication be carried out intensively and as quickly as possible. The eradication attempt

between 2001 and 2003 delivered bait in bait stations and could have killed the rats faster

than they were breeding, assuming they had access to the bait stations, there was enough bait 

in the stations, and rats consumed the bait and were susceptible to the rodenticide. 

Our assessment of the technique used in the previous eradication attempt focused on: 

• Bait availability – Did all rats have access to bait stations and bait within the 

bait stations?

• Bait palatability – Did rats eat the bait? 

• Bait susceptibility – Did all rats die after eating the bait? 

Bait Station Design 

The eradication of rats from Palmyra was initiated in 2001 initially with the placement of 

PVC tube bait stations placed on the ground. The stations certainly allowed rat access to the 

baits, but stations were readily overwhelmed by the abundant landcrabs and hermit crabs 

that were attracted to and consumed the bait. The stations were modified to elevated 

platforms with a small PVC tube that excluded some but not all landcrabs and hermit crabs 

from the stations. The final bait station design was made of empty 15 liter bait buckets 

modified to exclude crabs using a raised access hole (4.4 cm diameter, about 20 cm above 

ground) with bait suspended by wire near the bottom of the bucket. A baffle was put in 

place to prevent the large coconut crabs (which could not feasibly be excluded from the 

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buckets) from “sweeping” the station, with a claw, for the bait. For rats to gain access to the 

bait, rats had to jump up to the hole, climb through the hole, jump down into the bucket 

and/or over the baffle. Bait blocks had to be chewed off a wire, which required rats to 

either consume part of the block in the station, or only remove part of the block from the 

station. To exit the station, rats had to jump over or onto the baffle edge, then jump up or 

over to the access/exit hole. The stations were secured in place with a large piece of coral 

rubble found in the vicinity of the station. Landcrabs, cockroaches, and ants competed with 

the rats for access to the bait in all bait station designs. 

The third and final bait station design was successful in excluding the majority of landcrabs 

from gaining access to the bait within the stations (see Vice 2004,Appendix 1). However, 

there is a possibility, unconfirmed, that the modified bait stations design either physically or 

behaviorally excluded rats from the stations. Later in the project, personnel reported that 

rats routinely were observed to walk past armed bait stations, apparently ignoring the station. 

Similarly, there were reports of numerous bait stations that had no bait removed, yet live 

traps placed nearby or on top of the stations routinely captured rats. This indicates that

some rats could not, or would not, enter the bait stations. It is unclear if it was a problem 

with the bait station design physically excluding the rats, or if the attractiveness of the bait 

was not high enough compared to the abundant natural foods. In other words, it is 

unknown if some of the rats simply chose not to enter the stations. 

Bait Station Spacing 

The stations were placed at approximately 50 m intervals laid along transects that were cut 

perpendicular to the axis of each islet. It appeared from the map of bait stations, and from a 

general walk around on the atoll, that the spacing was accurate, and all peninsulas and small 

islets had bait stations. The use of 50 m spacing of bait stations was based on the successful 

use of 50 m spacing of stations at Kure and Midway Atolls, and is typically the standard 

applied to island Rattus rattus eradication in the more temperate climates. (Rattus exulans were 

removed from Rose Atoll (6 ha) using bait station spacing at 30 m, in addition to live traps 

and snap traps at 10 m intervals.) The 50 m spacing was established to ensure that there are 

at least two or more bait stations in each and every adult rat home range or territory. An 

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individual rat would require a minimum ranging area of 2500 m2

 to encounter at least one 

station within its territory. 

Our radio telemetry data comparing the movements of rats live-trapped in coconut palms 

with rats trapped on the ground demonstrated that rats on Palmyra live in a threedimensional environment, and regularly move between the tree canopy and the ground. The 

trees on the atoll, especially the abundant coconut palm, provide abundant food and shelter 

for rats. The ranging or planar movements of rats captured in coconut palms on Palmyra 

was particularly small, with a mean of 693 m2 and a maximum of 1215 m2. The planar 

ranging area of rats on Palmyra was measured to be smaller than typically measured 

elsewhere in more temperate climates, including Hawai`i. R. rattus in Hawai`ian forests were 

reported to have a mean home range of 3.6 ha (36,000 m2

) (range: 1.57-4.45 ha) (Lindsey et 

al. 1999) and R. rattus in New Zealand forests were noted as having home ranges as small as 

0.3 ha (3,000 m2 ) (Hooker and Innes 1995). The smaller planar movement measured on

Palmyra is likely due to both the three-dimensional environment available and the abundance 

of natural foods. Thus, the rats could live in high densities and not have to move great 

distances to meet their life needs – food, water, shelter and mates to reproduce. Thus, we 

hypothesize that the rats, especially those with small territories, could have likely survived 

and either never encountered or infrequently encountered bait stations spaced at 50 m 

intervals. Some of these rats which did not encounter or avoided contact with the bait 

stations likely formed part of the residual population that repopulated the island after the 

eradication efforts were suspended. 

Rat home ranges seem largely dependent on site-specific topography, rat density, 

habitat type, and food availability. Thus, to ensure a successful eradication, site-specific data 

must be relied upon as an indication of rat home ranges. Spacing of bait stations at 25 m 

intervals would ensure rats with territories as small as 625 m2

 would encounter at least one 

bait station within their territories.

Bait 

For a successful eradication of introduced rats from an island, the fundamental requirement 

is that every last rat is removed or killed. Leaving even one pregnant female alive on the 

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island, or failing to prevent future re-introductions, can negate the financial and time 

commitment devoted to eradicating rats initially. Thus, every effort must be made to get the 

last rat. The use of rodenticides for restoring islands is a powerful conservation tool. Used 

effectively, removal of the last rat is possible and rat eradications have been carried out over 

250 times worldwide (Island Conservation, unpub. database). 

To be an effective eradication tool, bait must: 

• contain an active ingredient that is known to be highly toxic to the target 

population, 

• be palatable and induce low or no bait shyness from the target population, 

• be consumed in sufficient amounts by each rat to receive a lethal dose. 

Of all known rat eradications worldwide, the vast majority have used the anticoagulant 

rodenticides, mainly brodifacoum (a second-generation anticoagulant), as the primary 

method of removal. The mode of action for brodifacoum is to prevent the production of 

active clotting factors by blocking the vitamin K-reductase enzyme in liver microsomes. The 

lack of active clotting factors leads to the inability of clot formation at sites of hemorrhage. 

The lack of clot formation leads to fatal hemorrhaging usually from a single point or 

multiple locations. Death typically results from complications due to hypovolemic shock. 

The major advantage of the anticoagulants is that the onset of poisoning symptoms is 

delayed until after consumption of a lethal dose. Thus, rats do not associate the symptoms 

of poisoning with the bait and bait shyness is avoided. 

Over half of known rat eradications worldwide have used brodifacoum exclusively; the 

remaining projects used additional rodenticides or trapping as a secondary or tertiary means 

of removing rats (Figure 4). The introduction of an alternate rodenticide is used as a strategy 

to deal with individual rats that may have avoided the primary rodenticide through taste or 

behavioral aversion (e.g. USDA 2002). On other tropical islands (Rose Atoll, Kure Atoll, 

Sand Island, East Island, Midway Atoll), brodifacoum has been used as the primary 

rodenticide and occasionally bromethalin (an acute rodenticide) has been used as the 

secondary rodenticide. The mode of action for bromethalin is to uncouple oxidative 

phosphorylation in the mitochondria in cells of the central nervous system leading to a 

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decreased production of ATP. Low levels of ATP inhibit the activity of the Na/K ATPase 

and lead to a subsequent buildup of cerebral spinal fluid. The increased cerebral spinal fluid 

results in high intracranial pressure, causing damage to nerve axons, inhibiting neural 

transmission and leading to paralysis, convulsions and death. 

In the first rat eradication attempt on Palmyra, two baits containing two active ingredients 

were used. The bait used most extensively was Weather Block XT (Syngenta Crop 

Protection Inc.) containing 50 ppm brodifacoum. The bait was a 20 g blue wax block with a 

small hole in the center. The USDA (2002) reported 1,764.5 kg of Weatherblock XT had 

been applied on Palmyra by June 11, 2002. The total amount used after June 11, 2002 

through August 2003 (end of eradication attempt) is not reported. 

The second bait type was Fastrac All Weather Blox (Bell Laboratories, Inc.), containing 100 

ppm bromethalin. The bait was a 20 g green wax block, tubular-shaped, with a small hole 

running through the longitudinal center of the block. The USDA (2002) reported that very 

little Fastrac bait containing bromethalin was used during the eradication attempt (25.3 kg) 

on “several islands” by June 11, 2002 during the first year of the eradication attempt. The 

amount of bromethalin used through the entire duration of the eradication attempt (through 

August 2003) was not reported. 

When applied correctly, the use of bait containing brodifacoum and bromethalin has a high 

probability of successfully eradicating rats from islands. The rodenticide choice for Palmyra 

was appropriate and had a high probability of facilitating a successful eradication had the rats 

consumed lethal amounts of bait. However, Weatherblock XT contains Bitrex (a brand 

name for the bittering agent known as denatonium benzoate). The intent of the addition of

Bitrex into rodenticide baits is to prevent the accidental consumption of rodent baits by 

children when used in urban settings. However, it is also known to reduce the acceptance of 

the bait to rats under laboratory conditions (Veitch 2002) and it is generally accepted that 

bait uptake declines with the addition of Bitrex into baits. Bait containing Bitrex is not 

recommended for use in island eradications due to the increased risk of bait shyness in 

individual rats potentially leading to eradication failure. On Palmyra, Bitrex may have caused 

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some rats to avoid the bait (bait shyness) and not consume a lethal dose. Thus, Bitrex is 

another factor that may have compromised the success of the first eradication attempt. 

The ongoing, chronic use of brodifacoum to control the rats on Palmyra may have led to the 

selection for individual rats that were physiologically more tolerant or resistant to the 

rodenticide. Over time, this can lead to the development of a resistant population, which 

makes it more and more difficult to control rats using that particular rodenticide. Although 

brodifacoum is highly toxic to rats, resistance to the second generation anticoagulants has 

been shown to develop in rodent populations in the United Kingdom (Cowan et al. 2004). 

Intensive baiting on Palmyra took place for a number of years (three years during the failed 

eradication attempt alone) around the camp complex on Cooper Island, primarily with 

brodifacoum, but also occasionally with diphacinone. The intensive rodent control may 

have been selecting for rats that are more tolerant of the rodenticides, either through the 

ability to metabolize and excrete the compound, or tolerance to higher doses. The 

investigation into resistance in August 2004 suggested that the early stages of brodifacoum 

resistance were present in the Cooper Island rat population (Pitt 2004, Appendix 2). Thus, 

ongoing baiting with brodifacoum alone could have led to the failure of eradication on 

Palmyra, even if all the additional biological problems were rectified. Ongoing use of 4-

hydroxycoumarin anticoagulants may result in a population of rats that are resistant to the 

entire suite of anticoagulant rodenticides (Macnicoll 1986). Thus, to overcome resistance, a 

non-anticoagulant, possibly bromethalin, would have to be used.

CONCLUSIONS ON PAST ERADICATION EFFORTS

The benefit of looking back on a failed eradication attempt is that the problems identified 

can be rectified in a new eradication plan for Palmyra and raise awareness for other tropical 

and non-tropical island ecosystems in which rat eradication is desired. The eradication 

attempt on Palmyra Atoll between 2001 and 2003 violated the first two rules for eradication: 

all individuals were not at risk from the eradication technique, and the rats were repopulating 

the island at least as quickly as they were removed from the ecosystem in the latter stages of 

the baiting operation. There were problems with the planning, communication, and funding 

that were complicated by the local biological conditions, especially the competition from 

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landcrabs and the small ranging territories of rats on the island. There was an assumption 

that the same management and eradication techniques applied successfully elsewhere could 

be applied on Palmyra without any background research or trials. A small scale trial would 

have revealed that the technique of eradication would not have been successful and could 

have allowed for research into new techniques, such as the effective bucket bait station that 

was ultimately designed and used. However, the bait buckets designed to exclude crabs 

could have excluded rats, the spacing of the bait stations physically excluded some rats from 

gaining access to the bait, the presence of Bitrex in the bait likely caused bait shyness in 

some individual rats, and the chronic baiting apparently resulted in slight brodifacoum 

resistance. Cumulatively, these problems presented insurmountable challenges to the 

eradication because there was no research/monitoring program built in to identify and then 

rectify problems. Had a project manager with expertise in rat eradication been involved with 

the project throughout, these problems could have been identified early, saving money, time, 

effort and frustration. Unfortunately it is unclear to what extent each of these problems 

alone or in combination caused the failure of the eradication. 

The adaptive management approach is necessary in all eradication attempts, as each project 

presents its own unique set of challenges. Although Palmyra’s ecosystem presents new 

challenges to rat eradication, they are not insurmountable and with the data collected during 

the site assessment in August 2004, an effective eradication plan can be developed. The 

eradication plan will need to be tested in a trial to identify potential problem areas and 

develop solutions to be implemented prior to the successful completion of an eradication on 

the atoll. 

STUDIES CONDUCTED ON PRE-ERADICATION TRIP ASSESSMENT 

We conducted the following research during the site visit and assessment in August 2004 to 

support the development of a rat eradication plan. 

Evaluate Arboreal Nature and Planar Movements of Rats on Palmyra Atoll 

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Methods 

Since the movement, behavior, and canopy use by rats on Palmyra Atoll was unknown, we 

monitored a group of radio-collared rats within a palm forest (5 ha) on Cooper Island. Live 

traps baited with fresh coconut were set both on the ground (25 m apart) and in coconut 

trees (20-50 m apart). Traps were checked and reset daily for one week. Radio collars were 

put on nine rats captured on the ground and 12 rats captured in the tree traps. We only put 

collars on rats that weighed >100 g (collar weight approximately 5g). All rats were fitted with 

radio collars, observed over a 24-hour period, and released on their respective capture site. 

Directional Yagi antennas and digital receivers were used to monitor rat activity daily. The 

study area was visited nightly (2100-0000) and alternately in the dawn (0430-0700) and 

afternoon hours (1300-1500) to assess movement and refuge behaviors. Individuals were 

tracked an average of 12.9 days (s.d.=6.4). Data recorded for each individual included 

active/inactive status, specific spatial location (bearing and distance from a fixed marker 

location), and whether the animal was on the ground or in a tree. Signals determined to be 

inactive for >1 week were excluded from analysis. Daytime and nighttime locations for each 

individual were georeferenced from fixed marker locations using Garmin MapSource 

software and imported to ArcView for further analysis. Range areas were determined using 

a maximum-area calculation from peripheral locations encompassing the majority of central 

locations (assumed or confirmed refuge locations) including any stray or outlying positions. 

We believe this to be an adequate measure of ranging area for the purpose of determining an 

adequate spacing of bait stations to ensure that all rats have access to stations. 

Results and Discussion 

Mean ranging area for rats trapped in trees was 693 m2 (s.d.=334 ) and 1091 m2 (s.d.=1174) 

for ground-trapped rats (Figs. 5 and 6). Males, in general, covered a larger home range area 

(mean = 1317 m2) than females (mean = 424 m2), which is typical for this species (Table 2). 

Our results indicate that ranging areas were surprisingly small, but may be explained by the 

year-round availability of nesting and food resources. Small home range areas are also 

consistent with observations of high rodent abundances, which usually result in each rat 

having a smaller ranging territory (H. Gellerman, pers. Comm..) The information about rat 

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Page 25 of 61 

movement therefore suggests that the distance between bait stations in previous eradication 

effort was likely too great to put all rats at risk of exposure. 

All tree-trapped individuals ventured down and spent nearly 51% of the measured time on 

the forest floor. Inversely, ground trapped rats were observed in the canopy 29% of the 

measured time. This result suggests no rats are strictly arboreal, which is particularly 

favorable if a bait station eradication approach is implemented. 

Although rats were more active during the evening hours, the Palmyra population showed a 

high level of diurnal activity compared to other populations. This may be related to the high 

Figure 5. Ranging areas of 9 ground captured radio collared rats, Palmyra Atoll, August 2005.
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percentage of foliage cover (both canopy and understory) and lack of predators, and/or the 

high density of rats competing for resources. 

 

Figure 6. Ranging areas of 11 tree captured, radio collared rats, Palmyra Atoll, August 2005.
Table 2. Mean, minimum, maximum and median ranging areas (m2

) of rats on 

Palmyra Atoll (2004). Median home ranges represent territory sizes. 

Mean Min Max Median

Male (10) 1317 429 3500 1008

Female (11) 424 145 744 367

Assuming that the ranging area data collected in August, 2004, is representative of rat 

ranging distances, it is clear that a very tight bait station spacing would be required to ensure 

delivery of bait to all rats. Using the lowest ranging territory measured, approximately 68 

bait stations per hectare would be required to capture every rat territory, or about 15,436 

stations atoll-wide. Installation of 15,000 bait stations may not be feasible because it would 

likely be expensive to install and maintain. 

Calibration of a Broadcast Application Rate 

If an aerial or hand bait application is used it is essential to apply enough bait so that it is 

available to rats for about four days. To calculate the appropriate bait application rate, one 

must consider both the uptake of bait by rats and by other species. In tropical systems such 

as Palmyra, land and hermit crabs would play a significant role in removing bait from the 

environment. Although crabs and other invertebrates are not susceptible to anticoagulant 

rodenticides, they are attracted to and compete with rats for bait. Thus, the total estimated 

uptake of bait by both rats and crabs must be considered for accurate bait application rate 

estimates. 

During the field assessment, bait uptake at various application rates was initially measured 

using placebo bait (bait without brodifacoum added) in a plot with an unmonitored buffer 

zone. The buffer zone was intended to reduce the attraction of crabs to the bait in the 

uptake plot. This method was abandoned after initial results demonstrated artificially high 

crab densities even with large buffer zones. Although there was an obvious edge effect to 

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the measured bait uptake, the required bait application rate using this method was 

approximated to be in excess of 60 kg/ha. 

Because of the complications associated with the uptake plots, we estimated the potential

uptake of bait loss by crabs using daily bait consumption rates of crabs in large cage trials 

multiplied by the density of crabs measured in the field. We acknowledge that this is a 

limited estimate and may not reflect true bait loss. It does, however, allow for “ballparking” 

a broadcast application rate. To estimate crab uptake across the atoll two factors were 

measured: 1) bait consumption for each species, and 2) number of individuals by species per 

unit area (crab density). Individual consumption rates for the four most abundant land crab 

species (Coenobita perlatus (N=3), Coenobita brevimanus (N=3), Cardisoma carniferex (n=5), 

Cardisoma rugosa (n=5)) were measured in captivity. All crabs were fed CI-25 placebo bait 

and consumption was measured using a digital balance every 12 hours over a four-day 

period. In collaboration with Alex Wegmann (University of Hawaii), an atoll-wide crab 

density survey for all five species was conducted. Five percent of the emergent land area 

across the major habitat types was surveyed and 250 m transects (2.5 m x 50 m) were 

randomly chosen from a geo-referenced Palmyra Atoll 25 m survey grid. All Coenobita, 

Cardisoma, and Birgus crabs encountered on the transects were counted with tally-counters to 

ensure accuracy. Prominent habitat type was recorded for each transect, and for transects 

that spanned more than one habitat type the habitat composing the majority of the transect 

was recorded. In addition, the time of day and weather conditions were recorded at the start 

of each transect. The survey results for each habitat type were used to extrapolate an atollwide population estimate for each species. 

Crab density data were not normal (left-skewed) when tested with normal probability plots. 

Square root transformation of the data solved this issue. Thus, density estimates were 

square-root-transformed to perform descriptive statistic analyses of the mean, standard 

deviation, upper and lower confidence intervals. Once descriptive statistics were 

performed, data were back-transformed to yield corrected density mean, standard deviation, 

and upper and lower confidence intervals. 

Major habitat types and their extension on Palmyra Atoll are described in Table 3, below: 

Page 28 of 61 
Table 3. Area (ha) of major habitat types on Palmyra 

Palm forest Open ground Pisonia forest Scaevola forest Terminalia forest ATOLL

98.2 20.8 23.8 65.5 19.2 227.6 

Results and Discussion 

The statistical estimates of the crab densities on the atoll are presented in Table 4. Red 

hermit crabs (Coenobita perlatus) were measured as the most abundant crab species on the 

atoll. 

Using the captive crab consumption/density approach to bait application estimate, we 

estimate the highest bait application required to overcome crab consumption over four days 

to be between 3.34 and 47.74 kg/ha, in addition to the application required to deliver bait to 

rats (Tables 5 and 6). 

Our results indicate both land and hermit crabs are important competitors with rats for bait. 

Hermit crabs consume less than land crabs, but are more abundant on the atoll. Due to 

logistical difficulties during the experiments (such as potential captive stress-level effects and 

weather conditions) the consumption rates by crabs may be underestimated. 

Page 29 of 61 
Purple hermit crab Red hermit crab Orange land crab Purple land crab All crabs

Forest Type

Mean (crabs/ha) 139 185 18 26 368

Standard Dev 19 68 1 0 88

Upper CI 205 296 33 40 574

Lower CI 87 99 7 15 209

Forest Type

Mean (crabs/ha) 14 179 46 9 248

Standard Dev 0 113 7 2 122

Upper CI 24 312 77 15 428

Lower CI 7 82 23 4 116

Forest Type

Mean (crabs/ha) 7 116 55 54 231

Standard Dev 8 39 17 13

Upper CI 9 190 97 93 390

Lower CI 4 60 25 26 115

Forest Type

Mean (crabs/ha) 5 15 4 5

Standard Dev 6 0 13 4

Upper CI 8 29 5 9

Lower CI 3 6 3 3

Forest Type

Mean (crabs/ha) 67 416 44 47 574

Standard Dev 6 182 4 5 197

Upper CI 100 631 69 75 874

Lower CI 40 246 24 26 336

Grand Total Means 232 910 166 142 1450

Coconut palm forest (98.2 ha)

Table 4. Estimated crab densities per hectare. Means, standard deviation, upper confidence intervals (Upper CI), and

lower confidence intervals (Lower CI) for Palmyra Atoll, 2004.

Terminalia forest (19.2 ha)

Scaevola forest (65.5 ha)

Pisonia forest (23.8 ha)

Open (20.8 ha)

Purple hermit crab Red hermit crab Orange land crab Purple land crab All crabs

Forest Type

Mean (crabs/ha) 139 185 18 26 368

Standard Dev 19 68 1 0 88

Upper CI 205 296 33 40 574

Lower CI 87 99 7 15 209

Forest Type

Mean (crabs/ha) 14 179 46 9 248

Standard Dev 0 113 7 2 122

Upper CI 24 312 77 15 428

Lower CI 7 82 23 4 116

Forest Type

Mean (crabs/ha) 7 116 55 54 231

Standard Dev 8 39 17 13

Upper CI 9 190 97 93 390

Lower CI 4 60 25 26 115

Forest Type

Mean (crabs/ha) 5 15 4 5

Standard Dev 6 0 13 4

Upper CI 8 29 5 9

Lower CI 3 6 3 3

Forest Type

Mean (crabs/ha) 67 416 44 47 574

Standard Dev 6 182 4 5 197

Upper CI 100 631 69 75 874

Lower CI 40 246 24 26 336

Grand Total Means 232 910 166 142 1450

Coconut palm forest (98.2 ha)

Table 4. Estimated crab densities per hectare. Means, standard deviation, upper confidence intervals (Upper CI), and

lower confidence intervals (Lower CI) for Palmyra Atoll, 2004.

Terminalia forest (19.2 ha)

Scaevola forest (65.5 ha)

Pisonia forest (23.8 ha)

Open (20.8 ha)

76

30

23

51

14

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76

30

23

51

14

Page 30 of 61 
Page 31 of 61 

Purple hermit crab Red hermit crab Orange land crab Purple land crab Pooled

Forest Type

Mean 0.53 0.71 0.07 0.1 1.41

Standard Dev 0.07 0.26 0 0

Upper CI 0.78 1.13 0.13 0.15 2.19

Lower CI 0.33 0.38 0.03 0.06 0.8

Forest Type

Mean 0.05 0.68 0.18 0.03 0.95

Standard Dev 0 0.43 0.03 0.01

Upper CI 0.09 1.19 0.3 0.06 1.64

Lower CI 0.03 0.31 0.09 0.02 0.44

Forest Type

Mean 0.03 0.44 0.21 0.21 0.88

Standard Dev 0.03 0.15 0.06 0.05

Upper CI 0.04 0.73 0.37 0.36 1.49

Lower CI 0.02 0.23 0.09 0.1 0.44

Forest Type

Mean 0.02 0.06 0.02 0.02 0.11

Standard Dev 0.02 0 0.05 0.02

Upper CI 0.03 0.11 0.02 0.03 0.19

Lower CI 0.01 0.02 0.01 0.01 0.05

Forest Type

Mean 0.25 1.59 0.17 0.18 2.19

Standard Dev 0.02 0.7 0.01 0.02

Upper CI 0.38 2.41 0.26 0.29 3.34

Lower CI 0.15 0.94 0.09 0.1 1.29

Open

Coconut palm forest

Table 5. Predicted crab bait consumption (kg/ha) (mean, std. dev, upper and lower confidence intervals) by species and 

habitat type over four days assuming mean consumption rate, Palmyra Atoll, 2004. Value highlighted in yellow indicates 

highest probabl application rate to overcome crab bait loss.

Terminalia forest

Scaevola forest

Pisonia forest
Purple hermit crab Red hermit crab Orange land crab Purple land crab Pooled

Forest Type

Mean 1.03 12.19 0.71 0.92 14.85

Standard Dev 0.14 4.5 0.03 0

Upper CI 1.51 19.54 1.31 1.41 23.77

Lower CI 0.64 6.57 0.29 0.53 8.03

Forest Type

Mean 0.11 11.8 1.81 0.31 14.03

Standard Dev 0 7.5 0.27 0.06

Upper CI 0.18 20.62 3.05 0.53 24.37

Lower CI 0.05 5.43 0.89 0.15 6.53

Forest Type

Mean 0.05 7.65 2.15 1.89 11.74

Standard Dev 0.06 2.55 0.66 0.44

Upper CI 0.07 12.58 3.81 3.25 19.71

Lower CI 0.03 3.95 0.97 0.9 5.85

Forest Type

Mean 0.04 1 0.16 0.18 1.38

Standard Dev 0.04 0.03 0.5 0.15

Upper CI 0.06 1.89 0.21 0.31 2.46

Lower CI 0.02 0.39 0.12 0.09 0.62

Forest Type

Mean 0.49 27.47 1.72 1.65 31.34

Standard Dev 0.04 12.02 0.14 0.18

Upper CI 0.74 41.67 2.71 2.62 47.74

Lower CI 0.3 16.22 0.96 0.91 18.39

Open

Coconut palm forest

Table 6. Predicted crab bait consumption (kg/ha) (mean, std. dev, upper and lower confidence intervals) by species and 

habitat type over four days assuming maximum consumption rate, Palmyra Atoll, 2004. Value highlighted in yellow

indicates application rate to overcome crab bait loss.

Terminalia forest

Scaevola forest

Pisonia forest

Purple hermit crab Red hermit crab Orange land crab Purple land crab Pooled

Forest Type

Mean 1.03 12.19 0.71 0.92 14.85

Standard Dev 0.14 4.5 0.03 0

Upper CI 1.51 19.54 1.31 1.41 23.77

Lower CI 0.64 6.57 0.29 0.53 8.03

Forest Type

Mean 0.11 11.8 1.81 0.31 14.03

Standard Dev 0 7.5 0.27 0.06

Upper CI 0.18 20.62 3.05 0.53 24.37

Lower CI 0.05 5.43 0.89 0.15 6.53

Forest Type

Mean 0.05 7.65 2.15 1.89 11.74

Standard Dev 0.06 2.55 0.66 0.44

Upper CI 0.07 12.58 3.81 3.25 19.71

Lower CI 0.03 3.95 0.97 0.9 5.85

Forest Type

Mean 0.04 1 0.16 0.18 1.38

Standard Dev 0.04 0.03 0.5 0.15

Upper CI 0.06 1.89 0.21 0.31 2.46

Lower CI 0.02 0.39 0.12 0.09 0.62

Forest Type

Mean 0.49 27.47 1.72 1.65 31.34

Standard Dev 0.04 12.02 0.14 0.18

Upper CI 0.74 41.67 2.71 2.62 47.74

Lower CI 0.3 16.22 0.96 0.91 18.39

Open

Coconut palm forest

Table 6. Predicted crab bait consumption (kg/ha) (mean, std. dev, upper and lower confidence intervals) by species and 

habitat type over four days assuming maximum consumption rate, Palmyra Atoll, 2004. Value highlighted in yellow

indicates application rate to overcome crab bait loss.

Terminalia forest

Scaevola forest

Pisonia forest

Page 32 of 61 
Brodifacoum Resistance 

We conducted two trials evaluating the susceptibility and potential resistance of rats to 

brodifacoum from long-term use on Cooper Island. The details of the study and results can 

be found in Pitt 2004 (attached). 

In summary, one of the rats, dosed at four times the LD50, died 21 days post-dosing and 

showed no symptoms characteristic of anticoagulant poisoning. This situation suggests that 

slight resistance to brodifacoum may occur within the population, and/or vitamin K (an 

antidote to brodifacoum) is abundantly available and consumed on the atoll. Vitamin K is

contained in coconut fruit, particularly in young green coconuts, but its relative importance 

in the diet of the rats on Palmyra is unclear. 

Rat Bait Preference 

Methods 

Potential baits for use during an eradication on Palmyra were tested for palatability in paired 

trials against other bait types or natural foods. Individual rats were live-trapped and held a 

minimum of 24 hours pre-trial. Trials consisted of 10 individuals each presented with paired 

food types. Food types were presented in random locations within the cage to reduce spatial 

selectivity. Trial results were determined by observation of first bait/food type selected. 

Thus, the first bait tasted by a rat was considered preferred. Each rat was observed for an 

additional period after the animal made its first choice to see if the rat switched and 

consumed the alternative bait/food type. The time to selection was recorded for each 

individual in addition to any switches made to the alternate bait/food choice during the trial. 

Three main trial types were conducted: 1) commercial bait vs. competing commercial bait to 

assess bait preference; 2) bait vs. bait of the same type at various stages of degradation to 

determine if bait exposed to environmental conditions was palatable; and 3) bait vs. natural 

foods known to be consumed by rats on Palmyra. 

Page 33 of 61 
Results and Discussion 

The results (Table 7) indicate that CI-25 (the bait developed by Bell Labs and Island 

Conservation for use on Anacapa Island, Channel Islands National Park, California) was the 

most preferred bait when compared to both natural foods and other baits. Ramik (2 g) was 

preferred to Ramik (8 g) and natural Terminalia fruit but not Weatherblock XT. As has been 

found in other studies (Howald et al.2005), bait exposed to environmental conditions and 

lightly covered with mold was preferred to fresh bait. 

Table 7. Results of rat preference trials, Palmyra Atoll, 2004. 

Baits in Trial Preferred Preference (%) 

Paired Bait Trials 

CI-25/Ramik (8g) CI-25 90 

CI-25/Ramik(broken 8 g) - 50 

CI-25/Ramik (2 g) CI-25 60 

CI-25/CI-25 (wax coat) CI-25 60 

Ramik (8 g)/Ramik (2 g) Ramik (2 g) 100 

Ramik (8 g)/Weatherblock Weatherblock 100 

Degraded Bait Trials 

Wblk/ Wblk (mold – 1 wk) Moldy Wblk 70 

Wblk/ Wblk (mold – 2 wk) Moldy Wblk 60 

Natural Food Trials 

CI-25/Coconut CI-25 100

Ramik (2 g) /Terminalia fruit Ramik (2 g) 60 

Bait Degradation 

In order to ensure effective bait delivery to rats on the island, the bait must be able to 

withstand the island’s climate and retain its size, shape and consistency. The rate of bait

degradation is related to weather conditions, and is more rapid under the hot, humid, and 

wet climate of Palmyra. 

Page 34 of 61 
Methods 

To determine how well different types of bait retain their consistency in the Palmyra 

environment, degradation trials were conducted in natural conditions and in bait stations. 

Details of the degradation trial can be found in McClelland (2004) (Appendix 2). 

Results and Discussion 

The degradation rate for each type of bait in natural conditions was very similar among 

habitat types, indicating that type of bait is more important than microhabitat (Tables 8 and 

9). The most preferred bait, CI-25, could not withstand the humid conditions and 

disintegrated rapidly (mean = 3 days). In addition we observed that insects, especially ants, 

proved to be moderate consumers of all baits when .the bait was on the ground for more 

than 10 days. 

In bait stations, Weatherblock withstood environmental conditions similarly among habitat 

types and resisted mold for one week longer than when fully exposed to the environmnent 

(Tables 8 and 9). 

Our results demonstrate that the Weatherblock bait and the large (8 g) Ramik placebo 

broadcast baits proved to be effective in withstanding degradation (mold/moisture). 

Table 8. Results of degradation trial by habitat type and fully exposed to the 

environment, Palmyra Atoll, 2004. 

Bait type Days to mold/crack Days to disintegration 

Scaevola 

CI-25 1 3

Ramik (2 g) 2 5 

Fastrac 4 >20

Generation block 4 >20 

Weatherblock 7 >20

Grassland

CI-25 1 3

Ramik (2 g) 3 4 

Fastrac 3 >20

Page 35 of 61 
Generation block 6 >20 

Weatherblock 6 >20

Terminalia 

CI-25 1 3

Ramik (2 g) 2 5 

Fastrac 3 >20

Generation block 7 >20 

Weatherblock 6 >20

Pisonia 

CI-25 1 3

Ramik (2 g) 2 3 

Fastrac 3 >20

Generation block 7 >20 

Weatherblock 7 >20

Cocos 

CI-25 1 3

Ramik (2 g) 2 4 

Fastrac 3 >20

Generation block 5 >20 

Weatherblock 5 >20

Mean degradation 

CI-25 1.0 (s.d.=0.0) 3.0 (s=0.0) 

Ramik (2 g) 2.2 (s.d.=.71) 4.2 (s=.84) 

Fastrac 3.6 (s.d.=.89) >20

Generation block 5.8 (s.d.=1.3) >20 

Weatherblock 6.2 (s.d.=.84) >20

Page 36 of 61 
Table 9. Results of Weatherblok XT degradation trial in bait stations by habitat type, 

Palmyra Atoll, 2004. 

Bait type Days to mold/crack Days to disintegration 

Scaevola

Weatherblock 13 > 20

Grassland 

Weatherblock 15 > 20

Terminalia 

Weatherblock 13 > 20

Cocos

Weatherblock 13 > 20

Pisonia 

Weatherblock 20 > 20

Mean degradation (days)

Weatherblock 14.8 (s.d.=3.03) > 20 

Non-Target Species and Mitigation Measures 

Palmyra supports several species that may be at risk of disturbance or exposure to 

rodenticide if basic mitigation measures are not adopted. The range of species includes 

landcrabs (if bromethalin is used), breeding seabirds, migratory shorebirds, two species of

sea turtles and possibly the Hawai`ian Monk Seal (Monachus schauinslandi). In addition, the 

two domestic cats and a dog on the island will require specific mitigation to prevent 

exposure to the rodenticides used. 

Specific mitigation measures will need to be developed for each species to minimize the 

impact of disturbance and/or rodenticide exposure. The primary mitigation is the timing of 

the bait operation to minimize the numbers of individuals of each species of concern on the 

island during baiting operation. Specific mitigation measures adopted are dependent on the 

eradication strategy used and will be developed further in a separate recommendation report. 

Page 37 of 61 
CONCLUSIONS FROM PRE-ERADICATION STUDIES

• Eradication of rats from Palmyra Atoll is quite feasible, however it is by no means 

trivial and there are several technical challenges. 

• No rats are exclusively arboreal 

• The planar movements of rats were relatively small, indicating that the distance 

between bait stations in previous work was too great for eradication. 

• Broadcast application rates may need to be in excess of 60 kg/ha to compensate for 

loss of bait to the high density of crabs found in various habitats throughout the 

atoll. 

• Possible mild resistance to brodifacoum exists within the rat population. 

• Palmyra rats prefer CI-25 bait over both other available baits and key, naturally 

abundant and available foods. 

• CI-25 bait degrades rapidly on Palmyra and does not last more than a few days. 

MANAGEMENT IMPLICATIONS FOR FUTURE ERADICATION EFFORT

• Both bait station and aerial application approaches could be used (and/or required) 

on Palmyra Atoll. 

• Broadcast application in excess of 60 kg/ha may be needed to compensate for crab 

uptake and competition for the bait, ensuring enough bait on the ground for 3-4 

days. 

• Both brodifacoum and a secondary rodenticide, such as bromethalin, could be used 

in the eradication attempt. Bromethalin should overcome any brodifacoum-resistant 

individual rats, but landcrabs are susceptible to bromethalin and would require 

specific mitigation if bromethalin is used, to prevent population level exposure. 

• A bait should be developed that is as palatable as CI-25 and that can withstand the 

Palmyra climate. 

Page 38 of 61 
• A bait is in development currently and will be in degradation/palatability tests on 

Palmyra in February 2005. 

RECOMMENDATIONS

1. Carry out specific research to conduct a trial eradication and refine a plan for 

eradication of rats from Palmyra Atoll, including: 

• Confirming broadcast application rate. 

• Developing a broadcast bait that can withstand the climate on Palmyra. 

• Testing rat use of elevated bait stations. 

2. Conduct a trial broadcast eradication on Palmyra Atoll, with two rodenticides. 

3. Review results and modify the approach to eradication as necessary; then begin 

planning the eradication of rats from Palmyra Atoll.

ACKNOWLEDGEMENTS

We wish to thank Mr. Ian Cumming for supporting the site assessment of Palmyra Atoll. 

We thank TNC Palmyra staff – Nancy Mackinnon, Matt Lange, Elizabeth Lange, Dacia, 

Danny, Joanne MacIsaac, and Chuck Cook for their assistance, guidance and support for our 

site visit to the atoll. Steve Barclay, Beth Flint, Don Palawski provided USFWS support. 

Jacob Sheppard, Nancy Ogle, Virginia McDermott and Holly Jones of Island Conservation 

assisted with logistics and provided general support. We acknowledge Jim Murphy of the 

USDA-WS for his moral support of this assessment and sharing data and insight into his 

experience on Palmyra Atoll. We thank Peter Dunlevy, Beth Flint, Gary Witmer and Lee 

Ann Woodward for reviewing an earlier draft of this trip report.

Page 39 of 61 
REFERENCES

Atkinson, I. A. E., 1985. The spread of commensal species of Rattus to oceanic islands and 

their effect on island avifaunas. In: Moors, P. J. (Ed.), Conservation of island birds Case 

studies for the management of threatened island species, International Council for Bird 

Preservation, Technical Publication 3, pp 35-81. 

Brown, K. P., 1997. Predation at nests of two New Zealand endemic passerines; 

implications for bird community restoration. Pacific Conservation Biology 3, 91-98. 

Brown, S., C. Hickey, B. Harrington and R.Gill (editors). 2001. United States Shorebird 

Conservation Plan. 2nd Edition. Manomet Center for Conservation Sciences, Manomet, 

Massachusetts. 

Cowan, D., G. Kerins, M. Lambert, A. Macnicoll and R. Quy. 2004. Anticoagulant 

resistance in farm rat populations in the UK: Implications for management and 

environmental impact. Abstract presentation to the 2nd Invasive Rodent Summit, National 

Wildlife Research Centre, Fort Collins, Colorado. 

Engilis, Jr., A. and Naughton, M. 2004. U.S. Pacific Islands Regional Shorebird Conservation 

Plan. U.S. Shorebird Conservation Plan. U.S. Department of the Interior, Fish and Wildlife 

Service, Portland, Oregon. 

Galvan, J.P., B. Tershys, G. Howald, A. Samaniego, B. Keitt, M. Browne, J. Russell, M. 

Pascal and J. Parkes. 2005. A review of commensal rodent eradications on islands. 

Presentation at the Pacific Seabird Group Meeting, Portland, Oregon, January 2005. 

Groombridge, B., 1992. World Conservation Monitoring Centre, British Museum (Natural 

History), International Union for Conservation of Nature and Natural Resources. Global 

biodiversity: status of the earth's living resources: a report. Chapman & Hall, London. 

Hooker, S. and J. Innes. 1995. Ranging behaviour of forest-dwelling ship rats, and effects of 

poisoning with brodifacoum. New Zealand Journal of Zoology. 22:291-304. 

Howald, G.R., Faulkner, K., B. R. Tershy, B. S. Keitt, H. Gellerman, E. M. Creel, M. 

Grinnell, S. Ortega and D.A. Croll. 2005. Eradication of Black Rats from Anacapa Island: 

Biological and Social Considerations. Proceedings of the Sixth California Islands 

Symposium, Ventura, California, December 1 – 3, 2003. Edited By 

D. K. Garcelon and C. A. Schwemm. Page 299-312. 

Lindsey, G. D., S. M. Mosher, S. G. Fancy, and T. D. Smucker. 1999. Population structure 

and movement patterns of black and Polynesian rats in a Hawaiian rainforest. Pacific 

Conservation Biology 5(2):94-102. 

Macnicoll, A.D. 1986. Resistance to 4-hydroxycoumarin anticoagulants in rodents. In: 

Pesticide Resistance: Strategies and Tactics for Management. National Academy Press, Washington, 

DC. 

Page 40 of 61 
Taylor, R.H. and Thomas, B.W. 1989. Eradication of Norway Rats (Rattus 

Norvegicus) from Hawea Island, Fiordland, using Brodifacoum. New Zealand Journal 

of Ecology 12:23-32. 

USDA. 2002. Report of rat eradication operations conducted under quarantine exemption 

to use Weatherblok XT containing brodifacoum and Fastrac Blox containing bromethalin in 

a field situation on Palmyra Atoll, Line Islands, Pacific Ocean. Report to the US. 

Environmental Protection Agency. 

Veitch, D.R. 2002. Eradication of Pacific Rats (Rattus exulans) from Fanal Island, New 

Zealand. Pages 357-359. In: C.R. Veitch and Clout, M.N. (eds). Turning the tide: the 

eradication of Invasive Species. IUCN SSC Invasive Species Specialist Group. IUCN, 

Gland Switzerland and Cambridge, UK. 

Whittaker, R.J. 1998. Island biogeography; ecology evolution, and conservation. Oxford 

University Press, Oxford. New York, New York. 

Page 41 of 61 
APPENDIX 1. BAIT STATION CRAB EXCLUSION DESIGN, D. VICE

Toxicant Delivery Stations and Terrestrial Crab Exclusion 

Project Summary – Palmyra Atoll

August 2004 

Prepared by: 

Daniel Vice 

Assistant State Director 

USDA, Wildlife Services 

1060 Route 16, Suite 103C 

Barrigada Heights, Guam 96913 

INTRODUCTION 

Successful delivery of anticoagulant poisons to every animal is the fundamental premise 

behind complete eradication of rats (Rattus spp.) from islands. In the absence of non-target 

species, bait delivered via aerial or hand broadcast can be made available to every animal in a 

defined time frame. However, non-target species often prevent the use of broadcast 

techniques, as primary and secondary uptake may adversely impact unintended targets 

and/or may limit bait availability to rats. On many tropical islands, terrestrial crabs occur in 

great abundance, and may consume bait directly, competing with rats and subsequently 

reducing bait availability. Additionally, crabs that have ingested toxicants become secondary 

hazards to migratory shorebirds, other native wildlife, and potentially, humans. To mitigate 

such hazards, anticoagulant toxicants are frequently delivered in secure bait stations. An 

ideal delivery device excludes all non-target hazards and allows free access to all sizes and 

species of rats. 

Beginning in 2000, Palmyra Atoll, the northern most island in the Line Island chain, was the 

site of a black rat (R. rattus) eradication attempt, utilizing brodifacoum delivered in bait 

stations. Initially delivered in 12” long, 1 1⁄2” diameter PVC pipes, hermit crabs (Coenobita

spp.), land crabs (Cardasoma spp.) and coconut crabs (Birgus latro) consumed large volumes of 

toxicant. To further exclude crabs, several modifications were made to the delivery device, 

including anchoring the pipe to the ground or a raised platform, as well as capping one end 

of the pipe. These modifications were not successful at eliminating bait take by crabs. 

Following approximately 6 months of use, these devices were abandoned. The use of an 

alternative design, consisting of a covered 4-gallon plastic pail, with a 1 1⁄2” diameter hole cut 

into the side approximately 8” up from the bottom of the pail, was implemented. This 

device provided some degree of exclusion for hermit crabs, land crabs, and coconut crabs. 

During this effort, at least one bristle-thighed curlew (Numenius tahitiensis), a species of 

concern, was killed through secondary toxicant uptake after eating hermit crabs that had 

ingested anticoagulant bait. Despite intensive poisoning over a 24 month period, the 

eradication effort at Palmyra was unsuccessful. 

Page 42 of 61 
Future eradication attempts on Palmyra may require the development and use of delivery 

devices that provide complete crab exclusion as well as accessibility to all rats. In support of 

this need, a series of in situ and in vitro bait station experiments were initiated on Palmyra. 

The primary objective of this project was to assess the ability of different bait delivery 

stations to exclude terrestrial crabs. 

METHODS 

Prototype toxicant delivery stations were constructed of materials available on Palmyra Atoll. 

Three general station types were developed. The first, a platform station, consisted of 2” 

outside diameter PVC pipe, fitted with a 12” x 12” x3/8” plywood square on top of the 

pipe. Affixed to the plywood was a Protecta© toxicant delivery box (11 1⁄2” x 12” x 6 1⁄2”, 2 

entry box). The PVC pipe was cut to provide an above-ground height of both 24” and 18”. 

This device will be referred to as the “box” station. 

The second station type was constructed of 1⁄2” inside diameter electrical magnetic tubing

(EMT; steel pipe) with a lid from a 5 gallon bucket firmly affixed to the pipe via a 1⁄2” hole 

drilled in the center of the lid. A second lid, to provide some protection from environmental 

conditions, was affixed approximately 10” above the first lid. The lower lid was set to 

provide an above-ground platform height of both 24” and 18”. This device will be referred 

to as the “pipe” station. 

The third station type consisted of a 4 gallon plastic bucket, fitted with a lid. A 1 1⁄2” 

diameter hole was cut in the side of the bucket, approximately 8” from the bottom of the 

bucket. To further facilitate rat entrances and reduce crab damage to the bucket, a variation 

on this design was constructed, which included a 2” outside diameter, 4” length PVC pipe 

sleeve, inserted into the hole on the side of the bucket. This device will be referred to as the 

“bucket” station. 

Evaluations of bait station crab exclusion were conducted inside a warehouse formerly 

utilized by a commercial fishing enterprise on Palmyra. Crabs were housed in 4’ x 4’ x 2.5’ 

rigid plastic “totes” which are widely used in the commercial fishing industry. The smooth 

inner surface of the bins prevented crabs from climbing out. A single trial was defined by 

the same population of crabs in the same tote with a single bait station design (Table 2). 

Any change in crab number, individuals, or bait station design constituted a new trial. The 

number of exposure hours represents the total hours of individual crab exposure to a given 

bait station (e.g., 5 crabs in a single trial for 24 hours = 120 crab exposure hours). 

 Terrestrial crabs were grouped in three taxonomic categories for evaluation: 1) Hermit crabs 

(Coenobita perlatus and C. brevimanus), 2) Coconut crabs, and 3) Land crabs (Cardasoma carnifex

and C. rugos). Live crabs were hand captured on Palmyra, placed inside totes, and exposed to 

bait stations. Hermit crabs were initially placed in groups of 55, with 35 adults and 20 subadults in each tote. Hermit crab densities were doubled to 110 individuals (70 adult and 40 

sub-adults) following 2 full days of trials. These densities were established to mimic the 

“piling” behavior that hermit crabs exhibit when a valuable food source is found. Hermit 

crabs were considered adults if they were using a Hawai`ian turban shell (Turbo sandwicenis); 

sub-adults were smaller crabs in any other shell. Land crabs were placed in groups of 5, and 

coconut crabs were held individually (this was done to reduce the probability of competitive 

Page 43 of 61 
interactions and subsequent injuries while in captivity). A single bait station was placed 

inside each tote. Stations were baited with placebo Ramik© bait (20 gram pellets) and 

roasted coconut mixed with peanut butter. Bait in each station was captivated with steel 

rods or tie wire to prevent removal. Entries into the pipe and box bait stations were 

documented through bait consumption. Entries into the bucket station were documented 

through bait consumption and crabs stuck inside the bait station. Because the number of 

nightly entry events could not be established through bait consumption, total entries were 

not documented. Exclusion capabilities are reported as “yes” or “no”. Crabs were provided 

ad lib water and alternate natural food items during the duration of the trials. 

Following the initial lab trials, a small number of field trials using the three bait station types 

were initiated. Seven bait stations (2 – 24” box stations, 1 – 18” box station, 2 - bucket 

stations without a PVC insert, 1 - bucket station with a PVC insert, and 1 – 18” pipe station) 

were placed in field use for three days, to assess crab exclusion and rat accessibility. Devices 

were baited in the same manner as in the lab trials. Crab and rat entrances were assessed 

using bait consumption and ink tracking boards. 

RESULTS 

Lab Trials 

Thirty five separate lab trials were initiated during this effort, with a total crab exposure time 

of 41,175 hours (Table 1). Of the three primary stations evaluated, only the pipe station was 

accessed by crabs, and coconut crabs were the only group that entered the station and 

consumed bait. The bucket stations excluded all crab entries across each taxonomic group, 

although coconut crabs easily accessed the top of the bucket station. As well, the box 

station excluded all crab entries across each taxonomic group. Coconut crabs were able to 

climb the PVC pipe that supported the box and reach the delivery device, but were unable to 

access the secured bait inside the box. 

Hermit crabs were able to climb the support pipe for both the pipe and box stations, but 

were unable to access bait as the platforms on both stations precluded entry. Only large 

adult hermit crabs were observed climbing the PVC pipe supporting the box station. Both 

adult and larger sub-adult hermit crabs were able to climb the 1⁄2” EMT supporting the pipe 

station. In several instances, sub-adult hermit crabs were observed clinging to the shell of

adult crabs as they climbed, and were therefore capable of reaching higher on the stations

than if climbing unaided. 

Land crabs were not observed making any entry attempts into any of the bait stations. It is 

apparent that land crabs will be a greater impact to eradication efforts if broadcast 

methodologies are incorporated. 

Field Trials

Given the small number of stations available and the short duration of testing, field 

evaluations provided limited information on crab exclusion and rat accessibility. In three 

nights of field use, only a single bucket station, without the PVC insert, received a rat visit. 

All stations were free of any indication of crab entries. 

Page 44 of 61 
TRIAL CRAB TYPE # CRABS 

/TRIAL 

# TRIALS # EXPOSURE 

HOURS 

CRAB 

ENTRIES

Bucket Land Crab 5 2 1195 No

Bucket Coconut Crab 1 4 101 No

Bucket Hermit Crab 55 3 8629.5 No

Bucket Hermit Crab 110 1 5170 No

24” Pipe Coconut Crab 1 2 36 Yes 

18” Pipe Hermit Crab 55 2 2585 No 

24” Pipe Hermit Crab 55 2 2585 No 

18” Pipe Land Crab 5 2 115 No 

24” Pipe Land Crab 5 2 120 No 

18” Pipe Hermit Crab 110 1 5170 No 

24” Box Coconut Crab 1 4 101 No 

18” Box Land Crab 5 2 495 No 

24” Box Land Crab 5 2 500 No 

18” Box Hermit Crab 55 2 2585 No 

24” Box Hermit Crab 55 3 6617.5 No 

18” Box Hermit Crab 110 1 5170 No 

Table 1. Exposure time and crab entrances for toxicant bait stations evaluated on 

Palmyra Atoll, August 2004. 

DISCUSSION 

The ideal toxicant bait station for use on Palmyra would have 100% crab exclusion, 100% 

accessibility to all rats, be cheap to build/purchase, and be simple to apply in the field. The 

three different bait station types evaluated here all appear to have significant crab exclusion 

qualities, and were constructed of readily available materials. The pipe and bucket stations 

would be easier to apply in field use than the box station, as the box station would require 

the use of rebar or some other support material for attachment to the ground. However, 

given the apparent repellency to coconut crabs offered by the box station, it may be the 

device of choice on islands with substantial coconut crab populations (i.e., Sand Island). 

Prior to implementing wide-scale use of any delivery device, the accessibility of the station to 

rats must be assessed. Each of these devices appears to have complete accessibility to rats, 

but this has not been verified. An important next step will be to complete lab trials using 

captive rats exposed to the delivery devices, to assess accessibility. 

A challenge for the application of any large-scale eradication attempt using bait stations will 

be quality control in field use. Any vegetation, litter, or other materials around a station may 

enhance the ability of non-targets to enter the station. Both hermit crabs and coconut crabs 

are extremely adept climbers, and small hermit crabs can support themselves on extremely 

thin branches or leaves. In addition, bait stations that are not well supported or anchored 

can be knocked over by coconut crabs, making bait subsequently available to non-target 

species. Mitigation for these potential hazards must be developed and implemented at the 

outset of any eradication attempt and frequent quality assurance reviews should be 

Page 45 of 61 
conducted at regular intervals to ensure field application techniques are meeting the 

prescribed use patterns. 

Page 46 of 61 
 

APPENDIX 2. BRODIFACOUM RESISTANCE STUDY, W. PITT. 

Study Title:

Resistance in roof rats (Rattus rattus) from Palmyra Atoll 

Prepared by: 

William C. Pitt, PhD 

USDA APHIS, WS, NWRC, Hawai`i Field Station 

Sponsor: 

 Name: Island Conservation Northwest 

1485 Crawford Road 

Kelowna, British Columbia, Canada 

 

Name: U.S. Fish and Wildlife Service 

Address: Pacific Islands Office 

 P.O. Box 50088

Honolulu, HI 96850

Page 47 of 61 
Introduction 

This field study is one component of continuing research to evaluate the reasons for an 

unsuccessful rodent eradication program and to determine the feasibility of future 

eradication efforts on Palmyra Atoll. Previously, the Nature Conservancy attempted an 

island eradication effort using bait stations with brodifacoum based baits. Baiting continued 

for more than two years and not all the rats were removed. Further, baiting around the 

housing complex has continued for 4 or more years with brodifacoum primarily but also 

with diphacinone baits. One possibility for the failed eradication effort is that a segment of 

the rat population was resistant to brodifacoum and thus not susceptible to control. The 

purpose of the current study was to evaluate if any portion of the rat population is resistant 

to brodifacoum due to previous baiting efforts. The rats most likely to show signs of 

resistance would be rats near the housing complex on Cooper Island where baiting with 

brodifacoum has been ongoing for the longest period of time. 

 

Methods and Results 

 

General Methods:

Black rats (Rattus rattus) were captured on Cooper Island near the base camp between 

August 7-14 2004. This area has had the longest history of brodifacoum use and if rats had 

developed resistance it would likely come from this population. All rats were sexed, weighed, 

and housed in individual cages. Rats were maintained under outdoor ambient conditions, 

but under a roofed structure to prevent wetting by precipitation or overheating by direct 

Page 48 of 61 
sunlight. Water was available ad libitum. CI-25 placebo bait was used as food and was 

always available for control animals and available to treatment animals after all treatment bait 

had been consumed. 

For treatment animals, an LD 50 of 0.7 mg/kg was used as the LD 50 based on the 

published range of 0.65 – 0.73 mg/kg for black rats. 

All rats were examined daily and the condition of the rats and any mortalities were recorded. 

Dead rats were weighed, sexed, and necropsied for signs of anticoagulant poisoning as 

described by Stone et al. (1999). The bait would be submitted for analysis if < 50% of the 

treatment rats are dead or appear moribund by the end of the feeding trial. This chemical 

analysis of the % active ingredient would have been done to assure that the low mortality 

rate was not a result of insufficient concentration of active ingredient. 

Resistance Trial A:

Twenty rats were used in resistance Trial A with equal numbers of males and females 

randomly placed into control and treatment groups (Table 1). Each treatment rat was fed 1 

Final block (50 ppm Brodifacoum) on two consecutive days (2 Final blocks total). The LD

50 dose varied according to weight of rats (0.014 g Final block per gram of animal). 

The rats were initially dosed on 8 August 2004 (1200 hrs) with 1 Final Block and again on 9 

August 2004 with a second Final Block. All treatment rats died 5-10 days after initial 

exposure to bait (13 – 18 August, 2004). 

Page 49 of 61 
Resistance Trial B: 

Twenty-eight rats (14 males, 14 females) were used in resistance Trial B (Table 2). Rats were 

captured 8 - 10 August 2004 on Cooper Island near the research complex. Each rat was

randomly placed into one of four treatment groups limited by having at least 3 of each sex in 

each treatment group. The treatment groups were control, LD 50 dose, twice LD 50 dose, 

and four times LD 50 dose. Each LD 50 dose was normalized based on mass of the rat. 

Each treatment rat was fed a single dose of CI -25 (25 ppm brodifacoum). 

The rats were initially dosed on 11 August 2004 (1300 hrs). All treatment rats died 5-21 days 

(mean = 8.7 days) after initial exposure to bait (16 August – 1 September, 2004). Four 

treatment rats persisted after 10 of the initial dose with death occurring on days 11, 11, 13, 

and 21 after initial dose. 

Necropsy

Two control rats (#13, 17) and one treatment rat (#32) were necropsied to document signs 

of bleeding or other abnormalities (Table 3). The control rats had been euthanized on 3 

September and the treatment rat had been found dead on 1 September, 2004. Necropsies 

included a gross physical examination, removal of the fascia, and internal examination of the 

organs to detect signs of bleeding. 

Page 50 of 61 
No obvious signs of bleeding were observed in any of the rats. Rat #32 had a small 

hematoma on the right front leg but this appeared to be a minor injury that had previously 

healed. Rat #32 had external trauma to its head but it was unclear if this happened pre or 

post mortem. The injuries to the head were sufficient to cause death. 

Discussion 

The eventual death of all rats suggests the majority of black rats on Palmyra Atoll are 

susceptible to the effects of brodifacoum. Seven rats died with a single dose at the LD 50

level for black rats. Further, 28 of 29 rats died within 2 weeks of the initial dose (one rat 

escaped). These results indicate that there is not a large portion of the population resistant 

to the effects of brodifacoum. Further, it is likely that there is not a significant source of 

Vitamin K in their diet to counteract the effects of the rodenticide. 

The length of time between initial dose and death of at least one rat suggests that a portion 

of the population may be resistant to effects of brodifacoum. This conclusion is further 

supported by the lack of hemorrhaging observed during the necropsy of a rat that persisted 

21 days after the initial dose. The rat received 4 times the LD 50 dose and did not show 

obvious signs of hemorrhaging. 

Rats survived an average of 7 days and 8.1 days (removing rat #32) after receiving the initial 

dose in resistance trials A and B respectively. Although rats did not die quickly from the 

high doses of brodifacoum provided, the survival duration after the initial dose is similar to 

Page 51 of 61 
other studies of brodifacoum (Gill and Redfern 1980). This length of survival after initial 

dosage is unremarkable. 

 

Recommendations 

1. A second baiting with another anticoagulant would be necessary to ensure complete 

eradication, if brodifacoum based bait is used to remove rats from Palmyra Atoll. 

2. Another anticoagulant could be used instead of brodifacoum due to little chance of 

cross-resistance among anticoagulants (Apperson et al. 1981). 

3. Continued haphazard baiting around the research station with brodifacoum should 

be terminated as soon as possible, if brodifacoum based baits will be used in an Atoll 

wide eradication effort. 

4. An intensive evaluation of the efficacy will be necessary to ensure complete 

eradication, if brodifacoum based baits are used. 

5. The brodifacoum LD 50 suggested for roof rats (0.65 – 0.73 mg/kg) appears to be 

adequate for rat eradication efforts on Palmyra Atoll. 

Page 52 of 61 
References:

Apperson, C. S., O. T. Sanders, and D. E. Kaukeinen. 1981. Laboratory and field trials of the 

rodenticide broadifaoum against warfarin-resistant Norway rats. Pesticide Science 

12:662-668.

Billing, J. and B. Harden. 2000. Control of introduced Rattus rattus on Lord Howe Island: 

the response of mouse populations to warfarin bait used to control rats. Wildlife 

Research 27:655-658. 

Buckle, A. and M. Fenn. 1992. Rodent control in the conservation of endangered species. 

Proc. Vertebr. Pest Conf. 15:36-41. 

Environmental Protection Agency. 1996. Ecological effects test guidelines: OPPTS 

850:2400. EPA 712-C-96-140. Washington, D.C. 

Gill, J. E. and R. Redfern. 1980. Laboratory trials of seven rodenticides for use against the 

cotton rat (Sigmodon hispidus). Journal of Hygiene 85:445-450. 

Hadler, M. and A. Buckle. 1992. Forty-five years of anticoagulant rodenticides: past, 

present, and future trends. Proc. Vertebr. Pest Conf. 15:149-155. 

Howald, G., P. Mineau, J. Elliott, and K. Cheng. 1999. Brodifacoum poisoning of avian 

scavengers during rat control at a seabird colony. Ecotoxicology 8:431-447. 

Key, G. and R. Hudson. 2000. The rat control program on the island of St. Helena. Proc. 

Vertebr. Pest Conf. 19:133-138. 

Stone, W., J. Okoniewski, and J. Stedelin. 1999. Poisoning of wildlife with anticoagulant 

rodenticides in New York. J. Wildl. Diseases 35:187-193. 

Witmer, G., E. Campbell, and F. Boyd. 1998. Rat management for endangered species 

protection in the U.S. Virgin Islands. Proc. Vertebr. Pest Conf. 18:281-286. 

Page 53 of 61 
Table 1. Black rats (Rattus rattus) mass, sex, treatment, and fate in resistance trial A on 

Palmyra Atoll. August 2004. 

Rat 

# Mass (g) Sex Treatment

8Aug 

bait 

Mass (g)

9Aug 

bait 

Mass (g)

Total 

Bait (g)

LD 50 bait 

mass 

normalized 

Multiple 

of LD50

Date of 

death 

2 150 Female Control NA NA NA NA NA NA

3 105 Female Control NA NA NA NA NA NA

4 200 Female Control NA NA NA NA NA NA

7 200 Female Control NA NA NA NA NA NA

8 215 Female Brodifacoum 20 20 40 3.01 13.3 8/14/2004

9 155 Female Brodifacoum 21 20 41 2.17 18.9 8/14/2004

10 220 Female Brodifacoum 20 20 40 3.08 13.0 8/15/2004

12 190 Female Brodifacoum 20 21 41 2.66 15.4 8/13/2004

13 205 Female Brodifacoum 21 20 41 2.87 14.3 8/15/2004

15 165 Female Brodifacoum NA NA NA NA NA NA

16 115 Female Control NA NA NA NA NA 8/18/2004

20 230 Male Control NA NA NA NA NA NA

21 210 Male Brodifacoum 20 20 40 2.94 13.6 8/16/2004

22 155 Male Brodifacoum 20 20 40 2.17 18.4 8/18/2004

24 190 Male Control NA NA NA NA NA NA

25 200 Male Brodifacoum 19 20 39 2.8 13.9 8/16/2004

26 170 Male Brodifacoum 20 20 40 2.38 16.8 8/15/2004

27 210 Male Control NA NA NA NA NA NA

28 140 Male Brodifacoum 20 20 40 1.96 20.4 8/14/2004

30 275 Male Control NA NA NA NA NA NA

31 200 Male Control NA NA NA NA NA NA

Page 54 of 61 
Table 2. Black rats (Rattus rattus) mass, sex, treatment, and fate in resistance trial B on 

Palmyra Atoll. August 2004. 

Rat Mass 

(g) Sex

Treatment 

Group 

LD 50 

multiple 

Brodifacoum 

(mg) Bait (g) Date of death 

245 Male 3 2 0.343 13.72 8/21/2004

195 Male 4 4 0.546 21.84 8/20/2004

195 Male 2 1 0.1365 5.46 8/20/2004

155 Female 2 1 0.1085 4.34 8/19/2004

155 Female 4 4 0.434 17.36 8/16/2004

160 Female 2 1 0.112 4.48 8/16/2004

140 Female 4 4 0.392 15.68 8/18/2004

220 Female 3 2 0.308 12.32 8/20/2004

160 Male 2 1 0.112 4.48 8/19/2004

195 Male 3 2 4 10.92 8/22/2004

195 Male 1 NA 0 10 NA

230 Male 1 NA 0 10 NA

140 Male 1 NA 0 10 NA

100 Female 3 2 0.14 5.6 8/23/2004

130 Female 1 NA 0 10 NA

155 Female 1 NA 0 10 NA

145 Female 4 4 0.406 16.24 8/20/2004

170 Female 1 NA 0 10 NA

145 Female 3 2 0.203 8.12 Escaped

170 Female 2 1 0.119 4.76 8/16/2004

155 Female 3 2 0.217 8.68 8/19/2004

160 Male 2 1 0.112 4.48 8/20/2004

225 Male 3 2 0.315 12.6 8/18/2004

190 Male 4 4 0.532 21.28 8/18/2004

225 Male 1 NA 0 10 NA

175 Male 3 2 0.245 9.8 8/17/2004

135 Female 2 1 0.0945 3.78 8/19/2004

225 Male 4 4 0.63 25.2 8/22/2004

175 Male 4 4 0.49 19.6 9/1/2004

Page 55 of 61 
Table 3. Necropsy results of rodents captured on Palmyra Atoll, August 2004. 

ID 

Numbe

r Sex

Date 

dead 

Body 

weig

ht (g) 

HeadBody 

length 

(mm) 

Tail 

lengt

h 

(mm

) 

Right 

hind 

foot 

length 

(mm) 

Right 

ear 

length 

(mm) 

Dorsal 

pelage 

color 

Ventral 

pelage 

color 

Reproducti

ve status 

Control 

(13) Male

9/3/

2004 

214.3

0 196.3 223.3 36 24.3

Long black 

guard hairs 

& grayish 

hairs with 

orange tips 

Grayish 

color 

with 

white 

cream 

tips 

descended 

testes 

Control 

(17) Female

9/3/

2004 

129.8

5 172 203.7 34.2 22

Long black 

guard hairs 

& grayish 

hairs with 

orange tips 

Grayish 

color 

with 

white 

cream 

tips 

Vagina 

perforate 

LD50X

4 (32) Male 

9/1/

2004 154 147 219.7 34.3

Not 

taken 

Long black 

guard hairs 

& grayish 

hairs with 

orange tips 

Grayish 

color 

with 

white 

cream 

tips 

descended 

testes 

Necropsy Notes: 

All the rats were classified as Rattus rattus by their morphological characteristics. 

When peeling of the entire fascia from the three rats, rat # 32 had signs of previous bleeding 

on the right front forelimb. 

The remaining muscle color throughout the rats’ bodies was pink and healthy. 

Rat # 17 had green color stains on its paws, tail, and near the anus. 

Rat # 32 had both its ears torn apart, missing both its eyes, and the left side of its rostrum 

had been scraped away. 

Rat # 32 had green color stains on its ventral pelage, paws, tail, and in the anus region. 

Overall, no obvious signs of hemorrhaging were seen. 

Page 56 of 61 
APPENDIX 3. BAIT WEATHERING TRIAL, P. MCCLELLAND

BAIT WEATHERING TRIAL

Prepared by: Pete McClelland, New Zealand Department of Conservation 

September 2004 

Summary

In order to ensure that bait is available for rats for the desired three nights following a 

broadcast operation the two available bait types were placed under rat and crab proof 

exclosures and their degradation monitored for four days. The small (1-2g) CI-25 baits 

broke down rapidly while the 8g Ramik bait was still in good condition at the completion of 

the trial. 

Methodology

The trial used five exclosures – approximately 50cm square with 15cm high sides, a 15cm 

foot coming out from the base to try and prevent rats or crabs digging under and 1cm 

square wielded wire mesh on the top to five the bait full access to the weather. These were 

placed in the 5 major habitat types found on the Island namely, 

a) Pisonia – tall forest with an open understorey, approximately 80% canopy cover and 

with a well drained storey substrate. 

b) Coconut Palms – tall forest, open understorey, approximately 80% canopy. 

Moderately drained sandy substrate. 

c) Terminalia – tall forest, approximately 95% canopy heavy fern ground cover, 

approximately 1m high. Leaf litter substrate. 

d) Open grass – no canopy, 100 % ground cover, compacted substrate 

e) Pandonas – low “forest” 100% canopy and heavy understorey of same vegetation. 

Fine gravel substrate and leaf litter. 

The sites were checked every 24 hours within 3 hours (after) of the rainfall being record for 

that period, and the condition of the bait recorded. Specifically the physical shape of the bait 

i.e. solid  soft  crumbly , retaining shape, degree of water absorption. Also, amount of

mould on the bait, likely palatable (very subjective) and ant activity. 

Results

Rainfall 

Page 57 of 61 
11 August 

12 August 

13 August 

14 August 

Bait Condition

11 August 

Plot A) CI-25 - swollen and crumbly, 100% moisture penetration, moderate ant 

activity 

Ramik – outer layer flaking 50% moisture penetration, no ant activity 

Plot B) CI-25 - swollen and crumbly, 100% moisture penetration, moderate ant 

activity. 

Ramik - outer layer flaking – 50% moisture penetration, no ant activity 

Plot C) CI-25 - all bait eaten by crabs 

Ramik – 100% moisture penetration, outer layers flaking 

Plot D) CI-25 – swollen and mushy, just holding shape, moderate ant activity 

Ramik – 100% moisture penetration, outer layer flaking (can crush with two 

fingers) still palatable. 

12 August 

Plot A) CI-25 – disintegrating but still in general shape 

Ramik – continued flaking – 2 layers 

Plot B) CI-25 – all eaten by crabs 

Ramik – 1st layer flaking – 100% moisture penetration 

Plot C) CI-25 – all bait eaten by crabs 

Page 58 of 61 
Ramik – all bait eaten by crabs 

Plot D) CI-25 – disintegrating – wet mush 

Ramik – 1st layer flaking 

Plot E) CI-25 – (new yesterday) 100% moisture penetration, bait swollen and 

crumbly 

Ramik – flaky 1st layer 

13 August 

Plot A) CI-25 – most bait eaten by crabs , rest mush 

Ramik – no change 

Plot B) All bait eaten by crabs 

Plot C) All bait eaten by crabs 

Plot D) CI-25 – 50% bait gone, not whole pallets – wet mushy – high ant numbers 

 Ramik – still holding shape but 50% flaking 

Plot E) CI-25 – disintegrating but still holding shape 

 Ramik – flaked 1st layer 

14 August 

Plot A) All bait eaten 

Plot B) No bait 

Plot C) No bait 

Plot D) CI-25 – 75% bait gone (ants?) 

Ramik – no change 

Page 59 of 61 
Plot E) All bait gone 

DISCUSSION

Keeping crabs out of the exclosures was more difficult than predicted as they tunnelled 

under the foot. In some cases 50+ crabs would be inside the enclosure overnight. There 

was no evidence of rats taking the bait so when bait was missing and crabs present it is 

assumed the crabs ate the bait. When bait was missing but no crab activity was found it was 

always when the CI-25 bait had gone mushy and its loss was attributed to ants. 

Even when the CI-25 bait was replaced it was always wet through and starting to breakdown 

by the next day. It is very unlikely, given the rainfall on Palmyra, that 1gm CI-25 baits would 

last three nights in a presentable state, even if the crabs/ants didn’t eat it. A large bait would 

have a reduced surface area: volume ratio and is likely to last better. The Ramik bait 

weathered well, even though it started flaking after one day it appeared to still hold its shape 

after three nights and may in fact have become more palatable as it got softer. 

CONCLUSION

The 1gm CI-25 bait is not suitable for use on Palmyra. The 8 gm Ramik bait does have the 

desirable weathering properties, but does have issues with sowing rate and possibly 

palatability. Therefore other bait types need to be explored and tested. 

RECOMMENDATION

That as many different bait types/sizes be tested for weathering as well as palatability etc to 

see if one that meets the tight requirements of Palmya can be found. If a suitable bait can be 

found – field trials should be carried out. 

Page 60 of 61 
Page 61 of 61 
1

APPENDIX D

PROGRESS IN PALMYRA ATOLL RESTORATION: RAT 

ERADICATION TRIAL 2005
2
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page i 

Stacey Buckelew 1

Gregg R. Howald 2*

Alex Wegmann 3

Jacob Sheppard 1

Jennifer Curl1

Pete McClelland 4

Bernie Tershy 1

Katie Swift 5

Earl Campbell 5

and 

Beth Flint 6

1 - Island Conservation 

Center for Ocean Health, University of California 

100 Shaffer Rd, Santa Cruz, CA 95060 

Telephone: (831) 459-1476 

Fax: (831) 459-3383 

www.islandconservation.org 

2 – Island Conservation Canada 

3 – University of Hawaii, Honolulu, Hawaii 

4 – New Zealand Department of Conservation 

5 – US Fish and Wildlife Service – Ecological 

Services, Honolulu, Hawaii 

6 – US Fish and Wildlife Service – Pacific Islands 

National Wildlife Refuges, Honolulu, Hawaii 

* Correspondence: 

Phone: (604) 628-0250 

Gregg.Howald@islandconservation.org 

PROGRESS IN PALMYRA ATOLL RESTORATION: 

RAT ERADICATION TRIAL 2005 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page ii 

Summary 

In July 2005, a team of 6 people returned to Palmyra Atoll to conduct a trial rat 

eradication building on the feasibility assessment. The main goals of this expedition 

were to: 

1. Evaluate the preference and efficacy of newly formulated bait (PI-25, containing 

25 ppm brodifacoum, Bell Laboratories, Inc.) on the local rat population under 

laboratory and field conditions. 

2. Conduct a broadcast trial rat eradication using PI-25. 

3. Evaluate rodenticide exposure risks to non-target species. 

Palmyra’s abundant rainfall and aseasonal environment are obstacles to successful rat 

eradication. They make it difficult to develop a bait that maintains its palatability over 

time and is more attractive to all rats than the abundant natural food resources. We found 

that PI-25 bait was preferred over natural food items in both laboratory and field 

conditions. The bait maintained its shape and integrity despite the high rainfall and was 

preferred over natural food items, even after absorbing moisture and the onset of mold 

growth, in both laboratory and field conditions. 

We conducted a trial eradication on a subset of 5 islands in Palmyra, totaling 4.08 ha. 

Each island was treated with PI-25 broadcast by hand to the ground, and delivered by 

slingshot, pole or broadcast into every coconut palm tree on each island. We targeted a 

bait application rate necessary to have enough bait available in every potential rat 

territory for a minimum of 4 days. A calibration trial indicated that between 60-90 kg/ha 

may be required, however, due to uncertainty in the data we initially applied high on the 

first treated island, and reduced the rate based on bait uptake monitoring. We broadcast 

bait at 60 (Little East Island), 70 (Bunker Island), 80 (Fern Island), 85 (Home Island) and 

95 kg/ha (Whippoorwill Island) and monitored bait uptake and impact on the local rat 

population. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page iii 

We determined that bait application of 80 kg/ha or less would be inadequate to ensure 

bait would be available in every potential rat territory for at least 4 days, on islands with a 

high abundance of landcrabs (Cardisoma spp.) and hermit crabs (Coenobita spp.) that 

consume the bait (but are not affected by the rodenticide). Our monitoring indicates that 

an application rate of 85 - 95 kg/ha would be adequate to overcome competition from 

landcrabs, with 99.9% bait removed from the islands by 7 days post broadcast. 

Our direct (radio collared rats and live traps) and indirect (wax chew blocks) monitoring 

of efficacy of the bait application on the rat population indicates that we were successful 

in eradicating rats from all the treated islets at all application rates. However, the islands 

with low application rates (<80 kg/ha) had no established hermit crab populations that 

were important consumers of bait and we believe the successful removal of rats from 

those islands with lower application rates was due, at least in part, to the absence of 

hermit crabs. A small juvenile, weanling rat was detected live on day 8 post broadcast on 

the 95 kg/ha treated island but was found moribund on day 10. The discovery of a live 

weanling rat strongly suggests that a second bait application is necessary to ensure bait is 

available to all weanling rats that had not yet left the nest and could escape exposure to 

bait after the first application. Therefore, for the rat eradication to have a high probability 

of succeeding by broadcast with PI-25, we recommend that bait be applied twice at 90 

kg/ha, 10-14 days apart, to overcome competition by the abundant landcrabs and hermit 

crabs and ensure enough bait is available to the entire rat population for a minimum of 4 

days. 

To evaluate the risk of rodenticide exposure to non-target species we monitored the local 

shorebird population and collected landcrabs to monitor for brodifacoum residues on 

days 2, 6, 10, 21 and 56 days post broadcast. For the four species of shorebirds that are 

known to use Palmyra, Numenius tahitiensis (Bristle-thighed Curlew), Heteroscelus 

incanus (Wandering Tattler), Pluvialis fulva (Pacific Golden-plover) and Arenaria 

interpres (Ruddy Turnstone), the curlew and plovers were believed to be at the greatest 

risk of secondary exposure to the rodenticide from feeding on hermit and landcrabs that 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page iv 

consume the bait under the forest canopy. The frequency of detection of these shorebirds 

were consistently higher post broadcast and was likely due to migratory influx. We did 

not detect any dead or moribund birds in the treated areas. Thus, the timing of the 

eradication prior to the arrival, or after the departure, of migratory shorebirds is effective 

at minimizing the risk of short term rodenticide exposure. A risk assessment is to be 

done for shorebirds based on the pending landcrab and hermit crab brodifacoum residue 

data. 

We conclude that rats can be eradicated from Palmyra Atoll with a high probability by 

broadcasting PI-25 bait containing 25 ppm brodifacoum. The relative long term risk of 

rodenticide exposure to non-target shorebirds is currently under evaluation. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 1 

Table of Contents

Table of Contents................................................................................................................ 1 

Introduction......................................................................................................................... 2 

Research and Monitoring Goals.......................................................................................... 4 

Study Area .......................................................................................................................... 4 

Pre- Eradication Trials ........................................................................................................ 7 

Laboratory Bait Efficacy................................................................................................. 7 

Methods....................................................................................................................... 7

Results and Discussion ............................................................................................... 8

Bait Preference................................................................................................................ 8 

Methods....................................................................................................................... 8

Results and Discussion ............................................................................................. 10

Validation of Application Rate ......................................................................................... 12 

Methods..................................................................................................................... 12

Results and Discussion ............................................................................................. 12

Trial Rat Eradication......................................................................................................... 14 

Island Selection............................................................................................................. 14 

Methods......................................................................................................................... 15 

Bait Application ........................................................................................................ 15

Measurement of Bait Uptake .................................................................................... 18

Results........................................................................................................................... 19 

Efficacy............................................................................................................................. 23 

Methods......................................................................................................................... 23 

Live Trapping............................................................................................................ 23

Chew Blocks.............................................................................................................. 25

Radio Telemetry........................................................................................................ 26

Results and Discussion ................................................................................................. 27 

Trapping.................................................................................................................... 27

Chew Blocks.............................................................................................................. 29

Radio Telemetry........................................................................................................ 31

Evaluation of Primary and Secondary Exposure Risks to Non-Target Species ............... 33 

Shorebirds ..................................................................................................................... 33 

Methods..................................................................................................................... 33

Results....................................................................................................................... 33

Land Crab Residue Analysis......................................................................................... 37 

Landcrab Population Index Monitoring........................................................................ 38 

Methods..................................................................................................................... 38

Results....................................................................................................................... 39

Environmental Fate of Bait............................................................................................... 40 

Non-Target Species Carcass Searching ............................................................................ 41 

Conclusions on Trial Eradication...................................................................................... 42 

Recommendations for Eradication of Rats from Palmyra Atoll....................................... 42 

References......................................................................................................................... 43 

Appendix A. Trial eradication islands and habitat composition...................................... 44 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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Introduction 

Island ecosystems, such as Palmyra Atoll, are key areas for conservation because they are 

essential habitat for seabirds, pinnipeds and sea turtles that use thousands of square 

kilometers of open ocean, but depend on islands for breeding, raising young, and resting. 

In addition, islands tend to be rich in endemic species and are home to 15-20% of all 

plant, reptile and bird species, even though they make up only about 3% of the earth’s 

area (Whittaker 1998). 

Unfortunately islands have been disproportionately affected by humans. More than 80% 

of all of recorded extinctions (excluding fish) have occurred on islands, and most of these 

were caused, at least in part, by invasive species (Island Conservation analysis of IUCN 

Global Red List data and Groombridge 1992). 

One of the most successful invasive species on islands are rats in the genus Rattus. They 

have been introduced onto about 82% of the world’s islands and/or island chains 

(Atkinson 1985), where they frequently have a quantifiable negative impact on the 

distribution and abundance of native flora and fauna. This is most pronounced on 

oceanic islands where native species have evolved in the absence of mammalian 

predators and thus have limited behavioral, morphological, and life-history defenses 

against rats (Brown 1997). Consequently, rats have been implicated in 40-60% of 

recorded bird and reptile extinctions since 1600 (Groombridge 1992). Fortunately, it is 

possible to eradicate all rats from many islands, and in the last 20 years there have been a 

series of technological innovations in the field of rat eradication that have dramatically 

increased the power of this important conservation tool (Galvan et al. 2005). Briefly, 

rats are eradicated by distributing a bait containing a rodenticide, usually brodifacoum, 

into all rat territories. Bait can be placed in bait stations spaced on a grid of 25x25m to 

100x100m, or can be broadcast evenly at a known density either by hand on small islands 

or with a helicopter using a bait spreading bucket on larger islands. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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Palmyra Atoll National Wildlife Refuge, located in the Line Islands, Pacific Ocean, 

approximately 1760 km south of the main Hawaiian Islands, likely never supported 

native mammals because of its remoteness. However, non-native black rats (Rattus 

rattus) were introduced to Palmyra, likely during the US military occupation of the atoll 

in the 1940’s. The establishment of rats on Palmyra is believed to have had a major 

negative impact on the ecosystem, especially on seabirds, invertebrates, and vegetation. 

Modeling successful projects carried out in New Zealand and those conducted in North 

America by Island Conservation and others, we initiated a trial eradication on Palmyra 

Atoll, Pacific Remote Islands National Wildlife Refuge Complex, USA. The trial 

eradication and associated research and monitoring was conducted on a subset of five 

islets within the atoll, comprising a total emergent land area equal to 4.08 ha, from June 

28 through August 14, 2005. 

The trial eradication built upon the feasibility study on Palmyra Atoll in 2004(Howald et 

al. 2004). The feasibility study evaluated rat susceptibility and attraction to various baits, 

monitored rat movement and habitat use via radio telemetry, conducted an atoll wide land 

crab density survey, and measured the rate of bait loss in the Palmyra environment. In 

addition the potential risks to other non-target species were assessed on the island and the 

operational logistics considered for an atoll wide eradication. The results from this 

preliminary phase indicated that a trial eradication of rats was necessary to assess the 

probability of success for an atoll-wide eradication (Howald et al. 2004). 

The objective of the June-August 2005 Palmyra visit was to perform a trial rat eradication 

on a subset of islets at Palmyra Atoll. The methodologies detailed below for the Palmyra 

Atoll trial eradication were designed to mimic an aerial broadcast of bait, which was 

identified as the preferred method during the 2004 feasibility study. The results of the 

trial eradication will be used to structure future eradication plans on the atoll. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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Figure 1. Palmyra Atoll, Line Islands, Pacific Ocean. 

Research and Monitoring Goals 

The goals of the research and monitoring during the eradication trial were to: 

1. Study rat preference and susceptibility to the proposed bait; 

2. Validate the bait application rate; 

3. Evaluate efficacy of bait application on the rat population; 

4. Evaluate potential rodenticide exposure risks to non-target species. 

Study Area 

Location: In the Line Islands, 1760 km south of Honolulu, Hawaii (Figure 1 and 

Appendix A). 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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Size and Topography: Palmyra Atoll is comprised of 54 islets encompassing 228 ha, 

rising to a maximum elevation of 2 m. The atoll is well within the size range of 

successful rat eradications (Figure 1). All of the land area can be accessed on foot, 

however, there are areas of thick vegetation, especially the Scaevola habitat, which 

precludes access without trail cutting. Although most of the islets are not connected, they 

can be reached by wading or swimming across the narrow channels that separate 

individual islets, or by boat. 

There are potential safety concerns to eradication staff from unexploded ordnance, 

contaminated dump sites, hidden bunkers and marine wildlife (e.g. sharks), which could 

limit the successful implementation of a ground-based operation. Barrier and Quail 

Islands are inaccessible due to unexploded ordnance concerns. 

Plants and Animals: The aseasonal climate on Palmyra supports dense vegetation of 

native and non-native trees and shrubs. A large portion of the atoll (approximately 48%) 

lies under a canopy of non-native coconut palm (Cocos nucifera). Other habitat types 

include broadleaf forest composed of Terminalia catappa, the native Pisonia grandis, 

and the shrub-like Scaevola sericea and Tournefortia argenatea. The Pisonia forest was 

once regarded as the best example of a pristine Pisonia forest in the American Pacific, 

but the trees are now dying due to stress response from introduced scale insects whose 

populations are inflated due to their symbiotic relationship with the introduced ant 

Pheidole megacephala. The decline of the Pisonia forest has caused dramatic changes in 

the Palmyra ecosystem. 

The terrestrial habitats on Palmyra support 10 species of breeding seabirds. There are no 

breeding landbirds on Palmyra, but the island supports overwintering populations of 

Bristle-thighed Curlews (Numenius tahitiensis) and other shorebird including Wandering 

Tattlers (Heterscelus incanus), Pacific Golden Plovers (Pluvialis fulva) and Ruddy 

Turnstones (Arenaria interpres). The curlew and Pacific Golden Plover are designated 

by the US and Region 1 Shorebird Conservation plans as Species of High Conservation 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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Concern because of limited breeding and non-breeding distributions in the Pacific, low 

relative abundance, and a decline in global populations. 

Palmyra supports a notably diverse assemblage of six landcrab species, including the 

large coconut crab (Birgus latro). The most abundant landcrab is the red hermit crab 

(Coenobita perlatus). Additional species include the purple hermit crab (Coenobita 

brevimanus), orange land crab (Cardisoma carnifex) and purple land crab (Cardisoma 

rotundum). Landcrabs are the primary competitors of rats for access to the bait. 

There are two terrestrial reptile species on Palmyra, an introduced house gecko 

(Hemidactylus frenatus) and a native mourning gecko (Lepidodactylus lugubris). 

Palmyra supports a diverse collection of both native and non-native insects, including 

cockroaches and ants that are known to compete with rats for access to bait. During the 

first eradication attempt, it was noted that ants overwhelmed some bait stations, 

completely consuming the bait present in the stations within 24 hours. 

Two domestic cats and a domestic dog are present as pets on the atoll, as well as one cat 

that is confined to a boat moored in the lagoon. Tropical vegetation including a mix of 

native and non-native plants and trees. 

Climate: Palmyra lies within the Inter-Tropical Convergence Zone (ITCZ), the band of 

low pressure along the equator formed by the upward convection of warm, moist air from 

the Earth’s surface. The climate of Palmyra is characterized by high humidity (>90%), 

warm temperatures (75 – 85 degrees Fahrenheit) with almost daily copious rainfall 

events. Mean annual rainfall on Palmyra is 4.06 m. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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Figure 2. PI-25 bait (Bell Laboratories, Inc) 

used on Palmyra Atoll National Wildlife 

Refuge, July 2005. 

Pre- Eradication Trials 

Prior to initiating the trial eradication we: 

1) Reconfirmed the effectiveness of the PI-25 bait (25 ppm brodifacoum, Bell 

Laboratories, Inc.). 

2) Reconfirmed the preference of bait in various stages of degradation (fresh vs. four 

days of weathering) versus naturally occurring foods in laboratory and field 

conditions. 

3) Calibrated an appropriate application rate using a non-toxic placebo bait in a 1.5 

ha plot. 

Laboratory Bait Efficacy 

Methods 

Prior to commencement of the trial eradication on the five treatment islets we conducted 

an on-island effectiveness trial with wild captive rats to confirm efficacy of the bait. A 

grain-based bait containing the rodenticide brodifacoum (currently named PI-25) was 

formulated by Bell Laboratories, Inc. to withstand the moist weather conditions 

encountered on Palmyra Atoll. The formulated bait is a 1/2” diameter, blue colored, 

highly compressed grain pellet (mean weight of 2.3 g) (Figure 2). 

The efficacy trial used 10 rats live-captured 

on Cooper Island. The rats were randomly 

assigned five each to an experimental and 

control group. The rats were sexed, 

weighed, and housed in individual cages 

inside a facility where conditions were 

darker, drier, and cooler than ambient 

conditions to prevent exposure to 

precipitation or direct sunlight. The five rats 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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in the experimental group were given, no choice, PI-25 bait, equivalent to four times the 

LD50 (LD50 = 0.7 mg/kg, based on published range of 0.65- 0.73 mg/kg for Rattus 

rattus)of brodifacoum (calculated based on each individual’s body mass) until all bait 

was consumed. After the toxic bait consumption, experimental rats were maintained on 

coconut, a non-toxic natural food source, until mortality or study end. The five rats in the 

control group were maintained on coconut for the duration of the trial. Water was 

available to all rats ad libitum. Rats were examined daily and the condition of each rat – 

whether active, lethargic, bleeding, moribund, or dead – was recorded. 

Results and Discussion 

Mortality of all rats in the experimental group occurred between Day Six and Day Nine 

post-treatment, with average mortality occurring on Day Seven post-treatment (n=5, 

s=1.2) (Table 2). Two of the five experimental rats were necropsied after death and 

hemorrhaging was detected at the base of the cerebrum for both specimens, symptomatic 

of brodifacoum toxicosis. No mortalities occurred for the five rats in the control group, 

their general condition remained healthy and active until euthanized. 

All of the rats died within the expected mortality window between 3-10 days typical after 

brodifacoum exposure. Although the sample size is low, the mortality of all 5 individuals 

exposed to brodifacoum is concurrent with the data from 2004 (Pitt 2004 in Howald et al. 

2004) suggesting that brodifacoum has a high probability of removing 100% of the local 

rat population. 

Bait Preference 

Methods 

We conducted both (a) laboratory based preference trial and (b) a field bait preference 

trials using motion sensing cameras on Cooper Island. Both trials consisted of five 

identical choice tests in which bait in different states of weathering was paired against 

naturally occurring food sources. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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The choice preferences tested were: 

1. Fresh bait vs. green coconut (Cocos nucifera) 

2. Fresh bait vs. Pandanus seeds (Pandanus tectorius) 

3. Fresh bait vs. weathered bait* 

4. Weathered bait* vs. green coconut 

5. Weathered bait* vs. Pandanus seeds 

*Bait was weathered four days by covering with a wire mesh cage, exposed to ambient 

weather conditions. General bait condition displayed <50% surface area mold and 

discoloration. 

Laboratory Preference Trials – Rats were initially sexed and weighed for choice 

preference trials conducted in a laboratory setting, then housed in individual cages before 

the trial began. Twenty-four hours prior to the start of the trial rats were fasted and given 

water only. Rats were maintained in conditions identical to bait validation trials – a dark, 

Table 2. Efficacy trial results and day of mortality post-treatment of 

experimental rats, Palmyra Atoll, July 2005. 

Treatment Rat # Sex Day of Visual 

Poisoning Symptoms Day of Mortality 

1 M 6 6 

2 M 4 9 

3 M 5 6 

4 F 5 7 

5 M 5 7 

Mean 5 7 

Experimental 

Std. Dev. - 1.2 

6 M NA NA 

7 M NA NA 

8 J NA NA 

9 M NA NA 

10 M NA NA 

Mean - - 

Control 

Std. Dev. - - 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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dry, cool location sheltered from exposure to precipitation or overheating by direct 

sunlight. 

 Each choice test was conducted using four individual rats. For each test, the two food 

choices were placed side by side in each cage with random placement of food orientation 

(i.e. left-right, or right-left). Food choice was determined as the first item to be wholly 

consumed by the rat. For each test using bait as a choice item, 3-5 pellets were placed in 

a small plastic cup inside the cage. For natural foods, one coconut or Pandanus seed was 

placed directly onto the floor of the cage. Food items were presented to each rat in the 

test and the time recorded. Observations of food choices were made from a distance of 3-

5 m from the cages. Time elapsed between presentation and when a food item was 

chosen was recorded for each rat. 

Motion Sensing Cameras – Motion sensing cameras were used to examine the food 

preferences of rats within their natural ecological setting, and to evaluate the effect that 

competitive interactions with other species may have to preference choices. 

Three motion-sensing cameras (Bushnell Trailscout 2.1 MP Digital Motion-Sensing 

Camera, Model # 11-9800) were randomly placed on Cooper Island over the duration of 

the seven weeks. Five food choice tests (mentioned in the above Laboratory Trial 

section) were performed of a total of six times each, three times in daylight and three 

times at night. Each choice test consisted of placing the two food items in front of a 

camera with a visible divider set in between. An identical control test (no camera) was 

placed >1m distance from each camera to control for any potential camera effect. 

Cameras were set to collect images at a rate of one image per 30 seconds. Food 

preference was determined only from images in which a clear choice was evident. 

Results and Discussion 

Laboratory Trials – The results from the lab trial suggest that both fresh and weathered 

bait were preferred over green coconut seeds, and that rats had an equal preference for 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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fresh and weathered bait when presented with both at the same time (Table 3). The 

results suggest that rats preferred Pandanus to both fresh and weathered bait. However, 

though six rats chose Pandanus seeds initially, all but two rats consumed some fresh or 

weathered bait later in the trial. This would suggest that some rats may avoid the bait in 

favor of Pandanus fruit in some situations. We believe that overall, the results from this 

laboratory study strongly suggest that rats prefer PI-25 bait pellets over coconut when 

given a choice between the two. The preference for PI-25 vs. Pandanus fruit remains 

equivocal under laboratory conditions. 

Table 3. Rat preference between natural food sources and grain-based bait pellets in a laboratory trial. 

 

Motion Sensing Cameras – In tests between fresh bait and natural food sources, on 

average, rats chose bait 91% of the time. In trials testing the choice of weathered (moldy) 

bait versus natural foods, rats chose weathered bait on average 93% of the time. The 

results also show that fresh bait is greatly desired (89%) over weathered bait, and that 

weathered bait is still preferred over natural food sources. The results suggest that in 

natural environments rats prefer grain-based bait to alternate food sources (Table 4). The 

evidence from the cameras would suggest that rats prefer fresh and degrading PI-25 to 

natural foods when given the choice on Palmyra Atoll. 

Table 4. Palatability trials with motion sensing cameras showing the percent of images demonstrating rat 

preference for a specific food option 

Trial Choice Number of Photos % images showing rat 

choice 

Fresh bait vs. Pandanus Bait 9 83 

Fresh bait vs. green coconut Bait 18 100 

Fresh bait vs. weathered bait Fresh bait 12 89 

Weathered bait vs. Pandanus Weathered bait 8 86 

Weathered bait vs. green coconut Weathered bait 7 100 

# Rats 

Sex Ratio 

(F:M) 

Trial Preference % Preference 

4 3:1 Coconut vs. fresh bait Fresh bait 100 

4 2:2 Pandanus vs. fresh bait Pandanus 75 

4 2:2 Pandanus vs. weathered bait Pandanus 75 

4 1:3 Fresh bait vs. weathered bait No preference 50 

4 3:1 Coconut vs. weathered bait Weathered bait 100 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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Validation of Application Rate 

Methods 

Prior to the distribution of PI-25 for the trial eradication, we calibrated the application 

rate using placebo compressed-grain bait pellets. Results from measured bait 

consumption (uptake) in fixed-area plots were used to calculate the rate of bait uptake 

into the environment and thus, translated into an application rate required to ensure 

enough bait was available on the ground, and in each potential rat territory, for four (4) 

days post application. 

The placebo bait pellets were similar in size and shape to the PI-25 bait, a 1/2” diameter, 

undyed, 2.3 g (mean weight) highly compressed grain pellet (Bell Laboratories, Inc.). 

Bait was applied by hand broadcast to a 1.5 ha ground area on Aviation Island at a rate of 

90 kg/ha. A crew of four persons, each spaced three meters apart, broadcast bait in 

consecutive cross-islet transects. Each person was responsible for applying bait at the 

target application rate to the 1.5 m radial area around him or her at each 1 m pace 

traveled along the transect. To best ensure uniform bait distribution all members of the 

team applied baited in unison across the width of the islets, each individual distributing 

bait to his or her respective transect. 

Consumption of bait pellets was measured over a four-day period in 20 1x5 m uptake 

plots. Pellets were individually placed and marked with a pin flag in the uptake plots at 

the concentration of four pellets/ m2

, an extrapolation from the application rate of 

90kg/ha. Plots were visited daily and the number of pellets remaining was recorded, and 

pin flags removed from where bait pellets were consumed. 

Results and Discussion 

Bait consumption calculated from uptake plots is presented as both mean rate of daily 

uptake (Table 5) and cumulative uptake (Table 6 and Figure 3). Bait loss (likely 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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attributable mostly to uptake by landcrabs and rats) averaged 45.5% (39.86 kg/ha) during 

the initial 24 hour period and continued at a rate of approximately 8% for the remaining 3 

days (Tables 5, 6). By Day Four post-application an average 30% (27.14 kg/ha) of the 

applied bait remained in the study area (Table 6). Consumption however varied 

significantly among individual uptake plots within the study area. At Day Four postapplication six plots experienced complete consumption of pellets initially applied 

whereas in seven plots ≥ 10 pellets (50% initial application) persisted. 

Based on the methods we used to measure bait loss in the validation trial, we 

conservatively estimated an application rate > 90 kg/ha would be necessary to ensure 

availability of bait to 100% of the rat population over a 4-day period. The wide variance 

in the data, likely due to the small measurement plots and variation in the distribution and 

abundance of crabs, precluded us from making a conclusive statement about application 

rate. 

Table 5. Mean placebo bait removed as measured daily in uptake plots (n= 20). 

Palmyra Atoll, July 2005. 

Day 

 # Pellets 

Removed 

(/m2) 

Std Dev 

Equivalent 

Uptake 

(kg/ha) 

Std Dev 

1 1.82 1.07 41.86 32.50 

2 2.21 1.08 8.97 7.53 

3 2.51 1.09 6.90 8.11 

4 2.82 1.07 7.13 11.12 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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Figure 3. Mean cumulative uptake of placebo bait, by weight measured in daily uptake plots (n=20), Palmyra 

Atoll, July 2005. 

0

10

20

30

40

50

60

70

80

90

100

1234

DAY POST-APPLICATION

BAIT UPTAKE (KG/HA)

Trial Rat Eradication 

Island Selection 

The trial eradication was conducted on a subset of five islets within Palmyra Atoll 

comprising a total emergent land area of 4.08 ha (Appendix A). Islets were selected 

based on their size, relative rat and crab densities, and predominant forest structure, and 

isolation (reduced probability of reinvasion during monitoring phase). Crab densities 

varied across islets from low to mean-high abundance (assessed during the 2004 

feasibility phase – see Howald et al. 2004) for both hermit and land crab species and rat 

populations were abundant on all treatment islets. To mimic aerial dispersal by 

Table 6. Mean percent consumption of placebo PI-25, 

 measured cumulatively in daily uptake plots (n= 20), 

Palmyra Atoll, July 2005. 

Day Uptake 

(kg/ha) 

Std Dev % Uptake 

1 41.86 24.52 46.50 

2 50.83 24.82 56.48 

3 57.73 25.08 64.14 

4 64.86 24.56 72.07 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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helicopter, bait was applied to both the ground and palm tree canopy on all treatment 

islets using a hand broadcast method. The trial eradication proceeded with a sequential 

approach to baiting islets (see Table 7 and map in Appendix A). 

The application rate between the islets was deliberately varied because of the uncertainty 

in the calibration experiment and we could adjust the rates on the other islands based on 

the bait uptake data from the previously treated islets. Bait was applied at a high 

application rate on Whippoorwill Island. Little East was applied at the lowest application 

rate because it had a low density of crabs and was believed to have a high probability of 

reinvasion due to its connection at low tide to the adjacent islands. 

Methods 

Bait Application 

Calibration – The success of a rat 

eradication by broadcasting bait 

is largely dependent on the 

availability of bait to all rats 

within their respective territories 

over a minimum of three to four 

days. Thus even bait distribution 

across the islets during the trial 

Figure 4. Hand broadcast calibration on the Palmyra Atoll 

airstrip using placebo PI-25, July 2005. 

 Table 7. Treated islands and emergent land area, Palmyra Atoll, July 2005. 

ISLAND APPLICATION DATE LAND AREA (ha) Application Rate 

(kg/ha) 

Whippoorwill 15-Jul 2005 1.45 95 

Bunker 16-Jul 2005 0.16 70 

Fern 21-Jul 2005 0.40 80 

Little East 21-Jul 2005 0.67 60 

Home 24-Jul 2005 1.40 85 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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was paramount. We calibrated bait application to refine hand broadcast methods on the 

airstrip on Palmyra prior to bait application on the trial islets (Figure 4). The calibration 

was designed to ensure that bait was applied in as evenly as possible during the bait 

application on the islets. 

Ground Application – Using a team of four to five persons spaced three meters apart, bait 

was applied in consecutive cross-islet transects. Each member of the team was 

responsible for applying bait at the target application rate, calculated to a set number of 

pellets to be dropped in the 1.5 m radial area around him or her at each 1 m pace traveled 

along the transect. To best ensure uniform bait distribution all members of the team 

applied baited in unison across the width of the islets, each individual distributing bait to 

his or her respective transect (Figure 5). 

 

We actively verified the bait application rate by sampling randomly placed three-meter 

radius circular plots continuously during the application process. A three meter long 

piece of flagging tied to a pole marking the plot’s center was stretched out and moved to 

define the plot’s perimeter. All pellets within the circle were marked with a pin flag and 

the pin flags counted and removed. The total number of bait pellets, mean, and the 

variance were calculated onsite and application rate was 

adjusted accordingly when 

necessary. 

Based on the target bait 

application rate (kg/ha) for 

each island, the total mass of 

bait to be applied on each 

islet was calculated using 

Figure 5. Hand broadcast application, Palmyra Atoll, 

July 2005. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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remotely measured islet surface areas. Polygon shapefiles were layered over Palmyra 

satellite imagery and the surface area calculated for non-tidal islet areas. After the entire 

islet was walked in transects, any bait remaining from the pre-determined total amount 

was applied uniformly throughout the islet. 

During the application one sample of bait per 10 kg bucket applied was collected for 

confirmation of the concentration of brodifacoum by HPLC analysis. 

Canopy application – Bait was applied to every coconut palm on each trial islet to: 

1. Best mimic a helicopter bait broadcast, and 

2. Provide additional insurance that bait is readily available to rats that are 

primarily arboreal. 

Each palm tree was baited with at least 6-12 bait pellets distributed into the palm crown. 

Trees were marked when they had been successfully treated to ensure that no trees were 

omitted. Bait was delivered into the canopy using several methods: 

1) “Bolos”. Bait pellets joined together by paraffin wax to make conglomerates of 

6-12 pellets, connected in pairs by a length of string. These “bolos” were shot 

into the canopy using a slingshot. A bolo delivery was considered successful if it 

lodged within 0.5 m of the core of the tree’s crown (Figure 5). 

2) Bait blocks. Bait pellets were embedded into paraffin wax to form conglomerates 

of 6-12 pellets, which were delivered into a palm crown using a long extension 

pole (Figure 5). 

3) Hand placement. Bait was placed directly by hand into palm crowns either from 

the ground or at canopy level by climbing an adjacent tree. 

4) Trunk placement. When bait could not be effectively delivered into a palm crown 

using any of the above methods, a bait conglomerate was secured to the trunk 2-3 

m above ground level. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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Figure 5. Slingshot and Pole Application of PI-25 into 

Coconut palm canopies, Palmyra Atoll, July 2005. 

Measurement of Bait Uptake 

 Uptake was measured using randomly placed three meter radius circular plots on one, 

two, three and four days post application on Home (n=30) and Whippoorwill (n=35) 

Islands, and due to logistical constraints on 1,2, and 3 days post application on Bunker 

Island (n=6). Remaining bait pellets within each circular plot were tallied and recorded. 

Uptake was not measured on Little East or Fern because of the extensive fern ground 

cover that made it impossible to establish and accurately find and count bait pellets. A 

general walk through on Little East and Fern islands on days 2 and day 3, respectively, 

post bait application were used to estimate bait availability/uptake. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 19 

Table 9. Mean consumption (w/ outliers) measured cumulatively 

in uptake plots, Palmyra Atoll, July 2005. 

Island Day Uptake 

(kg/ha) Std Dev % Uptake

1 26.24 26.49 26.70 

2 31.10 28.02 31.64 

3 59.44 19.48 60.49 

Whippoorwill 

4 65.09 20.44 66.24 

1 14.90 25.17 16.85 

2 31.56 25.89 35.68 

3 26.69 35.17 30.17 

Home 

4 44.65 29.62 50.47 

1 31.59 11.46 45.12 

Bunker 2 30.53 25.40 43.61 

3 40.05 22.29 57.21 

Results 

Bait application rates were achieved during each application but bait was unevenly 

distributed due to thick vegetation in some parts of the islands, and irregular uptake, in 

part due to the variation in distribution and abundance of Cardisoma landcrabs. The first 

two tables include the extreme outliers (Table 8, 9), and the later two tables reject the 

outliers (Table 10, 11). Figure 2 graphically depicts mean bait consumption, without 

outliers, by weight. By removing extreme outliers from the data set, there is a regular 

decline in percentage uptake of remaining bait from Day One to Day Four. 

 

 

Table 8. Mean consumption rate (w/ outliers) measured daily in uptake plots, Palmyra Atoll, July 

2005.

Island Day # Pellets 

(m2) Std Dev Uptake (kg/ha) Std Dev N Plots 

1 3.13 1.15 26.24 26.49 35 

2 2.92 1.22 4.86 28.02 35 

3 1.69 0.85 28.35 19.48 35 

Whippoorwill 

(95 kg/ha) 

4 1.44 0.89 5.65 20.44 35 

1 3.21 1.09 14.90 25.17 30 

2 2.56 1.13 16.67 25.89 30 

3 2.75 1.53 -4.87 35.17 30 

Home 

(85 kg/ha) 

4 1.84 1.29 17.96 29.62 30 

1 1.67 0.50 31.59 11.46 6 

2 1.72 1.10 -1.06 25.40 6 

Bunker 

(70 kg/ha) 

3 1.30 0.97 9.52 22.29 6 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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Table 10. Average consumption rate (w/o outliers) measured in uptake plots, Palmyra Atoll, July 2005. 

Island Day # Pellets 

(m2) Std Dev Uptake (kg/ha) Std Dev N 

1 2.97 0.96 29.86 22.11 19 

2 2.21 0.71 17.62 16.31 21 

3 1.54 0.76 15.43 17.47 14 

Whippoorwill 

4 0.95 0.58 13.42 13.26 21 

1 2.96 0.94 20.32 21.69 33 

2 2.37 0.90 13.60 20.61 22 

3 2.29 0.99 1.97 22.74 31 

Home 

4 1.64 1.06 14.95 24.39 23 

1 1.67 0.50 31.59 11.46 5 

Bunker 2 0.97 0.48 16.17 11.11 3 

3 0.73 0.46 5.56 10.60 4 

Table 11. Mean percent consumption (w/ outliers) measured in uptake 

 plots, Palmyra Atoll, July 2005. 

Island Day Uptake 

(kg/ha) Std Dev % Uptake

1 29.86 22.11 26.70 

2 47.48 16.31 31.64 

3 62.91 17.47 60.49 

Whippoorwill 

4 76.34 13.26 66.24 

1 20.32 21.69 16.85 

2 33.90 20.61 35.68 

3 35.87 22.74 30.17 

Home 

4 50.83 24.39 50.47 

1 31.59 11.46 45.12 

Bunker 2 47.75 11.11 43.61 

3 53.32 10.60 57.21 

The general walk through on day 2 post broadcast on Little East Island, an estimated 60-

70% of bait had been taken up, however, there was uneven distribution of bait 

availability. We estimated that 99.9% of the bait had been removed in prime rat and 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 21 

landcrab habitat above the shoreline leaving potential rat territory size areas free of bait. 

Further, Little East had no established hermit crab population which were an important 

driver of bait uptake on the remaining treated islands in the atoll. Thus, 60 kg/ha is too 

low an application rate to ensure bait is available to the entire rat population for a 

minimum of 4 days. 

By day 3 post broadcast on Fern Island (baited at 80 kg/ha), an estimated 60-70% of bait 

had been taken up. Bait was relatively evenly distributed across the island, which from 

observations of personnel experienced in aerial drops was as consistent as that spread 

from a helicopter, with bait available in even small rat territories. However, in areas of 

high density Cardisoma landcrab burrows, all the bait had been taken up. Further, Fern 

Island has no established hermit crab population that competes with landcrabs and rats 

for the bait. Therefore, it appears that 80 kg/ha may not be adequate to ensure bait is 

available to the entire rat population across the atoll for a minimum of 4 days. 

Our monitoring of uptake data from Whippoorwill and Home islands indicates on 

average 30% of applied bait still available to rats four days post application (Figure 6). 

On a walk through on Whippoorwill on day 7 post application we estimated that >99% of 

the bait pellets had been removed. Calculation of the 99.99% confidence interval 

indicates the relative probability of bait applied at different densities available to 100% of 

the rat population four days post application (Table 12). Results from Bunker Island 

indicate bait would not be detected in monitoring plots by day 3 post application when 

baited at 70 kg/ha. Bait would be detected in monitoring plots with an application rate of 

85-95 kg/ha to rats at 4 days post application. 

In evaluating the bait uptake data, and the subjective evaluation of bait spread across the 

treated islands, we believe an application rate of 90 kg/ha is appropriate to ensure enough 

bait is available to every rat across the atoll for a minimum of 4 days. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 22 

Figure 6. Cumulative bait consumption (w/o outliers) measured in uptake plots for a) 

Home Island (n=109); b) Whippoorwill Island (n=75); and c) Bunker Island (n=12). 

-10

0

10

20

30

40

50

60

70

80

123 4

Day post - appl ic at ion

0

10

20

30

40

50

60

70

80

90

100

1234

Day post-application

0

10

20

30

40

50

60

70

123

D ay post-ap plication

Bait Consumption (kg/ha) Bait Consumption (kg/ha) Bait Consumption (kg/ha) 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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Table 12. Bait remaining four days post application. Data are χ ± 99.99% 

 confidence limits of pellets per m2

. Palmyra Atoll, July 2005. 

Island 

Bait 

Application 

Rate (kg/ha) 

99.99% 

Confidence 

Limits 

Min # 

Pellets L1

Max # 

Pellets L2 

Whippoorwill 95.00 1.44 ± 0.49 0.95 1.94 

Home 85.00 1.65 ± 0.67 0.98 2.32 

Bunker 70.00 1.30 ± 1.30 0.00 2.60 

Efficacy 

Methods 

We used direct and indirect methods to monitor the effectiveness of the bait application 

in eradicating rats. The following techniques were used to measure efficacy : (1) pre and 

post bait broadcast live trapping on ground and in the coconut palm canopy, (2) pre and 

post bait broadcast wax indicator chew blocks, and (3) monitoring of radio collared rats. 

Live Trapping 

One week prior to the bait application one three-night trap session was conducted on each 

of the islets to assess rat presence and compare relative densities between islets. 

Haguruma brand live traps were armed with coconut and set both on the ground and in 

the coconut palm canopy (Table 13). Ground traps were set on overturned five-gallon 

buckets to minimize disturbance by land crabs and spaced 15-25 m apart. Traps set in 8-

20 m tall coconut palm trees were mounted with nails beneath the crown base and 

secured around the trunk with thin-gauged wire (Figure 7). 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 24 

Figure 7. Haguruma brand live rat traps mounted on buckets and in coconut palms, 

Palmyra Atoll, July 2005. 

Both ground and tree traps were checked daily and the condition or contents of each trap, 

whether rat, crab, or no catch, was recorded. All rats captured were marked with a 

uniquely numbered ear tag, and in some cases, a radio collar (see below), and the sex, 

weight and apparent reproductive condition were noted. Each rat was released at the 

point of capture. All traps were rearmed for each successive trap night and placed in the 

same location. 

Table 13. Number of ground traps and traps mounted in coconut palms for each 

treated island, Palmyra Atoll, July 2005. 

Island # of ground traps # of tree traps 

Whippoorwill/Bunker 55 10 

Home 35 10 

Little East 40 4 

Fern 25 10 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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Live trapping on the ground and trees resumed on all treatment islets one week post bait 

application. All traps were armed with fresh coconut, and checked daily for condition 

and contents. Trap effort was sustained for a total of 21, 16, 15, and 13 days on 

Whippoorwill/Bunker, Fern, Little East, and Home islands respectively. 

Ground based live trapping was conducted on untreated Cooper Island before and after 

the bait application for reference. No tree trapping was conducted on Cooper Island due 

to logistical constraints. 

Chew Blocks 

Peanut butter flavored paraffin wax chew blocks were 

used as an indirect method of detecting rat presence. 

Rats chewing on blocks left distinct incisor marks 

indicative of rat activity (Table 14 and Figure 8). 

Chew blocks were nailed to a tree two to three meters 

above the ground to minimize crab access. Prior to the 

application blocks were set in tandem with the threenight live trapping session on all treatment islets. 

Blocks were inspected daily for signsa of rat incisor marks, crab claws, or insects. Each 

chewed or marked block was replaced with a fresh block for the successive evening. 

Table 14. Number of chew blocks on each islet, Palmyra Atoll, July 2005. 

Island # of blocks 

Whippoorwill/Bunker 55 

Home 35 

Little East 40 

Fern 25 

Figure 8. Wax chew block 

with peanut butter. Note 

ants feeding on peanut 

butter, Palmyra Atoll, July 

2005. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 26 

Beginning one week post application blocks were set and inspected daily or bi-daily until 

August 13, 2005, after which blocks were checked at two-week intervals. Blocks were 

set and checked at the same interval as live traps for a total of 21, 16, 15, and 13 days on 

Whippoorwill, Fern, Little East, and Home islands respectively. 

Radio Telemetry 

Radio-collared rats were used as a direct indicator of efficacy. During the preapplication trapping sessions a total of 45 adult rats (Table 15) captured on the ground 

and in the trees (with exception of Little East island) were anaesthetized and fitted with 

radio collars programmed to a unique frequency (ATS, Minnesota) (Figure 9). Each rat 

fitted with a radio collar was also marked with a uniquely numbered ear tag and the sex 

and weight recorded. Collared rats were held in cages and observed over a 24-hour 

period until released on their respective capture site. 

Directional Yagi antennas and digital receivers were used to track rats at daily and/or 

nightly intervals to confirm movement of the radio signal (indicating that the rat was 

alive) prior to the bait application. All collared rats were determined to be active by 

direct visual observation, dynamic signal at the time of tracking (indicating that the rat 

was moving), or multiple refuge/nest locations between consecutive fixes. 

 

Figure 9. Radio collaring rats, Palmyra Atoll, July 2005. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 27 

Radio-collared rats were tracked and monitored on all treatment islets until mortality was 

detected or the radio signal was lost likely as a result of irreparable damage by crabs. 

Mortality was determined through carcass recovery or when the signal was located 

repeatedly in the same location over a period of seven days. At the time of recovery the 

location of death, whether ground, arboreal, or underground, and the condition of each 

carcass, whether scavenged or whole, was recorded. 

Results and Discussion 

Trapping 

Rats were detected on the ground prior to the bait application on all treatment islets, and 

in the palm canopy on all treatment islets except Little East which had only a few coconut 

palms. On the treatment islets pre-application ground trapping success for rats ranged 

between 19.7% and 46.3% (n= 533.5 trap nights) with a mean trap success of 29.4 % (s = 

11.5) (Table 16). The pre-application trap success at the reference location was 33.3% 

(n=45), a rate comparable to mean success on trial islets. Rats were captured in the palm 

canopy at a rate of 7.5% to 13.3 % (n= 155) (Table 17). No rats were trapped in the 

palm canopy on Little East, likely attributable to significantly lower palm tree density. 

Table 15. Number of rats fitted with radio collars captured in Ground and Tree placed 

live traps on treatment islets (Ratio= male:female:juvenile). 

ISLAND GROUND TREE TOTAL 

Whippoorwill 4 

(1:3) 

5 

(1:4) 

9 

(2:7) 

Home 13 

(5:7:1) 

3 

(2:1) 

16 

(7:8:1) 

Little East 13 

(6:7) 

0 

(0:0) 

13 

(6:7) 

Fern 4 

(1:3) 

3 

(1:2) 

7 

(2:5) 

TOTAL 34 

(13:20:1) 

11 

(2:3) 

45 

(17:27:1) 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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After the bait application, no rats were captured after 1542.5 trap nights across the treated 

islets. Rat trap success during the reference trapping effort on an untreated islet (Cooper) 

was 46.4% (n= 36.5 trap nights). 

Table 17. Pre and post bait application tree trap success, Palmyra Atoll, July 2005. 

SESSION ISLAND TRAP NIGHTS 

n= #traps – (0.5 x TNC*) 

% RAT SUCCESS 

Whippoorwill/ Bunker 45.0 13.3 

Home 40.0 7.5 

Little East 20.0 0.0 

Fern 50.0 12.0 

TOTAL= 155.0 8.2 

Pre-application 

Std. Dev. - 6.0 

Whippoorwill/ Bunker 130.0 0.0 

Home 80.0 0.0 

Little East 40.0 0.0 

Fern 100.0 0.0 

TOTAL = 350.0 0.0 

Post-application 

Std. Dev. - 0.0 

* TNC= Tripped no catch 

Table 16. Pre- and post-bait application ground trap success on trial islets and Cooper Island (reference site), 

Palmyra Atoll, July 2005. 

TRAP SUCCESS SESSION ISLAND TRAP NIGHTS 

TN= #traps –(0.5 xTNC*) RAT CRAB 

Whippoorwill/ Bunker 141.0 27.6 5.7 

Home 93.0 32.3 2.2 

Little East 232.5 19.7 5.1 

Fern 67.0 46.3 0.0 

TOTAL = 533.5 29.4 2.9 

Pre-application 

Std. Dev. - 11.5 2.3 

Reference (pre) Cooper 45.0 33.3 0.0 

Whippoorwill/ Bunker 653.5 0.0 1.5 

Home 264.0 0.0 1.9 

Little East 378.5 0.0 4.0 

Fern 246.5 0.0 0.4 

TOTAL = 1542.5 0.0 2.0 

Post-application 

Std. Dev. - 0.0 1.5 

Reference (post) Cooper 36.5 46.6 0.0 

* TNC = Tripped no catch. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 29 

Table 18. Chew block activity pre- and post-bait application on trial islets, July 2005, Palmyra Atoll. 

% CHEWED 

SESSION ISLAND BLOCKS 

(n) RAT CRAB ANT Block Gone 

Whippoorwill 164 81.7 0.0 0.0 17.1 

Bunker 16 100.0 0.0 0.0 0.0 

Home 277 35.4 0.0 0.7 5.4 

Little East 106 84.0 0.0 0.9 10.4 

Fern 75 70.7 0.0 8.0 1.3 

Total 638 74.3 0.0 1.9 6.8 

Pre-application 

Std. Dev. - 24.2 0.0 3.4 7.0 

Whippoorwill 676 0.0 15.4 40.1 12.7 

Bunker 88 0.0 6.8 29.5 2.3 

Home 400 0.0 4.3 52.0 12.8 

Little East 272 0.0 11.4 29.0 10.7 

Fern 250 0.0 2.0 41.2 0.8 

Total 1686 0.0 8.0 38.4 7.8 

Postapplication 

Std. Dev. - 0.0 5.4 9.5 5.8 

Chew Blocks 

Prior to the bait application on all treatment islets rat activity was detected using chew 

blocks. Rat activity ranged from 35.4 to 100.0%, with a mean rat activity of 74.3% 

(n=638, s= 24.2) (Table 18). Ants and crabs were responsible for less than 2% of activity 

and only 6.8% (s= 7.0) of blocks completely disappeared. 

No rat incisor maks were detected post bait application (n= 1686 block nights) (Table 

18). On average crabs and ants were responsible for 8% (s= 5.4) and 38.4% (s= 9.5) of 

activity respectively. Blocks completely disappeared at a mean of 7.8% (s=5.8) of the 

time. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 30 

Measures of activity on chew blocks four to five weeks post bait application (monitored 

at 14-day intervals) have indicated no rat presence on any treatment islet (Table 19). 

The two week interval between checks was due to logistical complications and lack of 

staffing. We recognize that the missing blocks complicate the data because it is 

impossible to conclude what removed the blocks. However, we hypothesize that hermit 

Table 19. Percent chew block activity measured post eradication on 5 trial islets, Palmyra Atoll, July 2005. 

Chew blocks were set 14 days prior to the sample date (n= 10 blocks per sample date). 

% SUCCESS 

ISLAND DATE Day postapplication RAT CRAB ANT Block Gone 

24-August 40 0.0 30.0 50.0 50.0 

7-September 54 0.0 10.0 10.0 90.0 

21-September 68 0.0 10.0 10.0 90.0 

Total - 0.0 16.7 23.3 76.7 

Whippoorwill/ 

Bunker 

Std. Dev. - 0.0 11.5 23.1 23.1 

24-August 31 0.0 30.0 40.0 60.0 

7-September 45 0.0 0.0 30.0 70.0 

21-September 59 0.0 40.0 40.0 60.0 

Total - 0.0 23.3 36.7 63.3 

Home 

Std. Dev. - 0.0 20.8 5.8 5.8 

24-August 34 0.0 0.0 0.0 100.0 

7-September 48 0.0 10.0 10.0 90.0 

21-September 62 0.0 30.0 30.0 70.0 

Total - 0.0 13.3 13.3 86.7 

Little East

Std. Dev. - 0.0 15.3 15.3 15.3 

24-August 34 0.0 0.0 70.0 30.0 

7-September 48 0.0 0.0 80.0 20.0 

21-September 62 0.0 0.0 90.0 10.0 

Total - 0.0 0.0 80.0 20.0 

Fern

Std. Dev. - 0.0 0.0 10.0 10.0 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 31 

crabs were likely responsible for the majority if not all the block removal because the 

removed blocks were on trees and vegetation that hermit crabs were routinely found and 

could easily climb. Further, the blocks were typically coated with a small layer of peanut 

butter and was not permeated through the block so as to discourage rats from consuming 

all of the wax and prior to the baiting, rats did not consume the entire wax block when 

given the opportunity. From the blocks that were remaining on trees, combined with the 

trap data, we conclude that the data would strongly suggest that the rats had successfully 

been removed from all of the treated islands.

Radio Telemetry 

Recovery of collared rats began five days post bait application on all treatment islets and 

continued until collar status was determined for all rats. Of radio collared rats, 27 were 

actively recovered (carcasses) and 9 were presumed dead (signal located repeatedly in the 

same location over a seven-day period). Four radio collar signals were lost and not 

recovered after the bait application, presumably damaged by crabs. Five radio-collared 

rats were omitted from analysis due to improperly functioning collars prior to the bait 

application. Mean day of carcass recovery was 7.2 days post bait application (n=40 rats, 

s= 2.3) (Table 20). 

 

A sub-sample of radio-collared carcasses in the most optimal condition were collected 

and submitted for brodifacoum residue analysis to National Wildlife Research Center, 

Fort Collins, Colorado (n=5). 

 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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The radio collar, live trap and chew block data together strongly suggest that the rats had 

been successfully removed from the treated islets. However, on day 8 post broadcast on 

Whippoorwill, a small, live juvenile rat was discovered in a rat nest with 2 adult sized, 

and dead, rats. The rat escaped and ran off quickly with no behavioral signs of 

anticoagulant poisoning. Two days later, during a check on the island, a similar sized rat 

was found alive in the same rat nest, but clearly lethargic, and was euthanized. The legs 

showed signs of hemorrhaging including the top and bottom of the feet. The lethargy and 

hemorrhaging were likely signs of exposure to brodifacoum, however, residue analysis is 

pending to confirm. 

We conclude that the bait application was effective in removing all of the rats from the 

treated islets, however, it is unclear how long the islets remained rat free. The discovery 

of the small, young rat at day 8 on Whippoorwill Is. was troubling as it confirms that rat 

eradications should take place at a time of year when there is no breeding so as to prevent 

young weanling rats escaping exposure to the bait when in the burrow, and surviving to 

repopulate the island causing the eradication to fail. Palmyra Atoll is an aseasonal 

environment and it is likely that rats are breeding year round making it difficult to ensure 

Table 20. a) Number and location of radio collared rats recovered or presumed dead: 

Ground (exposed or beneath foliage location), within burrow, or palm tree (presumed 

dead). b) Condition percentage of radio collared rats recovered or presumed dead: 

whole (fresh carcass, death <24 hr), decomposed (skeleton and sinew, death >48 hr), 

scavenged (collar only recovered), and unknown (collar not recovered)., Palmyra 

Atoll, July 2005 

a) LOCATION of DEATH (%) b) CONDITION (%) 

ISLAND 

GROUND BURROW TREE N WHOLE DECOM SCAVN UNK N 

Whippoorwill 87.5 12.5 0.0 8 37.5 50.0 12.5 0.0 8 

Home 66.7 22.2 11.1 9 0.0 55.6 22.2 22.2 9 

Little East 37.5 62.5 0.0 8 25.0 62.5 0.0 12.5 8 

Fern 66.7 0.0 16.7 6 16.7 50.0 0.0 16.7 6 

Total 64.5 25.8 6.5 31 19.4 54.8 9.7 16.1 31 

Std. Dev. 20.6 27.0 8.3 - 15.7 5.9 10.8 14.2 - 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 33 

bait is delivered to all rats including weanlings. Thus, to ensure bait availability to all 

rats including weanlings, we are recommending that bait be applied twice at the full 

application rate, 10-14 days apart, to ensure a high probability of successfully removing 

rats from Palmyra Atoll. 

Evaluation of Primary and Secondary Exposure Risks to Non-Target Species 

We monitored the movement of brodifacoum and/or its associated impact within the 

terrestrial ecosystems on all treatment islets. Within the terrestrial environment we: 

1. performed shorebird surveys to assess potential impact to migratory population, 

2. collected land and hermit crabs, which are known prey items of shorebirds, to 

measure brodifacoum residues over time, 

3. indexed crab populations pre- and post-application to measure potential impact, 

4. monitored in the environmental fate of bait over time, and 

5. searched for carcasses of non-target species to assess potential impact to nontarget species. 

Shorebirds 

Methods 

Informal shorebird surveys were conducted for the duration of the trial during most visits 

to the trial islets. Surveys were conducted by walking the perimeter of the islet and 

recording the number of each species of shorebird encountered on or in the immediate 

vicinity of the islet. The time, weather conditions, and tidal position were recorded. 

Results 

Four species (Numenius tahitiensis, Bristle-thighed Curlew [BRCU]; Heterscelus 

incanus, Wandering Tattler [ WATA]; Pluvialis fulva, Pacific Golden Plover [GOPL] and 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 34 

Arenaria interpres, Ruddy Turnstone [RUTU]) of shorebirds were encountered on each 

trial islet both previous to and up to three weeks post bait application (Figure 10). 

Shorebirds seen during the surveys were frequently observed traveling between islets and 

over the central lagoon, indicating a lack of site-specific fidelity Therefore, based on the 

broad utilization of habitat it is impossible to infer any effects of the trial eradication on 

Palmyra’s shorebird populations. However, the numbers of individuals observed during 

the surveys were higher post bait application than pre application for all species except 

Ruddy Turnstones on Little East islet and Wandering Tattlers on Whippoorwill, Home, 

and Little East islets (Table 21). The increased abundance of shorebirds sightings post 

application was more likely a result of migratory influx, which generally begins in the 

late summer months on the atoll, rather than an artifact of the trial itself. At a minimum 

the surveys conducted confirm the presence of shorebird species on each trial islet during 

the summer of 2005. This data, although unable to detect any direct impacts to the local 

population associated with the trial eradication, will prove useful for the logistical and 

operational planning of an atoll-wide rat eradication. 

Bristle-thighed Curlews, though generally observed along the shorelines and above open 

water, were occasionally sighted beneath the forest canopy in the interior of the islets. 

Although no foraging activity was observed, numerous husking stations attributed to the 

curlews were found beneath the canopy, containing fragments of the turbo snail shells 

used by hermit crabs. This evidence suggests that hermit crabs compose at least a portion 

of the curlew’s diet, confirming their potential risk of secondary exposure to the 

rodenticide. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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Figure 10. Frequency of sighting during pre and post-appIlcation shorebird surveys for species: a) Bristlethighed Curlew, b) Wandering Tattler, c) Pacific Golden Plover, and d) Ruddy Turnstone. 

a. Bristle-thighed Curlew 

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

FERN

HOM E

LEAST

WHIP

F requency o f Occurrence

Pre-application 

Post-application

b. Wandering Tattler 

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

FERN

HOM E

LEAST

WHIP

Frequency of Occurrence

Pre-application

Post-application

c. Pacific Golden Plover 

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

FERN

HOM E

LEAST

WHIP

Frequency of Occurrence

Pre-application

Post-application

d. Ruddy Turnstone 

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

FERN

HOM E

LEAST

WHIP

Frequency of Occurrence

Pre-application

Post-application
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

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Table 21. Mean species sighting per survey conducted for 5 trial islets. a) Pre-application 

surveys: Whippoorwill/Bunker (n=3); Little East (n=5); Home (n=5); and Fern (n=5). b) 

Post-application surveys: Whippoorwill/Bunker (n=13); Little East (n=6); Home (n=10); 

and Fern (n=8), Palmyra Atoll July-August 2005. 

Species Island Pre-application Post-application % Difference 

Whippoorwill/Bunker 0.00 0.13 100.00 

Little East 1.40 3.70 62.16 

Home 1.00 1.17 14.29 

Fern 0.00 0.85 100.00 

Mean 0.60 1.46 55.95 

BRCU 

Std. Dev. 0.71 1.56 40.67 

Whippoorwill/Bunker 0.80 0.13 -84.38 

Little East 3.80 2.00 -47.37 

Home 1.60 1.50 -6.25 

Fern 2.67 2.77 3.70 

Mean 2.22 1.60 -33.57 

WATA 

Std. Dev. 1.30 1.11 40.44 

Whippoorwill/Bunker 0.00 0.13 100.00 

Little East 1.20 1.60 25.00 

Home 0.40 0.83 52.00 

Fern 0.67 2.38 72.04 

Mean 0.57 1.24 62.26 

GOPL 

Std. Dev. 0.50 0.97 31.69 

Whippoorwill/Bunker 0.00 0.00 0.00 

Little East 0.60 0.80 25.00 

Home 0.40 0.00 -100.00 

Fern 0.00 0.15 100.00 

Mean 0.25 0.24 6.25 

RUTU 

Std. Dev. 0.30 0.38 82.60 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 37 

Land Crab Residue Analysis 

Palmyra hosts a diverse and abundant land crab community with six land crab species 

present throughout the atoll. The most abundant land crab is the red hermit crab 

(Coenobita perlatus). Additional species include the purple hermit crab (Coenobita 

brevimanus), orange land crab (Cardisoma carnifex) and purple land crab (Cardisoma 

rotundum), the large coconut crab (Birgus latro), and Geograpsis crinipes, which is 

present at low numbers on the atoll. 

Although crabs and other invertebrates are not known to be susceptible to anticoagulant 

rodenticides, they readily consume bait. Crabs were collected from each trial islet for 

analysis of tissue residues, including brodifacoum from bait ingestion, at 2, 6, 10 and 21 

days post bait application (Table 22). Five crabs from each of the two most abundant 

genera (Cardisoma spp. and Coenobita spp.) were collected on each sample day at 

Whippoorwill and Home islets. Due to low initial population sizes of Coenobita spp. on 

Little East and Fern islets, this genus was excluded from the collections made on these 

two trial islets. One B. latro individual was discovered dead in a live rat trap 21 days 

post application on Little East was submitted for tissue analysis. With the exception of 

the one dead B. latro specimen, all crabs sampled were collected live, euthanized by 

freezing, and submitted whole to the National Wildlife Research Center Analytical Lab 

for analysis. Results from the tissue analysis will be reported elsewhere. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 38 

Landcrab Population Index Monitoring 

Methods 

All five trial islands host multi-species land crab communities, though community 

composition varies between islands. Brodifacoum functions as an anticoagulant in 

mammalian and avian circulatory systems, but is believed to be innocuous to arthropods. 

We tested this hypothesis by indexing land crab populations before bait application, and 

15 days after bait application on four trial islets: Home, Whippoorwill, Little East, and 

Fern. 

Land crab population indices were achieved by sampling randomly placed 25 m x 5 m 

fixed-width transects; individual land crabs within the transect swath were identified by 

Table 22. Land crab collections from trial islets for brodifacoum residue analysis, Palmyra 

Atoll, July-August 2005. 

Island Day Post-application Cardisoma spp. Coenobita spp. 

2 5 5 

6 5 5 

10 5 5 

21 5 5 

Whippoorwill 

Total 20 20 

2 5 - 

6 5 - 

10 5 - 

21 5 - 

Little East 

Total 20 -

3 5 - 

6 5 - 

10 5 - 

21 5 - 

Fern 

Total 20 -

2 5 5 

6 5 5 

10 5 5 

19 5 5 

Home 

Total 20 20 

Grand Total 80 40 

* The day 21 samples will be analyzed first to determine if the day 56 collection is needed. Collection will be 

needed at day 56 if any of the samples on day 21 come back positive for brodifacoum residue. No samples will 

be collected after day 21 if no brodifacoum is detected. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 39 

species and counted. A sample was collected by walking 25 m in a randomly chosen 

direction from a random start point, counting only crabs within the transect swath and in 

front of the researcher. Cocos frond midribs fashioned to 2.5 m in length were carried 

and swung horizontally to delineate swath width while sampling transects. The number 

of samples per trial island is approximately equivalent to 1⁄4 (25%) of each island’s 

emergent land area. 

Data were corrected for non-normality using a square root transformation X’ = X + 0.5

(Bartlett 1936). A two-tailed t-test was used to evaluate differences in mean density, 

measured per 100m2

 (α =0.05). 

Results 

Results from the land crab population index study suggest that ground baiting with the 

brodifacoum-loaded rodenticide (PI-25) does not have a significant influence on 

Palmyra’s land crab populations. Results indicated a non-significant difference in crab 

density for all islands except Home Island, where a difference in Coenbita perlatus

density pre and post application was detected (Table 23). Difference in density, although 

significant, are not believed to suggest population impact from brodifacoum 

consumption. Crab densities have been observed to vary in correlation with weather 

conditions ( A. Wegmann, pers. comm.). During periods of foul weather (high winds and 

rainfall) and extreme sun exposure in the afternoon hours, crabs take refuge beneath 

foliage for protection from environmental elements making census of crab populations 

challenging. To minimize weather effect during crab index studies the majority of 

censuses were performed during the morning hours on days of non-extreme weather 

conditions. However, based on the unpredictable weather patterns and logitisical 

constraints often encountered on the atoll, the post application transects on Home Island 

were conducted in light rainfall during the afternoon hours. It is believed the difference 

in density can be better attributed to weather condition than rodenticide impact. Further, 

the predominant forest type on Home Island of Cocos nucifera and Pandanus tectorious

provide a dense understory of fronds and root structures used by non-burrowing crabs as 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 40 

refuge during extreme weather events. This “hiding” or refuge behavior results in 

extremely observer error or bias when censuses are performed. If difference in mean 

density were attributed to rodenticide impact it is expected that Coenbita perlatus

carcasses would have been detected during formal and informal carcass searches 

performed, especially as this is a non-burrowing species. However, during the 43 hours 

of carcass search effort on Home Island no hermit crab carcasses were encountered. 

Table 23. Land crab index pre- and post-bait application. Data are mean crab density per 100m2

± 95% confidence limits, Palmyra Atoll, July-August 2005.

Fern Island Home Island Little East Island Whippoorwill 

Island 

Pre 0.00 ± 0.00 (8) 22.9 ± 3.73 (26) 0.00 ± 0.00 (14) 7.86 ± 3.50 (29) 

Post 0.00 ± 0.00 (8) 9.32 ± 2.77 (26) 0.00 ± 0.00 (14) 11.2 ± 4.24 (29) Coenobita 

perlatus T-test n/a P < 0.01* n/a N.S. 

Pre 0.00 ± 0.00 (8) 0.06 ± 0.08 (26) 0.23 ± 0.29 (14) 1.60 ± 0.93 (29) 

Post 0.00 ± 0.00 (8) 0.03 ± 0.06 (26) 0.34 ± 0.67 (14) 0.72 ± 0.49 (29) Coenobita 

brevimanus T-test n/a N.S. N.S. N.S. 

Pre 1.20 ± 0.78 (8) 0.12 ± 0.19 (26) 2.63 ± 1.96 (14) 0.58 ± 0.42 (29) 

Post 0.70 ± 0.55 (8) 0.06 ± 0.08 (26) 0.40 ± 0.28 (14) 0.39 ± 0.26 (29) 

Cardisoma 

carnifex* 

T-test N.S. N.S. N.S. N.S. 

Pre 0.20 ± 0.39 (8) 0.12 ± 0.11 (26) 0.00 ± 0.00 (14) 0.05 ± 0.05 (29) 

Post 0.00 ± 0.00 (8) 0.00 ± 0.00 (26) 0.06 ± 0.11 (14) 0.03 ± 0.05 (29) 

Cardisoma 

rotundum* 

T-test n/a n/a n/a N.S. 

Pre 0.10 ± 0.20 (8) 0.00 ± 0.00 (26) 0.00 ± 0.00 (14) 0.00 ± 0.00 (29) 

Post 0.00 ± 0.00 (8) 0.03 ± 0.06 (26) 0.11 ± 0.15 (14) 0.00 ± 0.00 (29) Birgus 

latro T-test n/a n/a n/a n/a 

* Post bait application values for Cardisoma sp. might be biased by land crab sampling – 15 Cardisomas were removed 

from each island for toxin loading analysis prior to the post application index sampling. 

Environmental Fate of Bait 

The rate and characteristics of bait decomposition on each trial islet were monitored over 

time to better understand how bait withstands ambient environmental conditions on the 

atoll. Bait pellets were enclosed in cages to prevent consumption by crabs or rats, and 

left exposed to the ambient environment. Invertebrates were readily able to access the 

bait. A sub-sample of bait pellets was collected from each cage for brodifacoum residue 

analysis in a laboratory and the condition of bait noted at 3, 6, and 21 days post bait 

application. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 41 

In general the condition of bait at Day Three was swollen and tacky in texture while still 

relatively firm. By Day Six all bait pellets were swollen with moisture and soft to touch, 

but the pellets retained their original shape. The pellets could be molded but would not 

break into pieces under pressure. For two of the four treatment islets mold was noted 

growing on most pellets in the bait enclosures. By Day 21 crabs had effectively 

burrowed into the enclosures on Little East and Fern islets and consumed the bait within. 

For the remaining bait at Day 21 pellets were swollen to approximately 2-3 times the 

original, compressed size. Pellets had changed color from the dyed blue to a gray, 

greenish shade, and all pellets were entirely encased in mold. Bait pellets were well 

deteriorated, with texture spongy and would disintegrate with light pressure. 

Non-Target Species Carcass Searching 

Both formal (organized timed searches) and informal (opportunistic finds) carcass 

searches were conducted on all trial islets. Formal carcass searches were conducted at 

seven, 10, and 14 days post-application in which a team of two to three observers 

thoroughly covered all land area on the trial islets visually scanning for carcasses. 

Informal searches occurred opportunistically whenever field personnel visited trial islets 

for other scientific purposes. Carcasses found during both formal and informal searches 

were collected, and the general condition and location of recovery recorded, whether 

“exposed,” “under foliage,” or “in burrow.” All carcasses collected were bagged and 

frozen for potential residue analysis. 

A total of 169 person-hours were devoted to carcass searches. Forty-five rat carcasses 

were found. In addition, three land crab (Cardisoma carnifex) carcasses were found on 

Whippoorwill Islet and were submitted for brodifacoum residue analysis. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 42 

Conclusions on Trial Eradication 

We conclude that: 

1. The PI-25 bait containing 25 ppm brodifacoum was effective in removing all 

of the rats on the trial islands. 

2. PI-25 bait is an appropriate formulation to maintain its integrity in the wet, 

humid environment on Palmyra. 

3. PI-25 is preferred by the rats over natural food items, even after absorbing 

moisture and molding. 

4. Brodifacoum is an appropriate rodenticide to remove rats from Palmyra. 

5. Landcrabs are not negatively impacted by brodifacoum. 

6. No migrant shorebirds were detected dead or moribund in the study area. 

Recommendations for Eradication of Rats from Palmyra Atoll 

1. Rats can be removed from Palmyra Atoll with a high probability using a 

broadcast of PI-25 bait containing 25 ppm brodifacoum. 

2. Two applications of PI-25 at 90 kg/ha/application of the bait may be needed to 

overcome landcrab competition and to ensure bait is available to all rats, 

especially weanlings, for a minimum of 4 days. 

3. Applying bait prior to the arrival, or after departure, of migrant shorebirds is 

effective at minimizing risk of primary rodenticide exposure to non-target 

species. 
Progress in Palmyra Atoll Restoration: Trial Rat Eradication 

Page 43 

References 

Atkinson, I. A. E., 1985. The spread of commensal species of Rattus to oceanic islands 

and their effect on island avifaunas. In: Moors, P. J. (Ed.), Conservation of island 

birds Case studies for the management of threatened island species, International 

Council for Bird Preservation, Technical Publication 3, pp 35-81. 

Brown, K. P., 1997. Predation at nests of two New Zealand endemic passerines; 

implications for bird community restoration. Pacific Conservation Biology 3, 91-

98. 

Galvan, J.P., B. Tershy, G. R. Howald, A. Samaniego, B. Keitt, M. Brown, J. Russell, M. 

Pascal, and J. Parkes. 2005. A review of commensal rodent eradications on 

islands. Presentation to the 32nd Annual Pacific Seabird Group Meeting, January 

19-22, 2005, Portland, Oregon. 

Groombridge, B., 1992. World Conservation Monitoring Centre, British Museum 

(Natural History), International Union for Conservation of Nature and Natural 

Resources. Global biodiversity: status of the earth's living resources: a report. 

Chapman & Hall, London. 

Howald, G.R., A. Samaniego, S. Buckelew, P. McClelland, B. Keitt, A. Wegmann, W.C. 

Pitt, D.S. Vice, E. Campbell, K. Swift and S. Barclay. 2004. Palmyra Atoll Rat 

Eradication Assessment, August 2004: Trip Report. Technical report to US Fish 

and Wildlife Service, Honolulu, HI. 

Whittaker, R.J. 1998. Island biogeography; ecology evolution, and conservation. 

Oxford University Press, Oxford. New York, New York. 
Scaevola

Pisonia

Terminalia

Bare

ground 

Appendix A. Trial Eradication Islands and Habitat Composition Figure A. Palmyra Atoll National Wildlife Refuge: Primary Forest Type Map 

Forest Type % coverage sq meters hectaresCocos 42.67 975970 97.6Scaevola 29.50 674796 67.5Pisonia 11.94 273140 27.3Terminalia 6.24 142750 14.2Bare ground 9.10 208050 20.8Hibiscus 0.56 12730 1.3
Home Island: 1.2 ha; Cocos/Scaevola/Pisonia

Fern Island: 0.40 ha; Cocos

Figure B. Land area measurements and predominant forest structure for treatment islets: Fern and Home 
Figure C. Land area measurements and predominant forest structure for treatment islets: Whippoorwill/Bunker an

Whippoorwill & Bunker Islands:W = 1.7 ha, B = 0.2 ha;Scaevola/Cocos/Pisonia

Little East: 0.7 ha;Pisonia/Cocos
1

APPENDIX E

PALMYRA ATOLL RAT ERADICATION: BIOMARKER 

VALIDATION OF AN EFFECTIVE BAIT APPLICATION RATE, 19 

JUNE TO 5 JULY, 2008
2
PALMYRA ATOLL RAT ERADICATION: BIOMARKER VALIDATION OF AN EFFECTIVE BAIT APPLICATION RATE, JUNE 19 TO 5 JULY, 2008

PALMYRA ATOLL RAT ERADICATION: BIOMARKER 

VALIDATION OF AN EFFECTIVE BAIT APPLICATION RATE

19 JUNE TO 5 JULY, 2008

PREPARED BY: ISLAND CONSERVATION

Alexander Wegmann1

, Joel Helm1, Araceli Samaniego1, William Smith2, Bill Jacobs3, Don Drake4, Joanna 

Smith5

, Matthew McKown6, Adonia Henry2, Robert Fisher7, Stacie Hathaway7

1

Island Conservation, 2USFWS, 3EPA, 4University of Hawaii, 5University of Washington, 6University of North Carolina, 7USGS

Correspondence: Alexander Wegmann - 1925 Kirscher Rd #3, Kelowna BC, V1Y 4N7 Canada / 

alex.wegmann@islandconservation.org, / 250-870-1673

Recommended Citation: 

Wegmann, A., J. Helm, B. Jacobs, A. Samaniego, W. Smith, D. Drake, R. Fisher, S. Hathaway, A. Henry, 

J. Smith, M. McKown. 2009. Palmyra Atoll Rat Eradication: Biomarker Validation of an 

Effective Bait Application Rate, 19 June to 5 July, 2008. Technical Field Report. Island 

Conservation, Santa Cruz, California. 
PALMYRA ATOLL RAT ERADICATION: BIOMARKER VALIDATION OF AN EFFECTIVE BAIT APPLICATION RATE, JUNE 19 TO 5 JULY, 2008

2

1. EXECUTIVE SUMMARY

Pilot black rat eradication trials conducted in 2004 and 2005 by the US Fish and Wildlife Service 

(USFWS), Island Conservation (IC), US Department of Agriculture, and NZ Dept. of 

Conservation indicated that a bait application rate (60 – 95 kg/ha) might be necessary to 

successfully eradicate rats from Palmyra Atoll. The 2004-2005 work indicated that these bait 

application rates would likely be needed but did not set or confirm the rates. Rather, they 

provided a range of possibly suitable rates. The 2008 project attempted to determine whether 

lower applications rates might reach all rats sufficiently. However, the product label for 

Brodifacoum 25W (a bait product specially formulated for Palmyra’s wet, warm conditions) was 

approved with a maximum bait application rate of 18 kg/ha followed five to seven days later by a 

second application of 9 kg/ha. The purpose of the 2008 Palmyra rat eradication biomarker study 

was to assess the feasibility of using the maximum (18 kg/ha and 9 kg/ha) application rate for 

25W within Palmyra’s challenging environment, and to monitor non-target species exposure to 

broadcast bait pellets. 

From 19 June to 5 July 2008, eleven USFWS, IC, US Environmental Protection Agency (EPA), 

and volunteer personnel evaluated rat and non-target species exposure to placebo biomarker bait 

hand-broadcast to the ground and forest canopy at the label-specified maximum application rate 

(18 kg/ha followed by 9 kg/ha five days later) on 2 study islands, and at more than twice the 

maximum application rate (36 kg/ha followed by 36 kg/ha 5 days later) on a third study island. 

Study islands were chosen based on their similarities with regards to vegetation and rat and crab 

community composition. The following actions occurred in conjunction with the biomarker bait 

applications:

 Bait uptake plots to determine bait consumption rates: 

o 2,510 bait pellets in 47 plots were followed to determine bait consumption rates 

for both application regimes

 Live trapping effort to determine rat exposure to biomarker bait:

o At total of 196 live traps used at the three study sites were opened for six nights 

of post bait application rat sampling; total effort equaled 1,132 trap nights

 Rat sampling to determine exposure to the applied biomarker bait:

o 141 rats were captured and assessed for biomarker sign

o 60 rat stomachs (20 from each study site) were analyzed for food content and 

parasite load

 Captive rat biomarker detection study:

o 36 rats were assigned to one of three biomarker bait consumption treatments (1 

pellet, 3 pellets, no pellets) for three post consumption intervals (3 days, 6 days, 

and 9 days). Results from this study were used to estimate the levels of bait 

consumption by rats in the biomarker field study. 

 Hermit crab sampling to determine exposure to the applied biomarker bait:

o For eleven days after the initial bait application, hermit crabs (Coenobita 

perlatus; n = 310) in all three study sites were assessed for exposure to biomarker 

bait

 Captive hermit crab biomarker detection study:

o 27 hermit crabs were assigned to the same bait consumption and duration 

treatments as described above in the captive rat biomarker detection study. The 

results from this study corroborate the land crab field sampling results.

 Non-target species bait exposure study:

 During two nighttime sampling efforts (both 2 days after the second bait 

application) we assessed biomarker bait exposure for the following non-target 
PALMYRA ATOLL RAT ERADICATION: BIOMARKER VALIDATION OF AN EFFECTIVE BAIT APPLICATION RATE, JUNE 19 TO 5 JULY, 2008

3

species (amphipods (n=8), ants (n=52 ant trails), blister beetles (n = 2), 

cockroaches (n=59), geckos (n=53), katydids (n=49), and spiders (n=1)

Neither the current maximum application rate, nor twice the current maxim application rate for 

25W successfully exposed all rats on each of the study islands. 32% (29/91) of the rats captured 

on one of the islands treated with 18 kg/ha + 9 kg/ha (the maximum application rate for 25W) 

showed no biomarker sign. 5% (1/21) of the rats captured on the island treated with twice the 

allowable application rate for 25W (36 kg/ha + 36 kg/ha) showed no biomarker sign while 29% 

(6/21) of the rats that tested positive for exposure to the biomarker bait in this study site may not 

have been exposed to an amount of bait that would equal a lethal dose of 25W – based on a 

comparative biomarker sign ranking system advised by the captive rat biomarker detection study. 

Nearly all pellets monitored within the bait uptake plots were removed (consumed) within 48 

hours of bait application, and in some cases within 24 hours of bait application. Because the 

label-specified application rate did not expose 100% of the sampled rats within each of the three 

study sites, and the bait did not remain uniformly available to rats for four days post bait 

application, 25W’s current maximum application rate is too low to provide sufficient probability 

of eradication success for implementation at Palmyra. If the Brodifacoum 25W bait is to be 

broadcast on Palmyra Atoll to eradicate roof rats, use of an application rate higher than the label’s 

current limit will have to be authorized, perhaps via an emergency exemption or a label 

amendment.
PALMYRA ATOLL RAT ERADICATION: BIOMARKER VALIDATION OF AN EFFECTIVE BAIT APPLICATION RATE, JUNE 19 TO 5 JULY, 2008

4

2. TABLE OF CONTENTS

1. EXECUTIVE SUMMARY...................................................................................................................... 2

2. TABLE OF CONTENTS ......................................................................................................................... 4

3. INTRODUCTION .................................................................................................................................... 5

3. 1. PROJECT SETTING ............................................................................................................................. 5

3. 2. PROJECT BACKGROUND .................................................................................................................... 6

3. 4. STUDY SITES....................................................................................................................................... 8

3. 5. STUDY QUESTIONS............................................................................................................................. 8

4. METHODS...............................................................................................................................................11

4. 1. HAND BROADCAST BAITING ............................................................................................................11

4. 1. 1. Practice....................................................................................................................................11

4. 1. 2. Accuracy ..................................................................................................................................11

4. 1. 3. Baiting......................................................................................................................................13

4. 1. 4. 2.8 m radius circle plots...........................................................................................................13

4. 2. BAIT CONSUMPTION.........................................................................................................................14

4. 2. 1. Bait consumption plot design and placement...........................................................................14

4. 2. 2. Bait consumption plot sampling...............................................................................................14

4. 3. LAND CRAB INDEX OF ABUNDANCE (IOA)......................................................................................15

4. 4. RAT BIOMARKER DETECTION ASSAY ...............................................................................................15

4. 4. 1. Sampling ..................................................................................................................................15

4. 4. 2. Treatments................................................................................................................................15

4. 4. 3. Biomarker detection scoring system ........................................................................................16

4. 5. HERMIT CRAB BIOMARKER DETECTION ASSAY...............................................................................16

4. 6. FIELD-BASED BIOMARKER DETECTION IN RATS..............................................................................17

4. 6. 1. Sampling ..................................................................................................................................17

4. 6. 2. Scoring System.........................................................................................................................18

4. 7. FIELD-BASED BIOMARKER DETECTION IN HERMIT CRABS..............................................................18

4. 7. 1. Sampling ..................................................................................................................................18

4. 7. 2. Scoring system .........................................................................................................................18

4. 8. FIELD-BASED BIOMARKER DETECTION IN SUBDOMINANT BAIT CONSUMERS.................................18

4. 8. 1. Sampling ..................................................................................................................................18

4. 9. RAT CARCASS CONSUMPTION...........................................................................................................18

4. 9. 1. Placement and Sampling..........................................................................................................19

5. RESULTS.................................................................................................................................................19

5. 1. BAIT CONSUMPTION .........................................................................................................................19

5. 2. LAND CRAB IOA ..............................................................................................................................20

5. 3. RAT CAPTURE ...................................................................................................................................21

5. 5. BIOMARKER DETECTION IN FIELD-CAUGHT RATS...........................................................................23

5. 6. LAND CRAB BIOMARKER EXPOSURE ................................................................................................24

5. 6. 1. Hermit crab biomarker detection assay ...................................................................................24

5. 7. SUBDOMINANT CONSUMER EXPOSURE TO BIOMARKER BAIT .........................................................26

6. DISCUSSION...........................................................................................................................................27

8. APPENDIX A ..........................................................................................................................................31
PALMYRA ATOLL RAT ERADICATION: BIOMARKER VALIDATION OF AN EFFECTIVE BAIT APPLICATION RATE, JUNE 19 TO 5 JULY, 2008

5

3. INTRODUCTION

3. 1. Project setting

Tropical oceanic islands represent some of Earth’s most biologically unique 

ecosystems, yet the very remoteness that fuels high levels of endemicity and species 

radiations on islands also renders such systems vulnerable to invasive species. Invasive 

mammal eradications are a proven, effective method of restoring damaged ecosystems 

and preserving biodiversity on Islands. The presence of indigenous land crabs on most 

tropical islands poses a novel challenge to eradication projects, and especially 

eradications targeting rodents (Wegmann 2008). Land crab consumption of rodenticide 

bait complicates rodent eradication programs by requiring inflated bait application rates, 

which increases the risk of non-target species exposure to rodenticide. Because current 

rodent eradication practices are based on successful temperate or Subantarctic campaigns, 

the conservation community does not sufficient experience methods managing for land 

crab interference. Eradicating alien rats form Palmyra Atoll National Wildlife Refuge 

(Palmyra) would achieve a monumental conservation milestone for the Refuge, and 

would establish a benchmark for subsequent eradication campaigns on other tropical 

islands.

Palmyra Atoll’s native flora and fauna have been marginalized greatly due to WWIIera restructuring and introductions of non-native species, notably coconut palms, ants, 

scale insects, and black rats (Rattus rattus). Nevertheless, Palmyra is an important center 

of biodiversity and species abundance in the Central Pacific region. Now protected 

within the US Fish and Wildlife Service’s NWR system, Palmyra sharply contrasts with 

other moist Central Pacific island groups where the degradation of terrestrial and marine 

ecosystems keeps pace with increased anthropogenic resource exploitation. However, the 

continued presence of omnivorous black rats on the atoll will not allow recruitment or 

population establishment of those species which are vulnerable to black rats.

Palmyra is a breeding refuge for 11 seabird species; but, rat related egg and chick 

predation has likely led to the extirpation of four additional species (Table 1). Without 

the consumptive pressure of an established human population, Palmyra’s land crab 

community is among the richest and most robust in the Central Pacific region. Palmyra is 

home to six species of terrestrial crabs (excluding the intertidal families Grapsidae and 

Ocypodidae), 4 of which are super abundant (Table 2). 

Table 1. Breeding seabirds of Palmyra Atoll; * = Declining population trend

Family Common Name Scientific Name Breeding Pairs IUCN

Procellariidae Audubon’s Shearwater Puffinus lherminieri Believed extirpated LC

Wedge-tailed Shearwater Puffinus pacifica Extirpated LC

Phoenix Petrel Pterodroma alba Believed extirpated EN*

Hydrobatidae White-throated Storm Petrel Nesofregetta fuliginosa Believed extirpated VU*

Sternidae Black Noddy Anous minutus 2,500 LC

Blue Noddy Procelsterna cerulean Believed extirpated LC

Brown Noddy Anous stolidus 1000 LC

Sooty Tern Sterna fuscata 10,000 LC

Gray-backed Tern Sterna lunata Believed extirpated LC

White Tern Gygis alba 150 LC

Fregatidae Great Frigatebird Fregata minor 500 LC
PALMYRA ATOLL RAT ERADICATION: BIOMARKER VALIDATION OF AN EFFECTIVE BAIT APPLICATION RATE, JUNE 19 TO 5 JULY, 2008

6

Lesser Frigatebird Fregata aerial 100 LC

Phaethontidae White-tailed Tropicbird Phaethon lepturus 15 LC

Red-tailed Tropicbird Phaethon rubricauda 20 LC

Sulidae Red-footed Booby Sula sula 5,000 LC

Brown Booby Sula leucogaster 150 LC

Masked Booby Sula dactylatra 20 LC

Table 2. Land crab abundance survey results, Palmyra Atoll (Howald et al. 2004). Units represent 

#/hectare estimates. Five of Palmyra’s six land crab species were sampled; the sixth species (Geograpsus 

grayi) is rarely observed.

Land crab species Mean Standard dev. Mass (g)2

Birgus latro 7 381 1000

Cardisoma carnifex 46 8 300

Cardisoma rotundum 182 80 200

Coenobita. brevimanus 33 8 50

Coenobita perlatus 28 5 50 1 Large variance probably due to low frequency of encounter and patchy distribution.

2 Approximate adult mass

3. 2. Project background

From 2001 to 2003, The Nature Conservancy (TNC) and the US Fish and Wildlife 

Service (USFWS) maintained a bait-station based rat eradication effort at Palmyra. The 

campaign failed to remove all rats from the atoll, and the rat population has since reestablished to a density that exceeds the population measured prior to the eradication 

attempt (Flint et al. 1992, Wegmann and Middleton 2008). In 2004, IC, USFWS, and the 

US Department of Agriculture initiated the construction of a second rat eradication 

program for Palmyra. Field studies associated with this action led to the following 

pertinent discoveries (Howald et al. 2004): 

1) The rat population on Cooper Island showed tolerance to brodifacoum – one rat 

tested in a bait efficacy trial, dosed with brodifacoum at four times the LD50, died 

21 days post-dosing and showed no symptoms characteristic of anticoagulant 

poisoning.

2) R. rattus exploits the arboreal habitat created by monodominant Cocos nucifera 

stands

3) The R. rattus mean home range size at Palmyra (693m2

) is smaller than the baitavailability gaps in the first eradication attempt’s 50m x 50m bait-station grid.

4) Palmyra’s wet, tropical climate calls for a bait pellet matrix that withstands 

frequent saturation by rain and contact with moist soil. 
PALMYRA ATOLL RAT ERADICATION: BIOMARKER VALIDATION OF AN EFFECTIVE BAIT APPLICATION RATE, JUNE 19 TO 5 JULY, 2008

7

5) Land crabs – unaffected by anticoagulant rodenticides – consume large volumes 

of bait – up to 47 kg/ha over a four day period.

6) At-risk non-target species - Bristle-thighed Curlew (Numenius tahitiensis), and 

Pacific Golden Plover (Pluvialis fulva) are least common at Palmyra during the 

months of June and July

With the lessons learned from the failed eradication attempt (utilizing a bait station 

approach), and the new information on hand, the joint USFWS-IC-USDA team 

concluded that a subsequent eradication attempt will need to meet the following 

requirements:

1) The eradication will employ aerial broadcast as the primary bait delivery method 

to ensure that all rats have access to bait, including rats frequenting or residing in 

the forest canopy and because of the presence of unexploded ordnance from 

historical military activity on the atoll.

2) Because of the possibility of toxicant resistance from chronic, sub-lethal exposure 

to anticoagulant rodenticides during the previous rat eradication attempt, the 

toxicant used in the eradication will be a second generation anticoagulant.

3) The bait matrix must be able to maintain form for at least four days of exposure in 

Palmyra’s moist tropical climate.

4) The bait application rate will need to account for bait consumption by land crabs

while maintaining enough bait on the ground to ensure that all rats have access to 

a lethal dose for approximately four days post bait application. 

5) In order to minimize non-target species risk of exposure to rodenticide, the 

eradication will coincide with the low-abundance period (June-July) of migratory 

shorebirds, notably N. tahitiensis and P. fulva.

In 2005, IC and the USFWS conducted trial broadcast-based eradications on five 

islets totaling 4.08 ha (Buckelew et al. 2005). A concurrent bait consumption trial 

indicated that an application rate within 60-90 kg/ha will be necessary to ensure that, 

given land crab competition for broadcast bait pellets, all rats have access to a lethal 

amount of bait for four days post application. The five trial islets were each treated with 

moisture resistant compressed-grain pellets containing 25ppm brodifacoum, “25W” -

manufactured by Bell Laboratories, Inc. - hand-broadcast to the ground and forest canopy 

at application rates ranging from 60 to 95 kg/ha. Subsequent post-treatment monitoring 

(telemetry, trapping, and indicator blocks) revealed a lack of rat presence on all 5 

treatment islands.

The biomarker agent, pyranine, is a hydrophilic, pH-sensitive fluorescent dye from 

the group of chemicals known as arylsulfonates. Pyranine is soluble in water and has 

commercial application as a coloring agent, biological stain, optical detecting reagent, 

and a pH indicator. Pyranine is non-toxic, odorless and tasteless, and is fluorescent green 

when exposed to UV light. The use of pyranine as a biomarker agent within an 
PALMYRA ATOLL RAT ERADICATION: BIOMARKER VALIDATION OF AN EFFECTIVE BAIT APPLICATION RATE, JUNE 19 TO 5 JULY, 2008

8

eradication scenario is a fairly new convention (Towns and Broome 2003, Greene and 

Dilks 2004); therefore, this study provides an early assessment of this conservation tool.

3. 4. Study sites

Three islands were selected as study sites: Home (1.7 ha), Whippoorwill Island

(1.9 ha), and Portsmouth Island (0.8 ha) (Figure 1). Home and Whippoorwill Islands 

were used for the 2005 trial broadcast-based eradications (Buckelew et al. 2005), and 

were sampled for rat density in 2008 (Table 3) (Wegmann and Middleton 2008). Prior to 

the initiation of this study, Portsmouth Island was surveyed for rat presence, land crab 

community composition. These islands met the following selection criteria: 1) islands 

must be isolated by water that does not go “dry” drying low tide cycles 2) islands should 

host land crab and plant communities that are representative of the entire atoll in 

composition and structure, and 3) islands must be free of known WWII era unexploded 

ordinance. 

Fig. 1. Biomarker study site map. Distance to adjacent land is the shortest measure from the periphery of 

the study area to untreated land. 

3. 5. Study questions

1) Will sequential application rates of 18 kg/ha + 9 kg/ha be enough to ensure rodenticide 

Portsmouth Island

Broadcast effort: 16 person/hr

Home Island

Treatment area: 1.7 ha

Study area: 1.7 ha

Distance to adjacent land: 165m 

Broadcast effort: 33 person/hr

Whippoorwill Island

Treatment area: 1.9 ha

Study area: 1.9 ha

Distance to adjacent land: 70m

Broadcast effort: 37 person/hr

Distance to adjacent land: 30m

Study area: 0.8 ha

Treatment area: 0.8 ha
PALMYRA ATOLL RAT ERADICATION: BIOMARKER VALIDATION OF AN EFFECTIVE BAIT APPLICATION RATE, JUNE 19 TO 5 JULY, 2008

9

exposure to all rats within the study sites (Portsmouth and Whippoorwill Island)?

2) Will sequential treatments at the application rate of 36 kg/ha deliver bait to all rats 

within the study site (Home Island)?

3) Which types of non-target organisms are at risk of exposure to the rodenticide during a 

broadcast operation?

Table 3. Rat densities on three islands within Palmyra Atoll; values are from Wegmann and Middleton 

(2008). “Trap nights” equal the total number of active traps multiplied by the number of nights that the 

traps were active minus 0.5 trap nights for each trap that was tripped without capture. “Trap success” is the 

quotient of the total number of rat captures divided by trap nights for a given study site. 

Island Fern 

Island

Home 

Island

Whippoorwill 

Island

Cooper Island 

(reference)

Combined

Island area (ha) 0.5 1.7 1.9 - 4.1

Rats captured 31 15 27 21 94

Rats recaptured 13 5 2 - 20

Abundance estimate 150 42.5 176 - 123

Density estimate (rats/ha) 300 25 93 - 139

Trap nights 68.0 53.0 85.5 54.5 261

Trap success 65% 38% 34% 39% 44%

Trap nights 2005** 67 93 141 45 346

Trap success 2005** 46% 32% 28% 40% 37%

Male mean weight (g) 165 181.1 149.7 - 165.3

Female mean weight (g) 154.6 170 162.8 - 162.5

Female / male ratio 0.9 1.2 0.9 - 1.0
10

Table 4. Palmyra rat eradication biomarker study timeline and activity record

Th F S Su M T W Th F S Su M T W Th F S Su

1-18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4 5 6

Transit PA/HNL X X

Assemble/season traps X

Make coconut bait X X X X

Open reference trapline X

Sample reference trapline X X X X X X X X X X X X X X X

Practice hand braodcast X

Collect crabs from reference trial X

Crab biomarker detection trial X X X X X X X X X X X X X X

Rat biomarker detection trial X X X X X X X X X X X X X X

Establish ground traps W HP

Establish tree traps WH P

Stage bait

HW

P

Establish uptake plots W HP

Establish non-target plots W HP

Crab IOA sampling HWP

Bait Application 18 kg/ha WP

Bait Application 9 kg/ha WP

Bait Application 36 kg.ha H H

Monitor uptake plots H HWP HWP

HW

P

HW

P

HW

P

HW

P HWP HWP

Monitor non-target plots H HWP HWP 

HW

P 

HW

P 

HW

P 

HW

P HWP HWP 

Open traplines H WP H WP

Close traplines H WP

Sample rats H

HW

P WP H

HW

P

HW

P

HW

P WP

Sample night inverts / geckos H WP

Remove traplines H WP

H = Home Island, P = Portsmouth Island, W = Whippoorwill-Bunker Island

Project Activity

June July
11

4. METHODS

The day-to-day operations of this project are summarized in Gantt chart form (Table 4). 

4. 1. Hand Broadcast Baiting

4. 1. 1. Practice

Personnel practiced baiting protocols prior to applying bait in the study sites. The 

Cooper Island runway was used for this exercise. Pacing to 5 meters (distance between each 

bait line stop) was counted, and a baiting line was constructed (5 meters between each point) 

with obstacles (ladders, chairs, coconuts) for people to maneuver around while applying bait. 

A line boss controlled the movement and spacing of the baiting line. People applying bait 

wore “baiting bags” (JIM-GEM Tree Planting Bags, Forestry Suppliers Inc.). This exercise 

gave applicators the opportunity to practice applying the prescribed number of pellets to 25m2

areas (e.g. spread bait 2.5m from the center in four cardinal directions).

4. 1. 2. Accuracy

In order to quantify the amount of bait released into the environment, several steps were 

taken to assure appropriate application rates (18 kg/ha + 9 kg/ha and 36 kg/ha + 36 kg/ha) were 

correctly applied to the three treatment islands. Prior to bait application activities, island area

was derived from GIS layers. An island’s perimeter was defined as the outer vegetation line, 

since bait was not applied to coral rubble or sand beaches if the area in question was devoid of 

vegetation. 

Bait application rates were based on the maximum rates for sequential broadcast baiting 

that are indicated on the label for the Brodifacoum 25W product (18kg/ha + 9kg/ha). The 

following equations describe how we determined how many pellets needed to be applied to a 

25m2

area to achieve the desired bait application rates.

( ) plot size (m ) # of pellets needed

pellet weight (g)

application rate (g)/1hectare  × 2 →



 





Portsmouth and Whippoorwill Islands

[( ) ( )]

[( g)]

g m

2.3

18,000 / 10,000 2

× 25 m

2 = 19.56 or 20 pellets 

Home Island 

[( ) ( )]

[( g)]

g m

2.3

36,000 / 10,000 2

× 25 m

2 = 39.13 or 40 pellets
12

To mimic an aerial bait broadcast, and to expose canopy dwelling rats (Howald et al. 

2004, Wegmann et al. 2007), bait was applied to both the ground and forest canopy (Cocos 

nucifera trees only) (Table 5). The canopy was baited with “bait bolos” – bait pellets with 

holes drilled through the center and tied to 30-50cm of biodegradable twine. Bait bolos were 

carried around the island on branches and shot into the canopy using slingshots (Fig. 2). The 

total amount of bait needed to finish the trial was 195.3 kg, which is the combined amount of 

each application in each study site (Table 6)

Table 5. Bait application schedule, including application to ground and canopy areas; canopy baiting was 

restricted to Cocos nucifera trees

Study site Bait 

application 

rate

Bait 

applied 

to 

ground 

(kg/ha)

% 

trees 

treated

# trees 

treated

Bait 

applied 

to 

canopy 

(kg/ha)

Pellets per 25m2 

uptake plot

Pellets per 25m2 

applied to 

ground 

(adjusted)

Whippoorwill 18 16.6338 0.33 99 1.3662 20 18

9 8.2962 0.17 51 0.7038 10 9

Portsmouth 18 17.7723 0.33 17 0.2277 20 19

9 8.8827 0.17 9 0.1173 10 10

Home 36 34.8615 0.33 83 1.1385 40 38

36 34.8615 0.33 83 1.1385 40 38

Table 6. Total amount of bait applied to the study sites

Study site Application rate (kg/ha) Island area (ha) Total bait applied (kg)

Whipporwill 18 1.9 34.2

9 1.9 17.1

Portsmouth 18 0.8 14.4

9 0.8 7.2

Home 36 1.7 61.2

36 1.7 61.2
13

Fig. 2. Canopy baits (bait bolos) ready for delivery into Cocos nucifera crowns; each bait contained 6 x 2.3 g 

pellets.

4. 1. 3. Baiting

We broadcast placebo (non-toxic) 25W biomarker bait pellets to the ground and forest 

canopy at the label-specified maximum application rate (18 kg/ha followed by 9 kg/ha five 

days later) on 2 study islands, and at more than twice the maximum application rate (36 kg/ha 

followed by 36 kg/ha five days later) on a third study island.

Baiting began on 22 June, with a minimum of five nights between applications. 

Placebo 25W bait laced with a food-grade biomarker (pyranine or “Solvent Green 7”) was 

applied with a six-person baiting line in which broadcasters were spaced 5 m apart. 

Broadcasters counted the number of pellets to be applied to each successive 25m2 area. Each 

bait application was directed by a line boss who maintained the pace of the exercise and gave 

instructions when line orientation or spacing went askew. Broadcasters with end positions on 

the line flagged their baiting position at each 5m stop; this allowed the line to reference what 

had been treated already. Each applicator carried up to 10kg in a bait bag.

4. 1. 4. 2.8 m radius circle plots

During the bait applications, a two-person team sampled the amount (kg/ha) of bait 

being applied by counting pellets within randomly selected 2.8 m radius circle plots (area = 

25m2

). The 2.8 m radius plots were sampled with one person standing in the center of the plot 

holding onto the beginning of a 2.8 m piece of string or tape; the other person held the distal 

end and walked a complete circle around the person in the center. All bait pellets passing 

under the string were counted and vegetation and leaf-litter were moved to find hidden pellets. 

Major deviations from the target application rate were reported to the line boss, who then told 

the baiting line to either tighten or relax the spacing between broadcasters, which would result 

in heavier or lighter bait application. Due to Palmyra’s high abundance of hermit crabs, many 
14

pellets were “captured” by crabs prior to sampling the circle plots. To account for the captured 

bait, hermit crabs carrying bait pellets within the circle plots were counted as 1 pellet each.

4. 2. Bait Consumption

4. 2. 1. Bait consumption plot design and placement

Bait consumption data were collected to describe the amount of bait consumed by both 

target species as well as non target species. On June 20th and 2first, bait consumption plots 

were established within each study site: Whippoorwill (n = 18), Home (n = 22), and 

Portsmouth (n = 7). Plots were 25 m long X 1 m wide. Wire flags were scatter-planted in each 

plot, and a single bait pellet was placed at the base of each flag. Plots were calibrated to the 

different application rates: 9 kg/ha = 10 flags, 18kg/ha = 20 flags and 36 kg/ha = 40 flags. 

Plots were placed parallel to the trajectory of the baiting line to capture the bait application rate 

error from at least 4 broadcasters. After the bait line passed over the bait consumption plot, 

pellets near the plot were picked up and moved to the flags within the plot. 

Figure 2. Bait consumption plot; pin flags marked bait pellet location. Bait consumption rates were estimated by 

counting the number of pellets removed from each plot within 24 hr sample periods, and then averaging 

consumption rates across all plots within a study site.

4. 2. 2. Bait consumption plot sampling

Bait consumption plot sampling began the day after bait application and continued until 

100% of the bait was removed from each plot. Observers walked the length of every plot 

stopping at each flag to inspect the immediate area (5cm) for the presence or absence of a 

pellet. Flags without pellets were pulled and tallied. The total number of flags pulled from 
15

each plot (total number of pellets removed) was recorded. Bait consumption plot locations 

were maintained and plots were reset for the second round of bait applications.

4. 3. Land Crab Index of Abundance (IOA)

Land crab index of abundance (IOA) sampling took place on 3 and 4 July. Twenty crab 

IOA transects were surveyed on Whippoorwill and Home, and 10 transects were surveyed on 

Portsmouth. Transect start points and bearings were randomly selected. The 5 meter transect

width was maintained by a 2.5 m pole swung in a 180o arc pivoted from the center of the 

transect. All crabs detected within a distance of 2.5m from the central transect axis were 

identified to species (Coenobita brevimanus, Coenobita perlatus, Cardisoma carnifex, 

Cardisoma rotundum, and Birgus latro). Only crabs within the transect boundary were 

counted. The total number of crabs per transect was averaged within study sites.

4. 4. Rat biomarker detection assay

4. 4. 1. Sampling

Because the biomarker agent, pyranine, has only been employed once prior to this 

project to assess rat eradication bait application rates (Griffiths et al. 2008), we conducted a 

biomarker detection assay to define how long, at different bait consumption amounts, rats show 

biomarker sign. We trapped rats on Cooper Island with seasoned (vegetable oil and coconut 

milk) Hagaruma® and Tomahawk® traps baited with coconut covered with peanut butter. 

Captured rats were weighed, sexed, and then transferred into Tomahawk® traps (455 cm2

bottom) or wire cages (855-1400 cm2 bottom) placed on tables inside the North Road storage 

bunker (large WWII era cement bunker). The rat holding cages were placed on metal trays, 

and were elevated with wood strips so that urine and droppings would not collect in the cage 

bottoms. Trays were cleaned regularly, and all rats were provided ample food and water. Rats 

within the same treatment group shared pans.

4. 4. 2. Treatments

The rat biomarker detection assay involved nine biomarker exposure-duration 

treatments. Captured rats were assigned to the following biomarker bait exposure groups: 1 

pellet (1P), 3 pellets (3P), no pellets (coconut). Rats in each exposure group were then 

assigned to one of three sampling periods: three days post bait consumption, six days post bait 

consumption, and 9 days post bait consumption. Each pellet-fed treatment group contained 

five rats; coconut-fed treatment groups contained only one rat. The 1P treatments replicate a 

sub-lethal dose of the active 25W (25 ppm brodifacoum) bait, and the 3P groups replicate a 

lethal dosage; 1 pellet < LD50 (0.5 x LD50), 3 pellets > LD50 (1.4 x LD50) for the average (164 

g) male rat at Palmyra (Table 3). The LD50 value used for these calculations is 0.65-0.73 

mg/kg for Brodifacoum vs. balck rats (Dubock and Kaukeinen 1978, Wegmann and Middleton 

2008). 
16

After transfer to caging, rats were offered bait pellets or a chunk of coconut meat, 

depending on treatment group. After that was consumed, they were fed a mixture of peanut 

butter and StoveTop® stuffing until they were euthanized and sampled for external and internal 

biomarker sign. Separately, one adult female was offered 10 Inert Pellets/day, no-choice, for 4 

consecutive days. Another female was offered 10 Inert Pellets/day for 2 consecutive days, and 

a juvenile male was offered half of a typical sized Inert Pellet for one day. These last 3 

subjects were euthanized and examined at the end of their exposure regimes.

The control group consisted of 2 males and a female. The males weighed 138 and 168 

g at the time of transfer to caging. The control female weighed 192 g. There were 10 males 

(158-214 g) and 5 females (102-215 g) in the 1P group and 9 males (130-202 g) and 6 females 

(109-171 g) in the 3P group. The heaviest female in the 1P group delivered a litter of 7 pups 4 

days after capture and 3 days after consuming the bait pellet offered.

The rat offered 10 pellets/day for 4 consecutive days was a female that weighed 158 g 

at capture. The initial weight for the female rat offered 10 pellets/day for 2 consecutive days 

was 195 g. Neither of these rats consumed all of the pellets offered on any day. The rat 

offered half of a pellet for one day was a juvenile male that weighed 54 g at capture. This rat 

initially was fed coconut and then was maintained on the same feed mixture that was fed to all 

subjects after their bait or coconut exposure regimen was completed. Eight days after its 

capture, this rat was offered 1⁄2 a pellet, which it consumed overnight. The following day it was 

euthanized and assessed for fluorescence.

4. 4. 3. Biomarker detection scoring system

Rats were examined for fluorescence using handheld ultraviolet flashlights. After 

sacrifice, rats were examined externally for evidence of bright green fluorescence at the anus 

and elsewhere. Subsequently, rats were examined internally for evidence of fluorescence. 

Digestive organs (stomach, small intestine, ceacum and large intestine) were routinely 

assessed. Intensity of fluorescence was assessed qualitatively according to the rating scale 

shown below.

Score Description

- No fluorescence evident

+ Fluorescence detected but limited in intensity and/or area covered

++ Fluorescence moderate in intensity and/or area covered

+++ Fluorescence glowing in intensity and pervasive

Red hermit crabs were scored for fluorescence based on a negative or positive basis. 

Internal sign was classified as either positive or negative. Females with eggs were not part of 

the sample. 

4. 5. Hermit crab biomarker detection assay

4. 5. 1. Sampling
17

27 red hermit crabs (Coenobita perlatus) were collected from Cooper Island and 

housed, in buckets, in the North Road storage bunker. The hermit crabs were fed either pellets 

or coconut, according to treatment group directly after placement in the holding buckets. 

Crabs that received pellets were fed coconut after the pellets were consumed. All crabs were 

given ample food and water throughout the study.

4. 5. 2. Treatments

Hermit crabs were assigned to the same treatment groups established for the rat 

biomarker detection assay, except that only three crabs were assigned to each exposureduration grouping. To assess the presence or absence of biomarker sign, hermit crabs were 

chilled in a refrigerator at 5◦ C for 45 minutes. Chilling the crabs allowed us to extract the 

crabs from their gastropod shells in order to examine their abdomens with low risk of causing 

harm. Hermit crabs were scored as positive (+) or negative (-) for internal biomarker sign. 

Under UV light, biomarker could be detected through the translucent epidermis of the crabs’ 

abdomens (Fig. 4).

Fig. 4. A Hermit Crab (Coenobita perlatus) that tested positive for biomarker sign; “A” is under UV light, “B” is

the same crab under full spectrum light. 

4. 6. Field-based biomarker detection in rats

4. 6. 1. Sampling

Hagaruma traps that had been seasoned by dipping them in cooking oil were placed atop 

plastic 5 gallon buckets and baited with coconut and peanut butter. Traps were placed at a 

distance of approximately 10m from each other in transect(s) traveling the length of each 

treatment site. Tree traps were deployed in 5 coconut palms on each island in an attempt to 

detect biomarker presence in rats frequenting canopy habitat. A total of 1132 trap nights were 

logged over the course of the study: Home (n = 441.5), Whippoorwill (n = 489); Portsmouth (n 

= 201.5). Half trap-nights were counted when traps either caught an animal or were sprung 

without a capture. Traps were opened on all islands for 2 nights after the first baiting regime, 

and 4 nights after the second baiting regime. 

A B
18

4. 6. 2. Scoring System

Captured rats were brought to a central processing location established at each study 

site. Rats were first inspected for external biomarker sign using handheld UV flashlights. If a 

rat showed external biomarker sign (paws, anus, tail, mouth), it was euthanized and inspected

for internal biomarker sign. Internal and external fluorescence was scored according to the 

scoring system described above. Rats without external sign were marked with black sharpie on 

their tails and released at their point of capture.

4. 7. Field-based biomarker detection in hermit crabs

4. 7. 1. Sampling

Hermit crabs were collected from each study site every day for 11 days following the 

initial bait application. Ten hermit crab collection plots (PVC piping driven into the ground) 

were established on Home and Whippoorwill, and seven were established on Portsmouth. 

Each sample day, the crab closest to each plot pole was collected for biomarker presence 

assessment. External biomarker sign was assessed in the field, and internal biomarker sign was 

assessed several hours later, at the field camp, using the refrigeration method discussed above. 

.

4. 7. 2. Scoring system

Field scoring consisted of positive or negative sign for biomarker on the claw, mouth 

and shell. In camp, crabs were chilled in a refrigerator until they were relaxed enough for 

observers to remove them from the shell. All portions of the body were examined at this point 

and positive-negative scoring took place for the presence or absence of biomarker sign. Hermit 

crab bodies then were returned to their shells. In some instances, bodies would not come free 

from the shell easily. Such crabs were not assessed. Crabs were released back to their 

collection sites on the morning following the day of capture. Of the 330 crabs sampled, 4 died 

during captivity.

4. 8. Field-based biomarker detection in subdominant bait consumers

4. 8. 1. Sampling

Night surveys were conducted during the evenings of June 29 and 30. Five locations 

were chosen on each island in order to sample the following types of non-target organisms: 

amphipods, ants (ant trails), cockroaches, geckos, and katydids. Specimens were collected in 

plastic bags and taken back to camp for biomarker evaluation. Ant trails were evaluated on 

site. Ant observations consisted of watching a single ant trail for up to 5 minutes to determine 

if the ants were transporting biomarker bait particles.

4. 9. Rat carcass consumption
19

4. 9. 1. Placement and Sampling

Land crabs are capable scavengers and will readily consume carrion. In a toxin-based 

rat eradication scenario, rats that die from rodenticide exposure present a rodenticide exposure 

risk for non-target species. To determine the timeframe for the dead rat rodenticide exposure 

pathway, rat carcasses (captured rats that tested positive for external biomarker sign and had 

been euthanized and examined for internal biomarker sign) were placed at their point of 

capture and marked with a numbered flag. Carcasses were reassessed 24 hours after 

placement. The percent of each carcass remaining was recorded.

5. RESULTS

5. 1. Bait consumption

Bait consumption rates for each application regime were estimated by following bait 

pellets marked by wire flags (n = 2,510) in 47 plots: Home = 22 plots, Portsmouth = 7 plots, 

Whippoorwill = 18 plots. Rats were removed from the study sites following bait applications

(see section 5.3 Rat Capture). Lower application rates (9 kg/ha and 18 kg/ha) resulted in rapid 

bait consumption. Following the 9 kg/ha application on Whippoorwill, only 2 of 180 pellets 

(4.6g of 414g of bait) remained in 18 bait consumption plots (plots were loaded with 10 pellets 

each during the bait application) after a 24 hour period; the two remaining pellets were 

consumed by day 2 (Fig. 5). Bait consumption on Portsmouth showed a similar trend as nearly 

all of the 9 kg/ha application was consumed within 24 hrs, and all pellets within bait 

consumption plots were consumed within 3 days. The 18 kg/ha baiting regimes on Portsmouth 

and Whippoorwill resulted in more bait remaining after the initial 24 hours; however 100% 

bait consumption occurred in all plots on both islands within 3 days of the bait application. 

The 36 kg/ha baiting regimes at the Home study site resulted in 60% bait consumption within 

24 hours, and small amounts of bait persisting through day 5 in the first application, and day 6

in the second application. A one-way ANOVA test, with Tukey’s pairwise comparisons 

(MINITAB 2007), of daily mean bait consumption between all three study sites shows that 

Portsmouth and Whippoorwill experienced similar bait consumption patterns for both the 18 

kg/ha and 9 kg/ha bait application regimes; however, mean bait consumption at the Home site 

was significantly higher than recorded at Portsmouth or Whippoorwill for days 1 through 3 

after the first bait application, and days 1 through 4 after the second bait application (Table 7).

No bait remained on Portsmouth and Whippoorwill 2-3 days after the initial treatment 

at 18 kg/ha, and essentially no bait remained 2 days after the second treatment at 9 kg/ha (Fig. 

5). Bait lasted longer on Home; factors likely influencing this included the higher application 

rate and the lower initial and post-trapping rat densities on Home. 

Table 7. One-way ANOVA results for a between-site comparison of mean number of pellets removed from bait 

consumption plots by days post bait application for both the first and second bait application. 

Bait application Days post bait application F-statistic P-value

first 1 4.18 0.013

2 11.84 < 0.001
20

3 8.4 0.001

4 2.8 0.072

5 1.61 0.211

second 1 30.39 < 0.001

2 26.7 < 0.001

3 11.71 < 0.001

4 3.77 0.031

5 2.74 0.076

6 1.81 0.176

Days post bait application

1 2 3 4 5

Mean bait remaining (kg/ha 

+ 1 SE)

0

2

4

6

8

10

12

14

16

18

Home - 36 kg/ha

Portsmouth - 18 kg/ha

Whippoorwill - 18 kg/ha

Days post bait application

1 2 3 4 5 6 7

Home - 36 kg/ha

Portsmouth - 9 kg/ha

Whippoorwill - 9 kg/ha

A B

Fig. 5. Daily bait consumption estimates for the first “A” and second “B” bait applications on Home, Portsmouth, 

and Whippoorwill. Mean bait consumption was measured by observing bait pellet removal from fixed 25 m x 1 m 

plots: Home = 22 plots, Portsmouth = 7 plots, Whippoorwill = 18 plots. Error bars represent ± 1 standard error of 

the sample mean.

5. 2. Land Crab IOA

Land crab abundance rankings varied between study sites (Table 8). Home had 

relatively fewer land crabs than Portsmouth or Whippoorwill, and Whippoorwill had the 

highest crab density ranking.

Table 8. Index of Abundance (IOA) ranking for land crab species at the three study sites; 1 = lowest density, 3 = 

highest density. If the species densities are similar between study sites, the study sites received the same ranking. 

Study site Coenobita perlatus Coenobita brevimanus Cardisoma carnifex Cardisoma rotundum

Home 1 1 1 1

Portsmouth 2 1 1 2
21

Whippoorwill 3 2 1 1

5. 3. Rat capture

For two nights after the first round of bait applications, and 4 nights after the second 

round of applications, live-capture rat traps were opened on all three study sites: Home = 78 

traps, Portsmouth = 34 traps, Whippoorwill = 84 traps. The total trapping effort equaled 1,132 

trap nights. Trap success (captures / trap-nights; trap-nights = traps / island / night) was 

highest at Whippoorwill for all sample nights, and lowest at Home (Table 9).

Table 9. Rattus rattus trap success (captures / trap nights; trap nights = traps/island/night) proceeding first and 

second biomarker bait applications.

First application Second application

Sample 1 2 3 4 5 6

36 kg/ha + 36 kg/ha (Home) 15% 8% 0% 5% 0% 3%

18 kg/ha + 9 kg/ha (Portsmouth) 38% 29% 6% 9% 9% 3%

19 kg/ha + 9 kg/ha (Whippoorwill) 41% 30% 12% 12% 13% 5%

5. 4. Rat biomarker detection assay 

External and internal biomarker sign was still noticeable nine days after bait 

consumption for two rats in the 3P group. Internal biomarker was found in one of these rats 

(Table 10). Biomarker detection results for the 3P rats at 6 days post bait consumption were 

similar to the 3P – 9 day group. All 3P rats sampled 3 days post bait consumption showed 

external and internal biomarker sign. One 1P rat showed external biomarker sign at 6 days 

post bait consumption, and no 1P rats showed external or internal biomarker sign at 9 days post 

bait consumption. Four of five 1P rats showed external biomarker sign at 3 days; two of these 

rats also showed internal sign. Of significance, 1 rat in the 1P-3 day group and 4 rats in the 1P6 day group showed no biomarker sign, while all 3P-3 day rats and four of five 3P-6 day rats 

showed both or either external and internal biomarker sign. The difference in time-related 

biomarker detection between the 1P and 3P groups suggests that biomarker detection is a 

function of amount of bait consumed as well as time since bait consumption. 

We used a multiple linear regression model to assess the strength of the relationships 

between biomarker detection scores, amount of bait consumed, and time since bait 

consumption. Neither sex nor weight significantly influenced the biomarker detection score, 

while the number of pellets consumed and the exposure period (time since bait consumption) 

did influence the biomarker detection score (Table 11). The regression models for external and 

internal biomarker scores are: [(external score = 2.21 + 0.620(Pellets consumed) -

0.379(Exposure period)], and [(internal score = 2.81 + 0.989(Pellets consumed) -

0.561(Exposure period)]. 
22

Table 10. Lab-based biomarker detection results for three pellet consumption variables (0 pellets, 1 pellet, 3 

pellets) and three exposure variables (3 days, 6 days, 9 days); internal and external scores represent the sums of all 

internal or external detection factors.

Pellets consumed Exposure Period (days) Sex Weight (g) Total external score Total internal score

0 3 M 138 0 0

6 M 168 0 0

9 F 192 0 0

1 3 F 215 0 0

M 168 1 2

M 173 1 2

M 182 2 0

M 158 3 0

6 F 102 0 0

F 180 0 0

F 158 0 0

M 208 0 0

M 214 1 0

9 F 134 0 0

M 196 0 0

M 215 0 0

M 169 0 0

M 188 0 0

3 3 F 150 4 8

F 169 6 7

M 168 3 8

M 173 3 4

M 130 4 7

6 F 109 1 0

F 171 2 1

M 178 1 0

M 198 0 0

M 202 1 1

9 F 148 1 0

F 167 1 1

M 150 0 0

M 164 0 0

M 202 0 0
23

Table 11. Summary of linear regression analysis for variables predicting internal or external detection of 

biomarker (pyranine) residue in rats (R. rattus) fed 1 biomarker bait pellet (2.3g), 3 pellets, or 0 pellets (Pellets 

consumed) and sampled at 3 days, 6 days, or 9 days; External and Internal (n = 5 for each pellet-exposure

treatment group). * P < 0.01, ** P = 0.001, *** P < 0.001

Predictor External Internal

B SE (B) B SE (B)

Intercept 1.94 1.508 3.089 2.791

Pellets consumed 0.6071** 0.1603 0.9676* 0.2968

Post-exposure interval -0.38257*** 0.07337 -0.5591*** 0.1358

Sex 0.3366 0.3949 0.2702 0.731

Weight -0.000859 0.006876 -0.00363 0.01273

5. 5. Biomarker detection in field-caught rats

141 rats were captured and assessed for biomarker sign. Rats without external or 

internal biomarker sign were captured at all three study sites: 5% (1/21) at Home, 32% (29/91) 

at Whippoorwill, and 3% (1/31) at Portsmouth (Appendix A). 

Rats with external or internal biomarker scores lower than 2 (equated with rats that 

would have consumed Sub-Lethal quantities of brodifacoum had the 25W brodifacoum bait 

been used, or “SLrats”) might have consumed amounts of biomarker bait that would have been 

insufficient to cause death had a toxic bait been used. We used the linear regression equations 

described above to back solve for the amount of bait consumed by rats based on internal or

external inflorescence scores, and then compared brodifacoum exposure values - brodifacoum 

(mg) / rat (kg) - to sex-specific Rattus LD50 values (Dubock and Kaukeinen 1978) to obtain 

rough estimates of the LD50 exposure ratios for SLrats (Table 12). We found two Home SLrats, 

five Portsmouth SLrats, and nine Whippoorwill SLrats with estimated brodifacoum exposure 

values lower than 1 Rattus-brodifacoum LD50. 

Table 12. LD-50 exposure ratios for field-captured rats showing low (< 2) external or internal biomarker detection 

scores. Total brodifacoum exposure for the Home-21 rat was based on the internal biomarker score; total 

brodifacoum exposure estimates for the remaining rats were based on external biomarker score. An LD50 is the 

estimated brodifacoum exposure level that will produce 50% mortality in a given Rattus population. Rats marked 

by an asterisk (*) are those that were estimated, according to their weights and biomarker indices, to have 

consumed amounts of bait equal to less than the equivalent of an acute oral LD50 dosage of a 0.0025% 

Brodifacoum bait.

Study site Rat ID Weight (g) 

and sex

Estimated # 

of pellets 

consumed

Approximate 

brodifacoum 

exposure (mg)

Approximate 

brodifacoum 

(mg) per Rat 

(kg)

Approximate 

brodifacoum 

exposure 

estimate (x / 1 

LD-50)

Home 1 180 F 0.5 0.03 0.67 1

Home 2 205 M 2.1 0.12 0.31 0.4 *

Home 21 212 F 2.1 0.12 0.14 0.2 *

Portsmouth 10 185 M 3.7 0.21 0.17 0.3 *

Portsmouth 14 160 F 1.1 0.06 0.16 0.2 *

Portsmouth 17 180 M 2.7 0.16 1.19 1.8

Portsmouth 25 119 M 1.1 0.06 0.16 0.2 *

Portsmouth 30 141 M 3.3 0.19 0.53 0.7 *
24

Portsmouth 4 165 F 2.1 0.12 0.69 0.9 *

Whippoorwill 2 130 F 0.5 0.03 1.19 1.8

Whippoorwill 35 55 M 1.1 0.06 0.41 0.6 *

Whippoorwill 36 180 M 1.1 0.06 0.82 1.3

Whippoorwill 37 180 M 1.1 0.06 2.20 3

Whippoorwill 38 130 F 1.1 0.06 0.16 0.2 *

Whippoorwill 40 150 F 1.1 0.06 1.18 1.6

Whippoorwill 42 150 F 2.7 0.16 0.49 0.8 *

Whippoorwill 44 140 M 2.7 0.16 0.42 0.7 *

Whippoorwill 47 160 F 2.7 0.16 0.42 0.7 *

Whippoorwill 5 155 F 1.1 0.06 0.70 0.9 *

Whippoorwill 6 148 F 0.5 0.03 1.08 1.7

Whippoorwill 61 150 M 0.5 0.03 0.42 0.6 *

Whippoorwill 62 95 M 0.5 0.03 0.67 0.9 *

Whippoorwill 76 144 F 1.1 0.06 0.44 0.7 *

Whippoorwill 84 78 M 1.7 0.10 1.99 2.7

Whippoorwill 85 72 F 1.7 0.10 2.16 3.3

Whippoorwill 86 50 F 1.7 0.10 3.11 4.8

Whippoorwill 91 50 F 3.9 0.22 4.49 6.9

5. 6. Land crab biomarker exposure

5. 6. 1. Hermit crab biomarker detection assay

Twenty-seven hermit crabs (Coenobita perlatus) were also assigned to the same bait 

consumption and duration treatments as described above in the rat biomarker detection assay.

However, hermit crab biomarker sign was simply noted as present or absent rather than scored. 

The probability of detecting biomarker sign in hermit crabs is likely a function of time and 

amount of bait consumed. All crabs in the 1P group showed internal biomarker sign up to day 

six, and only one crab showed sign at day nine. Two of three crabs in the both the 3P-6 day 

and 3P-9 day groups showed biomarker sign (Table 13). The hermit crab biomarker detection 

assay results suggest that hermit crabs retain internal biomarker sign longer than rats, which is 

probably a function of the crabs’ lower basal metabolic rate.

Table 13. Hermit crab biomarker detection assay results; each pellet-exposure treatment group contained 3 crabs.

Pellets consumed Exposure period Internal biomarker sign

Absent Present

1 pellet 3 0 3

6 0 3

9 2 1

3 pellet 3 0 3

6 1 2

9 1 2

Reference (coconut) 3 3 0

6 3 0
25

9 3 0

5. 6. 2. Biomarker detection in field-captured hermit crabs

Table 14. The proportion (1-100) of hermit crabs that were positive for biomarker sign by study site and number 

of days after the first bait application, and number of gravid crabs (females) that were not inspected for internal 

biomarker sign. The second bait application occurred on the 6th day after the first bait application. Each day after 

the first bait application, ten crabs were sampled in each study site.

Island Days after first bait application Biomarker detection No. female crabs w/eggs

External Internal

Home 1 0.9 1 0

2 1 0.6 1

3 0.6 0.7 2

4 0.2 0.6 4

5 1 0.8 2

6 1 1 0

7 0.6 0.8 0

8 0.8 1 0

9 0.1 0.7 3

10 0.2 0.6 2

11 0.1 0.9 1

Portsmouth 1 0.9 0.6 1

2 0.7 0.4 2

3 0.8 0.6 2

4 0 0.6 1

5 0.8 0.5 1

6 0.9 0.5 2

7 1 0.8 0

8 0.7 0.7 2

9 0.6 0.6 2

10 0 0.3 1

11 0 0.8 0

Whippoorwill 1 1 0.3 3

2 0.5 0.1 4

3 0.4 0.7 0

5 1 0.5 5

6 0.8 0.8 2

7 0.3 0.8 0

8 0.1 0.5 3

9 0.2 0.3 6

10 0 0.4 3

11 0.1 0.7 2

Hermit crabs (Coenobita perlatus; n = 310) were collected from the study sites each 

day after the initial bait application, and were assessed for external and internal exposure to 

biomarker bait (Table 14). We used one-way ANOVA tests with Tukey’s pairwise 
26

comparisons to compare the mean number of crabs with and without internal or external 

biomarker sign between the sample sites. We found no significant between-site difference in 

the number of crabs without external (F = 0.6, P = 0.554) or internal (F = 0.51, P = 0.606) 

biomarker sign. Furthermore, We did not detect a significant difference in the number of 

biomarker-positive and biomarker-negative crabs between Portsmouth and Whippoorwill. 

5. 7. Subdominant consumer exposure to biomarker bait

Several non target species (excluding land crabs) were assessed for biomarker sign two 

nights after the second bait application at each study site: amphipods (n=8), ants (n=52 ant 

trails), blister beetles (n = 2), cockroaches (n=59), geckos (n=53), katydids (n=49), and spiders 

(n=1) (Table 15). We found external or internal biomarker sign with ants, amphipods, 

cockroaches, and katydids. There does not appear to be a difference in subdominant consumer 

exposure patterns between high (Home) and low (Whippoorwill and Portsmouth) bait 

application rates; however, larger sample sizes are needed to support this notion. 

Table 15. Assessment of subdominant consumer exposure to biomarker bait by study site. Biomarker presence is 

presented as the proportion of the total sample, by species and study site, that showed external or internal 

biomarker sign.

Study site Species No. sampled Biomarker presence (proportion)

External Internal

Home Amphipods 3 0.0 0.0

Ant 21 0.6 -

blister beetles 2 0.0 0.0

cockroach 19 0.5 0.6

gecko 25 0.0 0.0

katydid 25 0.0 0.0

spider 1 0.0 -

Portsmouth Amphipods 5 0.4 0.4

Ant 5 0.0 -

cockroach 15 0.1 0.3

gecko 20 0.0 0.0

katydid 20 0.1 0.1

Whippoorwill Ant 26 0.4 -

cockroach 25 0.4 0.4

gecko 8 0.0 0.0

katydid 4 0.0 0.3

5. 8. Rat carcass consumption

Rat carcasses were almost completely consumed within 24 hours of placement (Fig. 6).

Hermit crabs, apparently, were the primary consumers of rat carcass. A series of images, taken 

at 15 minute intervals by a motion sensing camera recorded only hermit crabs attending (and 

completely consuming) a rat carcass 15 hrs after placement. 
27

Study site

Home Portsmouth Whippoorwill

Mean % of carcass remaining after 24 hrs 

+ 1 SE

0

2

4

6

8

10

12

14

Fig. 6. Rat carcass consumption. Mean % of rat carcasses remaining after 24 hour exposure periods; hermit crabs 

were the primary carcass consumers.

6. DISCUSSION

6. 1. Will sequential application rates of 18 kg/ha + 9 kg/ha be enough to ensure 

rodenticide exposure to all rats within the study sites (Portsmouth and Whippoorwill 

Island)?

No. We captured rats lacking external or internal biomarker sign at both Portsmouth 

and Whippoorwill (Appendix A) within a post-bait application timeframe in which the 

biomarker is detectable in ≥ 75% of rats exposed to 3 pellets (Table 10). Furthermore, several 

rats captured at Portsmouth and Whippoorwill consumed, by our estimates, amounts of bait 

that translates to sub-lethal exposure in a 25W brodifacoum baiting scenario (Table 12). 

Bait consumption results from Portsmouth and Whippoorwill show that the 18 kg + 9 

kg baiting regime does not ensure that rats will have access to bait for four days (Fig. 5). 

Applying enough bait to ensure four days of rat exposure is a convention employed in many 

successful eradication campaigns (Wegmann 2008). The bait consumption trends at 

Portsmouth and Whippoorwill corroborate our biomarker-based assertion that an eradication 

program constrained by the maximum allowed application rate for 25W would have little 

chance of succeeding at Palmyra.

6. 2. Will sequential treatments at the application rate of 36 kg/ha deliver bait to all rats 

within the study site (Home Island)?
28

No. We captured one rat at five days after the first bait application to Home Island with 

no external or internal biomarker sign (Appendix A), and two rats that consumed, by our 

estimates, amounts of bait that translate to sub-lethal exposure in a 25W brodifacoum baiting 

scenario (Table 12). It is unlikely that the unmarked rat had invaded from Paradise Island – the 

nearest point of land 200 m across water. While some bait remained on the ground longer than 

four days after each 36 kg/ha application at Home, approximately 65% of the applied bait was 

consumed within the first 24 hr period, and 78% was consumed after 48 hrs. If rats (15 

removed from Home during biomarker detection sampling between the first and second bait 

applications) were accessing a sizeable percentage of the bait, we would expect a reduction in 

the bait consumption rate for the second application. However, we observed an increase in bait 

consumption during the second application (Fig. 5), which suggests that crab related bait 

consumption (crabs were not removed during the biomarker detection sampling) prevents 

repeat bait applications ≥ 5 days apart from having a cumulative effect on the amount of bait 

remaining on the ground. Because three rats at the Home site were not exposed to enough bait 

to incur a lethal response in a brodifacoum-based operation, it is improbable that the 36 kg/ha + 

36 kg/ha baiting regime would lead to eradication success at Palmyra. 

6. 3. Which types of non-target organisms are at risk of exposure to the rodenticide

during a broadcast operation?

We documented direct bait take (bait consumption or bait possession) by land crabs and 

other invertebrates (Table 15). All five of Palmyra’s land crab species (Table 2) consume 25W 

(active or placebo) bait pellets (A. Wegmann, personal observation). While brodifacoum is not 

toxic to land crabs (or other invertebrates) in a bait broadcast exposure scenario (Pain et al. 

2000), land crabs that consume bait must be thought of as potential bait-exposure pathways for 

non-target predators or scavengers (Wegmann 2008). Several subdominant consumers, 

notably ants, amphipods, cockroaches, and katydids were involved in direct bait take. 

Although, these organisms should not incur a lethal response from active bait consumption. 

However, they become potential rodenticide-exposure pathways for non-target predators. 

Because all of the listed subdominant consumers would be able to access bait housed in baitstations, an aerial broadcast does not increase the non-target exposure risk associated with the 

subdominant consumer pathway. Aerial application may decrease this risk by shortening the 

period in which bait is available to non-target organisms.

In any toxin based rat eradication, carcasses of rats that died from toxin exposure 

become potential pathways for non-target species exposure to the rodenticide. However, on 

islands with high land crab densities (Palmyra), the rat carcass exposure pathway is limited to a 

24-48 hr period after the rat dies (Fig. 6). 

7. CONCLUSION AND RECOMMENDATIONS

A rat eradication campaign at Palmyra atoll will face many challenges: remote location, 

extensive canopy habitat, high land crab densities, moist conditions, and the potential for 

rodenticide resistance from a previous eradication attempt. Aerial broadcast of second

generation anticoagulant rodenticide bait pellets has the best success record of any eradication 

method (Howald et al. 2007). Given the above-mentioned difficulties, aerial broadcast of a 

second generation anticoagulant rodenticide bait will deliver a high probability of eradication 
29

success at Palmyra (Howald et al. 2004, Buckelew et al. 2005). The 25W bait product was 

specifically designed for Palmyra’s moist climate. However, the label-specified maximum 

application rate would not be expected to expose every rat to an amount of bait equivalent to a 

lethal dosage of brodifacoum and, thus, seems insufficient to kill every rat present on Palmyra 

Atoll.

The strategy that has the greatest amount of potential for killing all rats without doing 

irreparable harm to any aspect of the ecosystem is the one that should be pursued. Whatever 

procedures might be employed to minimize risks of non-target organisms likely to be affected 

by the rodenticide should be put forward and discussed in future documents. The findings of 

this study suggest that two successive aerial bait applications within the range of application 

rates which likely killed all rats on the islands treated in 2005 (Buckelew et al. 2005) will lead 

to eradication success at Palmyra.

8. ACKNOWLEDGEMENTS

The following individuals contributed heavily to the success of this study. In addition to 

those names mentioned below, we would like to thank The Nature Conservancy personnel at 

the Palmyra Atoll field station for their ability and willingness to provide extraordinary 

logistical support and superior hospitality over the course of the entire project. 

Adonia Henry United State Fish and Wildlife Service 

Bill Jacobs Environmental Protection Agency

Bill Smith United State Fish and Wildlife Service 

Don Drake University of Hawaii – Manoa 

Joanna Smith University of Washington

Matthew McKown University of North Carolina

Robert Fischer United States Geological Survey

Stacey Hathaway United States Geological Survey
30

9. REFERENCES

Buckelew, S., G. R. Howald, A. Wegmann, J. Sheppard, J. Curl, P. McClelland, B. Tershy, K. 

Swift, E. Campbell, and B. Flint. 2005. Progress in Palmyra Atoll restoration: rat 

eradication trial, 2005. Island Conservation.

Dubock, A. C. and D. E. Kaukeinen. 1978. Brodifacoum (TALON Rodenticide), a novel 

concept. Pages 127-137 in 8th Vertebrate Pest Conference, Sacramento, CA.

Flint, E., K. McDermond, D. Herbst, A. Yuen, and D. Woodside. 1992. Survey of The 

Terrestrial Biota of Palmyra Atoll 18 February to 9 March 1992. Administrative 

Report, USFWS Honolulu.

Greene, T. C. and P. J. Dilks. 2004. Effects of non-toxic bait application on birds: assessing the 

impacts of a proposed kiore eradication programme on Little Barrier Island. 

Deporatment of Conservation, Wellington, New Zealand.

Griffiths, R., G. Climo, and A. Gouni. 2008. Ecological restoration of Vahanga Atoll, Acteon 

Group, Tuamotu Archipelago: Research Report 5 February 2008. Pacific Invasives 

Initiative, Auckland, NZ.

Howald, G., A. Samaniago, S. Buckelew, P. McClelland, B. Keitt, A. Wegmann, W.C. Pitt, 

D.S. Vice, E. Campbell, K. Swift, and S. Barclay. 2004. Palmyra Atoll rat eradication 

assessment trip report, August 2004. Island Conservation.

Howald, G., C. J. Donlan, J. P. Galvan, J. C. Russell, J. Parkes, A. Samaniego, Y. Wang, D. 

Veitch, P. Genovesi, M. Pascal, A. Saunders, and B. Tershy. 2007. Invasive Rodent 

Eradication on Islands. Conservation Biology 21:1258-1268.

MINITAB. 2007. Minitab® 15.1.1.0.

Pain, D. J., M. D. Brooke, J. K. Finnie, and A. Jackson. 2000. Effects of brodifacoum on the 

land crabs of Ascension Island. Journal of Wildlife Management 64:380-387.

Towns, D. R. and K. G. Broome. 2003. From small Maria to massive Campbell: forty yers of 

rat eradications from New Zealand islands. New Zealand Journal of Zoology 30:387-

398.

Wegmann, A. 2008. Land crab interference with eradication projects: Phase I - compendium of 

available information. Pacific Invasives Initiative, The University of Auckland, New 

Zealand.

Wegmann, A., R. Marquez, G. Howald, J. Curl, J. Helm, C. Llewellyn, and P. Shed. 2007. 

Pohnpei rat eradication research and demonstration project: Pohnpei, Federated States 

of Micronesia - 16 January to 7 March 2007. Island Conservation, Santa Cruz, USA.

Wegmann, A. and S. Middleton. 2008. Trip report, Jarvis Island National Wildlife Refuge and 

Palmyra Atoll National Wildlife Refuge visit and terrestrial assessment, 20 March to 8 

April 2008. US Fish and Wildlife Service - PRINWRC.
31

10. APPENDIX A

Biomarker Field detection results for Rattus rattus, Palmyra Atoll 2008. Rats that showed no biomarker sign are 

identified with “*.” Both internal and external biomarker presence was scored according to a system devised 

during the rat biomarker detection assay; the scores presented in this table are the sum total for each rat including 

anus, tail, and other external for “External biomarker score,” and “ stomach, small intestine, and ceacum for 

“Internal biomarker score.”

Study site Rat # Days post first

application

Days post second

application

External 

biomarker score

Internal 

biomarker score

Home 1 4 1 1

Home 2 4 2 0

Home 3 4 2 5

Home 4 4 3 8

Home 5 4 3 9

Home 6 4 2 9

Home 7 4 2 9

Home 8 4 2 9

Home 9 4 4 7

Home 10 4 3 7

Home 11 4 6 9

Home 12 5 1 7

Home 13 5 1 4

Home 14 5 1 3

Home 15 5 2 1

Home 16* 5 0 0

Home 17 10 5 5 6

Home 18 10 5 2 6

Home 19 10 5 3 3

Home 20 10 5 3 3

Home 21 12 7 0 1

Home 22 12 7 3 6

Port 1 4 1 3

Port 2 4 2 2

Port 3 4 2 2

Port 4 4 2 0

Port 5 4 2 6

Port 6 4 2 8

Port 7 4 2 9

Port 8 4 3 2

Port 9 4 3 1

Port 10 4 3 0

Port 11 4 3 5

Port 12 4 3 9

Port 13 4 3 9

Port 14 5 1 0

Port 15 5 2 1

Port 16 5 2 2

Port 17 5 2 0

Port 18 5 2 4
32

Study site Rat # Days post first

application

Days post second

application

External 

biomarker score

Internal 

biomarker score

Port 19 5 2 8

Port 20 5 2 5

Port 21 5 3 1

Port 22 5 3 2

Port 23 9 4 2 2

Port 24 9 4 3 5

Port 25 10 5 1 0

Port 26 10 5 2 4

Port 27 10 5 2 8

Port 28* 11 6 0 0

Port 29 11 6 2 3

Port 30 11 6 2 0

Port 31 12 7 2 3

Whip 1* 4 0 0

Whip 2 4 1 0

Whip 3 4 1 2

Whip 4 4 1 2

Whip 5 4 1 0

Whip 6 4 1 1

Whip 7 4 1 6

Whip 8 4 1 7

Whip 9 4 1 9

Whip 10 4 2 2

Whip 11 4 2 3

Whip 12 4 2 3

Whip 13 4 3 4

Whip 14 4 2 3

Whip 15 4 3 6

Whip 16 4 2 9

Whip 17 4 3 3

Whip 18 4 4 3

Whip 19 4 3 3

Whip 20 4 3 4

Whip 21 4 4 3

Whip 22 4 3 5

Whip 23 4 4 5

Whip 24 4 3 7

Whip 25 4 4 8

Whip 26 4 4 7

Whip 27 4 4 9

Whip 28 4 3 9

Whip 29 4 3 9

Whip 30 4 4 9

Whip 31 4 3 9

Whip 32* 5 0 0

Whip 33* 5 0 0

Whip 34* 5 0 0
33

Study site Rat # Days post first

application

Days post second

application

External 

biomarker score

Internal 

biomarker score

Whip 35 5 1 0

Whip 36 5 1 0

Whip 37 5 1 1

Whip 38 5 1 0

Whip 39 5 1 3

Whip 40 5 1 1

Whip 41 5 1 2

Whip 42 5 2 0

Whip 43 5 2 1

Whip 44 5 2 0

Whip 45 5 3 2

Whip 46 5 2 2

Whip 47 5 2 0

Whip 48 5 2 6

Whip 49 5 2 4

Whip 50 5 2 4

Whip 51 5 2 3

Whip 52 5 3 1

Whip 53 5 4 4

Whip 54 5 3 5

Whip 55 5 3 9

Whip 56* 9 4 0 0

Whip 57* 9 4 0 0

Whip 58* 9 4 0 0

Whip 59* 9 4 0 0

Whip 60* 9 4 0 0

Whip 61 9 4 1 0

Whip 62 9 4 1 0

Whip 63 9 4 3 3

Whip 64 9 4 3 4

Whip 65 9 4 3 8

Whip 66* 10 5 0 0

Whip 67* 10 5 0 0

Whip 68* 10 5 0 0

Whip 69* 10 5 0 0

Whip 70* 10 5 0 0

Whip 71* 10 5 0 0

Whip 72* 10 5 0 0

Whip 73* 10 5 0 0

Whip 74* 10 5 0 0

Whip 75* 10 5 0 0

Whip 76 10 5 1 0

Whip 77* 11 6 0 0

Whip 78* 11 6 0 0

Whip 79* 11 6 0 0

Whip 80* 11 6 0 0

Whip 81* 11 6 0 0
34

Study site Rat # Days post first

application

Days post second

application

External 

biomarker score

Internal 

biomarker score

Whip 82* 11 6 0 0

Whip 83* 11 6 0 0

Whip 84 11 6 1 0

Whip 85 11 6 1 0

Whip 86 11 6 1 0

Whip 87 11 6 2 1

Whip 88* 12 7 0 0

Whip 89* 12 7 0 0

Whip 90* 12 7 0 0

Whip 91 12 7 2 0
1

APPENDIX F

THE ECOTOXICOLOGY AND PALATABILITY OF TWO 

RODENTICIDE PRODUCTS: FIELD‐BASED ASSESSMENT AT 

PALMYRA ATOLL
2
THE ECOTOXICOLOGY AND PALATABILITY OF TWO 

RODENTICIDE PRODUCTS: FIELD-BASED ASSESSMENT AT 

PALMYRA ATOLL

PREPARED BY

ISLAND CONSERVATION: AURORA ALIFANO AND ALEX WEGMANN*

FOR

THE PALMYRA ATOLL RAINFOREST RESTORATION PROJECT

*Correspondence: Alex Wegmann, Island Conservation, 100 Shaffer Rd. Santa Cruz, CA, 95060 USA / +1831.359.4787 / 

alex.wegmann@islandconservation.org / www.islandconservation.org
2

1. EXECUTIVE SUMMARY

From 29 April to 28 May, 2010, two Island Conservation personnel visited Palmyra Atoll to 

assess the fate, palatability, and environmental impacts associated with the broadcast application 

of two rodenticide bait products. The main goals of this expedition were to:

1) Evaluate the environmental fate of the matrix and active ingredients of bait products currently 

approved for use to eradicate rats on Palmyra Atoll.

2) Determine the toxicity of rodenticide residue in body tissues and excrement after bait 

consumption by land crabs

3) Assess the palatability, for rats and land crabs, of the two bait products currently registered in the 

USA for broadcast application.

4) Conduct site-specific research needed to inform the development of an operational plan for a 

successful rat eradication at Palmyra Atoll. 

The palatability and rodenticide residue in soil and land crab excrement for two anticoagulant 

bait products was assessed in this study. The goal of this study was to better understand the 

potential efficacy and potential impact associated with the use of each bait product in a rat 

eradication at Palmyra Atoll (Palmyra). The two bait products tested were “25W” and “D50.” 

25W is a 2nd generation anticoagulant product manufactured by Bell Labs®(Madison, WI) that 

contains 25ppm brodifacoum. D50 is a rodenticide bait product manufactured by HACCO®

(Randolph, WI) that contains the first generation anticoagulant diphacinone. Both products were 

identified as potential candidates for use in the proposed eradication of Black rats (Rattus rattus)

from Palmyra.

Toxicant residue from the two bait products was not readily incorporated into or retained in the 

topsoil layer (< 2 cm) of either of Palmyra‟s two primary soil types – sandy and humus. All soil 

samples yielded very low concentrations of either toxicant despite abundant rainfall, insect 

consumption, and pellet degradation during the study period. Low toxicant detection in the soil 

samples suggests that the bait products tested here do not transfer high concentrations of 

rodenticide to Palmyra‟s topsoil. 

The concentration of brodifacoum found in crab tissue between day 2 and day 56 after initial 

exposure (1.8 – 0.01 ppm) (USDA-APHIS 2006) is less than the concentration of brodifacoum in 

the bait pellets that the crabs fed on (25 ppm), suggesting that some quantity of the toxicant is 

evacuated through defecation, metabolized by the crab, or both. In this study, captive crabs

(Cardisoma carnifex) fed ad lib on bait pellets for 7 days, with no cumulative increase of 

rodenticide concentrations in crab excrement between day 2 and day 6. When crabs were 

switched from a diet consisting entirely of bait pellets to a diet of food items from their natural 

environment (day 7), rodenticide concentrations in crab excrement dropped to near-trace levels 

within three days (day 10). 
3

Secondary consumers (hermit crabs and cockroaches) were observed consuming C. carnifex

excrement. Consumption of crab excrement by other invertebrates likely increases the 

rodenticide residue period for crabs, and possibly for other invertebrates, such as cockroaches; 

however, residue concentrations were not measured beyond the primary consumer.

Both 25W and D50 were found to be palatable to rats and crabs when presented alongside three 

commonly available food items: coconut endosperm (meat), the meristematic tissue of young 

coconut palms, and the fleshy mesocarp of Pandanus fruit. Both 25W and D50 were consumed 

by rats and crabs in the presence of other natural food items, and neither bait product was 

significantly more palatable than the other. The average time for consumption of a 1 g pellet of 

25W and D50 was 50 minutes, and the pellets were fully consumed in over 50% of the 

palatability trials. Coconut was the food item consumed most quickly and frequently. 

A total of 156 genetic samples were collected from individual R. rattus captured on 12 of 

Palmyra‟s 25 distinct landmasses. The genetic samples will be banked to assist in determining 

the source of any rats captured after the eradication.

Multiple locations exist around the atoll where coconut palms extend over the water. If an aerial 

broadcast method is selected for the eradication, the overhanging palm crowns will need to be 

baited by hand. The average number of C. nucifera palms with 100% canopy coverage extending 

beyond the high tide line of the shore, was estimated both inside and outside the lagoon. 

The preliminary results of egg predation monitoring and non-target species capture methods are 

also presented.
4

Table of Contents

1 INTRODUCTION ............................................................................................................... 7

1.1 Project Setting .................................................................................................................. 7

1.2 Project Background.......................................................................................................... 8

1.3 Study Sites........................................................................................................................ 8

1.4 Study Questions................................................................................................................ 9

1.4.1 Toxicant residue in soil ..................................................................................................................... 9

1.4.2 Toxicant residue in crab excrement................................................................................................... 9

1.4.3 Toxicant reside in hermit crab tissue ............................................................................................... 10

1.4.4 Crab excrement coprophagia ........................................................................................................... 10

1.4.5 Bait palatability ............................................................................................................................... 10

1.4.6 Live trapping and genetic sampling................................................................................................. 11

1.4.7 Bait application impacts on the marine environment ...................................................................... 11

1.4.8 Egg predation .................................................................................................................................. 12

1.4.9 Coconut palms (C. nucifera) that overhang mean high-tide line..................................................... 12

1.4.10 Curlew capture ............................................................................................................................ 12

2 METHODS ........................................................................................................................ 13

2.1 Toxicant Residue in Soil ................................................................................................ 13

2.1.1 Study locations and plot placement ................................................................................................. 13

2.1.2 Soil plot design................................................................................................................................ 13

2.1.3 Soil core sampling ........................................................................................................................... 14

2.2 Toxicant Residue in Crab Excrement............................................................................. 15

2.2.1 Crab selection and cage construction .............................................................................................. 15

2.2.2 Sampling.......................................................................................................................................... 17

2.3 Toxicant Residue in Crab Tissue ................................................................................... 18

2.3.1 Hermit crab collection and sampling............................................................................................... 18

2.4 Crab Excrement Coprophagia ........................................................................................ 18

2.4.1 Crab selection and bait consumption............................................................................................... 18

2.4.2 Cardisoma excrement consumption by cockroaches....................................................................... 19

2.4.3 Cardisoma excrement consumption by hermit crabs....................................................................... 19

2.5 Bait Palatability.............................................................................................................. 20

2.5.1 Rat capture....................................................................................................................................... 20

2.5.2 Rat palatability trials........................................................................................................................ 20

2.5.3 Crab palatability trials ..................................................................................................................... 20

2.6 Live Trapping and Genetic Sampling ............................................................................ 21

2.6.1 Live trapping ................................................................................................................................... 21

2.6.2 Genetic sampling............................................................................................................................. 21

2.7 Bait Application Impacts on the Marine Environment .................................................. 22

2.7.1 Shallow water trial........................................................................................................................... 22

2.7.2 Mid water trial ................................................................................................................................. 22

2.7.3 Deep water trial ............................................................................................................................... 22

2.7.4 Bait on the flats................................................................................................................................ 22

2.8 Egg Predation ................................................................................................................. 22

2.8.1 Egg predation monitoring................................................................................................................ 22
5

2.9 Toxicant concentrations in the bait products used in this study: brodifacoum in 25W 

and diphacinone in D50............................................................................................................. 23

2.10 Coconut palms (C. nucifera) that overhang mean high-tide line ................................... 23

2.10.1 C. nucifera canopy description.................................................................................................... 23

2.10.2 Overhanging palm crown estimation .......................................................................................... 24

2.11 Bristle-thighed Curlew Capture ..................................................................................... 24

2.11.1 Capture method ........................................................................................................................... 24

3 ANALYSIS:....................................................................................................................... 25

4 RESULTS .......................................................................................................................... 26

4.1 Toxicant Residue in Soil ................................................................................................ 26

4.2 Toxicant Residue in Crab Excrement............................................................................. 28

4.2.1 25W in crab excrement.................................................................................................................... 28

4.2.2 D50 in crab excrement..................................................................................................................... 29

4.3 Toxicant Residue in Crab Tissue ................................................................................... 29

4.4 Crab Excrement Coprophagia ........................................................................................ 30

4.4.1 C. carnifex excrement consumption by cockroaches and hermit crabs ........................................... 30

4.5 Consumption of Bait Pellets by C. Carnifex.................................................................. 31

4.5.1 Daily consumption of bait pellets by C. carnifex ............................................................................ 31

4.6 Bait Palatability.............................................................................................................. 31

4.6.1 Rat palatability................................................................................................................................. 31

4.6.2 Crab palatability .............................................................................................................................. 33

4.7 Live Trapping and Genetic Sampling ............................................................................ 34

4.8 Bait Pellet Consumption by Fish.................................................................................... 35

4.8.1 Fate of bait pellets ........................................................................................................................... 35

4.8.2 Intertidal fate of bait pellets............................................................................................................. 35

4.9 Egg Predation ................................................................................................................. 36

4.10 Toxicant Concentrations in the Bait Products................................................................ 36

4.11 C. nucifera Canopy Counts............................................................................................ 36

4.12 Bristle-thighed Curlew Capture ..................................................................................... 36

4.12.1 Runway ....................................................................................................................................... 36

4.12.2 Forest........................................................................................................................................... 37

4.12.3 North Beach ................................................................................................................................ 37

5 DISCUSSION.................................................................................................................... 37

5.1 Rodenticide Environmental Fate.................................................................................... 37

5.2 Toxicity of Rodenticide Residue in Crabs ..................................................................... 38

5.3 Rodenticide Palatability for Rats and Crabs .................................................................. 39

6 APPENDIX: RAW DATA ................................................................................................ 40
6

6.1 Toxicant Residue in Soil Results ................................................................................... 40

6.2 Toxicant Residue in Crab Excrement............................................................................. 42

6.3 Toxicant Concentration in Bait Pellets: 25W and D50.................................................. 44

6.3.1 25W - brodifacoum.......................................................................................................................... 44

6.3.2 D50 - diphacinone ........................................................................................................................... 46

6.4 Bait Product Labels........................................................................................................ 48

6.4.1 25W................................................................................................................................................. 48

6.4.2 D50 .................................................................................................................................................. 49

7 REFERENCES .................................................................................................................. 50
7

1 INTRODUCTION

1.1 Project Setting

Palmyra Atoll National Wildlife Refuge (Palmyra), at 6◦ N and 162◦ W in the Line Islands –

Central Pacific, represents a globally important conservation opportunity. The U.S. Fish and 

Wildlife Service (FWS) and The Nature Conservancy (TNC) co-manage Palmyra‟s emergent 

land area, while the FWS retains sole jurisdiction over marine resources extending 12 nautical 

miles out from the atoll. Palmyra is the only fully (federally) protected moist tropical forest 

ecosystem in the Central Pacific, yet native biota are currently threatened by an introduced, 

invasive rodent – the black rat (Rattus rattus). Palmyra provides important breeding habitat for 

10 seabird species; however, rat related egg and chick predation has likely led to the extirpation 

of six additional species (Table 1). Without the consumptive pressure of an established human 

population, Palmyra‟s land crab (“crab”) community is one of, if not the richest and most robust 

in the Central Pacific region. Palmyra is home to seven crab species (excluding the intertidal 

families Grapsidae and Ocypodidae), 4 of which are super abundant (Table 2). 

Table 1: Resident seabirds of Palmyra Atoll.

Family Common Name Scientific Name Breeding Pairs IUCN

Procellariidae Audubon‟s Shearwater Puffinus lherminieri Believed extirpated LC

Wedge-tailed Shearwater Puffinus pacifica Extirpated LC

Phoenix Petrel Pterodroma alba Believed extirpated EN*

Hydrobatidae White-throated Storm Petrel Nesofregetta fuliginosa Believed extirpated VU*

Sternidae Black Noddy Anous minutes 2,500 LC

Blue Noddy Procelsterna cerulea Believed extirpated LC

Brown Noddy Anous stolidus 1000 LC

Sooty Tern Sterna fuscata 10,000 LC

Gray-backed Tern Sterna lunata Believed extirpated LC

White Tern Gygis alba 150 LC

Fregatidae Great Frigatebird Fregata minor 500 LC

Lesser Frigatebird Fregata aerial Non-breeder LC

Phaethontidae White-tailed Tropicbird Phaethon rubricauda 15 LC

Red-tailed Tropicbird Phaethon rubricauda 20 LC

Sulidae Red-footed Booby Sula sula 5,000 LC

Brown Booby Sula leucogaster 150 LC

Masked Booby Sula dactylatra 20 LC

* = Declining population trend

Table 2: Crab abundance survey results, Palmyra Atoll (Howald et al. 2004). Units represent #/hectare estimates.

Crab species Mean Standard dev. Mass (g)2

Birgus latro 7 3811000

Coenobita brevimanus 46 8 50

Coenobita perlatus 182 80 50

Cardisoma carnifex 33 8 300

Cardisoma rotundum 28 5 300

1 Large variance probably due to low probability of encounter and patchy distribution.

2 Approximate adult mass
8

1.2 Project Background

Two bait products have been identified as potential candidates for use in the proposed

eradication of R. rattus from Palmyra Atoll: 25W and D50. 25W is a 2nd generation 

anticoagulant product manufactured by Bell Labs®that contains 25ppm brodifacoum. 25W was 

field-tested at Palmyra in 2005, when Island Conservation (IC) and the FWS conducted trial 

broadcast-based eradications on five islets totaling 4.08 ha (Buckelew et al. 2005). A concurrent 

bait consumption trial indicated that an application rate within 60-90 kg/ha will be necessary to 

ensure that all rats have access to bait for four days post application despite crab competition for 

bait pellets. Recent Section 3 registration of the 25W product label set the maximum aerial 

broadcast rates at 18 kg/ha for the first application, and 9kg/ha for the second application –

occurring five to seven days after the initial bait application. A 2008 assessment of bait 

application rates found that 25W‟s maximum application rate of 18 and 9 kg/ha will not 

effectively ensure that all rats have access to bait given the measured bait consumption capacity 

of the resident crab populations (Wegmann et al. 2008). 

Due to the persistence of brodifacoum in the environment, and its toxicity to birds (Eason et al. 

1999, Fisher et al. 2003, 2004, Alifano and Wegmann 2010), an alternative rodenticide “D50” is 

under consideration for use in the rat eradication effort. D50 is a rodenticide bait product 

manufactured by HACCO®that contains the first generation anticoagulant diphacinone. 

Diphacinone is less toxic to rats than brodifacoum, and typically requires multiple feedings over 

several days to illicit a toxic effect. To date, D50 has been field-tested at Palmyra Atoll only in 

brief palatability and bait degradation trials (Howald et al. 2004), though its palatability was not 

thoroughly tested against natural food items. Little is known about the fate or efficacy of D50 

within Palmyra‟s eradication environment; the reduced toxicity of D50 to at-risk non-target 

species warrants further investigation of this bait product. 

1.3 Study Sites

Palmyra consists of 250 ha of emergent land (fragmented into 25 islands), 16 of which were used 

during these studies. Rats were live-captured on the following islands: Strawn, Cooper,

Aviation, Quail, Whippoorwill and Bunker, Eastern, Portsmouth, Barren, the South Island 

Complex, Paradise, Home, Sand, Fern, Lost, and the North-South Causeway (Figure 1). Soil 

samples were obtained from Lost Island and Cooper Island. All Cardisoma carnifex were 

collected haphazardly from Cooper Island and Strawn Island. Coenobita perlatus were collected 

from Whippoorwill Island.
9

Figure 1. Islands from which samples were collected: (A) Strawn, (B) Cooper, (C) Aviation, (D) Quail, (E) 

Whippoorwill and Bunker, (F) Eastern, (G) Portsmouth, (H) Barren, (I) South Island Complex, (J) Paradise, (K) 

Home, (L) Sand, (M) Leslie, (N) Dudley, (O) North-South Causeway, (P) Fern, (Q) Lost.

1.4 Study Questions

1.4.1 Toxicant residue in soil

Study Question: For the rodenticide bait products 25W (containing brodifacoum) and D50

(containing diphacinone), will prolonged contact between a bait pellet and soil result in 

detectible concentrations of the given rodenticide in the soil environment, and if so, will the 

concentration decrease over time?

Although it is unlikely for a bait pellet to remain unconsumed on Palmyra for more than 4-7 days 

(Buckelew et al. 2005, Wegmann et al. 2008), it is currently unknown whether or not toxicants 

leach from bait pellets into the soil, and if so, how long the toxicant persists in the soil medium. 

In order to investigate the integration of rodenticides into soil, pellets of two bait products were 

placed on the two predominant soil types of Palmyra Atoll: sandy soil and humus soil. Soil was 

collected directly below each pellet at standardized depths and at specific time intervals. The 

concentration of toxicant in the sample was determined by High Performance Liquid 

Chromatography (HPLC) and mass spectrometry analysis performed by the California Animal 

Health and Food Safety Lab at the University of California, Davis.

1.4.2 Toxicant residue in crab excrement

Study Question: For the rodenticide bait products 25W (containing brodifacoum) and D50 

(containing diphacinone), will consumption of bait pellets result in detectible concentrations of 

the given rodenticide in the excrement of crabs, and if so, will the concentration of toxicant in 

the excrement decrease over time?

C. carnifex represent a large portion of the crab biomass at Palmyra and consume a wide 

assortment of items ranging from vegetation and seeds to abandoned seabird eggs and dead 

seabird chicks. These opportunistic omnivores are known to consume bait pellets, as 

documented in the 2008 biomarker study (Wegmann et al. 2008). Although anticoagulants are 

not thought to cause harm to invertebrates, some quantity of the consumed toxicant might 
10

become available to other organisms if it is incorporated in crab excrement. It is unknown if 

toxicants are incorporated into crab excrement following bait consumption, and if so, over what 

timeframe crabs continue to shed the toxicant via their excrement. After 56 days, crabs retain 

only trace amounts of brodifacoum in their tissues (USDA-APHIS 2006), and it is likely that 

diphacinone will have even a shorter residence period in crabs (Fisher 2009). This study 

examined toxicant concentrations in crab excrement at post bait consumption time intervals that 

range from 2 to 27 days. 

1.4.3 Toxicant reside in hermit crab tissue

Study Question: What is the average concentration of brodifacoum residue in hermit crab tissue

5 years post-exposure?

In 2005, a broadcast trial eradication was conducted at Palmyra Atoll using one bait product “PI25” - containing 25 ppm brodifacoum,- manufactured by Bell Laboratories Inc.) (Buckelew et al. 

2005). Tissue from hermit crabs on Home and Whippoorwill Islands were sampled at 2, 6, 10, 

and 56 days post-baiting and analyzed for brodifacoum residue by the National Wildlife 

Research Center Analytical Lab (USDA-APHIS 2006). In 2010, crabs were sampled and 

analyzed again, providing an opportunity to examine crab tissue for brodifacoum residue five 

years post-exposure.

1.4.4 Crab excrement coprophagia

Study Question: Do crabs and other invertebrates consume crab excrement?

Organisms that consume rodenticide bait may eliminate the toxic compounds through defecation, 

thus re-creating the potential availability of the toxicant to other organisms. Several factors 

determine the availability and concentration levels of eliminated rodenticide, including the rate 

of elimination by the organism and the transformation of the toxicant by internal metabolic 

processes. Rats and crabs consume nearly all of the available rodenticide pellets after a 

broadcast; however, little is known about the secondary pathways of the toxicant after primary 

consumption. The extent to which crab excrement is consumed by other organisms is unknown. 

If crab excrement does not serve as a trophic resource for Palmyra‟s scavengers, the toxicant 

consumed by crabs will be metabolized, or be eliminated in excrement and breakdown in the 

soil. Conversely, if small invertebrates such as cockroaches consume crab excrement they may 

become a tertiary toxicant pathway to other non-target species. Crab excrement consumption by 

invertebrates was examined to better understand this potential toxicant pathway. 

1.4.5 Bait palatability

Study Question: When exposed to one bait product (25W or D50) in the presence of natural food 

items, which product is more palatable to rats within a short (2 hour) exposure window 

(palatability is measured by first physical contact, taste, amount consumed, and time to entire 

consumption of bait pellet)? 

Little is known about the development of food preferences in wild rodents, but they usually 

select familiar foods (Jackson 1972). It is of the utmost importance that rodenticide bait product

utilized for an eradication be attractive enough that every rat will consume a lethal dose. From 

the 2005 and 2008 trials, 25W (in both active and inactive forms) was consumed by rats on 

several islands, including Home, Portsmouth, Whippoorwill, and Bunker. However, there has 

not been a concerted effort to assess the palatability of the two bait products under consideration 
11

for the Palmyra rat eradication: 25W and D50. This study challenged both bait products against 

natural food items. Palatability was primarily measured as the amount (g) of the bait pellet (1 g) 

eaten, in contrast to the amount (g) of the other food items consumed by the rat, and the 

following variables were also assessed: item first contacted, item first tasted, item first 

consumed.

1.4.6 Live trapping and genetic sampling

Study Question 1: Are rodenticide-resistant alleles present in the current (pre-eradication) 

population?

Resistance to anticoagulant rodenticides was first recorded in the Brown Rat, Rattus novegicus, 

in Scotland in 1958 and has since been found in other countries and species. Anticoagulant 

resistance is thought to be due to a single major gene, of which there are at least two or possibly 

more alleles whose effects are subject to the action of modifiers and whose phenotypic 

expression is usually dominant. Resistance by three commensal rodents (R. novegicus, R. rattus, 

and Mus musculus) has been widely documented for first-generation anticoagulants, like 

diphacinone, and cases of resistance for two of the three commonly used second-generation 

anticoagulants (diphenacoum and bromadiolone) are now known; however, resistance to 

brodifacoum by black rats (R. rattus) has not been documented, yet cases of high tolerance have 

been reported (Lund 1984). The presence of rodenticide resistance within Palmyra‟s rat 

population would greatly influence the design of the eradication program. Therefore, DNA 

samples (tail snips) collected from rats at Palmyra will be screened for the alleles that are 

associated with rodenticide resistance.

Study Question 2: In the event that rats are discovered on Palmyra Atoll post-eradication, are 

those individuals missed rats or do they represent a post-eradication incursion?

R. rattus is the only species of rat currently present at Palmyra. Recent rat density estimates

suggest that there could be as many as 139 rats/ha, resulting in a population size of

32,000 rats across the atoll (Wegmann et al. 2008). In case of eradication failure, analysis of R.

rattus DNA (tail snips) from the pre-eradication population was collected, and will allow the 

project Partnership to determine if rats that are found post-eradication are missed target animals 

or from an incursion. 

1.4.7 Bait application impacts on the marine environment

Study Question: In the event of bait drift during an aerial broadcast at Palmyra Atoll, how will 

marine organisms react to bait pellets in the marine environment?

The use of rodenticide bait is not anticipated to negatively impact marine organisms. Both 

toxicants in consideration for use on Palmyra (brodifacoum and diphacinone) have low solubility 

in water. Given the non-polarity of brodifacoum molecules and the ionic strength of seawater,

the solubility of brodifacoum is likely in the low parts per billion range (Pierce et al. 2008). 

Water sampling conducted after aerial application of diphacinone pellets to Mokapu Island, in 

February 2008, found no diphacinone residues in any seawater samples, and even in the extreme 

case of 20 tons of brodifacoum bait spilled into the ocean off New Zealand, brodifacoum levels 

were not detectable within 36 hours after the spill (Pierce et al. 2008). New Zealand scientists 
12

estimated that during a normal helicopter aerial bait application, incidental bait discharge into the 

nearshore marine waters resulted in 0.0000006 mg/l, or about seven orders of magnitude below 

the level known to be lethal to bluegill sunfish (New Zealand Department of Conservation 2000). 

Although the low water solubility of the toxicant and the use of a deflector on the bucket during

the aerial application decreases the likelihood of exposure to marine organisms to bait, the 

reaction of near-shore consumers to bait pellets should be examined. 

1.4.8 Egg predation

Study Question: Can rat predation of ground-nesting seabird eggs be captured on video?

Several cases are known where predation on seabirds can be reliably attributed to black rats. 

These include sooty terns (Sterna fuscata) in the Seychelles Islands (Feare 1979), Bonin petrels 

(Pterodroma hypoleuca) in Hawaii (Grant et al. 1981), Galapagos dark-rumped petrels 

(Pterodroma phaeopygia) in the Galapagos Islands (Harris, 1970), and white-tailed tropicbirds 

(Phaethon lepturus) in Bermuda (Gross, 1912). Rat husking stations on Palmyra Atoll 

containing seabird eggshells are frequently observed near seabird breeding colonies; however, no 

direct observation of rat predation on seabird eggs or chicks has been made. Here, we attempt to 

video- and photo-document rats preying on bird eggs. 

1.4.9 Coconut palms (C. nucifera) that overhang mean high-tide line

Study Question: How many coconut palms overhang the high-tide line?

To minimize the amount of bait that lands in the nearshore marine environment during an aerial 

broadcast at Palmyra, the pilot would apply bait, using a directional deflector, several meters 

inside the mean high-tide line. Palm trees seeking light often overhang the shoreline; such palms 

represent potential rat habitat yet they would not be baited during the aerial broadcast. 

Overhanging palms would be treated by hand-canopy baiting (Wegmann et al. 2008). To 

estimate the number of overhanging palms and the effort required to effectively bait them, we 

counted the number of palms along measured stretches of lagoon-facing and ocean-facing 

shoreline. 

1.4.10 Curlew capture

Study Question: Can curlews be successfully captured by noose carpet?

During the rat eradication, Bristle-thighed Curlews (Numenius tahitiensis) and Pacific Golden 

Plovers (Pluvialis fulva) will be put at risk of primary and secondary exposure to rodenticide. 

Active mitigation of this risk through a capture-hold or capture-translocation action may be 

required. However, capture, holding, and transport of wild birds can result in mortalities; care 

should be taken. This study tested the feasibility of one method of capture. 
13

2 METHODS

2.1 Toxicant Residue in Soil

2.1.1 Study locations and plot placement

Two predominant soil types exist at Palmyra Atoll. Within forests of Pisonia grandis, soils are 

highly phosphatic and composed almost entirely of organic matter (Christophersen 1927); we 

refer to this soil type as “humus.” In contrast, soils associated with C. nucifera (coconut palm) 

forests are sandy and non-phosphatic with medium or low organic matter (Christophersen 1927); 

we refer to this soil type as “sandy.” Soil nutrients are significantly elevated in dicot (Pisonia 

mixed with other tropical broadleaf tree species) forests (NO3

-

= 100.74 ± 26.10 μg/g; NH4

+ 

= 

65.09 ± 5.23μg/g) as compared to palm forests (NO3

-

= 8.04 ± 2.31 μg/g; NH4

+ = 39.59 ± 

6.21μg/g; n = 57). Isotopic values of δ15N in soil are significantly different across forest type; 

there are no significant differences in δ13C in soils across forest type (Young et al. 2010).

To estimate the maximum likely integration of rodenticide into Palmyra‟s soil after a broadcast 

bait application, bait pellets were placed directly on the soil for seven days. Samples of sandy 

soil were collected from Cooper Island, and samples of organic humus soil were collected from 

Lost Island. Application of rodenticide products have not occurred at either site since the 

culmination of the previous rat eradication attempt in 2002. During this study, pellets of two bait 

products (25W and D50), were left to naturally degrade in select locations for seven days. The 

soil directly beneath pellets was sampled after 2 days, 7 days, 28 days, and 50 days. 

2.1.2 Soil plot design

25W and D50 pellets of similar mass were selected to standardize, as best as we could, the 

amount of toxicant placed in each soil plot: 2.4 g ± 0.1 g for 25W, 1.04 g ± 0.1 g for D50. 

Exclusion tubes (7.6 cm x 5.1 cm PVC) with wire mesh over the top prevented the pellets from 

being disturbed by rats and crabs, while maintaining bait pellet exposure to weathering factors

such as sunlight, rain, humidity, small invertebrates, and micro-organisms. Each exclusion tube 

was secured to a 30 cm plastic stake driven into the ground – this prevented crabs from removing 

the tubes. One bait pellet was placed on the soil in the center of each exclusion tube. After 

seven days, or two days for the “2 day sample,” the tubes and intact portions of the pellets were 

removed. The exact location of each pellet within the tube was marked with two steel pins that 

defined each end of the pellet (Figures 2 and 3). Three replicate exclusion tubes containing one 

bait product were installed within the same microhabitat (1 sq meter plot); and plots containing 

25W were approximately 5 meters away from those containing D50. Natural degradation and 

weathering of the bait occurred over time, including disturbance and consumption by small 

organisms like ants and microbes. 
14

Figure 2. Cartoon of the toxicant residue in soil study plot.

Figure 3: Lost Island 28 day soil plot with stake, PVC crab exclusion 

tube with wire mesh, and one 25W bait pellet inside.

Three replicates for each bait product were sampled from both soil types, at four separate 

exposure periods, resulting in a total of 48 surface soil samples. Sub-surface samples were also 

collected at a depth of 6 cm during the 28 and 50 day collections to assess the depth of

penetration of the toxicant. Soil that was not exposed to bait pellets was collected from each 

study site during each sampling period. 

2.1.3 Soil core sampling

Soil samples were collected using a stainless-steel core (2.5 cm inside diameter x 70 cm length). 

Soil was carefully extracted from the core onto fresh wax paper for sample collection (Figure 4). 
15

Surface soil samples were collected from the top 2 cm of the core sample, while soil between 5.5 

and 6.5 cm depth was collected as sub-surface samples. Soil samples were transferred into 

sterile plastic vials with screw-top lids by scooping soil with a new plastic knife. The stainlesssteel soil core was sanitized with a 3-step process before and after the collection of each core

sample. Particulate matter was flushed from the core with salt water, the walls of the core were 

wiped down with acetone to remove toxicant residue, and then the core was rinsed thoroughly 

with fresh water. 

The soil core depth varied between study sites due to differences in the depth of soil above 

bedrock. The average core depth at Lost Island was 8 cm ± 2 cm; the core met refusal from 

bedrock between 9 and 11cm. The soil on Cooper Island was deep enough to allow core depths 

of 20 cm without refusal. To ensure consistency among locations, core depth at Cooper Island 

was limited to 10cm during sampling. To ensure that samples could be obtained from all 

locations and replicates, the sub-surface samples were taken from a core depth of 6 cm (for 28, 

36, and 50 plots only). Surface samples were collected from all soil samples in the top 2cm of 

the core. 

Sample vials were sealed with parafilm, labeled, and stored in a -80°C freezer to prevent further 

microbial degradation of the soil. High Performance Liquid Chromatography (HPLC) and mass 

spectrometry analysis was performed by the California Animal Health and Food Safety Lab at 

the University of California, Davis to quantify toxicant concentrations in each sample.

Figure 4: Soil core from Cooper Island with lighter colored sand at 

depth, and darker sand including organic content and plant matter at the 

surface. 

2.2 Toxicant Residue in Crab Excrement

2.2.1 Crab selection and cage construction

C. carnifex were selected as the subject of the toxicant residue in crab excrement study due to 

their relative abundance, and their role as primary consumers of bait. Thirty-two adult C. 
16

carnifex (mean weight = 370g ± 77g (1SD)) were haphazardly captured from Cooper Island for 

inclusion in this trial. Crab cages (N=8) (0.9 m x 0.9 m x 0.45 m) were constructed from 1.3cm

wire mesh (19 gauge), divided into four crab “apartments” per cage (46 cm x 46 cm x 46 cm) 

and filled with 20-30 cm of sand. Each apartment was fitted with a “pool” – a 10 cm diameter x 

8 cm high pail – that provided the crabs with a water source for brachial saturation. C. carnifex

were individually housed to prevent competition for bait or natural food items, and to prevent 

confrontations that would likely lead to injury during the course of the experiment (Figure 5). 

Four cages were dedicated to 16 C. carnifex that were fed 25W ad lib for seven days, and four 

cages were dedicated to 16 C. carnifex that were fed D50 ad lib for seven days. All four crabs 

housed within one cage were fed the same bait product. Crabs were weighed, sexed, and marked 

with a unique identifier at the initiation of the experiment. 

Figure 5: C. carnifex cage. Each cage contained 4 “apartments” with 

fresh sand, a pool, and individual access to standardized amounts of 

food items for the duration of the 28 day experiment. Each cage was 

dedicated to crabs consuming either 25W or D50.

The majority of bait applied during an aerial broadcast will only be available for 4 days on 

average, and it is extremely unlikely for bait to remain on the ground for longer than 7 days at 

Palmyra due to high rates of consumption by rats and crabs (Buckelew et al. 2005, Wegmann et 

al. 2008). To determine the maximum concentration of toxicant in C. carnifex excrement during 

a worst-case scenario, crabs were offered as much bait as they could consume for 7 continuous 

days (Figure 6). 
17

Figure 6: C. carnifex in a crab “apartment”, carrying a 25W bait pellet in 

each claw. All food items were delivered in the sandy area of each crab

apartment, but crabs frequently dragged food items into the pools for 

consumption.

After 7 days, all bait pellets were counted and removed from the crab cages. All sand and 

organic matter was also removed. The pools were scrubbed and rinsed with fresh water, wiped 

with acetone and rinsed again, and the cages were thoroughly rinsed with seawater to remove 

any bait pellet particles. Subsequently, the cages were refilled with fresh sand and the pools

were refilled with fresh water. Crabs were fed a diet of natural food items for the remainder of 

the experiment. Crabs were offered a mixture of food items that they were observed consuming

in their natural environment, including Pandanus fruit, coconut solid endosperm and meristem, 

fresh-cut grass, and Scaevola, Pisonia, and Tournafortia leaves. 

2.2.2 Sampling

Excrement collection occurred on days 2, 6, 10, and 27 post initiation of the experiment. To 

prevent excrement samples from being contaminated by bait product particles stuck to the crab‟s

legs and carapace, each crab was thoroughly rinsed with fresh water before being placed in a 2 

gallon bucket. Each crab was assigned to a bucket, which was scrubbed, rinsed with fresh water 

and wiped cleaned with acetone between each use to prevent cross-contamination of samples. 

Excrement collection was conducted using the thin edge of a sterile weigh boat to scrape the 

excrement into sterile screw-cap vials. If a crab provided less than 2 grams of excrement in 24 

hours, the excrement was pooled with the excrement of another crab from the same cage to meet 

the minimum weight requirements for HPLC analysis. Sample vials were sealed with parafilm, 

labeled, and stored in a -80°C freezer to stop microbial degradation of the toxicant. After the 

final excrement collection, crabs were released near their site of capture on Cooper Island. 
18

2.3 Toxicant Residue in Crab Tissue

2.3.1 Hermit crab collection and sampling

In 2005, a broadcast trial eradication was conducted at Palmyra using one bait product, PI-25 -

the prototype for 25W (Buckelew 2005). In association with this trial eradication, hermit crabs 

(Coenobita perlatus) from Home and Whippoorwill Islets were sampled at 2, 6, 10, and 56 days

post-baiting and analyzed for brodifacoum residue by the National Wildlife Research Center 

Analytical Lab (USDA-APHIS 2006). This visit to Palmyra provided an opportunity to sample 

crabs from Whippoorwill Island (baited at 95 kg/ha in 2005) and analyze crab tissue for 

brodifacoum residue 5 years post-exposure. On May 6th, 2010, ten adult C. perlatus were

collected from Whippoorwill Island, euthanized by freezing, and analyzed for brodifacoum 

residue at the USDA National Wildlife Research Center in Fort Collins, CO. Whole frozen 

hermit crabs were homogenized with a SPEX Certiprep Model 6850 Freezer Mill. Each sample 

was analyzed in duplicate. Brodifacoum residues were surrogate corrected with difenacoum.

2.4 Crab Excrement Coprophagia

2.4.1 Crab selection and bait consumption

Crabs are physiologically capable of eating great quantities of bait, resulting in potentially 

substantial amounts of toxicant-laden excrement made available to other consumers. To reduce 

variability in excrement production due to individual physiology or size during different life 

history stages, only large adult crabs were selected for this study. Orange land crabs (C.

carnifex) weighing 300-500 grams were offered more bait pellets than they could possibly 

consume in a 24 hour period. The average mass of 25W pellets (1.55g) was slightly more than 

the average mass of D50 pellets (1.02g) therefore the number of 25W pellets offered was 

adjusted to standardize the weight of bait product offered to both groups. C. carnifex in the 25W 

group (N=20) were given 15 25W pellets for a 24 hour period (Figure 7). C. carnifex in the D50 

group were exposed to 30 D50 pellets for a 24 hour period. After 24 hours, the number of pellets 

remaining were counted. Crab excrement that contained visible traces of bait (either blue or 

green stain) was collected and stored in a -80oC freezer.
19

Figure 7: A Cardisoma carnifex in a five-gallon bucket, consuming 

D50 pellets ad lib during a 24 hour bait consumption study.

Crab excrement from crabs that had not consumed either bait product was collected by placing 

crabs in a clean bucket for 24 hours. The resulting scat was collected and stored in a -80oC 

freezer.

2.4.2 Cardisoma excrement consumption by cockroaches

Three types of crab excrement were offered to other organisms to detect a difference in 

preference for excrement containing bait vs. natural excrement: excrement post-consumption of 

D50, excrement post-consumption of 25W, and excrement from crabs that had not consumed 

either bait product. Fourteen cockroaches were collected from Cooper Island, held in individual

plexiglass pens, and offered a standardized amount (0.2g) of crab excrement without other 

alternatives for 8 hours. The three types of excrement were placed in different corners of a pen. 

The fourth corner of the pen was left empty. Excrement was placed in the corners of the pen just 

before the cockroach was placed in the center. Presence or absence of the excrement in the pen at 

the end of the experiment was used to determine whether or not cockroaches consume crab 

excrement, and if so, do they prefer excrement from crabs that have recently consumed bait.

2.4.3 Cardisoma excrement consumption by hermit crabs

Forty-eight C. perlatus were collected from Cooper and Whippoorwill Island, held in individual 

plexiglass pens, and offered a weighed amount of crab excrement without other alternatives for 8 

hours. Excrement was placed in 3 corners of the pen, as described above. Excrement was placed 

in the corners of the pen just before the hermit crab was placed in the center. Presence or 

absence of each type of excrement in the pen at the end of the experiment was used to determine 

consumption of excrement by hermit crabs. Hermit crabs were marked with a sharpie to ensure 

that individuals were not resampled, and released on Cooper Island. 
20

2.5 Bait Palatability

2.5.1 Rat capture 

Rats were captured in live traps from 9 islets: Aviation, Barren, Cooper, Eastern, Fern, NorthSouth Causeway, Paradise, Sand, and Whippoorwill (Figure 1) and brought to Cooper Island for 

the bait palatability trials. These rats were trapped using peanut butter smeared on a plastic disc 

hung on the trigger hook of a Hagaruma®live-capture trap. Rats were held in individual 

TomahawkTM traps and given access to fresh water, during a 24 hr acclimatization period. Each 

rat was weighed, sexed, and assigned a unique number. 

2.5.2 Rat palatability trials

To accommodate the natural foraging pattern of the captive rats, trials were run at night with 

start times no earlier than 19:00. Just prior to a palatability trial, captured rats were transferred 

into 30 cm x 15 cm x 15 cm plastic pens. Each pen had a clear plexiglass lid with holes for 

ventilation and opaque walls so rats could not make visual contact with rats in neighboring pens 

or be subject to outside distractions during the trials. Four food items (solid coconut endosperm 

– “coconut meat”, coconut meristem, mesocarp from the Pandanus fischerianus propogule, and 

either 25W or D50) cut into pieces weighing 1 g ± 0.5 g were prepared prior to each trial. One 

food item was placed in each corner of the pen - placement was randomly selected for each rat 

using a random number generator (Haahr 1998). After the rat was transferred from the holding 

cage to the study pen, all four food items were staged on the four corners of the plexiglass lid, 

and were simultaneously inserted into the cage by pushing them through 0.5 cm radius holes 

positioned over each corner.

Each rat experienced concurrent exposure to the four food items for two hours. Trials consisted

of one rat per pen, monitored by a video camera to eliminate the disturbance that a human 

observer might cause. The number of rats (and pens) per trial ranged from one to six, and was 

dependent on the number of rats captured for that trial session. When the trial was complete, rats 

were removed from the pens and euthanized according to AMVA guidelines (AMVA 2007). 

After euthanizing the rats, a 1-2 cm section of the distal end of each rat‟s tail was collected and 

placed in a sample vial containing 95% ethanol; the tail segments were kept for genetic analysis 

(described in 4.6.2). Rat carcasses were incinerated to ensure that the toxicant residue from 

consumption of bait during the palatability trials was not available to other organisms. 

The remains of all four food items were weighed on an EscaliTM 50 gram electronic balance. 

This value was subtracted from the pre-trial weight of each item to determine the amount (g) 

consumed during the trial. Video footage was downloaded and analyzed for each rat trial, with 

the following variables recorded: item first contacted, item first tasted, item first consumed, and 

time to full consumption of the bait pellet and percent mass of the bait pellet remaining after two 

hours. 

2.5.3 Crab palatability trials

Thirty-two C. carnifex were collected for bait palatability trials. Crabs were collected at various 

locations on Cooper Island. Individual crab weight and sex was recorded prior to each trial. 

Crab weight ranged from 150 g to 550 g with a mean of 332 g (SD 82). C. carnifex were 

presented with 4 food options for 4 hours, after which percent remaining was determined for 

each item. Each crab was housed in a separate 5 gallon bucket. Four food items (coconut, 
21

coconut meristem, Pandanus, and a bait product: 25W or D50) were cut into pieces weighing 1g 

± 0.5g (measured on an EscaliTM 50 gram electronic balance). These items were placed 

simultaneously into the bucket and in front of the crab. A lid with holes for ventilation was 

placed on the bucket to prevent the crab from escaping. After the 4 hour study, crabs were

removed, marked with a permanent marker to prevent recapture, and released on Cooper Island.

All remaining food items were weighed immediately after the trial, and the mass was recorded 

for each item. All remaining bait products were incinerated. 

2.6 Live Trapping and Genetic Sampling

2.6.1 Live trapping

Hagaruma®live traps (with wire mesh bases) were systematically deployed at study sites 

throughout the atoll. Standardized trap lines were established within all study sites. Two 

methods of trapping were employed; some traps were placed on upside-down 20 liter plastic 

buckets on the ground to reduce crab interference, while other traps were nailed to tree trunks. 

On Sand Island, the high density of large coconut crabs required the use of more robust 

Tomahawk®traps secured to horizontal tree branches with bungee cords. Solid coconut 

endosperm coated with creamy peanut butter was used as bait for all rats that did not participate 

in the palatability trials. All traps were checked daily. 

2.6.2 Genetic sampling

A 2-3 cm section of each rat tail was collected using sterilized dissection shears and stored in a 

plastic screw-top vial containing 95% ethanol. All rat tail samples were transferred to a buffer 

solution containing the active ingredients dimethyl sulfoxide and ethylenediaminetetraacetic acid

to preserve DNA integrity and shipped to EcogeneTM, a subsidiary of Landcare Research New 

Zealand Ltd., for storage and analysis. In the event of a post-eradication rat detection (and 

collection), Ecogene will genotype the pre-eradication Palmyra rat population by obtaining 

multilocus microsatellite genotypes from each sample using a set of 9 loci (Abdelkrim et al. 

2007). Evidence for allelic drop-out, scoring error due to stutter, and presence and frequency of 

any null alleles will be assessed with MICRO-CHECKER (Oosterhout et al. 2004) using a 

Bonferroni adjusted 95% confidence interval and 10,000 repetitions. Genetic diversity indices 

will be calculated using GenAlEx v 6.2 (Peakall and Smouse 2006) and tests for HardyWeinberg and linkage disequilibrium will be conducted using GENEPOP v 4.0 (Raymond and 

Rousset 1995). Pairwise FST parameters for each population pair will be estimated according to

Weir and Cockerham (Weir and Cockerham 1984). The data will then be analysed using the 

Bayesian clustering method implemented in STRUCTURE ver 2.3 (Pritchard et al. 2000) to

provide another estimate of pairwise FST parameters and to determine the number of distinct 

genetic units (K) in the dataset. The same analysis will be applied to samples collected from any 

rats captured at Palmyra after the eradication operation.

Rodenticide resistance in the pre-eradication population will be assessed by Ecogene. Ecogene 

will screen for the amino acid substitution Tyr139 in the VKORC1 gene using the ARMS PCR 

technique (Pelz et al. 2005). Recent work has shown a larger range of mutations in the 

VKORC1 gene, including a Trp59Arg substitution found in Argentine rats that may also be 

associated with resistance (Rost et al. 2009). Following ARMS-PCR, DNA sequencing is then 
22

required to verify the presence of the Y139C mutations in Exon 3 and to look for other possible 

mutations. 

2.7 Bait Application Impacts on the Marine Environment

2.7.1 Shallow water trial

On May 21st, 2010, a placebo (non-toxic) version of 25W, in the same pellet configuration as the 

active form, was scattered into the near-shore water off of Cooper Island to simulate bait drift 

into the marine environment during an aerial broadcast; the water depth was approximately 1 

meter. Observers stood on a deck overhanging the study site. A ten minute observation period 

of the area resulted in the identification and recording of 16 fish species in the study area. 

Placebo 25W pellets were dropped into the water and reactions by fish were documented. Video 

monitoring of the site recorded some fish-bait interactions (no interest, investigated, bumped, 

mouthed and then spit out, consumed). Individual pellets were observed as they fell through the 

water column, and for three minutes once the pellet landed on the bottom. If no reaction was 

observed after three minutes, another pellet was dropped in a different location. This trial was 

repeated 12 times in the shallow water location.

2.7.2 Mid water trial

The shallow water trial was repeated in water approximately 3 meters in depth off the seaplane 

ramp on Cooper Island. Bait was dropped from the seaplane ramp and surface observations were 

made from the ramp. Due to the limited surface visibility, a snorkeler entered the water and used 

a video camera to record fish reactions to the placebo bait as it fell through the water column. 

This trial was replicated 5 times at this location.

2.7.3 Deep water trial

To assess the reaction of fish that may not frequent shallow water areas to bait pellets, placebo 

bait drop trials were conducted off of the ripple wharf on Cooper Island. The depth was 

approximately 10 m, and contained larger fish species such as sharks, snapper, and giant trevally. 

Bait was dropped by observers standing on the ripple wharf, and fish-bait interactions were 

recorded on video by a snorkeler. This trial was replicated 6 times at this location. 

2.7.4 Bait on the flats

To determine the reaction of intertidal organisms that may encounter a bait pellet on the sand 

flats inside the lagoon, 3 video stations were installed during low tide. 5 placebo bait pellets 

were placed on the sand in the presence of fiddler crabs (Uca sp.), Bristle-thighed Curlews, and 

Pacific Golden Plovers. Each set of five pellets was monitored by video for 2 hours.

Subsequently, the video stations were removed and all leftover placebo pellets were removed.

2.8 Egg Predation

2.8.1 Egg predation monitoring

Rats are known to prey on the eggs of ground- and tree-nesting seabirds (Jones et al. 2006, Jones 

et al. 2008), and are assumed to contribute to seabird egg and chick mortality at Palmyra Atoll. 

Attempts to capture egg predation by rats on film were conducted using chicken eggs. Eggs 
23

were removed from the refrigerator an hour prior to the trial, allowing the egg to reach the 

ambient temperature. At night, an egg was placed on the ground outside the Sooty Tern colony. 

The egg was dimly lit with a headlamp and monitored for two hours by a video camera (Figure 

8). 

Figure 8: Daytime trial of egg video monitoring near the range marker in the 

Sooty Tern Colony. 

In the event that the illumination of the egg was a deterrent for foraging rats, several trials were 

also conducted with an infrared camera and without lighting.

2.9 Toxicant concentrations in the bait products used in this study: brodifacoum in 25W 

and diphacinone in D50

The concentration of a toxicant individual bait pellets can vary. 25W and D50 were sampled to 

determine: 1) the variation of toxicant concentrations found bait pellets, and 2) the mean

concentration of toxicant for a small sample of pellets for each bait product. A bucket of bait for 

each product was haphazardly sampled by extracting 10 similar-mass bait pellets (± 0.3g). Each 

pellet was analyzed for toxicant concentration at the California Animal Health and Food Safety 

laboratory at the University of California, Davis. 

2.10 Coconut palms (C. nucifera) that overhang mean high-tide line

2.10.1 C. nucifera canopy description

In the event of an aerial broadcast, certain areas of the atoll would be baited by hand to prevent 

bait drift into the marine environment. To reduce the chance that bait drift will occur, aerial 

baiting operations will not target vegetation that overhangs the high-tide line. There are multiple 
24

locations around the atoll where coconut palms extend over the water; the crowns of such palms 

(Figure 9) need to be baited by hand.

Figure 9: C. nucifera on the ocean-facing side of Cooper Island (North 

Beach area) that extend over the high tide line. 

2.10.2 Overhanging palm crown estimation

To estimate the number of coconut palms that extend over the high tide line, we walked a 

measured section of shoreline, and counted each coconut palm overhanging the high tide line. 

The section of shoreline walked was tracked with a hand-held GPS, which provided a 

measurement of the length of shoreline sampled and the subsequent calculation of the number of 

overhanging palms in a given length of shoreline. Nine counts were conducted on the following 

islands: Cooper, Strawn, Holei, Papala, and Engineer. 

2.11 Bristle-thighed Curlew Capture

2.11.1 Capture method

This study field-tested a method for capturing curlews. Curlews were slowly herded towards a 

noose carpet placed on North beach, North Road, or the runway. The noose carpet consisted of a 

1 m x 5 m strip of astro-turf with hundreds of mono-filament nooses stitched in (Figure10). 

Curlews that walked across the carpet would become entangled in one or more of the nooses. 

Preparations were made to band all captured Curlews prior to release. 
25

Figure 10: The noose carpet stretched across North Road on Cooper 

Island in an area where curlews are frequently observed. Hundreds of 

monofilament nooses (20 lb test) are incorporated into the carpet.

3 ANALYSIS:

Statistical analysis was conducted in Minitab® 16 statistical software. We used an alpha level of 

.05 for all statistical tests. The quantitative analysis of toxicant residue in the soil samples did 

not always yield a reportable concentration. When the concentration of toxicant was below the 

stated reporting limit it was reported as “trace”, indicating that the analyte was detected but the 

concentration was between the reporting limit and zero. The reporting limit is the lowest 

routinely quantified concentration of an analyte in a sample. In soil samples, the reporting limit 

for brodifacoum was 0.2 ppm, and the reporting limit for diphacinone was 2.0 ppm. In crab

excrement samples, the reporting limit for brodifacoum was 0.2 ppm, and the reporting limit for 

diphacinone was 5 ppm. In “trace” instances, we assigned a value of 1⁄2 the reporting (detection) 

limit to the samples, as it would be inappropriate to analyze these results as zero concentration 

values. The difference in reporting limits is due to the difference in sensitivity of the 

instruments used to detect diphacinone and brodifacoum. 

A one way ANOVA was conducted to compare the concentrations of brodifacoum and 

diphacinone in soil over four temporal exposure periods 

A one-way ANOVA test with Tukey‟s pairwise comparisons was conducted to look for 

differences in the concentration of brodifacoum residue in crab excrement between the four 

exposure periods. A one-way ANOVA was used to look for differences in the concentrations of 

diphacinone in crab excrement for the 4 exposure periods. A two-sample t-test was used to 

determine if the number bait pellets from one product were preferentially consumed over the 

other, and to determine if, on average, crabs consumed different amounts of 25W and D50.
26

One-way ANOVA tests were conducted to look for differences in the amounts of three types of 

crab excrement consumed by cockroaches and hermit crabs. 

A two-sample t-test was conducted to determine if the amount (grams) of 25W consumed during 

rat palatability trials differed from the amount of D50 consumed. 

A one-way ANOVA test with Tukey‟s pairwise comparisons was conducted to look for 

differences in the time to consumption for 25W compared to the three other food items it was 

tested against. A one-way ANOVA test with Tukey‟s pairwise comparisons was also conducted 

to determine differences in the time to consumption for D50 in comparison to the same three 

food items.

4 RESULTS

4.1 Toxicant Residue in Soil

Bait pellets were removed from soil plots seven days after placement, with the exception of the 

two-day plots in which pellets were removed two days after placement. Visual estimates were 

made of the percent remaining of each pellet. In some instances, pellets remained intact and 

were simply removed by a gloved hand. All intact pellets or portions of pellets were removed at 

the allotted time: two days or seven days post placement. Pellet condition did not vary among 

study site replicates, but did vary between study sites (Table 3).

Disintegrated D50 Pellet

Cooper Island 

Disintegrated 25W Pellet

Cooper Island

Figure 11: Disintegration of bait pellets from Cooper Island plots, potentially due to ants, precipitation and 

weathering. D50 pellets (left) disintegrated more quickly and more frequently than 25W pellets (right).
27

The soil plots with the longest exposure period were installed on April 8th, 2010 and proceeded 

to run for 50 consecutive days. The total amount of precipitation during that period was 1,477 

mm; rainfall was an almost daily occurrence (Figure 12). The average daily maximum 

temperature was 29.1°C and fell to an average daily minimum of 25.1°C. 

4/12/10 4/19/10 4/26/10 5/3/10 5/10/10 5/17/10 5/24/10 

Precipitation (mm)

0

20

40

60

80

100

120

140 (mm) 

Monthly Average

Figure 12: Plot of daily rainfall at Palmyra Atoll measured each 

morning at 7:30am. The dashed line represents the monthly average 

precipitation (28.96 mm).

Table 3: Description of bait pellets remaining 2, 7, 28, 36, and 50 days after placement. Bait pellets that were not 

intact but had crumbs or other visible evidence remaining were classified as disintegrated. (-) indicates nonapplicable at that location.

Sample Day Cooper Island (Sandy Soil) Lost Island (Organic Soil)

25 W D50 25W D50

Day 2 Intact Disintegrated Intact Disintegrated

Day 7 (7day plots) Gone Gone Intact Gone

Day 7 (28 day plots) Gone Gone Intact Disintegrated

Day 7 (36 day plots) Gone Gone - -

Day 7 (50 day plots) - - Gone Gone

Low concentrations of rodenticide active ingredients were found in sandy and organic soil 

regardless of exposure period. We found no difference in brodifacoum concentration in sandy 

soil between exposure periods (DF=3 F=1.59 P= 0.26). Diphacinone was not detected in sandy 

soil samples, regardless of exposure period. We found no difference between exposure periods 

for brodifacoum concentration (DF= 3 F= 0.33 P=0.80), or diphacinone concentration (DF= 3 F= 

2.67 P= 0.11) in organic soil. 

Out of 48 samples (not including controls), only two contained a concentration of toxicant that 

was high enough to quantify. The rest of the samples yielded a zero value (toxicant not detected) 

or a „trace‟ value (toxicant detected but < MLOD) (Figure 13). 
28

Day

0 10 20 30 40 50 60

Toxicant Concentration (ppm)

0.0

0.2

0.4

0.6

0.8

1.0

Brodifcaoum in Sandy Soil

Diphacinone in Sandy Soil

Brodifacoum in Organic Soil

Diphacinone in Organic Soil

Figure 13: Mean concentration of brodifacoum (N=3 per day) and 

diphacinone (N=3 per day) found in surface samples of sandy soil and

organic humus soil over four exposure periods. Samples were taken directly 

beneath bait pellets (or remains of pellets) on day 2 and day 7. Samples 

taken on days 28, 36, and 50 were taken directly beneath where a pellet had 

rested for 7 days. 

4.2 Toxicant Residue in Crab Excrement 

The mean concentration of toxicant within crab excrement varied by exposure period for both 

analytes. Toxicants were most concentrated within crab excrement during the first two sampling 

periods. Both brodifacoum and diphacinone were actively consumed during these periods, until 

the bait products were removed from crab diets on day 7. A reduction in the toxicant 

concentration was observed between day 6 and day 10 (Table 4, Figure 14).

Table 4: Mean concentration of toxicant (ppm) within excrement samples from crabs 

that consumed 25W or D50 bait pellets ad lib for 7 days.

Analyte Day 2 concentration ± (1SD) Day 6 Day 10 Day 23

Brodifacoum (ppm) 2.8 (1.2) 2.6 (1.3) 1.0 (0.7) 0.25 (0.3)

Diphacinone (ppm) 8.4 (2.9) 8.9 (8.4) 2.5 (0) 2.5 (0)

4.2.1 25W in crab excrement

There was a significant effect of toxicant concentration at the p <0.05 level for the 4 exposure 

periods (DF=3 F = 8.10, P = 0.002). Post hoc comparisons using the Tukey HSD test indicated 

that the mean score of day 2 (M= 2.87 SD=1.28) and day 6 (M=2.64 SD=1.39) were 

significantly different from day 23 (M= 0.30 SD=0.30). However, day 10 (M= 1.06 SD=0.74) 

did not differ significantly from day 2, 6, or 23. 
29

4.2.2 D50 in crab excrement

One diphacinone value for day 6 was unusually higher than the rest, and was likely due to human 

error in removing the toxicant from the crab or the holding bucket. The outlying value was 

excluded from the analysis. There was a significant effect of the toxicant concentration at the p 

<0.05 level for the 4 exposure periods (DF=3 F = 3.67 P = 0.033), suggesting that diphacinone 

concentrations in crab excrement changed over time.

Sample Day

0 10 20 30 40 50 60

Toxicant Concentration (ppm)

0

5

10

15

20

Brodifacoum - excrement

Diphacinone - excrement

Brodifacoum - crab tissue

Figure 14: Comparison of the concentration (ppm) of brodifacoum in 

crab excrement and tissue over time to the concentration (ppm) of 

diphacinone in crab excrement. The concentration of brodifacoum in 

crab tissue was determined by the National Wildlife Research Center 

Analytical Lab (USDA-APHIS 2006) after a trial broadcast eradication in 

2005.

Crabs consumed rodenticide until day 7, and subsequently fed on natural 

food items. Positive “trace” results were included as 1⁄2 the reporting 

limit (0.1 for brodifacoum and 2.5 for diphacinone). 

4.3 Toxicant Residue in Crab Tissue

No brodifacoum residue was detected in hermit crab tissue samples from Whippoorwill Island 

five years after the trial broadcast eradication conducted in 2005. Quality control data reported 

recoveries that ranged from 93.8% to 99.8%. 
30

4.4 Crab Excrement Coprophagia

4.4.1 C. carnifex excrement consumption by cockroaches and hermit crabs

After an 8 hour exposure period to C. carnifex excrement containing 25W, D50, or no toxicant, 

cockroaches consumed at least 20% of each excrement type. There was no significant effect of 

excrement type on percent consumed by cockroaches at the p <0.05 level (DF=2 F = 0.72, P = 

0.492), which suggests that cockroaches do not exhibit a preference for crab excrement that 

comes from crabs who have recently consumed bait, or a preference for excrement that comes 

from crabs who have consumed D50 or 25W. 

Coenobita perlatus consumed more C. carnifex excrement than did cockroaches. On average, C. 

perlatus consumed 94% of 25W excrement, 98% of D50 excrement, and 77% of natural 

excrement, while cockroaches consumed, on average, 43% of 25W excrement, 21% of D50 

excrement, and 36% of natural excrement (Figure 15). 

Excrement Type

25W D50 Natural

% Complete Consumption

0

20

40

60

80

100

Hermit Crab

Cockroach

Figure 15: Hermit crab and cockroach consumption of three 

types of C. carnifex excrement.

Hermit crab consumption of the three crab excrement types differed significantly (DF=2 F = 5.41, P 

= 0.005). Post hoc comparisons using the Tukey HSD test indicated that the mean percent 

consumption of 25W excrement (M= 0.93 SD=0.24) and D50 excrement (M=0.95 SD=0.20) were 

significantly different from natural excrement (M= 0.77 SD=0.42). However, the percent

consumption of 25W excrement did not differ significantly from percent consumption of D50 

excrement after hermit crab consumption. 
31

4.5 Consumption of Bait Pellets by C. Carnifex

4.5.1 Daily consumption of bait pellets by C. carnifex

C. carnifex were divided into two treatment groups and offered either 25W or D50 pellets. The 

mean weight (±1 SD) of crabs in the 25W group 340.2g ± 80.1 was similar to that of crabs in the 

D50 group 338.8 ± 78.5. 

The amount of bait consumed varied among individual crabs. C. carnifex offered 25W pellets 

consumed 1.55 g to 21.7 g over a 24 hour period. C. carnifex offered D50 consumed 1.02 g to 

15.3 g over a 24 hour period. Despite individual variance, the mean number of pellets consumed 

and the mean total weight of pellets consumed remained similar for both treatment groups (Table 

8). We found no significant difference between the number of 25W pellets or the number of D50 

pellets consumed within a 24 hour period t(37)=-0.97 p= 0.339. On average, C. carnifex

consumed 2.5-3% of their body weight during the bait product feeding trials. We found no 

significant between-group difference in the amount (g) of bait consumed when compared to the 

weight (g) of the study crabs for t(37)= -0.21, p = 0.837.

Table 5: C. carnifex consumption of 25W and D50 pellets per 24 hour exposure period.

Bait Mean # of Mean Wt Mean %

Product Pellets Consumed

± (1SD)

Consumed (g) Body Wt Consumed

25W 6.8 (3.5) 10.5 (5.4) 3.0% (0.01)

D50 7.9 (3.8) 8.1 (3.8) 2.5% (0.01)

4.6 Bait Palatability

4.6.1 Rat palatability

Palatability trials were run on 68 rats. Rat weight ranged between 54 g to 212 g with a mean of 

145 g (SD 37.1). Coconut was the item fully consumed first, regardless of treatment group. 

Coconut was completely consumed by 83% of rats in the 25W group and by 88% of rats in the 

D50 group. 25W pellets were consumed in entirety by 53% of rats in that study group, while 

D50 pellets were eaten by 51% of rats in that study group. Meristem was fully consumed by 

57% of rats in the 25W group, and 68% of rats in the D50 group. Pandanus was consumed by 

37% of rats in the 25W group, and by 54% of rats in the D50 group. The amount (g) each food 

item consumed in each trial varied by study group and food item (Table 6). 

Table 6. Rattus rattus consumption of 4 food items in each trial, established by rank in order of preference and mean 

% consumed. 

Food Item Consumption Rank Mean % Consumed Std. Dev (%)

25W Trials

Coconut Endosperm 1 89.0 0.29

25W 2 60.5 0.45

Coconut Meristem 3 59.3 0.47

Pandanus 4 55.1 0.44

D50 Trials

Coconut Endosperm 1 86.0 0.34

Coconut Meristem 2 70.1 0.44
32

Pandanus 3 69.1 0.43

D50 4 54.5 0.46

Neither bait product was significantly more palatable than the other. Both 25W and D50 were 

consumed by rats in the presence of other natural food items. Results indicate no significant 

difference in percent consumed for 25W or for D50 t(65)= -0.47, p = 0.641.

Time to full consumption varied among food items and between treatment groups. Of the items 

that were completely consumed during the trial, coconut was consumed the quickest (Table 7).

Table 7. Mean time to consumption of items that were consumed in entirety (excludes items untouched or only 

tasted by rats).

Food Item # of rats that 

consumed item

Mean Time to 

Consumption (sec)

Maximum Time to 

Consumption (sec)

Minimum Time to

Consumption (sec)

25W Trials

Coconut Endosperm 26 1614 6127 226

Coconut Meristem 18 2304 5449 83

25W 15 2908 4964 232

Pandanus 12 2712 5744 151

D50 Trials

Coconut Endosperm 29 1458 4269 221

Coconut Meristem 21 2339 6310 458

D50 17 3019 6970 309

Pandanus 17 3382 5458 710

From initial bite until full consumption, the mean time for rats in the 25W group to consume 1g 

of coconut was 27 minutes, while rats in the D50 group averaged 24 minutes. There was no 

significant difference in the mean time for rat consumption of 1 g of 25W or D50; each averaged

49-50 minutes respectively. Similarly, rats consumed meristem in 37-38 minutes on average, 

regardless of treatment group. Rats in the 25W group consumed Pandanus in 45 minutes, while 

rats in the D50 group fully consumed it in 56 minutes. 

Although there was no difference in mean time to consumption of either bait product, results 

varied among treatments. Within the D50 treatment group, the consumption time of the four food 

items differed significantly (DF = 3 F = 5.51, P = 0.002) (Figure 16). Post hoc comparisons 

using the Tukey HSD test indicated that the mean time to consumption for coconut (M= 1458 

SD= 1219) differed significantly from D50 (M= 3019 SD= 2852) and Pandanus (M= 3382 SD= 

1593). Consumption time of coconut meristem was not significantly different from other food 

items. 
33

Coconut Meristem D50 Pandanus

Time to Consumption (seconds)

0

1000

2000

3000

4000

A

AB

B

B

Figure 16: Comparison of mean time to consumption in seconds for four food items (1g each) offered to rats 

participating in D50 trials. Mean values that do not share a letter are significantly different.

No significant difference in time to consumption was found among food items within the 25W 

treatment group (DF = 3, F= 2.47, P = 0.070) (Figure 17).

Coconut Meristem 25W Pandanus

Time to Consumption (seconds)

0

1000

2000

3000

4000

A

A

A

A

Figure 17: Comparison of mean time to consumption in seconds for four food items (1g each) offered to rats 

participating in 25W trials. The mean values all share a letter, indicating that they are not significantly different.

4.6.2 Crab palatability

Adult C. carnifex and C. rotundum (N=34) were collected for bait palatability trials. Pandanus

and solid coconut endosperm were the most palatable items for both species (Table 8). The two 
34

bait products, 25W and D50 were also frequently consumed, and on average were more than 

50% consumed after the 4 hour exposure period (Table 8). 

Table 8: Cardisoma consumption of 4 food items in each trial, established by rank in order of preference and mean 

% consumed. 

Food Item Consumption Rank Mean % Consumed Std. Dev

25W Trials

Pandanus 1 77.8 0.41

Coconut Endosperm 2 73.5 0.42

25 W 3 58.8 0.50

Coconut Meristem 4 31.9 0.45

D50 Trials

Pandanus 1 76.4 0.38

Coconut Endosperm 2 72.8 0.42

D50 3 53.4 0.50

Coconut Meristem 4 49.5 0.49

Neither bait product was found to be significantly more palatable than the other in comparison to 

natural food items. Results indicate no significant difference in percent consumed for 25W or 

for D50 t (31) = -0.31, p = 0.761.

4.7 Live Trapping and Genetic Sampling

The recommended genetic sampling of Palmyra Atoll (Ross 2009) calls for the collection of 477 

samples from different individuals trapped throughout the atoll. The sampling scheme allows for 

the assessment of the allele frequencies for each of Palmyra‟s landmasses and provides a 

sampling pool that can be used to determine the allele frequency of the whole atoll. The trapping 

effort conducted concurrently with the studies described in this report resulted in the completion 

of 3 landmasses and partial completion of 9 others (Table 9). A total of 156 genetic samples 

were obtained.

Table 9: Number of rat genetic samples obtained, grouped by landmass.

Landmass # Location # Required # of Rats Trapped % Complete

1 Cooper 50 54 100%

2 Quail 22 5 23%

3 Whippoorwill 26 12 46%

4 Eastern 50 4 8%

5 Portsmouth 11 6 63%

6 Barren 50 9 16%

7 Southern Complex 50 9 18%

8 Home 24 1 4%

9 Sand 50 26 52%

13 North-South Causeway 49 11 22%

14 Lost 6 7 100%

15 Fern 7 9 100%

R. rattus genetic samples were stored for genetic diagnostic analysis at EcogeneTM, Landcare 

Research Ltd. in New Zealand.
35

4.8 Bait Pellet Consumption by Fish

4.8.1 Fate of bait pellets

The reaction of fish to individual bait pellets falling through the shallow water column varied. 

During the first 3 trials, fish showed no interest in the bait pellets. Subsequent trials observed

Black-spot sergeant (Abudefduf sordidus), Stripe-belly puffer (Aronthron hispidus), and 

Camouflage grouper (Epinephelus polyphekadion) mouthing and consuming pellets (Table 10). 

Bait pellets dropped into the mid-water column were quickly consumed by Bohar (Lutjanus 

bohar). Black tail snapper (Lutjanus fulvus) also consumed bait pellets as they continued to sink. 

In 10m of water, both snapper and surgeonfish were observed grabbing bait pellets as the pellets 

sank, though complete consumption could not be confirmed due to limited visibility. 

Table 10: Interactions of species observed in Palmyra Lagoon during bait application trials. Location of

observations (S) shallow water, (M) mid-water, and (D) deep-water are indicated in parenthesis. 

Scientific Name Common Name Consumed Bait Mouthed Bait

Abudefduf septemfasciatus Seven Stripe Damselfish - -

Abudefduf sordidus Black-spot Sergeant Yes (S) Yes (S)

Acanthurus nigracans White-cheek Surgeonfish - -

Acanthurus triostegus Convict Tang - -

Arothron hispidus Stripe Belly Puffer Yes (S) Yes (S)

Caranx ignobilis Giant Trevally (Ulua) - -

Carcharhinus melanopterus Black-tip Reef Shark - -

Chaetodon auriga Thread-fin Butterflyfish - -

Chaetodon lunula Raccoon Butterflyfish - -

Ellochelon vaigiensis Squaretail Mullet - -

Epinephelus polyphekadion Camouflage Grouper Yes (S) Yes (S)

Lutjanus bohar Bohar Yes (M) Yes (M)

Lutjanus fulvus Black-tail Snapper Yes (M) Yes (M)

Lutjanus monostigma One-spot Snapper - -

Manta birostris Manta Ray - -

Moolgarda engeli Kanda Mullet - -

Mulloidichthys flavolineatus Yellow-Lined Goatfish - -

Pseudobalistes flavimarginatus Peach Faced Triggerfish - -

Stegastes nigracans Dusky Farmerfish - Yes (D)

Thalassoma lunare Moon Wrasse - -

4.8.2 Intertidal fate of bait pellets

There was no observed interaction between any organism (fiddler crab or shorebird) and the bait 

pellets placed on the tidal flats. 
36

4.9 Egg Predation

Eight unsuccessful attempts were made to video rat predation of chicken eggs. Analysis of the 

video footage showed that hermit crabs were unable to carry or break into the egg. Rats were not 

seen in the footage.

After several video trials without rat detection, two chicken eggs were placed on the ground, one 

near camp on Cooper Island, and the other at the Sooty Tern colony near Strawn Island. These 

eggs were checked daily. The egg on Cooper remained untouched for four days. On the fourth 

day, a small hole was poked into the shell, and the egg was subsequently devoured by hermit 

crabs. The egg on Strawn Island remained in place and intact for five days, after which it 

disappeared.

4.10 Toxicant Concentrations in the Bait Products

The average mass of the sampled 25W pellets (n = 10) was 2.73g ± 0.3g, and the concentration 

of brodifacoum in each pellet ranged from 30.2 ppm to 14.8 ppm, with a mean value of 21.4 ppm

(SD 63). The average mass of sampled D50 pellets (n = 10) was 1.04 g ± 0.15 g, and 

concentration of diphacinone in each pellet ranged from 16.7 ppm to 11.4 ppm, with a mean 

value of 14 ppm (SD 1.7). Alpo spike recovery rates measured during the analysis of the bait 

pellets were 84% and 94% for brodifacoum, and 83% and 85% for diphacinone.

4.11 C. nucifera Canopy Counts

C. nucifera are abundant at Palmyra Atoll, estimated at 119,425 individuals (0-30 m in height) 

(Wegmann 2009). The number of coconut palms that lean over the high tide line varies by 

location, with more occurring on lagoon-facing shores than on ocean-facing shores (Table 11).

Table 11: Average and maximum number of C. nucifera palms with 100% canopy coverage extending beyond the 

high tide line of the shore, inside and outside the lagoon.

Atoll Location Average # of Overhanging Palms/km (± 1 SD) Maximum # of Overhanging Palms/km

Lagoon 166 ± 47 215

Ocean 109 ± 55 187

4.12 Bristle-thighed Curlew Capture

4.12.1 Runway

Several attempts were made to capture Bristle-thighed Curlews on the runway. A 15 ft x 3 ft 

noose carpet was laid flat on the runway within 50 m of 5 curlews. A team of 3 people formed a 

line and slowly walked toward the curlews, herding them in the direction of the noose carpet. 

Curlews were able to be herded 20-30ft, after which they spooked and took flight, landing on the 

other side of the carpet. The team circled back and attempted to herd the curlews back toward 

the carpet several times, all unsuccessfully. 
37

4.12.2 Forest

The noose carpet was laid flat across North Road in the presence of curlews. The team retreated 

to the beach and approached the noose carpet from both sides, making several attempts to 

encounter a curlew between the team and the noose carpet, however no curlews were 

encountered.

4.12.3 North Beach

The noose carpet was laid flat on the beach at low tide near the water line and extended 15ft up 

the beach, no successful curlew captures were made.

5 DISCUSSION

The results of the three primary studies (toxicant residue in soil, toxicant residue in crab 

excrement, and bait palatability) are presented below. 

5.1 Rodenticide Environmental Fate

For the rodenticide bait products 25W (containing brodifacoum) and D50 (containing 

diphacinone), will prolonged contact between a bait pellet and soil result in detectible 

concentrations of the given rodenticide in the soil environment, and if so, will the 

concentration decrease over time?

Analysis of the top 2 cm of soil upon which bait pellets sat for seven days yielded extremely low 

concentrations of brodifacoum or diphacinone (less than 1 ppm) at all sampling periods. This 

suggests that toxicant residue from the two bait products is not readily incorporated into or 

retained in either of Palmyra‟s two primary soil types – sandy and humus. The consistently low 

detection of either toxicant supports other studies (Ogilvie et al. 1997) that suggest that 

anticoagulant rodenticide bait pellets used in broadcast eradications do not transfer high 

concentrations of toxicants to soil, even in warm, moist conditions where the breakdown of bait 

pellets is rapid. 

It must be noted that the measured concentration of brodifacoum and especially diphacinone in 

sampled 25W and D50 pellets, respectively, was lower than what is reported on the product 

labels. For 25W, the lapel states that pellets contain 25 ppm brodifacoum; we measured just over 

21 ppm. For D50, the lapel specifies 50 ppm of diphacinone, and we found the mean 

concentration to be 14 ppm. While the difference between the label-specified and measured 

concentration of brodifacoum in 25W pellets is probably too small to influence the results of this 

study, the low concentration of diphacinone measured in the sampled D50 pellets (36 ppm below 

what is stipulated on the product label) could have caused an underestimation of amount of 

diphacinone that transfers to the soil from D50 pellets. 

The degradation of the bait pellets may have been expedited by greater than usual rainfall (1,477

mm) during the course of the study. The 25W bait is manufactured with sorbitol, a sugar alcohol 
38

that prevents pellet fragmentation in moist environments; 25W pellets retained shape and 

cohesiveness longer than did D50 pellets. Despite moisture resistant properties, 25W pellets at 

the Cooper island site were completely consumed by small invertebrates (ants) and/or 

disintegrated between day 2 and day 7. On Lost Island, 25W pellets remained mostly intact for 7 

days. The difference between degradation rates for the two study sites could be due to 

differences in invertebrate (ant) populations; though, this was not measured. All samples yielded 

very low concentrations of either toxicant in topsoil despite (or because of) abundant rainfall, 

insect consumption, and pellet degradation during the study period. 

5.2 Toxicity of Rodenticide Residue in Crabs

For the rodenticide bait products 25W and D50, will consumption of bait pellets result in 

detectible concentrations of the given rodenticide in the excrement of crabs, and if so, will 

the concentration of toxicant in the excrement decrease over time?

While land crabs do not appear to be adversely affected by anticoagulant rodenticide compounds 

(Pain et al. 2000, Buckelew et al. 2005), crab competition with rodents for broadcast bait pellets 

constitutes a significant operational problem. Brodifacoum residue is found in crab tissue for up 

to 56 days after a bait broadcast, and the concentration of brodifacoum decreases from 1.8 ppm 

to 0.4 ppm in 10 days (USDA-APHIS 2006); however, until this study we did not know if crabs 

redistributed rodenticide through defecation, and if so at what concentration. 

The difference between the concentration of brodifacoum in the bait pellets that the crabs fed on 

in the 2006 study cited above (25 ppm), and the concentration of brodifacoum in crab tissue (1.8 

– 0.01 ppm) suggests that some quantity of the toxicant is either evacuated through defecation or 

metabolized by the crab. Crabs feed almost continuously and gastric evacuation (defecation) 

occurs within 12 hours of feeding (Nordhaus et al. 2006). Cardisomta guanhumi maintains a 

mean gut clearance rate of 6.6 hrs, with larger crabs (>170 g) having a longer gut passage time 

(9.4 hrs) and smaller crabs (<130 g) passing excrement over shorter time periods (3.5 hrs)

(Wolcott and Wolcott 1987). The rapid gut turnover rate indicates that the gastric residence time 

of items consumed by Cardisoma spp. is not likely to exceed 10 hours.

Brodifacoum and diphacinone concentrations within crab excrement did not increase from day 2 

to day 6, suggesting that as crabs continued to feed on bait pellets during the first week, there 

was no cumulative increase of toxicant concentrations in crab excrement. Consumption of bait 

pellets and nothing else for seven days resulted in an evacuation of brodifacoum and diphacinone 

at concentrations that were much lower than found in the bait pellets. Once the bait pellets were 

removed from the crabs‟ diet, the toxicant concentration in crab excrement dropped to near-trace

levels within three days. Two weeks after crabs stopped consuming bait pellets, the 

concentration of brodifacoum and diphacinone in crab excrement was below the mean level of 

detection.

This study did not attempt to identify or understand the process by which crabs metabolize or 

breakdown rodenticides, and no direct discussion of this could be found in the available 

literature. It is possible that neither brodifacoum nor diphacinone are metabolized by crabs, and 

that amount of toxicant that is not absorbed into the crabs‟ tissue is evacuated through 
39

defecation. If this is the case, the results from this study suggest that crabs reduce the risk of 

non-target organisms coming to harm through secondary and tertiary exposure to the applied 

rodenticide by reducing the concentration at which the rodenticide will be available. Because 

crab excrement contains detectable concentrations of brodifacoum or diphacinone for less than 

three days post consumption of rodenticide bait, it is unlikely that crab excrement is a significant 

vector of active rodenticide ingredients to secondary consumers.

Secondary consumers (hermit crabs and cockroaches) were observed eating C. carnifex

excrement. Cockroaches ate crab excrement infrequently (less than 50% of the time), and did 

not prefer crab excrement produced through the consumption of 25W or D50 excrement

produced by crabs on a „natural‟ diet. Consumption of crab excrement by other crabs is an 

environmental benefit, as there will be less bait-contaminated excrement available to other 

consumers that could potentially be harmed by exposure to the rodenticide. Because crabs 

readily consume bait pellets, and because the concentrations of brodifacoum or diphacinone in 

crab excrement are greatly diluted, crabs can to some extent bioremediate (or “biomitigate”) the 

risk of exposure to rodenticides for “at risk” non-target species. 

5.3 Rodenticide Palatability for Rats and Crabs

When exposed to one bait product (25W or D50) in the presence of natural food items, 

which product is most palatable to rats within a short (2 hour) exposure window 

(palatability is measured by first physical contact, taste, amount consumed, and time to 

entire consumption of bait pellet)? 

Palmyra presents a complex eradication environment where high levels of productivity are 

maintained by the aseasonal warm, moist climate and prodigious rainfall. At Palmyra, rats 

consume a wide array of food items, most of which are available year-round. Ideally, the 

rodenticide bait used to eradicate rats from Palmyra would be highly palatable, and would be 

preferred over available, natural food items.

This study found that both 25W and D50 bait are highly palatable in comparison to three 

commonly available food items: coconut endosperm (meat), the meristematic tissue of young 

coconut palms, and the fleshy mesocarp of Pandanus fruit. Coconut endosperm was the only 

food item that scored higher (1st to be consumed, shortest time to consumption) than did the bait 

products in the palatability trials. This suggests that coconut palm reduction may be beneficial to 

the eradication by reducing the amount of naturally available food that could distract rats from 

consuming bait pellets.
40

6 APPENDIX: RAW DATA

6.1 Toxicant Residue in Soil Results

Soil sample Location Analyte Sample day Result (ppm); trace values = 1⁄2 of the reporting limit*

C-5-9-10-2-25W-1 Cooper 25W 2 0.1

C-5-9-10-2-25W-2 Cooper 25W 2 0.2

C-5-9-10-2-25W-3 Cooper 25W 2 0.1

C-5-14-10-7-25W-1 Cooper 25W 7 0.8

C-5-14-10-7-25W-2 Cooper 25W 7 0.1

C-5-14-10-7-25W-3 Cooper 25W 7 0.1

C-5-28-10-28-25W-1 Cooper 25W 28 0.1

C-5-28-10-28-25W-2 Cooper 25W 28 0

C-5-28-10-28-25W-3 Cooper 25W 28 0

C-5-28-10-36-25W-1 Cooper 25W 36 0

C-5-28-10-36-25W-2 Cooper 25W 36 0

C-5-28-10-36-25W-3 Cooper 25W 36 0

L-5-9-10-2-25W-1 Lost 25W 2 0.1

L-5-9-10-2-25W-2 Lost 25W 2 0.1

L-5-9-10-2-25W-3 Lost 25W 2 0

L-5-14-10-7-25W-1 Lost 25W 7 0.1

L-5-14-10-7-25W-2 Lost 25W 7 0.1

L-5-14-10-7-25W-3 Lost 25W 7 0.1

L-5-28-10-28-25W-1 Lost 25W 28 0

L-5-28-10-28-25W-2 Lost 25W 28 0.1

L-5-28-10-28-25W-3 Lost 25W 28 0.1

L-5-28-10-50-25W-1 Lost 25W 50 0

L-5-28-10-50-25W-2 Lost 25W 50 0.1

L-5-28-10-50-25W-3 Lost 25W 50 0.1

C-5-9-10-2-D50-1 Cooper D50 2 0

C-5-9-10-2-D50-2 Cooper D50 2 0
41

Soil sample Location Analyte Sample day Result (ppm); trace values = 1⁄2 of the reporting limit*

C-5-9-10-2-D50-3 Cooper D50 2 0

C-5-14-10-7-D50-1 Cooper D50 7 0

C-5-14-10-7-D50-2 Cooper D50 7 0

C-5-14-10-7-D50-3 Cooper D50 7 0

C-5-28-10-28-D50-1 Cooper D50 28 0

C-5-28-10-28-D50-2 Cooper D50 28 0

C-5-28-10-28-D50-3 Cooper D50 28 0

C-5-28-10-36-D50-1 Cooper D50 36 0

C-5-28-10-36-D50-2 Cooper D50 36 0

C-5-28-10-36-D50-3 Cooper D50 36 0

L-5-9-10-2-D50-1 Lost D50 2 0

L-5-9-10-2-D50-2 Lost D50 2 1

L-5-9-10-2-D50-3 Lost D50 2 1

L-5-14-10-7-D50-1 Lost D50 7 0

L-5-14-10-7-D50-2 Lost D50 7 1

L-5-14-10-7-D50-3 Lost D50 7 1

L-5-28-10-28-D50-1 Lost D50 28 0

L-5-28-10-28-D50-2 Lost D50 28 0

L-5-28-10-28-D50-3 Lost D50 28 0

L-5-28-10-50-D50-1 Lost D50 50 0

L-5-28-10-50-D50-2 Lost D50 50 0

L-5-28-10-50-D50-3 Lost D50 50 0

L-5-9-10-2-Control Lost Control 2 0

C-5-9-10-2-Control Cooper Control 2 0

L-5-14-10-7-Control Lost Control 7 0

C-5-14-10-7-Control Cooper Control 7 0

L-5-28-10-28+36/50-Control Lost Control 28 + 36 0

C-5-28-10-28+36/50-Control Cooper Control 28 + 50 0

* Reporting limit for brodifacoum = 0.02 ppm. Reporting limit for diphacinone = 2 ppm.
42

6.2 Toxicant Residue in Crab Excrement

Excrement sample Analyte Exposure Time (days) Result (ppm); trace values = 1⁄2 of the reporting limit*

C-1p-2-25W 25W 2 2.2

C-3p-2-25W 25W 2 3.8

C-5p-2-25W 25W 2 4.1

C-7p-2-25W 25W 2 1.4

C-1p-6-25W 25W 6 4.3

C-3p-6-25W 25W 6 1.1

C-5p-6-25W 25W 6 3

C-7AB-6-25W 25W 6 3.5

C-7CD-6-25W 25W 6 1.3

C-1B-10-25W 25W 10 0.1

C-3D-10-25W 25W 10 0.5

C-3p-10-25W 25W 10 1.8

C-5p-10-25W 25W 10 1.7

C-7p-10-25W 25W 10 1.2

C-1B-23-25W 25W 23 0.1

C-3A-23-25W 25W 23 0.1

C-3p-23-25W 25W 23 0.3

C-5A-23-25W 25W 23 0.3

C-5B-23-25W 25W 23 0.9

C-7p-23-25W 25W 23 0.1

C-2p-2-D50 D50 2 5.3

C-4p-2-D50 D50 2 6.8

C-6p-2-D50 D50 2 9.5

C-8p-2-D50 D50 2 12

C-2p-6-D50 D50 6 2.5

C-4p-6-D50 D50 6 2.5

C-4C-6-D50 D50 6 2.5
43

Excrement sample Analyte Exposure Time (days) Result (ppm); trace values = 1⁄2 of the reporting limit*

C-6p-6-D50 D50 6 9.7

C-6B-6-D50 D50 6 2.5

C-8p-6-D50 D50 6 15

C-8C-6-D50 D50 6 11

C-2p-10-D50 D50 10 2.5

C-4p-10-D50 D50 10 2.5

C-6p-10-D50 D50 10 2.5

C-8A-10-D50 D50 10 2.5

C-8p-10-D50 D50 10 2.5

C-2p-23-D50 D50 23 2.5

C-4p-23-D50 D50 23 2.5

C-6p-23-D50 D50 23 2.5

C-8D-23-D50 D50 23 2.5

C-8p-23-D50 D50 23 2.5

* Reporting limit for brodifacoum = 0.02 ppm. Reporting limit for diphacinone = 2 ppm.
44

6.3 Toxicant Concentration in Bait Pellets: 25W and D50

6.3.1 25W - brodifacoum

Standard Curve

Standard ID Std (ng)

Peak 

Response 

(AU)

Respons

e Factor 

(AU/ng)

Avg 

Sens 

(AU/ng) S.D. %RSD r

2

051110A\AN000005 3 6207.266 2069.089

2168.20

0 94.53 4.36 0.9978

051110A\AN000006 1 2427.250 2427.250

051110A\AN000007 0.2 435.269 2176.345

051110A\AN000008 0.5 1089.340 2178.680

051110A\AN000013 0.5 1088.880 2177.760

051110A\AN000025 0.5 1064.535 2129.070

051110A\AN000041 0.5 1096.325 2192.650

051110A\AN000058 1 2152.673 2152.673

051110A\AN000059 0.2 425.797 2128.985

051110A\AN000060 0.5 1066.683 2133.366

051110A\AN000061 3 6252.981 2084.327

QC Data

Sample ID

Peak 

response 

(AU)

Calculate

d Amount 

(ng)*

Sample 

Amount 

inj (mg)

Spike 

Level 

(ppm)

ppm 

found

Adjusted 

ppm 

found

Recover

y (%)

reagent blank ND Nd NA ND

Alpo Check ND ND 1.0 NA ND

Alpo Spike1 420.121 0.168 1.0 0.2 0.168 0.168 84

Alpo Spike2 461.869 0.188 1.0 0.2 0.188 0.188 94

y = 2064.8x + 72.773

R2 = 0.9978

0

1000

2000

3000

4000

5000

6000

7000

0 0.5 1 1.5 2 2.5 3 3.5

Peak Area Units (AU)

Adj Amt (ng)

Standard Curve
45

Sample Data

Sample ID

Peak 

Response 

(AU)

Calculated 

Amount * 

(ng)

Sample 

Amount 

inj (mg) 

ppm 

found Average Comments

D1004428-01.0011 My60 bait 1292.163 0.591 0.02 29.53 30.3

D1004428-01.0011 My60 bait 3275.397 1.551 0.05 31.02

D1004428-01.0012 My60 bait 674.482 0.291 0.02 14.57 15.3

D1004428-01.0012 My60 bait 1730.983 0.803 0.05 16.06

D1004428-01.0013 My60 bait 703.926 0.306 0.02 15.28 15.9

D1004428-01.0013 My60 bait 1774.931 0.824 0.05 16.49

D1004428-01.0014 My60 bait 1241.878 0.566 0.02 28.31 28.8

D1004428-01.0014 My60 bait 3088.068 1.460 0.05 29.21

D1004428-01.0015 My60 bait 967.108 0.433 0.02 21.66 22.3

D1004428-01.0015 My60 bait 2441.785 1.147 0.05 22.95

D1004428-01.0016 My60 bait 1243.642 0.567 0.02 28.35 29.1

D1004428-01.0016 My60 bait 3163.777 1.497 0.05 29.94

D1004428-01.0017 My60 bait 997.655 0.448 0.02 22.40

D1004428-01.0017 My60 bait 2437.501 1.145 0.05 22.90 23.2

D1004428-01.0017 dup 1025.459 0.461 0.02 23.07

D1004428-01.0017 dup 2607.258 1.227 0.05 24.55

D1004428-01.0018 My60 bait 669.595 0.289 0.02 14.45 15.2

D1004428-01.0018 My60 bait 1715.479 0.796 0.05 15.91

D1004428-01.0019 My60 bait 652.256 0.281 0.02 14.03 14.7

D1004428-01.0019 My60 bait 1662.74 0.770 0.05 15.40

D1004428-01.0020 My60 bait 1920.431 0.895 0.05 17.90 17.8

* Note: Calculations based on Standard Curve
46

6.3.2 D50 - diphacinone

Standard Curve

Standard ID Std (ng)

Peak 

Response 

(AU)

Response 

Factor 

(AU/ng)

Avg 

Sens 

(AU/ng) S.D. %RSD r

2

051110A\AN000006 25 63.726 2.549 2.686 0.06 2.33 0.9966

051110A\AN000007 5 13.617 2.723

051110A\AN000008 12.5 33.601 2.688

051110A\AN000013 12.5 32.984 2.639

051110A\AN000025 12.5 33.687 2.695

051110A\AN000041 12.5 33.418 2.673

051110A\AN000058 25 67.746 2.710

051110A\AN000059 5 13.731 2.746

051110A\AN000060 12.5 34.418 2.753

QC Data

Sample ID

Peak 

response 

(AU)

Calculated 

Amount 

(ng)*

Sample 

Amount 

inj (mg)

Spike 

Level 

(ppm)

ppm 

found

Adjusted 

ppm 

found

Recovery 

(%)

reagent blank ND ND NA ND

Alpo Check ND ND 1.0 NA ND

Alpo Spike1 11.746 4.148 1.0 5.0 4.148 4.148 83

Alpo Spike2 11.990 4.242 1.0 5.0 4.242 4.242 85

y = 2.5974x + 0.9718

R2 = 0.9966

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30

Peak Area Units (AU)

Adj Amt (ng)

Standard Curve
47

Sample Data

Sample ID

Peak 

Response 

(AU)

Calculated 

Amount * 

(ng)

Sample 

Amount 

inj (mg) 

ppm 

found Comments

D1004428-01.0001 My60 bait 15.775 5.699 0.50 11.4

D1004428-01.0002 My60 bait 21.217 7.794 0.50 15.6

D1004428-01.0003 My60 bait 18.858 6.886 0.50 13.8

D1004428-01.0004 My60 bait 18.982 6.934 0.50 13.9

D1004428-01.0005 My60 bait 17.135 6.223 0.50 12.4

D1004428-01.0006 My60 bait 16.955 6.154 0.50 12.3

D1004428-01.0007 My60 bait 18.343 6.688 0.50 13.4

D1004428-01.0008 My60 bait 20.387 7.475 0.50 14.9

D1004428-01.0009 My60 bait 22.669 8.353 0.50 16.7

D1004428-01.0010 My60 bait 20.724 7.605 0.50 15.2

* Note: Calculations based on Standard Curve
48

6.4 Bait Product Labels

6.4.1 25W
49

6.4.2 D50
50

7 REFERENCES

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genetics: case study of ship rat eradication in Ste. Anne Archipelago. Conservation Biology 

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field-based assessment at Palmyra Atoll Island Conservation, Santa Cruz, CA.

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Hawaii.

Eason, C. T., L. Milne, M. Potts, G. Morriss, G. R. G. Wright, and O. R. W. Sutherland. 1999. Secondary 

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Fisher, P., C. O’Connor, G. Wright, and C. T. Eason. 2003. Persistence of four anticoagulant rodenticides 

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Conservation, Wellington, NZ.

Fisher, P., C. O’Connor, G. Wright, and C. T. Eason. 2004. Anticoagulant residues in rats and secondary 

non-target risk. DOC Science Internal Series 188 188, New Zealand Department of Conservation, 

Wellington, NZ.

Fisher, P. M. 2009. Residual Concentrations and Persistance of the Anticoagulant Rodenticides 

Brodifacoum and Diphacinone in Fauna. Lincoln University, Lincoln.

Grant, G. S., T. N. Pettit, and G. C. Whittow. 1981. Rat Predation on Bonin Petrel Eggs on Midway Atoll. 

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Howald, G., A. Samaniago, S. Buckelew, P. McClelland, B. Keitt, A. Wegmann, W. C. Pitt, D. S. Vice, E. 

Campbell, K. Swift, and S. Barclay. 2004. Palmyra Atoll rat eradication assessment trip report, 

August 2004. Island Conservation, Santa Cruz, California.

Jackson, W. B. 1972. Biological and behavioural studies of rodents as a basis for control. Bulletin of the 

World Health Organisation 47:281-286.

Jones, H. P., B. R. Tershy, E. S. Zavaleta, D. A. Croll, B. S. Keitt, M. E. Finkelstein, and G. R. Howald. 2008. 

Severity of the effects of invasive rats on seabirds: a global review. Conservation Biology 22:16-

26.

Jones, H. P., R. Williamhenry III, G. R. Howald, B. R. Tershy, and D. A. Croll. 2006. Predation of artificial 

Xantus’s murrelet (Synthliboramphus hypoleucus scrippsi) nests before and after black rat 

(Rattus rattus) eradication. Environmental Conservation:1-6.

Lund, M. 1984. Resistance to the second-generation anticoagulent rodenticides. Pages 89-94 in Eleventh 

Vertebrate Pest Conference. University of California, Davis, University of California, Davis, 

California.

New Zealand Department of Conservation. 2000. Assessement of Environmental effects for Norway Rat 

(Rattus norvegicus) eradication in the Campbell Island National Nature Reserve Operational 

Area.
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Nordhaus, I., M. Wolff, and K. Diele. 2006. Litter processing and population food intake of the mangrove 

crab Ucides cordatus in a high intertidal forest in northern Brazil. Estuarine, Coastal and Shelf 

Science 67:239-250.

Oosterhout, C., W. Hutchinson, D. Willds, and P. Shipley. 2004. MICROCHECKER: software for identifying 

and correcting genotyping errors in microsatellite data. Molecular Ecology Notes 4:535-538.

Pain, D. J., M. D. Brooke, J. K. Finnie, and A. Jackson. 2000. Effects of brodifacoum on the land crabs of 

Ascension Island. Journal of Wildlife Management 64:380-387.

Peakall, R. and P. E. Smouse. 2006. GENALEX 6: genetic analysis in Excel. Population genetic software for 

teaching and research. Molecular Ecology Notes 6:288-295.

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Walker, J. Oldenburg, and C. R. Muller. 2005. The genetic basis of resistance to anticoagulants in 

rodents. Genetics 170:1839-1847.

Pierce, R., N. Anterea, U. Anterea, D. Broome, L. Cooper, H. Edmonds, F. Muckle, B. Nagle, G. Oakes, M. 

Thorsen, and G. Wragg. 2008. Operational work undertaken to eradicate rats and rabbits in the 

Phoenix islands, Republic of Kiribait, May‐June 2008.

Pritchard, J. K., M. Stephens, and P. Donnelly. 2000. Inference of Population Structure Using Multilocus 

Genotype Data. Genetics 155:945-959.

Raymond, M. and F. Rousset. 1995. GENEPOP (version1.2): population genetics software for exact tests 

and ecumenicism. Journal of Heredity 86:248-249.

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2009. Novel mutations in the VKORC1 gene of wild rats and mice – a response to 50 years of 

selection pressure by warfarin? . BMC Genetics 10.

USDA-APHIS. 2006. Analysis of brodifacoum in crab tissues. USDA-APHIS National Wildlife Research 

Center.

Wegmann, A., J. Helm, A. Samaniego, W. Smith, B. Jacobs, D. Drake, J. Smith, M. McKown, A. Henry, S. 

Hathaway, and R. Fisher. 2008. Palmyra Atoll rat eradication: biomarker validation of an 

effective bait application rate, 19 June to 5 July, 2008. Island Conservation, Santa Cruz, 

California.

Wegmann, A. S. 2009. Limitations to tree seedling recruitment at Palmyra Atoll. University of Hawaii, 

Honolulu.

Weir, B. S. and C. C. Cockerham. 1984. Estimating F-statistics for the analysis of population structure. 

Evolution 38:1358-1370.

Wolcott, D. L. and T. G. Wolcott. 1987. Nitrogen Limitation in the Herbivorous Land Crab Cardisoma 

guanhumi. Physiological Zoology 60:262-268.

Young, H. S., D. J. McCauley, R. B. Dunbar, and R. Dirzo. 2010. Plants cause ecosystem nutrient depletion 

via the interruption of bird-derived spatial subsidies. Proceedings of the National Academy of 

Sciences of the United States of America 107:2072-2077.
1

APPENDIX G

PALMYRA ATOLL RAINFOREST RESTORATION PROJECT: RAT 

GENETIC SAMPLING, DETECTION METHOD TESTING, AND 

CANOPY BAIT TESTING
2
*Correspondence: Alex Wegmann, Island Conservation, 100 Shaffer Rd. Santa Cruz, CA, 95060 USA / +1831.359.4787 / 

alex.wegmann@islandconservation.org / www.islandconservation.org

PALMYRA ATOLL RAINFOREST RESTORATION PROJECT: RAT GENETIC SAMPLING, 

DETECTION METHOD TESTING, AND CANOPY BAIT TESTING 

September- October 2010

Island Conservation: Aurora Alifano, Alex Wegmann*, Madeleine Pott, Erik Oberg
2

1. Executive Summary

Primary Objectives:

 Collect genetic samples from the Rattus rattus population at Palmyra Atoll.

 Measure the baseline detection success of three devices: chew blocks, tracking 

tunnels, and live traps.

 Construct and deploy bait stations in a variety of environments to measure 

variability in bait removal rates, crab interference, structural integrity of the 

stations, and overall attractiveness to rats.

 Determine the degradation rates and effects of weathering and decay for different 

types of canopy bait designs and measure the persistence of canopy baits in the 

crowns of coconut palms.

 Photograph rats consuming pellets and canopy baits in the crowns of coconut 

palms; determine which type of bola material is preferred by rats.

 Field-test three canopy bait launching devices and establish the situations in 

which each performs best.

 Monitor placebo bait pellets in the marine environment to determine degradation 

rates of the matrix under varying conditions

 Quantify the degradation rate of rat carcasses in areas with high shorebird 

densities, and photograph any avian species interested in consuming the carcasses.

A team of three personnel (Aurora Alifano, Erik Oberg, and Madeleine Pott) conducted several 

studies at Palmyra Atoll from September 22, 2010 until Oct. 17th, 2010. Rodent live trapping 

confirmed that rats were present on all landmasses visited, with the exception of Dudley Island 

where no rats were detected. Captured rats (304 total) ranged from juvenile to adult (24 g to 227

g), indicating that breeding had recently taken place. Chew blocks were slightly more successful 

at detecting rats in comparison to live traps, but needed frequent replacement, as the hard candy 

interior lasted less than 24 hours due to rats, crabs, ants, and rain. Tracking tunnels were 

unsuccessful at detecting rat presence until coconut bait was placed inside as an added incentive. 

Bait station performance, pellet removal rate, and station resistance to crab-related interference

varied widely depending on the location of the station. 

Surgitube, a tubular gauze dressing, was the most effective material for canopy bait (“bola”) 

construction. It was easy for rats to chew through, retained pellets during high-velocity launches, 

and prevented inside bait from molding. Three launching devices were tested, the HyperDog 

slingshot, the Big Shot pole-mounted sling shot, and the Squall 250 air cannon. Each device 

performed best within specific conditions, and it was evident that a combination of methods may 

be required for fast and accurate canopy baiting. Once in place, bolas were typically consumed 

within 24 hours.
3

Placebo bait pellets placed in the marine environment degraded completely within 48 hours, 

disappearing faster on the intertidal ocean-facing side of the atoll (within 24 hours). Rat 

carcasses placed in locations frequented by shorebirds and typified by low crab densities (North 

Beach and along the runway) degraded due to consumption and environmental decay within 72 

hours; carcass feeding by shorebirds was not observed in the images captured by motion sensing 

cameras.
4

Contents

2. Introduction...............................................................................................................................................5

2.1 Project Setting.....................................................................................................................................5

2.2 Project Background.............................................................................................................................5

3. Methods ....................................................................................................................................................6

3.1 Rat Trapping and Detection ................................................................................................................6

3.1.1 Live Trapping Rattus rattus.........................................................................................................6

3.1.2 Genetic Sampling.........................................................................................................................7

3.1.3 Chew Blocks................................................................................................................................7

3.1.4 Tracking Tunnels.........................................................................................................................8

3.2 Bait Stations........................................................................................................................................9

3.2.1 Bait Station Construction.............................................................................................................9

3.2.2. Bait Station Sites.......................................................................................................................10

3.3 Bait in the Marine Environment........................................................................................................10

3.3.1 Intertidal and Subtidal Trials within the Lagoon .......................................................................10

3.3.2 Intertidal and Subtidal, Outer-Lagoon Trials.............................................................................11

3.4 Bolas .................................................................................................................................................11

3.4.1 Bola Construction ......................................................................................................................11

3.4.2 Bola Launching..........................................................................................................................12

3.4.3 Bait Bola Degradation................................................................................................................13

3.4.4 Bait Bola Fate in Palm Canopy..................................................................................................14

3.4.5 Rat Carcass Degradation............................................................................................................15

4. Analysis ..................................................................................................................................................15

5. Results.....................................................................................................................................................15

5.2 Bait Stations......................................................................................................................................18

5.3 Marine Environment .........................................................................................................................19

5.4 Bola Launching and Fate ..................................................................................................................19

5.5 Rat Carcass Degradation...................................................................................................................22

6. Discussion...............................................................................................................................................22

8. References...............................................................................................................................................26
5

2. Introduction

2.1 Project Setting

Palmyra Atoll National Wildlife Refuge (Palmyra), at 6◦ N and 162◦ W in the Line Islands –

Central Pacific, is a globally important refuge for populations of numerous indigenous animals 

and plants. The U.S. Fish and Wildlife Service (FWS) and The Nature Conservancy (TNC) comanage Palmyra’s emergent land area, while the FWS retains sole jurisdiction over marine 

resources extending 12 nautical miles out from the atoll. Palmyra is the only fully (federally) 

protected moist tropical forest ecosystem in the Central Pacific, yet native biota are currently 

threatened by an introduced, invasive rodent – the black rat (Rattus rattus). Palmyra provides 

important breeding habitat for 10 seabird species; however, rat related egg and chick predation 

has possibly led to the extirpation of six additional species.

Palmyra consists of 250 ha of emergent land (fragmented into 25 islands), 14 of which were 

investigated during these studies. Rats were live-captured on the following islands: Ainsley, 

Barren, Bunker, Dudley, Eastern, Home, Leslie, North Fighter Strip, South Fighter Strip, NorthSouth Causeway, Portsmouth, Quail, Sand, South Complex, Whippoorwill. 

Strawn Is.

Cooper Is. Aviation Is.

Whippoorwill Is.

Eastern Is.

Sand Is. Home Is.

Leslie Is.

Barren Is.

South Is. Complex

Dudley Is.

Fighter Strips

Portsmouth Is.

Quail

NS Causeway

Figure 1: The independent landmasses of Palmyra Atoll that were targeted for 

genetic samples.

2.2 Project Background

R. rattus is the only species of rat currently present at Palmyra. Recent rat density estimates 

suggest that there could be as many as 139 rats/ha, resulting in a maximum population size of

32,000 rats across the atoll (Wegmann and Middleton 2008). In case of eradication failure, 

analysis of R. rattus DNA from the pre-eradication population was collected, and will allow the 
6

project Partnership to determine if individuals that re-populate Palmyra are missed animals from 

the target population(s) or from a post-eradication incursion. 

The use of rodenticide bait is not anticipated to negatively impact marine organisms. Given the 

non-polarity of brodifacoum molecules and the ionic strength of seawater, the solubility of 

brodifacoum is likely in the low parts per billion range (Pierce et al. 2008). An extreme case of 

20 tons of brodifacoum bait spilled into the ocean off New Zealand found that brodifacoum 

levels were not detectable within 36 hours after the spill (Pierce et al. 2008). New Zealand 

scientists estimated that during a normal helicopter aerial bait application, incidental bait 

discharge into the nearshore marine waters resulted in 0.0000006 mg/l, or about seven orders of 

magnitude below the level known to be lethal to bluegill sunfish (New Zealand Department of 

Conservation 2000). Although the low water solubility of the toxicant and measures taken 

during the aerial application to decreases the likelihood of bait drift into marine environment, the 

degradation rate of bait pellets in the lagoon and ocean-facing reef should be assessed. 

To minimize the amount of bait that lands in the marine environment during an aerial broadcast 

at Palmyra, bait will be applied using a directional deflector, several meters inside the mean 

high-tide line. Palm trees seeking light often overhang the shoreline; such palms represent 

potential rat habitat yet they will not be baited during the aerial broadcast. Overhanging palms 

would be treated by hand-canopy baiting (Wegmann et al. 2008). To determine the efficacy of 

various bait application methods, several launching devices were used to shoot various types of 

canopy baits (“bolas”) into overhanging palms. 

3. Methods

3.1 Rat Trapping and Detection

3.1.1 Live Trapping Rattus rattus

Trap lines were established along transects of varying lengths, trap placement was standardized 

using predetermined GPS points to space traps 25 meters apart. The length of each transect 

depended upon the length of each landmass and the number of samples required from each site. 

Hagaruma®live traps (with wire mesh bases) were systematically deployed at study sites 

throughout the atoll. Two methods of trapping were employed; some traps were placed on 

upside-down 20 liter plastic buckets on the ground to reduce crab interference, while other traps 

were nailed to tree trunks. On Sand Island and Eastern Island, an abundance of large coconut 

crabs required the more robust Tomahawk®traps secured to horizontal tree branches with 

bungee cords. Solid coconut endosperm coated with creamy peanut butter was used as bait for 

all rats. All traps were checked daily.
7

3.1.2 Genetic Sampling

A 2-3 cm section of each rat tail was collected using sterilized dissection shears and stored in a 

plastic screw-top vial containing a DNA preserving solution called DMSO Buffer. All rat tail 

samples were transported in the buffer solution containing the active ingredients dimethyl 

sulfoxide and ethylenediaminetetraacetic acid to preserve DNA integrity and shipped to 

EcogeneTM, a subsidiary of Landcare Research New Zealand Ltd., for storage and analysis. In 

the event of a post-eradication rat detection (and collection), Ecogene will genotype the preeradication Palmyra rat population by obtaining multilocus microsatellite genotypes from each 

sample using a set of 9 loci (Abdelkrim et al. 2007). Evidence for allelic drop-out, scoring error 

due to stutter, and presence and frequency of any null alleles will be assessed with MICROCHECKER (Oosterhout et al. 2004) using a Bonferroni adjusted 95% confidence interval and 

10,000 repetitions. Genetic diversity indices will be calculated using GenAlEx v 6.2 (Peakall 

and Smouse 2006) and tests for Hardy-Weinberg and linkage disequilibrium will be conducted 

using GENEPOP v 4.0 (Raymond and Rousset 1995). Pairwise FST parameters for each 

population pair will be estimated according to Weir and Cockerham (Weir and Cockerham 

1984). The data will then be analysed using the Bayesian clustering method implemented in 

STRUCTURE ver 2.3 (Pritchard et al. 2000) to provide another estimate of pairwise FST 

parameters and to determine the number of distinct genetic units (K) in the dataset. The same 

analysis will be applied to samples collected from any rats captured at Palmyra after the 

eradication operation.

3.1.3 Chew Blocks

Trapping is one way to detect the presence of rodents, but some rats may be trap-shy or may not 

encounter a trap. Other indicators of rat presence like chew blocks and tracking tunnels may be 

more appealing or less threatening than traps. Chew blocks consist of small (2 cm x 2 cm) 

square sections of corrugated plastic, filled at one end with a hard candy (peanut butter and 

melted sugar mixture). Chew blocks were nailed to a tree within 3 meters the associated trap. 

When chewed by a rat, rodent incisor marks were easy to spot (Figure 2). This method was then 

compared to the success of tracking tunnels to determine which method provides more consistent 

and accurate detection measures.
8

Figure 2: Chew blocks gnawed by rat incisors, indicating rat presence. The smooth 

edges of the block are untouched; the chewed sides were originally filled with hard 

candy.

3.1.4 Tracking Tunnels

Tracking tunnels were constructed from 3” PVC pipes cut into 25cm sections and secured to the 

lid of a bucket with cable ties. Each tube was lined with paper with a felt pad in the center that 

was then moistened with black ink mixed with peanut oil. The scent of peanut oil was intended 

to attract rats, which would then enter the tube, leaving paw prints behind on the paper as they 

exit. A small squirt of oil-based ink and a few ounces of oil stirred in a 20 ml sample vial 

provided the correct consistency of ink and oil for Palmyra’s humid climate. Tracking tunnels 

were deployed on various islands with Bushnell Trophy Cam motion sensing cameras to measure 

the efficacy of tunnels to detect rat presence.
9

Figure 3: Rat investigating a tracking tunnel on the North Fighter Strip.

To increase the attractiveness of each tracking tunnel, diced shavings of fresh coconut were later 

sprinkled onto the felt ink pad during some trials. 

3.2 Bait Stations

3.2.1 Bait Station Construction

To create bait stations that made bait accessible for rats but not crabs, a “T” design was 

employed using PVC and a T fitting. Most crabs were unable to climb the slick sides of the PVC, 

but rats easily leaped from the ground to the T fitting. Several pieces of thin wall 4” PVC pipe 

were cut to pre-determined lengths to vertically support the T fitting. Bait stations were 

constructed to a variety of heights from 6 1⁄2” to 10 1⁄2”, to compare the effect of station height on 

pellet removal.

Four bait stations were fitted with curved 4” PVC elbows to allow rats access and prevent rain 

from entering the station. The vertical portion of each station was filled with a bag of sand and a 

small plastic baffle disc was placed inside as a platform for the bait. The baffle was placed 

approximately 3⁄4” below the T fitting. When loaded with bait, the loaded baffle was slightly 

lower than the two PVC elbow entrances. The internal sand bag provided a weighted, solid base. 

Each bait station was anchored with cable ties to a 1 meter length of rebar pounded into the 

ground to keep the station upright. 
10

Sand Bag Base Stabilizer

Placebo Bait Pellets

Rebar Staked into Ground

Motion Sensing Camera

Rat Entrances (2)

Cable Ties

Figure 4: Bait station illustration.

3.2.2. Bait Station Sites

Bait stations were installed in variety of environments to test the attractiveness to rats and the 

ability of the station to deter crabs. Bait station designs were tested at North Beach (Cooper 

Island), Compost Pit (Cooper Island), Strawn Trail (Cooper Island), Sand Island, and the North 

Fighter Strip. Bait stations remained in place until all pellets were gone, with the exception of 

Sand Island. Within 24 hours of deployment on Sand Island, bait stations and motion sensing 

cameras suffered so much damage from coconut crabs that they were removed and not 

redeployed.

3.3 Bait in the Marine Environment

3.3.1 Intertidal and Subtidal Trials within the Lagoon

To track the degradation of pellets inside the lagoon, 3 pellets were placed inside a round PVC 

exclusion cages with a mesh lid. Water and marine fauna smaller than 1⁄2 cm flowed freely in 

and out, but larger benthic or pelagic consumers were excluded. Exclusion cages were placed 4 

meters apart at the same tidal height. Plastic stakes 20cm in length were pounded into the sand 

and cable ties were used to secure exclusion cages to the stakes (one cage per stake). Three 

placebo bait pellets were placed in each exclusion cage (Figure 5). Three exclusion cages were 

installed in the shallow lagoon in a location that always remains subtidal, and three plots were 

installed in locations that go dry at least once per day. Plots were monitored daily, and the 

presence, absence, and status of pellets inside the cages were assessed using a pellet degradation 

scale (Table 1). Plots were monitored daily as long as bait pellets or fragments remained 

detectable.
11

Table 1: Bait pellet degradation scale

Bait Pellet Degradation Scale Bait Pellet Condition

1 Bait hard, intact, whole

2 Bait hard, intact, partially gone

3 Bait soft, intact, whole

4 Bait soft, intact, partially gone

5 Bait mushy, disintegrated

6 Bait dry, disintegrated

7 Bait pellet gone

Figure 5: Placebo bait pellets inside the PVC exclusion cage with mesh top (yellow 

stake visible). 

3.3.2 Intertidal and Subtidal, Outer-Lagoon Trials

This experiment was set up identically to the inner-lagoon trials discussed above, but was 

installed on the ocean-facing side of the atoll where bait pellets were exposed not only to tidal 

forces, but also increased wave action. Six plots were installed (3 intertidal, 3 subtidal) and 

monitored daily. 

3.4 Bolas

3.4.1 Bola Construction

Several bola prototypes were created to investigate both the palatability to rats and length of time 

that the bait pellets within the bolas persisted in the crowns of coconut palms. The criteria for the 

design of the bola was that the material be biodegradable, easily chewed through by rats, weather 

resistant, and easily launched. Prototypes bola designs consisted of tea filter bags, cheesecloth, 

and two variations of Surgitube dressings, one thin version were pellets were lined up vertically 
12

in a “tootsie roll” shape, and a second tube of large diameter in which pellets were stuffed to 

create a ball shape (Figure 6).

Figure 6: Three examples of bait bolas: from top to bottom: Tea bag, Cheesecloth, 

Surgitube ball.

To ensure uniformity of bola weight across the four prototypes, 25g ± 0.5g of placebo bait pellets 

were measured on an EscaliTM 50 gram electronic balance (approximately 10-14 pellets) and 

sealed inside each bola liner described above. Two bags were joined by 1.5 ft of 100% cotton 

twine, resulting in each bola weighing a total of 50g. 

Each bait bola was relatively easy to make. Tea filter bags were the fastest since the required 

number of bait pellets could be dispensed directly into the bag and tied off directly with twine. 

Surgitube dressings were also easy to construct. After being cut to 8-10 cm lengths, one end was 

tied in a knot and bait was dispensed inside before tying off the other end with the twine. Cheese 

cloth bolas required more effort to manufacture. Squares (8 cm x 8 cm) of cheesecloth were cut, 

bait placed inside, and edges of the cloth were then wrapped upward and tied off with the twine. 

This required some coordination to keep the edges pinched off while attempting to tie a knot of 

twine around them.

3.4.2 Bola Launching 

Bolas were launched into the crowns of coconut palms using three methods, the Hyper Dog Ball 

Launcher, the Big Shot, and the Squall 250. The Hyper Dog Ball Launcher made by Hyper 

Products® was a high performance dog toy slingshot designed to shoot a tennis ball over 200 ft. 

It consisted of a durable, high-quality steel frame constructed with a rust-resistant baked-on 

coating and webbed pouch bound to surgical-grade elastic tubing. 
13

The Big Shot, distributed by Sherrill Tree®, is a sling-shot mounted on an 8 ft fiberglass round 

pole. It is designed to be used by one person to launch climbing and throw lines over 100 ft into 

tree canopies. 

The Squall 250 was an air cannon rented from Air Cannons Inc. The cannon was fitted with a 

pressure regulator that controls bursts of compressed air, designed to launch tee-shirts and other 

paraphernalia into crowds at distances of 10- 250 ft. The 20” barrel was made of 100% 

aluminum and the cannon weighs approximately ten pounds with a full (20 oz) air cartridge. The 

cartridge was rated to 1800 psi, and was filled from a SCUBA cylinder using a High Pressure 

Fill Station adapter purchased from WaveToGo Paintball. When filling by cascade from a 3000 

psi SCUBA cylinder to a 20 oz cartridge rated to 1800 psi, special care was taken to fill slowly 

and monitor the gauge to prevent over-pressurization.

All methods were tested on trees of varying heights. Palm canopy height was estimated with a

laser range-finder (Laser Tech Inc. Impulse, Model 200). The tallest palm in which bait bolas 

were successfully planted was 21.3 meters (~70 ft). Bolas were also launched into smaller palms 

ranging from 14.8 to 10.2 meters in height. 

3.4.3 Bait Bola Degradation

To determine the natural degradation rate of each bait bola prototype, bolas were placed in palm 

crowns and monitored for two weeks. To prevent consumption of bait bolas by rats or other 

opportunistic consumers, three exclusion cages (0.9 m x 0.9 m x 0.45 m) were constructed from 

1.3 cm wire mesh (19 gauge). Bolas were secured to the roof of one wire cage contained within 

another mesh cage (Figure 7). The four bola types were hung inside each cage and placed on the 

roof of the research lab facility to allow maximum weathering and minimum interference from 

rats and crabs. All cages were deployed on October 3st, 2010, and remained until October 14th

2010. Each day, each cage was opened and each bola was checked for number of pellets, pellet 

condition (using the pellet degradation scale), and bola integrity. 
14

Figure 7: Bait bola degradation cages, designed to exclude large consumers (rats and 

crabs).

3.4.4 Bait Bola Fate in Palm Canopy

Bolas were placed into the canopy of low hanging palms and monitored daily with motion 

sensing cameras for bola integrity, bait degradation, and consumer activity (Figure 8). 

Figure 8: Bolas (cheesecloth in foreground, and Surgitube in background) placed on 

fronds of a palm canopy
15

3.4.5 Rat Carcass Degradation

To monitor the degradation of the carcass, eight rats were euthanized and the carcasses were

tethered to a stake or cinderblock. Rat carcasses were placed on the runway and on North Beach 

because both locations are frequented by shorebirds, and both are typified by a low density of 

crabs. A measurement for the rate at which rat carcasses are consumed high-density crab habitat 

exists; here we are interested in measuring the carcass degradation rate in low-density crab 

habitats. Motion sensing cameras were installed to monitor each carcass, and visual inspections 

of the remains and any consumers were recorded daily.

4. Analysis

Data on rodent capture was used to generate an index of trapping success by calculating the 

following. 

Total trap nights (TTN) = # nights that traps were open x # of traps Adjusted trap nights (ATN) = 

TTN-(# number of traps sprung without a rat capture/2) Trapping success = Rats captured/ATN 

= capture per trap night (CTN). The same formula was applied to the detection of rat presence 

by chew blocks. One chew night was assigned to chew blocks that contained rat incisor marks, 

as well as chew blocks that were unchewed with bait remaining after 24 hours. One half chew 

night was assigned to instances when bait was gone from the block, or when the block itself was 

missing. As the samples were drawn independently from each other, a two-sample t-test was 

conducted in Minitab 16 to test the difference between the two population means (Chew success 

vs. Trap success) 

5. Results

5.1. Genetic Sampling

Over the course of a 20-day trapping period, a total of 304 rats were captured and sampled

(Table 2). The sex ratio of captured rats was evenly distributed, with 150 females and 154 males: 

however this ratio varied among islands. On small islands (<10,000 m

2

), more female rats were 

caught than male rats, with a mean ratio of 0.77 (N=3). 

Table 2: Total number of rats captured per island, with island size (m2), sex ratio of 

female to male, and the mean weight of female and male rats.

Island

Total 

captured

Island size 

(m2)

Sex ratio 

F/M

Female mean 

weight (g)

Male mean 

weight (g)

Ainsley 10 1290 0.80 148 149

Barren 17 54130 0.35 134 162

Bunker 3 1840 0.67 147 139

Eastern 46 126646 0.39 142 148

Home 23 16711 0.35 148 171
16

Island

Total 

captured

Island size 

(m2)

Sex ratio 

F/M

Female mean 

weight (g)

Male mean 

weight (g)

Leslie 14 10040 0.43 120 152

North Fighter Strip 41 71440 0.51 124 144

NS Causeway 34 35190 0.38 133 116

Portsmouth 7 7740 0.86 133 29

Quail 19 16332 0.68 137 145

Sand 27 81660 0.59 119 161

South Complex 43 591240 0.49 136 156

South Fighter Strip 9 93330 0.33 109 192

Whippoorwill 11 17470 0.82 142 143

Trap status was checked daily, and resulted in 1,178 trap nights during the sampling period. No 

activity, meaning that bait was untouched and the trap door was open, was the most frequent 

occurrence (Table 3). Rat capture was the second most frequent occurrence, indicating that the 

traps worked effectively to trap rats when rats entered. 

Table 3: Tally of each potential trap status over 1178 trap nights.

Trap Status Count

Bait Gone 150

Crab 54

Trap Destroyed 7

Rat Escape 7

No Activity 407

Rat Capture 304

Rat Recapture 67

Trip No Capture 181

Grand Total 1178

Rat response to release from capture indicated that the majority of rats remained on the ground 

while fleeing (Table 4). A small subset of rats elected to run up nearby trees. Of the 13 rats that 

escaped into a tree, nearly 85% were female rats, indicating a potential sex difference in this 

behavior. 

Table 4: Rat response (to flee on ground or up a tree) to release after capture and 

genetic sampling.

Release response # of observations Female Male

Ground 278 48.92% 51.08%

Tree 13 84.62% 15.38%
17

During the trapping effort, 645 chew blocks were deployed, spaced with every other trap (Table 

5). Only 8 blocks (1%) were found missing from their original position of deployment and not 

recovered. 

Table 5: Number of chew block nights and chew block success vs. number of live trap 

nights and live trap success among islands.

Island Chew nights Chew Success Trap nights Trap success

Ainsley 8 38% 23 61%

Barren 37.5 29% 74 27%

Bunker 18 31% 24.5 16%

Dudley 8.5 0% 23.5 13%

Eastern 53.5 66% 104.5 62%

Home 39.5 85% 57.5 49%

Leslie 22.5 84% 27.5 65%

North Fighter Strip 34 46% 77.5 55%

NS Causeway 68.5 56% 155.5 33%

Portsmouth 14.5 34% 23 35%

Quail 39 38% 79 29%

Sand 37 62% 65 49%

South Complex 82 62% 163.5 30%

South Fighter Strip 9.5 42% 25 40%

Whippoorwill 38.5 44% 86 13%

TOTAL 510.5 48% 1009 38%

Chew blocks detected rat presence with 10% more success than did the live traps. A two-sample 

t-test did not find a significant difference between success of chew blocks and success of traps to 

detect rat presence (T = 1.28, P = 0.214, DF=26).

Tracking tunnels were deployed at 5 locations within the atoll. Tunnels that only used peanut oil 

to attract rats resulted in less rat detections. Small diced pieces of coconut were placed inside the 

tunnel on the ink pad to increase the incentive for rats to enter the tunnels, and yielded variable 

detection rates among locations (Table 6). Tunnels that offered coconut bait on the ink pad 

increased the number of successful rat tracks by 48%.

Table 6: Number of tunnel nights and percent of tunnel success for 5 locations.

Island

Tunnel Nights Tunnel Success

no bait bait no bait bait

Barren 38.5 - 3% -

Cooper North Road - 8 - 38%

Home 3 3 0% 33%

NS Causeway - 15 - 60%

South Complex 23 - 0% -
18

Island

Tunnel Nights Tunnel Success

no bait bait no bait bait

Grand Total 64.5 26 2% 50%

Tracking tunnels were deployed on Cooper Island in combination with motion sensing cameras 

that recorded rats and crabs nearby and on the tunnels. Photographs revealed rats entering and 

exiting the tunnels, but also provided evidence of rats investigating the tunnels without entering 

or leaving behind evidence of their presence. Both rats and crabs were detected passing through 

the site without physically investigating tracking tunnels.

5.2 Bait Stations

Removal of bait pellets from bait stations was not uniform between locations. Bait stations were 

first deployed at North Beach on Cooper Island. All bait was removed overnight, with camera 

footage depicting intense rat activity immediately after sunset until 2300. Trials were replicated 

3 times at this location with varying number of pellets inside each bait station (n = 20, 35, 75). 

The stations were consistently emptied by rats each night. Bait disappeared swiftly on the North 

Fighter Strip, with only 3 pellets remaining (out of 80) after the first day of bait station 

deployment. Rat activity was recorded by the motion sensing cameras; rats entered and exited 

each station multiple times throughout the evening. Land crabs (Cardisoma sp.) were present in 

the images recorded by the cameras, but they did not seem interested in the stations. Bait station 

height (6-10 in) had no effect on the removal of pellets by rats.

Bait removal rates from three locations on Cooper Island were highly variable (Table 7). Large 

quantities of bait were removed overnight from North Beach, while a small quantity of bait 

lasted more than four days at the compost pit and on the trail to Strawn Island. Although rat 

density estimates for these exact locations are unknown, rats were present in images taken by

cameras at all locations. Despite the images of rats near the stations, rats were not frequently 

observed entering and exiting from stations. Rats on the Strawn Trail took four days to remove a

significant quantity of bait from the stations. Rats at the compost pit began to remove bait after 

48 hours of exposure to the stations.

Table 7: Average percent of bait pellets removed from bait stations over a four day 

period. Each bait station (n=4) originally contained 20 pellets.

Location Day 1 Day 2 Day 3 Day 4 Rats Present

Cooper: Compost Pit 10.0% 44.4% 52.5% 75.0% Yes

North Fighter Strip 96.3% - - - Yes

Cooper: North Beach 100.0% - - - Yes

Sand Island 50.0% - - - Yes

Cooper: Strawn Trail 0.0% 0.0% 1.3% 53.8% Yes
19

Bait stations were deployed on Sand Island for 24 hours. Within 24 hours, all bait stations and 

some motion cameras were knocked over or otherwise compromised by coconut crabs. The 

destruction of equipment prevented further investigation of bait removal rates on this island, and 

no photographs of animal interactions with bait stations were captured.

5.3 Marine Environment

Placebo bait pellets degraded within two days in the marine environment (Table 8). Bait pellets 

in areas that went dry at low tide broke down more quickly than those that remained constantly

submerged. Pellets in the intertidal plots were exposed to longer periods of wave activity and 

sediment movement, in addition to potential consumption by subtidal and intertidal organisms. 

Pellets on the outer, ocean-facing edge of the atoll broke down more quickly than pellets within 

the lagoon. After one day in salt-water, pellets typically became soft and in some cases enlarged, 

obtaining a marshmallow-like consistency. After two days, pellets were mucilaginous in 

consistency, and were impossible to pick up as a unit. Any remains of a pellet after three days of 

exposure either adhered to the sandy substrate or was swept away with the tide.

Table 8: Measured degradation of placebo 25W bait pellets placed in the marine 

environment. Three plots were established at each location, and each plot consisted 

of a cage containing three pellets. “Pellets remaining” is the ratio of cages that 

contained pellets on the given day. Pellet condition was assessed for all remaining 

pellets on each sample day and follows this degradation scale: 1 = Bait pellet is hard, 

intact, whole; 2 = Bait pellet is hard, intact, partially gone; 3 = Bait pellet is soft, 

intact, whole; 4 = Bait pellet is soft, intact, partially gone; 5 = Bait pellet is mushy, 

disintegrated; 6 = Bait pellet is dry, disintegrated; 7 = Bait pellet is gone. The pellet 

condition value presented below is the mean value for all plots at the given location 

on the given day.

Location Day 1 Day 2 Day 3 Day 4

Pellets 

remaining

Pellet 

condition

Pellets 

remaining

Pellet 

condition

Pellets 

remaining

Pellet 

condition

Pellets 

remaining

Pellet 

condition

Lagoon Intertidal 3/12 3 2/12 3 1/12 5 0/12 7

Lagoon Subtidal 5/12 6 3/12 5 2/12 5 0/12 7

Ocean Intertidal 0/6 7 - - - - - -

Ocean Subtidal 3/3 4 3/3 4 2/3 5 0/3 7

5.4 Bola Launching and Fate

Bolas were launched into palm crowns with varying success. Successful bola placement

depended on the bola material, the launching device, and the operator. Making contact between 

the bola and the palm tree was successful 67% of the time, however, getting the bola to wrap and 

stick inside the palm crown was an added challenge (Table 9).
20

Table 9: Overall success of all bolas types launched using all devices.

Hit Palm Wrapped Remained Intact After Wrapping

67.5% 34.9% 61.0%

The success of each shot depended on the height of the tree and the device used to launch the 

bola. The air cannon consistently launched bait into tall palms (max 21.8 m in height) with 

greater accuracy than any other method (Table 10). The pole-mounted slingshot performed best 

when launching bait into palms between 10 and 20m high. The HyperDog slingshot varied in 

accuracy and performance depending on the skill and physical strength of the user, but was the 

most efficient of the three devices.

Table 10: Percent of successful canopy baiting attempts of three launching devices; 

the values presented here represent a pooling of all bola types.

Launching Device

# of 

Trials 

Hit 

Tree

Bola in 

canopy

Bola

Intact

10-15m 

Height

16-21m 

Height

Avg. Time to 

Shoot (sec)

Air Cannon 28 71.4% 35.7% 75.0% 64.7% 81.8% 49

HyperDog 25 60.0% 40.0% 56.0% 58.8% 62.5% 22

Pole-Mounted 30 70.0% 30.0% 58.6% 81.3% 57.1% 32

The air cannon was the most time consuming device to use, requiring the manipulation of the 

safety switch, pressure valve, careful loading of a towel used as wadding, careful packaging of 

the bola, and the subsequent location and collection of the towel after each shot. Overall, each 

launching device took less than 1 minute to complete one shot.

The material used for bola construction had a large impact on the success of bola application. 

Tea bags were the easiest bola to construct, but were far too thin to hold pellets when launched at 

high velocity. Tea bags remained intact less than half of the time, and frequently ripped or 

separated from the twine upon initial release, spilling bait during the launch (Table 11). 

Table 11: Percent success of bola integrity and percent success of type to remain in 

the palm canopy.

Bola Type Bola Intact Wrapped in Tree

Surgitube Ball 69.0% 40.5%

Cheese Cloth 68.8% 31.3%

Tea Filter Bag 41.7% 28.0%

Cheesecloth bolas were time consuming to construct. The process required cutting squares, 

wrapping up pellets inside, and knotting the twine around the cloth. Knots frequently slipped off 

the cheesecloth, causing the pellets to separate from the twine mid-flight. The stress of the 

launch occasionally caused the cheesecloth to separate and the weave to loosen, creating large 

holes that pellets fell out of. 
21

Surgitube bolas were easy to construct- the tubular gauze was cut to a predetermined length, a 

knot was tied in one end, and pellets were loaded from the other side. The tight weave of the 

Surgitube held pellets in place during launching and wrapping in the canopy. Failures were 

frequently attributed to a failed knot, as the Surgitube itself rarely sustained holes or damage to 

the sides. This bola type was the most structurally sound, and ranked highest in its ability to land 

in the palm canopy (Table 11).

Bait bola degradation was monitored for 12 days. All bolas remained intact during the first 

week, and bait pellets were hard and intact - a “1” on the degradation scale. On day 9, light rain 

fell (0.6 inches) and pellets inside the bolas were wet, soft, and intact. By day 10, fruit flies were 

observed in the cages, circling around the bolas. The tea bag material began to show 

discoloration on day 10 and the discoloration progressed until day 12, when the bolas were 

removed and inspected. Bait pellets inside the teabags had retained moisture and were moldy 

(Figure 9). 

Figure 9: Moldy bait pellets after 12 days inside a tea bag bola.

Pellets in other bolas types softened during the rain, but due to the ventilated nature of gauze 

fabrics, hardened again in the sun. These pellets were significantly harder than they had been 

originally, taking on a “petrified” appearance, impossible to indent with a fingernail. By the end 

of the experiment, 5 of the original 12 bolas were consumed or compromised by rats that had 

gotten into the cages. Rats entered the cage and pulled the bolas up by the string, consuming 

pellets through the bars of the inside cage. The first bola was attacked on day 6, the rest were 

attacked on the last day of the experiment (day 12).

Bolas placed in palm crowns were monitored with motion sensing cameras to determine if rats 

would chew bolas in the canopy. Of 29 bolas deployed, 82% disappeared within the first 24 
22

hours. All of the bolas disappeared within 48 hours of deployment. When a camera detected rat 

presence, the bola always disappeared the first night, suggesting that bolas that remained 

untouched the first night may not have been encountered by a rat. No preference by rats for a 

certain bola type was detected. Shredded remains of bola material found at the site was evidence 

that rats can and will chew into all bola types to get to the bait pellets.

5.5 Rat Carcass Degradation

At North Beach, rat carcasses degraded rapidly when exposed to the elements. Within 24 hours, 

the carcasses were torn open by crabs, and swarmed by ants. After 72 hours the carcasses were

hollowed, leaving only fur and bones around an empty body cavity. Motion sensing cameras 

detected coconut crabs, hermit crabs, and burrowing marine crabs consuming the carcasses, in 

addition to ants and other insect consumers. Several bird species were present within 4 ft of the 

carcass including Bristle-thighed Curlews, Pacific Golden Plovers, Wandering Tattlers, and Red 

Footed Boobies. Birds were photographed in the vicinity of the carcass, but were not observed 

feeding on or around the carcasses. 

6. Discussion

These studies were conducted at Palmyra during an unusual 3 month drought. The total rainfall 

during the study period was only 3.9 inches, with an average high temperature of 87° F. The 

drought may have negatively impacted the rat population on islands where water sources are 

naturally scarce. For example, the rat population on Barren Island appeared depressed compared 

to previous trapping efforts in that location. Barren Island is primarily coral rubble, and lacks the 

soil or lush forest characteristic of other islets at Palmyra. A long trap line averaged only 1 rat 

capture per day during the first week of trapping while using coconut and peanut butter as bait. 

During the last week, small plastic cups were secured to the cage interior and filled with water in 

an attempt to attract more rats. The first night water was offered in traps, 7 rats were caught on 

Barren Island. Without the typical rainfall that maintains Palmyra’s moist environment, rats may 

alter their foraging patterns and as a result might be harder to detect.

All rats that survived capture were released post-assessment and observed until they disappeared 

from view. Most rats (91%) fled on the ground. Rarely, a rat would run directly up a tree next to 

the trap that they were caught in. The majority of rats that climbed a tree immediately after 

being released were female (85%). It is possible that these females were actively tending nests 

in the canopy at the time of capture, resulting in behavior that differed from that of the captured 

male rats.

Chew blocks detected rat presence with 10% more success than standard live traps; however, 

whether chew blocks are more likely to detect rats than traps during periods of low rat density 

remains to be determined. Rat detection methods for post-eradication monitoring will likely use 

both traps and chew blocks, with the consideration that both are time-consuming methods and 

require daily checks/replacement. To ensure that tracking tunnels work effectively as a detection 
23

device, a more attractive bait than peanut oil must be used. Diced coconut was effective but was 

temporary. More effort could be spent to develop a long lasting attractant that can be placed in 

the tunnels, allowing for an extended time period between checks.

Bait pellet removal from bait stations was high in some locations. At North Beach, time stamped 

photographs show rats approaching the station within 30 seconds of the departure of the 

installment team. Rats at this location were photographed entering bait stations, carrying pellets 

in their mouth as they exited, and running up a nearby tree multiple times in an evening, 

suggesting that they were heavily utilizing the canopy habitat (Figure 10). 

1 2

3 4

Figure 10: Rat activity in a bait station at North Beach:1. Rats approached the 

station. 2. Rat investigated the station. 3. Rat jumped from the ground into the 

entrance. 4. Rat exited the station carrying a bait pellet in its mouth.

Bait stations could be improved by 1) developing a secure anchoring system that cannot be 

knocked over by coconut crabs, and 2) increasing the height of the bait station to deter 

Cardisoma and hermit crabs. Hermit crabs that could not climb the station sides were observed 

climbing Pandanus and other low hanging trees, then dropping onto the top of the bait station. If 

installed, care must be taken to clear all surrounding foliage from around the bait stations.

Placebo bait pellets degraded quickly in the marine environment, with most pellets breaking 

down within 24 hours of exposure. After more than one day of softening, the pellet matrix 

became so mucilaginous that the remains were impossible to pick up intact. If pellets are not 

immediately consumed by marine organisms, they are not likely to remain intact for more than

two days in the lagoon or ocean-facing near-shore marine environments.

Of the materials tested, Surgitube gauze was the best material for with which to construct bolas. 

It was the strongest and most durable bola bag, it was easily chewed through by rats, and it did 

not appear to deter rats from accessing the pellets contained within. The 100% cotton fabric 
24

weave allowed maximum aeration and deterred mold from accumulating on the pellets. 

Launching of the bait bolas was more complex, each method was both valuable yet limited in 

very different ways (Table 12). 

Table 12: Pros and cons of three bait bola launching devices tested on Palmyra Atoll.

Squall 250 Air Cannon

Pros Cons

Requires no muscle strength or effort Heavy to carry

Easily baits the tallest palm trees Must find/fetch towel after each shot

Easy to learn, easy to aim Limited # of shots (15 with 20 oz tank)

PSI may be adjusted for trees of different heights Lots of parts that can break in the field

Adaptable design, easily modified Expensive ($1,500), time consuming to fill

Adaptation: Carry larger air canister on a backpack for a longer-lasting air supply.

Hyper Dog Ball Launcher

Pros Cons

Small in size Tiresome, hard on forearms and muscles

Least expensive option ($35) Difficult for novices to aim

Lightweight, easily portable through forest Highly dependent on skill / strength of user

Fastest method per shot Amount of force needed is hard to estimate

Adaptation: Tighten wrist mount to increase accuracy, pad forearm to absorb shot pressure.

Big Shot Pole-Mounted Slingshot

Pros Cons

Lightweight, breaks down for storage Cumbersome to carry through thick forest

Anyone can aim and use without training Only shoots vertically, if canopy is thin 

Requires little force or strength Moderately expense ($130) 

Self supported, easier to operate 8 ft pole is too tall for some people to use

Adaptation: Cut or otherwise adjust pole length to be optimal for users of different heights.

The preferred method for launching bolas into the canopy depends on the following variables: 1) 

the size and strength of the operator, 2) the height of the palm, 3) thickness of the canopy, 4) the 

distance and density of trees between locations, 5) the amount of time allotted for baiting. The 

adaptations described in Table 12 may increase the effectiveness of all methods, and should be 

developed further. Bolas that were successfully launched into palm canopies were typically 

consumed by rats within 24 hours, indicating that this method could be a successful measure to 

ensure, that bait is delivered to all rat territories.

Research has shown that shorebirds may consume rodenticide bait pellets directly (Pierce et al. 

2008) or may sustain secondary or tertiary exposure to rodenticides after ingesting smaller 

organisms that previously consumed bait. The Bristle-thighed Curlew, a species classified as 

Vulnerable on the IUCN Red List 2008 (ICUN Red List of Threatened Species 2010) is at risk of 

exposure to rodenticide through direct and indirect pathways. Curlews were ever-present 
25

throughout the atoll during these studies, and were frequently captured in photographs by the 

motion sensing cameras that were monitoring bait stations, tracking tunnels, and rat carcasses. 

Though frequently sighted, curlews, plovers, wandering tattlers, and boobies seemed more 

interested in the camera itself than in the bait pellets or carcasses. Birds were occasionally 

photographed looking in the direction of a carcass or bait station, yet no close inspection or 

contact was made. 

Figure 11: Bristle-thighed Curlew inspecting a motion sensing camera on Strawn 

Island, bait station visible in the background.

The persistence of bait pellets in the crown of coconut palms was difficult to ascertain. Pellets 

that were placed in the crooks of palm fronds invariably slipped into a groove between the frond 

and the trunk, disappearing from view. Pellets were difficult to find, making accurate counts of 

pellet removal or observations of persistence nearly impossible. The natural shape of a coconut 

palm crown acts like a funnel, causing pellets to roll downhill into the tightest possible spaces. 

Special consideration should be given to locating pellets and sampling methods before repeating 

pellet fate trials in palm crowns. 
26

8. References

Abdelkrim, J., M. Pascal, and S. Samadi. 2007. Establishing causes of eradication 

failure based on genetics: case study of ship rat eradication in Ste. Anne 

Archipelago. Conservation Biology 21:719-730.

New Zealand Department of Conservation. 2000. Assessement of Environmental 

effects for Norway Rat (Rattus norvegicus) eradication in the Campbell 

Island National Nature Reserve Operational Area.

Oosterhout, C., W. Hutchinson, D. Willds, and P. Shipley. 2004. 

MICROCHECKER: software for identifying and correcting genotyping 

errors in microsatellite data. Molecular Ecology Notes 4:535-538.

Peakall, R. and P. E. Smouse. 2006. GENALEX 6: genetic analysis in Excel. 

Population genetic software for teaching and research. Molecular Ecology 

Notes 6:288-295.

Pierce, R., N. Anterea, U. Anterea, D. Broome, L. Cooper, H. Edmonds, F. 

Muckle, B. Nagle, G. Oakes, M. Thorsen, and G. Wragg. 2008. Operational 

work undertaken to eradicate rats and rabbits in the Phoenix islands, 

Republic of Kiribait, May‐June 2008.

Pritchard, J. K., M. Stephens, and P. Donnelly. 2000. Inference of Population 

Structure Using Multilocus Genotype Data. Genetics 155:945-959.

Raymond, M. and F. Rousset. 1995. GENEPOP (version1.2): population genetics 

software for exact tests and ecumenicism. Journal of Heredity 86:248-249.

Wegmann, A. and S. Middleton. 2008. Trip report, Jarvis Island National Wildlife 

Refuge and Palmyra Atoll National Wildlife Refuge visit and terrestrial 

assessment, 20 March to 8 April 2008. US Fish and Wildlife Service -

PRINWRC.

Weir, B. S. and C. C. Cockerham. 1984. Estimating F-statistics for the analysis of 

population structure. Evolution 38:1358-1370.
1

APPENDIX H

SUMMARY OF RISKS & POTENTIAL MITIGATION OPTIONS FOR 

BRISTLE-THIGHED CURLEWS (NUMENIUS TAHITIENSIS) AT 

PALMYRA ATOLL DURING A RAT ERADICATION CAMPAIGN
2
Summary of Risks & Potential Mitigation Options for 

Bristle-thighed Curlews (Numenius tahitiensis) 

at Palmyra Atoll during a Rat Eradication Campaign

Prepared for:

Palmyra Atoll Rainforest Restoration Project

September 16, 2010

Photo: © Glen Tepke

Prepared by:

Chris Gill, MSc.

Registered Professional Biologist

P: (250) 835-8256

e: chris@coastalconservation.ca
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

2

Table of Contents

Background.................................................................................................................................................... 3

Description .................................................................................................................................................... 3

Geographic Distribution ................................................................................................................................ 4

Population Size Estimate............................................................................................................................... 4

Threats........................................................................................................................................................... 6

Conservation Status ...................................................................................................................................... 6

Non-breeding Habitats.................................................................................................................................. 7

Summary of Risks to BTCUs during the Rat Eradication Campaign............................................................... 7

Impact on BTCU Population .......................................................................................................................... 7

Benefits of Rat Eradication to BTCU Population ......................................................................................... 13

Mitigation Options ...................................................................................................................................... 13

Summary ..................................................................................................................................................... 18

Recommended Additional Research........................................................................................................... 19

About the Author ........................................................................................................................................ 20

Literature Cited ........................................................................................................................................... 21

Appendix 1 – Expert opinions on live trapping BTCUs................................................................................ 26

Appendix 2 – Expert opinions on keeping BTCUs in captivity..................................................................... 28
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

3

Background

Palmyra Atoll National Wildlife Refuge (Palmyra), located in the Line Islands of the central Pacific Ocean

and approximately 1,693 kilometers south of the main Hawaiian Islands, is the northernmost atoll of the 

Line Islands chain and second largest of 10 atolls under U.S jurisdiction (The Nature Conservancy 2010).

The atoll is comprised of 54 islets encompassing 228 hectares that rise to a maximum elevation of 2 

metres. The atoll has a 1.6 kilometer long runway that is maintained by The Nature Conservancy staff.

Non-native black rats (Rattus rattus) were introduced to Palmyra, likely during the US military 

occupation of the atoll in the 1940s. The establishment of rats on Palmyra is considered to have had a 

major negative impact on the ecosystem, especially on seabirds, invertebrates, and vegetation (Howald 

et al. 2004).

The US Fish and Wildlife Service, in partnership with The Nature Conservancy and Island Conservation

began the Palmyra Atoll Rainforest Restoration Project (PARRP) to undertake a rat eradication campaign 

at Palmyra to restore the atoll’s terrestrial ecosystem. This campaign, however, places non-resident 

migratory shorebirds, including Bristle-thighed Curlews (Numenius tahitiensis), at risk of both primary 

and/or secondary exposure to rodenticide bait that will be deployed during the rat eradication. Due to 

its limited population size, the Bristle-thighed Curlew (BTCU) is classified as Vulnerable on the IUCN Red 

list (2008) because its population is small and believed to be declining, largely due to predation on the 

wintering grounds, when perhaps more than 50% of adults are flightless during autumn molt. The BTCU 

is also listed as a high conservation concern in the US Pacific Islands Regional Shorebird Conservation 

Plan (Engilis 2004) as well as the US Shorebird Conservation Plan (Brown et. al. 2001). This species is 

generally found on Palmyra during the non-breeding season although some individual juvenile birds are 

present throughout the year.

This document summarizes the risks to BTCUs posed by the eradication campaign and explores several 

potential mitigative measures that, if implemented, may minimize this species’ risk of exposure to the 

primary, secondary, and/or tertiary poisoning.

Description

The BTCU is a medium-sized curlew with a wingspan of approximately 40-44 cm and blue-gray legs. The 

moderately long and decurved bill is flesh colored at the base turning to brown near the tip and a dark 

lateral crown is present on the head along with eye stripes. The upperparts are spotted buff while the 

underparts are lighter with a few dark streaks on the flanks and more extending up the neck to the 

throat (Figure 1). The voice is a short ‘chi-u-it’, whistling ‘whe-whe-whe-whe’, and a ringing ‘wheewheeoo’ (Birdlife International 2010).

Their name comes from the bristle-like extensions at the base of their legs, although these are generally 

inconspicuous. Females are heavier than males and have longer wings and a shorter bill. Juveniles are 

similar to adults except for the presence of larger cinnamon-buff spots on the upperparts, and virtually 

unstreaked underparts (del Hoyo et. al. 1996).
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

4

Figure 1. Bristle-thighed Curlew. Photos © Glen Tepke.

Geographic Distribution

During the breeding season, BTCUs are found in the remote mountainous regions of western Alaska in 

the Andreafsky Wilderness Area north of the Yukon River mouth and on the central Seward Peninsula

(McCaffery and Peltola 1986, Kessel 1989, Gill et al. 1990, Marks et al. 2002). 

During the non-breeding season this species is found on remote Pacific Ocean islands and atolls (Marks 

et al. 1990) including the Hawaiian Islands (USA), US Minor Outlying Islands, Northern Mariana Islands 

(to USA), Federated States of Micronesia, Marshall Islands, Nauru, Kiribati, Tuvalu, Tokelau (to New 

Zealand), Fiji, Tonga, Niue (to New Zealand), Samoa, American Samoa, Cook Islands, and French 

Polynesia, also reaching the Solomon Islands, Norfolk Island (to Australia), Kermadec Islands (New 

Zealand), Pitcairn Islands (to UK) (notably Oeno) and Easter Island (Vilina et al. 1992, Brooke 1995b1

).

Sub-adults may remain in the Pacific until they are nearly three years old (Collar et al. 1992). Site fidelity 

on both the breeding and wintering grounds is high with many birds returning to the same location on an 

island for multiple years (Marks and Redmond 1996).

The geographic distribution of BTCUs has contracted in recent years (Marks et. al. 2002). 

Population Size Estimate

Based on comprehensive surveys of the known breeding range on the Seward Peninsula, the population 

size is estimated at approximately 3,200 breeding pairs (via a statistically valid sampling regime last 

assessed in 2000-2001, L. Tibbitts pers. comm.), while Engilis and Naughton (2004) state that the total 

number of Bristle-thighed Curlews is closer to 10,000. Numbers may be declining, although data on 

population trends are not available (Marks et. al. 2002).

This species breeds at two different locations in Alaska separated by approximately 300 km (C. Handel 

unpublished data2

 1 Source: 

). The two genetically distinct populations differ in size (the northern population is 

http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3010&m=0 2 Source; Marks, Jeffrey S., T. Lee Tibbitts, Robert E. Gill and Brian J. Mccaffery. 2002. Bristle-thighed Curlew 

(Numenius tahitiensis), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology. 

Downloaded from 
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

5

smaller), breeding phenology (southern birds breed slightly earlier than northern birds), morphology 

(northern birds are slightly larger), and location of core winter range (the northern population winters 

further south, Marks et. al. 2002). 

Two survey methodologies have been employed on the Atoll to count shorebirds including BTCUs: 

Runway counts and all-Atoll counts. 

Runway Counts

Runway counts were initiated in 2001 although the methodology used to conduct the survey was 

changed in 20083

. Runway counts are conducted on the island’s runway at high tide approximately once 

each week4

. One surveyor walks the runway in the direction of the wind and counts each individual 

bird. The resulting dataset is an indirect measure of the atoll’s population size; when runway count data 

is correlated with all-atoll count data, runway count values appear to represent 25% of the BTCU 

counted during the all-atoll counts (USFWS 2010, unpublished data).

Table 1 shows a comparison of 2009 and 2010 BTCU runway survey results for (June and July only). 

Average bird counts recorded for June 2009 and 2010 were similar (2009=38.4 birds, n=5 surveys; 2010= 

37 birds, n=5 surveys). July 2009 numbers were slightly higher (41.5 birds compared to 34 individuals in 

2010) although survey data is limited (2009 n=2 surveys, 2010, n=3 surveys). The lowest bird count 

occurred from late June to mid-July for both years. 

Unfortunately the age of birds was not recorded for either survey method, possibly because adult and 

sub-adult curlews can be somewhat difficult to distinguish. However, birds remaining through the austral 

winter are most likely sub-adults which do not migrate back north until they are approximately 34 

months old (Marks 1993, Marks and Redmond 1996).

Table 1. BTCU runway surveys. Comparison of numbers counted in June and early July in 2009 versus 2010.

2009 Survey Data 2010 Survey Data

Survey Date Count Survey Date Count

6/1/09 117 6/4/10 32

6/6/09 29 6/10/10 56

6/13/09 19 6/12/10 30

6/21/09 14 6/18/10 25

6/27/09 13 6/25/10 42

7/4/09 71 7/3/10 16

7/12/09 12 7/8/10 21

7/10/10 65

All-Atoll Counts

All-Atoll counts are conducted approximately once per month and involve a survey at low tide of all of 

the shorebird congregation sites including, but not limited to, beaches, lagoon flats, runway, and roads.

 

http://bna.birds.cornell.edu/bna/species/705/articles/introduction?must_change_password:int=0&initial_login:int=1 

on 13/09/2010.

3 From 2001 to Aug 2008, runway counts were conducted in the morning regardless of tidal conditions. Beginning 

in September 2008, runway counts were only conducted at high-tide - during low tide, most of the shorebirds are 

foraging on the exposed lagoon flats (A. Wegmann pers. comm.). Given the change in survey methodologies it is 

difficult to compare data collected prior to 2008 to the more recent data.

4 During low tide cycles the shorebirds forage on the lagoon flats but during high tide they congregate on the runway

(A. Wegmann pers. comm.).
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

6

The survey usually requires 5 to 6 people and takes at least 4 hours to complete. Figure 1 shows the 

areas surveyed during the all-Atoll count in 2010.

Figure 1. Areas surveyed during the all-Atoll count on Palmyra (USFWS unpublished data).

In July 2010, observers counted 149 BTCUs on the Atoll (USFWS unpublished data), which was higher 

than anticipated based on the results of the runway count. It is possible that the lack of Sooty Tern 

(Onychoprion fuscatus) breeding on the Atoll in 2010 could explain the higher than expected numbers. 

Sooty Tern eggs are a preferred food source for BTCUs (Bailey 1956, Ely and Clapp 1973) because the 

protein-rich eggs allow a rapid increase in body mass and condition in preparation for their migration 

back to the breeding grounds in Alaska. In 2010 the el Niño-Southern Oscillation (ENSO) returned to the 

tropical Pacific bringing warm, nutrient-poor water from the western Pacific in the equatorial current,

likely resulting in a reduction in prey availability for seabirds including the Sooty Tern and consequently 

the lack of breeding activity for this species on Palmyra Atoll in this year (Schreiber & Schreiber 1984, 

Forchhammer et. al. 1998, Post & Forchhammer 2002, Ramos et. al. 2002, Frederiksen et. al. 2004, 

Jaquement et. al. 2007). Therefore, the lack of Sooty Tern eggs in 2010 may have prevented some 

curlews from returning to their breeding grounds in Alaska (B. Flint email communication with M. 

Rubega, A. Wegmann pers. comm.) thus leading to an abnormally high all-Atoll count for that year.

Threats

Although its tundra breeding grounds have remained largely undisturbed, some researchers believe that 

BTCUs are negatively impacted by introduced mammalian predators including rats on their wintering 

grounds and atolls, including Palmyra Atoll (Marks et al. 1990). This is likely due to the fact that this 

species has evolved a rapid prebasic molt during which about 50% of the adults become flightless for 

approximately 92 days between August and December (Marks 1992, 1993). Consequently, disturbance

or mortalities on the wintering grounds could have a significant impact on the total population size.

Conservation Status
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

7

Classified as Vulnerable on the IUCN Red List 2008 (ICUN Red List of Threatened Species 2010). BTCUs 

are considered species of high conservation concern because of their small population size and because 

of anthropogenic pressures on the wintering grounds (habitat loss and degradation, introduced 

mammalian predators, etc). The risk of a steep and sudden population decline is serious threat because 

these birds are long-lived and site-faithful (L. Tibbitts pers. comm.).

Non-breeding Habitats

Winter habitats include ocean terraces or reef flats, ocean beaches, inter-islet channels, lagoon sand 

beaches, lagoon coral reefs, mudflats, saltpans, coconut groves, and vegetated clearings (Pratt et al. 

1987). Gill and Redmond (1992) found that wintering birds were associated principally with saltpans 

(36%) and inter-islet channels (27%). During molt, flightless birds take shelter during the day in dense 

stands of bunchgrass (Eragrostis variabilis) (Marks et al. 1990) and gather in communal nocturnal roosts 

in shallow water ponds of up to approximately 120 individuals (Tibbitts 1990). 

Summary of Risks to BTCUs during the Rat Eradication Campaign

In the non-breeding season BTCUs forage primarily in terrestrial habitats consuming spiders, land crabs, 

insects, seabird eggs, lizards, and carrion (Marks 1993). Stomach contents of 14 curlews collected in 

Polynesia contained vegetation, crustaceans, insects, gastropods, and scorpions (Johnsgard 1981).

Palmyra supports six land crab species including the large coconut crab (Birgus latro), two terrestrial 

reptile species - an introduced house gecko (Hemidactylus frenatus) and a native mourning gecko 

(Lepidodactylus lugubris), as well as a diverse collection of both native and non-native insects (Handler 

et. al. 2007, Howald et. al. 2004). Given the diverse diet of this species there are several potential 

secondary/tertiary exposure pathways including:

1. Feeding on land crabs or hermit crabs that have consumed bait or scavenged rat carcasses5

2. Feeding on insects that have consumed bait or scavenged rat carcasses;

;

3. Feeding on lizards that have consumed insects that have ingested the bait; and/or

4. Feeding directly on rat carcasses.

Additionally, research has shown that some BTCUs will ingest baits containing the rodenticide directly so 

the risks to this species are not confined to secondary poisoning (Pierce et. al. 2008).

Impact on BTCU Population

The 149 BTCUs counted on July 10, 2010 during the all-Atoll survey account for approximately 2% of the

total population estimate. It is possible that a significant portion of the population present on the Atoll 

during the eradication would be exposed to the rodenticide bait if no mitigative measures are 

implemented. 

 5 During a 2005 visit to the atoll by Island Conservation personnel, Bristle-thighed Curlews were observed along 

shorelines and above open water but also occasionally sighted beneath the forest canopy in the interior of the islets. 

Researchers found the evidence that these birds were foraging on hermit crabs which suggests that this species 

comprises at least a portion of the curlew’s diet, thereby confirming their potential risk of secondary exposure to the 

rodenticide (Buckelew et. al. 2005).
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

8

Merton et. al. (2002) reported mortality rates for several bird species following a rat eradication 

campaign on four islands in the Indian Ocean. Two of the species have similar diets to Bristle-thighed

Curlews: Ruddy Turnstone (Arenaria interpres) and Asiatic Whimbrel (Numenius phaeopus variegates). 

Green-dyed bait and 20ppm brodifacoum concentration was used for the eradication and following the 

campaign estimated population mortality rates were 61% for Turnstones and 20% for Asiatic Whimbrel). 

McClelland (2002) reported that 80% of fernbirds (Bowdleria punctata wilsoni), a warbler that forages on 

invertebrates, disappeared from a 25 hectare test plot that was used to assess risk of brodifacoum on 

non-target species prior to implementation of a rat eradication operation on Codfish Island, New 

Zealand. No birds in a neighboring control plot were lost, which suggested that the proposed aerial bait 

drop on Codfish Island posed a significant risk to the fernbirds at a population level. Although fernbirds 

are not closely related to BTCUs this data may be used to predict the potential impact of the Palmyra rat 

eradication operation on bird species at risk of high exposure to rodenticide.

Other eradication projects reported non-target mortality of BTCUs (e.g.: Pierce et al 2008). However 

surveys for dead or dying shorebirds were not comprehensive for most eradication projects (e.g. S. 

Cranwell pers. comm. regarding the Ringold (Fiji) rat eradication project and R. Pierce pers. comm. 

regarding the Phoenix Islands eradication project). It is also likely that most carcasses are rapidly 

consumed by scavengers making estimations of mortalities resulting from rodenticide bait difficult to 

predict. 

R. Pierce (pers. comm.) theorized that mortality rates of birds present on Palmyra Atoll at the time of the 

eradication campaign would be variable depending on factors such as rainfall (increasing bait 

palatability) and social facilitation (e.g. birds learning of the rodenticide bait palatability from watching a 

neighbour ingest it rather than learning by itself, Peirce et. al. 2008). 

Based on the non-target mortality rates reported by Merton et. al. (2002) and data from McClelland 

(2002) it may be reasonable to anticipate mortality rates in the range of 60-80% for BTCUs summering on 

the Atoll during the rat eradication campaign. Two questions remain: 1) what proportion of sub-adult 

population versus adult population present on the Atoll during the eradication will be impacted; and 2) 

how will these losses impact the total population size and stability?

Population viability analysis (completed by Island Conservation)

The following BTCU population viability analysis (PVA, Morris and Doak 2002, Doak et. al. 2009) was 

completed by the partnership behind PARRP (2010) to explore the implications of incidental poisoning 

mortality of BTCUs due to activities associated with the proposed rat eradication on Palmyra. The PVA 

uses a female-only stage structured matrix model (Table 2) parameterized using available data (Table 2). 

The model structure assumes birds pass through a series of immature life stages, with recruitment 

occurring at ages 3 - 5 (i.e., participation in migration starts at 35 – 59 months), and most birds recruiting 

at age 3 (Marks et al. 2002). In addition, a very small proportion of adults skip breeding in some years. 

The matrix assumes a pre-breeding census. 

At least some species-specific data were available for most parameters (Table 3), although data on 

reproduction was notably lacking. The modeler was forced to use surrogate data, in some cases from 

smaller-bodied shorebirds, for survival from egg to hatch, hatch to fledge, and fledge to first birthday. In 

addition, no information was available on temporal variance in survival rates, and thus, stochastic 

dynamics were explored by assuming a 10% coefficient of variation (CV) in adult survival and adult 

breeding probability (Sbr, Snb, Gbr, Gnb). A nest success CV of 73% was estimated from existing data. 

These CVs are consistent with expectations for more variable rates of reproduction than survival in long-
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

9

lived birds (Erikstad et al. 1998). Annual demographic rates for stochastically varying parameters were 

randomly chosen from a beta distribution (Morris and Doak 2002). 

Table 2: Stage structured matrix describing BTCU life history (see Table 2 for parameter definitions and values).

0 0 0 0 0 SR*CL*NS*EH*HF*FS 0

Snb *(1-G1) 0 0 0 0 0 0

0 Snb *(1-G2) 0 0 0 0 0

0 0 Snb *(1-G3) 0 0 0 0

0 0 0 Snb*(1-G4) 0 0 0

Snb * G1 Snb * G2 Snb * G3 Snb * G4 Snb *G5 Sbr *Gbr Snb * Gnb

0 0 0 0 0 Sbr*(1- Gbr) Snb *(1- Gnb)

The modeler explored the likely effects on global BTCU populations of mortality of 10, 50, and 150 BTCU

individuals on Palmyra Atoll. Given the timing of eradication, the majority of mortalities should be subadult birds remaining on the atoll during the breeding season, but we conservatively assume that 50% of 

the mortalities are adults. For all scenarios, a second conservative assumption of an additional 50 BTCU

lost due to a simultaneous but unrelated one-time event was added, again assumed to be 50% adults. 

The modeler assessed the effect of these spikes in mortality on the population futures of BTCU by 

simulating 20,000 replicate runs for each scenario, with the added mortality imposed in the first year, 

and tracking population trajectories over 50 years, and reported the extinction risk and projected 

median and lower 90th percentile of population size. 

The model does not account for demographic stochasticity, which is unlikely to be important at current 

population levels. Likewise, the model does not take into account uncertainty in parameter estimates, 

correlations in demographic rates, catastrophes, density dependence, possible Allee effects at low 

population levels, or implications for the local population on Palmyra.

Results and Discussion

The population growth rate (λ) for the deterministic matrix was 0.997, suggesting a population that is 

slowly declining in the absence of environmental fluctuations. Adding temporal variance in some 

demographic rates (Table 3) yields a stochastic λ estimate of 0.994, again suggesting a slowly declining 

population. The population is currently thought to be approximately stable, although some recent 

reports consider it declining (Morrison et al. 2006 and references therein). Thus, the modeled 

population generally accords with expectations, but may reflect some conservative assumptions. 

With a starting population of 10,000 (Morrison et al. 2006), 884 adults and 239 sub-adults are expected 

to die in the first year due to natural mortality, assuming a stable stage distribution. The mortality 

scenarios considered here (10 – 150 +50 individuals) represents a 3-8% increase in adult mortality and a 

13-31% increase in sub-adult mortality for one year. 

The mortality events considered here appear to have a minor and diminishing effect on projected 

population futures (Figure. 2). The one-time mortality events do not alter deterministic λ and result in 

only minor decreases in stochastic λ. In addition, the mortality events do not appear to put the 

population in danger of increased risk of stochastic extinction over 50 years. With the current 

parameter estimates, there is no risk of extinction over the next 50 years under any scenario (although 

with λ < 1, the modeled population is in a deterministic decline towards eventual extinction). 
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

10

An analysis of the sensitivity of deterministic λ to BTCU demographic rates indicates that the population 

growth rate is most responsive to changes in adult survival. Elasticity values, which denote proportional 

changes in λ for proportional changes in demographic rates, were 0.58 for adult survival, and 0.32 for 

sub-adult survival; all other demographic rates had elasticities of ≤0.10. These sensitivity results 

underscore the importance of minimizing adult mortalities.

These model predictions should be viewed as general qualitative descriptors of the BTCUs likely future 

dynamics under various one-time mortality scenarios. This PVA was constrained by available data – most 

demographic rates were estimated from sparse data, or were assumed or borrowed from surrogate 

species. Care should be taken to minimize BTCU mortalities, because at ~10,000 individuals, the global 

population size of BTCU is small. 

0 5 10 15 20 25

4000

4500

5000

5500

Years

Projected median number of females

0

10 + 50

50 + 50

100 +50

150 + 50

Medians of 20000 replicate runs for each scenario

Number of BTCU

killed in year 1:

0 5 10 15 20 25

2000

2500

3000

3500

4000

4500

5000

5500

Years

Projected lower 90th percentile of number of females

0

10 + 50

50 + 50

100 +50

150 + 50

Lower 90th percentiles of 20000 replicate runs for each scenario
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

11

Figure 2. Effect of Effects of one-time mortality events on BTCUs.

Table 3: Parameter values used in matrix population model for BTCU

Symbol Parameter Estimate Species Process 

variance 

(CV)

Source

Nstart Starting population size 10,000 BTCU Morrison et al. 2006

SR Egg sex ratio 0.50 Assumed. Also assumed no sex 

differences in age-specific 

survival throughout life (Marks 

et. al. 2002 reports no difference 

for adults)

CL Mean clutch size 3.85 BTCU Marks et. al. 2002

NS Probability of nest success 

(≥1 chick fledging)

0.37 BTCU 73% Marks et. al. 2002 (estimated 

from data therein, process 

variance estimated using 

Kendall’s method, (Kendall 

1998)

EH Probability of surviving, 

egg to hatch

0.95 LBCU Redmond and Jenni 1986 (reestimated to exclude livestock 

damaged eggs)

HF Probability of surviving, 

hatch to fledge

0.53 LBCU, 

PIPL

Mean: Long-billed curlew (0.39, 

Redmond and Jenni 1986) and 

Piping plover (0.66, Calvert et.

al. 2006) 

FS Probability of surviving, 

fledgling to 1st birthday

0.46 SNPL Stenzel et. al. 2007 

Snb Annual survival 

probability, nonbreeder

0.92 BTCU 10% Marks and Redmond 1996, 

process variance assumed

SB Annual survival 

probability, breeder

0.87 BTCU 10% Marks et. al. 2002, process 

variance assumed

G1 Probability of recruitment, 

1st year

0 BTCU Marks and Redmond 1996, 

Marks et. al. 2002

G2 Probability of recruitment, 

2nd year

0 BTCU Marks and Redmond 1996, 

Marks et. al. 2002

G3 Probability of recruitment, 

3rd year

0.91 BTCU Marks and Redmond 1996, 

Marks et. al. 2002

G4 Probability of recruitment, 

4th year

0.91 BTCU Marks and Redmond 1996, 

Marks et. al. 2002

G5 Probability of recruitment, 

5th year

1.00 BTCU Marks and Redmond 1996, 

Marks et. al. 2002

GBr Probability breeder 

remains a breeder, >5th 

year

0.98 BTCU 10% Marks and Redmond 1996, 

Marks et. al. 2002, process 

variance assumed

Lower 90th percentiles of 20000 replicate runs for each scenario
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

12

GNb Probability nonbreeder 

returns to breeding pool, 

>5th year

0.98 BTCU 10% Marks and Redmond 1996, 

Marks et. al. 2002, process 

variance assumed
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

13

Benefits of Rat Eradication to BTCU Population

Some researchers believe that BTCUs are being negatively impacted by introduced mammalian predators 

including rats on their wintering grounds and atolls, including Palmyra (Marks et al. 1990). Removal of 

rats from Palmyra would therefore have a positive impact on the population. In addition to this direct 

benefit, other researchers have suggested that the high density of introduced nest-predating rats greatly 

reduces ground nest success and fledging rates of Sooty Terns on Palmyra (USFWS 2010). Therefore 

removing rats from the Atoll may also indirectly benefit BTCUs by increasing the breeding population of 

Sooty Terns, and thus egg production on Palmyra - Sooty Tern eggs are a preferred food source for 

BTCUs (Bailey 1956, Ely and Clapp 1973) because the protein-rich eggs allow for a rapid increase in body 

mass and condition in preparation for their migration back to the breeding grounds in Alaska.

Mitigation Options

Several mitigative options have been proposed that could minimize exposure of BTCUs to bait containing 

the rodenticide during the eradication campaign on Palmyra Atoll (Flint 2010, G. Howald pers. comm.). 

These include:

1. Timing implementation of the eradication for when the population is lowest;

2. Modifying the methodology used to distribute the bait;

3. Trapping individuals and keeping them in captivity until risk of exposure is eliminated or greatly 

reduced or translocating trapped individuals to Christmas Island;

4. Hazing;

5. Supplemental feeding of a high lipid diet prior to implementation of the eradication campaign to 

increase fat stores, which may encourage more birds to migrate back to the breeding grounds in 

Alaska thereby exposing less birds to risks of primary and secondary poisonings.

However the main issue confronting these mitigative measures is that they cannot compromise the 

eradication campaign, otherwise the success of the project may be put at risk.

1. Timing of eradication implementation

During a 2004 assessment of Palmyra Atoll for eradication feasibility (Howald et. al. 2004), the 

assessment team concluded that the most effective mitigation for these species is to conduct the 

eradication between early June and mid-July when most adult BTCUs have left the atoll for their 

breeding grounds in Alaska (Howald et. al. 2004). This will minimize the risk of short term rodenticide 

exposure to the majority of curlews overwintering on the Atoll. Any birds remaining on the atoll at

this time of year are likely sub-adults (aged 1 to 3 years) that remain on the tropical Pacific islands 

until they mature (B. Gill email correspondence with B. Flint6

, Flint 2010).

Pierce et. al. (2008) noted that it was easier for Bristle-thighed Curlews to ingest rodenticide bait 

after it had been softened by rainfall. Therefore, if aerial broadcast will be employed it will be 

important to assess weather conditions prior to the bait drop in order to minimize exposure of the 

rodenticide bait to rainfall. 

 6 Wildlife Biologist, US Fish and Wildlife Service, Pacific Reefs National Wildlife Refuge Complex, 300 Ala Moana 

Blvd. Room 5-231, Honolulu, HI 96850.
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

14

2. Using an eradication method that may reduce exposure to the bait

A large portion of Palmyra Atoll (approximately 48%) is comprised of nonnative coconut palm (Cocos 

nucifera) forming a dense vegetative canopy over the island that is utilized by the rats (Howald et al. 

2004). Radio telemetry experiments on the Atoll compared the movements of rats live-trapped in 

coconut palms with rats trapped on the ground and demonstrated the use of a three dimensional 

environment with individuals regularly moving between the tree canopy and the ground (Howald et. 

al. 2004). Although logistically complex and costly, using a combination of bait stations and a 

modified aerial broadcast (or another method to accurately distribute bait into the palm trees) may 

be the best method to expose rats on the forest floor, as well as those inhabiting the vegetation 

canopy to the bait containing the rodenticide. These combined methodologies were used 

successfully during a ship rat (Rattus rattus), Norway rat (R. norvegicus) eradication campaign on 

islands in the Seychelles group, Indian Ocean (Merton et. al. 2002). If bait stations are not used there 

is an increased risk of primary and secondary poisoning of BTCUs because aerial broadcast will make 

the rodenticide bait more readily available to the birds and also to potential prey species such as 

land crabs and hermit crabs.

In addition to incorporating a combination of bait stations and selective aerial broadcast techniques, 

there are other ways to reduce rodenticide bait exposure and toxicity although some of these 

options could potentially compromise the eradication campaign7

:

a) Brodifacoum versus Diphacinone Rodenticide

The second generation anticoagulant brodifacoum is one of the most commonly used 

rodenticide for rat eradications around the world (Howald et. al. 2007) because of its high acute 

toxicity - a single feeding will induce death (Eason and Spurr 1995, G. Howald pers. comm.). 

However, brodifacoum is also highly toxic to other species including birds, which increases the 

risk of primary and secondary poisonings to species including BTCUs. 

Diphacinone, a first generation anticoagulant is less persistent and virtually non-toxic to birds 

when compared to brodifacoum (e.g. Newton et. al. 1990). However this rodenticide is most 

effective against rats when they can freely consume multiple doses for 10 days or more without 

running out of bait (Fisher & Broome 2004, Swift 1998). There are obvious challenges associated 

with using this rodenticide. For example:

• Rats must select the rodenticide bait over any naturally occurring food sources available to 

them on the Atoll. This is compounded by the palatability issues associated with diphacinone 

(G. Howald pers. comm.).

• Using diphacinone would require a significant amount of rodenticide bait being distributed 

on the Atoll- 100 tons compared to 50 tons if brodifacoum was used (G. Howald and A. 

Wegmann pers. comm.).

Although highly toxic to birds, brodifacoum is likely the preferred choice based on its acute 

toxicity and the obvious disadvantages of using diphacinone with respect to successful rat 

eradication on Palmyra Atoll.

 7 Note: it is not feasible to collect rat carcasses due to the density of vegetation on the islands and the rapidity in 

which land crabs consume carrion. Therefore this was not included in the list of proposed options to reduce 

rodenticide bait exposure.
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

15

b) Bait Coloration: 

The rodenticide bait used for the Palmyra Atoll eradication should be dyed blue-green, which is a 

color known to be least visible/preferred to non-target species including shorebirds (National 

Park Service 2000).

c) Bait Station Design 

Howald et. al. (2004) proposed a modified bait station design that would exclude the majority of 

land crabs and hermit crabs, which are preferred BTCU prey species. Using a design similar to 

this may help to reduce secondary exposure to the rodenticide. However, it is not possible to 

keep all hermit crabs and land crabs, or other BTCU prey, such as geckos and insects out the bait 

stations.

3. Capturing Bristle-thighed Curlews prior to the eradication campaign

Live trapping BTCUs prior to the eradication campaign and either holding the birds in captivity on the 

Atoll, or translocating them to another island would eliminate the risk of exposing these individuals 

to primary and/or secondary rodenticide exposure. Although feasible, it is unlikely that a significant 

portion of the wintering population, the majority of which are likely sub-adult birds (1-3 years old),

could be captured (please refer to Appendix 1 for opinions from several prominent wading bird 

specialists on the challenges of capturing BTCUs). Furthermore there are also risks associated with 

capturing birds, including physical injury and physiological stress that could result in the death of 

some individuals. 

If this mitigative option is selected, prior to undertaking a trapping campaign all communal sites 

would need to be identified because BTCUs tend to congregate in small groups when roosting or 

foraging. Several different trapping methods would need to be employed to maximize success

because this species tends to be extremely wary. Marks and Redmond (1994) captured Bristlethighed Curlews on Laysan Island in the South Pacific at night using a hoop net after temporarily 

blinding individuals with a flashlight. There are a number of other trapping options including walk in 

traps, although the potential of other species incapacitating the trap such as land crabs and rats 

would have to be taken into consideration. Consultation with shorebird/wading bird experts 

regarding trapping methodologies would be essential to maximize capture success.

If a trapping campaign is successful, the captured BTCUs could be:

a) held in captivity on the Atoll until during the eradication campaign until the bait has degraded 

and the toxicity in prey items such as land crabs has decreased to levels that will not put BTCUs 

at risk; or

b) transported and released on Christmas Island.

Both options have distinct advantages and disadvantages that are described in Table 4. 
Table 4. Pros and cons of temporary captivity on Palmyra Atoll versus translocation of trapped BTCUs to Christmas Island.

Capture/hold 

options Difficulty Risk to captive birds Cost Advantages Disadvantages

Option 1: Keep 

birds in 

captivity on 

Palmyra Atoll

High

•Maintaining wild 

birds in captivity can 

be challenging.

•Need experienced 

personnel dedicated 

to maintaining the 

captive birds.

•Birds would be in 

captivity for 

approximately 6

weeks8

.

High

• Stress.

• Injuries in captivity.

• Disease.

• Death.

• Diet challenges 

(keeping birds 

healthy).

Low/Moderate

• Build aviaries to 

house birds.

• Feed birds.

• Staff wages to 

maintain birds.

• Eliminates exposure to 

rodenticide bait for a 

portion of the BTCU

population. 

• Relatively inexpensive.

• Could lose birds as a result of

stress, injury, and/or starvation.

• BTCUs are quite aggressive so 

birds may need to be housed 

individually.

•Need experienced personnel 

dedicated to maintaining captive 

birds.

Option 2:

Translocate

birds to 

Christmas 

Island and 

release

High

•Temporarily holding 

and maintaining wild 

birds in captivity until 

enough birds are 

captured for 

translocation is 

challenging.

•Need experienced 

personnel dedicated 

to maintaining the 

captive birds.

•Transport logistics

(boat/helicopter).

High

•Stress.

•Injuries while being 

staged for 

translocation or 

during translocation.

•Disorientation/death

from moving birds to 

a foreign location.

•Diet challenges 

(keeping birds 

healthy while being 

staged for 

translocation or 

during translocation).

High

• Cost of boat or plane 

to translocate birds

• Build aviaries to 

temporarily house 

birds on Palmyra

until enough are 

captured to justify 

costs of transporting 

them to Christmas 

Island.

• Feed birds.

• Staff wages to 

maintain birds during 

staging and 

translocation.

• Eliminates exposure to 

rodenticide bait for a 

portion of the BTCU

population without 

having to hold birds 

for approximately 6

weeks. 

• Could lose birds as a result of 

stress, injury, starvation, or 

disorientation.

• Logistically difficult – need to 

house captured birds until 

transport is available. Birds may 

need to spend weeks in captivity 

until enough individuals can be 

captured to warrant the cost of 

transporting them. BTCUs are 

quite aggressive so birds may need 

to be housed individually.

• Need experienced personnel to 

take care of birds until they can be 

released on Christmas Island.

 8 The period when the bait is on the ground and toxicity in prey items such as land crabs is sufficiently high enough to harm BTCUs (Buckelew et. al. 2005).
Housing BTCUs on Palmyra Atoll may be less expensive and less logistically complex compared to 

translocating birds to Christmas Island. If translocation to Christmas Island is preferred there are 

several questions that must be answered prior to implementing this mitigative option:

• Is Christmas Island far enough from Palmyra Atoll to ensure that the birds do not 

immediately return to Palmyra Atoll upon release? BTCUs exhibit high site fidelity on their 

breeding and wintering grounds with many individuals observed occupying the same site on 

an island for multiple years (Marks and Redmond 1996). 

• Is the prey base for BTCUs on Christmas Island similar to that found on Palmyra Atoll?

• Will the birds be disoriented by the translocation with respect to route finding during 

migration to their breeding grounds in Alaska?

Holding birds in captivity - challenges

Although feasible, holding wild birds in captivity, especially active species such as waders can be very

challenging (please refer to Appendix 2 for opinions from several prominent wading bird specialists 

on the challenges of keeping BTCUs in captivity). However, several species of shorebirds and waders 

have been successfully held in captivity for short periods of time (D. Lank email correspondence with

B. Flint, R. Lanctot email correspondence with K. Swinnerton, M. Rubega email correspondence with 

K. Swinnerton. See Appendix 2 for additional information). Birds have also been successfully 

captured and temporarily housed for other rat eradication campaigns including a project recently

completed on Frégate Island (Merton et al. 2002). Prior to the operation 39 magpie-robins (100% of 

the island’s population) and 330 Seychelles fodys (50% of the island’s population) were taken into 

captivity before the eradication campaign was initiated. The birds were held in rat-proof enclosures 

until the rodenticide baits were no longer available (6 weeks). No magpie-robins died during the 

period of confinement although 7.5% of the fodys perished (Merton et. al. 2002).

It is possible that some BTCUs may die during the captivity period due to stress, injury or illness. 

Careful planning is required to ensure that the birds remain healthy during the period of 

confinement including consultation with shorebird/wading bird experts regarding housing options

(e.g. house birds separately or hold small groups in large, lightly netted aviaries) and avian 

nutritionists for diet and nutrition requirements. 

4. Hazing

Bird hazing and deterrent techniques are widely employed to disperse and exclude birds from 

croplands, aquiculture facilities, and airports. Hazing techniques rely on the use of auditory and 

visual devices to scare birds away from an area, e.g., bird distress calls, pyrotechnics, propane 

exploders, flashing lights, effigies of humans or predators, and flagging (Greer and O'Connor, 1994). 

However, birds can rapidly habituate to these tactics if the use of such devices falls into a predictable 

pattern (Brush, 1971; Bornford and O'Brien, 1990). Thus, hazing requires diligence to ensure the 

effectiveness of the negative stimuli.

Pierce et. a. (2008) suggested that it may be practical to attempt to scare BTCUs away from the 

target islands prior to implementing an eradication campaign if aerial broadcast of rodenticide bait is 

used. However, it is unlikely that this technique would be an effective solution to reducing exposure 

of BTCUs to the rodenticide bait given the mobility of this species, high site fidelity (Marks and 

Redmond 1996), and general logistics required to carry out an effective hazing operation. 
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

18

5. Supplemental feeding of a high lipid diet to encourage migration to breeding grounds

Migratory birds undergo an endogenously controlled seasonal onset of fat storage in preparation for 

departure to the breeding or wintering grounds (Gwinner 1990). Researchers have suggested that 

differences in fat deposit gains and migratory departure dates are correlated with food abundance 

(e.g. Bibby and Green 1981, Graber and Graber 1983). Supplemental feeding a high lipid diet 

(chicken eggs) to the BTCUs on Palmyra Atoll prior to implementation of the eradication operation 

may thus encourage more adults9 to depart for the Alaskan breeding grounds, or at least enable a 

subset of this population to reach the required body condition more rapidly, resulting in earlier 

departure dates from the Atoll. However, more recent studies suggest that birds possess heritable or 

acquired differences in fuelling efficiency and/or moulting resulting into variations of migration 

schedules (Moller 1994, Conklin et. al. 2010) while other experts have suggested that birds such as 

BTCU can assess conditions on their breeding grounds from great distances thus influencing whether 

or not birds migrate or delay their departure (B. Gill email communication with B. Flint). Therefore,

supplemental feeding of BTCUs may not greatly influence departure dates or the actual number of 

birds migrating back to the breeding grounds. 

Although supplemental feeding may not greatly affect departure dates or the number of birds 

migrating to the breeding grounds it is a relatively simple and low cost mitigative measure to 

implement. Therefore a pilot study should be initiated as soon as possible to determine if BTCUs will 

accept supplemental feeding (e.g. hardboiled chicken eggs). Consultation with avian nutrition 

experts regarding supplemental feeding would be required prior to implementing the pilot study.

Summary

Non-target impacts to species including shorebirds during invasive species eradication operations have 

been previously reported (e.g. Merton et. al. 2002, Pierce et. al. 2008). Based on these studies it is 

reasonable to anticipate that 60% or more of the BTCUs present on Palmyra Atoll during the eradication 

campaign may be at risk of primary and secondary poisoning. The population viability analysis 

completed by Island Conservation predicts that any BTCU mortalities resulting from the eradication 

operation would have a minor impact on the future population health. However the model predictions 

should be interpreted with caution based on the vulnerability of this species due to its small population 

size and current state of decline. 

The degree of impact to BTCUs will be influenced by the number of birds present on the Atoll during the 

eradiation operation, including the number of adults versus sub-adults10, as well as the method of bait 

disbursement. Although the significance of sub-adult mortalities versus adult mortalities on the 

population’s health is unknown, because this species is long-lived, the mortality of sub-adult birds may 

cause less of an impact than adult mortalities. 

Several mitigative options have been recommended in this document that may minimize, but not 

eliminate impacts to BTCUs during the eradication operation. There are risks to BTCUs associated with 

some of the measures, including physiological stress from disturbance and potential for accidental 

mortalities (e.g. resulting from live trapping). These risks must be weighed against the risk of exposure to 

the rodenticide bait. 

 9 It is unlikely that sub-adults will migrate to the breeding grounds even with supplemental feeding. 10 It is likely that a higher number of sub-adults will be present on the Atoll during the eradication operation.
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

19

It is also important to evaluate how the mitigative options may affect the outcome of the actual 

eradication operation. If the success of the campaign may be compromised by implementing the 

mitigative options, the anticipated risk to BTCUs may be too great (e.g. the eradication operation fails 

and BTCUs are killed).

However, if the outcome of the operation is not affected by implementing the mitigative options, the 

successful eradiation of rats from Palmyra Atoll can result in direct and indirect benefits to BTCUs, 

including reduced disturbance (Marks et. al. 1990) and a potential increase in the breeding population of

Sooty Terns (Sooty Tern eggs are a preferred food source of BTCUs, Bailey 1956, Ely and Clapp 1973). 

Therefore, the potential loss of a portion of the wintering BTCU population on Palmyra during the 

eradication campaign may be offset by the long-term benefits to the overall population health of this 

species, to other species on the Atoll, and to the island ecosystems as a whole (Dowding et al. 1999, 

Empson & Miskelly 1999, Lovegrove & Ritchie 2005).

Recommended Additional Research

1. Conduct all-Atoll and runway surveys in 2011 between June and early July. Compare survey results to 

2010 (e.g. was 2010 all-Atoll survey an anomaly?). Identify numbers of adults versus sub-adults

present on the Atoll at this time;

2. If BTCUs will be trapped, identify day/night roost sites and other aggregation sites;

3. Undertake a pilot study to determine if BTCUs will accept supplemental feeding (e.g. hardboiled 

chicken eggs);

4. Investigate options that can be implemented to accurately disperse rodenticide bait into the 

vegetative canopy.
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

20

About the Author

Chris Gill is a registered professional biologist with a Master of Science degree in environmental 

toxicology from Simon Fraser University (1998). He is currently involved in two proposed invasive 

mammal eradication projects in British Columbia in collaboration with Island Conservation. Previously 

Chris has provided expert opinion on the impact of the Anacapa Island rat eradication project (Island 

Conservation) on the resident raptor population and has worked throughout North American including 

projects in Florida (effects of mercury contamination in wading birds), California (impact of wind 

generation plants on Golden Eagles), Arizona (bald eagle research project), Montana (raptor migration 

study), and Idaho (wild turkey research, radio tracking falcons). Chris has coauthored papers on the

effects of food supply, environmental contaminants, tides, and weather on raptor and wading bird 

populations. 
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

21

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(Codfish Island), Putauhinu and Rarotoka Islands, New Zealand. International Conference on Eradication 

of Island Invasives. P.173-181.

Merton, D., G. Climo, V. Laboudallon, S. Robert, and C. Mander.2002. Alien mammal eradication and 

quarantine on inhabited islands in the Seychelles. Pp. 182–198 in: Veitch, CR & Clout, MN (eds) Turning 
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24

the tide: the eradication of invasive species. IUCN SSC Invasive Species Specialist Group, Gland, 

Switzerland.

Moller, A.P. 1994. Phenotype-dependent arrival time and its consequences in a migratory bird. Behav. 

Ecol. Sociobiol. 35, 115–122.

Morris, W.F., and D.F. Doak. 2002. Quantitative conservation biology: theory and practice of population 

viability analysis. Sinauer and Associates Inc., Sunderland, MA.

Morrison, R.I.G., B.J. Mccaffery, R.E. Gill, S.K. Skagen, S.L. Jones, G.W. Page, C.L. Gratto-Trevor, and B.A. 

Andres. 2006. Population estimates of North American shorebirds, 2006. Wader Study Group Bulletin 

111:67-85.

National Park Service. 2000. Anacapa Island Restoration Project. Final Environmental Impact Statement. 

139pp.

Newton, I., I. Wyllie, and P. Freestone. 1990: Rodenticides in British barn owls. Environmental

pollution 68: 101-117.

Pierce, R., N. Anterea, U. Anterea, K. Broome, D. Brown, L. Cooper, H. Edmonds, F. Muckle, B. Nagle, G. 

Oakes, M. Thorsen, G. Wragg. 2008. Operational work undertaken to eradicate rats and rabbits in the 

Phoenix islands, Republic of Kiribait, May-June 2008. 73pp.

Post, E., and M.C. Forchhammer. 2002. Synchronization of animal population dynamics by

large-scale climate. Nature 420, 168-171.

Pratt, H.D., P.L. Bruner, and D.G. Berrett. 1987. A Field Guide to the Birds of Hawaii and the Tropical 

Pacific. Princeton University Press, Princeton, New Jersey. 409 pp. + 45 plates.

Ramos, J.A., A.M. Maul, V. Ayrton, I. Bullock, J. Hunter, J. Bowler, G. Castle, R. Mileto, and C. Pacheco. 

2002. Influence of local and large-scale weather events and timing of breeding on tropical Roseate Tern 

reproductive parameters. Marine Ecology Progress Series 243:271–279.

Redmond, R.l., and D.A. Jenni. 1986. Population ecology of the Long-billed curlew (Numenius 

americanus) in Western idaho. Auk 103:755-767.

Schreiber, R.W., and E.A. Schreiber. 1984. Central Pacific seabirds and the El Nino Southern

Oscillation: 1982-1983 perspectives. Science 225 713-716.

Stenzel, L.E., G.W. Page, J.C. Warriner, J.S. Warriner, D.E. George, C.R. Eyster, B.A. Ramer, and K.K. 

Neuman. 2007. Survival and natal dispersal of juvenile snowy plovers (Charadrius alexandrinus) in central 

coastal California. The Auk 124:1023-1036.

Swift, C.E. 1998. Laboratory bioassays with wild-caught roof (Rattus rattus) and Polynesian (R. exulans) 

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Tibbitts, L. 1990. Phenology and habitat use during ground surveys of the Yukon-Kuskokwim River Delta. 

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C.M. Handel, compilers). U.S. Fish and Wildlife Service, Anchorage, AK.

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Vilina, Y.A., A. Larrea, and J.E. Gibbons. 1992. First record of the Bristle-thighed Curlew Numenius 

tahitiensis in Easter Island, Chile. Wader Study Group Bull. 66:43-44.
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26

Appendix 1 – Expert opinions on live trapping BTCUs

Eight scientists with significant field experience working with BTCUs or similar species were consulted by 

Flint (2010), A. Wegmann, or K. Swinnerton regarding the feasibility of capturing this species. Below are 

pertinent excerpts from their email communications or conversations. 

Jeff Marks 

Director of Bird Conservation for Montana Audubon

...I think it would be difficult to catch a lot of birds, and perhaps even more difficult to hold them... 

Lee Tibbitts

USGS, 4210 University Dr., Anchorage, AK 

..I agree that it would be very difficult to capture a large number of birds in the time frame that you 

would like (i.e., around the application time)... 

Wally Johnson

Plover expert

...In my opinion, it would be nearly impossible to catch/transport/hold BTCUs. Seems like it would be a 

huge challenge to capture more than a few... 

Bob Gill

Shorebird research program, U.S. Geological Survey, Alaska Science Center.

...very unlikely that a meaningful number could be captured.... 

David Lank

Dept. of Biological Sciences, Simon Fraser University, Burnaby BC Canada

...You are dealing with a single location, have more infrastructure to work out of and a more focused 

goal. I am only in part being naive here. I know that both species are wary, no doubt about that, 

particularly the curlews, but we could give it a try... 

Richard Lanctot

Shorebird Coordinator, Alaska Region, US Fish and Wildlife Service, Migratory Bird Management, 

Anchorage, AK 

...Capturing all or a significant portion of the bird population would be difficult. To capture these birds 

would require as Dov [Lank] said a very focused effort and a large effort. 

Bristle-thigheds don't go around in huge flocks so the reward for effort might be a bit meager!... 
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

27

Simon Tonge 

Executive Director, Paignton Zoo Environmental Park., Totnes Road, Paignton, Devon 

...Catching the birds could also be extremely difficult, I would guess...

Margaret Rubega

Associate Professor of Ecology and Evolutionary Biology, University of Connecticut

...In principle, I don't see why it wouldn't be possible to catch and hold the number of birds you are talking 

about... 
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

28

Appendix 2 – Expert opinions on keeping BTCUs in captivity

Eight scientists with significant field experience working with BTCUs or similar species were consulted by 

Flint (2010), A. Wegmann, or K. Swinnerton regarding the feasibility of housing this species. Below are 

pertinent excerpts from their email communications or conversations. 

Jeff Marks

” I held birds over night several times without incident until the night when I put two in the screen tent. 

One was dead by morning, for reasons unknown. They did not seem to eat (dead and incapacitated 

ghost crabs) or drink overnight, but sample sizes were small.”

Lee Tibbitts 

...I doubt you could hold them in captivity and keep them healthy; stress levels would be so high in the 

captive birds and we've found that stress is a big factor in how curlews ultimately tolerate banding and 

satellite-tagging... 

Wally Johnson

In my opinion, it would be nearly impossible to catch/transport/hold BTCUs. Seems like it would be a 

huge challenge to capture more than a few, and there would be injuries and problems trying to hold them 

for longer than the usual time required for routine banding. I guess I'd view it as a necessary trade-off -

the loss of some birds for the long-term good of the atoll...

Bob Gill

...Any curlew husbandry should be thoroughly evaluated a year ahead of time (different needs by age, 

sex, molt status, etc.). Recent experience with Dunlin and Rock Sandpipers was very enlightening and not 

something I'd want to jump into with curlews...

D. Lank email correspondence with B. Flint (message truncated)

If you captured the birds, I believe that you could keep them. I have maintained golden plovers in 

captivity for over a year. The curlews might be more of a challenge, but I believe that they could handle 

crowding for a month. They may be in the wild quite territorial, but like other shorebirds, would adapt to 

situations. The golden plover, for example, can either be territorial during the winter or flock. I don't see 

fundamentally why the curlews would not do so as well.

R. Lanctot email correspondence with K. Swinnerton
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

29

As a general rule with waders the bigger they are the more of a challenge they become because they are 

aggressive to each other, when confined, and as they are so mobile they are extremely prone to trauma 

injuries when flying into fence posts etc. Our experience with black-tailed godwits at Living Coasts was 

not a happy one for that reason.

If it has to be done in the winter I am sure that you could probably hold small groups of birds in large, 

lightly-netted aviaries, and if they are like other curlews they should be pretty catholic feeders that will 

learn quite quickly to take food from a dish (but do we know much about their feeding ecology?). So from 

that perspective the task is 'doable' but you will almost certainly get losses from trauma unless you 

feather clip them but then you would be stuck with them for a year.

Simon Tonge email correspondence with K. Swinnerton, Island Conservation (message truncated)

... If it has to be done in the winter I am sure that you could probably hold small groups of birds in large, 

lightly-netted aviaries, and if they are like other curlews they should be pretty catholic feeders that will 

learn quite quickly to take food from a dish (but do we know much about their feeding ecology?). So from 

that perspective the task is 'doable' but you will almost certainly get losses from trauma unless you 

feather clip them but then you would be stuck with them for a year.

Margaret Rubega email correspondence with K. Swinnerton (message truncated)

...In principle, I don't see why it wouldn't be possible to catch and hold the number of birds you are talking 

about. I would be more than happy to work with you on this, assuming that you really have exhausted all 

the other possibilities, because catching and holding the birds seems to me like a very labor and resourceintensive way to achieve the ultimate goal...

....Jacklighting them on a high tide?....

So: to be clear: I don't think holding the birds would be that much of a challenge, though it will likely be 

expensive --- it will either be labor intensive, so you'll need a lot of people, or it can be less labor intensive, 

but then you have to build good facilities. 

Dov [Lank] holds that many birds all the time, though not in temporary facilities. I've held....10 species of 

shorebird now, for periods ranging up to 3 years, although none since UConn closed the animal care 

facility containing my spaces. I've advised a couple of zoos on a number of other species, and I believe 

you can hold pretty much anything in captivity for six weeks with the right resources and careful planning 

ahead of time.

Kendall, B. E. 1998. Estimating the magnitude of environmental stochasticity in survivorship 

data. Ecological Applications 8:184-193.

Marks, J. S. and R. L. Redmond. 1996. Demography of bristle-thighed curlews, Numenius 

tahitiensis, wintering on Laysan Island. Ibis 138:438-447.

Marks, J. S., T. L. Tibbitts, R. E. Gill, and B. J. McCaffery. 2002. Bristle-thighed curlew 

(Numenius tahitiensis). Birds of North America 705.

Morrison, R. I. G., B. J. Mccaffery, R. E. Gill, S. K. Skagen, S. L. Jones, G. W. Page, C. L. 

Gratto-Trevor, and B. A. Andres. 2006. Population estimates of North American 

shorebirds, 2006. Wader Study Group Bulletin 111:67-85.
Risks & Mitigation Options for Bristle-thighed Curlews on Palmyra Atoll during Rat Eradication

30

Redmond, R. l. and D. A. Jenni. 1986. Population ecology of the Long-billed curlew (Numenius 

americanus) in Western idaho. Auk 103:755-767.

Stenzel, L. E., G. W. Page, J. C. Warriner, J. S. Warriner, D. E. George, C. R. Eyster, B. A. 

Ramer, and K. K. Neuman. 2007. Survival and natal dispersal of juvenile snowy plovers 

(Charadrius alexandrinus) in central coastal California. The Auk 124:1023-1036.
1

APPENDIX I

HERMIT CRAB PREDATION BY BRISTLE‐THIGHED CURLEWS
2
1

Slamming Crabs: Bristle-thighed Curlew predation 

of hermit crabs (Coenobita sp.) at Palmyra Atoll

A technical report prepared for the US Fish and Wildlife Service, Palmyra Atoll 

National Wildlife Refuge

Alexander Wegmann*, February 1, 2011.

*Contact: Island Conservation, 100 Shaffer Rd, Santa Cruz, California, 95060, +1-831-359-4787; alex.wegmann@islandconservation.org

INTRODUCTION

Several million shorebirds annually migrate from summer Arctic breeding grounds to 

winter foraging areas (Morrison et al. 2000) along nine primary north-to-south flyways 

(Piersma and Lindstrom 2004). Many species spend non-breeding months on Polynesian 

islands in the tropical pacific. This habitat shift, from Arctic tundra to tropical islands, often 

requires diversified foraging behavior by migratory birds. The Bristle-thighed Curlew 

(Numenius tahitiensis), one of the largest wading birds (Scolopacidae) in the world, winters 

on islands from the Northwestern Hawaiian Archipelago well into the south Pacific. Bristlethighed Curlews (BTCU) leave Pacific wintering islands in late July, and depart for Arctic 

breeding grounds in early May (Marks 2002). The BTCU is the only migratory shorebird 

that winters exclusively on oceanic islands, the only shorebird that becomes flightless while 

molting feathers, and the only shorebird known to use “tools” (Marks and Hall 1992) while 

foraging. BTCUs engage in “slamming,” to break shells and carapaces to access high yield 

food resources like seabird eggs and crustaceans (Marshall 1951, Child 1960, Carpenter et 

al. 1968, Marks and Hall 1992). When slamming, a bird holds the prey in its beak, raises it 

overhead, and hurls it against a flat rock or hard patch of earth. This action repeats until the 

prey, or the prey’s protective cover, is broken and easily consumed. 

On many tropical islands, land crabs, as the largest, native terrestrial consumers influence 

plant recruitment through decomposition of leaf-litter (O'Dowd et al. 2003) seed dispersal 

(Lindquist and Carroll 2004), and seed and seedling predation (Sherman 2002, Lindquist 

and Carroll 2004) . Few records of BTCU foraging behavior document hermit crab 

predation (Marshall 1951, Gill and Redmond 1992), while most published accounts 

involving terrestrial decapods and BTCUs discuss shore crabs (Hemigrapsus sp.) (Leeman et 

al. 2001), ghost crabs (Uca sp.) and fiddler crabs (Ocypode sp.) (Marks et al. 2002). This 

study provides the first quantitative account of hermit crab predation by BTCUs, and 

discusses how this foraging activity may put BTCUs at risk of secondary poisoning during 

toxicant based invasive mammal eradication programs. 
2

METHODS

This study lasted 106 days, from 30 June to 14 October, 2006, at Palmyra National Wildlife 

Refuge (Palmyra) in the Line Island Archipelago (5o 52’ N, 162 o 06’ W). Palmyra is a tight 

formation of 25 small, low islands totaling 218 hectare of emergent land; shallow coral reef 

stretches 16 km east to west by 3 km north to south. Rainfall on Palmyra often exceeds 

4000 mm annually (Depkin 2002), and Palmyra’s tropical climate promotes impressive 

vegetative growth. The atoll is home to five native land crab species, and one introduced 

rodent (Rattus rattus). Eleven seabird species nest and roost at Palmyra, while ten

shorebird species migrate to the atoll seasonally (Wegmann 2006). Of Palmyra’s five land 

crab species, the two hermit crabs, Coenobita perlatus and C. brevimanus, are most 

abundant. An atoll-wide land crab population survey conducted in July, 2004, measured the 

following mean hermit crab densities (crabs/ha.) for the three dominant forest types: 

Pisonia grandis forest, Tournefortia argentea forest, and Terminalia catappa forest; 123 ± 47 

(SD), 193 ± 113 (SD), and 324 ± 87 (SD) (Howald et al. 2004). 

I monitored eight BTCU slamming stations in three different forest habitats on two islands 

at Palmyra; One station in T. argentea forest, two stations in T. catappa forest, and five 

stations in Pisonia grandis forest. I identified slamming stations by the conspicuous 

arrangement of tens to hundreds of fractured turban snail (Turbanidae) shells and other 

gastropod shells surrounding a flat stone. At each station I first counted the number of 

slammed shells by collecting and tallying only whole shells or apex shell fragments, thus 

avoiding multiple tallies from fragments of the same shell, and then swept all shell 

fragments clear from a 1 m. diameter swath around the slamming rock (Figure 1). The 

swaths were cleaned again after each sample. Each shell tallied equaled one hermit crab 

predation event. Turban snail shells (2-5 cm long), were counted as adult hermit crab 

predation events, and smaller gastropod shells (0.5-2 cm long) equaled juvenile hermit crab 

predation events. After initial sampling, I opportunistically re-sampled each slamming 

station; shells in the previously-swept perimeter around the slamming stone counted as

new predation events.

From 30 August to 7 September, I positioned a Bushnell Trail Scout® digital motion-sensing 

camera trap at one BTCU slamming station in P. grandis habitat to identify other potential 

organisms responsible for broken turban snail shells near slamming stations. BTCUs are 

easily disturbed by humans, often flushing 30-50 meters away from an observer (A. 

Wegmann per. obs.); camera traps allow for direct observation of slamming stations. The 

camera trap recorded still images and fifteen-second video clips.

RESULTS

Periodic sampling of BTCU slamming stations at Palmyra Atoll shows that hermit crab 

predation rates vary by station, and predation on adults is more intense than predation on 

juveniles (one-tailed T test, T = 1.99, P = 0.03) (Table 1). The five slamming stations

sampled in P. grandis forest represent all of the slamming stations on 1.2 ha Home Island. 

The median slamming rate for Home Island is 0.23 hermit crab predation events per day; 

scaled to the island’s area, this becomes 0.19 crab predation events per day, per hectare. 

Palmyra Atoll’s hermit crab population is estimated at 248,956 individuals (Howald et al. 

2004). Based on the Home Island median slamming rate per hectare, Palmyra’s BTCU 
3

population of 250-300 individuals (USFWS unpublished data 2010) slams and consumes

1,306 hermit crabs during their 315 day wintering season at Palmyra.

The camera trap captured 26 images (still images and video clips) where a BTCU was near 

or standing on the slamming stone, four images with a Pacific Golden Plover (Pluvialis fulva) 

near the slamming stone, and two images with a large land crab (Cardisoma carnifex) near 

the slamming stone. Of the 26 BTCU images, six images show BTCUs in close association (< 

0.5 m) with a hermit crab, three images show BTCUs touching the crab with their bills, and 

one video clip shows a BTCU slamming an adult hermit crab. 

There is no information available on individual BTCU behavior variation at Palmyra. We do 

not know whether some individuals are hermit crab specialists and others do not engage in 

this behavior, or whether all of Palmyra’s BTCU prey on hermit crabs.

REFERENCES CITED

Carpenter, M. L., W. B. Jackson, and M. W. Fall. 1968. Bird populations at Eniwetok Atoll. 

Micronesica 4:295-307.

Child, P. 1960. Birds of the Gilbert and Ellice Islands Colony. Atoll Research Bulletin 74.

Depkin, C. 2002. Palmyra Atoll NWR, 06 August 2001 to 03 September 2002., US Fish and 

Wildlife Service - Pacific Remote Islands National Wildlife Complex, Honolulu.

Gill, R. E., Jr. and R. L. Redmond. 1992. Distribution, numbers, and habitat of Bristle-thighed 

Curlews (Numenius tahitiensis) on Rangiroa Atoll. Notornis 39:17-26.

Howald, G., A. Samaniago, S. Buckelew, P. McClelland, B. Keitt, A. Wegmann, W. C. Pitt, D. S. 

Vice, E. Campbell, K. Swift, and S. Barclay. 2004. Palmyra Atoll rat eradication 

assessment trip report, August 2004. Island Conservation, Santa Cruz, California.

Leeman, L. W., M.A. Colwell, T.S. Leeman, and R. L. Mathis. 2001. Diets, energy intake, and 

kleptoparasitism o fnonbreeding Long-billed Curlews in a northern California 

esturay. The Wilson Bulletin 113:194-201.

Lindquist, E. S. and C. R. Carroll. 2004. Differential seed and seedling predation by crabs: 

impacts on tropical coastal forest composition. Oecologia 141:661 - 671.

Marks, J. S. and C. S. Hall. 1992. Tool use by Bristle-thighed Curlews feeding on Albatross 

eggs. Condor 94:1032-1034.

Marks, J. S., T. L. Tibbots, R. E. Gill, B. J. McCaffery. 2002. Bristle-thighed Curlew (Numenius 

tahitiensis). The Birds of North America 705.

Marks, J. S., T. L. Tibbots, R. E. Gill, and B. J. McCaffery, editors. 2002. Bristle-thighed Curlew 

(Numenius tahitiensis). The Birds of North America, Inc., Philadelphia, PA.

Marshall, J. T. J. 1951. Vertebrate ecology of Arno Atoll, Marshall Islands. Atoll Research 

Bulletin 3.

Morrison, R. I. G., R.E. Gill, B.A. Harrington, S. Skagnen, G.W. Page, C.L. Gratto-Trevor, and S. 

M. Haig. 2000. Population estimates of near-arctic shorebirds. Waterbirds 23:337-

352.

O'Dowd, D. J., P. T. Green, and P. S. Lake. 2003. Invasional 'Meltdown' On An Oceanic Island. 

Ecology Letters 6:812-817.

Piersma, T. and A. Lindstrom. 2004. Migrating shorebirds as integrative sentinels of global 

environmental change. Ibis 146:61-69.

Sherman, P. M. 2002. Effects of Land Crabs on Seedling Densities and Distributions In a 

Mainland Neotropical Rain Forest. 18.
4

Wegmann, A. 2006. The Influence of Native and Non-native Herbivores on Forest Dynamics 

in an Atoll Ecosystem: How will Palmyra Atoll's Flora Respond To the Removal of 

Rattus rattus? University of Hawaii.

TABLES AND FIGURES

Table 1. Number of hermit crab predation events at BTCU slamming stations by habitat type and 

number of days after the initial sample. Predation rate is a measure of individual crabs taken per 

day. A median predation rate is only shown for the P. grandis habitat as this was the only grouping of 

slamming stations with both adult and juvenile predation events

Days Since Initial Sample Predation 

Rate 

Station Habitat Initial sample 18 34 41

Ad. Jv. Ad. Jv. Ad. Jv. Ad. Jv. Ad. Juv.

1 T. argentea 149 23 * * * * 0 0 0 0

2 P. grandis 70 9 * * 1 1 4 0 0.30 0.03

3 P. grandis 27 5 * * 2 0 0 0 0.06 0

4 P. grandis 168 21 * * 8 0 14 5 1.12 0.12

5 P. grandis 762 288 * * 5 4 * * 0.15 0.12

6 P. grandis 135 14 * * 14 2 * * 0.41 0.06

7 T.catappa 1 14 * * 0 0 * * 0 0

8 T.catappa 18 4 7 0 * * * * 0.39 0

* Data is not available

Figure 1. (A) Turban Snail shell carried by a hermit crab (Coenobita perlatus), the arrow indicates the 

shell’s apex. (B) Slamming station prior to initial assessment; note the C. perlatus on the slamming 

rock and surrounding shell fragments. (C) Slamming station swept clean to 1m radius from the stone. 
1

APPENDIX J

PALMYRA FOOD WEB
2
Appendix J.		Palmyra Food Webs
Figure	3:	Palmyra	food	web	with	rats	removed.	
Figure 4. A simplified, terrestrial food-web for Palmyra Atoll that centers on direct and indirect consumption 

of Brodifacoum 25Wtm and subsequent exposure to brodifacoum through secondary pathways. Primary 

consumption pathways are represented by solid lines, and secondary consumption pathways are represented 

by dashed lines. Line thickness is scaled to the likelihood of a consumption pathway being realized; a thicker 

line indicates that the indicated consumption pathway is “more” likely to occur given the foraging biology of 

the organisms involved in the pathway. Arrows indicate the direction of the pathway, and circles are nodes 

that connect similar pathways.
** THIS IS A WORKING DOCUMENT -- DO NOT CITE ** v. 4-19-2011

1

Draft Operational Details: 

Palmyra Atoll Rat Eradication – Alternative C

(Preferred Alternative)

Prepared by:

Island Conservation

100 Shaffer Rd

Santa Cruz, CA 95060

Contact:

Alex Wegmann

alex.wegmann@islandconservation.org
TABLE OF CONTENTS

1 INTRODUCTION ...................................................................................................................................... 4

1.1 PURPOSE........................................................................................................................................................................................... 4

1.2 AGENCIES.......................................................................................................................................................................................... 5

2 GOALS, OBJECTIVES, OUTCOMES ........................................................................................................... 5

2.1 GOALS................................................................................................................................................................................................ 5

2.2 OBJECTIVES ...................................................................................................................................................................................... 5

2.3 OUTCOMES ....................................................................................................................................................................................... 5

3 PROJECT SITE.......................................................................................................................................... 6

3.1 BIOGEOGRAPHY ............................................................................................................................................................................... 6

3.2 PALMYRA'S ERADICATION ENVIRONMENT.................................................................................................................................. 7

3.3 FACILITIES........................................................................................................................................................................................ 9

4 SITE PREPARATION................................................................................................................................ 9

4.1 FACILITIES AND INFRASTRUCTURE............................................................................................................................................... 9

5 ERADICATION TECHNIQUE ...................................................................................................................10

5.1 BAIT AND BAIT SOWAGE RATES ..................................................................................................................................................11

5.1.1 Bait transport and storage ..................................................................................................................................................12

5.2 AERIAL BROADCAST......................................................................................................................................................................13

5.2.1 Helicopter operations plan ..................................................................................................................................................13

5.2.2 Preventing bait spread into the marine environment.............................................................................................13

5.2.3 Coverage of baiting gaps......................................................................................................................................................14

5.2.4 Resuming baiting after unplanned stops.......................................................................................................................14

5.2.5 Baiting of Cooper Island........................................................................................................................................................14

5.2.6 Baiting of land areas other than Cooper Island .........................................................................................................16

5.3 HAND BROADCAST ........................................................................................................................................................................16

5.4 BAIT STATIONS ..............................................................................................................................................................................17

5.4.1 Bait station placement guidelines for commensal buildings................................................................................17

5.5 CRITERIA FOR SELECTING BAIT APPLICATION METHODS........................................................................................................19

6 SHOREBIRD PROTECTION.....................................................................................................................21

6.1 POPULATION MONITORING TO IDENTIFY OPTIMUM RODENTICIDE BROADCAST SCHEDULE THAT WILL MINIMIZE 

SHOREBIRD EXPOSURE TO BAIT...................................................................................................................................................................21

6.2 CAPTURE OF OVER-SUMMERING SHOREBIRDS FOR PROTECTIVE CAPTIVE CARE.................................................................22

6.3 HANDLING PROTOCOLS................................................................................................................................................................22

6.4 AVIARY FACILITIES .......................................................................................................................................................................22

6.5 BIRD CARE PERSONNEL ...............................................................................................................................................................22

6.6 POST-ERADICATION PROTOCOL..................................................................................................................................................23

7 OPERATIONS TEAM ...............................................................................................................................24

7.1 POSITION DESCRIPTIONS AND RESPONSIBILITIES ....................................................................................................................26

8 OPERATIONS COMMUNICATION PLAN......................................................................................................31

8.1.2 Emergency Traffic....................................................................................................................................................................32

9 BRIEFING, TRAINING, AND DEBRIEFING.....................................................................................................37

9.1.1 Briefing and Training.............................................................................................................................................................37

9.1.2 Hot Debriefing ...........................................................................................................................................................................37
9.1.3 Post Operation Audit ..............................................................................................................................................................37

10 TIMING................................................................................................................................................37

10.1 BIOLOGICAL WINDOW...................................................................................................................................................................37

11 MONITORING......................................................................................................................................37

12 HEALTH AND SAFETY........................................................................................................................37

12.1 SAFETY PLAN.................................................................................................................................................................................37

12.2 DOMESTIC ANIMAL CARE ............................................................................................................................................................37

13 IMPLEMENTATION TIMELINE ....................................................................................................................38

14 DEMOBILIZATION..............................................................................................................................40

14.1 EXCESS BAIT DISPOSAL.................................................................................................................................................................40

14.1.1 Supplies, equipment and infrastructure (TBD).....................................................................................................40

15 REFERENCES CITED ...........................................................................................................................40

16 APPENDIX: HELICOPTER OPERATIONS PLAN .................................................................................42

16.1 LOADING ZONE (LZ)....................................................................................................................................................................42

16.1.1 Communications (Air Ops).............................................................................................................................................42

16.2 WEATHER FORECASTS..................................................................................................................................................................43

16.3 HELICOPTER STORAGE.................................................................................................................................................................43

16.4 AERIAL OPERATIONS SAFETY .....................................................................................................................................................43

16.4.1 Hazard Identification and Mitigation.......................................................................................................................44

16.4.2 Flight Following (on island)...........................................................................................................................................44

16.4.3 Overdue Aircraft/Emergency Response ...................................................................................................................45

16.4.4 Personnel Experience/Training ...................................................................................................................................45

16.4.5 Personnel Protective Equipment (PPE)....................................................................................................................45

16.5 MARSHALLING / CRASH RESCUE................................................................................................................................................46

16.6 AERIAL BROADCAST IMPLEMENTATION ...................................................................................................................................46

16.6.1 Aerial Ops Command Structure....................................................................................................................................46

16.6.2 Commencement of Application.....................................................................................................................................46

16.6.3 Daily decision to apply bait............................................................................................................................................46

16.6.4 Daily schedule of events...................................................................................................................................................47

16.6.5 Bait-bucket Loading Procedures.................................................................................................................................48

16.6.6 Aerial Data.............................................................................................................................................................................48

16.6.7 Refueling.................................................................................................................................................................................49
4

1 INTRODUCTION

1.1 Purpose

The purpose of this conservation project is to aid in the protection and restoration of the 

unique native species and habitats of Palmyra Atoll (Palmyra) by removing non-native rats 

from the atoll that harm native trees, seabirds, land crabs, other populations of native 

species, and ecosystem processes.

Given the widespread successful colonization of rats on islands and their impact on native 

species, rats are identified as key species for eradication. The most pronounced impact of 

introduced rats on island ecosystems is the extinction of endemic species of mammals, 

birds and invertebrates (Andrews 1909, Daniel and Williams 1984, Atkinson 1985, Howald 

et al. 2007) (Meads et al. 1984; Hindwood 1940; Tomich 1986). Even if species are not 

completely extirpated, rats can have negative direct and indirect effects on native species 

and ecosystem function. For example, comparisons of rat-infested and rodent-free islands, 

and pre- and post-rat eradication experiments, have shown that rats depress the 

population size and recruitment of birds (Thibault 1995, Jouventin et al. 2003) (Campbell 

1991), reptiles (Whitaker 1973) (Bullock 1986; Cree et al. 1995; Towns 1991), plants 

(Campbell et al. 1984; Pyle et al. 1999; Wegmann 2009) and terrestrial invertebrates 

(Ramsey 1978; Bremner et al. 1984).

In addition to preying on seabird chicks, eggs, and sometimes adults, introduced rats feed 

opportunistically on plants, and alter the floral communities of island ecosystems 

(Campbell and Atkinson 2002, Wegmann 2009), in some cases degrading the quality of 

nesting habitat for birds that depend on the vegetation (Young et al. 2010). On Tiritiri 

Matangi Island, New Zealand, ripe fruits, seeds, and understory vegetation underwent 

significant increases after rats were eradicated from the island, indicating their previous 

impacts on the vegetation (Graham and Veitch 2002). At Palmyra, the native tree 

Neisosperma oppositifolium established on islands that were temporarily cleared of rats –

this is the first record of N. oppositifolium recruitment since rats were introduced to 

Palmyra 60 years prior.

Rats are known to cause disturbance to sensitive breeding seabirds, resulting in failed 

breeding attempts and higher susceptibility to predation by other species (Tomkins 1985, 

Jouventin et al. 2003). Rats also affect the abundance and age structure of intertidal 

invertebrates (Navarrete and Castilla 1993). Rats alter key ecosystem properties; for 

example, total soil carbon, nitrogen, phosphorous, mineral nitrogen, marine-derived 

nitrogen and pH are lower on invaded islands relative to rat-free controls (Fukami et al. 

2006). Such changes are a result of indirect negative effects of rats mediated by the 

reduction in seabird populations – rat predation often drives seabird colonies to nearextirpation (Moller 1983, Atkinson 1985, McChesney and Tershy 1998), resulting in the 

loss of seabird-derived nutrients on islands (Fukami et al. 2006).

By removing rats from Palmyra, we aim to safeguard the atoll’s indigenous flora and fauna, 

and create a refuge for species within the central Pacific region that are at risk of extinction. 
5

This project will achieve a monumental conservation milestone for the Refuge, and will 

establish a benchmark for subsequent eradication campaigns on other tropical islands.

1.2 Agencies

In 2001, after a long history of military and private ownership, most of Palmyra and the 

surrounding coral reef were designated as a National Wildlife Refuge by the Secretary of 

the Interior. The U.S. Fish and Wildlife Service (FWS) and The Nature Conservancy (TNC) 

co-manage Palmyra’s emergent land area, and in 2009 Palmyra was included within the 

Pacific Remote Islands Marine National Monument. 

In 2008, a three-party partnership (FWS, TNC, and Island Conservation (IC)) was formed to 

seek funding for, develop, and implement a rat eradication program at Palmyra.

2 GOALS, OBJECTIVES, OUTCOMES

2.1 Goals

The goal of this project is to aid in the protection and restoration of Palmyra’s unique 

native species and habitats by removing non-native rats that harm populations of native 

trees, nesting seabirds, and land crabs.

2.2 Objectives

The objectives of this project are:

The complete and permanent removal of black rats from Palmyra with minimal 

negative impact to native biota.

Testing and documentation of rodent eradication tools and monitoring methods 

tailored for tropical environments.

2.3 Outcomes

The anticipated outcomes from this conservation action are:

Increased recruitment of native tree species

Increased fledging success for several seabird species, and possible recruitment of 

several species that were likely extirpated from the atoll in the 20th century.

Creation of potential refuge for two critically endangered land bird species: 

Acrocephalus aequinoctialis (Christmas Island Warbler) and Prosobonia cancellata

(Tuamotu Sandpiper).

Development of conservation tools that will benefit future rodent eradication 

campaigns on tropical islands.
6

3 PROJECT SITE

3.1 Biogeography

Palmyra is among the most isolated island systems in the world. It lies in the central Pacific

approximately 350 nautical miles north of the equator: longitude 162 04’ 59.05" W, latitude 

005 52’ 55.54" N (Figure 1). Palmyra is part of the chain of islands called the Northern Line 

Islands, along with Kingman Reef to its northwest and the Kiribati Line Islands to its south.

Similar in climate to archetypal continental and high island tropical rainforests, yet 

drastically dissimilar in biogeography, the tropical forest systems in the Northern Line 

Islands lack species richness and diversity of flora and fauna (Rock 1916, Mueller-Dombois 

and Fosberg 1998). Palmyra has a remnant, regional flora that is typified by low species 

richness and low rates of endemism (Wester 1985, Mueller-Dombois and Fosberg 1998), 

yet this atoll provides important habitat for resident and migratory fauna, including 

seabirds, shorebirds, reptiles, and land crabs. 

Through the last two-hundred years, Palmyra experienced major habitat manipulation and 

numerous plant and animal invasions, including the introduction of black rats (Rattus 

rattus). Palmyra’s biotic community is no longer subject to direct anthropogenic 

disturbance, and this latter factor renders Palmyra’s biotic community unique among 

Central Pacific tropical moist forest systems.

Figure 1. Geographic map of Palmyra Atoll (Collen et al. 2009). 

Palmyra’s native flora and fauna have been marginalized due to WWII-era landform 

restructuring and introductions of non-native species, notably coconut palms, ants, scale 

insects, and black rats. Nevertheless, Palmyra is an important center of biodiversity and 
7

species abundance in the Central Pacific region. Now protected within the US Fish and 

Wildlife Service’s National Wildlife Refuge system, Palmyra sharply contrasts with other 

moist Central Pacific island groups where the degradation of terrestrial and marine 

ecosystems keeps pace with increased anthropogenic resource exploitation. However, the 

continued presence of omnivorous black rats on the atoll will not allow recruitment or 

population establishment of those species which are limited by the direct or indirect 

impact of the alien rat population.

3.2 Palmyra's eradication environment

Tropical oceanic islands represent some of Earth’s most biologically unique ecosystems, yet 

the very remoteness that fuels high levels of endemicity and species radiations on islands 

also renders such systems vulnerable to invasive species. Invasive mammal eradications 

are a proven, effective method of restoring damaged ecosystems and preserving 

biodiversity on Islands (Towns and Broome 2003, Howald et al. 2007). The presence of 

indigenous land crabs on most tropical islands poses a novel challenge to eradication 

projects, and especially eradications targeting rodents (Wegmann 2008). Land crab 

consumption of rodenticide bait complicates rodent eradication programs by requiring 

inflated bait application rates, which increases the risk of non-target species exposure to 

rodenticide. Because current rodent eradication practices are based on successful 

temperate or subantarctic campaigns, the conservation community does not have timetested methods for mitigating land crab interference; Palmyra’s eradication environment 

presents a novel suite of challenges.

Palmyra’s emergent land area consists of 25 distinct islands ranging in size from < 0.1 ha to 

over 100 ha. The islands are separated by shallow channels or lagoon flats, some of which 

are emergent at low tide. Three deep lagoons run east-west between the two major island 

groups, and a thin (10-20m) wide causeway runs north-south between the Center Lagoon 

and Eastern Lagoon (Figure 1). 

Palmyra is a breeding refuge for 10 seabird species; however, rat related egg and chick 

predation may have led to the extirpation of six additional species (Table 1). Without the 

consumptive pressure of an established human population, Palmyra’s land crab community

is among the richest and most robust in the Central Pacific region. Palmyra is home to six 

species of terrestrial crabs (excluding the intertidal families Grapsidae and Ocypodidae), 4 

of which are super abundant (Table 2). Palmyra’s crab community includes the coconut 

crab (Birgus latro), the world’s largest terrestrial invertebrate. 

Table 1. Breeding seabirds of Palmyra Atoll; * = Declining population trend

Family Common Name Scientific Name Breeding Pairs IUCN

Procellariidae Audubon’s Shearwater Puffinus lherminieri Believed extirpated LC

Wedge-tailed Shearwater Puffinus pacifica Extirpated LC

Phoenix Petrel Pterodroma alba Believed extirpated EN*

Hydrobatidae Polynesian Storm Petrel Nesofregetta fuliginosa Believed extirpated VU*

Sternidae Black Noddy Anous minutus 2,500 LC

Blue Noddy Procelsterna cerulean Believed extirpated LC

Brown Noddy Anous stolidus 1000 LC
8

Family Common Name Scientific Name Breeding Pairs IUCN

Sooty Tern Sterna fuscata 10,000 LC

Gray-backed Tern Sterna lunata Believed extirpated LC

White Tern Gygis alba 150 LC

Fregatidae Great Frigatebird Fregata minor 500 LC

Lesser Frigatebird Fregata aerial Non-breeder LC

Phaethontidae White-tailed Tropicbird Phaethon lepturus 15 LC

Red-tailed Tropicbird Phaethon rubricauda 20 LC

Sulidae Red-footed Booby Sula sula 5,000 LC

Brown Booby Sula leucogaster 150 LC

Masked Booby Sula dactylatra 20 LC

Table 2. Land crab and rat abundance survey results, Palmyra Atoll (Flint 1992, Howald et al. 2004). Units 

represent #/hectare estimates and range in measured body mass. a (Burggren and McMahon 1988), 

b(Wegmann and Middleton 2008).

Species Mean (#/ha) ± SD Adult mass (g)

Land Crabs Birgus latro 7 ± 38 5000a

Cardisoma carnifex 33 ± 8 300a

Cardisoma rotundum 28 ± 5 200a

Coenobita brevimanus 46 ± 8 100a

Coenobita perlatus 182 ± 80 100a

Rodent Rattus rattus 90 ± 60 164b

Palmyra’s plant community includes five distinct associations: Lepturus repens grassland, 

Hibiscus tiliaceus forest, Terminalia catappa forest, Pandanus fischerianus forest, and 

Phymatosorus grossus meadow. Presently, C. nucifera forest and S. taccada – T. argentea

forest respectively cover 40% and 30% of Palmyra’s land area. Patchy stands of Pisonia 

grandis, Pandanus fischerianus, H. tiliaceus, T. catappa, and meadows of L. repens and 

Phymatosorus grossus constitute the remaining 30%; nine additional tree species occur in 

low numbers at Palmyra. Mature C. nucifera trees comprise 45% of Palmyra’s forest 

canopy. Much of Palmyra’s vegetated area is difficult to traverse by foot, and paths cut 

through the dense vegetation require frequent maintenance

Palmyra’s WWII legacy includes remnant concrete structures (bunkers, gun emplacements, 

pill boxes) and unexploded ordinance (UXO). The enclosed concrete structures, along with 

structures associated with the PARC research station, provide refuge for rats and will be 

treated as rat habitat during the eradication. 

Lying within the Intertropical Convergence Zone, Palmyra is frequented by low pressure 

systems that result in over 400 cm of rain each year. A summary of several climate factors 

measured at Palmyra (2002 – 2009) for June and July, the months targeted for this 

operation, is presented in Table 3.
9

Table 3. A summary of climate factors measured at Palmyra between the years 2002 and 2009.

Month Daily Monthly

Max 

precip 

(mm)

Mean 

precip 

(mm)

Mean # of days 

with < 10 mm of 

precip

Mean max 

temp in the 

shade (°C)

Mean wind 

direction

(°)

Min wind 

speed (kts)

Mean of 

max wind 

(kts)

June 190 13 20 31 80 4 10

July 108 15 17 31 83 3 10

3.3 Facilities 

In 2004, TNC partnered with 10 academic institutions and government agencies in the 

establishment of the Palmyra Atoll Research Consortium (PARC). In 2005, a research 

station was constructed on Cooper Island (TNC 2005). The station includes 16 small 

residential cottages, a galley, shower house, bathrooms, a research laboratory, a wharf for 

offloading supplies from large ships and barges, tractors (with forks) and flat-bed trucks, a 

backhoe, three 15’ lagoon boats, a 25’ offshore boat, and a large workshop area. The 

station is capable of housing and supporting 25 staff and researchers at one time. Fresh 

water is supplied through a refurbished 100,000-gallon rainwater catchment tank. Electric 

power is generated and transmitted by two 50 kW diesel generators, and a satellite dish 

was installed in 2006 to supply the station with internet connectivity and web-based 

telephones. Pre-existing infrastructure in use on Cooper Island includes a seaplane ramp, a 

crushed-coral runway, and several WWII era concrete foundations and bunkers used for 

storage of supplies.

4 SITE PREPARATION

4.1 Facilities and infrastructure

While the PARC facility will provide many advantages to the eradication operation (use of 

equipment, vehicles, storage, meeting, and office space), the structures are potential rat 

habitat and the presence of human food and food-based refuse create regular feeding 

opportunities for rats; these factors warrant mitigation. 

Food within the camp provides potential sustenance for rats. To avoid providing 

opportunity for rats to eat anything other than bait during the implementation, all food 

stores in camp and kitchen areas will be secured. Personnel will work with the Palmyra 

Field Station Manager to ensure the security of all food storage areas. The compost pit, used 

for years, has been buried and all food and food-related waste is incinerated daily. 

Fresh potable water is supplied through a refurbished 100,000-gallon fresh water 

catchment tank (Figure 2). Personnel will cover the roof of the water catchment with large 

tarps to ensure that bait applied during the aerial broadcast does not contaminate the 

potable water supply, and the screening around the top three feet of the tanks walls will be 

reinforced to make sure that potential bait consumers (rats, cockroaches, etc) will not 

contaminate the potable water system. Other non-potable water supply catchment tanks 
10

are within the hand broadcast area and will not need to be covered; however, screens will 

be placed over the intake ports for all non-potable water tanks to prevent rats and 

invertebrates that have been exposed to the rodenticide from entering the tanks. After the 

baiting operation has been completed, samples from the potable water system will be 

tested for brodifacoum residue. If brodifacoum residue is detected, an alternate potable 

water system will be established and used until the primary system has been cleaned and 

subsequent tests fail to detect brodifacoum residue.

The dry lab facility will be converted into the base of operations during the 

implementation. Electronics will be stored inside the air-conditioned lab facility. Other 

supplies will be stored outside the lab on concrete and protected from the elements by a 

roof. The large shop area will be used to house the helicopters, and buckets, and for shortterm storage of bait pods. 

5 ERADICATION TECHNIQUE

The rat eradication action at Palmyra will include several bait application techniques that 

have been tailored to suit Palmyra’s eradication environment. US Environmental 

Protection Agency (EPA) regulations restrict the intentional spread of bait into the marine 

environment. Given Palmyra’s tortuous coastline and the small size of some of the islands 

(Figure 1), several broadcast baiting strategies will be employed to minimize the accidental 

spread of bait into the water bodies, which is termed “bait drift,” and maintain a uniform 

bait application at the designated sowage rates across the entire treatment area.

In order to ensure eradication success a second bait application will occur 10 to 14 days 

after the first to minimize the likelihood of missing competitively inferior adult rats or 

juvenile rats that survive the initial broadcast because they did not have an opportunity to 

feed on bait. For each bait application, there will likely be two to three consecutive days of 

bait broadcast. The extra four days allotted for the time between broadcasts will be 

contingency time in case of a delay with the first application.

Bait will be applied according to the limitations set by the EPA’s pesticide regulations. The 

bait application rate for the Palmyra rat eradication is based on the results of several bait 

availability studies conducted at Palmyra (Buckelew et al. 2005b, Wegmann et al. 2008). 

“Bait availability” is the time period within which rats have direct access to bait pellets 

broadcast on the ground. The 2005 trial eradication found that with bait application rates 

as high as 90 kg/ha, bait is available to rats for a maximum of seven days, and is only 

uniformly available for four days. Bait consumption by land crabs (c. 300 crabs/ha) is the 

primary factor determining bait availability. In order to ensure that rats have access to bait 

for four days, this operation requires bait application rates that exceed the maximum bait 

application rate specified by the bait product’s FIFRA registration. The project partnership 

is currently working with the US Department of Agriculture – National Wildlife Research 

Center to develop a supplementary registration specifically designed for and exclusive to 

use in Palmyra’s eradication environment. 
11

5.1 Bait and bait sowage rates

During the operation, the baiting plan calls for 39,147kg of 25W to treat Palmyra’s 250ha of 

emergent land twice at a sowage rate of 80kg/ha for the first application, and 75 kg/ha for 

the second application. An additional 10% of this amount will be brought as contingency 

bait (Table 4). The contingency bait will replace spoiled, spilled, or otherwise unusable 

bait, and will be used to fill in significant (≥ 10m) gaps between swaths of bait applied by 

air, but will not be applied to the treatment area in an amount that, when summed with 

amounts of bait previously applied to the same area during the same application, is in 

excess of the maximum bait application rate specified by the supplemental bait label (the 

supplemental label is in development and on scheduled to be released on 15 April, 2011). 

The target sowage rate for the second application will be lowered to 75kg/ha to account for 

an expected reduction in the number of bait consumers (rats) following the first bait 

application. 

Table 4. Bait usage table for the Palmyra Atoll rat eradication operation. The treatment area (Palmyra’s total 

emergent land area) is 250 ha. The target bait sowage rates are presented in the Notes column.

Bait application type

Bait 

brought 

to 

Palmyra 

(kg) Contingency

Bait for 

application 

(kg) Calculation notes

Aerial Application 40,920 10% 37,200

AERIAL APPLICATION: 1st 

application @80kg/ha, 2nd

application @75kg/ha (240 ha -

accounts for areas baited by 

hand) + 10% contingency

Hand Application 1,947 10% 1770

HAND APPLICATION: 1st 

application @80kg/ha, 2nd

application @75kg/ha (10 ha) + 

bait for bait stations: 150 

stations x 120g/application x 10 

applications + bait for abandoned 

structures: 100 structures @ 

200g/structure x 2 applications + 

10% contingency

Canopy Bait 195 10% 177

CANOPY: 2 applications @ 

25g/crown (3546 crowns) + 

10% contingency

TOTAL BAIT -

TREATMENT OF 

EMERGENT LAND 42,867 10% 38,970

TOTAL BAIT -

TREATMENT OF 

OVERHANING PALM 

CANOPY 195 10% 177

TOTALS 43,062 10% 39,147
12

5.1.1 Bait transport and storage

Any damage (fragmentation, molding) to the bait that happens during the transportation 

process could inhibit the bait application. Therefore, specific precaution will be taken with 

regard to handling, packing, transport, and storage to ensure that bait is in the optimal 

condition when it reaches Palmyra.

Following manufacture, bait will be packed and shipped from Bell Labs in Madison 

Wisconsin to the support vessel in Seattle, Washington. One bulk bag (Flexible 

Intermediate Bulk Container custom manufactured by BulkLift®) containing 318 kg of bait

will be placed inside a large plastic bag, and then inside a Buckhorn® Fixed Wall container 

(“pod”): [external dimensions (with lid in place) 47.9” x 43.8” x 31”) (internal dimensions 

45.6” x 42.0” x 23.9”). While inside the pod, each bulk bags will be filled with 318 kg of bait. 

When full, a desiccant pack will be placed between the bulk bag and the large plastic bag, 

the plastic bag will be sealed, and the pod’s lid will be secured in place. The pods will be 

stored inside 20 ft and 40 ft shipping containers. The 20’ containers will be loaded directly 

onto the deck of the support vessel, while the pods in the 40’ containers will be transferred 

from the containers to below-deck hold space on the vessel. Pods will be moved into and 

out of the containers with a forklift or pallet jack.

In addition to bait packaged in the bulk bags and pods, bait will be shipped in 11.3 kg (20 l) 

buckets. Bait from the 20 l buckets will be used to hand-bait areas of the atoll that cannot 

be baited via helicopter, and to fill and refill bait stations. The buckets will be strapped to 

pallets for secure transport and placed inside the 20’shipping container that is partially 

filled with pods.

Prior to shipment, temperature and humidity data loggers will be placed in seven pods: 2 

pods from the beginning of the bait manufacturing process, 3 pods from the middle, and 2 

pods from the end. The containers will remain unopened until the vessel makes a port call 

in Honolulu in route to Palmyra. At this point, each container will be opened and the bait 

inside one pod in each container will be inspected and the data from the data logger will be 

downloaded and assessed. Bait in at least one pod in each of the ship’s below-deck holds 

will also be inspected at this time and the data loggers (one in a pod in each hold) will be 

retrieved and the data will be assessed. All data loggers will be placed back in the pods 

from which they came, and will be checked again when the ship arrives at Palmyra. If the 

bait appears moist or moldy, immediate action will be taken to dehumidify the containers 

and the holds.

Upon arrival at Palmyra, the vessel will tie up at the Wharf (Figure 2) and offload the three 

pods containing non-toxic bait (for bucket calibration) and 60 pods of active bait for the 

first bait application. The pods will be retrieved from the 20’ containers by using a 

motorized pallet-jack, and then the pods will be lifted from the ship’s deck with a 10 ton 50 

ft telescopic crane. A second crane (12 ton 40 ft reach) will be used as a spare in the event 

of failure of the first crane. The empty containers will remain on the ship for the duration 

of the implementation. This process of offloading bait pods from the ship to the Wharf will 

be repeated prior to the second bait application.
13

Figure 2. Location of primary operational components for the Palmyra rat eradication project.

5.2 Aerial broadcast

Bait broadcast by helicopter will consist of multiple low-altitude overflights of Palmyra’s 

emergent land area. The baiting system will follow a script (Section 5.5) that is specifically 

designed to minimize bait spread into the marine environment while maintaining 

uniformity and compliance with the targeted sowage rates.

5.2.1 Helicopter operations plan

Refer to Appendix for a presentation of the helicopter operations plan.

5.2.2 Preventing bait spread into the marine environment

Every reasonable effort would be made to minimize the risk of bait broadcast into the 

marine ecosystem. A directional deflector will be attached to the hopper for all treatment 

of areas where the use of a full swath bucket would result in the application of bait into the 

marine environment. The deflector will broadcast bait to the onshore side of the 

helicopter, to minimize the risk of bait entering the ocean on the opposite, or seaward, side. 

Additionally, the hopper will be used with the broadcast motor off and spinner removed to 

sow narrow swaths of bait onto land areas that are less than 20 m and greater than 10 m 

wide. 

Palm trees growing along the shoreline commonly hang over the high tide line. To prevent 

bait from entering the marine environment, overhanging palms will be baited by hand 

(Wegmann et al. 2008) rather than with the helicopter and bait hopper. 
14

5.2.3 Coverage of baiting gaps

In cases where it is evident or suspected that a portion of the targeted land area greater 

than 5 m x 10m did not receive full coverage from aerial or hand baiting, there will be 

supplemental, systematic broadcast by hand or helicopter to fill in the gap.

5.2.4 Resuming baiting after unplanned stops

Bait will be applied to the atoll according to a section-by-section plan, so that an 

unexpected halt to baiting operations will result in a minimized unbaited edge for the 

previously baited section(s). When baiting resumes after the application was halted due to 

poor weather conditions, mechanical failure or other unforeseen logistical problems, the 

following guidelines direct how far back into previously baited areas baiting should 

commence to target rats that may have reinvaded treated areas.

Time delay Strategy to resume baiting

1 day At boundary of previous drop

2-3 days 2-4 swath widths behind the boundary (20-80 m)

> 3 days 4-6 swath widths behind the boundary (80 – 160m)

5.2.5 Baiting of Cooper Island

For Cooper Island, bait will be applied to the coastal block with the directional swath 

bucket, and each pass will be baited at 100% of the target sowage rate. A second, nonoverlapping pass will be made with a directional swath bucket along the inland edge of the 

coastal block – this block will be baited at 50% of the target sowage rate and will be 

overlapped by 50% of a swath laid down by the full swath bucket (Figure 3). With the full 

swath bucket, each bait swath will overlap the previous swath by approximately 50 percent 

to prevent the formation of gaps between baiting lines. The runway on Cooper Island will 

not be baited as it is not a refuge for rats and it is the primary roosting site for Palmyra’s 

shorebird populations (Figure 4). Other exclusions from the aerial baiting will include the 

camp area, inland bodies of water, and very small islets that are prominent shorebird 

roosting sites: Rust, Pillbox, and Dadu islets.
15

Figure 3. A depiction of the bait application strategy that will be used to transition from treatment of the 

coastal block to treatment of the interior block. The shapes to the left of the water indicate baiting blocks that 

are over the treatment area. The arrows at the top of the blocks indicate the relative direction of the bait flow 

from the baiting bucket. The flight lines will be along the left edge of the swaths that are sown with the 

directional swath bucket, and they will be down the center of the swaths that are sown with the full swath 

bucket. 

Figure 4. Strategy for excluding the runway on Cooper Island from the aerial bait application
16

5.2.6 Baiting of land areas other than Cooper Island

Other land areas will be treated with both the directional swath bucket, and the narrow 

swath bucket. All aerial bait application will be guided by a TracMap® GPS guidance 

system that shows baiting coverage and cautions the pilot against baiting outside 

predetermined areas. Adjustments in bait flow rates, helicopter speed, and flight lines will 

be made as is necessary to meet the optimal application rate, and while staying within the 

bait application limits legally required by the bait product’s FIFRA registration.

5.3 Hand broadcast

Concurrent to the aerial bait application, four to eight personnel trained in hand broadcast 

baiting (Wegmann et al. 2008) will treat land areas that are too narrow for aerial treatment

and the camp area – 2.7 ha (Figure 5). The hand broadcast team will apply bait at the 

prescribed application rates at each pre-determined baiting point. The hand broadcast 

team will take care to ensure that the bait spread is uniform and that there are no gaps 

between the hand broadcast area and the aerial broadcast area. Areas slated for hand 

broadcast will be treated directly after the adjacent area is treated by aerial broadcast. Bait 

will also be broadcast directly inside abandoned buildings at a rate that does not exceed 

the specifications of the bait product use label. After a building has been baited it will be 

marked (waypointed) with a GPS unit. Sixty abandoned structures have been located and 

mapped (waypointed); additional structures that are found during eradication activities 

will be mapped and treated accordingly.

Figure 5. The camp area exclusion from the aerial broadcast treatment. The camp area (2.7 ha) will be 

treated by hand broadcast of bait to the ground and palm canopy, and placement of bait stations in and 

directly around buildings. 
17

5.4 Bait stations

As a precautionary measure, bait stations containing 25W bait pellets will be placed around 

the research station, the wharf, and at select shorebird roosting sites (120 g/station x 50)

(Figure 6). Bait stations will be at a density that is in compliance with the 25W product use 

label. Bait stations will be loaded with 120 g of 25W bait pellets (the same bait that would 

be used for the broadcast portion of the bait application) at the onset of the bait 

application. All stations will be checked every five days, and bait will be refreshed as 

needed, and at least every two weeks for two months. All bait stations will be put in place 

at least four weeks prior to the operation.

Figure 6. Areas that will be treated with bait stations during the Palmyra Atoll rat eradication

5.4.1 Bait station placement guidelines for commensal buildings

Tamper-resistant bait stations will be placed in and around inhabited buildings in the camp 

area 6 weeks prior to the initiation of the bait broadcast. All bait stations locations have 

been mapped (waypointed). The following protocols were used to situate the stations and 

reduce a neophobic response by rats when the stations are activated.

1. Bait station quantities and spacing

a. Quantity of stations around the outside of each building

i. 1 station for every 400 ft2 of building

Shorebird roosting sights that will be treated with bait stations

The research station area that will be treated with bait stations and bait broadcast do

by hand
18

b. Quantity of stations inside each building

i. 1 station for every 200 ft2 of building

c. Station spacing

i. Space stations 5 – 50 m apart

2. Bait station placement

a. Placement of stations around the outside of buildings

i. Place each station on an overturned 5 gal bucket or other (slippery 

plastic) stand crabs cannot climb. 

1. Secure each station to the stand with a cable tie, string, or wire. 

ii. Stations should be placed along the edges of buildings and (if 

possible) in the shade and/or under some type of protective cover

1. Placing the stations in a protected location will increase the 

probability that rats will access the stations due to rat 

preference for covered/protected habitat

2. The bait stations themselves do not need to be covered or 

sheltered from rain/sun

iii. Mark each station placement with flagging tape, permanent marker, 

or by some other means

b. Placement of stations inside buildings

i. Place each station on the floor and against a wall – rats are more likely 

to run along walls than across an open space

ii. Stations should be placed near points where rats are expected to 

enter or exit the building – e.g., near the back doors at the galley. 

iii. If the building contains potential sources of food for rats (dishwasher, 

food prep area, food stores, shorebird feed, pet feed, etc.), stations 

should be placed near the food source. 

iv. Stations should be placed out of the way of everyday foot traffic. 
19

5.5 Criteria for selecting bait application methods

The following script explains the criteria by which different bait application methods will 

be selected. The script uses the type of treatment area as the primary factor (underlined), 

and then describes the bait application process through an ordered presentation of the 

following factors: bait application method (e.g., hand broadcast), sowage rate (e.g., 80 

kg/ha) and sowage features (e.g., 5 m swath, 0% overlap), treatment of gaps in the initial 

application, and exclusions from bait application. The aerial baiting components of this 

script pertain to the first bait application; for the second bait application, sowage rate 

values will change from 80 kg/ha to 75 kg/ha, and from 40 kg/ha, to 37.5 kg/ha.

1. Land 1 – 10 m wide

a. Hand broadcast

i. 80 kg/ha, 5 m swath, 0% swath overlap

1. Follows aerial treatment of adjacent blocks - occurs within 2 

hours of aerial treatment

ii. Exclusions

1. Active seabird nests on the ground

a. 2 m exclusion of bait broadcast around each nest

2. Water bodies

a. 1 m exclusion of bait broadcast along the edge of the 

water body

b. Exclusion of bait broadcast below the high water line

3. Inhabited structures

a. 1 m exclusion of bait broadcast around each inhabited 

building, no bait broadcast inside inhabited buildings

2. Land > 10 m wide

a. Aerial broadcast

i. Land 10 – 20 m wide

1. Narrow swath bucket

a. 80 kg/ha, 5 m swath, 0% swath overlap

ii. Land > 20 m wide except for Cooper Island

1. Coast & Interior

a. Directional swath bucket

i. 80 kg/ha, 20 m swath, 0% swath overlap

2. Gaps 

a. Narrow swath bucket

i. 80 kg/ha, 5 m swath, 0% swath overlap

iii. Cooper Island

1. Coast

a. Directional swath bucket

i. Outside pass

1. 80 kg/ha, 20 m swath, 0% swath overlap

ii. Inside pass
20

1. 40 kg/ha, 20 m swath, 0% swath overlap, 

50 % overlap with Interior passes -

assuming 20 m "throw-forward" at the 

beginning and end of each Interior line

2. Interior

a. Full swath bucket

i. 40 kg/ha, 40 m swath, 50% swath overlap

3. Gaps > 5 m wide and 10 m long

a. 0 kg/h recorded

i. Narrow swath bucket

1. 80 kg/ha, 5 m swath, 0% swath overlap

b. 40 kg/ha recorded

i. Narrow swath bucket

1. 40 kg/ha, 5 m swath, 0% swath overlap

iv. Exclusions

1. Cooper Island Runway

a. Full swath bucket

i. 40 kg/ha, 40 m swath along outside edge of 

runway, 50% overlap starting 20 m out from 

edge of runway

1. The grass fringe surrounding the runway 

(20 m) will receive 40 kg/ha

2. Camp

a. Full swath bucket

i. 40 kg/ha, 40 m swath centered on the camp 

exclusion boundary, 50% overlap starting 20 m 

inside the camp exclusion boundary

1. 50% overlap with the hand baited area 

will result in 80 kg/ha treatment across 

the camp exclusion boundary

3. Inland water bodies

a. Land 10-20 m wide

i. Narrow swath bucket

1. 80 kg/ha, 5 m swath around the edge of 

the water body

a. 1 m exclusion of bait broadcast 

around the edge of the water body 

4. Land > 20 m wide except Cooper Island

a. Directional swath bucket

i. 80 kg/h, 20 m swath along the edge of the water 

body

1. Gaps > 5 m wide and 10 m long

a. Narrow swath bucket

i. 80 kg/ha, 5 m swath, 0% 

overlap
21

5. Coast

a. Exclusion of bait broadcast below the high water line

3. Abandoned structure

a. Hand Broadcast

i. Up to 200 g of bait broadcast into structures less than 2,500 ft2, up to 

450 g of bait broadcast into structures greater than 2,500 ft2.

4. Palm crown overhanging water

a. Canopy bait

i. Crown overhanging ocean-facing shoreline that is inaccessible by foot

1. Air

a. 50 g bait bola dropped into every stand alone crown, or 

every 3rd interconnected crown

ii. Crown overhanging lagoon-facing shoreline

1. Ground

a. 50 g bait bola shot into every stand alone crown, or 

every 3rd interconnected crown

5. Inhabited structure

a. Bait Stations

i. Inside

1. 1 station for every 19 sq m of building space, 120 g of bait per 

station

ii. Outside

1. 1 station for every 37 sq m of building space, 120 g of bait per 

station

b. Traps (glue, snap)

i. Inside

1. 1 trap (glue and snap) for every 37 sq m of building space

6. Shorebird roosting islets not treated by broadcast baiting (Rust, Pillbox, Dadu)

a. Bait Stations

i. 1 - 2 stations per islet, 120 g bait/station

6 SHOREBIRD PROTECTION

6.1 Population Monitoring to identify optimum rodenticide broadcast schedule that will 

minimize shorebird exposure to bait.

Surveys will be conducted pre-broadcast to detect migration pulses and stabilization of 

summer numbers once all migrants have departed. Remaining birds will be captured when 

shorebird numbers remain low for 3 days. Weekly high tide counts serve as an index to 

shorebird numbers at Palmyra and have been done continuously since 2009. They will 

continue to be made once per week during the highest weekly tide until June 1 when they 

will be carried out daily. Atoll wide low tide counts are done once per month depending on 
22

available staff. Low tide counts count of all the shorebirds on Palmyra will be done twice in 

May and once between June 1 and June 7 at the best tide available.

6.2 Capture of over-summering shorebirds for protective captive care

Capture sites have been identified on the 6,000 foot crushed coral runway, North Beach, tidal flats 

and known roost sites. The utility of any particular capture location will depend on the tide, time 

of day, weather and bird behavior. Methods of capture to be employed include: decoys and call 

playback in combination with net-guns, mist-nets, noose carpets, drop nets and a catapult net.

6.3 Handling Protocols

Once shorebirds are captured they will be covered with a towel to reduce stress and banded. 

Morphological measurements, blood, and feather samples will also be taken. Birds will be placed 

in a plywood transport box (18”x16”x16”) and transported to the aviary. Before release into the 

aviary birds will have primary feathers trimmed to restrict flight and reduce the chance of injury. 

Bristle-thighed Curlews are unusual among shorebirds in that they go through a flightless period 

when they molt and are scheduled to molt 1 to 2 months after they are released from protective 

care.

6.4 Aviary Facilities

The aviary frame is made of 1” metal conduit that is divided into 10 10’x8’ pens (Total = 50’x16’) 

and covered with 70% shade cloth. The bottom outside edge will be covered with a 2’ aluminum 

sheeting to act as a visual barrier and to prevent rats and crabs from entering. The structure will 

be attached to the ground with concrete anchors to prevent wind damage. The flooring will 

consist of a rubberized flooring (Elephant BarkTM) that sits on top of a 6” layer of sand. The aviary 

will be outfitted with an irrigation system that will provide water flow over the floor periodically 

during the day. This will prevent overheating, aid in cleaning and help maintain feathers. Natural 

and artificial visual barriers within the aviary and along will give birds the opportunity to hide and 

help reduce the urge to pace. Each pen will have a capture door to aid in capture and reduce risk 

of injury. 

6.5 Bird Care Personnel

The veterinary doctor and wildlife biologists will monitor behavior, food consumption, water

intake, temperature, ventilation, fecal output, signs of capture myopathy, and stress of the birds 3 

times a day. Behavioral observations will be made from a blind and activity and noise will be 

restricted in the vicinity of the aviary. Birds with significant loss in body weight will be given 

gavage treatment. If a bird shows increasing signs of stress, the veterinarian will treat it as 

appropriate. Talking and visitation by nonessential personnel will be prohibited. The number of 

birds captured and put in each 10’x8’ pen will depend on the levels of intra-specific aggression 

they show. 
23

Birds in the aviary will be offered fresh and salt water, trout chow, locally collected seeds 

and invertebrates (pre-broadcast), hard-boiled egg yolk and vitamin/mineral supplements. 

Unconsumed food and water will be removed from the aviary each day.

6.6 Post-eradication Protocol

Healthy birds will be released with their aviary mates at their respective capture sites in the early 

morning once the toxicant in no longer a threat. The released birds will not be disturbed but will 

be monitored with a spotting scope or binoculars. Sightings of the color-banded birds will be 

recorded during the weekly high tide shorebird count. 

Food bowls will be placed at release sites to provide supplemental feeding opportunities for birds 

with clipped primaries until they molt and are again flighted. Feedings will occur during the same 

times as they were in the aviaries. 

 
24

7 OPERATIONS TEAM

The operations team for the Palmyra rat eradication will entail 39 personnel who will fill 51 positions, with some staff filling more than one 

position. Reporting will follow the command structure from the bottom up (Figure 7). 
25

Figure 7. Command structure for the Palmyra rat eradication operations team.
26

7.1 Position descriptions and responsibilities

Brief descriptions of each position are given below. A more detailed explanation of positions 

including the inherent roles and responsibilities will be provided to personnel prior to the 

operation.

Incident Advisory Group (IAG)

The IAG will include the Incident Commander, the Deputy Incident Commander, and the Chiefs; 

Supervisors, Directors, and other personnel will be brought into IAG meetings when needed. The 

IAG will be lead by the IC, and the IC will facilitate IAG meetings. 

Incident Commander (IC)

The IC is ultimately responsible for the entire operation, all Chiefs report to the IC.

Deputy Incident Commander (DIC)

The DIC will assume responsibility for the operation if the IC is no longer able to do so. 

TNC On Island Point of Contact

The TNC On Island Point of Contact will represent TNC’s interests during the operation, will 

partake in IAG meetings.

Off Island Partnership Communication Team

The Off Island Partnership Communication Team will receive reports from the IC, and will be 

responsible for communications with media. 

Off Island Point of Contact

The Off Island Points of Contact will be available for consultation on operational, regulatory, or 

partnership issues that need an audience that is larger than the IAG. The Off Island Support 

person may be included on IAG discussions and debriefs.

DOI Certified Pesticide Applicator (CPA)

The CPA ensures that the pesticide application follows federal (EPA, FIFRA) and DOI regulations. 

The CPA is on site for the entire bait application. The CPA reports to the IC.

Baiting Chief (BC)

The BC is responsible for all aspects of the bait application section, including logistics and safety. 

The BC reports to the CPA and the IC. 

Shorebird Mitigation Chief (SMC)

The SMC is responsible for all aspects of the shorebird capture and care section. The SMC reports 

to the IC.
27

Shorebird Care Specialist (SCS)

The SCS, a wildlife veterinarian, supervises and is directly involved in the capturing of and caring 

for Bristle-thighed Curlews and Pacific Golden Plovers. The SCS reports to the SMC. 

Monitoring Chief (MC)

The MC is responsible for all aspects of the monitoring section. The MC reports to the IC.

Supervisory Wildlife Biologist (SWB)

The SWB, a USFWS biologist, ensures that the monitoring actions are in compliance with Refuge 

policy and have minimal impact to native flora and fauna. The SWB reports to the MC. 

Monitoring Crew (M-Crew)

The M-Crew works with the MC and SWB to carry out the monitoring tasks. M-Crew personnel 

report to the MC.

Domestic Animal Chief (DAC)

The DAC is responsible for all aspects of domestic animal section. The DAC reports to the IC.

Domestic Animal Specialist (DAS)

The DAS, a wildlife veterinarian, supervises the care of the domestic animals (1 dog, 2 cats) and 

ensures that they are removed from risk of exposure to rodenticide. The DAS reports to the DAC.

Domestic Animal Assistant (DAA)

The DAA’s work with the DAS to ensure that the domestic animals are cared for according to the 

guidelines determined by the DAC and DAS. The DAA’s report to the DAS.

Operations Planning and Intelligence Director (OPID)

The OPID is responsible for the bait application unit, including ground and air operations, and GIS 

intelligence. The OPID reports to the BC.

GIS Supervisor (GSU)

The GSU is responsible for recording, summarizing, and reporting the GPS-based data generated 

during aerial and ground baiting operations, and is specifically responsible for the data generated 

by the air operations. The GSU reports to the OPID.

GIS Specialist (GSP)

The GSP works with the GSU to manage the GPS-based data generated during baiting operations, 

and is specifically responsible for the management of data generated by ground operations. The 

GSP is will exchange memory sticks with the Broadcast Baiting Pilots during air-based baiting 

operations. The GSP reports to the GSU.
28

Ground Operations Supervisor (GOS)

The GOS is responsible for all ground-based bating operations during the two bait applications, 

including hand broadcast baiting and structure bating. The GOS reports to the OPID.

Hand Broadcast Leader (HBL)

The HBL is responsible for all hand broadcast operations, including the hand broadcast treatment 

of the camp area. The HBL is responsible for training and equipping personnel involved in hand 

broadcast operations. The HBL reports to the GOS.

Hand Broadcast Crew (HBC)

The HBC works with the HBL to complete all hand broadcast assignments. HBC members report to 

the HBL. 

Structure Baiting Leader (SBL)

The SBL is responsible for all structure baiting operations, including the baiting of inhabited 

structures in camp and abandoned structures throughout the atoll. The SBL is responsible for 

training and equipping personnel involved in structure baiting operations. The SBL reports to the 

GOS. 

Structure Baiting Crew (SBC)

The SBC works with the SBL to complete structure baiting assignments. SBC members report to 

the SBL. 

Air Operations Supervisor (AOS)

The AOS is the site controller for helicopter operations and will be the point of contact for the 

helicopter pilots during baiting operations. During aerial baiting operations, the AIS will relay bait 

bucket load statistics to the GS. The AOS will report to the OPID.

Broadcast Baiting Pilot (BBP)

The BBP is responsible for all aspects of the helicopter during aerial baiting operations. The BBP 

is responsible for the aerial application of bait in accordance with the bait application plan. The 

BBP will consult with the OPID and BC on the bait application plan. While piloting the helicopter, 

the BBP reports to the AOS. 

Helicopter Refueling and Maintenance Specialist (HRMS)

The HRMS is responsible for the maintenance of the helicopters and refueling the helicopters 

during air operations. The HRMS will supervise the reassembly and disassembly of the 

helicopters when they are removed from and put back in the shipping containers. The HRMS 

works with the pilots to identify and address helicopter maintenance needs. During air 

operations, the HRMS reports to the AOS.
29

Bait Loading Leader (BLL)

The BLL is responsible for the loading of the bait bucket during air baiting operations, including 

the staging of bait pods, the securing of pod lids and empty bulk bags, and loading the bait bucket 

with the prescribed amount of bait. The BLL reports to the AOS.

Bait Loading Specialist (BLS)

The BLS works with the BLL to stage bait pods, secure pod lids and empty bulk bags, and load the 

bait bucket. The BLS reports to the BLL.

Backhoe Driver

The Backhoe Driver lifts the bulk bags from the pods and positions them over the bait bucket. The 

Backhoe Driver reports to the BLL.

Tractor Driver

The Tractor Driver moves full bait pods from the Pod Storage Bay to Staging Area 1 and from 

Staging Area 1 to Staging Area 2 (Appendix). The Tractor Driver reports to the BLL. 

Canopy Baiting Supervisor (CBS)

The CBS is responsible for all aspects of the canopy baiting operation, including air and ground 

operations. The CBS directs the canopy baiting operation from the command center. The CBS 

reports to the OPID.

Canopy Baiting Leader – Ground Operations (CBL-G)

The CBL-G is responsible for the implementation of the ground-based canopy baiting operation. 

The CBL-G orients personnel to canopy baiting techniques and directs the ground-based canopy 

bating effort from the field. The CBL-G reports to the CBS.

Canopy Baiting Crew – Ground Operations (CBC-G)

The CBC-G works with the CBL-G to implement the ground-based canopy baiting operation. CBC-G 

personnel report to the CBL-G.

Canopy Baiting Leader – Air Operations (CBL-A)

The CBL-A is responsible for the implementation of the air-based canopy baiting operation. The 

CBL-A orients personnel to canopy baiting techniques and directs the air-based canopy baiting 

effort from the field. The CBL-A reports to the CBS.

Canopy Baiting Pilot (CBP)

The CBP is responsible for piloting the helicopter during air-based canopy baiting operations. The 

CBP will work with the CBL-A to develop a flight plan. The CBP reports to the CBL-A.

Spotter
30

The Spotter rides in the helicopter during air-based canopy baiting operations and observes the 

bait application. The Spotter reports to the CBP.

Canopy Baiter - Air Operations (CB-A)

The CB-A is responsible for the placement of canopy baits (“bolas”) in designated palm crowns. 

The CB-A reports to the CBP.

Logistics Director (LD)

The LD is responsible for the logistical aspects of the operation, including station facilities and 

assets, and the alliance between the station and the support vessel. The LM reports to the BC. 

Station Supervisor (SS)

The SS is responsible for the functioning of the station, including all station facilities and assets. 

The SS reports to the LD.

Marine Operations Leader (MOL)

The MOL oversees all small boat operations, including boat-based transportation of field staff and 

equipment, boat maintenance, and providing personnel with boat operation training. The MOL 

reports to the SS.

Galley Leader (GL)

The GL is responsible for the operation of the station’s housing facilities, including the galley, the 

shower house, toilet house, and the laundry. The GL reports to the SS

Galley Specialist (GS)

The (GS) assists the GL with the operation of the station’s housing facilities. The GS reports to the 

GL.

Maintenance Leader (ML)

The Maintenance Leader is responsible for the operation and care of the station’s assets, including 

the power and water systems, vehicles and heavy equipment, and structures. The ML reports to 

the SS.

Maintenance Specialist (MS)

The MS works with the ML to care for the station’s assets. The MS reports to the ML.

M/V AQUILA Captain

The Captain of the AQUILA is responsible for the vessel and the vessel’s crew, for directing the 

offloading and loading of project supplies and equipment, for transporting personnel to and from 

the project site, and for housing personnel during the operation.
31

M/V AQUILA 1st Mate

The 1st Mate of the AQUILA works with the Captain to manage the vessel and the associated 

responsibilities. The 1st Mate will assume responsibility of the vessel if the Captain is no longer 

able to do so. The 1st Mate reports to the Captain.

M/V AQUILA Crew

The Crew of the AQUILA work with the 1st Mate and Captain to maintain the vessel and support 

the operation. The Crew report to the Captain. 

Safety Director (SD)

The SD’s responsibilities include: ensuring that personnel are briefed on safety issues and plans, 

that personnel have access to appropriate PPE, that safety issues are addressed and resolved, and 

that the medics are prepped to respond to a medical emergency. The SM reports to the BC.

EMT

The EMT will assist personnel with minor to moderate medical needs, and will be the primary care 

giver and liaison with off-site medical advisors during medical emergencies. The EMT reports to 

the SD. 

8 OPERATIONS COMMUNICATION PLAN 

Communication between project personnel will be via VHF radio and will be structured to reduce 

the amount of traffic to any one individual. Without a clear communications plan that is strictly 

followed, communication channels can be easily overwhelmed or personnel may find it difficult to 

sift out extraneous information during operations based communications. The communication 

plan mirrors the incident command structure, allowing for diffusion of information through the 

appropriate personnel channels. Information should move freely up and down the chain of 

command, utilizing the “talk up one and down one” concept; meaning personnel need to talk up 

the command chain one slot to their supervisor and down one to everyone they supervise. 

However, this should not prevent Operational Groups from communicating and sharing 

information.

A total of 23 portable VHF radios will be required to support this operation (Table 5). Portable 

radios will be programmed to operate on ten unique channels (Figure 8). Channels will be 

assigned for communication with and between six operational groups: Command, Ground Ops, Air 

Ops, Logistics, Monitoring, and Emergency. Personnel will be briefed on radio use and procedures 

prior to operating in the field. A pocket card will be distributed to all personnel outlining the 

schedule of radio frequencies and the radio call signs for all project positions (Figure 9). General 

Radio Procedures:

Be specific: Before transmitting, know what you are going to say. 
32

Indicate objectives: Personnel should know exactly where to go, to whom they should 

report, the task and its objective. 

Use clear tone/effective rate: Speak clearly at a normal rate, not too fast or too slow.

Well timed/spaced transmissions: Prioritize your messages. Do not waste valuable airtime 

with unimportant messages and insignificant details. Maintain an awareness of the overall 

situation and how you fit in. Wait until a message transaction has been completed before 

transmitting. 

Pause between concurrent messages: A pause makes it clear when one message has been 

completed and another started. It will also give other personnel a chance to transmit 

important messages.

8.1.1.1 Making a Transmission

Transmission procedures should ensure that messages are received and comprehended. Radio 

tranmissions are initiated when the intended receiver indicates readiness to receive a message. 

The 

message is transmitted and the receiver restates the message to confirm that it was understood. If 

correct, the original sender confirms, completing the communications sequence. For example, an 

exchange between the Ground Ops Supervisor and the Struture Baiting Supervisor would follow 

these five steps:

1. “Structure Baiting Supervisor, this is Ground Ops Supervisor on Marine 1A.”

2. “Ground Ops Supervisor, Structure Baiting Supervisor.” (Sructure Baiting Sup. 

transmitting)

3. “Move your team to structure 43 and begin application.” (Ground Ops Sup. transmitting)

4. “Team to structure 43, begin application.” (Structure Baiting Sup. transmitting)

5. “Affirmative.” (Ground Ops Sup. transmitting)

8.1.2 Emergency Traffic

The phrase “emergency traffic” is used to gain priority access to the emergency channel or an 

operational channel (if needed). The phrase is transmitted by the personnel in need, causing the 

Safety Director to defer to the caller until normal traffic can resume.

An example exchange: 

1. “All personnel, standby for emergency traffic.” (This statement gains priority access)

2. “Safety Director, this is Monitoring Chief on Marine 16.”

3. “Monitoring Chief, Safety Director.”

4. “Need immediate medical attention at location X, possible heat exhaustion.”

5. “Medical attention needed for heat exhaustion at location X.”
33

6. “Affirmative.”

Table 5. Portable VHF radios and radio headsets (blue shading) required during the PARRP Operations.

Position Radios needed

Incident Commander 1

Deputy Incident Commander 1

Shorebird Mitigation Chief 1

Shorebird Care Specialist 1

Monitoring Chief 1

Supervisory Wildlife Biologist 1

Baiting Chief 1

Safety Director 1

Logistics Director 1

Station Supervisor 1

Marine Operations Supervisor 1

Galley Supervisor 1

Galley Specialist 1

Operations Planning and Intelligence Director 1

Air Ops Supervisor 1

Bait Loading Leader 1

Bait Loading Specialist 1

Backhoe Driver 0

Tractor Driver 1

Helicopter Refueling and Maintenance Specialst 1

Ground Ops Supervisor 1

Structure Baiting Leader 1

Structure Baiting Crew 1

GIS Supervisor 1

Radios provided by IC 13

Radios provided by TNC 5

Radios provided by USFWS 5

TOTAL RADIOS NEEDED 23

TOTAL HEADSETS NEEDED 6
34

Figure 8. PARRP Radio Channels by Operational Group.
35

Figure 8. PARRP Radio Channels by Operational Group.
36

Figure 8. PARRP Radio Channels by Operational Group.

Group ID Who Frequency

Command Marine 05A Incident Command 156.2500

Ground Ops Marine 01A Hand Broadcast Personnel 156.0500

Marine 03A Structure Baiting Personnel 156.1500

Air Ops Marine 06 Pilots, Ground Ops 156.3000

Marine 07A Air Ops Personnel 156.3500

Air Command Pilots, Incident Command 151.7600

Logistics Marine 09 Station/Vessel/Animal Care 156.4500

Marine 08 Open Channel 156.4000

Monitoring Marine 10 Monitoring Personnel 156.5000

Emergency Marine 16 All Personnel 156.8000

Figure 9. PARRP Radio Pocket Card all personnel will carry in the field.
37

9 BRIEFING, TRAINING, AND DEBRIEFING

9.1.1 Briefing and Training

After all project personnel arrive at Palmyra and before the commencement of the first bait 

application, briefings and training sessions covering all operational, safety, and teamwork aspects 

will occur. 

9.1.2 Hot Debriefing

On site debriefings will happen every evening of the operation. General debriefings will be held 

with the entire operations crew (Figure 7) and led by the IC. Specific debriefings will be held with 

the IAG.

9.1.3 Post Operation Audit

Following the operation, a full audit will be conducted by an outside party and the results of that 

audit will be recorded and disseminated to all partners and stakeholders. 

10 TIMING

10.1 Biological window

This operation will be implemented when the non-target species that are at the greatest risk of 

harmful exposure to rodenticide (shorebirds) are least abundant at Palmyra – during the summer 

breeding season: June through July (Gill et al. 1990, Marks et al. 2002). 

11 MONITORING

Monitoring of the eradication action will occur according to the eradication Monitoring Plan (Pitt 

et al. 2011)

12 HEALTH AND SAFETY

12.1 Safety Plan

Refer to the Helicopter Operations Plan – Appendix. A Palmyra Rat Eradication Safety Plan is in 

development

12.2 Domestic Animal Care

There are three elderly domestic animals that have resided on Palmyra Atoll for many years. The 2 

cats and 1 dog live at research station on Cooper Island. The animals will be cared for during the 
38

operation to prevent any exposure to the rodenticide or animals that have consumed the 

rodenticide that they might eat.

Months preceding the eradication the animals will be crate trained to reduce stress during their 

period of restraint. During the operation, the animals will be housed in a vessel with operational 

personnel, stationed offshore. They will be attended by a veterinarian and two animal care 

specialists. After the vessel departs the animals will be kept indoors on the station for an 

additional two to four weeks. During this time, the veterinarian will continuously evaluate 

whether or not prophylactic Vitamin K would be necessary.

13 IMPLEMENTATION TIMELINE

Refer to Table 6 for project of the sequencing of the major activities that will be undertaken during 

this operation.
39

Table 6. Activity chart for the implementation phase of the Palmyra rat eradication project. 

Implementation 

Timeline

Implementation Day

-

7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Activity

Strike team arrives at 

Palmyra X

Prep station for 

operation X X X X X X

Vessel arrives at 

Palmyra X

Offload 

equipment/supplies X X

Operations team 

arrives at Palmyra X

Vessel moves from 

wharf to mooring

X

Establish bucket 

loading site X X X X

Aerial bait application X X X X X X

Hand bait application X X X X X X

Commensal bait 

application X X X X X X

Arm bait stations X

Check bait stations X X X X X X X X X X X X

Refresh bait in bait 

stations X

Canopy bait 

overhanging palms X X X X X X X X X X

Demobilize aerial 

baiting operation

X X X

Vessel moves from 

mooring to wharf

X X

Load vessel X X

Vessel departs 

Palmyra1

X

Operations team 

departs Palmyra2

X

1Four extra days have been allotted to the operation as “contingency” time. 2Personnel will remain behind to continue monitoring tasks
40

14 DEMOBILIZATION

14.1 Excess bait disposal 

Excess bait will be left on island to support the treatment of a residual population of rats if one is 

found after the eradication operation has finished. All bait will be appropriately labeled and 

stored in a dry location. Unused bait will be sent back to Honolulu in February 2012, and will be 

disposed of in a manner that is in accordance with FIFRA regulations. 

14.1.1 Supplies, equipment and infrastructure (TBD)

The fate of supplies and equipment will be determined prior to the implementation of this project

15 REFERENCES CITED

Alifano, A. and A. Wegmann. 2010. The ecotoxicology and palatability of two rodenticide bait 

products: field-based assessment at Palmyra Atoll. Island Conservation, Santa Cruz, CA.

Andrews, C. W. 1909. On the fauna of Christmas Island. Proceedings of the Zoological Society of 

London:101-103.

Atkinson, I. A. E. 1985. The spread of commensal species of Rattus to oceanic islands and their effect 

on island avifaunas. Pages 35-81 in P. J. Moors, editor. Conservation of Island Birds. 

International Council for Bird Preservation, Cambridge.

Buckelew, S., G. Howald, A. Wegmann, J. Sheppard, J. Curl, P. McClelland, B. Tershy, K. Swift, E. 

Campbell, and B. Flint. 2005a. Progress in Palmyra Atoll restoration: Rat eradication trial, 2005. 

Island Conservation, Santa Cruz CA.

Buckelew, S., G. R. Howald, A. Wegmann, J. Sheppard, J. Curl, P. McClelland, B. Tershy, K. Swift, E. 

Campbell, and B. Flint. 2005b. Progress in Palmyra Atoll restoration: rat eradication trial, 2005. 

Island Conservation, Santa Cruz, California.

Burggren, W. W. and B. R. McMahon, editors. 1988. Biology of the Land Crabs. Cambridge University 

Press, Cambridge.

Campbell, D. J. and I. A. E. Atkinson. 2002. Depression of tree recruitment by the Pacific rat (Rattus 

exulans Peale) on New Zealand's northern offshore islands. Biological Conservation 107:19-35.

Collen, J. D., D. W. Garton, and J. P. A. Gardner. 2009. Shoreline changes and sediment redistribution 

at Palmyra Atoll (Equatorial Pacific Ocean): 1874-present. Journal of Coastal Research: In Press.

Daniel, M. J. and G. R. Williams. 1984. A survey of the distribution, seasonal activity and roost sites of 

New Zealand bats. New Zealand Journal of Ecology 7:9-25.

Fair, J., E. Paul, and J. Jones, Eds. 2010. Guidelines to the Use of Wild Birds in Research. Washington, 

D.C.: Ornithological Council. 

(http://oacu.od.nih.gov/WildBirdGuide.pdf)

Gill, C. 2010. Summary of risks and potential mitigation options for bristle-thighed curlews (Numenius 

tahitiensis) at Palmyra Atoll during a rat eradication campaign. Prepared for the Palmyra Atoll 

Rainforest Restoration Project. Coastal Conservation.
41

Gill, R. E., R. B. Lancot, J. D. Mason, and C. M. Handel. 1990. Observations on habitat use, breeding 

chronology, and parental care in bristle-thighed curlews on the seward Peninsula, Alaska. Wader 

Study Group Bulletin 61:28-36.

Graham, M. F. and C. R. Veitch. 2002. Changes in bird numbers on Tiritiri Matangi Island, New 

Zealand, over the period of rat eradication. Pages 120-123 in C. R. Veitch and M. N. Clout, 

editors. Turning the tide: the eradication of invasive species. IUCN SSC Invasive Species 

Specialist Group, Gland, Switzerland.

Howald, G., C. J. Donlan, J. P. Galvan, J. C. Russell, J. Parkes, A. Samaniego, Y. Wang, D. Veitch, P. 

Genovesi, M. Pascal, A. Saunders, and B. Tershy. 2007. Invasive Rodent Eradication on Islands. 

Conservation Biology 21:1258-1268.

Howald, G., B. Keitt, A. Samaniego, S. Buckelew, P. McClelland, B. Keitt, A. Wegmann, W. Pitt, D. 

Vice, E. Campbell, K. Swift, and S. Barclay. 2004. Trip Report: Palmyra atoll rat eradication 

assessment.

Jouventin, P., J. Bried, and T. Micol. 2003. Insular bird populations can be saved from rats: a long-term 

experimental study of white-chinned petrels Procellaria aequinoctialis on Ile de la Possession 

(Crozet archipelago). Polar Biology 26:371-378.

Marks, J. S., T. L. Tibbitts, R. E. Gill, and B. J. McCaffery. 2002. Bristle-thighed Curlew.in A. Poole 

and F. Gill, editors. Birds of North America. Academy of Natural Sciences, Philadelphia.

McChesney, G. J. and B. R. Tershy. 1998. History and status of introduced mammals and impacts to 

breeding seabirds on the California Channel and northwestern Baja California Islands. Colonial 

Waterbirds 21:335-347.

Moller, A. P. 1983. Damage by Rats Rattus norvegicus to Breeding Birds on Danish Islands. Biological 

Conservation 25:5-18.

Mueller-Dombois, D. and F. R. Fosberg. 1998. Vegetation of the Tropical Pacific Islands. Springer 

Press, New York.

Pierce, R., N. Anterea, U. Anterea, K. Broome, D. Brown, L. Cooper, H. Edmonds, F. Muckle, B. 

Nagle, G. Oakes, M. Thorsen, and G. Wragg. 2008. Operational work undertaken to eradicate 

rats and rabbits in the Phoenix Islands, Republic of Kiribati, May - June 2008. Pacific 

Expeditions Ltd.

Pitt, W., A. Wegmann, J. Eisemann, and G. Howald. 2011. Palmyra Atoll Rainforest Restoration 

Project: rat eradication monitoring plan for all aerial broadcast alternatives. Island Conservation, 

Santa Cruz, California.

Rock, J. F. 1916. Palmyra Island with a description of its flora. College of Hawaii Publications. 

University of Hawaii, Honolulu.

Thibault, J.-C. 1995. Effect of predation by the black rat Rattus rattus on the breeding success of Cory's 

shearwater Calonectris diomedea in Corsica. Marine Ornithology 23:1-10.

TNC. 2005. The Nature Conservancy joins world's top scientists to launch climate change research 

station on Pacific Atoll. The Nature Conservancy: 

http://www.nature.org/wherewework/asiapacific/palmyra/press/press2152.html Accessed 

1/19/2010.

Tomkins, R. J. 1985. Breeding success and mortality of Dark-rumped Petrels in the Galàpagos, and 

control of their predators. Pages 159-175 in P. J. Moors, editor. Conservation of island birds: 

case studies for the management of threatened island birds. International Council for Bird 

Preservation, Cambridge.

Towns, D. and K. Broome. 2003. From small Maria to massive Campbell: forty years of rat eradications 

from New Zealand islands. New Zealand Journal of Ecology 30:377-398.
42

USDA. 2006. Analysis of Brodifacoum in Crab Tissues - Baiting Operation Palmyra Atoll. Animal 

Plant Health Inspection Service.

Wegmann, A. 2008. Land crab interference with eradication projects: Phase I - compendium of available 

information. Pacific Invasives Initiative, The University of Auckland, New Zealand.

Wegmann, A., J. Helm, A. Samaniego, W. Smith, B. Jacobs, D. Drake, J. Smith, M. McKown, A. 

Henry, S. Hathaway, and R. Fisher. 2008. Palmyra Atoll rat eradication: biomarker validation of 

an effective bait application rate, 19 June to 5 July, 2008. Island Conservation, Santa Cruz, 

California.

Wegmann, A., J. Helm, N. Torr, C. Golding, and G. Howald. 2009. Wake Atoll rat eradication strategic 

plan: biomarker study trip report (27 February to 27 March, 2009). Island Conservation, 

Kelowna, Canada.

Wegmann, A. and S. Middleton. 2008. Trip report, Jarvis Island National Wildlife Refuge and Palmyra 

Atoll National Wildlife Refuge visit and terrestrial assessment, 20 March to 8 April 2008. US 

Fish and Wildlife Service - PRINWRC

Wegmann, A. S. 2009. Limitations to tree seedling recruitment at Palmyra Atoll. University of Hawaii, 

Honolulu.

Wester, L. 1985. Checklist of the vascular plants of the Northern Line Islands. Atoll Research Bulletin.

Whitaker, A. H. 1973. Lizard populations on islands with and without Polynesian rats Rattus exulans

(Peale). Proceedings of the New Zealand Ecological Society 20:121-130.

Young, H. S., D. J. McCAuley, R. B. Dunbar, and R. Dirzo. 2010. Plants cause ecosystem nutrient 

depletion via the interruption of bird-derived spatial subsidies. PNAS Early edition:1-6.

16 APPENDIX: HELICOPTER OPERATIONS PLAN

16.1 Loading Zone (LZ)

The LZ will be located on Ripple wharf and serve as the location for all ground based activities 

associated with aerial operations. The LZ shall consist of one bait loading zone, one refueling pad, 

and two helicopter parking pads. The LZ will be outfitted with multiple wind indicators and each 

pad marked for aerial identification to ensure clear communication and safety between ground 

personnel and pilots. The perimeter of the LZ will be identified and marked using strung pennant 

flagging to ensure site security during operations. Additionally, a minimum of three 20-pound 40-

B:C fire extinguishers will be available for placement at active pads. The set-up and layout of the 

LZ will be directed by the Air Operations Supervisor (AOS), with recommendations made by the 

pilots.

The LZ will also host a work station, located in the Dry Lab, equipped for monitoring of the 

helicopter GPS data during the operation. The equipment at the LZ work station will include:

computers and printers (main and backup sets), island maps (paper and laminated), whiteboard, 

VHF radios. Additionally, a kit for first aid and crash rescue will be established at the LZ. 

16.1.1 Communications (Air Ops)

Communication between pilots and ground crew will be via VHF radio and structured to reduce 

the amount of traffic to pilots and the AOS. All team members will be briefed on radio use and the 

schedule of radio frequencies prior to the start of operations. Radios are required for all members 
43

of the Air Operations team. See the Operations Communications Plan in the Operational Plan for 

more detail on communications related it Air Ops.

16.2 Weather forecasts

The NOAA-National Weather Service (NWS) will be utilized as the source for weather predictions. 

The primary means of acquiring forecast information will be through the following web pages: 

http://www.prh.noaa.gov/hnl/pages/aviation.php

http://www.prh.noaa.gov/hnl/pages/marine.php

Due to the isolated location of the operational area, a specific weather forecast product is not 

readily available. However, general trends and potential disruptive weather can be acquired 

through the combination of marine and aviation forecasts. AOS is responsible for receiving daily 

weather forecasts and communicating these to the Baiting Chief (BC), Operations Planning and 

Intelligence Director (OPID), and pilots. In the event further weather forecasting is desired, the 

Incident Commander (IC) will maintain a communication schedule with a NOAA-NWS 

representative from the Weather Forecasting Office in Honolulu, HI. 

16.3 Helicopter Storage

When not flying, the helicopters will be parked and stored at the designated parking pads of the 

LZ, unless a more suitable area is identified following recommendations by the Chief Pilot, 

mechanic, and the Station Supervisor. Anchoring systems will be installed according to and under 

the direct supervision of the pilots and/or mechanic. Anchoring systems for helicopters may 

include: concrete anchors for belly hook attachment; tie point attachments from the skids, blades 

and mast; a pole support system for reducing blade mobility; and a combination of earth auger 

and duckbill anchoring systems. 

The helicopter storage location will also be where the mechanic services the helicopters at night 

and where role equipment will be staged when not in use. All equipment required to maintain the 

helicopters while in the field, including, but not limited to, ladders, floodlights, tooling and wash 

down/decontamination supplies, aircraft auxiliary power unit, etc. will be supplied by the 

helicopter operator. 

In the event of a major storm event helicopters may seek emergency shelter in the TNC 

warehouse. Prior to initiating the bait application the helicopter mechanic and pilots will examine 

the warehouse location to determine the protocol for movement and storage of the helicopter in 

the warehouse. 

16.4 Aerial Operations Safety

It is essential that all aviation operations be planned with the utmost consideration given to safety 

and operational efficiency. Missions can be accomplished safely and efficiently, provided that a 

high degree of pre-planning, risk analysis, and management is applied. Many users have developed 

Standard Operating Procedures (SOP) that streamline the planning process, incorporate the 

lessons learned from others experience, and utilize the best practices that balance the demands 

for safety and efficiency.
44

Helicopter safety is the responsibility of every individual on the project; however oversight of 

helicopter-specific safety is the responsibility of the helicopter vendor and pilots. Given the 

remote location, helicopter operations on the island are considered high risk. To ensure that a 

high standard of safety is maintained during the project a separate safety plan will be prepared 

that details general helicopter safety procedures, flight following, and emergency or crash 

response procedures. Additionally, the helicopter vendor will provide an Aviation Safety Plan 

detailing emergency equipment and response. All safety protocols and procedures will follow 

standard FAA guidelines. 

The safety procedures covered in the Palmyra Safety Plan will include external load operations, 

bait handling & loading, and aerial bait broadcast. The safety plan will also include, but not be 

limited to, the following:

Method for the identification of all hazards, including new hazards.

How these hazardous can be eliminated, or reduced. 

Detail safety equipment and training required for both the positioning and aerial work 

operations for both flight crews and ground crews.

Nominate a person responsible and accountable for safety on site.

Method for dealing with emergencies.

Method of reporting incidents and accidents.

The following information serves as an overview of aerial operations safety procedures and 

guidelines to be followed on this project. Refer to Island Conservation Helicopter Operations SOP, 

July 2008 for full detail.

16.4.1 Hazard Identification and Mitigation

The BC and OPID will work jointly with the pilots to manage hazards associated with aerial 

operations. Common hazards associated with a helicopter mission –crew fitness, distraction, 

mission focus, communication, weather, takeoff or landing weights, landing areas, other aircraft, 

wire and other obstructions – must be identified and controls provided to mitigate the hazard(s). 

Preflight project planning for baiting operations should be intensive because the aircraft and crew 

are placed in a less forgiving environment. The BC will aid the pilots in aerial hazard identification, 

creating a hazard map if necessary, and ensure a high-level reconnaissance is made prior to lowlevel flight 

16.4.2 Flight Following (on island)

Flight following requirements will be clearly identified, including check-in procedures, time and 

locations, individuals responsible for flight following, radio frequencies to be used, and any special 

circumstances requiring check-ins. The flight following personnel must document position reports 

to assist in locating an overdue or missing aircraft. 

Flight following on island will be coordinated by the OPID, in accordance with the vendor 

company’s Aviation Safety Plan. The AOS or designee will have radio contact with the pilots; 

check-in intervals will be determined by the BC and pilots prior to operations commencing. Check-
45

ins during flights will be documented by the AOS or designee, in addition to load calculations, 

cargo and passenger manifests, and flight plans that will be kept on hand at the LZ. Information to 

be recorded includes: the name of each passenger, the intended destination, load weights, time enroute and estimated time of return. 

16.4.3 Overdue Aircraft/Emergency Response

Aircraft mishap, accident and emergency will be managed by the vendor helicopter contractor, 

unless otherwise arranged. Overdue or missing aircraft will be managed by the vendor helicopter 

contract. Protocols for aircraft accident reporting and management, and procedures for overdue 

or missing aircraft should be detailed in the vendor company’s Aviation Safety Plan. 

16.4.4 Personnel Experience/Training

Inexperience with aerial operations could potentially present safety concerns, as well as reduce 

operational efficiency. Priority will be given to staffing aerial operation positions with personnel 

who posses significant aviation experience. If positions are to be filled by in/under-experienced 

personnel, those team members must complete a helicopter training program combining 

classroom and field practical, specific to the work being done on the island. 

16.4.5 Personnel Protective Equipment (PPE)

16.4.5.1 Helicopter

Personnel working around operating helicopters will wear the following PPE:

Fire resistant or all-natural fiber clothing (long-sleeved shirt and pants, or flight suit)

High visibility vest/jacket

Hardhat with chinstrap, or flight helmet

Fire resistant or leather gloves

All leather boots

Eye protection

Hearing protection

During refueling operations, the helicopter mechanic will wear appropriate PPE for dispensing 

aviation fuel, including ‘non-static’ clothing.

16.4.5.2 Bait Handling and Loading

All personnel that handle bait or monitor the bait application in the field will meet or exceed all 

requirements for PPE described on the bait’s EPA pesticide label. In addition to the required 

helicopter PPE, the Bait Loading Leader and the Bait Loader Driver will wear disposable masks or 

respirators when filling the bait buckets. 

All personal will wear required PPE (see PPE above) when handling/loading bait to prevent 

exposure to potentially harmful pesticides. An aerial baiting operation requires adherence to 

standard practices similar to those for external cargo load operations. The bait loading team 
46

should remain clear of the loading area until the AOS signals that the bucket is placed into 

position; no other personnel should be near the site unless approved by the AOS.

The bucket should be placed on the ground by the pilot at the designated loading spot before bait 

is loaded, and not be pulled into position by the loaders. The bucket should always remain 

between the bait loading team and the helicopter. When bait loading has been completed, the AOS

may signal the pilot to begin movement of the bucket. As the bucket is lifted, ground personnel 

should keep out of the flight path to avoid injury. The AOS must pay close attention as the 

helicopter lifts up and tension is applied to the bucket line, if there is a problem with the bucket, 

the AOS should communicate appropriately with the pilot. The Bait Loading Leader (BLL) will be 

responsible for securing the empty bulk bags as they are emptied to prevent the potential for 

foreign object damage (FOD). 

16.5 Marshalling / Crash Rescue

The AOS is responsible for directing helicopters during bait reloading operations and relaying 

helicopter traffic updates to ground staff. The AOS should direct the pilot by radio and remain 

visible to the pilot at all times. In the event of an aircraft emergency in the LZ, the AOS can respond 

quickly utilizing the pad’s fire extinguisher and initiating crash rescue procedures.

16.6 Aerial Broadcast Implementation

16.6.1 Aerial Ops Command Structure

The command structure of personnel for the aerial broadcast operation is shown Section 8 of the 

Operational Plan. This diagram is intended to be as closely representative of the actual structure 

as possible, anticipating that actual roles may change prior to or during aerial baiting operations.

The roles and responsibilities of the field team during the aerial baiting operations are listed in 

Section 8.1 of the Operational Plan. While the specific tasks required during the aerial baiting 

operations are fixed, additional tasks may be required of the field team during the aerial baiting 

operations. Of note, the AOS will serve as the Site Controller for the LZ; however if multiple 

aircraft are operating within the LZ at one time, separate site controllers will be needed to manage 

each aircraft. Individuals may also be rotated between non-specialist roles (e.g. Bait Loading 

Specialist) depending on the needs of the team or operations on any given day. 

16.6.2 Commencement of Application

Prior to initiating aerial baiting operation, an operations checklist will be reviewed by the BC and 

OPID to ensure that all equipment has been adequately and safely installed. The checklist 

prepared by the AOS will be reviewed and approved by the Incident Advisory Team. Following 

approval, the authorization to commence aerial baiting operations will be given to the baiting 

pilots. While the BC will be responsible for detailing daily flight activities, the decision to fly on any 

given day will ultimately be made by the baiting pilots and will depend on suitable weather 

conditions for safe, effective baiting. 

16.6.3 Daily decision to apply bait

Every day following the authorization to commence will be treated as an opportune window for 

aerial bait application, unless declared otherwise. Before dawn each day the IC, BC, OPID, AOS, and 
47

baiting pilots will consult on local weather conditions and forecasts to assess whether they are 

suitable for baiting (Fig. 9). If conditions are deemed suitable, the team will proceed with 

preparation and positioning for baiting (see Daily schedule of events below). 

Poor weather conditions may cause baiting operations to be halted, changed, or delayed. Daily 

baiting will be delayed (or discontinued if flying has already commenced) if the weather is 

unsuitable, and/or the pilots feel it is no longer possible to continue flying in a safe manner. 

Weather conditions in which baiting may be halted or delayed are:

wind speeds average 25 knots or gusts to over 30 knots

visibility conditions in the area being treated are obscured by low clouds, inhibiting the 

pilot’s ability to safely operate

conditions of heavy rain (loading bait buckets in heavy rainfall may cause “gumming” of 

bait and potentially cause bait bucket to jam or clog)

16.6.4 Daily schedule of events

16.6.4.1 Pilot preparation:

The BC will discuss the daily flight plan with the pilots and the IAT the night before flying, in order 

to maximize all optimal weather conditions for aerial baiting. The daily flight plan will be based on 

several criteria, including: the predicted weather forecast, the area(s) of the island previously 

treated, the prioritization criteria for applying bait, and the current stage of the operational 

timeline. 

16.6.4.2 Air Ops team preparation:

The BC will conduct a nightly briefing with the field team to review: weather forecasts, baiting 

plans, task allocation, transportation plans, safety, and any other relevant issues. On each day 

scheduled for flying, the BC, OPID, and baiting pilots will assess weather conditions at dawn. If 

conditions are suitable for dropping bait the BC will notify the team and preparations will begin 

for baiting. Daily preparations will include:

team briefing of weather forecast

team briefing of action plan for the day

review of task requirements of team members

radio check

Once preparations are complete the bait loading teams and helicopters will be positioned to begin 

baiting. If weather conditions are not suitable for flying the field team will stand-by, and later in 

the morning a briefing will occur to inform the team of the updated action plan and assign tasks 

for the day. All team members will be on stand-by during days of no flying in the event weather 

conditions become suitable for flying.
48

16.6.5 Bait-bucket Loading Procedures

Prior to beginning bait operations for the day, the AOS and BLL will oversee that the loading site is 

properly prepared for operations, including ensuring an adequate amount of bait for the planned 

daily operation (determined by the BC) is present at Staging Area 1 (approximately 20 pods will 

be transferred from the pod storage bay in the shop to this location prior to baiting operations),

and all required safety equipment is in place. The Tractor Driver will move pods from Staging Area 

1 (SA1) to SA2 (at SA2, the lid will be removed from the pod and the bulk bag will be attached to 

the bucket of the Backhoe). The bait loading team will consist of 5 people: The AOS (site 

controller), the BLL, a Bait Loading Specialist, the Backhoe Driver, and the Tractor Driver.

Once the all the bait in the bucket has been sown, or the targeted area has been treated, the pilot 

will notify the AOS via radio and return for reloading at the LZ. When the helicopter arrives to the 

loading site the AOS will direct the pilot in placing the bucket for reloading. Prior to reloading the 

bucket at the LZ, the BLL will check the bottom of the bucket for an approximate fistful amount of 

bait remaining from the previous bucket load – this residual bait is an indicator that the actual 

area baited is was recorded by the GPS tracking system. The remaining contents of the bucket will 

be indicated to the AOS. If no bait remains in the bottom of the bucket prior to reloading the OPID

will be consulted and the pilot may be required to re-bait a portion of the previously treated area. 

When the bucket is on the ground and the remaining contents checked, the Backhoe Driver will 

approach the bucket with the bulk bag. The BLL will assist the Backhoe Driver in positioning the 

bulk bag over the bucket, once the bulk bag is in place the BLL will pull the release to fill the 

bucket with bait. After emptying the bulk bag, the Backhoe Driver and BLL will move away from 

the bucket ensuring the empty bulk bag is secure and preventing the bulk bag from being blown 

away or interfering with the flight of the helicopter. The Bait Loading Specialist will roll up empty 

bulk bags and secure them in a predetermined location. Once the helicopter departs the LZ, the 

bait loading team will immediately attach another bulk bag to the Backhoe and reposition in 

preparation for the next bucket loading.

16.6.6 Aerial Data

16.6.6.1 Baiting

At each bucket reload the pilot will communicate via radio to the AOS the amount of area 

(measured in ha) that was previously treated with bait. The AOS will relay this information, along 

with the amount of bait dispensed to the GIS Supervisor (GSU), to be recorded into a baitapplication monitoring spreadsheet. 

16.6.6.2 GPS

On aerial baiting days, GPS information will be downloaded after the first 3 bucket loads applied 

by each pilot, allowing for any possible errors in flight lines, GPS logging, or bait application rates 

to be detected. Once the systems are verified, GPS information will be downloaded required by the 

OPID or BC.
49

16.6.6.3 Flight Log

A log of all flight activity and onboard passengers will be kept by the GSU, and will include 

significant aviation activities such as: time helicopter begins flying, time when helicopter arrives 

back to reload, refueling events, all engine shut downs, arrival/departure times, and passenger 

manifests. The GSU will maintain the log via direct observations at the LZ and refueling area, or by 

radio communications with the AOS. A copy of the log will be kept at the point of departure. 

Should the GSU be unable to observe and document flight activities, another designated person 

will maintain the flight log. 

16.6.7 Refueling

Helicopter refueling will occur in the designated fuel area at the LZ. During helicopter refueling, 

the bait bucket motor will be refueled with unleaded fuel dispensed from a small jerry can. Fueling 

will be the responsibility of the Helicopter Refueling and Maintenance Specialist. The fuel drums 

will be appropriately positioned with the refueling equipment and nozzle bonded to the helicopter 

before starting the refueling operation. To control spills, self-closing nozzles will be used and not 

blocked open or dragged along the ground. Additionally, a fuel catchment pan will be placed 

beneath the helicopter to prevent spillage onto the ground. 
1

APPENDIX L

BRODIFACOUM-25W CONSERVATION LABEL & 

SUPPLEMENTAL LABELING FOR BRODIFACOUM-25W 

CONSERVATION TO CONTROL AND ERADICATE BLACK RATS 

ON PALMYRA ATOLL 

EPA REGISTRATION NO. 56228-36
2
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animals and pets. If

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MSHA/NIOSH

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ire label and follow

n, pets or other non

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and unused,

specified in the

ction.

SE RESTRICTIONS)

RESTRICTED USE PESTICIDE

DUE TO HAZARDS TO NON-TARGET SPECIES

For retail sale only to: USDA Animal and Plant Health Inspection

Service Wildlife Services, U.S. Fish and Wildlife Service, and the U.S.

National Park Service to be used only by Certified Applicators or

persons under their direct supervision and only for those uses

covered by the Certified Applicators certification.

BRODIFACOUM-25W

CONSERVATION

PELLETED RODENTICIDE BAIT FOR

CONSERVATION PURPOSES

For control or eradication of invasive rodents in wet climates on

islands or vessels for conservation purposes

ACTIVE INGREDIENTBrodifacoum (CAS No. 56073-10-0) ............. 0.0025%INERT INGREDIENTS............................... 99.9975%

TOTAL .................................................... 100.0000%

KEEP OUT OF REACH OF CHILDREN

CAUTION

First Aid

If swallowed -Call a physician or poison control center immediately for

treatment advice.-Have person sip a glass of water if able to swallow.-Do not induce vomiting unless told to do so by a poison controlcenter or doctor.-Do not give anything by mouth to an unconscious person.

If on skin -Take off contaminated clothing.or clothing -Rinse skin immediately with plenty of water for 15-20 minutes.

-Call a poison control center or doctor for treatment advice.

If inhaled -Move person to fresh air.

-If person is not breathing, call 911 or an ambulance, then giveartificial respiration, preferably mouth-to-mouth if possible.-Call a poison control center or doctor for further treatment advice.

If in eyes -Hold eye open and rinse slowly and gently with water for 15-20

minutes. Remove contact lenses, if present, after the first 5minutes, then continue rinsing eye.-Call a poison control center or doctor for treatment advice.

Have the product container or label with you when calling a poison control centeror doctor, or when going for treatment.For a medical emergency involving this product, call (877) 854-2494NOTE TO PHYSICIAN: If swallowed, this material may reduce the clotting abilityof blood and cause bleeding. If ingested, administer Vitamin K1, intramuscularly

or orally, as indicated in bishydroxycoumarin overdose. Repeat as necessarybased on monitoring of prothrombin times.

USE RESTRICTIONS, (CONT)

This product may be used to control or eradicateNorway rats (Rattus norvegicus), roof rats (Rattus

rattus), Polynesian rats (Rattus exulans), house mice(Mus musculus) or other types of invasive rodents onislands for conservation purposes, or on groundedvessels or vessels in peril of grounding.This product may be applied using bait stations,burrow baiting, canopy baiting or by aerial andground broadcast application techniques.This product is to be used for the protection of Stateor Federally-listed Threatened or EndangeredSpecies or other species determined to require specialprotection.Do not apply this product to food or feed.Treated areas must be posted with warning signsappropriate to the current rodent control project.This product is for use in wet climates.

DIRECTIONS FOR USE

BAIT STATIONS: Tamper-resistant bait stations mustbe used when applying this product to groundedvessels or vessels in peril of grounding, or when usedin areas of human habitation. Bait must be appliedin locations out of reach of children, non-targetwildlife, or domestic animals, or in tamper-resistantbait stations.TO BAIT RATS: Apply 4 to 16 ounces (113 to 454

grams) of bait per placement. Space placements atintervals of 16 to 160 ft (about 5 to 50 meters).Placements should be made in a grid over the areafor which rodent control is desired.

TO BAIT MICE: Apply 0.25 to 0.5 ounces (7 to 14

grams) of bait per placement. Space placements atintervals of 6 to 12 ft (about 2 to 4 meters). Largerplacements, up to 2 ounces (57 grams) may be neededat points of very high mouse activity. Placementsshould be made in a grid over the area for whichrodent control is desired.

FOR BOTH RAT AND MOUSE BAITING: Maintain

an uninterrupted supply of fresh bait for at least 15days or until signs of rodent activity cease. Where acontinuous source of infestation is present, permanentbait stations may be established and bait replenishedas needed.

Page 1 of 2

EPA Reg. No. 56228-36

Revised 11/23/2009
E (CONT.)

urrows only if this can be

al for ejection of bait and

s.

ces (85 to 113 g) of bait

used in burrows may be

alable plastic bags. The

e sealed to avoid spillage

ic bags to allow the bait

y 0.25 ounces (7 grams)

 in each active burrow.

ING: Place one such bag

w opening and push bag

presence can barely be

ated burrows and inspect

Maintain an uninterrupted

s or until rodent activity

 if there is evidence that

ment in the canopy of

ere sufficient food and

pulations of rodents in

nopy baiting should be

roximately 4 to 7 ounces

 be placed in a cloth or

s should be knotted or

nd holes should be made

or to escape. Using long

d, bait filled bags should

 shrubs. Baits should be

160 ft (about 50 meters)

 of rodent infestation in

 types, bait stations may

 stay in the canopy.

STORAGE AND DISPOSAL

Do not contaminate water, food, or feed by storage ordisposal.STORAGE: Store only in original closed container ina cool, dry place inaccessible to unauthorized people,children and pets. Store separately from fertilizer andaway from products with strong odors, which maycontaminate the bait and reduce acceptability. Spillage should be carefully swept up and collected for

disposal.PESTICIDE DISPOSAL: Wastes resulting from theuse of this product may be disposed of at an approved waste disposal facility.CONTAINER DISPOSAL: Nonrefillable container. Donot reuse or refill this container. Offer for recycling, ifavailable. Otherwise, dispose of empty container insanitary landfill or by incineration, or, if allowed byState and local authorities, by burning. If burned,stay out of smoke.NOTICE: Buyer assumes all risks of use, storage, orhandling of the material not in strict accordance withdirections given herewith. The efficacy of the product may be reduced under high moisture conditions.

UNITED STATES DEPARTMENT OF AGRICULTURE

ANIMAL AND PLANT HEALTH INSPECTION SERVICE

Riverdale, MD 20737-1237

EPA Est. No. 56228-ID-1

EPA Reg. No. 56228-36

Net Weight __________________

Batch Code No.: _______________

BROADCAST APPLICATION: Broadcast applications areprohibited on vessels or in areas of human habitation. Broadcastbait using aircraft, ground-based mechanical equipment, or bygloved hand at a rate no greater than 16 lbs of bait per acre (18kg bait/hectare) per application. Make a second broadcastapplication, typically 5 to 7 days after the first application,depending on local weather conditions, at a rate no higher than8 lbs. of bait per acre (9 kg bait/hectare). In situations whereweather or logistics only allow one bait application, a singleapplication may be made at a rate no higher than 16 lbs. bait peracre (18 kg/ha).Aerial (helicopter) applications may not be made in winds higherthan 35 mph (30 knots). Pilot in command has final authority fordetermining safe flying conditions. However, aerial applicationswill be terminated when the following conditions are present:

Windspeed in excess of 25 knots with an evaluationof the terrain and impact of the wind conditions andnot to exceed a steady wind velocity of 30 knots.

Set the application rate according to the extent of the infestationand apparent population density. For eradication operations, treatentire land masses.Assess baited areas for signs of residual rodent activity (typically7 to 10 days post-treatment). If rodent activity persists, set upand maintain tamper-resistant bait stations or apply bait directlyto rodent burrows in areas where rodents remain active. If terraindoes not permit use of bait stations or burrow baiting, continuewith broadcast baiting, limiting such treatments to areas whereactive signs of rodents are seen. Maintain treatments for as longas rodent activity is evident in the area and rodents appear to beaccepting bait.For all methods of baiting, monitor the baited area periodicallyand, using gloves, collect and dispose of any dead animals andspilled bait properly.

DIRECTIONS FOR USE (CONT.)

Page 2 of 2

EPA Reg. No. 56228-36

Revised 11/23/2009




1

APPENDIX M

COMMENTS RECEIVED AND RESPONSES TO COMMENTS
2
Public Comment on the February 2011 Draft Environmental Impact 

Statement: Palmyra Atoll National Wildlife Refuge Rat Eradication 

Project 

In accordance with the National Environmental Policy Act (NEPA) of 1969 and implementing 

regulations, this final environmental impact statement provides responses to comments on the 

Palmyra Atoll National Wildlife Refuge Rat Eradication Project Draft Environmental Impact 

Statement. In compliance with the regulations, this final document includes a list of agencies, 

organizations and individuals commenting on the DEIS; copies of their comments; and responses 

to the substantive environmental issues raised in the comments.

The DEIS for the eradication of rats from Palmyra Atoll was released for a 45-day public 

comment period from February 25, 2011 to April 11, 2011 through notice in the Federal Register 

and letters sent direct to known persons of interest. Written comments were accepted via email 

and individual letters through the comment period. A total of 21 written or email comments were 

received. 

The following pages show comments received for the DEIS and the Fish and Wildlife Service’s

responses to those comments. The Service reviewed and considered all comments and 

determined whether or not they were substantive and warranted further analysis and 

documentation. Modifications (greater than a few words) to the DEIS are italicized in the Final 

EIS. While the Service greatly appreciates the participation of all those who commented; not all 

comments required further analysis or changes to the Final EIS. Individual responses are noted 

when further analysis or modifications are made. 

Overall characterization:

We received 21 comments in total:

15 (71%) individuals

3 (14%) government agencies

3 (14%) organizations

Individual comments:

Eric Barker Kevin Lafferty Kim Williams

Ralph Black Cara Losier Anita Kihei Wintner

John D. Collen John P. McLaughlin Chelsea L. Wood

Jonathan Gardner Carl E. Orazio Hillary S. Young

Wayne Johnson Mark Rauzon

Organizations comments:

American Bird Conservancy (ABC)

Michael Fry, PhD, Director of Conservation Advocacy

Marine Conservation Biology Institute (MCBI)

Lance Morgan, PhD, Vice President
Pacific Seabird Group (PSG)

Craig S. Harrison, Vice Chair for Conservation

Governmental agencies comments:

Protected Resources Division of the NOAA Fisheries Pacific Islands Regional Office

Kim Maison, Sea Turtle Biologist

Alecia VanAtta, Assistant Regional Administrator for Protected Resources

Official DEIS comment (PIRO PRD2)

National Parks Service, Environmental Quality Division (NPS-EQ)

Melia Lane-Kamahele, Acting Pacific Area Director

USDA Animal and Plant Health Inspection Service – Wildlife Services (USDA)

William H. Clay, Deputy Administrator

U.S. Environmental Protection Agency, Region IX (EPA)

Enrique Manzanilla, Director, Communities and Ecosystems Division
Comment # Reviewer Section Comment Response to comment

1 NMFS PIRO PRD General NOAA Fisheries was recently petitioned under the ESA to list the bumphead parrotfish (Bolbometopon muricatum ), as well as 82 species of coral, 21 of which are found within the waters surrounding Palmyra Atoll. Our agency is currently evaluating the petitions to determine whether any of those species warrant listing under the ESA. Comment noted. No response needed.

2 NMFS PIRO PRD General Appendices are labeled with letters but referred to at times in the text as being numbered (example: pg. 42 refers to Appendix 7 which is actually Appendix G). We have corrected the errors.3 NMFS PIRO PRD 3.2.7

The list of marine mammals observed in pelagic waters surrounding Palmyra described here does not agree with the list contained on pages 101-102 in Section 4.4.2.2 Special significance considerations for listed marine mammals under the Marine Mammal Protection Act (MMPA). It is recommended that all marine mammals known to inhabit the waters surrounding Palmyra be given special significance consideration under the MMPA.

We have amended section 4.4.2.2 to reflect thPalmyra. 

4 NMFS PIRO PRD 4.4.2.2

The DEIS incorrectly states that “MMPA regulations prohibit “disturbance” of marine mammals, which is a lower threshold of effect than mortality.” The MMPA prohibits “take” of marine mammals, which is defined as “to harass, hunt, capture, or kill, or

attempt to harass, hunt, capture, or kill any marine mammal” (16 U.S.C. 1362 Sec. 3(13)). Further, the term “harassment” is defined as “any act of pursuit, torment, or annoyance which – (i) has the potential to injure a marine mammal or marine mammal stock in the wild; or (ii) has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering” 

(16 U.S.C. 1362 Sec. 3(18)(A)). The acts described in the subparagraphs (A)(i) and (A)(ii) are also referred to as Level A and Level B harassment, respectively (16 U.S.C. 1362 Sec. 3(18)(C) and Sec. 3(18)(D).

Thank you for the clarification. The documenprohibited under MMPA.

5 NMFS PIRO PRD 4.4.2.2

If your agency determines there is potential for “take” of any marine mammal species resulting from the proposed action, you may be required to apply for an Incidental Harassment Authorization (IHA) or a Letter of Authorization (LOA) through the 

NOAA Fisheries Office of Protected Resources. Please refer to the following website for more information on obtaining permits 

under the MMPA: http://nmfs.noaa.gov/pr/permits/types.htm

Comment noted. No response needed.

6 NMFS PIRO PRD 4.4.2.1 The DEIS acknowledges that the bumphead parrotfish is designated as a candidate species. However, there is no analysis provided in the DEIS on potential impacts to this fish species. We suggest that you provide information on how this species may or may not be at risk of primary or secondary exposure to the toxin. We have modified the document in section 4.

7 NMFS PIRO PRD 3.2.7 Given the fact that surveys have documented Palmyra to be a significant chelonian foraging area, PIRO PRD is concerned that the potential impacts to sea turtles have not been adequately addressed in the DEIS. The following comments and questions specifically relate to potential impacts of sea turtles (Comment 14-21).8 NMFS PIRO PRD 2.4.10 Sea turtles can be opportunistic feeders, and have been known to ingest pieces of plastic and other debris of varying sizes and colors; therefore, they could very possibly ingest any bait pellets that end up in the marine environment.9 NMFS PIRO PRD 2.4.10 Sea turtles can be opportunistic feeders, and have been known to ingest pieces of plastic and other debris of varying sizes and colors; therefore, they could very possibly ingest any bait pellets that end up in the marine environment.10 NMFS PIRO PRD 4.4.4.4

Toxicant risk section: It is reasonable to assume that green or hawksbill turtles would potentially consume bait pellets if they were to come in contact with them in the marine environment. A wide range of life stages are present at Palmyra and juvenile green turtles in particular are more omnivorous and opportunistic feeders. Once they have recruited to nearshore environments like Palmyra, sub-adults and adults tend to primarily feed as herbivores but may still be opportunistic at times. Many necropsies of turtles of all size classes reveal plastic and other types of debris that have been ingested; bait pellets would not appear much different than floating or sunken bits of debris that turtles have been known to ingest.

11 NMFS PIRO PRD 4.4.4.1 Primary exposure section: there is no mention of potential ingestion by sea turtles if pellets unintentionally end up in the marine environment. While accidental entry into the marine environment will be ‘minimized’, it can not be eliminated; can you quantify how much of the toxicant is likely to enter the marine environment?12 NMFS PIRO PRD 2.4.6 Would measures also be in place to monitor the health of sea turtles potentially exposed to toxicant and is it possible to administer the antidote to reptiles? Marine turtles would be observed for general 

island would be available to provide wildlife 

13 NMFS PIRO PRD 3.2.7 Green turtles should not be included in the section on reef fishes; they are discussed in the next section on turtles. We have made the modification.

14 NMFS PIRO PRD 3.2.7 East Pacific greens are also distinguished by different shell morphology but can only be confirmed with genetic analysis. It is recommended that you remove the term ‘rare’. We have corrected the error.15 NMFS PIRO PRD 3.2.7 Algae section: McFadden, Sterling, and Naro-Maciel et al . may have more info on algal species and abundance on the north and south reef flats as a result of a portion of their research involving algae transects in relation to green turtle food source studies. We have included the reference in the Affecte

16 NMFS PIRO PRD 3.2.7 Green turtle nesting has only rarely been observed at Palmyra so it is difficult to make a connection between rat eradication and the potential to establish or reestablish nesters at this site, especially if there is no evidence that Palmyra was a nesting site used historically with any regularity. We believe predator-free sites in areas where 

potential for increasing in importance as nestthe Northwestern Hawaiian Islands, nesting i

17 W. Johnson General This plan will cause enormous suffering and agony to living creatures and the blood will be squarely on your hands. Comment noted. No response needed.

Comment Response Matrix

Please see modifications to Section 4.4.4 relaEvery effort would be made to prevent accidethe unlikely event that 1 kg of bait pellets entintroduce 0.025 grams of toxicant. There are of research specific to marine reptiles, but calon study of ornate wood turtles by U.S. DepaResearch Center, when applied to adult green could consume at least 40.5 lbs (18.4 kg) or 9consume at least 15.4 lbs (7 kg) with no signs 

Final Environmental Impact Statement, April 2011:Palmyra Atoll National Wildlife Refuge Rat Eradication Project
Comment # Reviewer Section Comment Response to comment

Comment Response MatrixFinal Environmental Impact Statement, April 2011:Palmyra Atoll National Wildlife Refuge Rat Eradication Project

18

E. Barker, K. Williams, U. Heinz

General Please extend the contact period. A minimum 45-day comment period is requir

expertise in these matters thoroughly respond

19

E. Barker, K. Williams, U. Heinz

General Asked for a public hearing on Oahu/Honolulu. Palmyra is an unincorporated territory in the 

world. Comments were sought from all inter

20 K. Williams General I strongly OPPOSE The Nature Conservancy and the USFWS using an aerially dispersion of brodifacoum on Palmyra Atoll. The use of poison does more harm to the environment than good. Comment noted. No response needed.21 C. Losier General

I urge you to reconsider this course of action or take steps to halt the progress of this project. This poison causes extremelypainful death to the animals who come in contact with it, which is clearly inhumane. Please consider the lives of the animals who will be affected before condoning this project.

Comment noted. No response needed..

22 U. Heinz General Please provide for time to create a better alternative strategy. We considered a wide range of alternatives. P23

C. Wood, J. Gardner, J. McLaughlin, J. Collen, H. Young, C. Orazio

General

I've reviewed the [DEIS] and support the proposed actions, ...to protect Palmyra's unique species and habitats. 

....look forward to watching the recovery of the atoll's terrestrial ecosystems in the future. ....believe the project is likely to succeed and should result in positive net benefits for the seabird community at Palmyra, 

providing important nest site protection for many species that are globally declining. ....[support] Based on the science, supporting information, and options presented in the DEIS. 

Comment noted. No response needed.

24 J. Gardner General This is a necessary and important project which will lead to significant beneficial conservation outcomes. Comment noted. No response needed.25 J. Collen General

 From my personal knowledge both of Palmyra Atoll and of the pest eradication projects undertaken in New Zealand (which includes visits to many of NZ's now pest-free offshore and Subantarctic islands), I would like to comment that the proposal is necessary, relevant and well constructed. 

Comment noted. No response needed.

26 K. Lafferty General

Having studied black rats on Palmyra Atoll, I can testify to their incredible numbers and the need to remove them from the Atoll to help project the area's rich and valuable native diversity. The level of study and forethought that has gone into this restoration effort is admirable.

Comment noted. No response needed.

27 C. Orazio General The proposed actions support the efforts to protect and restore Palmyra Atoll's ecosystem. Comment noted. No response needed.28 R. Black General

[We support actions] free of chemical eradication for the rats...and will be willing to work along side the providers or caretakers of the palms or any and all that are being decimated by the rats or any foreign invaders of any nature to the atull [sic] islands. And also if empowered to partial chemical eradications we would care to not assist in the chemical portion. But to referee as safeguard for areas too delicate for chemical eradication. As we contend not even a biodegradable is safe for all the atull [sic] islands we believe we have all natural procedures that alone or combined will safely eradicate by well proven and longstanding american means with proven and safe track record with positive final result. 

Comment noted. No response needed.

29 M. Rauzon General

I am familiar with Palmyra from two prior visits and have surveyed the island for seabirds. I have seen firsthand the potentialfor seabird restoration and have also witnessed the effects of the failed 2001 rat eradication attempt, both on the island and in the community of eradicators. That is why I advocate pressing forward with rat eradication and especially Alternative C that best copes with the very challenging environment that Palmyra presents.

Comment noted. No response needed.

30 M. Rauzon General The Palmyra rat eradication has had the greatest breadth of research and preparation than any other US eradication. Since the 2001-02 eradication attempt, research into why it failed and what can be learned, has been on-going. Comment noted. No response needed.31 M. Rauzon General

Overall, the completeness of this EIS, the comprehensive appendices that review the past and future options, determine LD’s of toxins, etc. is very remarkable and admirable in scope, showing again how seriously you take your duty to be thorough, responsible and transparent. I say overall, for I did not see what happens if rats are detected after the second drop...

After the rat eradication, contingency bait woremnant rats if any are detected, and a detectithis action. The detection response plan is di

32 NPS General We support the Refuge’s goal of eradications rats from Palmyra and anticipate that the project also will yield valuable information on refinement of eradication and follow-up monitoring techniques, particularly for equatorial island environments. Comment noted. No response needed.33 NPS General

The EIS should more clearly state the reasons that diphacinone was not considered appropriate for this particular project. We feel this specificity and additional supporting information are important in light of possible future rodent eradication attempts where diphacinone could be the more appropriate tool.

34 NPS 2.3.6

This section [2.3.6] would be clearer if the opening paragraph was expanded on or otherwise revised - all five factors contributing to the decision not to further consider the use of diphacinone as an alternative need additional supporting or explanatory information (specified in comments #3-X listed below).

See section 2.3.6 for revised explanation of othat required the use of Diphacinone-50 prod
Comment # Reviewer Section Comment Response to comment

Comment Response MatrixFinal Environmental Impact Statement, April 2011:Palmyra Atoll National Wildlife Refuge Rat Eradication Project

35 NPS 2.3.6

The toxicity of the product is confusing in light of later information about the higher toxicity and slower environmental degradation of brodifacoum. The EIS should clarify why and how the lower toxicity of diphacinone (vs. brodifacoum) figured into the decision not to use diphacinone.

The relatively lower toxicity of Diphacinone-Brodifacoum means that more doses of Diphaeffects to those caused by Brodifacoum 25WDiphacinone for all rodents for up to 12 days 4 days exposure necessary for Brodifacoum 2information.

36 NPS 2.3.6

Efficacy, including palatability is also mentioned as a consideration, but then later (page 22, lines 15-16 and elsewhere), the EIS judges that the 2 toxicants are of equal and adequate palatability. If efficacy other than palatability is a major issue, this should be more clearly stated in this section, including in this introductory paragraph.

Palatability was inferred from studies that looalternate food (choice tests). Choice tests in tdifferent results. These differing results led to about palability is a factor that influenced our 

37 NPS 2.3.6 " ... the extremely dense vegetation at Palmyra inhibiting distribution of product" does not appear to be specific to the use of diphacinone. It instead seems a concern that is related to the method of distribution of any bait. The document was modified to remove this f38 NPS 2.3.6 " .. , the safety of personnel in applying product, including consideration of unknown but documented unexploded ordnance in the atoll" also is not specific to the use of diphacinone. The document was modified to remove this f39 NPS 2.3.6 " ... the inordinately dense population of land crabs, their extreme ability to penetrate enclosures, and their voracity of consumption" again does not appear to relate specifically to the use of diphacinone.

The high density of land crabs is germane becland crabs. The lower toxicity of Diphacinonmuch longer to result in 100% mortality of raextremely difficult to retain enough bait for rnecessary for complete kill of all rats.

40 NPS General

We also suggest including in this section consideration of the performance of diphacinone if applied atsowage rates comparable to that proposed for brodifacoum in Alternatives B-D. Would this increase change the likely performance of this first generation 

toxicant and its assessment in the DEIS?

The sowage rates for Diphacinone-50 would bait remaining on the ground for the entire peFailure to provide adequate bait exposure per

41 NPS 4.4.4.1

We also are concerned about the potential for bristle-thighed curlew mortality. The stated Palmyra resident population of up to

182 birds constitutes roughly 2% of the estimated world population of approximately 10,000 individuals. The DEIS considers population modeling that suggests" ... minor decreases in the population growth rate with diminishing impacts on the projected future population," resulting from a theoretical 80% mortality of resident BTCU at Palmyra (page 113, lines 26-30). Because the species is thought to be in decline, we urge caution and prudence ill light of other factors outside the control of the FWS that may impact this species now and in the future. We ask the FWS to consider additional actions to minimize exposure of curlews to the toxicant; for example, removing crab carcasses and other avenues for secondary poisoning in the days immediately following baiting in areas of high curlew densities, and/or using bait stations rather than aerial broadcast on key curlew islands 

or in key curlew habitat if feasible.

Alternative C, our Preferred Alternative, instishorebird protection will be employed includof any carcasses, bait stations only at major cand feeding of non-breeders prior to bait broa

42 NPS General

Lastly, we call your attention to the recent report by Parkes and Fisher (parkes, J and P Fisher. 2011.) "Review of the Lehua Island Rat Eradication Project", Landcare Research Contract Report LC 129 for the Lehua Island. Their catalog of rodent eradication attempts differs from that of this DEIS and may be more complete. Additionally, their simple statistical evaluations 

of diphacinone vs brodifacoum provide an additional way of viewing the track record of these two toxicants and emphasize the need for more data. Finally, some of the lessons learned from Lehua may be applicable to the Palmyra project.

We have modified Section 2.3.6 to reflect the Fisher, 2011. All recommendations from this inform this project.

43 ABC General We support Alternative C . . . for the eradication to minimize effects on nontarget species. Comment noted. No response needed.44 ABC

[Recommendations on experts in shorebird capture and care to consult] . . . Peter Doherty, Virginia Beach, VA, who produces capture nets specifically designed for shorebirds. . . . Monterey Bay aquarium . . . International Bird Rescue Research in Cordelia, CA.

We appreciate the information and will consu

45 ABC General

Long-legged waders are extremely difficult to capture and hold and can be subject to high rates of mortality during capture andin captivity. It may be useful to try to manage expectations by providing a tentative estimate of mortality in both processes, based on available data.

We recognize there are logistical challenges aholding of long-legged waders and agree it is nontarget mortality. We understand, in the wocould cause the death of all bristle-thighed cube at Palmyra during the operation and while to lethal amounts of brodifacoum. Any indivcaptivity would reduce the overall impact of tpopulation of that species.

46 ABC General We have concerns about the cement slab on which it is proposed to maintain the birds on Cooper Island, because curlews tend to develop foot problems in uniform substrates without tidal action.

In an effort to address potential foot problemplanned to consist of a 6 inch layer of sand anmatting (elephant bark) that will be flushed waway effluent and deter ants from accessing f
Comment # Reviewer Section Comment Response to comment

Comment Response MatrixFinal Environmental Impact Statement, April 2011:Palmyra Atoll National Wildlife Refuge Rat Eradication Project

47 ABC General

[The wildlife veterinarian who will be onsite] has plans to monitor fecal corticosteroids, fecal parasites, and blood for CBC and 

chemistry profiles. ABC thinks this could be a very useful monitoring program to evaluate these fragile birds in captivity and to develop additional expertise for future captive holding of vulnerable birds during island eradications.

Comment noted. No response needed.

48 ABC General

We expect the risk of conspecific aggression to be low among these birds, because of the timing of the operation and because most will not yet be of breeding age, but if the birds are held in some sort of aviary, provisions should be made for separating some birds and providing a visual barrier for any aggressive individuals.

Captured shorebirds would be held in aviariesuggested, aggressive individuals will be sepa

49 ABC General One interesting option for the capture and holding of the curlews may be to place them on a nearby islet or rock, if such a place were available and not subject to baiting. Comment noted.50 ABC General The field studies to determine the amount of rodenticide bait needed to insure adequate coverage of all rat territories appear to have been well planned and executed. Comment noted.51 ABC General

The metabolic fate of brodifacoum and mass balance of residues were not reported in the prior study given in Appendix F of the Draft EIS. The residue analysis for that study was conducted by the California Animal Health and Food Safety Laboratory at UC Davis, and they may have retained the mass spectrometer reconstructed ion chromatograms, which could identify whether any of these potential metabolic products or other products were present in the crab tissues and excreta analyzed in the 2010 study. We strongly suggest contacting them and trying to have the spectroscopist attempt to determine what metabolic products of brodifacoum were present in the feces in addition to the parent compound. . . Without a study of the fate of brodifacoum ingested by crabs, the fate and residue composition of the large amount of brodifacoum spread over Palmyra Atoll will be unclear.

The crab excrement samples collected during metabolic fate of brodifacoum, and unfortunaavailable for further analysis. 

52 ABC General 

We suggest that when samples are collected and analyzed from the planned Palmyra project, APHIS (and any other lab contracted) report as many residues and metabolic products as possible, and use the information to construct a mass balance. The persistence and toxicity of any identified products should be available from prior studies. We suggest using this data to calculate the expected persistence and toxicity to non-targets (such as curlews) and to hold the curlews in captivity until the

toxic residues have dissipated in the Palmyra environment.

We have forwarded these recommendations tmonitoring plan.

53 ABC General

We found that the low level of detail in [Appendix A] precluded a careful evaluation of the bird monitoring protocols, and suggest that further definition be given to the a) statistical design of the pre- and post-eradication bird monitoring 2) the time frame for evaluation of the persistence of bait in the palm canopy, which should be continued until none is detected or some minimal level is reached.

The bird populations monitoring is a part of rwill continue. The description of the bird monproject has been modified to reflect that bait fundetectable.

54 ABC General We would like to see an evaluation of the shorebird population in subsequent years, though we assume this is part of the long- term strategy for documenting the effect of the action on the atoll. Evaluation of Palmyra's shorebird community 

effort as one of the Refuge's standard monitor

55 ABC General

The detail given for the food web monitoring was minimal, with only a sketchy description given on where pooled samples will be collected. We believe these should be representative of the entire atoll. 84 samples of non-target terrestrial animals and 80 

samples of fish appears to be an adequate number of samples to determine the distribution and fate of rodenticide on the atoll.

To ensure that bait would be delivered to all racross the atoll's emergent land area. Becaussignificant driver of variance in residue valuefrom locations that both represent the primary practical sampling sites.

56 ABC General We recommend that a subset of split samples of the rats, fish, gecko, crabs, and bird samples be sent to the U.S. Geological Survey Madison, WI Lab and the USDA National Wildlife Health Center for independent analyses.

Supplementary analysis of split samples at laFort Collins, CO is not currently budgeted fothe possibility of archiving a subset of sampleresults from the NWRC analysis are cause fo

57 ABC General

We believe that directed searches (as opposed to opportunistic searches) for non-target carcasses be conducted in transects for

longer than 10 days after the 2nd application in shore bird roosting sites, and that these also concentrate on places where intoxicated curlews might hide to avoid detection. The monitoring plan does not give detail about how often these searches willbe conducted.

We have modified the monitoring plan to incBeach and on the Runway (the Atoll's largest days after the second bait application. 

58 ABC General

In conclusion, ABC supports the effort to eradicate rats from Palmyra, as it is an important center of biodiversity and speciesabundance. Specifically, we support the Alternative C (aerial broadcast with capture of shorebirds) option listed in the Draft EIS. We believe this project has been organized and planned carefully, although we would like to have a more complete analysis of the fate of rodenticide moving through the Palmyra ecosystem.

Comment noted. No response needed.

59 MCBI General

MCBI believes Alternative C (as outlined in the DEIS): Aerial broadcast of brodifacoum, with proactive mitigation of risk for vulnerable shorebird taxa offers the highest probability of removing the nonnative rats while also minimizing harm to the marine and terrestrial ecosystems.

Comment noted. No response needed.

60 MCBI General

In order to make a more informed decision, a cost comparison of each alternative would have been helpful in determining the efficient use of resources. Regardless of cost, MCBI supports the eradication of nonnative rats on Palmyra Atoll in an effort to restore native wildlife populations.

Table 2.8 has been added and compares costs 
Comment # Reviewer Section Comment Response to comment

Comment Response MatrixFinal Environmental Impact Statement, April 2011:Palmyra Atoll National Wildlife Refuge Rat Eradication Project

61 USDA General The FWS should proceed cautiously and make every effort to document the impacts of this project. Documentation of environmental impacts should be evaluated by an independent party to ensure absolute transparency.

The Palmyra Partnership is securing assistancmonitoring for this project (Appendix A). ThUSDA-NWRC, the monitoring action would samples would be analyzed and the results wopersonnel will also continue to monitor wildlmonitoring activities.

62 USDA General

We have also worked cooperatively to draft a post-application monitoring plan to properly document the short-term environmental impacts of this activity. Specifically addressing the high rates of brodifacoum application proposed in AlternativeB and C: first application rate is 4.5 times higher than currently allowed rate, second application is nearly 6 times higher than 

currently allowed rate, total application rate (134 kg/ha) will exceed the current total label allowance (27 kg/ha) by 107 kg/ha.

We worked with USDA and USEPA to develspecific to this eradication action at Palmyra application rates discussed in Chapter 2 of the in Appendix L.

63 USDA General

Massive non-target mortality of shorebirds and other species could occur as a result of primary or secondary exposure. Therefore, this could be interpreted as a direct violation of the Migratory Bird Treaty Act; the FWS should secure a take permit 

under the Act.

In Chapter 4 of the FEIS we evaluate the nonfrom primary and/or secondary exposure. Wmortality of shorebirds, but do not expect mafrom shorebirds, no land-foraging birds occur Also, great effort would be taken to prevent bfurther reducing risks there. We will secure a for the anticipated worst-case migratory bird 

64 USDA 4.4.4.1 The range of birds listed on page 107 of the DEIS that will likely be lethally taken on do not quite match with the expected lethal take given in the individual accounts discussed starting on page 119.

The population ranges present on page 107 of includes the winter months when shorebirds alethal take values for bird species starting on from all atoll counts conducted during the samwoudl be implemented (June-July). We have 

65 USDA 4.4.4

We believe that the nontarget lethal take in the DEIS is understated and that the marine reptiles, namely sea turtles, need to be included because they will eat pelleted bait and it is anticipated that broadcast bait will wind up in waters where they could be exposed.

Please see modifications to Section 4.4.4 relaEvery effort would be made to prevent accidethe unlikely event that 1 kg of bait pellets entintroduce 0.025 grams of toxicant. There are of research specific to marine reptiles, but calon study of ornate wood turtles by U.S. DepaResearch Center, when applied to adult green could consume at least 40.5 lbs (18.4 kg) or 9consume at least 15.4 lbs (7 kg) with no signs 

66 USDA 2.3

The DEIS should have included a wider range of Alternatives such as an Integrated Rat Eradication Alternative. In particular, we expected to see the use of other rodenticides as considered alternatives analyzed in detail. Worldwide literature strongly supports first generation rodenticide operations more than is indicated in the DEIS, including tropical environments in Australia and Pacific Islands (Varnham 2010). An example of a recent rat eradication success in a tropical environment using an integrated approach included rodent eradication on Cocos Island, Guam (Lujan et al., 24th Vertebr. Pest Conference, 2010, in press). 

Alternatives involving other rodenticides werDifferent factors were considered, including iat Palmyra. While tropical, the eradication enfrom that at Palmyra, notably in the density opopulations. The preferred alterntative (C) ieradicating rats and minimizes risk to non- taspecific environments. 

67 USDA 2.4.13

A great uncertainty in the rodent eradication plan is the rats’ use of the coconut canopy and the ability to adequately treat the palm canopy. It is our understanding that the Refuge has discussed eradicating coconut palms (potentially another invasive species) from Palmyra Atoll. A viable alternative to one of the alternatives in the DEIS would be to remove the coconut palms prior to the eradication, simplifying the rodent eradication.

Removal of the coconut palms is an on-going with the current focus targeting palms over-hremoval of coconut palms was considered earactivity. We concluded that while this action greatly hinder movement on the ground (becaresulting light gaps), and would remove a largwithin Palmyra's terrestrial envrionment (the crowns would not be availble to land crabs, bAppendix C. We have added Section 2.4.13 t

68 USDA 2.4.6

The DEIS suggests that rodenticide resistance is unlikely because it has been 6 years since the last treatment. This is an incorrect assumption as it is possible to still have some rodenticide residue in the rats on Palmyra Atoll. The DEIS relies on old information and the reference to Pitt (2010) is erroneous.

We continue to believe it the risk of having rehave modified Section 2.4.6 to further addres
Comment # Reviewer Section Comment Response to comment

Comment Response MatrixFinal Environmental Impact Statement, April 2011:Palmyra Atoll National Wildlife Refuge Rat Eradication Project

69 USDA General

Another concern of ours is baiting in and around human habitation because it is unclear exactly what the protocol will be. Thisshould be explicitly stated in the DEIS. Additionally, if baits are currently being used in these areas, the type of bait, active ingredient, application rate, and duration of baiting being used should be documented.

The use of tamper reistant bait stations in and conducted in accordiance with the bait produoperational details in Appendix K, and will pplan at http://www.fws.gov/palmyraatoll/rain

70 USDA 2.3.6

A clarification/correction needs to be made in the DEIS regarding Diphacinone 50:Conservation and Ramik Green. In numerous places in the DEIS reference is made to the differences in the performance of Diphacinone 50:Conservation and Ramik Green [sic] when used in rodent eradication or control projects. These two products are exactly the same formulation. Diphacinone 50:Conservation is simply a repack of Ramik Green [sic]. Consequently, questions raised in the DEIS regarding the uncertainty about relating the performance of the two products is nullified because they are directly comparable.

We have modifed the document to refer to th50:Conservation or Diphacinone-50. Ramikis only referenced from literature where it wa

71 USDA 4.3.1.1

We feel ideas presented in the DEIS regarding the potential residues in surface water mislead the reader. On this page you present the summary of an aquatic risk assessment conducted by Syngenta Crop Protection Inc. (2003). This risk assessment reported residues resulting in surface water from an application of 18 kg/ha brodifacoum. No risk is indicated for fish in thisassessment. The proposed application rate in Alternative B and C are 4.6 times higher than 18 kg/ha. Even at this higher application rate, no risk is indicated for fish. However, it is critical to point out in this section that the application rate proposed on Palmyra Atoll will be much higher than that used by Syngenta and, thus, may not result in similar conclusions as suggested.

We have made modifications to Section 4.3.1

72 USDA General

The DEIS predicts the impact of brodifacoum on nontarget species, especially birds and reptiles. However, the true extent of impacts on nontarget species are largely unknown because many facets of the persistence of brodifacoum are unknown, such as the length of time it remains intact in soils and other environmental compartments and the duration of primary and secondary impacts to aquatic and terrestrial organisms. The longevity of active brodifacoum could become a great concern beyond the 2-month window when birds are relatively rare on the island and potentially long beyond the 1-month monitoring proposed in the included monitoring plan. As a result of the unknowns, monitoring will be extremely important and valuable. We understand the

logistical difficulties of keeping a monitoring crew on the atoll beyond 1 month. However, collection of environmental samples during follow-up visits on day 56, 6 months, 1 and 2 years are very important to document the residue decline in the environment.

We agree it is desirable to understand the potassociated with this eradication action and recresources accordingly. We will continue collsamples beyond what is scheduled in the monUSDA (Appendix A), as well as presence/absand other indices of ecosystem health through and within the limitations of funding.

73 USDA General

The DEIS should include a discussion of professional wildlife damage management principals which guide agency decision making beyond efficacy, such as the intent to minimize adverse effects on non-target animals, and economic (e.g. program cost/benefit) and social factors (public acceptance of various alternatives).

Please see Sections 1.4 through 1.7, Sections 

74 USDA General The DEIS should include lessons learned from Rat Island, with recommendations made by FWS and the Ornithological Council (Salmon and Paul 2010) as they may apply to Palmyra. 

We have reviewed the report and lessons learMany of the recommendations are incorporatincluded many preliminary operational detaildraft version of the operations plan at http://www.fws.gov/palmyraatoll/rainforestrereport in the FEIS.

75 USDA General For disclosure, the label should be included in the Final EIS to ensure that the proposed action is in conformation with label restrictions. We have included the label and supplemental 76 USDA General

The DEIS did not cite literature that included pertinent information relevant to the analysis of the effects of brodifacoum anddiphacinone that should be considered in an objective analysis of both toxicants including information on the effects of nontargets (Cox and Smith 1990, Dowding et al. 2006, Salmon and Paul 2010), effectiveness on formulations on targets (Swift 1998), registration/environmental concerns (U.S. Environmental Protection Agency 1998), and rat ecology (Varnham 2010).

We have reviewed the literature and modified Please see Sections 2.6.4 and 4.4.4.1. 

77 USDA General As the registrant of the only brodifacoum labels currently approved for using broadcast application to undertake this type of a project, WS is very interested in the short- and long-term effects from this rodenticide. Comment noted. No response needed.78 EPA General

We have rated Alternative A (No Action) as Environmental Concerns Insufficient Information (EC-2): “EC” (Environmental Concerns). The EPA review has identified environmental impacts that should be avoided in order to fully protect the environment. Corrective measures may require changes to the preferred alternative or application of mitigation measures that can reduce the environmental impact. EPA would like to work with the lead agency to reduce these impacts. Category “2” (Insufficient Information). The Draft EIS does not contain sufficient information for EPA to fully assess environmental impactsthat should be avoided in order to fully protect the environment, or the EPA reviewer has identified new reasonably available alternatives that are within the spectrum of alternatives analyzed in the Draft EIS, which could reduce the environmental impacts of the action. The identified additional information, data, analyses, or discussion should be included in the Final EIS.

We have made modifications throughout the information on items identified during public 
Comment # Reviewer Section Comment Response to comment

Comment Response MatrixFinal Environmental Impact Statement, April 2011:Palmyra Atoll National Wildlife Refuge Rat Eradication Project

79 EPA General

We have rated Alternative B (aerial broadcast of brodifacoum) and Alternative C (Alternative B with added bird capture to avoid poisoning) as Environmental Objections Insufficient Information (EO-2). “EO” (Environmental Objections). The EPA review has identified significant environmental impacts that should be avoided in order to provide adequate protection for the environment. Corrective measures may require substantial changes to the preferred alternative or consideration of some other 

project alternative (including the no action alternative or a new alternative). EPA intends to work with the lead agency to reduce these impacts. Category “2” (Insufficient Information) - see comment #2 for definition.

We have made modifications throughout the information on items identified during public 

80 EPA General

The alternatives analysis in the FEIS should clearly identify the criteria used in screening potential alternatives to determine 

which would be brought forward and evaluated in the NEPA document, and these criteria should be consistently applied to all potential alternatives. An objective evaluation of diphacinone alternatives, in a side-by-side comparison, would be helpful to the public and the decision-maker and is recommended. Discuss and define feasibility and how it was assessed for the alternatives. Include cost data, which are likely to be relevant and important to the decision, so that an evaluation of the person-hours andmitigation proposals can be made.

Please refer to modifications made to Section 

81 EPA 2.4

Include a discussion of the management structure for project implementation, and the staff who would be involved, including their expertise in rat eradications. Include a communication plan as an appendix to the FEIS. Discuss budget concerns or limitations. This information is relevant to environment impacts and should be included. FWS may choose to include this information in an adaptive management plan. if so, we recommend it be appended to the FEIS.

82 EPA General

Clearly present the aerial application rates for both the first and second applications. The EPA recommends that the second application rate be lower than the first unless between-treatment monitoring of other evidence indicates the presence of significant rat activity in a particular area. Once rates are established, they should be adhered to during the operation, and changes only made according to a clear protocol... deviating from the target application rate, should be avoided. Changes to baiting rates in the field should be thoroughly documented. In no case may the limits on application rate established by the label 

for the product used in the project be exceeded, with some allowances for swath overlap (as covered by the labeling). As recommended in the Rat Island critical evaluation, planning should occur for contingencies and for each... that evaluation recommends developing... “A structured decision-making tool for application of bait other than as planned would require a written assessment of the amount of bait already on the ground, a comparison to the approved label rate and target rates, a written assessment of the additional bait to be applied, a calculation of the total amount of bait that would be applied, and increase in potential risk nontarget species”.

83 EPA General

The FEIS should disclose how excess bait will be disposed (or shipped off-island) and whether funding for bait disposal will be

included in the project, and should include clear directions for proper excess bait disposal in a communication plan. As mentioned above, decisions regarding disposal of bait should be clearly outlined in a structured decision-making tool.

Disposal will be in compliance with directionEPA. 

84 EPA General The FEIS should document a more appropriate post-treatment monitoring plan. The EPA recommends monitoring between aerial treatments and shortly after the second round of baiting. Frequent monitoring should occur in bait station areas. We think that the USDA-NWRC monitoring 

indicated in this comment.

85 EPA Appendix B.

We strongly recommend that the biosecurity plan be as comprehensive as possible. We recommend that it include quarantine, surveillance, and contingency components, and provide references and/or discussion that demonstrate thatthe plan has thoroughly considered which, of the proven biosecurity approaches available, will work best for Palmyra. The FEIS should also identify who would implement the biosecurity actions, whether their implementation is dependent on funding, and if so any expectancy of funding deficiences.

We have modifed the modified working-draft incorporate many of these recommendations.

86 EPA General

The FEIS should devote more analysis to logistics and manpower needs of the alternatives, especially since effective canopy baiting is crucial to the success of the project. (See also comment below regarding reducing palms prior to eradication). As recommended above, define and discuss feasibility in relation to the alternatives, and whether sufficient funding is available to 

meet manpower and all logistical needs.

We have included many preliminary operatioworking draft version of the operations plan ahttp://www.fws.gov/palmyraatoll/rainforestre

87 EPA 2.4.4

Correct the statements regarding RUP certification in the FEIS. The FEIS should document if and how responsible parties are following the record keeping requirements for sale and use of RUPs, including the company selling them and the applicator whois using them. Ensuring that all of the restricted use pesticides are accounted for could be a homeland security issue, especially 

in the quantities being proposed.

We made corrections to Section 2.4.4. We arregarding record keeping for sale and use of R

88 EPA 2.4.4

There is reference to “EPA —approved label instructions” that do not currently exist. As noted above, the existing label for EPA Reg. No. 56228-36 would have to be amended or Palmyra-specific application directions would have to be authorized via another provision of FIFRA.

Comment noted. No response required.

89 EPA 2.5.1

The name, registrant, and registration number of the product intended to be used on Palmyra are misidentified on page 29 and elsewhere. The product’s name is “brodifacoum-25W Conservation”, without a trademark symbol. The registrant is the Animal and Plant Health Inspection Service (APHIS), USDA. The registration number is 56228-36.

We have corrected the errors.We have included many preliminary operatioworking draft version of the operations plan ahttp://www.fws.gov/palmyraatoll/rainforestre

Specific Recommendations from USEPA
Comment # Reviewer Section Comment Response to comment

Comment Response MatrixFinal Environmental Impact Statement, April 2011:Palmyra Atoll National Wildlife Refuge Rat Eradication Project

90 EPA 2.5.1

The discussion of first and second-generation anticoagulants on p. 30 is not completely accurate. The “generation” designationsfor anticoagulants are not strictly “according to when they were first developed as rodenticides” although they relate indirectly to their toxicity.

We have modified the Section to include the 

91 EPA 2.5.1

Discussion on p. 30 concludes that “any rodenticide can be effectively used to eradicate an entire rodent population if all individuals within the population consume enough bait over an appropriate amount of time.” This sentence does not address the possibility of resistant individuals within the population.

We have modified the sentence to include res

92 EPA 2.5 Assessing the weather conditions and prohibiting bait broadcast if rainfall is forecast (Appendix H, p. 12). More detail about effectiveness and implementation of this measure should be included in the FEIS. Please refer to Sections 2.4.9 and 2.6.3, Table 

preliminary operational details in Appendix Koperations plan at http://www.fws.gov/palmy

93 EPA General

Securing a tarp over the drinking water catchment to prevent aerially broadcast bait from entering the drinking water supply. We recommend adding to this measure that the tarp would be inspected (or reinstalled if it was removed) prior to a second aerial application.

 We have modified the document to clarify thtarp covering the catchment system after each 

94 EPA General

Dying the bait blue to make pellets less attractive to birds. We believe the conclusion that blue dye used in EPA Reg. No. 56228-

36 would make pellets less attractive to birds is overdrawn. The degree of repellency would depend upon the shade of blue and the perceptions and food habits of each bird species. Birds that eat fruits or some types of insects might not be predisposed against eating blue things. It is not clear to what extent the factors affecting eat/don’t-eat decisions for the types of birds that occur on Palmyra have been studied.

There are no Palmyra-specific studies of whiccomponent of this project.

95 EPA General

Capture and treatment of all sick and moribund shorebirds found during and directly after the eradication, and treatment with Vitamin K, an antidote to anticoagulants (p. 26). The planned collection and Vitamin-K treatments of sick or moribund shorebirds should be evaluated for feasibility and effectiveness in the FEIS. Treatments would likely have to be extensive if experiences with various mammals (including humans) are predictive of what would be needed to savebirds.

Please see Shorebird protection protocol in thAppendix K where we have included many ppost a working draft version of the operations http://www.fws.gov/palmyraatoll/rainforestre

96 EPA General

For Alternative D (bait station alternative), the DEIS indicates that, while mortality risk from toxicants is high for some birds (BTCU, Pacific golden plover, ruddy turnstones, laughing and Franklin’s gulls, Northern shoveler and Northern pintail duck), the exposure risk is low (p. 136- 139). This does not fully consider the fact that the bait would be present in the atoll environment for approximately 2 years, which would offer long-term secondary pathway toxicityopportunities.

Comment noted. No response required as Al

97 EPA General The issue of preventing rats in the bait station areas of the aerially broadcast alternatives repopulating aerially eradicated areas should be addressed in the project design. All rats would be exposed to rodenticide duri

source populations to re-populate other areas

98 EPA General Capturing, holding, and maintaining individuals of the native gecko species should be considered as a mitigation measure. A tropical gecko specialist is on the monitorin

capture, hold, and maintain native geckos.

99 EPA General

Reevaluate impacts to soils and water resources from the aerial broadcast alternatives using the quantity of bait expected to be applied for the project. If the active ingredient infiltrates vertically into soils, the Alifano and Wegmann (2010) data likelywould overestimate the extent of island-wide contamination, although it is possible that material might congregate in some lower areas due to surface flow resulting from heavy rain events. Due to the composition of the islands, however, puddles tend to be short-lived, even after extensive heavy rains.

We prefer to stay with the precautionary resuis better than underestimating it.

100 EPA General

For impacts from the bait stations (which are part of all action alternatives), these discussions should note the possibility of bait stations becoming damaged or being dumped, either of which could result in a concentration of several ounces or more of bait at one spot. Describing the bait stations as being “durable enough to stay in place for 2 years and prevent crabs from entering or destroying them” is fine in theory, but realistic assumptions would expect some error. It also is not clear that a specific design of bait station has been selected for use in this project.

Tamper-resistant bait stations would be purchhabitation. For uninhabited areas of the atoll, constructed with off-the-shelf materials (Appthat any bait on the ground would be quickly 

101 EPA 2.5.2

Last paragraph, running over to p. 36. The characterization that detection of shore birds was consistently higher post-treatment than pre-treatment for the 2005 mini-eradication effort is not consistent with the narrative in, nor “Figure 10” of, the report by Buckelew, et al (2005).

Page 35 of the DEIS repeats a Section of the Restoration: Rat eradication trial 2005’ (Appedetection of these shorebirds were consistentlmigratory influx.” The 2005 report states thesnumbers of individuals observed during the spre application for all species except Ruddy TTattlers on Whippoorwill, Home, and Little Epresented in Table 10. Therefore, the DEIS acBuckelew et al. (2005) report.

102 EPA 2.5.2

“Figure 2.1”. The numbers illustrated in this figure are not consistent with those shown in “Fig. 5” in the Wegmann, et al. (2008) report. The narrative on page 37 of the draft EIS is more accurately reflected by Fig. 5” of Wegmann, et al. (2008), than by “Figure 2.1” on page 38 of the Draft EIS.

The values in the FEIS represent an updated vaccurate.
Comment # Reviewer Section Comment Response to comment

Comment Response MatrixFinal Environmental Impact Statement, April 2011:Palmyra Atoll National Wildlife Refuge Rat Eradication Project

103 EPA 2.5.2 The first line of this paragraph should be corrected factually as well as grammatically. We have made the correction.104 EPA 2.6.2

The number (332) given here for “successfully reported island eradication efforts world wide” differs from the number (278) cited from the same reference on page 31. At least one of those numbers must be wrong. The correct number, if known, should be used. “Brodifacoum-25” is not one “specific product”. This paragraph itself acknowledges the existence of a “Brodifacoum25D” and a “Brodifacoum-25W’.

For clarity, one number refers to all eradicatiorodendticide used is known. Both numbers ar

105 EPA 2.6.4

Table 2.5, and relevant discussions on page 51. The result on Whippoorwill Island is reported as having been “Successful” despite the finding of one or more live rats 8 and 10 days after bait application. All of the localized rat eradication efforts on Palmyra in 2005 would be judged as “Failed” if the standard index of no signs of rat activity for 2 years following treatment were applied. Although reinvasion from very nearby untreated islands might have been the cause of the reappearance of rats on those islands, the standard for successful eradication should be greater than obtaining zero scores for various activity measures shortly after treatment. By the latter standard, the brodifacoum/Bromethalin trials on Palmyra Atoll in 200 1-2003 probably would have been judged “Successful”, at least for some of the islands; and the same would have held for some islands in the diphacinone work in the Bay of Islands, Adak, AK, 2003-2004. The 2008 trials on Palmyra involved placebo baits which, presumably, did not directly kill any rats. The “Failed” status is visited upon them because one or more rats live trapped posttreatment showed no evidence of the Pyranine “biomarker”, and some others were marked only to a degree like the captive roof rats that were fed only one placebo bait pellet. The two failures for Polynesian rats (R. exulans) might have resulted in part through use of a bait moiety that was less than optimal for controlling that species. The 25W bait was not accepted especially well by captive Polynesian rats in trials conducted on Wake Atoll in 2007.

The Whippoorwill Island rat was lethargic aneradication there was classified as a success.

106 EPA 2.1

“Table 2.7”. “Canopy baiting” is mentioned as one of the “Secondary bait delivery methods” that would be used for “Alterative D” [sic] (bait stations), but not for the aerial application options which the narrative to the Draft EIS indicates would be supplemented by baiting trees that overhang water.

We have corrected the error.

107 EPA 4.4.4.1 Whether a single “dose” of brodifacoum would be lethal would depend upon the amount received, through ingestion in this case. The LD50 is not really a “threshold”, as some individuals would be expected to die after receiving lower dosages. We have corrected the error.108 EPA 4.5.2 Under this alternative, there would not be an eradication effort. Therefore, signs (or “sings”, line 17) would not have to be posted. We have corrected the error.109 EPA 2.5.1

The last sentence of the first paragraph under “Brodifacoum25WTM bait product” does not follow from the rest of the paragraph. It appears that 14 (7%) of 197 successful eradications using brodifacoum as the “primary rodenticide” were effected using “aerial broadcast supplemented with hand-broadcast” but that technique would have been less “commonly used” than bait stations (47% or ~93 instances), aerial-broadcast alone (29% or ~57 instances), or hand-broadcast (21% or ~41 instances).

We have modified this Section for clarity.

110 EPA 2.3

In approaches dismissed, the DEIS identifies fertility control and discusses oral contraceptives. We are aware that research is

being conducted towards the development of chemical sterilants that could offer a less toxic alternative to rodenticides. FWS should monitor this development for possible future use.

Comment noted. No response needed.

111 EPA 4.4.3.1 The DEIS says that successful turtle nesting attempts have not been recorded on Palmyra; but, on p. 83, it says that green turtle nesting has been documented at least twice at Palmyra, primarily on the northwest side of Cooper island. Nesting attempts have been documented but n112 EPA 4.4.2.1 DEIS states that informal Sect 7 consultation will be conducted “for any case deemed necessary by the FWS”. The FEIS should indicate whether informal consultation has occurred. Informal ESA Section 7 Consultation is curre

Resources Division.

113 EPA Appx. C Appendix C pp. 14 and 37 indicate that 2 cats and a dog (and a cat on a boat) were present in 2004. State whether these animals are still present and how they will avoid poisoning. Domestic animals currently at Palmyra are 2 

operation is included in the draft operational 

114 EPA Pages bearing these numbers are missing from the copy of the draft EIS that was reviewed; but, seemingly, with no loss of intended text. Subsection “5.1” appears on page 151; and subsection “5.2” appears on page 189 We have corrected the pagination error.



Best Management Practices (BMPs) for General In-Water 

Work Including Boat and Diver Operations 

January 5, 2011 

NMFS Protected Resources Division recommends implementation of the following 

BMPs to reduce potential adverse affects on protected marine species. These BMPs are in 

no way intended to supersede or replace measures required by any other agency 

including, but not limited to the ACOE, USFWS, USEPA, or NMFS Habitat 

Conservation Division. Compliance with these BMPs is secondary to safety concerns. 

A. Constant vigilance shall be kept for the presence of ESA-listed marine species during 

all aspects of the proposed action, particularly in-water activities such as boat operations, 

diving, and deployment of anchors and mooring lines. 

1. The project manager shall designate an appropriate number of competent 

observers to survey the marine areas adjacent to the proposed action for ESAlisted marine species. 

2. Surveys shall be made prior to the start of work each day, and prior to resumption 

of work following any break of more than one half hour. Periodic additional 

surveys throughout the work day are strongly recommended. 

3. All in-water work shall be postponed or halted when ESA-listed marine species 

are within 50 yards of the proposed work, and shall only begin/resume after the 

animals have voluntarily departed the area. If ESA-listed marine species are 

noticed within 50 yards after work has already begun, that work may continue 

only if, in the best judgment of the project supervisor, that there is no way for the 

activity to adversely affect the animal(s). For example; divers performing surveys 

or underwater work would likely be permissible, whereas operation of heavy 

equipment is likely not. 

4. When piloting vessels, vessel operators shall alter course to remain at least 100 

yards from whales, and at least 50 yards from other marine mammals and sea 

turtles. 

5. Reduce vessel speed to 10 knots or less when piloting vessels at or within the 

ranges described above from marine mammals and sea turtles. Operators shall be 

particularly vigilant to watch for turtles at or near the surface in areas of known or 

suspected turtle activity, and if practicable, reduce vessel speed to 5 knots or less. 

6. If despite efforts to maintain the distances and speeds described above, a marine 

mammal or turtle approaches the vessel, put the engine in neutral until the animal 

is at least 50 feet away, and then slowly move away to the prescribed distance. 

7. Marine mammals and sea turtles should not be encircled or trapped between 

multiple vessels or between vessels and the shore. 

8. Do not attempt to feed, touch, ride, or otherwise intentionally interact with any 

ESA-listed marine species. 
B. No contamination of the marine environment should result from project-related 

activities. 

9. A contingency plan to control toxic materials is required. 

10. Appropriate materials to contain and clean potential spills will be stored at the 

work site, and be readily available. 

11. All project-related materials and equipment placed in the water will be free of 

pollutants. The project manager and heavy equipment operators will perform 

daily pre-work equipment inspections for cleanliness and leaks. All heavy 

equipment operations will be postponed or halted should a leak be detected, and 

will not proceed until the leak is repaired and equipment cleaned. 

12. Fueling of land-based vehicles and equipment should take place at least 50 feet 

away from the water, preferably over an impervious surface. Fueling of vessels 

should be done at approved fueling facilities. 

13. Turbidity and siltation from project-related work should be minimized and 

contained through the appropriate use of effective silt containment devices and 

the curtailment of work during adverse tidal and weather conditions. 

14. A plan will be developed to prevent debris and other wastes from entering or 

remaining in the marine environment during the project. 
USDA


-

United States 

Department of 

Agriculture 

Marketing and 

Regulatory 

Programs 

Animal and 

Plant Health 

Inspection 

Service 

Wildlife Services 

Washington, DC 

20250 

April 8, 2011 

Dr. Elizabeth Flint 

Pacific Reefs National Wildlife 

Refuge Complex 

300 Ala Moana Blvd. 

Room 5-231 

Honolulu, HI 96850. 

Dear Dr. Flint: 

We have reviewed the draft Environmental Impact Statement, "Palmyra Atoll National 

Wildlife Refuge Rat Eradication Project" (DEIS) and your intent to pursue island 

restoration activities on Palmyra Atoll. Wildlife Services shares your interest in using 

rodent eradication as a means of achieving conservation goals on islands to restore 

indigenous populations ofwildlife. We believe that should rat eradication on Palmyra 

be achieved, native plants and wildlife, primarily the nesting seabirds and reptiles, will 

once again flourish as you have described. 

As you effectively point out in the DEIS, eradication of invasive rodents on islands has 

potential for enormous conservation benefits. We agree with you and the larger 

conservation community that this management technique should be embraced. It may be 

the single most important conservation tool land managers have to protect native island 

habitats and their associated faunal communities. However, we also recognize that an 

eradication project that suffers unacceptable short- or long-term negative impacts could 

eliminate the use ofthis tool for future predator management activities. As a result, the 

U.S. Fish and Wildlife Service (FWS) should proceed cautiously and make every effort 

to document the impacts ofthis project. Documentation of environmental impacts 

should be evaluated by an independent party to ensure absolute transparency. 

The project proposed in Alternatives Band C ofthe DEIS represents the largest 

application of brodifacoum we are aware of anywhere in the world. The application 

rates proposed in these options are 4.5 times higher than the currently allowed rate for 

the first application and nearly 6 times higher than the currently allowed second 

application rate. If either Alternative B or C is chosen for this project, the total 

application rate (134 kg/ha) will exceed the current total label allowance (27 kg/ha) by 

107 kg/ha. Since the proposed application rates exceed the currently allowed rates, the 

effects of such application levels on the Palmyra Atoll ecosystem are not fully known. 

APIIIS Safeguarding American Agriculture 

APHIS is an agency of USDA's Marketing and Regulatory Program 

..An Equal Opportunity Provider and Employer 
2 Dr. Elizabeth Flint 

Wildlife Services is participating in the proposed rodent eradication to the extent that we have 

worked with FWS. ~d Island Conser:ation to draft a time-limited, Palmyra Atoll specific, 

supp~emental pestl.clde la?el fo~ Brod~fac?um 25W:Conservation. This label, if approved, should 

pro~Ide you suffiCIent latltude III apphcatIOn methods to successfully complete this eradication 

project. We have also worked cooperatively to draft a post- application monitoring plan to 

properly document the short-term environmental impacts ofthis activity. 

We concur with the DEIS that the application could result in a massive non-target mortality of 

shorebirds and other species that directly consume bait. In addition, we believe this project could 

result in significant secondary exposure and mortality ofspecies consuming dead or dying rats, or 

other food items incorporating brodifacoum into their tissues. Because this could be interpreted 

as a direct violation ofthe Migratory Bird Treaty Act, FWS should secure a take permit under the 

Act which specifies the number of each species listed in the DEIS allowed to be taken by this 

project. It should be noted that the range of birds listed page 107 ofthe DEIS that will likely be 

lethally taken on do not quite match with the expected lethal take given in the individual accounts 

discussed starting on page 119. Additionally, we believe that the nontarget lethal take in the 

DEIS is understated and that marine reptiles, namely sea turtles, need to be included because they 

will eat pelleted bait and it is anticipated that broadcast bait will wind up in waters where they 

could be exposed. 

We believe that the DEIS should have included a wider range ofAlternatives such as an 

Integrated Rat Eradication Alternative. In particular, we expected to see the use of other 

rodenticides as considered alternatives analyzed in detail. Worldwide literature strongly supports 

first generation rodenticide operations more than is indicated in the DEIS, including tropical 

environments in Australia and Pacific Islands (Varnham 2010). An example of a recent rat 

eradication success in a tropical environment using an integrated approach included rodent 

eradication on Cocos Island, Guam (Lujan et aI., 24th Vertebr. Pest Conference, 2010, in press). 

A great uncertainty in the rodent eradication plan is the rats' use ofthe coconut canopy and the 

ability to adequately treat the palm canopy. It is our understanding that the Refuge has discussed 

eradicating coconut palms (potentially another invasive species) from Palmyra Atoll. A viable 

alternative to one ofthe alternatives in the DEIS would be to remove the coconut palms prior to 

the eradication, simplifying the rodent eradication. 

The DEIS on page 25 suggests that rodenticide resistance is unlikely because it has been 6 years 

since the last treatment. This is an incorrect assumption as it is possible to still have some 

rodenticide resistance in the rats at Palmyra Atoll. The DEIS relies on old information and the 

reference to Pitt (2010) is erroneous. 

Another concern ofours is baiting in and around human habitation because it is unclear exactly 

what the protocol will be. This should be explicitly stated in the DEIS. Additionally, ifbaits are 

currently being used in these areas, the type of bait, active ingredient, application rate, and 

duration of baiting being used should be documented. 

APHIS Safeguarding American Agriculture 

APHIS is an agency of USDA's Marlleting and Regulatory Program 

..An Equal Opportunity Provider and Employer 
3 

Dr. Elizabeth Flint 

A clarification/correction needs to be made in the OEIS regarding Oiphacinone 50:Conservation 

and Ramik Green (OEIS Section 2.3.6). In numerous places in the OEIS reference is made to 

differences in the performance ofOiphacinone 50:Conservation and Ramik Green when used in 

rodent eradication or control projects. These two products are exactly the same formulation. 

O~phru:inone 50:Conservation is simply a repack of Ramik Green. Consequently, questions 

ratsed III the OEIS regarding the uncertainty about relating the performance of the two products 

is nullified because they are directly comparable. 

We feel ideas presented on page 970fthe OEIS regarding the potential residues in surface water 

mislead the reader. On this page you present a summary of an aquatic risk assessment 

conducted by Syngenta Crop Protection Inc. (2003). This risk assessment reported residues 

resulting in surface water from an application of 18 kglha brodifacoum. No risk is indicated for 

fish in this assessment. The proposed application rate in Alternatives B and C are 4.6 times 

higher than 18 kglha. Even at this higher application rate, no risk is indicated for fish. 

However, it is critical to point out in this section that the application rate proposed on Palmyra 

Atoll will be much higher than that used by Syngenta and, thus, may not result in similar 

conclusions as suggested. 

The OEIS predicts the impact of brodifacoum on nontarget species, especially birds and reptiles. 

However, the true extent of impacts on nontarget species are largely unknown because many 

facets of the persistence of brodifacoum are unknown, such as the length of time it remains 

intact in soils and other environmental compartments and the duration ofprimary and secondary 

impacts to aquatic and terrestrial organisms. The longevity of active brodifacoum could become 

a great concern beyond the 2-month window when birds are relatively rare on the island and 

potentially long beyond the I-month monitoring proposed in the included monitoring plan. As a 

result ofthe unknowns, monitoring will be extremely important and valuable. We understand 

the logistical difficulties ofkeeping a monitoring crew on the atoll beyond one month. 

However, collection of environmental samples during follow-up visits on day 56, 6 months, I 

and 2 years are important to document the residue decline in the environment. 

We believe that the OEIS should include a discussion ofprofessional wildlife damage 

management principals which guide agency decision making beyond efficacy, such as the intent 

to minimize adverse effects on non-target animals, and economic (e.g. program costlbenefit) and 

social factors (public acceptance ofvarious alternatives). In addition, the OEIS should include 

lessons learned from Rat Island, with recommendations made by FWS and the Ornithological 

Council (Paul and Salmon 2010) as they may apply to Palmyra. For disclosure, the label should 

be included in the Final EIS to ensure that the proposed action is in conformance with label 

restrictions. Additionally, the DEIS did not cite literature that included pertinent information 

relevant to the analysis of the effects ofbrodifacoum and diphacinone that should be considered 
Dr. 4 Elizabeth Flint 

in an objective analysis of both toxicants including infonnation on the effects to nontargets (Cox 

and Smith 1992, Dowding et al. 2006, Paul and Salmon 2010), effectiveness of fonnulations on 

targets (Swift 1998), registration/environmental concerns (U.S. Environmental Protection Agency 

1998), and rat ecology (Varnham 2010). 

As the registrant of the only brodifacoum labels currently approved for using broadcast 

application to undertake this type of a project, WS is very interested in the short- and long-tenn 

effects from this rodenticide. We have a great interest in ensuring the availability and safe use of 

this important management tooL 

We look forward to providing you with continued assistance as needed for the project. 

Sincerely, 

William H. Clay 

Deputy Administrator 

APHIS Safeguarding American Agriculture 

APHIS is an agency of USDA's Marketing and Regulatory Program 

..An Equal Opportunity Provider and Employer 
Literature Cited 

Cox, P. R. and R. H. Smith. 1990. Rodenticide ecotoxicology: Assessing non-target population 

effects. Functional Ecology 4:315-320. 

Dowding, J. E., T. G. Lovegrove, J. Ritchie, S. N. Kast, and M. Puckett. 2006. Mortality of 

northern New Zealand dotterels (Charadrius obscurus aquilonius) following an aerial 

poisoning operation. Notornis 53:235-239. 

Nelson, J.T., L. Bethany, S.G. Fancy, G.D. Lindsey, and E.J. Tweed. 2002. Effectiveness of 

rodent control and monitoring techniques for a montane forest. Wildlife Society Bulletin 

30(1 ):82-92. 

Paul, E. and T. Salmon. 2010. The rat island rat eradication project: A critical evaluation of 

nontarget mortality. The Ornithological Council final report. December. 85 pp. 

Swift, C.E. 1998. Laboratory bioassays with wild-caught black (Rattus rattus) and Polynesian 

(R. exulans) rats to determine minimum amounts ofRamik Green (0.005% diphacinone) 

and exposure times for field broadcast applications in Hawai'i. M.S. Thesis, University 

ofHawai'i Manoa, Honolulu, HI. 92 pp. 

U.S. Environmental Protection Agency. 	 1998. Reregistration Eligibility Decision (RED): 

Rodenticide Cluster. EPA 738-R-98-007. 319 pp. 

Varnham, K. 2010. Invasive rats on tropical islands: Their history, ecology, impacts and 

eradication. RSPB Research Report No. 41. Royal Society for the Protection of Birds, 

Sandy, Bedfordshire, UK. ISBN 978-1-905601-28-8. 
• Pacific Reefs National Wildlife Refuge Complex

300 Ala Moana Blvd., Room 5-23 1

Honolulu, HI 96850

Subject: Draft Environmental Impact Statement (DEIS), Palmyra Atoll National Wildlife

Refuge Rat Eradication Project (CEQ # 20110049)

• Dear Ms. Flint:

The U.S. Environmental Protection Agency (EPA) has reviewed the above-referenced

document pursuant to the National Environmental Policy Act (NEPA), Council on

Environmental Quality (CEQ) regulations (40 CFR Parts 1500-1508), and our NEPA review

authority under Section 309 of the Clean Air Act. Our detailed comments are enclosed.

The Fish and Wildlife Service (FWS) proposes to eradicate non-native black (roof) rats

on Palmyra Atoll National Wildlife Refuge to help restore this important center of biodiversity

and species abundance in the Central Pacific. It evaluates four alternatives: aerial broadcast of

the rodenticide brodifacoum (Alternative B), aerial broadcast of the rodenticide brodifacoumwith the addition of bird capture to avoid poisoning (Alternative C), bait stations using

brodifacoum (Alternative D) and No Action (Alternative A). The DEIS does not identify a

preferred alternative.

We note that the use of the rodenticide diphacinone was not evaluated as a NEPA

alternative in the DEIS. Diphacinone is less persistent and virtually non-toxic to birds when

compared to brodifacoum (Appendix H, p. 13). The rationale for dismissing diphacinone fromfurther analysis did not demonstrate that it was an unreasonable alternative’, and without this

analysis, the decision-maker and the public are deprived of valuable information regarding itscomparative impacts and efficacy. The DEIS does retain apparently less feasible alternatives for

• full NEPA analysis. This, coupled with a description in Appendix A that describes the action as

imminent (taking place in June of 2011 and consisting of an aerial broadcast of brodifacoum)

seem to imply that the decision has already been made. NEPA requires that environmental

1 Under NEPA, reasonable alternatives are those that are practical or feasible from a technical and economic

perspective and that are based on common sense (Council on Environmental Quality’s 40 Most Asked Questions

about NEPA, # 2a)

V

V
p

g 

listed in the DEIS. We have rated Alternative A (No Action) as Environmental Concerns — Insufficient Information (EC-2) (see enclosed “Summary of Rating Defmitions”). The DEIS

describes the impacts that rats are having on island ecosystems in general, and the likely effects

on the Palmyra ecosystem in particular. It documents the benefits of rat eradications worldwide

as well as the expected biodiversity benefits to Palmyra. Specific rat impacts on biological

resources are largely speculative for most species; however, and additional information is needed

to fully document and predict how no action will affect population trends. This rating also

considers the concerns identified below regarding the aerial broadcast alternatives, to which the

No Action alternative is compared.

We have rated Alternative B (aerial broadcast of brodifacoum) and Alternative C

(Alternative B with added bird capture to avoid poisoning) as Environmental Objections -

Insufficient Information (EO-2). We are concerned that proceeding with these alternatives,without sufficient consideration of a less-toxic and less-persistent rodenticide, would set aprecedent for future eradication projects that collectively could result in significant impacts tonon-target species. In addition, the DEIS, as written, does not provide sufficient assurances that

all contingencies have been planned for to avoid mistakes made during previous rat eradicationson Palmyra and elsewhere. Alternatives B and C would deposit tremendous quantities of bait on

Palmyra that would go into alternative food chains. This may be justified for a potential longterm benefit to shorebirds; however, if such quantities would be used, it is important that the

project be designed to ensure the best possibility of success, lest impacts to non-target species

occur without the benefit of a complete eradication.

While there is ample evidence of pre-operation research and planning, the DEIS does not

demonstrate how the causes of a previous rat eradication failure on Palmyra (ineffective

management structure, staff and volunteers with no expertise in rat eradication, poor

communication between the involved parties, and an inadequate budget) will be avoided for theproposed project. It also is not clear that the project has incorporated lessons learned from thehigh non-target mortality from the Rat Island aerial eradication, the causes of which are

attributed, in part, to the upward adjustment of bait application rates during the operation,disposal of extra or contingency bait by application, and poor communication. Our objections

also pertain to insufficient post-treatment monitoring proposed for Alternatives B and C, and a

scope of the biosecurity plan that does not appear commensurate with the high risk of rat

repopulation identified. Regarding Alternative C, the bird capture component does not appear

feasible and was not recommended by bird experts who were consulted on the matter, some ofwhom described it as difficult if not impossible. Capture and retention would be very labor and

resource intensive, and would stress and cause death, injury, and suffering to birds. The DEIS

2
requirements. There is also insufficient information regarding the difficulty of installing bait

stations on islands with unexploded ordnance. If additional information is provided to address

these concerns and the alternative can be established as feasible, we would have no objections to

this alternative.

EPA appreciates the opportunity to review this DEIS. When the Final EIS is released for

public review, please send one copy to the address above (mail code: CED-2). If you have

any questions, please contact me at (415) 972-3521, or contact Karen Vitulano, the lead reviewer

for this project, at 415-947-4178 or vitulano.karen@epa.gov.

Smely )

Enrique Manzanilla, Director

Communities and Ecosystems Division

Enclosure: Summary of EPA Rating Definitions

EPA’s Detailed Comments

cc: William W. Jacobs, Registration Division, EPA HQ, Office of Pesticide Programs

Jennifer Gaines, Registration Division, EPA HQ, Office of Pesticide Programs

Patti TenBrook, EPA Region 9 Pesticides Office

3

using brodifacoum is well known (p. 108, 109), as is the high secondary exposure from eating

crabs or other animals that have been exposed, yet use of the much less toxic diphacinone

rodenticide bait was not brought forward as a NEPA alternativç for evaluation. This omission is

especially confusing considering that the alternatives that were brought forward for full NEPA

analysis appear to either have significant barriers to feasibility, or lack information to determine

feasibility. Finally, the criteria for eliminating alternatives in the DEIS do not appear to be

consistently applied. See below.

Elimination ofDiphacinone

Factors for screening alternatives

Diphacinone, the other bait product besides brodifacoum that is registered with EPA for

conservation-based rodent eradications on islands, has a low toxicity to birds when comparedwith brodifacoum (p. 18), yet was dismissed from detailed analysis in the DEIS. The DEISidentifies the factors used in this decision as:

1. the toxicity of the product

2. the efficacy of the product (including palatability)3. the extremely dense vegetation at Palmyra inhibiting distribution of the product

4. Palmyra’s series of large and small islands that challenge dispersal of product and the

feasibility of applying product to required concentrations and replicates,

5. the safety of personnel in applying product, including consideration of unknown but

documented unexploded ordnance in the atoll, and

6. the inordinately dense population of land crabs, their extreme ability to penetrate

enclosures, and their voracity of consumption.

Discussion of these factors does not seem to support removal of this alternative from study. Thetoxicity of the product, in relation to non-target species at least, would favor diphacinone.

Considering that the stated project purpose and need is to deliver toxicant in a way that

“minimizes harm to the ecosystem” (p. 24), it is not clear how this factor would eliminate

diphacinone alternatives.The discussion on page 17 does not address bait palatability. As the palatability study performed

in 2010 found both brodifacoum and diphacinone to be highly palatable in comparison tocommonly available food items (Appendix F, p. 39), this factor does not support elimination ofdiphacinone alternatives. The palatability and general suitability of anticoagulant rodenticide

bait formulations for use in specific situations is governed more by the nature of the “inert”

components of the bait than by the specific anticoagulant used.

1
y 

y 

personnel from unexploded ordnance while installing bait stations would be a factor in any bait

station alternative, and would require initial clearing or marking regardless of the bait used or

refill frequency. Consequently, this factor would not preclude use of diphacinone nor distinguish

it in a significant manner from brodifacoum regarding safety such that all options involvingdiphacinone would have to be eliminated.Bait EfficacyBait efficacy appears to be the most important factor considering the objective is to eradicaterats. The DEIS discusses risks associated with using diphacinone, especially in relation to the

perceived need for rats to feed on it multiple times in order to be be killed (whereas, withbrodifacoum, a rat would be more likely than with diphacinone to consume a lethal amount ofbait in one night’s feeding). However, these are probabilities rather than hard-and-fast rules as

the DEIS seems to imply. Some rats could ingest enough diphacinone bait in one night to cause

mortality, while reluctant feeders on a brodifacoum bait might need several nights of opportunity

before they consume a lethal dose. With any anticoagulant, the time to death from the onset ofbait ingestion follows a similar course. The animals feed and behave normally for several days

and then gradually weaken and die. Even rats that have consumed a lethal dose during the first

night of feeding will ingest more bait until the symptoms of anticoagulant poisoning set in. It isnot clear, then, that twice as many rounds of treatment, or twice as much bait, would be needed

for a diphacinone project vs. a brodifacoum project.The DEIS states that the Fish and Wildlife Service (FWS) does not have enough information onthe efficacy of diphacinone within Palmyra’s rat eradication environment to proceed with

analysis of this bait (p. 17). Diphacinone has been used successfully in 10 island rodenteradications. Substantially more experience has occurred using brodifacoum (197 successfulapplications, p. 31), with almost half using bait stations alone, and 29% using aerial broadcast

primarily 2.The DEIS concludes that additional successful rat eradications using diphacinone

would be needed (p. 18), but it is unclear what number would be sufficient to allow for full

analysis as a NEPA alternative. Some criteria should be established and discussed to elaborateon this conclusion.

2 There is some confusion regarding these numbers — 29% of the 197 applications would translate to 57 successfulaerial applications, but the DEIS also states that compressed cereal products containing brodifacoum 25 ppm have

been used to successfully eradicate rats from at least 5 islands using aerial broadcast as the primary technique (p. 31,

line 30)

2
brodifacoum” (p. 69). It also concludes that the island restoration community has not made

sufficient efforts to develop successful methodology for the use of diphacinone (p. 35).

The DEIS’ apparent bias toward use of brodifacoum is likely attributable to the fact that most

successful eradications, to date, involved use of brodifacoum; however, CEQ’ s NEPA

regulations require agencies to “rigorously explore and objectively evaluate all reasonable

alternatives” (40 CFR 1502. 14a), and the DEIS has not demonstrated that an alternativeinvolving use of diphacinone is unreasonable. The claim that, prior to 2004, diphacinone had not

proven “to be an effective tool for eradication of rats from tropical islands” (p. 17) is incorrect,

since the Buck Island eradication was successful. The DEIS highlights the failure ofdiphacinone on Lehua (p. 17, 21) without discussing the fact that the failure could well have

resulted from the need to keep bait well back from the shoreline, in response to a requirement

imposed by the State of Hawaii. This use limitation is mentioned on page 22, but text there does

not address whether brodifacoum might also have failed if subjected to the same limitations.Additionally, as discussed above, the inference that more treatment and more bait would be

needed for diphacinone vs. brodifacoum applications is not fully supported.Resistence to rodenticides was not discussed in the efficacy evaluation that eliminated

diphacinone as a NEPA alternative. Appendix C notes that feeding trials with captive rats

suggested that there is some tolerance or resistence to brodifacoum in the rat population on

Palmyra. The inference that absence of brodifacoum use on Palmyra for 6 years means “that it ishighly likely that any rats that supported rodenticide resistance have been selected against and

are no longer present in the population” (p. 25) is not fully supported. Individual rats alive in2005 almost certainly have died, but they have reproduced and probably passed any resistanceconferring alleles on to some of their descendents. Rather than its complete disappearance, onemight predict reversion to a low frequency for a somewhat disadvantageous (relatively low

affinity for Vitamin K) allele in the absence of selective pressure favoring it. Alleles conferring

resistance to anticoagulants seem to have been present in murid rodent populations well before

warfarin was discovered and first used as a rodenticide. Consequently, they were available for

selection when anticoagulant rodenticides first came into use and did not disappear from rodent

populations despite no obvious selective pressure favoring them until the advent of anticoagulantrodenticides.

The DEIS states that the decision to not evaluate a diphacinone alternative also stems from a

collaborative report that followed the 2004 rat eradication feasibility study conducted at Palmyra(Howard et al 2004) (p. 17); however, there was no discussion of diphacinone in that report,

presented in Appendix C. The limited consideration of diphacinone in that study was based on

3
Suitability for aerial broadcast appears to be used as a screening factor, but this is not identified

as such nor is it consistently applied. For example, in the discussion on page 21 dismissing adiphacinone alternative, the DEIS states that a strategy for aerial application of diphacinone “has

not been extensively tested” (p. 21). Similarly, one of the reasons given for eliminating use ofother toxicants is the lack of EPA registration for aerial broadcast (p. 23). The purpose and needdoes not establish aerial application as a condition for the action; indeed, a bait station alternative

using brodifacoum was brought forward for analysis. If aerial application is deemed necessaryfor an alternative to be considered feasible, this should have been identified in the purpose and

need statement and applied to the screening of all potential alternatives. The FEIS shouldexplain how and why aerial broadcast suitability was factored into the assessment of rodenticide

alternatives.

Feasibility ofAlternatives

Alternative C

The elimination of a diphacinone alternative is especially confusing considering that the othertwo alternatives that were brought forward for full NEPA analysis have questionable feasibility.Alternative C is comprised of Alternative B (brodifacoum aerial application) with additional

mitigation of risk for shorebirds that could be poisoned by bait broadcast. This alternative

proposes to capture and hold shorebirds prior to and during the period when they would be at

risk of lethal exposure to rodenticide. We commend the good intentions of this alternative;

however, there is no indication in the DEIS that successful capture of shorebirds --primarily

bristle-thigh curlews (BTCU) and Pacific golden plovers (PGPL) --would be expected.

Shorebird experts maintain that it would be very difficult to capture BTCU (p. 58), and capturing

birds and holding them for the required period 3(until land crabs consumed by the birds have low

The DEIS does not identify the required period of time, requiring the reader to attempt to calculate it. Our

estimate: to allow for two applications 10-14 days apart, 10 days for all phases of bait application (including trees

overhanging water) associated with the second round of treatment to be completed, 7 days for disappearance of

nearly all bait after the second application, and reductions in residues in terrestrial crabs and other invertebrates

would take an additional 2+ weeks at least. The minimum holding period would have to extend >3 weeks beyondthe date of the completion of the last component of second treatment round on any island. Measured from the dateof first application, a semi-conservative calculation would put the minimum holding period at -7 weeks, plus anyholding time prior to the initiation of bait applications. With bait stations being used in the camp area, there would

be extended potential for secondary exposure to curlews that congregate on the runway (which is close to the camp

area).

4
like a very labor intensive and resource intensive way to achieve the ultimate goal” (App. H, p.28).

Alternative D

It is not clear whether FWS believes this alternative is feasible. Because of the rat’s small range,

due to its ue of tree canopies and abundant year round food sources, a large number of bait

stations would be needed. The DEIS estimates that 1,862 bait stations 4plus an additional 20%

would be used for Alternative D, and that every 3” palm tree would be baited, presumably by

launching bait filled sacks or “bolas” into them, 4 times (DEIS p. 60, Appendix G). Anevaluation of effort was included for the alternatives and revealed that Alternative D would be

four times more effort intensive (2,475 person-days versus 616 or 684 person-days for

Alternatives B and C respectively). Because no information regarding funding for the project

was included, it is unclear whether this substantially larger effort would render the alternative

infeasible. Additionally, the presence of unexploded ordnance on Quail and Barren islandswould require clearance or marking by qualified personnel (p. 60). No further information is

provided, and it is not clear if these qualified personnel were included in the person-hours

determination in Table 2.4, nor whether this aspect of the project would present insurmountable

logistical difficulties. Because a lack of manpower contributed to previous eradication failures,the availability of the workforce for the alternatives should be discussed, as should any funding

limitations.

The availability of the bait stations is also unclear. The DEIS references development of a bait

station by U.S. Department of Agriculture -Animal and Plant Health Inspection Service -

Wildlife Services (p. 29) that would be used for Palmyra, but its availability is not discussed.Elsewhere, the DEIS references bait stations being “purchased”

(p.

59), and it is unclear whether

these stations would be available for purchase in the quantities needed or if they would have to

be constructed by project personnel or modified by them so as to be rendered crab-resistant and

otherwise suitable for use on Palmyra.

Cost considerations, objective decision-makingIn the discussion on page 21 dismissing a diphacinone alternative, the DEIS describes aerial

broadcast of brodifacoum as more cost-effective and effort efficient. These criteria were not

identified as factors to be considered in screening potential alternatives. In fact, the DEIS states

C, p. 27 states that over 15,000 bait stations would be needed

5
Information regarding costs and the funding available for the project would be helpful in

interpreting information in the document. NEPA does not require a cost-benefit analysis, but theCouncil on Environmental Quality (CEQ) Regulations implementing the National Environmental

Policy Act (NEPA) state that an environmental impact statement should at least indicate those

considerations, including factors not related to environmental quality, which are likely to be

relevant and important to a decision (40 CFR 1502.23).

The monitoring plan in Appendix A describes the action as imminent (taking place in June 2011)

and consisting of an aerial broadcast of brodifacoum (Appendix A, p. 1). CEQ’s Regulationsstate that NEPA procedures must ensure that environmental information is available to public

officials and citizens before decisions are made (40 CFR 1500.1(b)), and that EnvironmentalImpact Statements shall serve as the means of assessing the environmental impact of proposed

agency actions, rather than justifying decisions already made (40 CFR 1502.2(g)). Additionally,

the CEQ regulations include a provision in 40 CFR 1506.5(ë) that addresses objectivity for any

contractors involved in the preparation of the NEPA document, including a lack of financial orother interest in the outcome of the project. Because Island Conservation will be the

implementing entity for the project, FWS should ensure that their substantial involvement and

contribution of information is incorporated into the document in a way that meets the letter and

spirit of 40 CFR 1506.5(c).

Recommendations: The alternatives analysis in the FEIS should clearly identify the

criteria used in screening potential alternatives to determine which would be broughtforward and evaluated in the NEPA document, and these criteria should be consistently

applied to all potential alternatives. An objective evaluation of diphacinone alternatives,

in a side-by-side comparison, would be helpful to the public and the decision-maker and

is recommended.

Discuss and defme feasibility and how it was assessed for the alternatives. Include cost

data, which are likely to be relevant and important to the decision, so that an evaluationof the person-hours and mitigation proposals can be made.

From DOl Directive 517 DM 1: “While management costs are important, they are not the primary deciding factor

in selecting a management approach”. From FWS’s 569 FW 1: 1.7 How does the Service choose which pest

management methods to use? We choose pest management methods by considering the following in this order of

importance: A. Human safety, B. Environmental integrity, C. Effectiveness, and D. Cost.

6
feedback to management and technical support, which contributed to a failed eradication

(Appendix C, p. 15).

Although it is clear that far more initial research and planning has preceded the project beingproposed now than was the case for the 200 1-2003 effort, the project description in the DEIS

does not clearly identify how these errors will be avoided in this project. The DEIS does identify

adaptive management as a feature common to all alternatives (p. 24) and adaptive management

could help address monitoring and communication issues; however, the adaptive management

discussion is a presentation of the concept only, with no development of a plan specific to the

project. Because avoiding the deficiencies identified above is crucial to project success, it is

important that this project element be more fully developed 6.

Recommendation: In Section 2.4 — Features Common to All Action Alternatives, include

a discussion of the management structure for project implementation, and the staff who

would be involved, including their expertise in rat eradications. Include a communicationplan as an appendix to the FEIS. Discuss budget concerns or limitations. This

information is relevant to environment impacts and should be included. FWS maychoose to include this information in an adaptive management plan. if so, we

recommend it be appended to the FEIS.

Bait Application RateThe DEIS does not identify a preferred alternative; however, we are aware that Alternative B ispreferred by the project partners. Alternative B would consist of two rounds of aerial application

of brodifacoum, 10-14 days apart, at 90 kilograms/hectare (kg/ha) (approximately 80 pounds(lbs)/acre) per treatment, supplemented by hand-broadcast applications and bait station

applications in certain locations, and arboreal applications of bait to trees that overhang the

marine environment. The proposed maximum rate for broadcast application is five times themaximum rate indicated on the current label for the product (EPA Reg. No. 56228-36) that is

intended to be used in the project. The DEIS indicates that the proposed bait application rate is

6 The report Modernizing NEPA Implementation (the NEPA Task Force report to the Council on Environmental

Quality, 2003) suggests that the extent of the discussion of adaptive management in a NEPA document depends onits importance to the proposed action and the impacts being considered. When adaptive management is being used

to adjust to unanticipated impacts of project implementation, the extent and detail of the adaptive management

action would likely be extensive.

7
A specific sowing (broadcast application) rate is not established. The product label has

instructions for determining the application rates. It states “The primary method of determiningapplication rate should be calculated on data from onboard bait metering software and GPS flight

path data [area treated (acres or ha) and total bait applied (lbs or kg)]. Where feasible, groundtruthing should occur to verify application rate.” Any proposed increase in maximum rates

above current limits set by the label for EPA Reg. No. 56228-36 must be accepted, under the

provisions of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) as amended, byEPA’s Office of Pesticide Programs through amendment of the label for that registered product

or by some other applicable authorized mechanism.

The DEIS states that, for the project to be successful, an application rate greater than 36 kg/ha

would be required (p. 39). There is a substantial difference between 36 kg/ha and 90 kg/ha. In at

least one place (p. 47), FWS allows that the second application would be lower than the first (“toaccount for the reduëtion in bait consumers — rats that died from the first bait application”). The

first treatment would go on at 90 kg/ha, while the second would be at 60 kg/ha. However, this

information is at odds with text on pages 35-39, specifically the conclusion on p. 38 that “the baitapplication rate for the second broadcast should be as high as the first”.

According to the full report for the 2005 visit, the “small juvenile, weanling rat” found alive 8

days after treatment on Whippoorwill Island may or may not have been the “similar sized rat”(Buckelew, et al, 2005) found (“in the same nest”) to be “clearly lethargic” and dispatched 2days later. The fact that one, or a few rats survived an initial hand-broadcast of 25 ppm

brodifacoum bait at 95 kg/ha does not, by itself support a second broadcast at the same rate. All

evidence assembled thus far indicates that the first broadcast would take most of the rats, even if

made at a rate much lower than 90 kg/ha. The highest reported projections for bait take by crabs

are well below 90 kg/ha.

The first paragraph on page 39 is not clear, but seems to indicate that making more bait available

attracts more crabs, meaning that bait availability might be more important than crab density in

determining how much of the applied bait is taken by crabs and how much remains for other

organisms, including rats. The argument for making two applications at the same rate is,

basically, that such a negligible percentage of what is applied would go to rats that the high rate

is driven almost entirely by the need to have some bait not be eaten by crabs. The calculationsdiscussed in Howald, et a!, (2004) of potential bait take by crabs, especially the upper limits of it,

should be discussed in this EIS, including how this information could inform bait application

rates.

8
automatically follow that increasing the application rate to -90 kg/ha (-.21⁄2 times 36 kg/ha) also

would result in no bait being left after 3 days. In the 2008 “biomarker” trials, all types ofpotential primary consumers of bait that were examined showed evidence of the fluorescent dye;

and those treatments were at 10%, 20% and 40% of the maximum rate contemplated for use. Itseems fairly certain that less bait would be needed in a second round of treatment to reach allindividuals in the residual rat population, but it also would be difficult to detennine where and at

what densities rats remained on the various islands and various areas on those islands, especially

without significant activity monitoring between applications.. We understand the proposal to useenough bait for it to be present for 4 days (p. 47) when anything short of full eradication meansfailure; but that approach would require putting out tremendous quantities of bait that would go

into alternative food chains.

Recommendation: The FEIS should clearly present the aerial application rates for both

the first and second applications. EPA recommends that the second application rate be

lower than the first unless between-treatment monitoring of other evidence indicates the

presence of significant rat activity in a particular area. Once rates are,established, they

should be adhered to during the operation, and changes only made according to a clear

protocol. The miscommunications and errors made during the Rat Island eradication,

during which Island Conservation applied bait at a rate significantly deviating from the

target application rate, should be avoided. Changes to baiting rates in the field should bethoroughly documented. In no case may the limits on application rate established by the

label for the product used in the project be exceeded, with some allowances for swathoverlap (as covered by the labeling). As recommended in the Rat Island criticalevaluation, planning should occur for contingencies that are reasonably foreseeable. Foreach contingency, that evaluation recommends developing a structured decision-makingtool that provides much more detail than did Island Conservation’s Rat Island risk andcontingency plan. Specifically, “A structured decision-making tool for application of baitother than as planned would require a written assessment of the amount of bait already onthe ground, a comparison to the approved label rate and target rates, a written assessmentof the additional bait to be applied, a calculation of the total amount of bait that would be

applied, and the increase in the potential risk to nontarget species”.

Contingency Bait

The DEIS does not reveal whether there will be additional or “contingency” bait for use toreplace bait that spoiled or spilled and to fill gaps in coverage from aerial applications, nor does

it discuss the disposition of excess bait. A major error that occurred with the Rat Islanderadication, according to the Rat Island critical evaluation, was that all the contingency bait was

9
plan. As mentioned above, decisions regarding disposal of bait should be clearly outlined

in a structured decision-making tool.

Post-treatment MonitoringThe DEIS does not document sufficient post-treatment monitoring. “Passive observation byfield station staff” (p. 25) would not, as asserted, “be a very effective post-eradication monitoring

method”. It might indeed detect “a remnant rat population ... within 1 year of the eradicationeffort”; but that would be much too late for any remedial action to influence the outcome of theproject. Even planned post-treatment monitoring 4-6 weeks after aerial application (p. 24) would

be too late for localized remedial baiting. Monitoring rat activity between treatments would

inform adjustment of the application rate for the second aerial broadcast. Monitoring shortlyafter the second round of baiting might detect residual rat activity which, if localized, might beeliminated via intense additional control activities. Additionally, the areas where bait stations

are used, and zones bordering those areas, should be monitored intensively for any signs of ratactivity during and for months after the broadcast baiting period, to avoid any rat migration intoaerially treated areas to become founders of a rebounding rat population.

Recommendation: The FEIS should document a more appropriate post-treatment

monitoring plan. EPA recommends monitoring between aerial treatments and shortly

after the 2m1 round of baiting. Frequent monitoring should occur in bait station areas.

Biosecurity PlanThe DEIS states that the risk of rat reintroduction is high because Palmyra Atoll is a remoterefuge and scientific research station that is maintained through periodic shipments of supplies

including consumable and bulk goods, as well as personnel via regular airplane and annual barge

service from Honolulu (p. 29). The biosecurity plan included in Appendix B does not appear ascomprehensive as is needed for a high reintroduction risk. J.C. Russell, et a17 recommend that

biosecurity plans include quarantine, surveillance, and contingency response components. It is

also not clear who would implement the different components.

Recommendation: We strongly recommend that the biosecurity plan be as

comprehensive as possible. We recommend that it include quarantine, surveillance, and

Russell, J.C. et al. 2008. Review ofrat invasion biology, Implicationsfor island biosecurity. New Zealand

Department of Conservation. Available: http://www.stat.auck1and.ac.nz/jrusse11/fi1es/papers/sfc286.pdf

10
Manpower and logistical concerns

The planned use of “bob” baiting would not coincide with broadcast baiting but rather would

start after 3 days of broadcast-baiting and go on for 7 days, with the first round of bob baiting

ending the day before the second round of broadcast baiting might begin (p. 47). With anestimated 3,546 overhanging palms on the atoll (p. 53), project personnel would have to treat 500

palms/day, which works out to approximately 50 palms/hour (1.2 minutes per palm) if personnel

are able to devote 10 person-hours/day to this activity alone. At approximately 6° north latitude,

Palmyra’s photoperiod varies little over the course of a year. In June and July, there might be

121⁄2 hours between sunrise and sunset, with little usable dusk-and-dawn time outside of that

period. Clearly, significant rain events, which happen often there, would further restrict the time

available for baiting overhanging palms. This means that several crews would have to be

devoted to palm baiting. Non-overhanging palms and other trees in hand-baited and bait-station

treated areas would also have to be treated, apparently, but such activities might be concurrent

with helicopter broadcasts.

It appears that only 4-5 people would be available for hand-broadcast baiting. That could be a

problem in the event of helicopter equipment failure or exhaustion of helicopter fuel (p. 46).

It is not clear that the “Person-Days” of “effort” calculations for the aerial application options inTable 2.4 account for hand-broadcasting, baiting trees that overhang water, and bait station

establishment and maintenance in the camp area. Those days may have been included in the 460

“Person-Days” indicated for “Aerial broadcast — 25W” (p. 62).

Recommendation: The FEIS should devote more analysis to logistics and manpower

needs of the alternatives, especially since effective canopy baiting is crucial to the

success of the project. (See also comment below regarding reducing palms prior to

eradication). As recommended above, defme and discuss feasibility in relation to the

alternatives, and whether sufficient funding is available to meet manpower and alllogistical needs.

Restricted Use Pesticide (RUP) Certification

The DEIS does not indicate a clear understanding of EPA’s certification requirements for use ofRestricted Use Pesticides (RUPs). The DEIS states that “all bait application activities will be

conducted under the supervision of a Pesticide Applicator certified by the EPA” (p. 25), and that

“the product may only be applied by Certified Pesticide Applicators (a certification for Palmyra

generally provided by the State or Territory in which the bait is to be applied) or persons under

their direct supervision” (p. 30). These statements are not correct.

11
y 

y 

y 

g 

p

state or tribe, there is no state or tribal certification plan that would legally cover applicators for

this project.FWS does not have a plan for certifying applicators for this project. Given the scope and huge

quantities of restricted use pesticides used for the rat eradication projects (of which Palmyra isonly one), FWS should develop and submit to EPA, for approval, its own certification plan that

would cover these applications. We note that, even if FWS did have an EPA-approved

certification plan, it would only cover FWS employees, and not contractors (even in an “underthe supervision-of” situation described at 171.2(a)(28).

To be in compliance with FIFRA, no RUPs should be applied; however, in this circumstance,EPA’s Office of Pesticide Programs suggests that it would be minimally acceptable for the

applicator to be certified as a commercial applicator in an appropriate category by the State of

Hawaii. Charles Nagamine, a University of Hawaii Extension agent, suggested that either

Category 2 (Forest Pest Control) or Category 7c (General Pest Control) would be appropriate.

Please consult with Mr. Nagamine (Phone: 808-956-6007). (Certification by other Pacific

Islands such as Guam, CNMI, and American Samoa should not be pursued as their certification

programs are not finalized).

Recommendation: Correct the statements regarding RUP certification in the FEIS. The

FEIS should document if and how responsible parties are following the record keepingrequirements for sale and use of RUP’s, including the company selling them and the

applicator who is using them. Ensuring that all of the restricted use pesticides areaccounted for could be a homeland security issue, especially in the quantities being

proposed.

Pesticide Information and Corrections

The name, registrant, and registration number of the product intended to be used on Palmyra aremisidentified on page 29 and elsewhere. The product’s name is “brodifacoum-25W

Conservation”, without a trademark symbol. The registrant is the Animal and Plant HealthInspection Service (APHIS), USDA. The registration number is 56228-36. See the product’slabel (e.g., on page 48 of Appendix F).The discussion of first and second-generation anticoagulants on p. 30 is not completely accurate.

The “generation” designations for anticoagulants are not strictly “according to when they werefirst developed as rodenticides” although they relate indirectly to their toxicity. Another “first

generation” type of anticoagulant could be developed this year, if anyone were interested in

12
are resistant to warfarin, pindone, diphacinone, chlorophacinone, and other “first-generation”anticoagulants. See also Jackson and Ashton (1992 — cited in the DEIS). Why the “secondgeneration” anticoagulants can kill warfarin-resistant individuals (greater affmity for the“Vitamin-K receptor”) was fully characterized after the compounds were put into use as

rodenticides. The so-called “single-feeding” effect attributed to brodifacoum (Dubock and

Kaukeinen, 1978) and other second-generation anticoagulants results from this greater affmity,

but is dependent upon the amount of the compound that is ingested on the first day of exposure

to it. The amount of anticoagulant ingested on the first day of exposure is determined by therodent’s willingness to consider the bait as a food item; the concentration of the rodenticide inthe bait; the palatability of the bait to the rodent; and, in a control situation, the amount of bait

available to the rodent. The last of these is an issue on Palmyra due to documented competition

for bait with other terrestrial animals, chiefly crabs.This discussion on page 30 concludes that “any rodenticide can be effectively used to eradicate

an entire rodent population if all individuals within the population consume enough bait over anappropriate amount of time.” This sentence does not address the possibility of resistantindividuals within the population. It has been shown with captive animals that Norway ratsgenetically resistant to warfarin eventually can be killed by warfarin if consumption continues

for many days. It is doubtful, however, whether that would occur.in practice before such rodents

were able to reproduce and before the baiting program was stopped.The product (EPA Reg. No. 56228-36) under consideration for the Palmyra project is not labeled -for use for “agricultural operations” or “professional pest control operations”, apart fromconservation uses, as started on page 32 of the DEIS. EPA did not decide to make 56228-36 a

restricted use pesticide after a period of registration without such designation, as the paragraph

implies. Rather, the product was proposed by its applicant to be a restricted use pesticide.

There is reference to “EPA —approved label instructions” in Section 2.4.4 (pp. 24-25) that do not

currently exist. As noted above, the existing label for EPA Reg. No. 56228-36 would have to be

amended or Palmyra-specific application directions would have to be authorized via another

provision of F1FRA.

Recommendation: The information provided above should be used to make the necessary

corrections in the FEIS.

13
products in the palatability trials. This suggests that coconut palm reduction may be beneficial tothe eradication by reducing the amount of naturally available food that could distract rats from

consuming the bait pellets (Appendix F, p. 39).In its discussion of brodifacoum resistance seen in an eradication trial, the DEIS notes thatVitamin K, which is an antidote to brodifacoum, is contained in coconut fruit. Additionally, to

avoid bait drift into the marine environment, the project must hand bait coconut palms that

overhang the water if aerial broadcast is selected. Removing coconut palms that extend 100%over the lagoon and ocean would minimize risk of impacting water resources with rodenticide.

Removing coconut palms near the marine environment could also benefit green turtles, since one

hypothesis for lack of nesting on Palmyra is the extreme abundance of coconut palms close to the

beach where turtles might otherwise attempt to dig nesting pits (p. 78).

The DEIS indicates that coconut palm removal is a potential future action (p. 149). It also statesthat rat eradication is the first step in a series of restoration efforts because it is relatively simple

and fast and provides the framework to initiate the palm removal stage of the restoration process(p. 10). The DEIS does not make clear why conducting the rat eradication first is most

beneficial (for example, how it sets the framework for the palm removal). Coordinating the

timing of the palm removal to precede the rat eradication should be strongly considered, if itwould substantially increase the success of the eradication.

Recommendation: As a mitigation measure, the FEIS should discuss the feasibility and

benefits of reducing the number of coconut palms on the island prior to the eradication,

especially those that extend over the marine environment or are likely to present thegreatest problems for the rat eradication. The FEIS should discuss the extent thatconducting the palm removal first would increase the effectiveness of the rat eradicationeffort, and how impacts of the action would change as a result.

Timing ofShorebird Migration

The most important mitigation measure identified is the timing of the eradication to coincidewith the period when the least number of migratory shorebirds are present. The DEIS estimatesthis time to be June and July, when many adult shorebirds return to breeding grounds in theArctic (p. 28).Because this is the primary mitigation measure for impacts to shorebirds, it is important thatmigration timing be confirmed. Shorebirds are affected by the weather (Appendix H discussesthe lack of migration of the Sooty Tern from the 2009-2010 El Nino Southern Oscillation) and

14
conducting shorebird surveys prior to the eradication to confirm that a low number of

shorebirds are present, as predicted in the DEIS. Discuss possible climate change effects

on the project in the FEIS.

Mitigation Measures Committed to as Part ofthe Project

Mitigation measures are mentioned in the DEIS and appendices but it is not clear which will be

adopted for the project or incorporated as components of the proposed action. CEQ recently

released guidance to federal departments and agencies on the appropriate use of mitigation and

monitoring in NEPA documents 9.In this guidance, CEQ makes clear that mitigation

commitments should be carefully specified in terms of measurable performance standards or

expected results, so as to establish clear performance expectations. CEQ also states that agenciesshould not commit to mitigation measures considered in an ETS absent authority or expectation

of resources to ensure that mitigation is performed.

Recommendation: Project mitigation measures should be explicitly identified in the PETS

•and included in FWS’s Record of Decision. A discussion of the effectiveness/expected

results of these measures should be included. FWS should discuss funding and indicate

whether the resources are available to ensure implementation of proposed mitigation

measures, as well as the party responsible for implementation. If an adaptivemanagement plan will be developed, identify mitigation measures that would apply in the

event that initial mitigation commitments are not implemented or effective.

The following were identified in the DEIS as possible mitigation measures:

• Assessing the weather conditions and prohibiting bait broadcast if rainfall is

forecast (Appendix H, p. 12). More detail about effectiveness and implementation of this measure should be included in the FEIS.

• Securing a tarp over the drinking water catchment to prevent aerially broadcast

bait from entering the drinking water supply (p. 96). We recommend adding tothis measure that the tarp would be inspected (or reinstalled if it was removed)

prior to a second aerial application.

8 Crick, H. Q. P. (2004), The impact of climate change on birds. This, 146: 48—56. doi: 10.111 1/j. 1474-

91 9X.2004.00327.x

http://cea.hss.doe.aov/current developments/docsfMitigation and Monitoring Guidance l4Jan2OI 1.ndf

15
g

for the types of birds that occur on Palmyra have been studied.

• Capture and treatment of all sick and moribund shorebirds found during and

directly after the eradication, and treatment with Vitamin K, an antidote to

anticoagulants (p. 26). The planned collection and Vitamin-K treatments of sick

or moribund shorebirds should be evaluated for feasibility and effectiveness in the

FEIS. Treatments would likely have to be extensive if experiences with various

mammals (including humans) are predictive of what would be needed to save

birds.

Impact Assessment

Impacts to Biological Resources

Potentially significant impacts from bait station use not consideredFor Alternative D (bait station alternative), the DEIS indicates that, while mortality risk from

toxicants is high for some birds (BTCU, Pacific golden plover, ruddy turnstones, laughing and

Granklin’s gulls, Northern shoveler and Northern pintail duck), the exposure risk is low (p. 136-

139). This does not fully consider the fact that the bait would be present in the atoll environment

for approximately 2 years, which would offer long-term secondary pathway toxicity

opportunities.

The aerial broadcast alternatives would also use bait stations; specifically, on Cooper Island on

or near the runway and in the camp area, where Nature Conservancy staff and researchers and

project personnel reside and where the drinking water and waste treatment facilities are located.

A discussion of the efficacy of bait stations should be included. It appears possible that bait

stations might not expose all rats due to some individuals not entering bait stations, especially as

the units would have to be elevated and otherwise crab-proofed.

In addition, even for the aerial broadcastalternatives, baiting in the areas mentioned above would

have to continue for approximately 2 years, and any rats residing in that area that were not taken

during the same period of time when broadcast bait was present on the island could emigrate intopreviously treated areas and become founders of a rebounding rat population on Cooper Island

and, eventually, the rest of the atoll.

Recommendation: The above impacts should be included in the impact assessment in the

FEIS. The issue of preventing rats in the bait station areas of the aerially broadcast

alternatives repopulating aerially eradicated areas should be addressed in the project

design.

16
to rodenticide through the consumption of invertebrates that had previously consumed bait,

however, it concludes that none of the 50 geckos sampled during the 2008 biomarker study

showed any sign of primary or secondary exposure to bait (p. 116). This is not sufficient basis

for this conclusion. As pyranine, a biomarker agent, does not appear to be systemic as

afluorescent dye, its absence from geckos in the 2008 biomarker trial does not predict nonexposure to brodifacoum. Invertebrates would retain the rodenticide differently than they would

pyranine.

Recommendation: The above impacts should be included in the impact assessment in the

FEIS. Capturing, holding, and maintaining individuals of the native gecko species should

be considered as a mitigation measure.

Impacts to Soils and Water Resources

The DEIS references the rat eradication on Anacapa island to support its conclusion that the

aerial alternatives would not have a noticeable effect on soil contamination (p. 98). For the

Anaàapa Island project, however, bait was not applied at the rate planned for the Palmyra project

(two applications at S 90-kg/ha). Consequently, a low likelihood of contaminated soil samples

for Palmyra does not necessarily follow from the results on Anacapa. The data from Alifano andWegmann (2010) came from isolated pellets rather than baits applied according to how they areplanned to be used at Palmyra.

The worst-case calculations presented for impacts to water resources (p. 97) are not based upon the proposed application rate of up to 90 kg/ha (-80 lbs/acre), which is 5 times the maximumrate currently indicated on the label for EPA Reg. No. 56228-36 for the first island-wide

broadcast application and 10 times the maximum rate indicated for the second broadcast

application.

Recommendation: Reevaluate impacts to soils and water resources from the aerialbroadcast alternatives using the quantity of bait expected to be applied for the project. If

the active ingredient infiltrates vertically into soils, the Aiifano and Wegmann (2010)

data likely would overestimate the extent of island-wide contamination, although it is

possible that material might congregate in some lower areas due to surface flow resulting

from heavy rain events. Due to the composition of the islands, however, puddles tend to

be short-lived, even after extensive heavy rains.

For impacts from the bait stations (which are part of all action alternatives), these

discussions should note the possibility of bait stations becoming damaged or being

17
Errors in the Document

The following were identified as errors occurring in the document. EPA recommends that these

errors be corrected for the FEIS:

• Page 35, last paragraph, running over to page 36. The characterization that detection of

shore birds was consistently higher post-treatment than pre-treatment for the 2005 minieradication effort is not consistent with the narrative in, nor “Figure 10” of, the report by

Buckelew, et al (2005).

• Page 38, “Figure 2.1”. The numbers illustrated in this figure are not consistent with those

shown in “Fig. 5” in the Wegmann, et al (2008) report. The narrative on page 37 of thedraft EIS is more accurately reflected by Fig. 5” of Wegmann, et al (2008), than by“Figure 2.1”.on page 38 of the draft EIS.

• Page 39, bottom paragraph. The first line of this paragraph should be corrected factually

as well as grammatically.

• Page 45, first “Rationale” paragraph. The number (332) given here for “successfully

reported island eradication efforts world wide” differs from the number (278) cited fromthe same reference on page 31. At least one of those numbers must be wrong. Thecorrect number, if known, should be used. “Brodifacoum-25” is not one “specificproduct”. This paragraph itself acknowledges the existence of a “Brodifacoum-25D” and

a “Brodifacoum-25W’.

• Page 50, Table 2.5, and relevant discussions on page 51. The result on Whippoorwill

Island is reported as having been “Successful” despite the fmding of one or more live rats

8 and 10 days after bait application. All of the localized rat eradication efforts on

Palmyra in 2005 would be judged as “Failed” if the standard index of no signs of rat

activity for 2 years following treatment were applied. Although reinvasion from very

nearby untreated islands might have been the cause of the reappearance of rats on those

islands, the standard for successful eradication should be greater than obtaining zeroscores for various activity measures shortly after treatment. By the latter standard, the

brodifacoum/Bromethalin trials on Palmyra Atoll in 200 1-2003 probably would havebeen judged “Successful”, at least for some of the islands; and the same would have held

for some islands in the diphacinone work in the Bay of Islands, Adak, AK, 2003-2004.The 2008 trials on Palmyra involved placebo baits which, presumably, did not directly

kill any rats. The “Failed” status is visited upon them because one or more rats livetrapped post-treatment showed no evidence of the Pyranine “biomarker”, and some others

were marked only to a degree like the captive roof rats that were fed only one placebo

18
delivery methods

that would be used for 

AltemativeD

[sic] (bait stations), but not for

the aerial application options which the narrative to the draft EIS indicates would be

supplemented by baiting trees that overhang water.

• Page 107, second full paragraph. Whether a single “dose” of brodifacoum would be

lethal would depend upon the amount received, through ingestion in this case. The LD50

is not really a “threshold”, as some individuals would be expected to die after receiving

lower dosages.

• Page 145, “Alternative A — No Action” paragraph. Under this alternative, there would

not be an eradication effort. Therefore, signs (or “sings”, line 17) would not have to beposted.

• Page 31, first full paragraph. The last sentence of the first paragraph under

“Brodifacoum25WTM bait product” does not follow from the rest of the paragraph. Itappears that 14 (7%) of 197 successful eradications using brodifacoum as the “primary

rodenticide” were effected using “aerial broadcast supplemented with hand-broadcast”

but that technique would have been less “commonly used” than bait stations (47% or —93

instances), aerial-broadcast alone (29% or —57 instances), or hand-broadcast (21% or —41

instances).

Minor comments / discrepancies

• In approaches dismissed, the DEIS identifies fertility control (p. 17) and discusses oral contraceptives. We are aware that research is being conducted towards the development

of chemical sterilants that could offer a less toxic alternative to rodenticides. FWS

should monitor this development for possible future use.

• On p. 103, the DEIS says that successful turtle nesting attempts have not been recorded

on Palmyra; but, on p. 83, it says that green turtle nesting has been documented at least

twice at Palmyra, primarily on the northwest side of Cooper island.

• The DEIS states that informal Sect 7 consultation will be conducted “for áhy case

deemed necessary by the FWS” (p. 101). The FEIS should indicate whether informalconsultation has occurred.

• Appendix C pp. 14 and 37 indicate that 2 cats and a dog (and a cat on a boat) were

present in 2004. State whetherthese animals are still present and how they will avoid

poisoning.

• Pages 152-188. Pages bearing these numbers are missing from the copy of the draft EIS

that was reviewed; but, seemingly, with no loss of intended text. Subsection “5.1”

appears on page 151; and subsection “5.2” appears on page 189

• Some references to appendices in the draft EIS are by number (eg. p, 17), but the

19
There were many typos in the document. A 

a

e:

-On p. 60, Alternative E should read Alternative D

-On p. 145, the word “signs” should replace “sings” in lines 25, 33 and 39

-On p. 150, the last sentences of paragraphs “4.6.1.5” and “4.6.1.6” should correspond

to the correct alternative (C and D)

ReferencesBuckelew, S., Howald, G.R., Wegmann, A., Sheppard, J., Curl, J., McClelland, P., Tershey, B.,

Swift, K., Campbell, E., and Flint, B. (2005) Progress in Palmyra Atoll restoration: rateradication trial 2005. Unpublished report, Island Conservation group, Santa Cruz, CA, 50 pp.

Dubock, A.C. and Kaukeinen, D.E. (1978) brodifacoum (Talon TMRodenticide), a novel concept.

Proceedings: 8th Vertebrate Pest Conference (Howard, W.E. and March, R.E., eds.), Universityof California, Davis, CA, 127-137.

Hadler, M.R. and Shadbolt, R.S. (1975) Novel 4-hydroxycoumarin anticoagulants active against

resistant rats. Nature, 253, 275-277.

Howald, G.R., Samaniego, A., Buckelew, S., McClelland, P., Keitt, B., Wegmann, A., Pitt,

W.C., Vice, D.S., Campbell, E., Swift, K., and Barclay, 5. (2004) Palmyra Atoll rat eradication

assessment trip report August 2004. Unpublished report, Island Conservation group, Santa

Clara, CA, 61 pp.Jackson, W.B and Ashton, A.D. (1992) A review of available anticoagulants and their use in theUnited States. Proceedings: 15th Vertebrate Pest Conference (J.E. Borrecco and R.E. Marsh,

eds.), University of California, Davis, CA, 156-160.

Marsh, R.E., Howard, W.E., and Jackson, W.B. (1980) Bromadiolone: a new toxicant for rodent

control. Pest Control, 48, pp. 22, 24, 28.Wegmann, A., Helm, J., Samaniego, A., Smith, B., Jacobs, B., Drake, D., Smith, J., McKown,

M., Henry, A., Fisher, R., and Hathaway, S. (2008) Palmyra Atoll rat eradication: biomarkervalidation of an effective bait application rate 19 June to 5 July, 2008. Unpublished report, Island

Conservation, Santa Cruz, CA, 35

20


Dr. Patrick Jodice 

Chair 

South Carolina Cooperative 

Fish & Wildlife Research Unit 

Clemson University 

Clemson, SC 29634 

864-656-6190 

PJodice@clemson.ed

Craig S. Harrison, Esq. 

Vice-Chair for Conservation 

4953 Sonoma Mountain Road 

Santa Rosa, CA 95404 

202-778-2240 

charrison@hunton.com 

Kim Rivera 

Chair-Elect 

NOAA Fisheries 

709 West 9th, Room 461 

Juneau, AK 99802 

907- 586-7424 

Kim.Rivera@noaa.gov 

pacific_reefs@fws.gov 

April 4, 2011 

Susan White 

U.S. Fish and Wildlife Service 

Project Leader 

Pacific Reefs NWR Complex 

300 Ala Moana Blvd. 

Honolulu, HI 96850 

Re: Draft EIS for Palmyra Rat Eradication Project 

Dear Ms. White: 

On behalf of the Pacific Seabird Group (PSG), we offer these comments on the draft 

Environmental Impact Statement (DEIS) for the Palmyra Atoll National Wildlife Refuge Rat 

Eradication Project. PSG is an international, non-profit organization that was founded in 1972 to 

promote the knowledge, study, and conservation of Pacific seabirds. It has a membership drawn 

from the entire Pacific basin, including Canada, Mexico, Russia, Japan, China, Australia, New 

Zealand, and the USA. PSG's members include biologists who have research interests in Pacific 

seabirds, government officials who manage seabird refuges and populations, and individuals who 

are interested in marine conservation. PSG has long been concerned about nonnative creatures 

such as rodents on seabird breeding islands. We have a history of supporting projects that 

remove nonnative species to allow indigenous fauna, especially seabirds, to achieve healthy, 

sustainable populations. For example, in recent years PSG has supported rodent eradication 

projects on Lehua Island (Hawaii), Rat Island (Alaska) and Anacapa Island (California). 

Through its conservation fund, PSG has sponsored an eradication project in Fiji. 

PSG strongly supports the proposed plan to eradicate ship rats (Rattus rattus) at Palmyra to aid in 

the conservation of seabirds and their habitat. Rats are notorious for their depredations on bird 

chicks and eggs as well as adults of the smaller species (I. A. E. Atkinson, 1985, The spread of 

commensal species of Rattus to oceanic islands and their effect on island avifaunas. In: P. J. 

Moors (ed.), Conservation of Island Birds, ICBP Tech. Pub. 3: 35-81). The introduction of rats 
Ms. Susan White 

April 4, 2011 

Page 2 

on Midway during 1943 decreased seabird populations there and caused the extinction of the 

Laysan rail and Laysan finch (H. I. Fisher and P. H. Baldwin, 1946, War and the Birds of 

Midway Atoll, Condor 48:1-15). The successful eradication of rats on Midway in the 1990s has 

had positive impacts on small nesting seabirds such as Bonin petrels and storm-petrels (M. J. 

Rauzon, Island Restoration: Exploring the Past, Anticipating the Future, Marine Ornithology 35: 

97-107, 2007). Restoring the Palmyra ecosystem by removing ship rats will pay huge dividends 

for seabirds and the island ecosystem. For example, small and vulnerable seabird species such as 

sooty terns, brown noddies and black noddies will almost immediately benefit from the 

eradication of rats. Many of the eight seabird species that were apparently extirpated from 

Palmyra by rats (Audubon’s shearwater, Christmas Island shearwater, wedge-tailed shearwater, 

Phoenix petrel, white-throated storm-petrel, Bulwer’s petrel, blue noddy and gray-backed tern) 

may reappear, some possibly very quickly. Rat predation on bristle-thighed curlews may occur 

on Palmyra because curlews experience a period of flightlessness while molting there (DEIS, p. 

103). It is evident that the restoration of Palmyra will allow many species to reclaim their former 

ranges. 

USFWS’ Regional Marine Bird Policy for over 25 years has stated that its goal is to “remove all 

introduced predators from marine bird colonies on all National Wildlife Refuges and encourage 

their removal from all other colonies.” (November 15, 1985). The proposed rat removal project 

furthers that policy, and completes the eradication of rats from all the remote refuge islands. 

Although PSG recognizes that the elimination of alien predators that devastate natural 

communities and drive some species to extinction sometimes is controversial, we have supported 

USFWS and other agencies in the past when groups that are ignorant about wildlife management 

attempt to thwart projects such as this, sometimes by force of litigation. PSG will gladly lend its 

name and expertise to joint press releases concerning this project to help educate anyone who 

may be initially opposed to this project. 

PSG believes that the goals of this project must be complete eradication. We want to avoid 

situations that require perpetual control, perpetual funding and perpetual vigilance. Long-term 

rodent control projects raise secondary poisoning issues over a long period as well as the risk that 

rats will develop a resistance to poisons. In our considerable experience, we have learned that 

half-measures are inefficient and are simply a waste of funds. 

PSG supports of the use of brodificoum, which is capable of killing a rat after a single feeding. 

Palmyra is a challenging three-dimensional environment for rat eradication because of the 

prevalence of crab bait competitors, 50-foot coconut trees, and almost daily rain showers. Rats 

may only have a single chance to find the bait under these difficult conditions. There was a failed 

attempt to remove rats in 2001-2002 on Palmyra, and we urge you to make every effort to make 

this attempt a success. The techniques of aerial broadcasting of bait has greatly improved since 

2001, and recent successes include Rat Island (Alaska) and Anacapa Island (California). In 

contrast to these examples, we have analyzed the “Review of the Lehua Island Rat Eradication 
Ms. Susan White 

April 4, 2011 

Page 3 

Project” by Landcare Research, New Zealand (January 2011) where a rat eradication failed. We 

conclude that the use of a weaker rodenticide (diphacinone, which requires multiple feeds to 

deliver a lethal dose) and unreasonable restrictions on its use near the shoreline led to failure. 

Unfortunately, the Lehua project was ultimately a complete waste of funds and human effort. 

We would like to benefit from lessons learned at Lehua and would object to such restrictions at 

Palmyra. 

 

The DEIS presents four alternatives: (A) no action; (B) aerial broadcast of brodificoum; (C) 

aerial broadcast of brodificoum with proactive mitigation of risk for vulnerable bristle-thighed 

curlews; and (D) bait stations with brodificoum with canopy baiting. We believe that the 

chances of success will be improved by using large amounts of bait with high toxicity because 

hermit crabs, not rats, will consume much of the bait. The project may pose a risk to non-target 

species such as bristle-thighed curlews. During the summer (June-July) window for this 

operation a small number of young, non-breeding curlews may be present at Palmyra, and 

significant efforts should be made to protect those birds. For this reason we support Alternative 

C. We recognize that some curlews may be lost if they eat poisoned hermit crabs, but we believe 

those losses, while unfortunate, may be a necessary cost to achieve a rat-free environment on 

Palmyra which will benefit generations of seabirds and shorebirds. 

Thank you for the opportunity to comment on the DEIS. Please contact us if we can be of 

further assistance. 

Sincerely, 

Craig S. Harrison 

Vice Chair for Conservation 
1731 Connecticut Avenue, NW, 3rd Floor  Washington, D.C. 20009

Tel: 202-234-7181  Fax: 202-234-7182  abc@abcbirds.org  www.abcbirds.org

April 11, 2011

Regulatory Public Docket

US Fish and Wildlife Service 

Pacific Reefs National Wildlife Refuge Complex 

300 Ala Moana Blvd., Room 5-231

Honolulu, HI 96850

Re: Palmyra Atoll National Wildlife Refuge, U.S. Pacific Island Territory; Nonnative Rat Eradication 

Project, Draft Environmental Impact Statement (FWS-R1-R-2011-N011)

American Bird Conservancy (ABC) welcomes the opportunity to comment on the effort to 

eradicate rats from Palmyra Atoll (Palmyra), as it is an important center of biodiversity and species 

abundance in the Central Pacific area. Specifically, we support the Alternative C (aerial broadcast with 

capture of shorebirds) for the eradication effort to minimize effects on nontarget species.

Capture and holding: As stated above, we support the option with proactive mitigation of risk 

for shorebirds, both out of specific concern for the birds in question, especially the Bristle-thighed 

Curlew, which is estimated to have only 2600 breeding pairs and which is listed on the ABC/Audubon 

WatchList 2007 and is considered Vulnerable by the IUCN Red List. Bristle-thighed Curlews potentially 

face high mortality if not captured and removed from the island during eradication. We believe it is 

incumbent on the project to take all possible active measures to avoid non-target mortalities. We also 

found the experts listed in the Appendix 1 and 2 to be an excellent list of people, which should inspire 

confidence in the level of planning and outreach that has gone on thus far in the project. We appreciate 

that the capture methods have not yet been finalized in the Draft EIS.

ABC also believes there are serious risks to the shorebirds under any scenario, and suggest 

consideration of the following in continued planning:

1) ABC has been in contact with Peter Doherty, Virginia Beach, VA, who produces capture nets 

specifically designed for shorebirds. We have informed him of this project and he is willing to 

provide expertise, if needed. Mr. Doherty’s expertise in capturing shorebirds could be of value 

in this project. 

2) Long-legged waders are extremely difficult to capture and hold and can be subject to high rates 

of mortality during capture and in captivity. It may be useful to try to manage expectations by 

providing a tentative estimate of mortality in both processes, based on available data.

3) There are few shorebirds in captivity, but one of the largest we know of is the flock of about 35 

birds in Monterey Bay aquarium, which included a curlew for the past 20 years, and several 

other large-bodied waders. International Bird Rescue Research in Cordelia, California also has 

expertise in handling birds for rehabilitation after oil spills, and has developed techniques to 

house difficult species. The plan may wish to draw on the expertise of those managers. 

4) We have concerns about the cement slab on which it is proposed to maintain the birds on 

Cooper Island, because curlews tend to develop foot problems in uniform substrates without 

tidal action.
1731 Connecticut Avenue, NW, 3rd Floor  Washington, D.C. 20009

Tel: 202-234-7181  Fax: 202-234-7182  abc@abcbirds.org  www.abcbirds.org

5) We have been in contact with Dr. Lesanna Lahner, School of Veterinary Medicine, Univ. 

Wisconsin, Madison, who will be the supervising veterinarian monitoring the curlews for 

physiological effects during their captivity. She has plans to monitor fecal corticosteroids, fecal 

parasites, and blood for CBC and chemistry profiles. ABC thinks this could be a very useful 

monitoring program to evaluate these fragile birds in captivity and to develop additional 

expertise for future captive holding of vulnerable birds during island eradications. 

6) We expect the risk of conspecific aggression to be low among these birds, because of the timing 

of the operation and because most will not yet be of breeding age, but if the birds are held in 

some sort of aviary, provisions should be made for separating some birds and providing a visual 

barrier for any aggressive individuals.

7) One interesting option for the capture and holding of the curlews may be to place them on a 

nearby islet or rock, if such a place were available and not subject to baiting. The birds may be 

rendered flightless by plucking a few primaries, which would begin to grow back immediately, 

though the birds may require supplemental feeding. Flightlessness should not provide a huge 

obstacle for these birds, because they are accustomed to losing their ability to fly during the 

molt. 

The preparations and prior studies provided in the Appendices to the Draft EIA show great 

attention to detail and extensive planning to overcome the significant obstacles presented by the large 

number of land crabs on Palmyra Atoll. The field studies to determine the amount of rodenticide bait 

needed to insure adequate coverage of all rat territories appear to have been well planned and 

executed. It is indeed unfortunate that such large amounts of rodenticide bait will be needed to 

overcome the scavenging by land crabs, but the proponents have presented a good case for the need 

for their recommended applications. 

American Bird Conservancy does have concerns as to the fate of rodenticide bait and 

metabolism by crabs and other organisms on Palmyra, and the level of knowledge of the mass balance 

of bait and metabolic products produced when ingested and subsequently excreted by crabs. The 

potential toxicity of excreted metabolic residues of brodifacoum is of particular concern. After the rat 

eradication successfully completed on Rat Island, AK, residues of difenicoum and bromadialone were 

detected in tissues of gulls (Ebbert and Huntington 2010). Both of these rodenticides or close analogs

appear to be metabolic products of brodifacoum (see Figure 1). Debromination of brodifacoum at 

position ❶produces difenacoum, which would be a plausible metabolic route in many animals. 

Similarly, Coumatetralyl would be produced by hydrolytic removal of the bromobiphenyl chain at 

position❷. Hydrolysis of the -napthyl moiety of brodicacoum at position ❸would produce a close 

structural analog of bromodialone. Hydroxycoumarin would be produced through hydrolysis at position 

❹ of the molecule. Any of these catalytic reactions could be plausible metabolic routes leading to toxic 

residues in tissues or excreta of crabs or cockroaches. It is equally plausible that crabs metabolize 

brodifacoum and excrete only a small fraction of any toxic product in their feces, in which case the risk 

will be minimized. 
1731 Connecticut Avenue, NW, 3rd Floor  Washington, D.C. 20009

Tel: 202-234-7181  Fax: 202-234-7182  abc@abcbirds.org  www.abcbirds.org

The metabolic fate of brodifacoum and mass balance of residues were not reported in the 

prior study given in Appendix F of the Draft EIS. The residue analysis for that study was conducted by 

the California Animal Health and Food Safety Laboratory at UC Davis, and they may have retained the 

mass spectrometer reconstructed ion chromatograms, which could identify whether any of these 

potential metabolic products or other products were present in the crab tissues and excreta analyzed in 

the 2010 study. We strongly suggest contacting them and trying to have the spectroscopist attempt to 

determine what metabolic products of brodifacoum were present in the feces in addition to the parent 

compound. If a mass balance of the rodenticide can be elucidated, it would be very helpful in the risk 

analysis. Without a study of the fate of brodifacoum ingested by crabs, the fate and residue 

composition of the large amount of brodufacoum spread over Palmyra Atoll will be unclear. We suggest 

that when samples are collected and analyzed from the planned Palmyra project, APHIS (and any other 

lab contracted) report as many residues and metabolic products as possible, and use the information to 

construct a mass balance. The persistence and toxicity of any identified products should be available 

from prior studies. We suggest using this data to calculate the expected persistence and toxicity to nontargets (such as curlews) and to hold the curlews in captivity until the toxic residues have dissipated in 

the Palmyra environment.
1731 Connecticut Avenue, NW, 3rd Floor  Washington, D.C. 20009

Tel: 202-234-7181  Fax: 202-234-7182  abc@abcbirds.org  www.abcbirds.org

ABC also reviewed “Palmyra Atoll Rainforest Restoration Project: Rat Eradication Monitoring 

Plan for Alternatives B and C”, with particular attention to Section 2.3, Impacts to Target and Non-Target 

Organisms (Rats, Fish, Geckos, Crabs, Birds). We found that the low level of detail in this document 

precluded a careful evaluation of the bird monitoring protocols, and suggest that further definition be 

given to the a) statistical design of the pre- and post-eradication bird monitoring 2) the time frame for 

evaluation of the persistence of bait in the palm canopy, which should be continued until none is 

detected or some minimal level is reached. Additionally, we would like to see an evaluation of the 

shorebird population in subsequent years, though we assume this is part of the long term strategy for 

documenting the effect of the action on the atoll. 

The detail given for the foodweb monitoring was minimal, with only a sketchy description given 

on where pooled samples will be collected. We believe these should be representative of the entire 

atoll. 84 samples of non-target terrestrial animals and 80 samples of fish appears to be an adequate 

number of samples to determine the distribution and fate of rodenticide on the atoll. Also, we 

recommend that a subset of split samples of the rats, fish, gecko, crabs, and bird samples be sent to the 

U.S. Geological Survey Madison, WI Lab and the USDA National Wildlife Health Center for independent

analyses. We urge the project to attempt to determine a mass balance of the fate and residue products 

to insure residual toxicity does not remain on the atoll. Finally, we believe that directed searches (as 

opposed to opportunistic searches) for non-target carcasses be conducted in transects for longer than 

10 days after the 2nd application in shore bird roosting sites, and that these also concentrate on places 

where intoxicated curlews might hide to avoid detection. The monitoring plan does not give detail 

about how often these searches will be conducted. 

In conclusion, ABC supports the effort to eradicate rats from Palmyra, as it is an important 

center of biodiversity and species abundance. Specifically, we support the Alternative C (aerial 

broadcast with capture of shorebirds) option listed in the Draft EIS. We believe this project has been 

organized and planned carefully, although we would like to have a more complete analysis of the fate of 

rodenticide moving through the Palmyra ecosystem. We would be pleased to offer comments on a 

more detailed draft of the monitoring procedures.

Sincerely,

Michael Fry, PhD George Wallace, PhD

Director of Conservation Advocacy Vice President for Oceans and Islands

 

Jessica Hardesty Norris, PhD Moira McKernan, PhD

Seabird Program Director Pesticides and Birds Program Director
         

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Individual Comments to DEIS received via email:

March 1-9, 2011

∙ Wayne Johnson, PhD, Honolulu resident –

Dr. Flint, this plan will cause enormous suffering and agony to living creatures and the 

blood will be squarely on your hands. 

∙ Eric Barker, individual –

Please extend the contact period for this plan.

Additionally, I would like to attend and encourage others to participate in a public 

hearing on Oahu for this issue.

∙ Kim Williams (Aiea), individual –

I strongly OPPOSE The Nature Conservancy and the USFWS using an aerially 

dispersion of brodifacoum on Palmyra Atoll. The use of poison does more harm to the 

environment than good. There has to be more better method. Please postpone the start 

date of this dispersion. And please hold a public hearing in Honolulu before any plan is 

implemented.

∙ Anita Wintner, Hawaii resident –

The Nature Conservancy doesn't protect nature. They get $$$ for doing reports and say 

lets poison, not doing a report that shows what happens to birds, or runoff to the ocean. 

What a waste of a million dollars! 

∙ Cara Losier, individual –

It has recently come to my attention that rodenticide poison will be dispensed on Palmyra 

Atoll. I urge you to reconsider this course of action or take steps to halt the progress of 

this project. This poison causes extremely painful death to the animals who come in 

contact with it, which is clearly inhumane. Please consider the lives of the animals who 

will be affected before condoning this project.

∙ Ursula Heinz, individual –

I am asking for a public hearing in Honolulu and for an extension of the contact period 

concerning this devastating project which will kill indiscriminately birds and fish in the 

involved areas. Please provide for time to create a better alternative strategy.

April 10-31, 2011

∙ Mark Rauzon, Laney College, Geography Department - Chair –

Thank you for the invitation to comment on the Palmyra Atoll National Wildlife Refuge 

Rat Eradication Project - Draft Environmental Impact Statement. After reviewing the 

document I would like to nominate Alternative C as the preferred option, for the 

following reasons. 

I am familiar with Palmyra from two prior visits and have surveyed the island for 

seabirds. I have seen firsthand the potential for seabird restoration and have also 

witnessed the effects of the failed 2001 rat eradication attempt, both on the island and in 

the community of eradicators. That is why I advocate pressing forward with rat 
eradication and especially Alternative C that best copes with the very challenging 

environment that Palymra presents. The Palmyra rat eradication has had the greatest 

breadth of research and preparation than any other US eradication. Since the 2001-02 

eradication attempt, research into why it failed and what can be learned, has been ongoing. Research into bait stations began with the 2001-2002-eradication attempt. Jim 

Murphy former USDA manager of the rat eradication wrote: “Took 11 weeks ...to pound 

out 36 miles of transects and 1198 bait stations on 34 isles from tabletop size with 1 

coconut to rats to 100‟s of acres with rats. Some were loaded with hermit crabs, some had 

none, some had lots of coconut crabs, and some had none. I believe some islands are rat 

free, and rest are 95+% [rat-free]” (J. Murphy, pers. comm.).

Some of these isles remain rat-free today, but given the logistics described by Murphy, 

there are several ways to fail. The investigation into this effort found the bait station 

spacing of 50 x 50 m used was placed too far apart. For future eradication projects, it was 

recommended that a 25 m grid for the placement of bait stations would be needed, but 

that alone might not be adequate to intercept all rats. Palmyra is a unique challenge with 

high rainfall and humidity, crabs and coconut trees 50 feet tall. The three-dimensional 

wet environment, literally crawling with bait competitors in the form of crabs. In 2004,

Alex Weggman began crab studies, the large but unknown factor in tropical rat 

eradications. The 2005 trial eradications demonstrated that rats can be eradicated from 

islands with high land crab densities when bait is broadcast at rates from 85kg/ha to 95 

kg/ha.

Bait in sufficient quantity must be available to all rats for at least one meal, even if the 

rate appears high, and the bait choice should be of sufficient toxicity that rodents need 

only one-visit. I am glad to see the bait choice limited to brodificoum. The 2001-02 

failure using brodificoum set back the field of eradication substantially, but the risk of 

second eradication failure in not an option. Using a toxic bait that requires more than one 

feeding is a recipe for another failure- and as such, an unacceptable risk given the 

planning and investment.

Past feasible evaluations determined „exhaustive planning” was required in order to 

achieve a successful eradication outcome at Palmyra. Apparently this policy has been 

followed. This project is the culmination of years of research and a beneficiary to all the 

lessons learned during past eradications and especially builds on the success in the 

rapidly evolving field of aerial baiting techniques. In 2001, aerial broadcast of bait was in 

its infancy, now it is state-of-the-art. Helicopter broadcast into the three dimensional 

habitat would be an equalizer in distributing to bait to all areas, not just those within

human reach, which in 2002 was insufficient.

The applicators, Island Conservation, has been involved from the US first aerial drop on 

Anacapa Island to the latest at the Rat Island, Alaska in 2009. They have join forces with 

federal and private conservation entities to become the Palmyra Atoll Rainforest 

Restoration Project (PARRP). The project is also informed by the recent 2011 Galapagos 

and South Georgia Island aerial bait drops.
Unfortunately, increased bait toxicity poses high non-target risks. The greatest forseeable 

risks in this effort may be the threat to Bristle-thighed curlews (BTCU). I appreciate the 

concern expressed by the proposed capture and hold of „catchable‟ curlews, and all the 

careful efforts to have minimal effect on the captive birds. While losing a curlew would 

be most unfortunate, some loss must be expected. Investing in the future ecological 

health requires the sacrifice of some individuals, and fortunately the loss of summering 

sub-adult birds is not of population level significance, which is what makes the most

biological and ecological sense.

The lamentable non-target loss has recently been brought to the public attention with the 

loss of eagles and gulls at Rat Island and a call for public discussion. The death of rats, 

themselves violate Buddhist principals for the sanctity of all sentient life forms. So 

eradication failures cause needless loss of life (rats) since there is no ecological gain. 

Thus some overkill involving non-target loss must be seen as investment in complete 

eradication success measured on an ecological level that justifies all the incipient death 

that occurs, target and non-target alike. This must be accepted as a fair trade for future

curlews may benefit from a rat-free Palmyra in unanticipated ways, such as increased 

sooty tern egg densities, but other species will clearly benefit in the short term. Palmyra 

becomes one of the rare few tropical forest island free of rats, as such it become the site 

to transplant Line Island endemics. With a rapidly changing climate and sea level rising, 

Palmyra must be rat-free, if only to mitigate the use of the island habitat for a research 

station with a substantial carbon footprint.

Overall, the completeness of this EIS, the comprehensive appendices that review the past 

and future options, determine LD‟s of toxins, etc. is very remarkable and admirable in 

scope, showing again how seriously you take your duty to be thorough, responsible and 

transparent. I say overall, for I did not see what happens if rats are detected after the 

second drop, but I stopped looking. Nevertheless, your team is to be congratulated on the 

research effort taken to insure this rat eradication will be successful and allow Palmyra to 

be all that it can be. I endorse Alternative C as the scenerio most likely to succeed in a 

cost-effective and efficient manner, recognized some non-target loss will be unavoidable.

Good luck.

April 1-6, 2011

∙ Kevin Lafferty, Marine Ecologist, US Geological Survey –

Having studied black rats on Palmyra Atoll, I can testify to their incredible numbers and 

the need to remove them from the Atoll to help project the area's rich and valuable native 

diversity. The level of study and forethought that has gone into this restoration effort is 

admirable. I support the effect and have high hopes that it will succeed.

∙ Dr. John D. Collen, Associate Professor in Geology, Victoria University of Wellington –

I have carefully read and reviewed the Draft EIS relating to the Palmyra Restoration 

Project. From my personal knowledge both of Palmyra Atoll and of the pest eradication 

projects undertaken in New Zealand (which includes visits to many of NZ's now pest-free 

offshore and Subantarctic islands), I would like to comment that the proposal is 

necessary, relevant and well constructed. I fully support the actions outlined in the Draft 
EIS and look forward to watching the recovery of the atoll's terrestrial ecosystems in the 

future.

∙ Jonathan Gardner, Ph.D., Professor of Marine Biology, Victoria University of Wellington –

Having reviewed the draft EIS for the Palmyra Atoll restoration project I am pleased to 

support the actions described which will help protect Palmyra‟s species and habitats. In 

my view, this is a necessary and important project which will lead to significant 

beneficial conservation outcomes.

∙ Chelsea L. Wood, Ph.D. Candidate –

I am a Ph.D. student at Stanford University and have conducted research in the lagoon 

sand flats of Palmyra Atoll for two years. I've just reviewed the draft EIS for the 

proposed rat eradication, and wanted to let you know that I support the proposed actions.

April 7-12, 2011

∙ John P. McLaughlin, Dept. Ecology, Evolution and Marine Biology, University of 

California Santa Barbara –

I have reviewed the Draft EIS for the Palmyra Restoration Project and I support the 

actions outlined to protect Palmyra‟s unique species and habitats.

∙ Hillary S. Young, Stanford University –

I have reviewd the Draft EIS for the Palmyra Rat Eradication project and believe the 

project is likely to succeed and should result in positive net benefits for the seabird 

community at Palmyra, providing important nest site protection for many species that are 

globally declining.

∙ Carl E. Orazio, PhD, Environmental Scientist, USGS Columbia Environmental Research 

Center –

I reviewed the Draft EIS for the Palmyra Atoll rat eradication. Based on the science, 

supporting information, and options presented in the DEIS, I am supportive of the actions 

described in the DEIS for the rat eradication: The proposed actions support the efforts to 

protect and restore Palmyra Atoll's ecosystem.
From: RALPH BLACK

To: pacific_reefs@fws.gov; RALPH BLACK

Subject: ‘‘Palmyra rat project’’/Attn: Dr. Elizabeth Flint

Date: 04/11/2011 10:53 AM

‘‘Palmyra rat project’’/Attn: Dr. Elizabeth Flint/

DEAR: Dr. Elizabeth Flint

INFORMATION.

E-mail: pacific_reefs@fws.gov. Include

‘‘Palmyra rat project’’ in subject line.

Fax: Attn: Dr. Elizabeth Flint, 808–

792–9586.

U.S. Mail: Pacific Reefs National

Wildlife Refuge Complex, 300 Ala

Moana Blvd., Room 5–231, Honolulu,

HI 96850.

FOR FURTHER INFORMATION CONTACT:

Elizabeth Flint, Supervisory Wildlife

Biologist, (808) 792–9553.

SUPPLEMENTARY INFORMATION:

Introduction

With this notice, we continue the

public involvement process for our

DEIS, in accordance with the National

Environmental Policy Act (NEPA; 42

U.S.C. 4321 et seq.), as amended, and its

implementing regulations. We started

the process through RESPONCE TO A a notice in the

Federal Register (75 FR 2158) published AND THIS COPY OF LETTER SENT TO

APRIL/11/2011

Ken Salazar, Secretary of the Interior Robyn Thorson, Regional Director

U.S. Department of the Interior U.S. Fish & Wildlife Service

1849 C Street N.W. Pacific Region

Washington, DC 20240 911 NE 11th Ave

Portland, Oregon 97232

P.S. Dr. Elizabeth Flint/ IF YOU COULD PLEASE SUPPLY ME WITH A E-MAIL ADDRESS OFFICIAL AND AS TO COMMUNICATE ABOUT 

‘‘Palmyra rat project’’/‘‘Palmyra rat project’’/

COPY

PETITION TO LIST THE ATULL ISLANDS Endangered Species ANY AND ALL INFINITE AND THE `I`IWI (VESTIARIA

COCCINEA) AS

THREATENED OR ENDANGERED UNDER THE U.S. ENDANGERED

SPECIES ACT/Endangered Species; Marine Mammals, Hawaii Bottomfish,

Seamount Groundfish Fisheries,Endangered Species ANY AND ALL

INFINITE AND THE `I`IWI (VESTIARIA COCCINEA)

APRIL/11/2011

ATULL ISLANDS Endangered Species ANY AND ALL INFINITE AND THE

ATULL ISLANDS Endangered Species ANY AND ALL INFINITE AND THE

`I`IWI (VESTIARIA COCCINEA)

APRIL/11/2011

Ken Salazar, Secretary of the Interior Robyn Thorson, Regional Director

U.S. Department of the Interior U.S. Fish & Wildlife Service

1849 C Street N.W. Pacific Region

Washington, DC 20240 911 NE 11th Ave

Portland, Oregon 97232

Dear Secretary Salazar,

The FRIENDS OF ATULL ISLANDS Marine Mammals, Hawaii Bottom fish, Seamount Groundfish Fisheries Endangered Species ANY AND

ALL INFINITE AND THE `I`IWI (VESTIARIA COCCINEA) AND BIRDS OF A FEATHER

OR FEATHERS.

to list the ATULL ISLANDS Endangered Species ANY AND ALL INFINITE AND THE `I`IWI (VESTIARIA

COCCINEA`I`iwi (Vestiaria coccinea) as a threatened or endangered species pursuant to the

Endangered Species Act (ESA), 16 U.S.C. §1531 et seq. This petition is filed under 5 U.S.C.

553(e) and 50 CFR 424.14 (1990), which grant interested parties the right to petition for issuance

of a rule from the Secretary of Interior.

Under the ESA, a threatened species includes “any species which is likely to become an

endangered species within the foreseeable future throughout all or a signification portion of its
range.” An “endangered species” is one that is in danger of extinction.

The `I`iwi AND ANY OF AND ALL OF threatened species warrants listing because it is imperiled by climate change and disease in combination

with other factors, SUCH AS POSSIABLE SPRAYING OF CHEMICALS COULD IMPACT AND ADD TO THE declining OF ANY OF AND

ALL OF threatened species in population size and range, and ARE not adequately protected by

existing regulatory mechanisms. With climate AND POSSIABLE RADDS FROM FUKASHIMA DISASTER change forcing the spread of avian

malaria and

avian pox, CESIAM 131,137 the `I`iwi AND ANY OF AND ALL OF threatened species is in danger of near term extinction in the western

portion of its range (the

islands of Kauai, Oahu, and Molokai, west Maui AND ALL THE ATULL ISLANDS), and severe population declines with

risk of extinction within the foreseeable future across its eastern range (east Maui the island

of Hawaii AND THE ATULL ISLANDS).

Petitioners also request that critical habitat be designated concurrent with the listing, pursuant to

50 CFR 424.12, and pursuant to the Administrative Procedures Act (5 U.S.C. 553).

For the petitioners,

/s/

ROWN PAUL BROWN SR.

Director FOR FREE THE ATULL ISLANDS Endangered Species; Marine Mammals, Hawaii Bottomfish, Seamount Groundfish &

ARRADICATE THE RATS

Executive Summary SINCE Current situation after accident in Fukushima,

JAPAN (update: 2. April 2011 12:00) status of the radioactivity

measurements 

the world-wide measurements of the radioactivity in the context of the

comprehensive atomic test stop agreement(CTBT) show at present (status of

the measurements: 29. March 2011) further that traces of iodine and cesium

are to be found at present at nearly all measuring points of the north

hemisphere. To Europe the stations point in Freiburg/Germany and

Stockholm/Sweden Jod-131 concentrations of 250 and/or 1700 μBqm-3. Such

values were registered also The material measured at present was already set

free 14 days ago in Japan

advance upslope in response to higher ambient temperatures. FOR THE

ATULL ISLANDS Endangered Species ANY AND ALL INFINITE AND The

`I`iwi, are iconic surviving native'S of Hawaii, The `I`iwi itself,is recognized by its bright scarlet and

black plumage and long curved beak. Once widespread, the species now occurs only in upper

elevation areas where avian disease is infrequent or absent. Increasing ambient temperature,

driven by global climate change, is facilitating the spread of deadly avian malaria to remaining

occupied habitat. The species is in danger of immediate or near term extinction across the entire

western portion of its geographic range, namely, on the lower elevation islands of Kauai, Oahu,

Molokai, and west Maui. The `I`iwi also faces extinction within the foreseeable future in higher

elevation terrain on east Maui and the island of Hawaii as mosquito-borne avian malaria

advances upslope.

`I`iwi populations are severely reduced on Kauai, Oahu, Molokai, west Maui and THE ATULL ISLANDS and have

declined on all islands. Relatively large populations still occur above 1250 m elevation on east

Maui and the island of Hawaii, where disease incidence is currently low or absent. Climate

change is projected to greatly diminish or eliminate disease free areas for `I`iwi.

We petition to list the `I`iwi as threatened or endangered under the U.S. Endangered Species Act

(ESA). The species `I`iwi and THE ATULL ISLANDS Endangered Species ANY AND ALL INFINITE qualifie for ESA protection as per four

statutory factors used by the

Secretary of Interior to determine if listing is warranted:

Present or threatened destruction, modification, or curtailment of habitat or range – `I`iwi

habitat throughout Hawaii is adversely impacted by invasive, non-native animals and plants,

and, on the island of Hawaii, by land development.

Disease or predation – The best available data indicate that the ongoing spread of avian malaria

and avian pox endangers the smaller `I`iwi populations on Kauai, Oahu, Molokai, and West

Maui, and threatens the larger ones on East Maui and Hawaii Island. Population-level resistance

or tolerance to these deadly diseases is lacking. Climate modeling based on a conservative

estimate of a 2° C increase in ambient temperature projects avian malaria to reach elevations up

to or beyond 1900 m, affecting most if not all presently occupied `I`iwi habitat. Hawaii is

experiencing a long-term increase in temperature and an accelerated rate of increase over the past

few decades consistent with global climatic trends. Parasitism by bird lice and predation by alien

rats, mongoose, and feral cats may accelerate the decline of `I`iwi populations subject to higher

disease incidence.

Inadequacy of existing regulatory mechanisms – Under current national and international

policies on greenhouse gas emissions, there is virtually no chance of limiting global heating to 2° C even with full policy implementation. Moreover, regulatory mechanisms are lacking to protect

and restore forest habitat needed to expand 'I'iwi populations at highest elevations, as a means to

reduce their vulnerability to avian diseases and fragmentation. State and private lands, which

include most existing and potential upper elevation habitat for 'I'iwi, are generally not managed
for forest bird recovery.

Other natural or manmade factors affecting its continued existence – Global warming threatens

`I`iwi by increasing the elevation at which regular transmission of avian malaria and avian pox

virus

4

occurs. Moreover, evidence suggests that epizootics could in the near term eliminate the

small

`I`iwi populations on Kauai, Oahu, and Molokai, and diminish and fragment larger populations

on East Maui and Hawaii Island. Hurricanes, likely to intensify in a warmer climate, and

volcanism may further reduce 'I'iwi habitat. Small `I`iwi populations are at heightened risk of

extinction from random demographic fluctuations, localized catastrophes (severe storms, wild fire,

disease outbreaks, volcanism, etc.), inbreeding depression, and genetic drift.

This petition includes a request for critical habitat designation for the `I`iwi at the time of listing.

Critical habitat should include areas of sufficient forest habitat for viable or potentially viable

`I`iwi populations on Kauai, Oahu, Molokai, Maui, and Hawaii Island, as each island represents

a significant portion of the species’ natural range. Designation would require that federal actions

promote conservation of essential `I`iwi habitat, and help resolve conflicts that undermine its

protection and restoration. It would provide added impetus to re-establish native trees, remove

ungulates, reduce depredation by rats and other introduced predators, control invasive plants, and

otherwise manage vital habitat to improve prospects for 'I'iwi survival in a climatically

challenged environment.

In conclusion, the spread of avian disease driven by climate change, severe range curtailment,

ongoing loss of suitable habitat, and the history of forest bird extinctions on Hawaii are

compelling reasons to list the `I`iwi as a threatened or endangered species.

I. Introduction

The `I`iwi is one of 17 surviving Hawaiian honeycreepers (Fringillidae: Drepanidinae) of 37

species known historically and 55 extant prior to human arrival on Hawaii (Pratt 2009). Its

closest relative is the extinct Hawaii Mamo (Drepanis pacifica) (Pratt 2005). Disease and habitat

loss are primary reasons for the decline of Hawaiian honeycreepers and other native forest birds.

Extinctions continue to this day, with the most recent being the Poo-uli (Melamprosops

phaeosoma) in 2004.

The `I`iwi, a scarlet bird with black wings and tail, and a long curved, salmon-colored bill. It is

generally placed in the monotypic genus Vestiaria. It is a largely nectarivorous species that

occurs commonly in closed canopy, high-stature native forests above 1500 m elevation (Fancy

and Ralph 1998). `I`iwi breed and winter primarily in mesic and wet forests dominated by native

'ōhi'a (Metrosideros polymorpha) and koa (Acacia koa) trees (Scott et al. 1986). They often

travel widely in search of ‘ōhi‘a flowers and are important ‘ōhi‘a pollinators (Mitchel et al.

2005). The birds respond to seasonal flowering patterns, often moving to lower elevations where

they are exposed to deadly disease (Pratt 2005). The `I`iwi uses its long bill to extract nectar

from decurved corollas of Hawaiian lobelioids, which have become far less common on Hawaii

over the past century (Smith et al. 1995).

Female `I`iwi typically lay two eggs, and they alone are thought to incubate eggs and brood

young (Mitchel et al. 2005). Males provision females with food off the nest. Breeding takes place

predominantly from February to June, and is usually associated with peak flowering of 'ōhi'a

(Fancy and Ralph 1998).

5

For native Hawaiians, THE ATULL ISLANDS Endangered Species ANY AND ALL INFINITE and`I`iwi and other forest birds have a spiritual

nexus. Feathered objects

represented gods, ancestors, and divine lineage (Amante-Helweg and Conant 2009) even to this day. Red feathers

of clothing, such as cloaks, capes, and helmets, were predominantly from `I`iwi. Once a familiar

sight on all main Hawaiian Islands, THE ATULL ISLANDS Endangered Species ANY AND ALL INFINITE remain an icon's of Hawaii’s native

forests and over all exsitence sea and land.

Today `I`iwi occur in higher elevation habitats largely free of avian disease, to which the species

is highly susceptible. With climate change, the recent Fucashima ,JAPAN disaster RADDS,ANY OF AND ALL OF threatened species warrants

listing because it is imperiled by climate change and disease in combination

with other factors, SUCH AS POSSIABLE SPRAYING OF CHEMICALS COULD IMPACT AND ADD TO THE declining OF ANY OF AND

ALL OF threatened species in population size and range these safe refugia may be lost entirely as pathogens

vectors AND Current situation after accident in Fukushima (update: 2. April 2011 12:00) status of the radioactivity measurements 

the world-wide measurements of the radioactivity in the context of the comprehensive atomic test stop agreement(CTBT) show at present (status

of the measurements: 29. March 2011) further that traces of iodine and cesium are to be found at present at nearly all measuring points of the

north hemisphere. To Europe the stations point in Freiburg/Germany and Stockholm/Sweden Jod-131 concentrations of 250 and/or 1700 μBqm-3.

Such values were registered also The material measured at present was already set free 14 days ago in Japan

advance upslope in response to higher ambient temperatures.

This petition reflects the needs for swift remedial action under the U.S. Endangered Species Act

to preventTHE ATULL ISLANDS Endangered Species ANY AND ALL INFINITE AND `I`iwi from joining the tragically long list of extinct or

feared extinct Hawaiian

birds (Banko and Banko 2009). It explains how climate change, disease, and other factors

threaten the survival of the `I`iwi.

II. Population Status

Distribution, abundance, and trends

The `I`iwi occurs on the Hawaiian islands of Kauai, Oahu, Maui, Molokai, Hawaii AND ATULL ISLANDS Endangered Species ANY AND ALL

INFINITE (Gorresen

et al. 2009). Once widely distributed in native forests on all major Hawaiian Islands, the species

is now mostly restricted to elevations above 1250 m because of avian diseases and habitat loss
elsewhere (Warner 1968, Scott et al. 1986, Fancy and Ralph 1998, Pratt 2005). `I`iwi are

declining everywhere in Hawaii except at high elevation on East Maui and northeast Hawaii

Island (Gorresen et al. 2009) (Table 1). `I`iwi population extinctions are impending throughout

Hawaii (Banko and Banko 2009).

Oahu, Molokai, and the isolated western area of Maui have small remnant `I`iwi populations at

high risk of extinction (Gorresen et al. 2009). `I`iwi are gone from nearby Lanai. These four

areas comprise the central portion of the species’ geographic range and are therefore significant.

On Kauai, in the western portion of the species’ range, the `I`iwi has declined sharply (Table 1).

Risk of extirpation from the island is of immediate concern because of severely diminished

disease-free habitat.

On east Maui and the Island of Hawaii, forming the eastern part of the species’ range, `I`iwi

populations are restricted to high elevations (Table 1). While some populations are still large,

they are at risk of fragmentation and decimation resulting from the spread of avian disease driven

by climate warming (Pratt et al. 2009). Scott et al. (1986) estimated the population of ‘I’iwi in

high elevation areas of the Island of Hawaii may be as large as 340,000 birds, suggesting that in

this area they remain abundant. This estimate, however, is more than two decades old, the

species has been declining, and even within the portion of range, which represents a fraction of

the species’ historic range, the ‘I’iwi is threatened by upslope movement of mosquitoes with

climate change.

Declines in `I`iwi abundance corresponding with reduced lower elevation range since the early

1970s are consistent with anticipated impacts of mosquito borne disease (Foster et al. 2004).

6

The population trend is downward on all islands, with some stability in high elevation areas

(Pratt et al. 2009). Climate change AND Current situation after accident in Fukushima (update: 2. April 2011 12:00) status of the radioactivity

measurements 

the world-wide measurements of the radioactivity in the context of the comprehensive atomic test stop agreement(CTBT) show at present (status

of the measurements: 29. March 2011) further that traces of iodine and cesium are to be found at present at nearly all measuring points of the

north hemisphere. To Europe the stations point in Freiburg/Germany and Stockholm/Sweden Jod-131 concentrations of 250 and/or 1700 μBqm-3.

Such values were registered also The material measured at present was already set free 14 days ago in Japan

is now setting the stage for widespread disease transmission at

the highest elevations on Maui and Hawaii Island (Benning et al. 2002; LaPointe et al. 2005).

Reproduction and Survivorship

`I`iwi pairs are reported to produce on average only 1.33 chicks per year, reflecting low

productivity characteristic of Hawaiian forest birds in general (Woodworth and Pratt 2009).

However, the `I`iwi has the lowest annual survivorship reported (55% ± 12 SE for adults and 9%

± 5 for juveniles) for any extant species of honeycreeper, reflecting the impact of malaria and

avian pox and/or low re-sighting probabilities (Fancy and Ralph 1998; Pratt 2005).

Table 1. `I`iwi population estimates for Hawaiian islands.

-------------------------------------------------------------------------------------------------------------------

Kauai -- `I`iwi numbers decreased by 62%, from 26,000 + 3,000 to 9,985 + 960, between the

1970s and

2000 (Foster et al. 2004, Gorresen et al. 2009);. `I`iwi range contracted from 140 to 110 sq

km, consistent

with a shift in its low elevation boundary from ~900 m to >1,100 m.

Oahu – Few, if any, birds remain; 8 individuals dispersed in 3 isolated locations were

reported in 1994-

1996 (VanderWerf and Rohrer 1996).

Molokai -- Few birds (1-3) were detected from 1988-2004 (Reynolds and Snetsinger 2001,

Gorresen et

al. 2009), contrasting with 12 in 1979 (Scott et al. 1986).

Maui -- About 19,000 + 2,000 individuals occurred in restricted upper elevation habitats of

east Maui

(Scott et al. 1986); ~ 180 + 150 birds were reported in isolated west Maui prior to 1980

(Scott et al.

1986); the west Maui population persists today at a very low number (Gorresen et al. 2009).

Hawaii Island – 340,000 ± 12,000 birds were estimated in higher elevation range; ~1,000

birds in lower

elevation Kohala and Puna areas (Scott et al. 1986). These estimates, however, are over two

decades old

and there have been overall downward trends in recent decades (Camp et al. 2009a, Gorresen

et al. 2009);

of 10 study locations, `I`iwi appear now absent at one, declining at 5, stable at 3, with no

estimate for 1

(Gorresen et al. 2009).

Regional breakout of data for Hawaii Island:
Northeast area: For the Hakalau Forest National Wildlife Refuge (Hakalau Unit; 1,500-2,000

m elevation)

population trend data vary from stable (over a 21-year period) to declining (during a recent

9-year

period), except for increasing numbers in limited newly restored upper elevation habitat

(Camp et al.

2009a). Recent `I`iwi numbers were estimated at ~61,000 birds.

Central windward area: `I`iwi frequency decreased 54% between late 1970s and 1986-2000

periods in

National Park and Hamakua areas, with specific study area declines and evidence of upward

range

contraction (Gorresen et al. 2005, Camp et al. 2009b);`I`iwi showed pronounced decline at

lower

elevations (East Rift, <1,000 m elev., and `Ōla`a, ~1,200-1,400 m, 1977-1994 data); modest

declines

(Kūlani-Keauhou, 1,500-2,000 m, 1977-2003 data) or stability (Mauna Loa Strip, ~1,500-

2,000 m, 1977-

1994 data) at higher elevations.

7

Southeast area: Lower `I`iwi density in the Ka`û area (2002 and 2005 data) than previously

(1976 and

1993 data) (Gorresen et al. 2009); recent estimate of ~ 78,000 bird, with 60% occurring

above 1,500 m

(Gorresen et al. 2007).

Leeward (western) area: `I`iwi densities have dramatically declined in the Hualâlai and Kona

regions

(1997-2000); they are decreasing at lower elevations (<1,500 m; Kona Forest Unit, Hakalau

Forest

National Wildlife Refuge); stable only at upper elevations (Gorresen et al. 2009); `I`iwi range

is

contracting upslope, with few occurrences below 1,100 m during the breeding season (Camp

et al. 2002).

AND THE ATULL ISLANDS YET TO BE STUDIED

-----------------------------------------------------------------------------------------------------

----------------------

III. Five-Factor Analysis

Under the ESA, 16 U.S.C. § 1533(a)(1), The U.S. Fish and Wildlife Service (USFWS) is

required to list an organism for protection if it is in danger of extinction or threatened by possible

extinction in all or a significant portion of its range. In making such a determination, USFWS

must analyze the `I`iwi’s status in light of five statutory listing factors:

(A) the present or threatened destruction, modification, or curtailment of its habitat or

range;

(B) overutilization for commercial, recreational, scientific, or educational purposes;

(C) disease or predation;

(D) the inadequacy of existing regulatory mechanisms; and,

(E) other natural or manmade factors affecting its continued existence.

For each factor, we provide the following analysis in support of our petition:

A. The present or threatened destruction, modification, or curtailment of habitat or range.

Climate change AND Current situation after accident in Fukushima , JAPAN (update: 2. April 2011 12:00) status of the radioactivity

measurements 

the world-wide measurements of the radioactivity in the context of the comprehensive atomic test stop agreement(CTBT) show at present (status

of the measurements: 29. March 2011) further that traces of iodine and cesium are to be found at present at nearly all measuring points of the

north hemisphere. To Europe the stations point in Freiburg/Germany and Stockholm/Sweden Jod-131 concentrations of 250 and/or 1700 μBqm-3.

Such values were registered also The material measured at present was already set free 14 days ago in Japan

advance upslope in response to higher ambient temperatures. facilitating the spread of avian disease threatens severe curtailment of the

`I`iwi’s current range (see discussion under C below).

Most of the `I`iwi’s original forest habitat has been cleared for food crops, livestock grazing, tree
plantations, and land development, with habitat losses since human settlement ranging from 52%

on Hawaii Island to 85% on O'ahu (Fancy and Ralph 1998). The amount of habitat available to

the ‘I’iwi and other forest birds has declined over the past few decades as many areas become

dominated by invasive non-native species (Price et al. 2009). On the island of Hawaii, additional

forest habitat loss results from land development, logging, and conversion to livestock pasture.

`I`iwi habitat across Hawaii is primarily threatened by destruction and adverse modification by

feral pigs and other exotic ungulates (goats, sheep, mouflon, deer, cattle) (USFWS 2006, Pratt et

al. 2009). Alien animals destroy forest understory vegetation, eliminate food plants for birds,

create mosquito breeding sites through ground disturbances, provide openings on the forest floor

for weeds, transport weed seeds to native forests, cause soil erosion, disrupt seedling

regeneration of native plants, and girdle young trees (Fancy and Ralph 1998; Pratt 2005; USFWS

2006). Spread of exotic ungulates that are especially difficult to contain (i.e., axis deer on Maui

and Molokai, black-tailed deer on Kauai, and mouflon sheep on Hawaii Island) represent a

8

growing threat to `I`iwi habitat as these high-jumping species invade areas even with fencing

designed to exclude feral pigs and goats (Price et al. 2009). Browsing and soil compaction by

feral pigs, goats, and deer in Molokai has reduced 'ōhi'a forest to grassy scrubland (Hess 2008).

Hawaiian forests are severely modified by invasive alien plant species that displace native plants

used by foraging and nesting birds (Scott et al. 1986; Foster et al. 2004) and increase the

frequency of forest fires (Pratt et al. 2009). Herbivory by the introduced black rat on the flowers

and fruits of native plants may also reduce food resources for native birds and impact

regeneration of native plants (Banko and Banko 1976). Introduced predatory insects also may

reduce or eliminate specialized native insects that are needed for pollination of plants important

to `I`iwi.

Habitat degradation by non-native mammals, plants, and invertebrates will likely continue to

result in loss, modification, and curtailment of `I`iwi habitat and range.

B. Overutilization for commercial, recreational, scientific, or educational purposes.

Not considered a threat at this time.

C. Disease or predation.

Disease

The `I`iwi survives in habitat largely free of avian malaria (Plasmodium reluctum) and bird pox

(Aviapoxvirus). Such habitat is currently limited to 22 acres on Kauai, 6,500 acres on Maui, and

16,000 acres on Hawaii Island (with virtually none on Oahu and Molokai) (Pratt et al. 2009). The

best available data indicate that the elevational advance of these pathogens driven by climate

change endangers the smaller `I`iwi populations on Kauai, Oahu, Molokai, and west Maui, and

threatens the larger ones on east Maui and Hawaii Island.

`I`iwi is highly vulnerable to disease

Avian disease is a primary reason for the decline of I`iwi and other Hawaiian honeycreepers

(Pratt 2005, Atkinson and LaPointe 2009). Warner (1968) demonstrated high susceptibility of

honeycreepers that died from avian malaria and bird pox after experimental exposure to

mosquito infested lower elevations where the birds were absent. Van Ripper et al. (1986) also

provided experimental evidence of high susceptibility of I`iwi to avian malaria. More recently,

Atkinson et al. (1995) experimentally exposed several species of honeycreepers to a single bite

of a malaria infected mosquito and found that effects were most severe in `I`iwi with

significantly higher mortality and clear manifestations of malaria disease at death. `I`iwi were

infected by either single (low-dose) or multiple (high-dose) mosquito bites. Mortality in both

groups was significantly higher than in uninfected controls, reaching 100% of high-dose birds

and 90% (9 of 10) in low-dose birds.

While some individual I`iwi are known to have at least temporarily survived malaria, we find no

evidence of population level tolerance or resistance to the disease. Atkinson et al. (1995) found

9

that the one `I`iwi that survived malaria after a single experimental bite from an infected

mosquito did not develop new parasitemia after multiple bites from infected mosquitoes. This

indicated that `I`iwi are capable of an immunological response at least to the administered strain

of malaria. Freed et al. (2005) discovered tolerance to malaria in two wild `I`iwi that successfully

bred 2-years post infection. However, broken head feathers in these birds suggested

physiological costs of malarial tolerance that could reduce survivorship of wild birds. Studies of

experimentally infected birds indicate that tolerant birds likely retain chronic infection for life

(Atkinson et al. 2001, Valkiunas 2005). Challenges to the immune system by stress or excessive

energy expenditure can result in recrudescence of a chronic infection to higher parasitemia levels

(Freed et al. 2005). Infected birds lose weight and suffer malaria related pathologies (Atkinson et

al. 2001), and would be expected to be more susceptible than healthy birds to predation,

competition, avian pox, unfavorable weather, and other stressors. A comparison of infection

incidence in `I`iwi and other Hawaii forest birds suggests that few `I`iwi survive exposure in the

wild (Atkinson et al. 2005).

Lethal effects of avian poxvirus have also been experimentally demonstrated in Hawaiian

honeycreepers (Jarvi et al. 2008). Freed et al. (2005) found a dead `I`iwi in the field with massive

poxvirus sores on its ankles. The bird also tested positive for malaria. A significantly high

proportion of Hawaiian forest birds with avian pox also had chronic malaria, suggesting

interaction between the two diseases (Atkinson et al. 2005).

The downward trajectory of `I`iwi populations (Table 1) indicates a pattern of decline similar to

ESA-listed Hawaiian forest birds vulnerable to disease, and dissimilar to populations of the

unlisted Amakihi (Hemignathus spp.) (Shehata et al. 2001, Woodworth et al. 2005) and Apapane

(Atkinson et al. 2005) which have shown some disease resistance and population persistence at

lower elevations.

Among the most endangered Hawaiian bird species, the `Ō`ū, (Psittirostra psittacea), like the

`I`iwi, was widespread on all main islands across a wide range of habitats a century ago

(USFWS 2006). However, Ō`ū primarily inhabited the lower to mid-elevation forests where the

impact of introduced mosquito-borne diseases was first manifested. Today, the `Ō`ū is probably

extinct. Similar widespread exposure of `I`iwi to avian diseases can be expected in coming
decades as a consequence of climate change.

Disease will spread over `I`iwi range as ambient temperatures rise I.E. AND Current situation after accident in Fukushima (update: 2. April

2011 12:00) status of the radioactivity measurements 

the world-wide measurements of the radioactivity in the context of the comprehensive atomic test stop agreement(CTBT) show at present

(status of the measurements: 29. March 2011) further that traces of iodine and cesium are to be found at present at nearly all measuring

points of the north hemisphere. To Europe the stations point in Freiburg/Germany and Stockholm/Sweden Jod-131 concentrations of 250

and/or 1700 μBqm-3. AND THE KNOWN IF THESE ARE AND ARE CEISIUM 137 MUST BE PRESENT Such values were registered also

The material measured at present was already set free 14 days ago in Japan

advance upslope in response to higher ambient temperatures.

Avian malaria in Hawaii has been mostly confined to elevations below 1500 m (van Riper et al.

1986) where cool temperatures limit mosquito presence and development of the malaria parasite

(LaPointe 2000). Recent climate modeling, however, has projected avian malaria to reach

elevations up to or beyond 1900 m within this century, affecting most if not all remaining forest

bird habitat (Benning et al. 2002).

Benning et al. (2002) modeled changes in malaria prevalence for Hawaiian honeycreepers at

high quality habitat sites, assuming a 2° Celsius (C) increase in regional temperatures (based on

International Panel on Climate Change 2007 projections; see Meehl et al. 2007). Current lowrisk

habitat diminished by 57% (665 to 285 ha) at the Hanawi Natural Area Reserve, Maui. Lowrisk

habitat at the Hakalau National Wildlife Refuge on Hawaii Island declined by 96% (3,120 to

10

130 ha). On Kauai (the Alakai Swamp), currently with little or no malaria free habitat, a 2° C

warming placed most habitat (84%) at highest risk for malaria infection in native birds. Current

mean ambient temperatures are believed to already allow limited disease transmission

throughout Kauai as all `I`iwi habitat occurs below 1600 m elevation (LaPointe et al. 2005).

The effects of a 2° C warming would almost certainly eliminate the small `I`iwi populations

from the lower-elevation islands of Kauai, Molokai, and Oahu, and from West Maui. Larger

populations on East Maui and Hawaii Island would be expected to decline severely in a manner

corresponding to decreases (~60-96%) in high elevation, disease-free refuges (Atkinson and

LaPointe 2009).

The prognosis for `I`iwi and many other native forest birds appears worse than indicated by the

Benning et al. (2002) model. The model assumed an increase of 2° C above current temperature,

corresponding to ~2.7° C increase above pre-industrial levels. However, recent analysis of global

heating indicates that temperature increases in Hawaii and elsewhere are unlikely to be limited to

2° C in this century. Increases in global temperature are currently on a trajectory to reach 2° C

(above pre-industrial levels) by mid-century and about 5° C by 2100 (Meinshausen et al. 2009,

Sokolov et al. 2009). Global greenhouse gas emissions would need to be halved by 2050 (from

1990 levels) to keep near the 2° C level with a high probability (55-88%) (Meinshausen et al.

2009). Unfortunately, under current multi-national policies regarding greenhouse gas emissions,

there is virtually no chance of limiting heating to 2° C even with full policy implementation

(Rogelj et al. 2009). For Hawaii, only a low global emissions scenario would likely keep

temperature increases to 2° C (Karl et al. 2009).

An added concern is the risk of abrupt increases in global temperature unaccounted for in most

modeled climate projections (Lovelock 2009). For example, a global climate model used by

Sokolov et al. (2009) did not fully incorporate positive feedbacks that may occur, for example, if

increased temperatures cause a large-scale melting of permafrost in arctic regions and

subsequently release large quantities of methane, a very potent greenhouse gas (Rice 2009). If

these positive feedback loops should occur, and evidence in mounting that they will (McCarthy

2010), temperatures are likely to increase to an even greater degree in Hawaii.

For Hawaii, Giambelluca et al. (2008) document a long-term increase in temperature and an

accelerated rate of increase over the past few decades consistent with global trends (0.04° C

C/decade over an 88-year period, and about 0.2° C/decade since 1975). Moreover, since 1975

higher elevation temperatures exceeded average warming (a 0.27° C/decade increase) with

steepest increases in minimum (night time) temperature (near 0.5° C/decade), which is likely the

most limiting for malaria transmission. The recent surface temperature trend in Hawaii is only

slightly lower than the overall global trend. Similar surface warming has been detected elsewhere

in the Pacific, and is associated with an increase in sea surface temperatures, upper ocean heat

content, and sea level height (Richards and Timmermann 2008).

In Hawaii, the upper limit of mosquito presence appears to have increased substantially, from

about 600 m in the late 1960s to 1100-1500 m in recent decades (Pratt 2005). Freed et al. (2005)

reported that prevalence of malaria in Hawaiian forest birds at 1900 m on the island of Hawai‘i

more than doubled over a decade. A highly significant increase of malaria in `I`iwi was

11

associated with much warmer summertime air temperatures. The 13° C threshold for malaria

development projected for 1900 m sites by the conservative Benning et al. (2002) model was

surpassed in 2001 by a wide margin (4.4° C; Freed et al. 2005). Measured temperatures were

believed to exceed model expectations because the site was strongly affected by the island’s

trade wind inversion layer related to tropical air circulation. The altitude of the inversion has

averaged 1900 m, above which cooler, drier conditions prevail (Atlas of Hawaii, 3rd edition). The

response of the inversion layer to climate heating is uncertain (Pounds et al. 1999, Loope and

Giambelluca1998). If the inversion layer rises, disease epizootics could become commonplace at

higher elevations with devastating short-term consequences for `I`iwi. If the inversion falls, and

higher temperatures become associated with high-elevation drought, the effects would be very

damaging to upper elevation Hawaiian forests and ultimately to surviving honeycreepers

including the `I`iwi (Benning et al. 2002). Given that scenario, or if the inversion layer remains

stable, high-elevation forest bird populations may be squeezed between expanding disease

transmission from lower elevations and the upper limits of suitable habitat (Atkinson and

LaPointe 2009).

Hawaii may see an increased frequency of heavy rain events and increased rainfall during

summer months (Karl et al. 2009), conditions that, along with increased temperature, are likely
to facilitate breeding of malaria-carrying mosquitoes (Ahumada et al. 2004). At the same time,

overall annual precipitation for the Hawaiian Islands may decline (Chu and Chen 2005) thereby

affecting habitat quality (e.g., ‘ōhi‘a forest) for the `I`iwi.

Ectoparasites, particularly chewing lice (Phthiraptera), may impact `I`iwi by increasing

morbidity and reducing the ability of birds to survive environmental challenges.

Freed et al. (2008) documented an explosive increase in the prevalence of chewing lice in all bird

host species at a study site on Hawaii Island. The number of major fault bars in wing and tail

feathers, a sign of nutritive stress, was correlated with intensity of infection, suggesting an

indirect cost to parasitized birds. Poorer body condition preceded the outbreak indicating the

synergistic effect of multiple stressors on forest birds. At a minimum, chewing lice will increase

food requirements of hosts. This indirect cost may be especially relevant because it can affect the

ability of birds to mount a sufficient immune defense against diseases like avian malaria and pox.

Chewing lice may also directly contribute to bird mortality (Freed et al. 2008).

Additional risks to `I`iwi from disease include potential introductions of West Nile virus, new

avian malaria vectors (such as temperate varieties of Culex quinquefaciatus), or biting midges

(Culicoides) that transmit avian diseases.

Predation

Introduced rats are serious predators on adults and nests of Hawaiian forest birds, and are

abundant in high elevation habitats (Atkinson 1977, Scott et al. 1986, Fancy and Ralph 1998,

VanderWerf and Smith 2002). Feral cats, introduced small Indian mongoose, and the native

Short-eared Owl and introduced Barn Owl may also impact native Hawaiian birds (Scott et al

1986; Kowalsky et al. 2002). Predator control efforts generally have not been conducted over

areas large enough to result in significant improvement in the status of imperiled forest birds

12

(USFWS 2006). Logistical and other obstacles to predator control can be great, especially in

rugged bird habitat.

D. Inadequacy of existing regulatory mechanisms.

Existing international and U.S. regulatory mechanisms to reduce global greenhouse gas

emissions are clearly inadequate to safeguard the `I`iwi against extinction resulting from climate

change, which is expected to cause a severe shrinkage of disease free habitat for the ‘I’iwi.

United States Climate Initiatives are Ineffective

The United States is responsible for over 20% of worldwide carbon dioxide emissions (USEIA

2004), yet does not currently have adequate regulations to reduce greenhouse gas emissions.

This was acknowledged by the Department of Interior in the final listing rule for the polar bear,

which concluded that regulatory mechanisms in the United States are inadequate to effectively

address climate change (73 Fed. Reg. 28287-28288). While existing laws including the Clean Air

Act, Energy Policy and Conservation Act, Clean Water Act, Endangered Species Act, and others

provide authority to executive branch agencies to require greenhouse gas emissions reductions

from virtually all major sources in the U.S., these agencies are either failing to implement or only

partially implementing these laws for greenhouse gases. For example, the EPA has recently

issued a rulemaking regulating greenhouse gas emissions from automobiles (75 Fed. Reg. 25324,

Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy

Standards; Final Rule), but has to date failed to implement the majority of other Clean Air Act

programs, such as the new source review, the new source pollution standards, or the criteria air

pollutant/national ambient air quality standards programs, to address the climate crisis (See, e.g.

75 Fed. Reg. 17004, Reconsideration of Interpretation of Regulations That Determine Pollutants

Covered by Clean Air Act Permitting Programs). While full implementation of these flagship

environmental laws, particularly the Clean Air Act, would provide an effective and

comprehensive greenhouse gas reduction strategy, due to their non-implementation, existing

regulatory mechanisms must be considered inadequate to protect the ‘I’iwi from climate change.

International Climate Initiatives are Ineffective

The primary international regulatory mechanisms addressing greenhouse gas emissions are the

United Nations Framework Convention on Climate Change and the Kyoto Protocol. As

acknowledged by the Department of Interior in the final listing rule for the polar bear, these

international initiatives are inadequate to effectively address climate change (73 Fed. Reg.

28287-28288). Additionally, the Kyoto Protocol’s first commitment period only sets targets for

action through 2012. Importantly, there is still no international agreement governing greenhouse

gas emissions in the years beyond 2012. Thus international regulatory mechanisms must be

considered inadequate to protect the ‘I’iwi from climate change.

While the 2009 U.N. Climate Change Conference in Copenhagen called on countries to hold the

increase in global temperature below 2 degrees Celsius, the non-binding “Copenhagen Accord”

that emerged from the conference fails to enact binding regulations that limit emissions to reach

this goal. Even if country’s did meet their pledges, a summary by the Pew Center (2010) of four

13

analytical reviews of the Accord found that collective national pledges to cut greenhouse gas

emissions are inadequate to achieve the 2° C goal, and instead suggest emission scenarios

leading to a 3 to 3.9° C warming.

Regulations to protect high elevation forests that could serve as refugium for ‘I’iwi are

inadequate

Current regulatory mechanisms are inadequate to conserve high elevation forests needed to

buffer the `I`iwi and other susceptible forest birds against the upslope advance of avian diseases

driven by global heating. While some progress has been made to reforest former upper elevation

habitat areas with native trees and reduce or eliminate harmful alien species from existing ones,

huge tracts of land needed for forest bird conservation in Hawaii remain degraded or without

native tree cover (USFWS 2009). A preponderance of lands intended for forest bird recovery are

not managed conservation lands (Pratt et al. 2009). Management actions identified in existing

forest bird recovery plans have not been implemented at ecologically relevant scales, and

successful efforts to restore higher elevation forests must occur across tens of thousands of areas,

not hundreds (Scott 2009). On the Island of Maui, for example, more than half of the lands

identified for forest bird recovery remain without native forests, have only remnant forest
patches, or are dominated by introduced tree species and other alien vegetation (A. Povilitis,

pers. com.). Yet restoration of high elevation koa/`ōhi`a forest to protect native birds is clearly a

conservation priority (Scott et al.1986, USFWS 2006)

At current rates, reforestation and forest enhancement efforts for Hawaiian forest birds will not

achieve habitat conservation goals in time to build and expand populations robust enough to

withstand avian malaria and other consequences of climate change. Of over 140 actions for

forest bird recovery relating to reforestation and securing recovery areas (USFWS 2006), 61%

have not begun, 37% are ongoing, and only 2% are complete or partially so (USFWS 2009).

Likewise, of more than 160 actions designed to reduce or eliminate exotic ungulates and

mammalian bird-predators, 71% are not yet underway, 27% are ongoing, and less than 2 % are

complete or partially complete.

Poor political and policy decisions are responsible for the current inadequacy of regulatory

mechanisms to prevent forest bird extinctions. The problem includes conflicting management

goals and policies, most notably involving state forest lands (USFWS 2006, 2009), and failure to

provide necessary funding (Leonard 2008).

Leonard (2009) discusses political obstacles to saving Hawaiian forest birds, including a state

mandate to provide public hunting opportunities of exotic ungulates even where incompatible

with conservation of native birds. Actions such as fencing and ungulate control for bird

conservation may result in the loss of hunting areas, which is very controversial within his state

agency (Leonard 2008). Even proposals for protecting limited forest in areas of little or no

public access receive fierce opposition from local hunters (San Nicolas 2010). Native forest

restoration is also hampered by agency decisions favoring exotic tree species or leasing for

livestock (USFWS 2006).

14

The `I`iwi, like all other Hawaiian honeycreepers, is not included on the list of species protected

under the Migratory Bird Treaty Act and thus receives no protection under federal law.

E. Other natural or manmade factors affecting its continued existence.

Climate change

Global heating threatens `I`iwi by increasing the elevation at which regular transmission of

avian

malaria and avian pox virus occurs (Benning et al. 2002, Harvell et al. 2002). It is the primary

reason

why the species merits listing under ESA at this time (review discussion under section C for

details).

Catastrophic events

Epizootics involving avian malaria or other pathogens could eliminate remaining `I`iwi from the

lower elevation islands of Kauai, Oahu, and Molokai, and from west Maui in the near term, and

could diminish and fragment 'I'iwi populations on higher elevation east Maui and Hawaii Island.

There is currently no habitat on Kauai, Oahu, and Molokai where mean ambient temperature

entirely

restrict malaria development (Benning et al. 2002). These islands are vulnerable to avian

malaria at

all elevations on a more or less ongoing basis. A recent avian malaria outbreak on Hawaii

Island

was associated with increases in summertime temperatures related to tropical inversion layer

conditions (Freed et al. 2005). Outbreaks of malaria can be triggered by warm periods linked

to

inversion layer dynamics or El Niño events, and will likely intensify and persist longer with

ongoing

climate change.

Hurricanes are known for their devastating effects on island birds (Foster et al. 2004). They

reduce habitat by blowing down trees and by creating forest openings that facilitate the spread

of

invasive alien plants. The `I`iwi decline on Kauai after a 1992 hurricane may have partially

resulted from the birds seeking substitute nectar resources at lower elevations where risk of

malaria transmission is highest (Foster et al. 2004).

Hurricanes are likely to intensify in a warmer climate (Meehl et al. 2007) in terms of wind

speeds and precipitation, though the number of storms may be fewer (Bengtsson et al. 2007).

Infectious mosquitoes can be carried upslope in strong winds, a probable factor in malaria

outbreaks on Hawaii above 1900 m elevation (Freed et al. 2005).

On Hawaii Island, volcanism presents a potential threat to substantial acreage of forest bird

habitat. For example, a large portion of the Upper Waiākea Forest Reserve, location of some of

the last observations of `Ō`ū and considered prime habitat for the species, was inundated by the

1984 Mauna Loa lava flow which destroyed thousands of acres of forest and created a treeless

corridor over 1 km wide (USFWS 2006).

Introduced Competitors

Introduced species of insects and birds can compete with native birds for food and other
resources. `I`iwi may face competition from Japanese White-eye (Zosterops japonicas)

(Mountainspring and Scott 1985), a malaria resistant species, whose numbers have increased at

least on Kauai over the past 30 years (Foster et al. 2004). Negative correlations between `I`iwi

15

and Japanese White-eye densities may stem from competition for limited nectar resources (Fancy

and Ralph 1998). There are no current efforts to control competing species within the recovery

areas of endangered forest birds (USFWS 2006).

Population fragmentation and isolation

'I'iwi populations have suffered from fragmentation as well as reduced size and range. Small

population units are at risk of extinction from random demographic fluctuations, localized

catastrophes (severe storms, wild fire, disease outbreaks, volcanism, etc.), inbreeding

depression,

and genetic drift (Primack 2006).

IV. Request for Critical Habitat SINCE Current situation after accident in

Fukushima, JAPAN (update: 2. April 2011 12:00) status of the radioactivity

measurements 

the world-wide measurements of the radioactivity in the context of the

comprehensive atomic test stop agreement(CTBT) show at present (status of

the measurements: 29. March 2011) further that traces of iodine and cesium

are to be found at present at nearly all measuring points of the north

hemisphere. To Europe the stations point in Freiburg/Germany and

Stockholm/Sweden Jod-131 concentrations of 250 and/or 1700 μBqm-3. Such

values were registered also The material measured at present was already set

free 14 days ago in Japan

advance upslope in response to higher ambient temperatures.

When the USFWS lists a species as endangered or threatened under ESA it must concurrently

designate critical habitat for that species “to the maximum extent prudent and determinable.” The

ESA defines the term “critical habitat” to mean: i. the specific areas within the geographical area

occupied by the species, at the time it is listed . . . on which are found those physical or

biological features (I) essential to the conservation of the species and (II) which may require

special management considerations or protection; and ii. specific areas outside the geographical

area occupied by the species at the time it is listed . . . upon a determination by the Secretary [of

Interior] that such areas are essential for the conservation of the species.

Critical habitat for `I`iwi is needed to ensure that federal actions avoid jeopardizing the species

and help promote its conservation. Designation would help inform federal and state governments

and private landowners on conservation planning, habitat management, and other actions needed

to secure habitat, and help address conflicts that undermine its protection and restoration.

To reduce the climate change/disease threat, `I`iwi habitat requires special management

including reforestation and forest protection adequate to sustain the species. Specific measures

include elimination or control of alien species inimical to the survival of `I`iwi, and special

measures to monitor and reduce (or eliminate) occurrence of avian malaria vectors. Programs to

re-establish native forests, reduce rat depredation, control weeds, and fence out and remove

ungulates are essential for forest bird recovery in high elevation habitats that serve as native bird

refugia (Gorresen et al. 2005). Reducing mortality, such as that caused by rodent predation, may

lessen the threat from disease by improving survival and reproduction of any birds with disease

tolerance or natural immunity (VanderWerf and Smith 2002). The evolutionary acceleration of

disease resistance through rodent control is possible (USFWS 2006).

Critical habitat should include all areas needed to provide sufficient forested habitat to support

viable or potentially viable `I`iwi populations on Kauai, Oahu, Molokai, Maui, and Hawaii

Island, as each island represents a significant portion of the species’ natural range. This should

include areas on Maui and Hawaii Island above the current limit of tree growth to accommodate

any forest expansion resulting from climate change.

16

Critical habitat designation for `I`iwi will extend habitat protection to other listed endangered

Hawaiian birds, where ranges overlap. Unfortunately, most currently listed forest birds do not

have critical habitat designations.

V. Conclusion

The best available science indicates that global warming

Current situation after accident in Fukushima, JAPAN (update: 2. April 2011 12:00) status of the radioactivity measurements 

the world-wide measurements of the radioactivity in the context of the comprehensive atomic test stop agreement(CTBT) show at present (status

of the measurements: 29. March 2011) further that traces of iodine and cesium are to be found at present at nearly all measuring points of the

north hemisphere. To Europe the stations point in Freiburg/Germany and Stockholm/Sweden Jod-131 concentrations of 250 and/or 1700 μBqm3.ALSO CEISIUM 137 Such values were registered also The material measured at present was already set free 14 days ago in Japan

advance upslope in response to higher ambient temperatures.

,RADDS its contribution to future elNINIO EFFECT , AND CHEMICALS will allow avian diseases to spread

throughout most or all of the `I`iwi’s geographic range. The `I`iwi is highly vulnerable to avian

diseases and cannot sustain itself where disease prevails.
`I`iwi in the central portion of the species’ range (Oahu, Molokai, and west Maui AND THE ATULL ISLANDS ) are critically

endangered because of small population sizes and exposure to malaria. Those to the west (on

Kauai) are severely threatened as disease free habitat is fast disappearing. `I`iwi AND THE ATULL ISLANDS Endangered Species ANY AND

ALL INFINITE in the eastern

portion of the range (east Maui Hawaii Island AND THE ATULL ISLANDS ) face further population declines and eventual

extinction with ongoing climate change.

The `I`iwi warrants listing under the US Endangered Species Act with concurrent designation of

critical habitat.

VI. Literature Cited

Director FOR FREE THE ATULL ISLANDS Endangered Species; Marine

Mammals, Hawaii Bottom fish, Seamount Ground fish & ERADICATE

THE RATS /DIRECTOR ROWN PAUL BROWN SR.

Current situation after accident in Fukushima, JAPAN (update: 2. April

2011 12:00) status of the radioactivity measurements 

the world-wide measurements of the radioactivity in the context of the

comprehensive atomic test stop agreement(CTBT) show at present (status of

the measurements: 29. March 2011) further that traces of iodine and cesium

are to be found at present at nearly all measuring points of the north

hemisphere. To Europe the stations point in Freiburg/Germany and

Stockholm/Sweden Jod-131 concentrations of 250 and/or 1700 μBqm-3.ALSO

CEISIUM 137 Such values were registered also The material measured at

present was already set free 14 days ago in Japan

advance upslope in response to higher ambient temperatures.

AND THESE

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P.S. Dr. Elizabeth Flint/ IF YOU COULD PLEASE SUPPLY ME WITH A E-MAIL ADDRESS OFFICIAL AND AS TO COMMUNICATE

ABOUT 

‘‘Palmyra rat project’’/
CONFIDENTIALITY NOTICE: This email transmission, including any attachments, is LEGAL PRIVILEGED intended only for the

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From: RALPH BLACK

To: pacific_reefs@fws.gov; RALPH BLACK

Subject: ‘‘Palmyra rat project’’ in subject line/THANKS

Date: 04/12/2011 07:12 AM

DEAR: Dr. Elizabeth Flint THANKS FOR YOUR OFFICE QUICK RESPONSE The FRIENDS OF ATULL

ISLANDS Marine Mammals, Hawaii Bottom fish, Seamount Ground fish Fisheries Endangered Species

ANY AND ALL INFINITE /PETITION TO LIST THE ATULL ISLANDS Endangered Species ANY AND

ALL INFINITE

‘‘Palmyra rat project’’ DEPARTMENT OF THE INTERIOR/PRAYER FOR TIME ‘‘Palmyra rat project’’ 

WE LOOK FORWARD TO SERVING Endangered Species / PROTECTED AREAS OF ATULL ISLANDS

AND YOUR OFFICE / WE WILL BE HERE AND AT PHONE#[209] 985 1257

24/7 AND PLEASE CONTACT US AS SOON AS POSSIBLE AS FUEL COST'S GOING UP AND

MARINE DONATIONS FOR SUPPORT ARE HARDER BY THE DAY AS ALSO AVIATION FUEL IF

ALLOWED AIR ACCESS FOR THE HELP OF ALL CONCERNED TO ATULL ISLANDS. MY /OUR/ US

AND FRIENDS BELIEVE WE HAVE A FREE OF CHEMICAL ERADICATION FOR THE RATS OF

‘‘Palmyra rat project’’ ATULL ISLANDS AND WILL BE WILLING TO WORK ALONG SIDE THE

PROVIDERS OR CARETAKERS OF THE PALMS OR ANY AND ALL THAT ARE BEING DECIMATED

BY THE RATS OR ANY FOREIGN INVADERS OF ANY NATURE TO THE ATULL ISLANDS. AND

ALSO IF EMPOWERED TO PARTIAL CHEMICAL ERADICATIONS WE WOULD CARE TO NOT

ASSIST IN THE CHEMICAL PORTION. BUT TO REFEREE AS SAFEGUARD FOR AREAS TOO

DELICATE FOR CHEMICAL ERADICATION. AS WE CONTEND NOT EVEN A BIODEGRADABLE IS

SAFE FOR ALL THE ATULL ISLANDS WE BELIEVE WE HAVE ALL NATURAL PROCEDURES

THAT ALONE OR COMBINED WILL SAFELY ERADICATE BY WELL PROVEN AND

LONGSTANDING AMERICAN MEANS WITH PROVEN AND SAFE TRACK RECORD WITH POSITIVE

FINAL RESULT. A.K.A.RALPH BLACK = ROWN PAUL BROWN SR.= @BEARBOOBOO1@LIVE.COM

FOR MODERN DAY ELECTRONIC COMMUNICATION PLEASE NOTIFY THIS E-MAIL ADDRESS & PHONE NUMBER PROVIDED

ABOVE FOR ANY LEGAL NECESSITY FOR LEGAL PAPER MOVEING FOR THE SAFE GAURD OF THE ATULL ISLANDS.

E-mail: pacific_reefs@fws.gov. Include

‘‘Palmyra rat project’’ in subject line

ROWN PAUL BROWN SR.

Director FOR FREE THE ATULL ISLANDS Endangered Species; Marine Mammals, Hawaii Bottomfish, Seamount Groundfish &

ARRADICATE THE RATS

A.K.A.RALPH BLACK = ROWN PAUL BROWN SR.= @BEARBOOBOO1@LIVE.COM

CONFIDENTIALITY NOTICE: This email transmission, including any attachments, is LEGAL PRIVILEGED intended only for the

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permanently delete this transmission, including any attachments
U.S. Department of the Interior

U.S. Fish and Wildlife Service

Pacific Remote Islands Marine National Monument

Palmyra Atoll National Wildlife Refuge

300 Ala Moana Boulevard, Suite 5-231

Box 50167

Honolulu, HI 96850

http://www.fws.gov

May 2011