U.S. Fish & Wildlife Service

Midway Seabird

Protection Project

Draft Environmental Assessment

Sand Island, Midway Atoll,

Papaha

-

naumokua

-

kea Marine National

Monument
Front cover:

A male albatross bonds with his chick Ku

-

kini, 

a Hawaiian word for messenger. The mother - 

an albatross named Wisdom who is the world’s 

oldest known wild bird - is off foraging at sea. 

In her lifetime, Wisdom has raised over 35 

chicks.

Credit: Kiah Walker/USFWS Volunteer
Midway Seabird Protection Project

Draft Environmental Assessment

Sand Island, Midway Atoll, 

Papahanaumokuakea Marine National Monument

Prepared for:

U.S. Fish and Wildlife Service

Cooperating Agency

USDA APHIS Wildlife Services

National Wildlife Research Center

Prepared by: 

Hamer Environmental L.P. and Planning Solutions, Inc.

March 2018

- -

DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

EXECUTIVE SUMMARY

ES-1 

EXECUTIVE SUMMARY

Midway Atoll National Wildlife Refuge (MANWR) lies in the North Pacific Ocean 

approximately equidistant between North America and Asia. The refuge is also designated the 

Battle of Midway National Memorial and is within the Papahānaumokuākea Marine National 

Monument. The fringing coral reef, shallow lagoons, and 3 low-lying islands (Sand, Eastern, 

and Spit Islands), are the breeding grounds for millions of seabirds, the wintering grounds for 

thousands of shorebirds, and a refuge for critically endangered species like the Hawaiian monk 

seal (Monachus schauinslandi) and Laysan duck (Anas laysanensis). Over 70% of the total 

global population of Laysan albatross (Phoebastria immutabilis) breeds at the refuge; with the 

majority of the Midway population nesting on the 1,128-acre Sand Island.

This Environmental Assessment (EA) documents an action proposed by the United States Fish 

and Wildlife Service (USFWS), Papahānaumokuākea Marine National Monument (PMNM) and 

presents the anticipated environmental effects of both the Proposed Action and a No Action 

alternative. The Proposed Action is to eradicate house mice (Mus musculus) from Sand Island by 

delivering a lethal dose of rodenticide to every rodent in a manner that minimizes harm to island 

residents and the ecosystem while still maintaining a high probability of success, and to maintain 

the island in rodent-free status in perpetuity. The toxicant to be employed as part of the Proposed 

Action would be Brodifacoum-25D Conservation, a pelleted rodenticide bait intended for 

conservation purposes for the control or eradication of invasive rodents on islands or vessels. 

Implementation of the proposed action is currently being considered for Summer, 2019. 

This action was identified in the Papahānaumokuākea Monument Management Plan (PMMP), 

completed in December 2008, as Strategy AS-4 with a goal of developing an eradication plan 

within 5 years. The need for the action was reinforced when, in 2015, mice were confirmed to 

be feeding on the backs and necks of adult albatross nesting on Sand Island, leading to nest 

abandonment and mortality of adults, eggs and chicks. The Proposed Action was identified in 

the PMMP for many reasons, among them the fact that worldwide invasive species are a leading 

cause of island species extinctions including mammal, bird, reptile, and invertebrates. Forty to 

sixty % of all recorded bird and reptile extinctions are attributed to invasive rodents. 

The USFWS is proposing the Action to protect seabirds and their habitats on MANWR’s Sand 

Island. The other islands of MANWR, Eastern and Spit, are not included because mice are not 

currently present on them. The USFWS is planning and would conduct the Action with technical 

support from Island Conservation (IC) and the Midway Restoration Partnership Group, which is 

a multidisciplinary stakeholder body including representatives from USFWS, Island 

Conservation, American Bird Conservancy, U.S. Department of Agriculture (USDA) Animal 

and Plant Health Inspection Service (APHIS) National Wildlife Research Center (NWRC), the 

National Oceanographic and Atmospheric Agency (NOAA), U.S. Geological Survey (USGS), 

and the State of Hawaiʻi Office of Hawaiian Affairs.

Removing mice would improve the MANWR’s ability to restore the natural island ecosystem, 

benefitting native coastal plants and insects. The proposed action would improve seabird nesting 

habitat and could aid in the recovery of rare seabirds such as the short-tailed albatross 
MIDWAY SEABIRD PROTECTION PROJECT DRAFT ENVIRONMENTAL ASSESSMENT

EXECUTIVE SUMMARY 

ES-2 

(Phoebastria albatrus), Bulwer’s petrel (Bulweria bulwerii), and Tristram’s storm-petrel 

(Oceanodroma tristrami).

The proposed action involves the aerial broadcast of bait pellets containing rodenticide into all 

potential mouse territories on Sand Island along with supplemental hand broadcasting of bait in 

sensitive areas (e.g., narrow shorelines) and placing bait stations in commensal areas. The 

USFWS also considered other alternatives and methods to eradicate mice on Sand Island but 

these were dismissed from analysis since they failed to meet the purpose and need of the project. 

Mouse eradication would occur in the summer dry season to maximize the probability of success 

by targeting mice when their food resources are lowest and their abundance is declining. 

Conducting the operation during this period would also minimize the risk of rain washing 

rodenticide pellets into the ocean and is also a period of low winds, which makes bait application 

easier to control. It is also the time of year when relatively few wintering shorebirds, which may 

be susceptible to primary and secondary poisoning, are present; relatively few seabirds are also 

present at this time because the majority have completed breeding and have left the island. The

lower numbers of seabirds present on MANWR at this time of year also reduces, but does not 

eliminate, the potential for collisions between operational aircraft and seabirds. 

The endangered Laysan duck, a year-round resident species, would be present at this time. Also, 

several species of water and land birds may be present during implementation. Protective 

measures would be implemented to avoid and minimize impacts to them. This EA evaluates the 

likelihood and magnitude of these incidental bird mortalities, and decribes the avoidance and 

minimization measures that will be implemented to reduce bird mortalities. This EA will also be 

used for consultation under Section 7 of the Endangered Species Act and for consulting with 

NOAA related to Essential Fish Habitat. 

The USFWS is responsible for the final decision on the Action along with the plans for 

implementation and monitoring. The USFWS anticipates that the Proposed Action would have a 

less than significant adverse impact on the environment when it is conducted as outlined in this 

EA, including the implementation of the avoidance, minimization, and mitigation policies and 

actions.
DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

EXECUTIVE SUMMARY

ES-3 

Project: Midway Seabird Protection Project

Agency: U.S. Fish and Wildlife Service

Papahānaumokuākea Marine National Monument 

300 Ala Moana Boulevard, Room 5-231 

Honolulu, Hawai‘i 96850 

Submit Comments to: Midway_Comments@fws.gov

Cooperating Agencies: USDA APHIS NWRC

Affected Location: Sand Island, MANWR, Northwestern Hawaiian Islands

Proposed Action: Eradication of invasive mice on Sand Island, MANWR

via rodenticide.

Island & Project Area: 1,128 acres (456.5 hectares)

Required Permits & Approvals: • National Environmental Policy Act (NEPA) 

Environmental Assessment 

• Section 7, Endangered Species Act (ESA) 

• Section 106, National Historic Preservation Act 

(NHPA)

• Essential Fish Habitat

• Federal Insecticide, Fungicide, and Rodenticide 

Act (FIFRA) Supplemental Label

• National Pollutant Discharge Elimination 

System (NPDES) Permit

• Marine National Monument Permit 

Anticipated Determination: No Significant Impacts 

Parties Consulted: See Chapter 7.0

Consultants: Hamer Environmental

Planning Solutions, Inc.
MIDWAY SEABIRD PROTECTION PROJECT DRAFT ENVIRONMENTAL ASSESSMENT

EXECUTIVE SUMMARY 

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THIS PAGE INTENTIONALLY LEFT BLANK 
DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

TABLE OF CONTENTS

i 

TABLE OF CONTENTS

CHAPTER 1: PURPOSE AND NEED .................................................................................... 1-1

1.1 INTRODUCTION..................................................................................................................................................1-1

1.2 PURPOSE OF THE ACTION ..................................................................................................................................1-2

1.3 NEED FOR THE ACTION......................................................................................................................................1-3

1.3.1 Effects of Introduced Invasive Species on Islands .................................................................................1-3

1.3.2 Effects of Introduced mice on MANWR................................................................................................1-4

1.3.3 MANWR Ecosystem Management and conservation plans...................................................................1-6

1.3.3.1 Papahānaumokuākea Monument Management Plan (PMMP) .........................................................1-6

1.3.3.2 Conservation Action Plan for Black-footed albatross and Laysan albatross.....................................1-7

1.3.3.3 U.S. Fish and Wildlife Service Regional Seabird Conservation Plan...............................................1-7

1.4 REGULATORY REQUIREMENTS ..........................................................................................................................1-8

1.5 PROJECT PARTICIPANTS ....................................................................................................................................1-9

1.5.1 U.S. Fish and Wildlife Service (USFWS), - Lead Agency.....................................................................1-9

1.5.2 U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife services (WS) 

and the National Wildlife Research Center (NWRC) - Cooperating Agency.......................................1-10

1.5.3 Memorandum of Understanding (MOU) Between Island Conservation, USDA (APHIS), American Bird 

Conservancy and the USFWS ..............................................................................................................1-10

1.5.4 Island Conservation ..............................................................................................................................1-11

1.5.5 Midway Restoration Partnership ..........................................................................................................1-11

1.6 ORGANIZATION OF THE EA .............................................................................................................................1-11

CHAPTER 2: DESCRIPTION OF THE PROJECT AND ALTERNATIVES ................... 2-1

2.1 PRINCIPLES OF RODENT ERADICATION IN ISLAND ECOSYSTEMS.......................................................................2-1

2.2 MANWR TECHNICAL CONSIDERATIONS ..........................................................................................................2-3

2.2.1 Constraints on Successful Eradication....................................................................................................2-3

2.2.1.1 Manmade Structures .........................................................................................................................2-4

2.2.1.2 Native Species...................................................................................................................................2-5

2.2.1.3 Resident Community on Sand Island................................................................................................2-5

2.2.2 Bait Distribution Approaches.................................................................................................................2-6

2.2.2.1 Bait Stations......................................................................................................................................2-6

2.2.2.2 Broadcast ..........................................................................................................................................2-6

2.2.2.2.1 Hand Broadcast .....................................................................................................................2-7

2.2.2.2.2 Aerial Broadcast....................................................................................................................2-7

2.2.2.3 Summary...........................................................................................................................................2-8

2.2.3 Rodenticide and Bait Considerations......................................................................................................2-9

2.3 PREFERRED ALTERNATIVE: MOUSE ERADICATION WITH RODENTICIDE VIA MULTIPLE DISTRIBUTION METHODS2-10

2.3.1 Bait and Its Distribution Methods.........................................................................................................2-10

2.3.1.1 Primary Distribution Method – Aerial Broadcast ...........................................................................2-11

2.3.1.2 Secondary Distribution Method – Supplemental Hand Broadcast..................................................2-12

2.3.2 Number and Rate of Bait Applications.................................................................................................2-12

2.3.3 Mechanical Trapping............................................................................................................................2-13

2.3.4 Pre-Application Preparations................................................................................................................2-13

2.3.5 Application Schedule............................................................................................................................2-14

2.3.6 Mitigation Actions and Effectiveness Monitoring................................................................................2-15

2.3.7 Post-Application Actions......................................................................................................................2-15

2.3.8 Contingency Planning...........................................................................................................................2-16

2.4 ALTERNATIVE 2: NO ACTION ..........................................................................................................................2-16
ii

2.5 ALTERNATIVES CONSIDERED BUT REJECTED ..................................................................................................2-17

2.5.1 Emerging Technologies........................................................................................................................2-18

2.5.2 Mouse Eradication Using Cholecalciferal (Agrid3) Rodenticide .........................................................2-18

2.5.3 Use of First-Generation Rodenticide ....................................................................................................2-18

2.5.4 Mouse-Proofing Structures...................................................................................................................2-20

2.5.5 Aerial Broadcast Rodenticide Only ......................................................................................................2-20

2.5.6 Hand Broadcast Rodenticide Only .......................................................................................................2-20

2.5.7 Bait Station Rodenticide Only ..............................................................................................................2-21

2.5.7.1 Non-Target Species.........................................................................................................................2-21

2.5.7.2 Operational Challenges...................................................................................................................2-21

2.5.8 Mouse Control......................................................................................................................................2-22

2.6 PROJECT COSTS...............................................................................................................................................2-22

CHAPTER 3: AFFECTED ENVIRONMENT, ENVIRONMENTAL IMPACTS, & 

MINIMIZATION MEASURES ................................................................................... 3-1

3.1 GENERAL DESCRIPTION OF MANWR ...............................................................................................................3-1

3.2 RESOURCE TOPICS EXCLUDED FROM DETAILED ANALYSIS..............................................................................3-2

3.2.1 Land Use.................................................................................................................................................3-2

3.2.1.1 Wildlife Refuge.................................................................................................................................3-3

3.2.1.2 National Memorial............................................................................................................................3-4

3.2.1.3 Airport...............................................................................................................................................3-4

3.2.2 Access.....................................................................................................................................................3-4

3.2.2.1 Air Transportation.............................................................................................................................3-4

3.2.2.2 Marine Transportation ......................................................................................................................3-5

3.2.3 Climate ...................................................................................................................................................3-5

3.2.4 Visual Resources ....................................................................................................................................3-6

3.2.5 Fuel Facilities .........................................................................................................................................3-6

3.2.6 Energy ....................................................................................................................................................3-6

3.2.7 Communications.....................................................................................................................................3-6

3.2.8 Air Quality..............................................................................................................................................3-7

3.2.9 Geologic Resources................................................................................................................................3-7

3.2.10 Socioeconomic and Environmental Justice ............................................................................................3-7

3.2.11 Solid Waste Disposal..............................................................................................................................3-8

3.2.12 Historical and Cultural Resources and Values........................................................................................3-8

3.2.12.1 Programmatic Agreement and Treatment of Midway’s Historic Properties...................................3-10

3.2.12.2 Historic Preservation Plan...............................................................................................................3-10

3.3 RESOURCES TOPICS ANALYZED IN DETAIL IN THIS EA ...................................................................................3-10

3.3.1 Airfield Operations...............................................................................................................................3-10

3.3.1.1 Existing Conditions.........................................................................................................................3-10

3.3.1.2 Probable Impacts.............................................................................................................................3-11

3.3.2 Water Resources...................................................................................................................................3-11

3.3.2.1 Existing Conditions: Groundwater..................................................................................................3-11

3.3.2.2 Existing Conditions: Surface Water................................................................................................3-12

3.3.2.3 Existing Conditions: Potable and Non-Potable Water Systems......................................................3-12

3.3.2.4 Probable Impacts.............................................................................................................................3-13

3.3.3 Noise.....................................................................................................................................................3-15

3.3.3.1 Existing Conditions.........................................................................................................................3-15

3.3.3.2 Probable Impacts.............................................................................................................................3-16

3.3.4 Wastewater and Storm water................................................................................................................3-17

3.3.4.1 Existing Conditions.........................................................................................................................3-17

3.3.4.2 Probable Impacts.............................................................................................................................3-18

3.3.5 Hazardous Materials and Wastes..........................................................................................................3-18
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iii

3.3.5.1 Existing Conditions.........................................................................................................................3-18

3.3.5.2 Probable Impacts.............................................................................................................................3-21

3.3.6 Biological Resources............................................................................................................................3-22

3.3.6.1 Evaluation Criteria for Effects on Biological Resources ................................................................3-22

3.3.6.2 Non-Target Species.........................................................................................................................3-23

3.3.6.3 Environmental Fate of Brodifacoum in Soil and Water..................................................................3-26

3.3.6.4 Terrestrial Environment..................................................................................................................3-30

3.3.6.4.1 Terrestrial Vegetation: Existing Conditions........................................................................3-30

3.3.6.4.2 Dominant Vegetation Types................................................................................................3-31

3.3.6.4.3 Endangered Plants...............................................................................................................3-34

3.3.6.4.4 Probable Impacts: No Action Alternative ...........................................................................3-35

3.3.6.4.5 Probable Impacts: Preferred Alternative .............................................................................3-35

3.3.6.5 Seabirds...........................................................................................................................................3-37

3.3.6.5.1 Existing Conditions: Albatrosses ........................................................................................3-37

3.3.6.5.2 Existing Conditions: Nocturnal seabirds.............................................................................3-38

3.3.6.5.3 Existing Conditions: Noddies..............................................................................................3-39

3.3.6.5.4 Existing Conditions: Terns..................................................................................................3-40

3.3.6.5.5 Existing Conditions: Great Frigatebird ...............................................................................3-40

3.3.6.5.6 Existing Conditions: Tropicbirds ........................................................................................3-41

3.3.6.5.7 Existing Conditions: Boobies..............................................................................................3-41

3.3.6.5.8 Probable Impacts: No Action Alternative ...........................................................................3-41

3.3.6.5.9 Probable Impacts: Preferred Alternative .............................................................................3-42

3.3.6.6 Shorebirds.......................................................................................................................................3-51

3.3.6.6.1 Existing Conditions.............................................................................................................3-51

3.3.6.6.2 Pacific golden plover...........................................................................................................3-51

3.3.6.6.3 Ruddy turnstone ..................................................................................................................3-52

3.3.6.6.4 Wandering tattler.................................................................................................................3-52

3.3.6.6.5 Sanderling ...........................................................................................................................3-52

3.3.6.6.6 Probable Impacts: No Action Alternative ...........................................................................3-55

3.3.6.6.7 Probable Impacts: Preferred Alternative .............................................................................3-55

3.3.6.7 Bristle-thighed curlew.....................................................................................................................3-59

3.3.6.7.1 Existing Conditions.............................................................................................................3-59

3.3.6.7.2 Probable Impacts: No Action Alternative ...........................................................................3-60

3.3.6.7.3 Probable Impacts: Preferred Alternative .............................................................................3-61

3.3.6.8 Laysan duck ....................................................................................................................................3-65

3.3.6.8.1 Existing Conditions.............................................................................................................3-65

3.3.6.8.2 Probable Impacts: No Action Alternative ...........................................................................3-66

3.3.6.8.3 Probable Impacts: Preferred Alternative .............................................................................3-67

3.3.6.9 Land Birds ......................................................................................................................................3-71

3.3.6.9.1 Existing Conditions.............................................................................................................3-71

3.3.6.9.2 Probable Impacts: No Action Alternative ...........................................................................3-73

3.3.6.9.3 Probable Impacts: Preferred Alternative .............................................................................3-73

3.3.6.10 Cattle Egrets....................................................................................................................................3-75

3.3.6.10.1 Existing Conditions ...........................................................................................................3-75

3.3.6.10.2 Probable Impacts: No Action Alternative .........................................................................3-76

3.3.6.10.3 Probable Impacts: Preferred Alternative ...........................................................................3-76

3.3.6.11 Terrestrial Mammals.......................................................................................................................3-77

3.3.6.11.1 Existing Conditions...........................................................................................................3-77

3.3.6.11.2 Probable Impacts: No Action Alternative .........................................................................3-77

3.3.6.11.3 Probable Impacts: Preferred Alternative ...........................................................................3-77

3.3.6.12 Herpetofauna...................................................................................................................................3-77

3.3.6.12.1 Existing Conditions...........................................................................................................3-77

3.3.6.12.2 Probable Impacts: No Action Alternative .........................................................................3-78

3.3.6.12.3 Probable Impacts: Preferred Alternative ...........................................................................3-78

3.3.6.13 Terrestrial Invertebrates..................................................................................................................3-79

3.3.6.13.1 Existing Conditions...........................................................................................................3-79
iv

3.3.6.13.2 Probable Impacts: No Action Alternative .........................................................................3-79

3.3.6.13.3 Probable Impacts: Preferred Alternative ...........................................................................3-79

3.3.6.14 Marine Fish.....................................................................................................................................3-80

3.3.6.14.1 Existing Conditions...........................................................................................................3-80

3.3.6.14.2 Probable Impacts: No Action Alternative .........................................................................3-81

3.3.6.14.3 Probable Impacts: Preferred Alternative ...........................................................................3-81

3.3.6.15 Coral ...............................................................................................................................................3-84

3.3.6.15.1 Existing Conditions...........................................................................................................3-84

3.3.6.15.2 Probable Impacts: No Action Alternative .........................................................................3-86

3.3.6.15.3 Probable Impacts: Preferred Alternative ...........................................................................3-86

3.3.6.16 Essential Fish Habitat .....................................................................................................................3-87

3.3.6.16.1 Existing Conditions...........................................................................................................3-87

3.3.6.16.2 Probable Impacts: No Action Alternative .........................................................................3-91

3.3.6.16.3 Probable Impacts: Preferred Alternative ...........................................................................3-91

3.3.6.17 Marine Invertebrates.......................................................................................................................3-92

3.3.6.17.1 Existing Conditions...........................................................................................................3-92

3.3.6.17.2 Probable Impacts: No Action Alternative .........................................................................3-93

3.3.6.17.3 Probable Impacts: Preferred Alternative ...........................................................................3-93

3.3.6.18 Algae...............................................................................................................................................3-94

3.3.6.18.1 Existing Conditions...........................................................................................................3-94

3.3.6.18.2 Probable Impacts: No Action Alternative .........................................................................3-95

3.3.6.18.3 Probable Impacts: Preferred Alternative ...........................................................................3-95

3.3.6.19 Sea Turtles......................................................................................................................................3-96

3.3.6.19.1 Existing Conditions...........................................................................................................3-96

3.3.6.19.2 Probable Impacts: No Action Alternative .........................................................................3-96

3.3.6.19.3 Probable Impacts: Preferred Alternative ...........................................................................3-97

3.3.6.20 Marine mammals ............................................................................................................................3-98

3.3.6.20.1 Existing Conditions...........................................................................................................3-98

3.3.6.20.2 Probable Impacts: No Action Alternative ....................................................................... 3-102

3.3.6.20.3 Probable Impacts: Preferred Alternative ......................................................................... 3-102

3.3.6.21 Human Health and Safety ............................................................................................................. 3-104

3.3.6.21.1 Existing Environment...................................................................................................... 3-104

3.3.6.21.2 Aerial Operations Safety ................................................................................................. 3-105

3.3.6.21.3 Ground Operations Safety ............................................................................................... 3-105

3.3.6.21.4 Probable Impacts............................................................................................................. 3-106

CHAPTER 4: CUMULATIVE IMPACTS ............................................................................. 4-1

4.1 CUMULATIVE IMPACTS......................................................................................................................................4-1

4.2 PAST ACTIONS...................................................................................................................................................4-1

4.3 CURRENT ACTIONS ...........................................................................................................................................4-2

4.3.1 Plant Restoration and Invasive Weed Control........................................................................................4-2

4.3.2 Lead Abatement......................................................................................................................................4-2

4.3.3 Marine Debris Removal..........................................................................................................................4-2

4.3.4 Mouse Control/Management efforts.......................................................................................................4-2

4.4 FUTURE ACTIONS ..............................................................................................................................................4-3

4.5 PROBABLE CUMULATIVE IMPACTS....................................................................................................................4-3

4.5.1 No Action Alternative ............................................................................................................................4-3

4.5.2 Preferred Alternative ..............................................................................................................................4-4

CHAPTER 5: LIST OF PREPARERS AND CONTRIBUTORS ......................................... 5-1

5.1 PREPARERS........................................................................................................................................................5-1

5.2 CONTRIBUTORS .................................................................................................................................................5-1
DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

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v 

CHAPTER 6: REFERENCES .................................................................................................. 6-1

CHAPTER 7: CONSULTATION & DISTRIBUTION ......................................................... 7-1

7.1 PRE-DRAFT SCOPING PROCESS..........................................................................................................................7-1

7.2 INTERVIEW PROCESS .........................................................................................................................................7-1

CHAPTER 8: STATEMENT OF COMPLIANCE FOR IMPLEMENTATION OF THE 

PROPOSED ACTION AT MANWR ........................................................................... 8-1

8.1 NATIONAL ENVIRONMENTAL POLICY ACT (1969) ............................................................................................8-1

8.2 NATIONAL HISTORIC PRESERVATION ACT (1966).............................................................................................8-1

8.3 EO 12372 INTERGOVERNMENTAL REVIEW .......................................................................................................8-1

8.4 ENDANGERED SPECIES ACT OF 1973.................................................................................................................8-1

8.5 MAGNUSON-STEVENS ACT ESSENTIAL FISH HABITAT......................................................................................8-1

8.6 MIGRATORY BIRD TREATY ACT AND EO 13186 FEDERAL PROTECTION OF MIGRATORY BIRDS ......................8-1

8.7 EO 13112 RESPONSIBILITIES OF FEDERAL AGENCIES PERTAINING TO INVASIVE SPECIES ................................8-2

8.8 INTEGRATED PEST MANAGEMENT, 517 DM 1 AND 569 FW 1 ...........................................................................8-2

8.9 EPA-APPROVED RODENTICIDE LABEL..............................................................................................................8-2

8.10 EPA – NATIONAL POLLUTION DISCHARGE ELIMINATION (NPDES) SYSTEM GENERAL PERMIT ......................8-2

8.11 PAPAHĀNAUMOKUĀKEA MARINE NATIONAL MONUMENT (PMNM) PERMIT...................................................8-2

8.12 EO 12898. FEDERAL ACTIONS TO ADDRESS ENVIRONMENTAL JUSTICE IN MINORITY AND LOW-INCOME 

POPULATIONS..............................................................................................................................................................8-3

8.13 PESTICIDE APPLICATOR CERTIFICATION ...........................................................................................................8-3

CHAPTER 9: GLOSSARY OF TERMS ................................................................................. 9-1

APPENDIX A. MIDWAY ATOLL NATIONAL WILDLIFE REFUGE BIO-SECURITY 

PLAN ....................................................................................................................... A-1

APPENDIX B. SUMMARY OF PROPOSED MONITORING .........................................B-1
vi

LIST OF FIGURES

FIGURE 1.1 LOCATION MAP....................................................................................................................................1-1

FIGURE 1.2 MIDWAY ATOLL NATIONAL WILDLIFE REFUGE (MANWR) ...............................................................1-2

FIGURE 1.3 SAND ISLAND, MANWR .....................................................................................................................1-3

FIGURE 1.4 ADULT LAYSAN ALBATROSS ON SAND ISLAND SHOWING EFFECTS OF PREDATORY MICE.....................1-5

FIGURE 1.5 MOUSE BITING THE HEAD OF ADULT LAYSAN ALBATROSS ON SAND ISLAND ......................................1-5

FIGURE 2.1 GLOBAL MOUSE ERADICATION ATTEMPTS ON ISLANDS OVER TIME AND BY ISLAND SIZE .................2-2

FIGURE 3.1 GENERALIZED LAND USES ON SAND ISLAND.......................................................................................3-3

FIGURE 3.2 WATER RESOURCES ON SAND ISLAND, MANWR..............................................................................3-13

FIGURE 3.3 MONTHLY SPECIES ABUNDANCE OR BREEDING ACTIVITY ON SAND ISLAND, MANWR...................3-25

FIGURE 3.4 MAP OF VEGETATIVE COVER ON SAND ISLAND, MANWR ...............................................................3-31

FIGURE 3.5 MEAN COUNTS FOR YEARS 1993-2001 AND 2017 OF BRISTLE-THIGHED CURLEW, PACIFIC GOLDEN 

PLOVER, WANDERING TATTLER, AND RUDDY TURNSTONE COMBINED BY MONTH ON MANWR ........3-53

FIGURE 3.6 MONTHLY COUNTS ON MANWR CONDUCTED IN 2017 FOR BRISTLE-THIGHED CURLEWS (BTCU),

PACIFIC GOLDEN PLOVERS (PGPL), WANDERING TATTLERS (WATA), AND RUDDY TURNSTONES

(RUTU) .............................................................................................................................................3-55

FIGURE 3.7 BRISTLE-THIGHED CURLEW................................................................................................................3-59

FIGURE 3.8 LAYSAN DUCK FAMILY.......................................................................................................................3-65

FIGURE 3.9 RESULTS OF ISLAND-WIDE MONTHLY AVIAN SURVEYS CONDUCTED FROM JUNE THROUGH SEPTEMBER 

2017 FOR LAND BIRDS ........................................................................................................................3-72

FIGURE 3.10 SPATIAL DISTRIBUTION OF BENTHIC COVER AND CORAL COMPOSITION AT NOAA CREP RAPID 

ECOLOGICAL ASSESSMENT SITES AT MIDWAY IN 2008 .....................................................................3-85

FIGURE 3.11 NOAA MIDWAY ISLAND DETAILED HABITAT COVER IMAGE AT 13M RESOLUTION..........................3-87

FIGURE 3.12 AUGMENTATION OF SAND ISLAND DURING THE COLD WAR..............................................................3-89

FIGURE 3.13 MARINE SURVEY AREA FOR SEAWALL REPAIR PROJECT...................................................................3-90

FIGURE 3.14 POSSIBLE CORAL TRANSLOCATION SITE FOR THE SEAWALL REPAIR PROJECT ..................................3-90

FIGURE 3.15 HAWAIIAN MONK SEAL ......................................................................................................................3-98

FIGURE 3.16 SAND ISLAND HAWAIIAN MONK SEAL SIGHTINGS: 2012-2016........................................................ 3-100
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LIST OF TABLES

TABLE 1.1 STRATEGY AS-4 OF THE PMMP ..........................................................................................................1-7

TABLE 2.1 PRINCIPLES OF SUCCESSFUL RAT AND MOUSE ERADICATIONS............................................................2-3

TABLE 2.2 MANMADE STRUCTURES ON SAND ISLAND, MANWR ........................................................................2-4

TABLE 2.3 SUMMARY OF TECHNICAL CONSIDERATIONS.......................................................................................2-8

TABLE 2.4 RODENTICIDES APPROVED FOR CONSERVATION USE IN THE UNITED STATES .....................................2-9

TABLE 3.1 MANWR ADMINISTRATIVE CO-TRUSTEES .........................................................................................3-1

TABLE 3.2 SUMMARY OF THE BUILT ENVIRONMENT ON SAND ISLAND, MANWR ...............................................3-2

TABLE 3.3 AVERAGE RAINFALL ON SAND ISLAND, MANWR...............................................................................3-6

TABLE 3.4 TYPICAL PERSONNEL PRESENT ON SAND ISLAND, MANWR...............................................................3-8

TABLE 3.5 EFFECTIVE PERCEIVED NOISE LEVEL OF SELECTED AIRCRAFT..........................................................3-17

TABLE 3.6 LUC SITES ON SAND ISLAND, MANWR............................................................................................3-20

TABLE 3.7 PROJECT RELATED HAZARDOUS MATERIALS, WASTE, AND TOXINS .................................................3-21

TABLE 3.8 GENERALIZED PROPORTION OF DAILY FOOD INTAKE THAT MUST BE BAIT FOR BIRDS TO REACH AN LD50

THRESHOLD WHERE THE DOSAGE (D) OF A TOXIN IS LETHAL (L) TO 50% OF ANIMALS OF THE SPECIES IN 

LABORATORY TESTS...........................................................................................................................3-23

TABLE 3.9 SUMMARY OF RISKS TO NONTARGET SPECIES ...................................................................................3-23

TABLE 3.10 PRELIMINARY RISK ASSESSMENT BY SPECIES, CONSEQUENCE, AND POTENTIAL MITIGATION ..........3-27

TABLE 3.11 VEGETATION COMMUNITIES AND PLANT ASSOCIATIONS ON SAND ISLAND, MANWR .....................3-32

TABLE 3.12 BREEDING SEABIRDS OF MANWR (N = 21 SPECIES) ..........................................................................3-37

TABLE 3.13 PRIMARY AND SECONDARY TOXICITY OF BRODIFACOUM..................................................................3-44

TABLE 3.14 NUMBER AND SPECIES OF BIRDS REPORTED STRUCK BY AIRPLANES AT HENDERSON FIELD, MANWR:

2004-2010..........................................................................................................................................3-48

TABLE 3.15 DUCKS, SHOREBIRDS, AND WADING BIRDS OF MANWR (N = 7 SPECIES) ...........................................3-51

TABLE 3.16 PRIMARY AND SECONDARY TOXICITY OF BRODIFACOUM TO SHOREBIRDS ON MANWR ALONG WITH 

THE LAYSAN DUCK AND CATTLE EGRET.............................................................................................3-56

TABLE 3.17 PRIMARY AND SECONDARY TOXICITY OF BRODIFACOUM TO PASSERINES ON MANWR....................3-74

TABLE 3.18 ADDITIONAL SPECIES RECORDED AT EACH SITE AT MANWR DURING ROVING DIVER SURVEY..........3-95

TABLE 3.19 HAWAIIAN MONK SEAL BEACH COUNT DATA SUMMARIZED BY SECTOR ....................................... 3-101

TABLE 3.20 HAWAIIAN MONK SEAL BEACH COUNT DATA SUMMARIZED BY MONTH........................................ 3-102

TABLE 5.1 PRINCIPAL PREPARES OF THIS ENVIRONMENTAL ASSESSMENT............................................................5-1

TABLE 5.2 CONTRIBUTORS TO THIS ENVIRONMENTAL ASSESSMENT.....................................................................5-1

TABLE 7.1 SCOPING LETTER RECIPIENTS ..............................................................................................................7-1

TABLE 7.2 SUMMARY OF SCOPING INTERVIEW......................................................................................................7-2
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viii

ACRONYMS AND ABBREVIATIONS 

Acronym Phrase

a.i. Active Ingredient

ARFF Aircraft Rescue and Fire Fighting

ARMCO 1942 Battle of Midway structure (hut)

ASAP Alien Species Action Plan

AST Above-ground Storage Tank

BASH Bird Aircraft Strike Hazard

BMP Best Management Practices

BOQ Bachelor Officer Quarters

CAMU Corrective Action Management Unit

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

CFR Code of Federal Regulations

COPC Chemicals of Potential Concern 

CR Critically Endangered

D Dose

dB Decibels

DNL Day-Night Average - Noise Level

EA Environmental Assessment

EC50 Half Maximal Effective Concentration (of a toxicant; measured in ppm)

EIS Environmental Impact Statement

EPNdB Effective Perceived Noise Level (in decibels)

EO Executive Order

ESA Endangered Species Act of 1973

ETOPS Extended Twin-Engine Operations

FAA Federal Aviation Association

FIRFA Federal Insecticide, Fungicide and Rodenticide Act

FOD Foreign Object Debris

FONSI Finding of No Significant Impact

GIS Geographic Information System

GPS Global Positioning Satellite

HDLNR Hawai‘i Department of Land and Natural Resources

IUCN International Union for Conservation of Nature

L Lethal

LD50 Lethal Dosage of a toxin to 50 % of laboratory tested animals; measured in 

mg (D)/kg of animal body weight

LOAEL Lowest Observable Adverse Effect Level

LUC Land Use Controls

MANWR Midway Atoll National Wildlife Refuge/Battle of Midway National 

Memorial

MBTA Migratory Bird Treaty Act

MG Million Gallon

MMPA Marine Mammal Protection Act

MSL Mean Sea Level
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Acronym Phrase

NAF Naval Air Facilities

NEPA National Environmental Policy Act

NGO Non-governmental Organization

NHPA National Historic Preservation Act

NISA National Invasive Species Act

NISC National Invasive Species Council

NOAEL No Observable Adverse Effect Level

NT Near Threatened

NWHI Northwestern Hawaiian Islands

NWR National Wildlife Refuge

NWRC National Wildlife Research Center/Complex

NWRS National Wildlife Refuge System

OBWLF Old Bulky Waste Landfill 

OSHA Occupational Safety and Health Administration

PCB Polychlorinated Biphenyl 

pH Potential of Hydrogen

PMDY Henderson Field Airport International Air Transport Assoc. Airport Code

PMMP Papahānaumokuākea Monument Management Plan

PMNM Papahānaumokuākea Marine National Monument

PPE Personal Protection Equipment

ppm Parts Per Million

RCRA Resource Conservation and Recovery Act

SARA Superfund Amendments and Reauthorization Act

SMP Structure Management Plan

TACA Toxic Substances Control Act

USC United States Code of Laws

USDA U.S. Department of Agriculture

USEPA United States Environmental Protection Agency

USFWS U.S. Fish and Wildlife Service

UST Underground Storage Tank
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CHAPTER 1: PURPOSE AND NEED

1.1 INTRODUCTION

This Environmental Assessment (EA) evaluates the potential environmental effects of one action 

alternative and the No Action Alternative for mouse eradication on Sand Island, Midway Atoll 

National Wildlife Refuge (MANWR). The MANWR is located within the Papahānaumokuākea 

Marine National Monument (PMNM), located in the Northwestern Hawaiian Islands (NWHI) 

(see Figure 1.1, Figure 1.2, and Figure 1.3). Over 3 million birds, encompassing 25 different 

species, can be found on MANWR’s 3 islands and all of them are susceptible to predation by 

mice. MANWR is home to the largest albatross colony in the world and is the most important 

and successful breeding ground for black-footed albatross (Phoebastria nigripes) and Laysan 

albatross (Phoebastria immutabilis). The NWHI are, respectively, home to approximately 97.5 

and 99.7% of the total worldwide population of these 2 species, and both of these species are 

considered “near threatened” (NT) by the International Union for Conservation of Nature 

(IUCN). MANWR alone is globally significant, supporting 36% of all Black-footed albatross 

and 73% of all Laysan albatross. Sand Island alone has approximately 360,000 pairs of Laysan 

albatross and 15,084 pairs of black-footed albatross. As of 2004, MANWR also now hosts a 

translocated population of Laysan ducks (Anas laysanensis), which are considered “critically 

endangered” (CR) by the IUCN and is listed as endangered under the Endangered Species Act of 

1973 (ESA), as amended. 

This draft EA will be used by U.S. Fish and Wildlife Service (USFWS) to solicit public input 

and determine whether implementation of the alternatives would have a significant impact on the 

environment. This EA is part of the USFWS decision-making process in accordance with the 

National Environmental Policy Act (NEPA), as amended and its implementing regulations. 

Figure 1.1 Location Map

Source: https://www.papahanaumokuakea.gov/visit/ (2017)
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1.2 PURPOSE OF THE ACTION 

The purpose of the proposed action is to implement Strategy AS-4 from the PMMP and 

completely eradicate the invasive house mouse from Sand Island within the MANWR and to 

maintain its rodent-free status in perpetuity. To eradicate invasive mice, a lethal dose of 

rodenticide would be delivered to every rodent on the island in a manner that minimizes harm to 

island residents and the ecosystem while still maintaining a high probability of successful 

eradication. 

Figure 1.2 Midway Atoll National Wildlife Refuge (MANWR)

Source: Planning Solutions, Inc. (2017)

Within 1 year of project implementation, non-native mice will be eradicated (population = 0) 

from Sand Island on Midway Atoll National Wildlife Refuge for the benefit and protection of 

nesting albatross species (e.g., Laysan, short-tailed, and black-footed), other nesting seabirds 

(e.g., Bonin Petrel), and their habitats. 
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Figure 1.3 Sand Island, MANWR

Source: Planning Solutions, Inc. (2017)

1.3 NEED FOR THE ACTION

1.3.1 EFFECTS OF INTRODUCED INVASIVE SPECIES ON ISLANDS

Worldwide, invasive species are causing negative ecological and economic impacts. The impacts 

from invasive predatory mammals, including mice and rats, are one of the leading causes of 

species extinction on islands (Blackburn et al. 2004; Duncan and Blackburn 2007). The 

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

to the impact of invasive rodents (Andrews 1909, Atkinson 1985, Daniel and Williams 1984, 

Hutton et al. 1984, Tomich 1986), with estimates of between 40-60% of all recorded bird and 

reptile extinctions globally being directly attributable to invasive rodents (Atkinson 1985). 
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1.3.2 EFFECTS OF INTRODUCED MICE ON MANWR

Invasive house mice and black rats (Rattus rattus) became established on MANWR’s Sand 

Island more than 75 years ago during military occupancy. Black rats were eradicated in 1996 and 

house mice are now the sole rodent and invasive mammal present in the NWHI.1 Mouse 

predation of albatross on Sand Island was first identified in 2015 and the area where mouse 

predation occurs and the number of birds bitten has been observed to increase with each 

successive year. Mice were confirmed as the ultimate cause of death for bitten Laysan albatross 

during the 2015/2016 breeding season on MANWR with 42 dead adults and 70 nests abandoned 

in a 4 ac. (1.6 ha) area. Time lapse photography recorded mice repeatedly crawling onto and 

biting the head, neck, and backs of adult birds (see Figure 1.4 and Figure 1.5). Necropsy and 

histopathology results from recovered carcasses indicate bacterial infection from wounds as the 

cause of death (USGS, National Wildlife Health Center, Honolulu). This same phenomenon was 

again present in the 2016/2017 breeding season with a 6-fold increase in the number of affected 

albatross to 242 dead adults, 1,218 bitten birds, and 994 abandoned nests and site locations from 

3 to 50 distinct areas, as well as an expansion of total affected area from 4 acres to 27 acres (11 

ha) (USFWS, Unpublished b). Mouse attacks declined in 2017/2018, however, the reason for the 

decline is not known. A combination of environmental conditions, the cyclical nature of mouse 

populations, and active management to reduce attacks are thought to have played a role. 

Beyond the predation of seabirds, rodents have deleterious effects on entire island ecosystems. 

Briefly summarized, they:

• Are a disease vector.

• Feed opportunistically on plants and alter the floral communities of island ecosystems 

(Campbell and Atkinson 2002). Their feeding competes with native species and in some 

cases degrades the quality of nesting habitat for birds that depend on the vegetation 

(Wegmann 2009, Young et al. 2010). 

• Prey upon terrestrial invertebrates and reptiles, affecting the abundance and age structure 

of intertidal invertebrates directly (Navarrete and Castilla 1993).

• Have been demonstrated to lower total soil carbon, nitrogen, phosphorous, mineral 

nitrogen, marine-derived nitrogen, and pH relative to rodent-free islands (Fukami et al. 

2006). 

• Affect invertebrate and marine algal abundance, changing intertidal community structure 

from an algae-dominated system in rodent free areas to an invertebrate dominated system 

in rodent-invaded areas (Kurle et al. 2008). 

 

1 The 1996 eradication effort was geared solely towards black rats and was not intended to eliminate house mice. 
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Figure 1.4 Adult Laysan albatross on Sand Island showing effects of predatory mice

Source: USFWS (2016)

Figure 1.5 Mouse biting the head of Adult Laysan albatross on Sand Island 

Source: USFWS (2016)

A comparison of rodent-infested and rodent-free islands, and pre- and post-rodent eradication 

projects have shown that rodents depressed the population size and recruitment of birds 

(Campbell 1991, Jouventin et al. 2003, Thibault 1995), reptiles (Bullock 1986, Cree et al. 1995, 

Towns 1991, Whitaker 1973), plants (Pye et al. 1999), and terrestrial invertebrates (Bremner et 

al. 1984, Campbell et al. 1984). In an analysis by Brooke et al. (2017), drawing on data of 

eradication of non-native mammals on islands from around the world, they examined the 

population growth rates (lambda) of 181 seabird populations of 69 seabird species following 

successful mammal eradication projects. Rate of growth (lambda) is the ratio of population size 

at the end of one interval to population size at the end of the previous interval. When lambda = 

1.0 the population density is stable while values >1.0 indicate increasing populations. After 
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1-6 

successful eradication, the median population growth rate (lambda) was 1.119 and seabird 

populations with positive growth rates greatly outnumbered those in decline. Their study 

confirmed that invasive mammal eradication is usually followed by growth of seabird 

populations. 

Predation of vulnerable populations of native seabirds is a real and ongoing threat on Sand Island 

and demands an immediate and effective response. Eradication of the house mouse from 

MANWR would also facilitate the protection and restoration of multiple native species and 

habitats present in the refuge. 

1.3.3 MANWR ECOSYSTEM MANAGEMENT AND CONSERVATION PLANS 

1.3.3.1 Papahānaumokuākea Monument Management Plan (PMMP)

The PMMP, completed in December 2008, was the result of an extensive public review process 

and identified 6 priority management needs, with supporting action plans and corresponding 

desired outcomes, for the PMNM. The 6 priorities were (PMMP, ES-3 to ES-5):

1. Understanding and Interpreting the Northwestern Hawaiian Islands; 

2. Conserving Wildlife and Habitats; 

3. Reducing Threats to Monument Resources; 

4. Managing Human Uses; 

5. Coordinating Conservation and Management Activities; and 

6. Achieving Effective Monument Operations. 

As evidenced by these priorities, protecting the land and waters of the NWHI from the impacts 

of alien species is critical to achieving the Monument’s primary goal of resource protection. A 

specific component of Priority 3 was the development of an Alien Species Action Plan (ASAP). 

The ASAP advanced a series of strategies to address and mitigate the ongoing effects of invasive 

alien species on the PMNM. Specifically, the ASAP identified the eradication of the house 

mouse on Sand Island, MANWR as Strategy AS-4 (see Table 1.1). 
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Table 1.1 Strategy AS-4 of the PMMP 

Strategy AS-4: Eradicate the house mouse population on Sand Island, Midway Atoll, within 15 years.

After the eradication of the black rat (Rattus rattus) at Midway Atoll and the Polynesian rat (Rattus exulans) at 

Kure Atoll, the house mouse (Mus musculus) on Sand Island, Midway, remains the only invasive mammal left in 

the NWHI. Mice can cause high mortality in seabirds as large as albatrosses (Wanless et al. 2007). In addition, 

Midway now hosts a translocated population of endangered Laysan ducks that are likely to be negatively affected 

by the high mouse populations. Mice are also a threat to native plants and terrestrial invertebrates. 

Activity AS-4.1: Produce a house mouse eradication plan within 5 years and procure appropriate permits 

for chosen eradication techniques. 

The eradication of introduced rodents from islands is routine, and the successful removal of black rats at Midway 

Atoll in recent years has provided a model for mouse eradication. Mice present additional challenges, however, 

as they have much smaller home range sizes and different foraging and reproductive ecology. A careful planning 

effort that emphasizes the minimization of effects to nontarget organisms at the site and the other biological 

differences that may affect the operation is necessary. 

Activity AS-4.2: Implement and complete house mouse eradication.

All of Sand Island 1,128 acres (456 ha) will be treated with rodenticide, with active management to prevent 

nontarget impacts to native wildlife. Surveys of the affected ecosystem components before and after the 

operation will provide a valuable demonstration of the effects of introduced mice on biological communities. 

Source: Alien Species Action Plan, Papahānaumokuākea Monument Management Plan (USFWS, December 2008)

One reason the PMMP-ASAP identified Strategy AS-4 was Wanless et al.’s (2007) observations 

that mice can and will predate seabirds once their competitors are removed. During the 

preparation of the PMMP, Wanless et al. (2007) observed mice depredating on Tristan albatross 

(Diomedea dabbenena) and Atlantic petrels (Pterodroma incerta) on Gough Island in the South 

Atlantic Ocean. Based on their experience on Gough Island, they suggested that once mice are 

released from the ecological effects of other predators and competitors (e.g., on Sand Island, 

MANWR where rats have been removed and mice are the sole alien mammal), the mice may 

begin to predate seabird chicks. Since completion of the PMMP in 2008, Wanless et al.’s 

predictions have been shown to be accurate on Sand Island, MANWR where mice are now the 

sole alien mammal. 

1.3.3.2 Conservation Action Plan for Black-footed albatross and Laysan albatross 

In a multi-agency report on conservation action plans for the black-footed albatross and Laysan 

albatross (Naughton et al. 2007), the authors state that one of the primary threats to these 2 

species is predation by introduced mammals. The authors recommended a conservation action to 

eradicate house mice from MANWR to protect these 2 species of seabirds. 

1.3.3.3 U.S. Fish and Wildlife Service Regional Seabird Conservation Plan 

In addition, the USFWS Regional Seabird Conservation Plan (USFWS 2005) identified the 

eradication or control of introduced predators and other invasive species that have a negative 

impact on seabirds as one of the top priorities for seabird conservation. They specifically 

recommend eradicating introduced predators in the Pacific Islands where the Laysan and blackfooted albatross breed or have historically bred. 
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1.4 REGULATORY REQUIREMENTS 

The proposed action of eradicating invasive mice on Sand Island, MANWR by the USFWS, 

Papahānaumokuākea Marine National Monument, constitutes a Federal action, which makes it 

subject to review under the National Environmental Protection Act (NEPA) and other applicable 

statutes, regulations, and EOs. USFWS is required to integrate and consider the potential 

environmental effects that its actions may have on the human and natural environment prior to 

taking action. It accomplishes this by evaluating the environmental consequences of proposals to 

ensure that environmental values are given appropriate consideration in agency decision-making 

along with economic and technical factors within the agency’s mission. 

This EA has been prepared in consultation with other agencies, private organizations, and the 

public. If, after circulating the report for public and agency comment, USFWS finds that the 

proposed project would not have a significant adverse effect on the quality of the environment, it 

would prepare a Finding of No Significant Impact (FONSI). Notification of the EA and FONSI 

will be available at: 

https://www.papahanaumokuakea.gov

If at any point in the preparation of an EA, USFWS determines that the proposal would have a 

significant adverse effect on the quality of the environment, it would initiate preparation of an 

Environmental Impact Statement (EIS). 

In addition to NEPA, other applicable laws and regulations include Section 7 of the Endangered 

Species Act (ESA) of 1973, Essential Fish Habitat under Magnuson-Stevens Conservation and 

Management Act and the Migratory Bird Treaty Act (MBTA) of 1918. Specific Federal laws that 

apply in addressing alien species and invasive species in the NWHI, in addition to the ESA, 

include the Lacey Act of 1900, as amended (18 USC 42, 16 USC 3371), and the National 

Invasive Species Act (NISA) of 1996. This EA is intended to address and satisfy many, but not 

all, of the above requirements. A full list of compliance needs for this project can be found in 

Chapter 8. 

The Magnuson-Stevens Act mandates that Federal Agencies conduct an Essential Fish Habitat 

(EFH) consultation with NOAA Fisheries regarding any actions authorized, funded, or 

undertaken that may adversely affect EFH. This EA serves as a basis for EFH impact review and 

consultation for the proposed action to eradicate mice at MANWR. 

The USFWS’s resource managers are authorized, and mandated by law, to conserve and restore 

wildlife and habitats that are under the agency’s jurisdiction. With a mission to work 

collaboratively with others to “conserve, protect, and enhance fish, wildlife, and plants and their 

habitats for the continuing benefit of the American people,” it is the responsibility of USFWS to 

address any threats that introduced species pose to the habitat and native wildlife of MANWR. 

Eliminating invasive mice from MANWR’s Sand Island is pertinent to the management strategy 

of USFWS for the refuge.

The proposed action would be carried out in compliance with various Federal laws, EOs, and 

legislative acts including: 

• National Wildife Refuge System Improvement Act of 1997 (Public law 105-57); 
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• The Fish and Wildlife Act of 1956 (16 U.S.C. 742a-742j, not including 742 d-l, 70 

Stat. 1119), as amended; 

• National Environmental Policy Act of 1969 (NEPA); 

• Endangered Species Act (ESA) of 1973 (16 U.S.C. 1531-1544, 87 Stat. 884); 

• Migratory Bird Treaty Act of 1918 (MBTA)2

; 

• EO 13186 Responsibilities of Federal Agencies to Protect Migratory Birds (66 FR 

3853, Jan. 17, 2001); 

• Marine Mammal Protection Act of 1972 (MMPA), as amended; 

• Magnuson-Stevens Fishery Conservation and Management Act and Essential Fish 

Habitat; 

• EO 13089 Coral Reef Protection (June 11, 1998); 

• Water Pollution Control Act of 1948, as amended; 

• EO 13112 Invasive Species as amended 12/08/2016 by E0 13751; 

• National Historic Preservation Act of 1966 (NHPA); 

• Federal Insecticide, Fungicide, and Rodenticide Act of 1947 (FIFRA); and

• Papahānaumokuākea Marine National Monument 50 CFR Part 404 – Permit 

Requirement. 

1.5 PROJECT PARTICIPANTS

1.5.1 U.S. FISH AND WILDLIFE SERVICE (USFWS), - LEAD AGENCY

The U.S. Fish and Wildlife Service is a bureau of the U.S. Department of Interior that works 

with others to conserve, protect, and enhance fish, wildlife, and plants and their habitats for the 

continuing benefit of the American people. The National Wildlife Refuge System within the 

USFWS has primary jurisdiction and statutory authority for management of MANWR resources, 

thus it is the Lead agency for this Seabird Protection Project. 

MANWR is part of the Papahānaumokuākea Marine National Monument, the largest contiguous 

fully protected conservation area under the U.S. flag, and one of the largest marine conservation 

areas in the world. It encompasses 582,578 square miles (mi2

) (1,508,870 square kilometers

[km2]) of the Pacific Ocean, an area larger than all the country's national parks combined. The 

Northwestern Hawaiian Islands Marine National Monument was established by Presidential 

Proclamation 8031 on June 15, 2006 under the authority of the Antiquities Act (16 U.S.C. §431-

433). A year later, it was given its Hawaiian name, Papahānaumokuākea under Presidential 

 

2

 The Department of the Interior Solicitor's Office issued a binding opinion (M-Opinion) on December 22, 2017 (Memorandum 

M-37050) which states that a permit is not required for incidental take of migratory birds. Therefore, an MBTA permit will 

not be sought. However, this document does analyze the effects to migratory birds and avoidance and minimization measures 

that will be implemented as part of the USFWS' responsibility to conserve the trust resource of migratory birds (See 1.4.5)
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Proclamation 8112. The Monument was expanded by Presidential Proclamation 9478 on August 

26, 2016. It was expressly created to protect an exceptional array of natural and cultural 

resources. The stated mission of PMNM is to carry out seamless integrated management of the 

monument to ensure ecological integrity and achieve strong, long-term protection and 

perpetuation of NWHI ecosystems, Native Hawaiian culture, and heritage resources for current 

and future generations. 

1.5.2 U.S. DEPARTMENT OF AGRICULTURE, ANIMAL AND PLANT HEALTH INSPECTION 

SERVICE, WILDLIFE SERVICES (WS) AND THE NATIONAL WILDLIFE RESEARCH CENTER 

(NWRC) - COOPERATING AGENCY

The mission of USDA APHIS Wildlife Services (WS) is to provide Federal leadership and 

expertise to resolve wildlife conflicts to allow people and wildlife to coexist. WS conducts 

program delivery, research, and other activities through its Regional and State Offices, the 

NWRC and NWRC Field Stations, as well as through its National Programs. The NWRC is the 

federal institution devoted to resolving problems caused by the interaction of wild animals and 

society. The NWRC applies scientific expertise to the development of practical methods to 

resolve these problems and to maintain the quality of the environments shared with wildlife.

NWRC has special expertise with respect to this proposed project and has agreed to be a 

Cooperating Agency.

NWRC actions in this project include:

• NWRC might be considered for the chemical analysis of pre- and post-application 

brodifacoum residues in rodents or non-target animals. NWRC’s involvement would 

be limited to receiving samples from Midway project managers, conducting 

laboratory-based chemical analysis, and disposing of biological and chemical waste 

resulting from the analytical process in the NWRC waste management program.

• The NWRC Registration Unit will, with direction from the Midway project planners, 

conduct all activities associated with preparation of a specific label for the APHIS 

rodenticide product Brodificoum 25D Conservation (EPA Reg. No. 56228-37) used 

for the mouse eradication attempt, submission of the supplemental registration 

application to the Environmental Protection Agency and all communication required 

to obtain a registration approval. 

1.5.3 MEMORANDUM OF UNDERSTANDING (MOU) BETWEEN ISLAND CONSERVATION,

USDA (APHIS), AMERICAN BIRD CONSERVANCY AND THE USFWS

In April 2015, the USFWS entered into agreement with Island Conservation for the “purpose of 

furthering wildlife conservation and ecosystem management interests and responsibilities for the 

islands, atolls, and reefs under the jurisdiction of the United States.” This partnership promotes 

an integrated and coordinated approach to protecting, restoring and managing native populations 

of plants and animals and island ecosystems impacted by invasive alien species including but not 

limited to rodents, ants, cats and plants. In 2016, 2 additional parties were added to this national 

level agreement, including APHIS and the American Bird Conservancy. 
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1.5.4 ISLAND CONSERVATION

Island Conservation (IC) is an active partner in this Seabird Protection Project under the MOU. 

IC is a non-profit organization with the mission “to prevent extinctions by removing invasive 

species from islands.” Working in partnership with local communities, government management 

agencies, and conservation organizations, Island Conservation seeks to identify islands that have 

the greatest potential for preventing extinction of globally threatened species classified as 

Critically Endangered or Endangered (i.e., CR or EN) on the IUCN’s Red List of Threatened 

Species. Island Conservation develops plans for, and implements the removal of, invasive alien 

species and conducts field research to document the environmental effects of this work in order 

to inform the planning and execution of future conservation projects. 

Island Conservation seeks to prevent extinctions by focusing its efforts on islands where the 

concentration of biodiversity, and consequently the threat of species extinction, is greatest. Of 

the 245 recorded animal extinctions since 1500 AD, 80% were on islands. Of those, in cases 

where causes could be identified, non-native and invasive species were responsible for 54% of 

these extinctions. Eradicating the primary threat—introduced invasive vertebrates—is one of the 

most critical and effective means for preserving threatened populations of plants and animals and 

restoring island ecosystems. To date, Island Conservation has deployed teams to protect 994 

populations of 389 species on 52 islands. 

1.5.5 MIDWAY RESTORATION PARTNERSHIP

For the Midway project, and consistent with the National MOU, Island Conservation formed a 

partnership team with a variety of regulatory agencies and conservation organizations to provide 

individual input and project support in the planning phase of the mouse eradication. Participants 

in the Midway Restoration Partnership include the USFWS; USDA, APHIS WS and NWRC; 

NOAA; U.S. Geological Survey; Office of Hawaiian Affairs; and the American Bird 

Conservancy. 

1.6 ORGANIZATION OF THE EA 

The remainder of this document is organized as follows: 

• Chapter 2 describes the proposed action and its alternatives in detail, including those 

alternatives that were initially considered but ultimately rejected from further 

evaluation. 

• Chapter 3 provides information regarding the existing environment and identifies the 

kinds of environmental effects which each alternative is likely to have.

• Chapter 4 discusses the potential for cumulative effects. 

• Chapter 5 lists the agencies, organizations, and individuals who prepared and 

contributed to this report. 

• Chapter 6 provides the references for the information sources that were relied upon 

during preparation of this report. 
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• Chapter 7 describes the scoping process which was implemented during the planning 

process.

• Chapter 8 includes a statement of the project’s consistency and compliance with 

relevant laws, EOs, agency policies and permits. 

• Chapter 9 provides a glossary of terms. 

 
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CHAPTER 2: DESCRIPTION OF THE PROJECT AND 

ALTERNATIVES 

This chapter provides detailed information about the Proposed Action and alternatives to the 

Proposed Action, including those alternatives that were initially considered but ultimately 

rejected from further evaluation because they did not meet the project objectives outlined in

Section 1.2. It also describes the procedures that would be used in the implementation of the 

project, methods, estimated costs, and the anticipated schedule for project implementation. 

The information contained in this chapter draws from the Feasibility Study: House Mouse 

Eradication on MANWR (Island Conservation 2017), including the discussion of methods and 

potential alternatives. Sections 2.1 and 2.2 provide principles and considerations that all 

alternatives must address to fulfill the project’s objectives. Section 2.3 presents the details of the 

proposed action; Section 2.4 outlines the No Action Alternative; and Section 2.5 discusses the 

alternatives that have been considered but rejected.

2.1 PRINCIPLES OF RODENT ERADICATION IN ISLAND 

ECOSYSTEMS 

Rodent eradication has become a common tool for agencies charged with the maintenance and 

management of island ecosystems, and its use to protect and conserve threatened species and 

ecosystems has increased significantly over the past decade. By 2015, there were 944 

documented attempts at rodent eradication—across 10 different rodent species—on 692 islands 

globally (Samaniego-Herrera 2016). In total, 87 (9.2%) of those attempts were specifically 

related to mouse eradication; these attempts were reported from 76 islands in 17 countries 

(Samaniego 2016). Most of these mouse eradication attempts were in the temperate region, with 

only 32 of the 87 (36%) of them being mouse eradication attempts on tropical islands. 

Island size does not appear to be a limiting factor for successful eradication. Eradication attempts 

and successful eradication operations have been reported from small offshore islets to very large 

islands, including the largest known mouse eradication on Macquarie Island at approximately 

31,810 acres (12,873 hectares). Mouse eradications are currently being planned or considered for 

very large islands such as Floreana Island in the Galapagos archipelago (~44,478 ac or 18,000 

ha) and Marion Island in South Africa (~82,780 ac or ~33,500 ha) (Parkes 2014). Figure 2.1

below summarizes the outcomes of attempts globally at mouse eradication on islands over time 

and by island size. 
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Figure 2.1 Global Mouse Eradication Attempts on Islands Over Time and by Island Size

Source: DIISE 2016; Samaniego 2016 cited in Island Conservation (2017)

While no guarantee of success exists, as evidenced by Figure 2.1, mouse eradication from islands 

is achievable provided that basic principles of rodent eradication are applied. Attempted mouse 

eradication from all islands between 1975 and 2015 had an overall success rate of 71%. In 

comparison, success of rat eradication programs is approximately 87% (Russell and Holmes 

2015). The reason(s) behind the lower success rate of mouse eradications is undetermined and 

has been the subject of several investigations (Samaniego 2016, Mackay 2011). Factors 

contributing to failure could include some, or a combination of, the following factors: (i) natural 

history differences between rats and mice could make it harder to target the complete population 

of mice, including their foraging behavior, travel distances, and home range sizes; (ii) the fact 

that mice have been a secondary target of multi-species eradication efforts; or (iii) ineffective 

eradication strategies or management approaches that failed to reach all mice, so that remnant 

mice remain and recolonize the island. 

More recently, 6 of 10 mouse eradication projects on islands greater than 988 ac (400 ha) have 

been successful. All of these projects were conducted as multi-species eradications, typically 

known to be more challenging than single-species eradications, and were in temperate regions. 

Within the tropics, the largest mouse eradication attempt to-date has been on Mer Island (~1,134 

ac or 459 ha) and is still being evaluated for success. Of the 3 largest mouse eradication attempts 

where a positive or negative outcome has been determined (i.e., success or failure), 2 were 

successful (Samaniego 2016). 

Between 2005 and 2015, the success of mouse eradications increased to 93.3% of 31 attempted 

eradications. This increase in the success rate has been attributed to better international 
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cooperation and knowledge sharing between eradication practitioners regarding lessons learned 

(Veitch et al. 2002, 2011), and the establishment of best practices principles for the eradication 

of rodents in temperate (Broome et al. 2014) and tropical ecosystems (Keitt et al. 2015). Today, 

successful rodent eradications on all but the smallest of islands (i.e., less than ~12 ac or 5 ha) 

rely on the use of rodenticides, and specifically, anticoagulant rodenticides (Database of Island 

Invasive Species Eradications [DIISE] 2016). 

All successful eradications, regardless of species or location, are based on 3 fundamental 

principles (Cromarty et al. 2002): 

1. Every individual of the target species must be put at risk with the proposed 

eradication technique(s). 

2. The technique(s) employed must remove individuals from the target population at a 

rate greater than they can breed (i.e., their replacement rate). 

3. Immigration of new specimens of the target species must be zero, or effectively 

managed to zero, by identifying and eliminating immigrant specimens. 

These principles have been further developed with specific regard to rat and mouse eradications 

as summarized in Table 2.1 below (see Howald et al. 2007). 

Table 2.1 Principles of Successful Rat and Mouse Eradications 

No. Principle

1 Deliver a highly palatable bait containing a toxic rodenticide into every potential rodent territory.

2 Ensure bait is available in enough quantity and for long enough that every mouse has access to a lethal 

dose.

3 Time the baiting operation to when the rodent population is most likely to consume the bait. 

4 The short-term risks and impacts to nontarget wildlife, people, and the environment from disturbance and 

the rodenticide is minimized wherever possible. The benefits of eradication must outweigh the costs. 

5 Biosecurity procedures must be able to sustain the eradication, with effective prevention, detection, and 

an effective response to any incursion. 

Source: Howald et al. 2007 cited in Island Conservation (2017). 

The principles outlined in Table 2.1 have been further refined into best practice guidelines for 

maximizing the probability of successful rodent eradications from temperate islands in New 

Zealand (Broome et al. 2014) and from tropical islands (Keitt et al. 2015). 

2.2 MANWR TECHNICAL CONSIDERATIONS

Island Conservation, in its 2017 Feasibility Report, acknowledges that, “the feasibility of an 

eradication is a multi-dimensional analysis that considers technical, environmental, social, 

political, and legal factors.” These factors must all be considered, both individually and 

cumulatively, to determine if, and how, a successful mouse eradication can be achieved at Sand 

Island, MANWR. 

2.2.1 CONSTRAINTS ON SUCCESSFUL ERADICATION

While all rodent eradications from large islands apply the same fundamental set of principles 

(see Table 2.1 above), the technical approach to each project must be tailored to the unique 
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environmental context, including its wildlife communities, ecosystem function, and landscape 

features. Because of this, the first step in evaluating the best technical approach consists of 

identifying the local constraints acting on the operation and how they impact the overall 

probability of success, as well as the potential for concomitant adverse impacts to the local 

environment. These constraints have the potential to limit the likelihood of a successful 

eradication if they are not understood, minimized, mitigated, or eliminated. 

The major constraints present on Sand Island, MANWR which must be considered in project 

design include the presence of manmade structures, underground utilities, native species that 

inhabit the island, and the resident community. These are discussed in the following sections. 

2.2.1.1 Manmade Structures 

The built environment on Sand Island is extensive, and is the result of a long history of human 

habitation and infrastructure development over more than a century. The structures on Sand 

Island vary in age, construction type, condition, and whether and how they are used. The entire 

built environment on Sand Island can be divided into one of 3 categories, summarized in Table 

2.2 below. 

Table 2.2 Manmade Structures on Sand Island, MANWR

Construction Category Use Description

Vertical Inhabited Living 

Spaces

Buildings that provide housing and dining facilities, food 

storage, and food preparation areas. 

Work Spaces Buildings that provide offices, utility buildings, covered storage, 

recreation facilities, covered garden, and nurseries. 

Abandoned Condemned 

Spaces

Structures and spaces where human access is restricted or no 

longer permitted due to physical or other safety reasons. 

Horizontal In-use Airfield An active 7,897-foot (2,407 m) long and 151-foot (46 m) wide 

airfield, certified by the Federal Aviation Administration 

(FAA).3

 The runway and taxiway is maintained as an 

emergency landing site for extended twin-engine operations 

(ETOPS) flights across the Pacific Ocean.

Subterranean (both in use 

and abandon)

Utilities, 

Access Points

Military 

Structures

High-voltage service boxes.

Electrical conduit junction sites.

Sewer system access points.

Waterline junction sites and valves.

Abandoned junction points for water, oil, and electrical services. 

Source: Island Conservation (2017). 

All categories comprising the built environment on Sand Island present unique challenges to a 

successful eradication effort. These 3 categories of infrastructure each require specific strategies 

to ensure that rodenticide is applied to every potential mouse territory. 

 

3 In 2004, FAA issued a final rule that revised the Federal airport certification regulation [Title 14, Code of Federal Regulations 

(CFR), Part 139 (14 CFR Part 139)] and established certification requirements for airports serving scheduled air carrier 

operations in aircraft designed for more than 9 passenger seats but less than 31 passenger seats. In addition, this final rule 

amended a section of an air carrier operation regulation (14 CFR Part 121) so it would conform with changes to airport 

certification requirements. The revised Federal airport certification requirements went into effect on June 9, 2004.
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2.2.1.2 Native Species

The presence of wildlife on and around islands targeted for eradication efforts present an 

inherent challenge. In essence, the operation must be able to deliver bait to every mouse on the 

island while minimizing the availability of or the exposure to the rodenticide to other non-target 

species susceptible to it. In addition to the toxicological risks, the operation may also impose 

disturbances and habitat alterations that could have negative impacts on the ecosystem as a 

whole. 

Although impacts to native species are only ecologically significant if they pose a populationlevel threat, in principle all risks to wildlife should be avoided, minimized, or mitigated 

whenever reasonably practicable. As noted in the discussion of principles of successful rodent 

eradication, the benefits of the effort must outweigh the environmental costs and mitigation 

strategies must be considered in the tradeoff framework (Broome et al. 2014). 

MANWR is of great significance (see Section 3.3.6) to several terrestrial and marine species, 

including: 

• The critically endangered, non-migratory resident Laysan duck. 

• The endangered short-tailed albatross (Phoebastria albatrus). 

• High-density breeding populations of Laysan albatross and black-footed albatross. 

• Threatened green sea turtles (Chelonia mydas) use the beach for basking and nesting; 

endangered hawksbill sea turtles (Eretmochelys imbricate) may also be present in 

MANWR but have not been confirmed to bask or nest there. 

• Endangered Hawaiian monk seals (Neomonachus schauinslandi) that use the beaches 

and fore-shore vegetation for resting and pupping. 

2.2.1.3 Resident Community on Sand Island 

Successful island-based rodent eradications have been, for the most part, conducted on remote, 

uninhabited islands free from permanent human settlements or development. Human settlements, 

inadvertently, provide food and shelter to rodents. This situation is referred to as “commensal” in 

that it is used by both humans and rodents; it is a relationship in which the rodents benefit from 

the presence of the humans while the humans can be largely unaffected by the presence of 

rodents. This commensal behavior can represent a significant risk to an eradication attempt, 

decreasing the probability of success. There is precedent to rodent eradications from human 

inhabited islands—a total of 94 documented cases—but these operations require supplemental 

treatment strategies such as targeted hand application of baitmechanical devices (e.g., traps) and 

modification of bait strategies (DIISE 2016). The infrastructure of Sand Island would be no 

exception.

Local communities are frequently key-stakeholders in island eradication projects and must be 

considered from the outset where an eradication effort takes place on an inhabited island. The 

year-round community on MANWR numbers roughly 57 people and includes: (i) USFWS staff 

and volunteers; (ii) base operations staff from Chugach Alaska Corp.; and (iii) transient 

contractors or researchers. The community would bear the direct or indirect negative impacts of 
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invasive rodent infestations and stand to benefit from the outcomes of eradication and 

subsequent restoration efforts. Moreover, these local communities play a significant role in the 

eradication process and maintaining the rodent-free status of Sand Island, which frequently 

requires changes in behavior. In brief, their involvement is essential to the success of all effective 

eradication projects. 

2.2.2 BAIT DISTRIBUTION APPROACHES

The only viable approach to completely remove the house mouse from Sand Island, MANWR is 

the use of rodenticide(s). Other tools and strategies used to control mice were considered but 

rejected because there is no evidence that they would have a reasonable probability of 

eradicating mice on MANWR. See Section 2.5 for a more detailed discussion of approaches 

which were considered but ultimately rejected from further evaluation. 

Use of rodenticide requires the delivery of rodenticide-impregnated bait into every potential 

mouse territory. In order to accomplish this, there are 3 basic methods, and a fourth hybrid 

method: (i) bait stations; (ii) hand broadcast; (iii) aerial broadcast using a helicopter and baitsowing bucket; and (iv) a combination of the above methods. Each of these methods is described 

in greater detail in the following subsections.

2.2.2.1 Bait Stations 

Bait stations have been used in rodent eradication projects on islands ranging from very small to 

relatively large (DIISE 2016). Bait stations typically used in island eradications have been either 

commercially manufactured plastic bait boxes, or plastic pipes, or other similar material. Either 

design allows rodents to enter the stations freely to access bait placed within it, but prevent 

larger, non-target species from easily entering and feeding on the bait and greatly extend the 

longevity of the bait. The major advantage of bait stations is that the bait can be delivered to all 

mice while preventing most non-target species from gaining access to the station or the poisoned 

bait within. 

For eradication purposes, bait stations are systematically placed on a grid pattern in all habitats 

across the entire island. Once placed, bait crews would arm and check stations regularly and rearm each station over a period of months until bait take by rodents declines to zero. Bait stations 

were previously and successfully used at MANWR in the 1990s to eradicate R. rattus. In that 

effort, bait stations were spaced at ~164 ft. (50 m) intervals with live traps in between, ensuring 

that at least 2 stations were found in every potential rat home range. Due to smaller territory size 

when targeting mice, bait stations would need to be at smaller intervals. 

2.2.2.2 Broadcast 

In the 1990s, island managers began to explore more efficient techniques to undertake 

eradications more quickly and on larger islands, and adopted methods of broadcasting 

rodenticide impregnated bait using both hand broadcast and aerial broadcast (see additional 

discussion below). Bait, in the form of cylindrical or spherical pellets, is broadcast evenly across 

the landscape at a prescribed application rate calculated as kilograms per hectare or pounds per

acre (i.e., kg/ha or lbs./ac.) so that all rodents have access to it for long enough to find the bait, 

overcome any neophobia, and consume a lethal dose. 
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A strategy which broadcasts bait across the island, whether by hand, helicopter, or both can 

achieve success in a significantly shorter timeframe than with bait stations as it exposes all target 

individuals at one time and avoids the risk of neophobia related to animals entering bait stations. 

2.2.2.2.1 Hand Broadcast 

Broadcast of bait by hand is the second most-documented approach to island rodent eradication 

efforts (DIISE 2016). Bait is typically distributed by a team of baiters who systematically walk 

on parallel transects, stopping at predetermined intervals to distribute pellets as evenly as 

possible in a quadrant or circle.4 As the end of one transect is approached, the teams move over 

to the next transects and start anew, treating the entire area of the island in a “rolling front”. 

For successful hand broadcast of bait, significant advance preparation is required to ensure 

efficient application and to minimize delays and errors in bait application. Complexity increases 

with the size of the land area and the topography of the island being treated. Transects through 

heavy vegetation would be opened using mechanical or hand tools to create a path to all baiting 

points in advance, and each broadcast point would be marked using flagging or pins, and 

recorded by global positioning system (GPS) technology. Bait must also be staged at various 

accessible locations across the island to minimize the time and effort needed for baiters to refresh 

their supplies as they progress across the treatment transects. 

2.2.2.2.2 Aerial Broadcast 

Aerial broadcast for rodent eradication projects involves using a commercial-grade bait bucket 

slung under a helicopter, guided by GPS to evenly distribute bait across the entire area of the 

island. The set rate at which the bait exits the bucket, the width of the treatment swath, and flight 

speed are calibrated to achieve a desired application rate. The pilot is guided by a computer 

connected to a GPS and guidance system to keep the helicopter on pre-programmed bait 

application flight lines. The bait flow from the bucket is controlled by the pilot at all times, 

opening and closing the bait bucket on demand to apply bait in desired areas and minimize bait 

application in other areas, such as the marine environment. The hopper can be fitted with a 

deflector to broadcast bait out to one side, allowing the helicopter to fly parallel to and along the 

shoreline with minimal unintentional bait applications. Bait application along the shoreline can 

be accomplished with minimal bait drift into the marine environment with the use of a deflector. 

The infrastructure on MANWR, provides a highly suitable base from which to implement an 

aerial broadcast operation. This includes support equipment for loading bait and large 

operational areas for loading and refueling. The airfield services available there include: (i) 

equipment staging; (ii) aircraft storage; (iii) fuel supply; and (iv) necessary fire, medical, and 

support infrastructure. 

 

4 See: http://rce.pacificinvasivesinitiative.org 
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2.2.2.3 Summary 

Table 2.3 below summarizes the relative advantages and disadvantages of the 3 methods of bait 

application discussed in the preceding sections. 

Table 2.3 Summary of Technical Considerations 

Method Advantages Disadvantages

Bait 

Stations • Requires least total bait.

• Controlled bait delivery.

• Lower mobilization of 

bait into ecosystem.

• Easier removal of 

residual bait when effort 

concluded.

• Lower risk of primary 

exposure to non-target 

species.

• Limits requirement for 

specialized skills.

• Rodents are often neophobic and take time to enter bait stations.

• Difficult to ensure all rodents have access to bait.

• Labor intensive and significan set up time.

• Presents logistical challenges and safety risks related to managing a 

large team conducting repetitive and demanding physical labor and 

accessing all parts of the island. 

• Relatively slow, with total eradication requiring a period of between 

several months to several years. 

• Non-target species are exposed to secondary risks for a prolonged 

period. 

• Requires a very large number of bait stations and access trails to 

bait stations with prolonged impact to vegetation. 

• Prolongs potential for direct impacts to ground-nesting seabirds and 

seabird burrows and repeated disturbance to monk seals and turtles. 

Broadcast 

in general • High likelihood that all 

rodents have access to 

bait.

• Minimizes any 

neophobic behavior 

towards bait delivery 

devices

• Shorter period of bait 

availabillity.

• Requires more bait.

• Bait is readily available to non-target species.

Hand 

Broadcast 

specific

• Allows greater control 

over bait application.

• Limits requirement for 

specialized skills.

• Labor intensive.

• Presents logistical challenges and safety risks related to managing a 

large team conducting repetitive and demanding physical labor. 

• Requires transect paths along with access to all areas with dense 

vegetation and fragile areas. It is not possible to bait entire island in 

a single day. Precision needed is not achievable.

• Potential for direct impact to ground-nesting seabirds and seabird 

burrows and repeated disturbance to monk seals and turtles. 

Aerial 

Broadcast 

specific

• Fastest method for 

applying bait to a large 

area.

• Relies on a smaller team 

of workers.

• No need to clear trails.

• Requires specialized skills and equipment. 

• Depending on the label, may or may not be restricted over inhabited 

areas. 

• Distribution is limited to exposed areas and does not allow 

distribution of bait within buildings, under structures or 

underground. 

• May result in some unintentional bait entering the ocean. 

Source: Island Conservation (2017)
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2.2.3 RODENTICIDE AND BAIT CONSIDERATIONS

Several factors must be considered in the selection of a bait product and associated toxicant for 

rodent eradication. Under ideal conditions, the bait product would have demonstrated 100% 

efficacy under both laboratory and field trials on the target island. In addition, it would have been 

successfully used to eradicate the target species (i.e., house mice) on other islands. It would also 

have low risk to non-target species. From an eradication perspective, the rodenticide used on 

Sand Island, MANWR must: 

• Contain an active ingredient that is known to be highly toxic to mice; 

• Be palatable and demonstrated to cause little or no aversion in mice; 

• Be deliverable to every potential mouse territory on the island; 

• Be legally registered for use in compliance with the Federal Insecticide, Fungicide 

and Rodenticide Act (FIRFA); 

• Kill mice with a single application to avoid bait shyness; and

• Be of low attractiveness to non-target species. 

Presently there are 10 different rodenticides approved for use and available on the market in the 

United States. However, only 3 anticoagulant rodenticide products are currently registered for 

conservation use and therefore available for the eradication of rodents from island ecosystems; 

they are characterized in Table 2.4 below. 

Table 2.4 Rodenticides Approved for Conservation Use in the United States 

Name Description

Diphacinone D50 A 0.07 to 0.17 ounces (oz) (2-5 g) pelleted bait product containing 50 parts per million 

(ppm) diphacinone, adopted for use primarily in Hawaiʻi for main island conservation, 

landscape control, and eradication from offshore islets. It is made by Hacco, Inc. and 

Ditrac 50D by Bell Labs

Brodifacoum-25D A 0.03 to 0.07 oz (1-2 g) pelleted bait product containing 25 ppm brodifacoum, designed 

for use on islands with Mediterranean climates. It is produced by Bell Labratories, Inc.

Brodifacoum-25W A 0.07 oz (2 g) pelleted bait containing 25 ppm brodifacoum, designed for use on islands 

with wet to very wet climates. It is produced by Bell Laboratories, Inc. 

Source: Island Conservation (2017)

The major advantage of anticoagulant rodenticides is the delayed onset of symptoms, usually 

requiring between 2 and 3 days to take effect. They are not known to cause aversion, referred to 

as “bait shyness,” as per acute toxicants which rodents may learn to associate with their sublethal 

effects, and rodents would continue to feed on the bait even after symptoms develop (Parkes et 

al. 2011). Some rodents are even known to continue to feed on bait during the latent period, the 

time between ingestion of a lethal dose and mortality (Howald et al. 2005, Buckelew et al. 2005). 

First generation anticoagulant rodenticides, such as diphacinone (see Table 2.4), are multi-feed 

rodenticides and rodents need to consume bait over a sustained period of days to achieve 

mortality, which may vary from 3 to 12 days of ingestion for a lethal dose. Diphacinone has been 

successfully used to eradicate rats from islands, typically delivered by bait stations with 

relatively few instances of broadcast being the delivery method (DIISE 2016). It has been used in 
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efforts to eradicate house mice on islands twice, with one instance being a reported success and 

one a failure (Samaniego 2016). 

Second generation anticoagulant rodenticides, such as brodifacoum, can be toxic after a single 

exposure or feeding event to sensitive rodents (Kaukeinen 1993). In some laboratory trials of 

brodifacoum, 100% mortality of rats and mice have been reported after a 3-day choice test (Pitt 

et al. 2011). Globally, a total of 87 house mouse eradication attempts have been carried out, and 

all but the 2 mentioned above using diphacinone, utilized brodifacoum. 

2.3 PREFERRED ALTERNATIVE: MOUSE ERADICATION WITH 

RODENTICIDE VIA MULTIPLE DISTRIBUTION METHODS 

The Preferred Alternative consists broadly of: 

• The use of Brodifacoum-25D rodenticide with supplemental trapping.

• Multiple bait distribution methods – primarily aerial broadcast but also supplemental 

hand broadcast and bait stations (Section 2.3.1).

• Three bait applications spaced roughly 7-10 days apart (Section 2.3.2), projected to

start in early July (Section 2.3.5).

• Implementing mitigation measures identified for selected species in Chapter 3. 

• Implementing effectiveness monitoring to assure mitigation is carried out and 

determine if mitigation is producing the desired results. 

• Employing long-term biosecurity protocols to prevent the reinvasion of the island by 

mice and rats. See Appendix A for a summary of long-term biosecurity protocols 

developed for MANWR. 

Implementation of the proposed action is currently being considered for July/August 2019. 

2.3.1 BAIT AND ITS DISTRIBUTION METHODS

The toxicant to be employed as part of the Preferred Alternative would be Brodifacoum-25D 

Conservation, a pelleted rodenticide bait intended for conservation purposes for the control or 

eradication of invasive rodents on islands or vessels. Island Conservation’s Feasibility Report

(2017) specifically recommends the use of a bait containing brodifacoum and notes that use of a 

less robust alternative rodenticide could compromise the success of the eradication effort. The 

rodenticide bait used for Sand Island would be dyed a green color to reduce the likelihood of 

birds picking up the bait. 

The Preferred Alternative consists of the use of brodificoum to eradicate all mice on Sand Island, 

MANWR via 1 primary method and 2 supplemental distribution methods. The 3 methods (Island 

Conservation 2017) are discussed in the following 3 subsections. 
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2.3.1.1 Primary Distribution Method – Aerial Broadcast 

Aerial broadcast (Section 2.2.2.2.2) of a pelleted bait containing rodenticide across the entire 

emergent land area, except:

• The portion of the airfield within the Foreign Object Debris (FOD) management area, 

which is delineated by large, conspicuous painted aircraft control lines on the tarmac. 

• Portions of the coastal fringe where metal retaining structures combine with eroding 

sand to create undercut areas, rock piles, and piers. 

• Within a buffer zone around the fresh water ponds that cannot be covered by tarps or 

cannot be protected by other means. 

• Indoor residential/commensal areas; aerially baiting over all buildings will occur if 

the supplemental label allows. 

Bait would be applied using bait stations or by hand broadcast and along the narrow sea wall on 

the harbor entrance. Aerial broadcast would also likely occur over rock piles on the island. These

piles are rock staged for shore stabilization. Aerial broadcast is the most widely-used method of 

delivery of pelletized bait on islands, and is effective in delivering bait into every potential open 

above ground mouse territory. The helicopter broadcasting the rodenticide would fly at speeds 

ranging from 29-58 mph (46 - 93 km/hr.) and at an average expected altitude of approximately 

164 ft. (50 m) above the ground. The bait hopper would be on a long-line 20-30 ft. (6 - 9 m) 

slung below the helicopter. Therefore, the bait hopper would be approximately 134 to 144 ft. (41 

– 44 m) above the ground during the rodenticide drop. Except for landings and take-offs at the 

runway, the helicopter would fly at an average altitude of 164 ft. (50 m) and the bucket would be 

>134 ft. (>41 m) above the ground most of the time. The height of the helicopter would likely be 

higher when over forested areas or buildings. These numbers are an estimate and may change as 

needed to complete the baiting operation safely and effectively. The helicopter pilot would be 

certified for aerial bait application and in compliance with FAA safety requirements.

Three bait drops are planned on Sand Island using 2 helicopters to maximize the chance of 

completing each drop in a single day. It is expected each drop would take a total of 20 flight 

hours or 60 total flight hours for the entire operation; total flight time could be longer. Check 

flights and boundary flights will also add to the total flight time. 

Bait would be delivered in shipping containers from the point of manufacture in the Mainland 

U.S. The rodenticide bait would be stored in locked shipping containers. The shipping containers 

would protect the bait from exposure to the elements and would allow a controllable area to 

access bait during aerial broadcast operations.

Bait would be packaged in either 50 lbs. (23 kg) bags, or in large (up to 700 lbs. or 318 kg) bags, 

and loaded into large cardboard boxes on skids. The shipping containers would remain locked, 

and staged in a large storage building adjacent to the airport runway on Sand Island and opened 

periodically for inspection prior to the eradication, and during the baiting operation. Bait would 

be loaded either manually by hand from bags into the hopper, or directly from bulk bags. 
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2.3.1.2 Secondary Distribution Method – Supplemental Hand Broadcast 

Supplemental hand broadcast of pelleted bait and the use of bait stations (Section 2.2.2.1) with 

rodenticide would be used in the following areas: 

• The locations listed above where aerial broadcast would not be conducted. 

• Key shoreline habitats (e.g., across causeways too narrow for aerial broadcast and 

along seawalls or armored shorelines). 

• In commensal environments such as within aboveground and underground structures. 

Within the commensal environment, where people are typically not present, hand broadcast may

be employed, along with the following supplemental bait station methods for distributing bait 

inside occupied structures: 

• Hand placement of loose bait trays, with an open top to expose bait. 

• Bait bolas, where the bait is held within rodent accessible material that can be hung in 

place to keep out of water. 

• Enclosed bait stations (either tubes or bait boxes with lids). 

Each structure, in use, abandoned, or condemned and above ground or below ground, would be 

individually identified and assigned a unique mouse removal strategy, known as a Structure 

Management Plan (SMP); all SMPs would outline a structure-specific mixture of secondary 

distribution methods (hand broadcast and/or bait stations) plus the possible use of traps. The 

following factors would be considered and recorded when developing each individual SMP: 

• Structure category and use;

• Numerical identification;

• GPS coordinates and GIS map; and

• Details regarding how it is to be treated throughout the implementation period

including detailed maps of bait application and placement. 

When available, photographs of the structure and a floor plan showing treatment options may be 

included. 

2.3.2 NUMBER AND RATE OF BAIT APPLICATIONS 

Bait must be delivered at an application rate that ensures bait is made available to all mice on the 

island for long enough that each individual mouse would be exposed to, and consume a lethal 

dose of the toxicant. The application rate needs to account for other species that compete with 

mice to gain access to the bait. Some competitor species, like invertebrates such as crabs and 

insects, can consume a significant amount of the bait but are not affected by the rodenticide

(Island Conservation 2017). Other avian competitor species, such as the myna, cattle egret, 

canary and Laysan duck, could also consume bait and would be negatively affected by the 

exposure. Bait application rates are set to ensure that adequate amounts of bait are available for 

long enough, regardless of the number of species or individuals that consume it. Based on other 

eradication efforts, a minimum of 4 nights bait availability may be necessary (Keitt et al. 2015). 
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Three bait drops are planned on Sand Island using 2 helicopters to maximize the chance of 

completing each drop in a single day. These drops would be spaced 7-10 days apart. Overall, the 

expected target application rate on Sand Island would be 65 lbs./ac. (73kg/hectare) with further 

refinement based on ongoing field trials with non-toxic bait. This approach would ensure that 

bait is available for a minimum of 4 nights each drop, and it would intercept any new generations 

of mice that may have been missed during or emerge after earlier bait applications. All 

applications would be made in compliance with the EPA bait label. 

The bait would be applied according to a helicopter flight plan that would take into account the 

need to: (i) apply bait relatively evenly and to prevent any gaps in coverage; (ii) accommodate 

island topography; (iii) minimize bait spread into the marine environment; (iv) minimize 

disturbance to native wildlife and; (v) ensure human safety.

The onboard computer linked to the GPS would serve as the primary method of monitoring 

where bait has been applied to the island. Data from the onboard computer would be downloaded 

from the computer and evaluated on a laptop computer to assess where bait has been applied and 

total area treated, in order to calculate the approximate actual bait application rate.

A monitoring team would be staged on Sand Island to collect near-real time data during the bait 

application to ensure that the application rate stays within the legal and optimal application rates. 

In addition, a monitoring plan would be implemented to determine if: (i) eradication of mice is 

progressing as expected (mice mortality), and (ii) potential risks and expected impacts of the 

rodenticide in the environment and to non- native species are documented and in compliance 

with applicable permits and guidelines (e.g., NEPA permits and labels). At a minimum, sampling 

of marine water, fish, birds, and rodents would be made. To implement the monitoring plan, a 

field team would be present on Sand Island for approximately 6 weeks.

2.3.3 MECHANICAL TRAPPING

Mechanical traps including, but not restricted to, snap-traps and glue boards would be employed 

in conjunction with hand broadcast and/or bait stations in the commensal environment and other 

areas where bait is not aerially broadcast, as deemed appropriate per the terms of each structure’s 

SMP (see Section 2.3.1). These traps would be used as an additional detection and removal 

method within structures to appropriately target mice. Traps would be activated and checked on 

the same schedule as bait stations within buildings, except live traps, which would be checked 

daily. 

2.3.4 PRE-APPLICATION PREPARATIONS

The collection of water in the storage tanks would be maximized prior to the eradication effort. 

The water storage tanks, when filled to capacity, have the ability to provide water to the island 

for a 2-year period. Once the tanks are full, they would be disconnected from the water collection 

system and the intake-grates covered prior to bait application. 

MANWR must remain an active residential community before, during, and after the Midway 

Seabird Protection Project. Certain activities, such as maintaining the airfield’s operability, 

potential construction projects, biological monitoring, and maintenance of facilities and utilities 

would continue and the eradication effort must accommodate these activities. However, 
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modifications to the day-to-day systems, processes, and infrastructure can, and in certain cases 

must, be made to minimize the risk of eradication failure. These may include: 

• Procedural changes to food delivery, handling, storage, and disposal. 

• Procedural changes to grow operations at the hydroponic gardens. 

• Procedural changes to food preparation and consumption. 

• Modifications to waste disposal and the on-island landfill.

• Development of a biosecurity plan which would prevent reintroduction of mice and 

rats. See Appendix A for a summary of the biosecurity plan developed for MANWR. 

Food would be stored at all times in rodent proof containers. Some food comes in rodent proof 

containers (e.g. canned food), but food that may be more accessible (loose vegetables, bags of 

rice) would be put in containers that can be closed tight. Additional bait stations/traps may be 

deployed in areas where food is stored as well. At a minimum, each grow operation (e.g. tables, 

pots on ground) would be assessed and determined if it should be removed or modified to 

prevent mice from accessing food. Baits stations, bait trays, and/or traps would be placed in the 

shade house and modifications may be made to further prevent mice from accessing food. Any 

food growing operation would be closely monitored for signs of mouse activity and be responded 

to accordingly.

For food preparation and consumption, personnel would be trained in proper procedures, which 

would likely include emphasis on not leaving food out and immediate clean up. Garbage would

be stored in sealed containers at all phases (in buildings, outside, when awaiting incineration), 

and the garbage collection schedule may likely be modified to include more frequent collections

and complete incineration. Additional discussion of human health and safety factors are provided 

in Section 3.3.6.21. 

2.3.5 APPLICATION SCHEDULE

In MANWR, the average period of lowest rainfall is from April through July, with increasing 

rainfall from late summer through winter. Reports from island biologists suggest that the 

condition of low vegetation such as grasses are deteriorated due to dry conditions and trampling 

by albatross chicks. Thus, the lowest availability of vegetation as a food source to mice, and 

likely low point in their annual population cycle, is probably between May and July. The low 

precipitation and low level of vegetation food sources make the summer a very attractive 

timeframe for an eradication effort employing bait broadcast. 

The role that nesting albatross play in providing alternative food sources to mice (i.e., dead 

chicks and adults, and regurgitated food), and the influence it may have on the annual mouse 

population cycle is unclear, but it may be relevant. To date, there is no data available on the 

annual mouse population cycle, but for the purposes of this eradication effort it is assumed that 

the mice breed year-round, even though it is likely that the rate at which they breed fluctuates on 

an annual and intra-annual basis, depending on climate (Brown and Singleton 1999, Drost and 

Fellers 1991). 
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The presence of potential nontarget species on Midway is another consideration in selecting the 

rodenticide application period. There is no point in the year when non-target species are not 

present on Sand Island; however, the late summer timeframe is considered better than other 

times because relatively few potential non-target species are typically present (see Section 3.3.6).

Based on these considerations, the first rodenticide application would occur in early July. A 

second application would occur roughly 7-10 days later, and a third application conducted 

roughly 7-10 days after the second application. 

If a significant storm event (i.e., tropical storm) is forecast to occur within 7 days after the 

application of the rodenticide, then the application would be postponed until the threat of the 

storm has past. Other dynamic elements, such as the presence of bird airstrike hazards (BASH), 

high winds, and other factors may also require adjustments in the project implementation 

schedule. This measure, like many other considerations detailed in this Chapter, is included to

avoid and minimize potential adverse environmental effects and increase the potential for 

success.

2.3.6 MITIGATION ACTIONS AND EFFECTIVENESS MONITORING 

Mitigation measures and actions identified for multiple species in Chapter 3 would be carried out 

and monitored for their effectiveness. Effectiveness monitoring tracks the success in achieving 

desired outcomes and evaluating environmental effects. Mitigation includes specific measures or 

practices that would reduce, avoid or eliminate the effect of the proposed action on non target 

species. In this EA, the identified mitigation measures are part of the proposed action (project) 

and necessary to support a FONSI. Examples of mitigation measures in Chapter 3 include: 

training ground-based staff to identify endangered plants and how to avoid stepping on burrows; 

capturing and moving vulnerable species to avoid rodenticide exposure; measures to minimize 

bait entering the marine environment; and measures to reduce impacts to sea turtles and monk 

seals. For detailed descriptions see the mitigation section for each species in Chapter 3. 

2.3.7 POST-APPLICATION ACTIONS

Post-application actions include 3 critical tasks: 

• Post-treatment efficacy monitoring and post reatment environmental effects and 

residue monitoring for rodenticide in the terrestrial, freshwater aquatic, and marine 

environments and for documenting mortality of non-target organisms. 

• The remaining potable water would undergo additional filtration and no additional 

fresh water would be collected until a monitored degradation of residual bait pellets 

and rodenticide residue indicated that the potable water system was free of 

rodenticide. See Section 3.3.2 for a detailed discussion of water resources and 

management systems present on Sand Island, MANWR. 

• Implementation of the long-term biosecurity plan to prevent the reintroduction of 

mice on Sand Island, MANWR (see Appendix A). 
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2.3.8 CONTINGENCY PLANNING

There is a chance that the project could fail to eradicate all mice after the main implementation 

phase. The follow-up actions should one or more mice be detected after the project is 

implemented will vary based on the time and circumstances of the detection. Additional baiting 

may occur in areas where mice are found if the circumstances dictate there is a reasonable 

chance of eliminating any remaining mice without additional adverse effects. Should the project 

fail entirely and a mouse population persists, the partners will undergo reviews to determine the 

main causes of failure, and to identify possible solutions to those failures to inform a new 

strategy for future eradication attempts. Mouse population control using cholecalciferol would 

continue proactively and reactively to reduce mouse attacks on albatross while a new eradication 

strategy is being developed.

2.4 ALTERNATIVE 2: NO ACTION 

Analysis of the “No Action” Alternative, the alternative in which current conditions and trends 

are projected into the future in the absence of the proposed action, is required pursuant to NEPA 

[40 CFR 1502.14(d)]. In this case, under the No Action Alternative, Sand Island’s mouse 

population would not be the subject of a targeted eradication project, but mouse control efforts 

started in 2016 would continue to protect nesting seabirds and human health and safety. 

Mouse control on Sand Island currently consists of: (i) using traps and rodenticide bait stations in 

commensal areas such as food storage and preparation areas to maintain human health standards, 

as well as in areas near buildings, manmade structures, at the airport, and on shipping docks 

receiving conveyances; (ii) multi-catch live trapping; and (iii) rodenticide bait stations and hand 

broadcasting of AGRID3 Pelleted Bait for seabird and listed candidate plant protection in areas 

where mouse predation of seabirds and mouse damage to listed or candidate plants is detected. 

The bait product AGRID3, (active ingredient 0.075% cholecalciferol; Bell Laboratories, Madison, 

WI; approved for restricted use at MANWR under a supplemental label for mouse control) is a 

non-anticoagulant. It disrupts calcium homeostasis by increasing calcium absorption from the 

small intestine and mobilization from the bones into the blood stream, as well as decreasing 

calcium excretion by the kidneys. The effectiveness of this product on rodents has been proven

in limited hand-broadcast situations, and it is relatively safe to nontarget species if used 

according to label directions (Marshall 1984, Eason et al. 2000, DurShultz et al. in press, 

USFWS, Unpublished b).

Trapping includes: (i) multi-catch live traps; and (ii) mechanical traps (snap-traps and glue 

boards) used in the commensal environment as deemed appropriate per the terms of each 

structure’s SMP (see Section 2.3.1). 

Hand broadcasting previously involved 2 separate hand-broadcast applications of AGRID3

pellets. Following label instructions, a 17.8 lbs./ac. (20 kg/ha) application rate was used over 27 

ac (11 ha) where evidence of mouse attacks occurred in 2016. Future applications starting in 

November 2017 prior to the albatross’s main egg laying season, would occur at the same rate and 

area and then would occur as needed if and where mouse attacks occur throughout the incubation 

period, up until the following February. 
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It should be noted that there were no observations of any non-target organism such as shorebirds 

or Laysan ducks interacting with AGRID3 bait pellets in the field or being found sick or dead in 

the colony as a result of the baiting process in 2016/2017 (DurShultz et al, in press; USFWS, 

Unpublished b). Toxicity tests by Eason et al. (2000) found that the lethal dose for a mallard

duck is 4.4 lbs. (2000 g) of 0.08% cholecalciferol. There is the potential for Laysan ducks to

consume some bait, but it is unlikely they would consume lethal amounts. Further, to reach a 

lethal dose, a Laysan duck would need to ingest 3 times its body weight in pellets, which is 

unlikely to occur (DurShultz et al. in press). Both control measures (i.e., trapping and rodenticide 

treatment) are ongoing.

There are currently no other activities taking place at Sand Island, MANWR in terms of mouse 

management or control; however, other unrelated invasive species management and conservation 

operations at MANWR would continue per their respective agency plans. In addition, any other 

non-USFWS programs or projects would continue to be implemented under their respective 

authorities. 

The No Action Alternative would be contrary to: (i) general principles of wildlife management; 

(ii) the PMMP’s strategy AS-4; which calls for conservation actions to continue predator control 

and eradication of predators at Laysan and black-footed albatross nesting colonies; (iii) multiagency conservation action plans for the black-footed and Laysan albatross (Naughton et al. 

2007) that recommend eradicating house mice from MANWR to protect these 2 species of 

seabirds; and (iv) the USFWS Regional Seabird Conservation Plan (USFWS 2005) that 

identified the eradication or control of introduced predators and other invasive species that have 

a negative impact on seabirds as one of the top priorities for seabird conservation. The USFWS 

Regional Seabird Conservation Plan specifically recommended eradicating introduced predators 

in the Pacific Islands where the Laysan and black-footed albatross breed. 

The purpose of the NWRS is to administer a national network of lands and waters for the 

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

resources and their habitats within the US and outlying territories for the benefit of present and 

future generations of Americans. Further, the No Action Alternative would be contrary to the 

USFWS’ policy on maintaining the biological integrity, diversity, and environmental health of 

the NWRS. Finally, it would not achieve the USFWS’s project objectives summarized in Section 

1.2. It is included here because it is appropriate under the environmental review process 

mandated by NEPA, and to provide a baseline for comparison with the potential impacts of the 

proposed action. 

2.5 ALTERNATIVES CONSIDERED BUT REJECTED 

The USFWS evaluated several different approaches to house mouse eradication. Ultimately the 

alternative approaches summarized below were rejected from further evaluation because of the 

lack of evidence that these alternative tools and strategies would have a reasonable likelihood of 

eradicating mice on MANWR or thus achieving the purpose and need for the Project. These 

approaches are briefly described in the following subsections. 
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2.5.1 EMERGING TECHNOLOGIES 

Ongoing research continues into the development of technologies for the control of introduced 

rodents. If these tools, currently in development, ultimately become available they may have 

either incremental or transformative impacts on the way in which eradication projects are 

approached. These technologies include: (i) reproductive inhibitors; (ii) species or genus specific 

toxins; and (iii) genetic bio-control. In a review of rodent control methods, Buckle and Smith 

(2015) state that reproductive control is not yet safe or effective for field use. Fertility control has 

been used with limited success as a method of pest management in a few species. Experimental 

sterilization methods have included chemicals and proteins delivered by vaccine, and 

genetically-modified viral pathogens. However, the effectiveness of these experimental 

techniques in the wild, and their impacts to nontarget animals are unknown. Aerial application of 

rodenticide is a more practical, effective, and a safer method to eradicate rats than repeated 

baiting of uncertain oral contraceptives on a remote island across seasons or capturing, 

vaccinating, and releasing every member of a single gender of the Palmyra rat population. This 

lack of data and tools disqualifies the use of fertility control from detailed consideration (Tobin 

and Fall 2005). 

Currently, however, the several methods mentioned above are in development and none are 

likely to be available prior to 2023, the deadline for eradication of house mice on Sand Island, 

Midway Atoll established by the PMMP-ASAP Strategy AS-4. Therefore, this approach was 

rejected from further evaluation because it would not achieve the project objectives summarized 

in Section 1.2. 

2.5.2 MOUSE ERADICATION USING CHOLECALCIFERAL (AGRID3) RODENTICIDE

Cholecalciferol (Agrid 3 by Bell Labs), a non-anticoagulant rodenticide, can kill rodents more 

quickly than the anticoagulant rodenticides by disrupting calcium absorption and decreasing 

calcium excretion in the kidneys. It is an attractive alternative because of its lower toxicity to 

birds. This product is currently being used at MANWR to control mice (not eradicate them) by 

hand broadcast in limited areas. However, these non-anticoagulant rodenticides are untested on 

islands larger than 22 ha (~54 ac) (Howald et al. 2007). Furthermore, there is no cholecalciferal 

product registered by the EPA for aerial broadcast and the purpose of island-wide eradications

for mice. Using MANWR as a test island, without a high probability of success, would be 

inappropriate due to the high financial cost of the operation. These factors, lack of field-testing 

on islands comparable to Midway, potential bait avoidance, and greater human safety risk 

disqualifies them from detailed consideration for use on a MANWR eradication.

2.5.3 USE OF FIRST-GENERATION RODENTICIDE

Island Conservation’s Feasibility Report (2017) specifically recommends the use of a bait 

containing brodifacoum and notes that use of a less robust alternative rodenticide could 

compromise the success of the eradication effort. As mentioned in Section 2.2.3, first generation 

anticoagulant rodenticides, such as diphacinone, are multi-feed rodenticides and rodents need to 

consume bait over a sustained period of days to achieve mortality, which may vary from 3-12 

days of ingestion of a lethal dose. Diphacinone has been successfully used to eradicate rats from 

islands, typically delivered by bait stations with relatively few instances of broadcast being the 
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delivery method (DIISE 2016). It has been used in efforts to eradicate house mice on islands 

only twice, with one instance being a reported success and one a failure (Samaniego 2016). 

Second generation anticoagulant rodenticides, such as brodifacoum, can be toxic after a single 

exposure or feeding event to sensitive rodents (Kaukeinen 1993). In some laboratory trials of

brodifacoum, 100% mortality of rats and mice have been reported after a 3-day choice test (Pitt 

et al. 2011). Globally, a total of 87 house mouse eradication attempts have been carried out, and 

all but the 2 mentioned above using diphacinone, utilized brodifacoum. Of the 31 house mouse 

eradication attempts carried out between 2005 and 2015, 28 of them were successful; this 

represents a 93.3% success rate (DIISE 2016). 

The anticoagulants brodifacoum and diphacinone both bind to the same molecular site in the 

liver. Ingestion of these compounds would only lead to death in the exposed animal if a toxic 

threshold of one or more of these compounds is maintained in the liver consistently for a 

sufficient period of time. Brodifacoum molecules bind comparatively tightly in the liver, so the 

same brodifacoum molecules that are ingested on Day 0 are highly likely to remain in the liver 

for an extended period (Fisher et al. 2003). 

Thus, a single feeding of a threshold quantity of brodifacoum is sufficient to ultimately induce 

lethal toxic effects in the exposed animal. Diphacinone, on the other hand, binds comparatively 

loosely in the liver, with a half-life measured in days (Fisher et al. 2003), so diphacinone 

molecules ingested on Day 0 are much less likely to remain in the liver for multiple days from a 

single feeding. Thus, to maintain a threshold lethal level of diphacinone in the liver consistently 

for sufficient time, a rodent needs to consume diphacinone in multiple feedings over multiple 

days so that it accumulates in the system faster than the liver processes it out. In application, this 

means bait must be available to each rodent to feed on at multiple times over a few days, and 

thus a longer period of time compared to brodifacoum. 

Comparisons of Diphacinone to Brodifacoum 

Diphacinone presents less risk to non-target species than brodifacoum (Howald et al. 2007, 

Erickson and Urban 2004). As described above, species that might ingest bait pellets 

opportunistically or accidentally are much less likely to ingest a lethal amount of diphacinone in 

one exposure (Hoare and Hare 2006). Predatory and scavenger species are also less likely to 

consume a lethal amount of toxin when preying on individuals that are dead or dying from 

primary exposure to the rodenticide, since diphacinone is retained only at a low level in body 

tissues. However, the successful eradication of rodents on islands using baits is partly dependent 

upon overcoming bait avoidance by rodents and inadequate bait consumption. While 

diphacinone generally presents less risk to non-target species than brodifacoum, its low retention 

in body tissues and its multiple feeding requirement results in a higher risk of failure in rodent 

eradication efforts (Donlan et al. 2003). All other operational considerations being equal, the task 

of delivering enough bait to all rodents on the island to ensure 100 % mortality is less certain to 

succeed when using diphacinone than when using brodifacoum. Rodents that survive 

diphacinone bait application may be resistant to first-generation anticoagulants (e.g., 

diphacinone), or could be unable to find or consume adequate bait to maintain lethal effects of 

diphacinone dose, avoid bait after a single feeding, or a combination of these. These rodents, and 

possibly their offspring, could consequently be more difficult to eradicate from the island in any 
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subsequent attempts. The use of the much more field-tested brodifacoum provides a greater 

degree of confidence that the eradication program would succeed.

While both sides of this balancing equation are important, the need to ensure eradication success 

is particularly acute. An incomplete eradication attempt would provide few conservation returns 

in the long term, since mice at low densities have the ability to reproduce at higher rates and 

would quickly reoccupy vacant territories throughout the island. The only way to attain costeffective, and ecologically secure, long-term conservation returns on this investment is through a 

successful and complete eradication. In summary, the safety risks associated with an aerial or 

hand broadcast operation can be somewhat mitigated with the use of a more potent toxicant such 

as brodifacoum. Therefore, the USFWS has rejected this alternative from further consideration. 

2.5.4 MOUSE-PROOFING STRUCTURES 

Modifying existing manmade structures to be rodent-free may be a viable strategy to eliminate 

house mice within buildings, but would come with considerable cost and have little utility once 

mice were eradicated from the remainder of the island. Further, mouse-proofing would not 

achieve the project objectives outlined in Section 1.2, and therefore has been rejected as an 

eradication strategy. It is more efficient and cost-effective to specifically target mice in and 

around manmade structures as part of a comprehensive eradication campaign. Therefore, the 

USFWS has rejected this alternative from further consideration. 

2.5.5 AERIAL BROADCAST RODENTICIDE ONLY 

An aerial broadcast only approach to mouse eradication on Sand Island, MANWR would not 

effectively administer bait to the buildings and other infrastructure located there, whether 

occupied or abandoned. This factor alone means that a supplemental treatment by some other 

method, such as hand broadcast, would be required to address this mouse habitat. Conducting a 

mouse eradication project on Sand Island, MANWR solely relying on aerial broadcast of 

rodenticide would be incomplete in its application (i.e., within structures and in below-ground 

infrastructure) and unlikely to attain the project objectives outlined in Section 1.2. Aerial 

broadcast only would also potentially lead to some bait drifting into the marine environment in 

areas where the shoreline is too narrow for aerial applications such as causeways or where 

seawalls and armored shorelines exist. Therefore, the USFWS has rejected this alternative from 

further consideration. 

2.5.6 HAND BROADCAST RODENTICIDE ONLY 

If hand broadcast alone were employed, then distribution transects would need to be spaced a

maximum of approximately 66 ft. (~20 m) apart to ensure enough bait was available in every 

mouse territory. To achieve that end, Island Conservation (2017) estimates that more than 200 

worker-days would be necessary to achieve a single complete hand broadcast operation across all 

of Sand Island, MANWR. This approach would: (i) be very labor-intensive; (ii) would need to be 

very carefully implemented and managed; (iii) would require a period of 2 or more months to 

complete, assuming a work crew of 40 individuals and between 2 and 3 bait applications across 

the entire area of Sand Island; and (iv) would increase the risk of damage to seabird burrows and 

vegetation as a result of worker movements. It is unlikely that MANWR’s facilities and 
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resources could effectively accommodate the large workforce needed to complete each 

application in a single day. Reducing the number of individuals working on the eradication 

would increase the number of days needed per application and would increase the complexity of 

the project. Finally, this time-estimate does not include applying bait within condemned and 

abandoned structures, where hand broadcast is not considered a viable method due to human 

health and safety concerns. Conducting a mouse eradication project on Sand Island, MANWR 

solely relying on hand broadcast of rodenticide would be time consuming, costly, unable to be 

adequately applied in some condemned structures, and unlikely to attain the project objectives 

outlined in Section 1.2. Therefore, the USFWS has rejected this alternative from further 

consideration. 

2.5.7 BAIT STATION RODENTICIDE ONLY 

Specific considerations related to using bait stations as the sole means of mouse eradication on 

Sand Island, MANWR work against this alternative include the following: 

2.5.7.1 Non-Target Species

One of the benefits of bait stations is the reduced level of primary exposure to non-target species. 

On MANWR, bait stations would offer some, but not complete protection to terrestrial birds. 

Moreover, bait stations would not eliminate the secondary exposure risk through mobilization of 

rodenticide into the environment by contaminated insects (e.g., cockroaches, ants, etc.) and other 

invertebrates (e.g., crabs). As such, a bait station approach would minimize the non-target 

poisoning risk but would not eliminate the need for additional mitigation measures to protect the 

Laysan duck and shorebirds. 

2.5.7.2 Operational Challenges 

The logistics of implementing mouse eradication on Sand Island, MANWR using bait stations 

alone would be significantly more complex than rat eradication, primarily due to their smaller 

home range, which would require a much higher density of bait stations. Bait stations would 

need to be deployed at a maximum of approximately 66 ft. (~20 m) intervals, with approximately 

33 ft. (~10 m) offering greater confidence that at least one bait station would be accessible to 

each mouse on the island. Assuming a 33 ft. x 33 ft. (10 m x 10 m) grid across the island, Island 

Conservation estimates that a minimum of 45,200 bait stations would be needed to cover the 

total area of Sand Island. This figure does not account for key commensal habitat which would 

require additional treatments. The Feasibility Report (Island Conservation 2017) estimates that 

more than approximately 280 miles (mi.) (450 kilometers [km]) of trails would need to be 

opened, flagged and maintained to support crews walking to install, service, monitor, and 

decommission these stations. These trails would need to be opened in key habitat such as the 

coastal fringe in high density Scaevola sp. and through habitat with Bonin petrel burrows, which 

are found wherever the substrate allows for excavation by the birds and thus are common on 

Sand Island. It is likely some burrows would be stepped on and collapse suffocating adults or 

young. Island Conservation estimates that, assuming a manageable crew size of 40 workers, this 

would require 200+ days, and an individual station would need to be visited at a minimum of 5-

day intervals. 
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Because conducting a mouse eradication project on Sand Island, MANWR relying solely on bait 

stations would be time consuming, impactful to sensitive seabird habitat, incomplete in its 

application (i.e., within condemned structures), and unlikely to attain the project objectives 

outlined in Section 1.2, the USFWS has rejected this alternative from further consideration. 

2.5.8 MOUSE CONTROL 

Under this potential alternative, project planners considered mouse removal with the goal of 

reducing but not eliminating the mouse population on Sand Island, MANWR. A Mouse Control 

alternative would create and implement a strategic plan for long-term mouse control, with a 

regimented management plan written and approved, funds allocated, staff assigned, progress 

reports, and other elements that would distinguish it in scale, intensity, and duration from the 

mouse control efforts currently underway at Sand Island, MANWR. The net conservation benefit 

achieved by successful mouse control, as compared to total eradication, could be similar. 

However, the risk posed to non-target wildlife and island personnel as a result of continued 

control operations are greater than the risks related to an eradication operation due to the 

indefinite timeline for which a control operation would need to persist. The long-term presence 

of rodenticide and the repeated disturbances related to ongoing control operations would place 

non-target species at a continuous risk. 

In addition, should the scheduled operations be interrupted due to inclement weather or some 

other circumstance, the mice could quickly reproduce to, or beyond, current levels and 

repopulate Sand Island, MANWR. Should this occur, it would require a further intensification of 

control operations once more. Control of the island-wide mouse population to levels low enough 

to eliminate them as an ecosystem-wide threat would require constant maintenance of an 

ecologically beneficial mouse control program. Doing so would be far less cost-effective, 

increase personnel safety risks, and would not result in the permanent conservation benefit 

derived from island-wide eradication of house mice. Because this alternative would not achieve 

the project objectives in Section 1.2, the USFWS has rejected this alternative from further 

consideration. 

2.6 PROJECT COSTS

The USFWS’ total estimated implementation budget for the Midway Seabird Protection Project 

is $3.5 million dollars. 
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CHAPTER 3: AFFECTED ENVIRONMENT, ENVIRONMENTAL 

IMPACTS, & MINIMIZATION MEASURES 

3.1 GENERAL DESCRIPTION OF MANWR

MANWR is located at approximately 28 ̊15ʹ N and 177 ̊20ʹ W in the NWHI, and consists of 3 

sandy islets. Sand Island, where the mouse eradication project would take place, is the largest 

islet at 1,117 acres (452 ha); the other 2 islets are Eastern Island 366 acres (148 ha) and Spit 

Island 15 acres (6.1 ha) (Figure 1.2). Together, they encompass a total land area of 1,549 acres 

(627 ha) with a mean elevation of approximately 10 ft. (3 m) above mean sea level (+MSL). 

Together these 3 islets lie in the southern portion of a large, elliptical barrier reef measuring 

nearly 5 mi (8 km) in diameter. MANWR is one of the northernmost land masses in the NWHI, 

located approximately 1,313 mi (2,113 km) northwest of Honolulu, Hawaiʻi (see Figure 1.1).

MANWR became an overlay refuge in 1988, while remaining under the jurisdiction of the 

Department of the Navy. On October 31, 1996 President William Clinton officially established 

MANWR as a standalone refuge by Presidential EO No. 13022. On September 13, 2000, the 

lands and waters of MANWR were designated as the Battle of Midway National Memorial. In 

addition, on June 15, 2006, the lands and waters of MANWR were incorporated into the PMNM 

by President George Bush’s Presidential Proclamation No. 8031. MANWR’s Co-Trustees in 

administrative matters, along with their respective responsibilities are summarized in Table 3.1

below. 

Table 3.1 MANWR Administrative Co-Trustees 

Co-Trustee Responsibilities

Secretary of Commerce, National 

Ocean Atmospheric 

Administration (NOAA)

Primary responsibility regarding the management of the marine areas of the 

Monument, in consultation with the Secretary of the Interior.

Secretary of the Interior, USFWS Sole responsibility for the areas of the Monument that overlay MANWR, 

the Battle of Midway National Memorial, and the Hawaiian Islands 

National Wildlife Refuge, in consultation with the Secretary of Commerce.

State of Hawaiʻi, Department of 

Land and Natural Resources

Primary responsibility for the Northwestern Hawaiian Islands Marine 

Refuge and State Seabird Sanctuary on Kure Atoll. Nothing in the 

Proclamation diminishes or enlarges the jurisdiction of the State of Hawaiʻi.

State of Hawaiʻi, Office of 

Hawaiian Affairs

Consultation on matters pertaining to Native Hawaiian culture. 

Source: USFWS (2017)

Together, USFWS and its Co-Trustees coordinate with the U.S. Coast Guard as they exercise 

their law enforcement, search and rescue, and medical evacuation responsibilities in the Central 

Pacific. The Coast Guard works with USFWS to store aircraft fuel on MANWR for missionrelated use, and occasionally crews will stay on Midway during extended operations. 

Although geographically part of the Hawaiian Islands archipelago, MANWR is not part of the 

State of Hawaiʻi and is an unincorporated territory of the United States. Therefore, the State 

Hawaiʻi has no jurisdiction on MANWR. Current funding to operate MANWR comes from the 

USFWS, supplemented by the FAA, which fully funds airport operations costs and a share of 
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infrastructure operations costs. A small amount of funding is generated by the other users of 

MANWR, such as other Federal agencies conducting activities on Midway. 

3.2 RESOURCE TOPICS EXCLUDED FROM DETAILED ANALYSIS

The resource topics in this section are those that do not have the potential to be affected by the 

proposed action or action alternatives. They are briefly summarized here in the interest of 

completeness and to provide context for readers, but there is no attendant discussion of impacts 

because no such potential exists. 

3.2.1 LAND USE

The built environment on Sand Island is extensive and a result of a long history of human 

habitation and infrastructure, representing over a century of occupation. The structures on Sand

Island vary in age, construction type, condition, and on how they are used (if at all). The oldest 

structure dates back to 1903 and the Commercial Pacific Cable Company (one structure remains 

from that time); this and other historic buildings are discussed in Section 3.2.12. Nearly all the 

other structures, except the memorials, date to the Navy’s use of Midway from the 1930s to 

1993. The types of structures present on Sand Island and their use are summarized in Table 3.2; 

more generalized land uses are shown in Figure 3.2. 

Table 3.2 Summary of the Built Environment on Sand Island, MANWR

Type Use

Inhabited Space Living spaces, such as housing and dining and recreation facilities, food storage, and food 

preparation sites. These include:

• Clipper House dining hall

• Captain Brooks pub

• Charlie Barracks

• Houses near Charlie Barracks (i.e., Pranee, Dolphin, and Yoodee houses)

• Midway Mall, which includes a store among other facilities

Work spaces, including offices (NWR Visitor Center and Chugach offices), Aircraft Rescue 

and Fire Fighting (ARFF) facilities, utility buildings, covered storage, covered gardens, and 

plant nurseries. 

Abandoned 

Structures

Condemned structures where routine access is not permitted due to safety or other concerns, 

but all buildings can be entered with proper personal protection equipment (PPE).

Memorials Monuments to the Battle of Midway and other features of historic importance.

Aboveground 

Utility 

Infrastructure

Including water tanks, fuel storage tanks, electrical equipment, and other facilities. 

Subterranean Utility 

Infrastructure

The majority of this infrastructure is defunct and has been abandoned in place, but select 

facilities are still in use in inhabited areas and include utility service boxes, electrical and 

communications conduits, water and fuel pipelines and valves, and wastewater pipelines and 

valves. 

Source: USFWS (2017)
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Figure 3.1 Generalized Land Uses on Sand Island

Source: USFWS (2017)

In addition to the physical infrastructure summarized above, there are 3 types of land use 

designations present on Sand Island, MANWR. Each is summarized in one of the following 

subsections. 

3.2.1.1 Wildlife Refuge

As noted above, on October 31, 1996, President William Clinton officially established MANWR 

as a standalone refuge via EO No. 13022. The refuge encompasses all islands and waters within 

the 12-nautical mi. territorial sea of the atoll, totaling 581,864 ac. (235,472 ha). The refuge is 

administered by the USFWS in order to: 

• Maintain and restore natural biological diversity within the refuge. 

• Provide for the conservation and management of fish and wildlife, and their habitats, 

within the refuge.

• Fulfill the international treaty obligations of the United States with respect to fish and 

wildlife. 

• Provide opportunities for scientific research, environmental education, and 

compatible wildlife-dependent recreation activities.
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• Recognize and maintain the historic significance of MANWR in a manner compatible 

with refuge purposes. 

NOAA National Marine Fisheries Service (NMFS) also monitors Hawaiian monk seals in 

MANWR and has taken periodic actions with seals to enhance their survivability as part of a 

cooperative conservation effort between NOAA, USFWS, USCG, and several non-governmental 

organizations (NGOs). 

3.2.1.2 National Memorial 

On September 13, 2000, Secretary of the Interior Bruce Babbitt designated the lands and water 

of MANWR as being within the Battle of Midway Memorial, “so that the heroic courage and 

sacrifice of those who fought against overwhelming odds to win an incredible victory will never 

be forgotten.” MANWR is the first National Memorial co-located with a National Wildlife 

Refuge. Several monuments are present on Sand Island, honoring those who sacrificed their lives 

with remnants of the actual historic Battle of Midway during the Second World War. 

3.2.1.3 Airport 

Henderson Field Airport, designated by the International Air Transport Association as airport 

code PMDY, has a 7,900 ft. (2,407 m) runway capable of handling almost any type of aircraft. 

PMDY is a fully-certified airport maintained according to the standards specified in the FAA’s 

Title 14 CFR, Part 139. Midway is used as a required emergency landing site for extended twinengine operations (ETOPS) flights across the Pacific Ocean. Under current regulations, twinengine aircraft must be within a maximum of 180 minutes from a Title 14 CFR Part 139-certified 

airfield in case of an emergency. 

3.2.2 ACCESS

MANWR and PMNM are not typically open to visitors, and only those with a role in the 

operation, maintenance, or purpose of the refuge or the monument can access Sand Island. The 

only means of accessing MANWR are via air transport or surface vessel. These means of access 

currently adhear to a biosecurity plan designed to address a myriad of threats and concerns 

across the entire PMNM, adhearance to the biosecurity plan to prevent the reintroduction of mice 

on Sand Island (see Appendix A) will not adversely affect continued access to MANWR and 

PMNM.

3.2.2.1 Air Transportation 

Currently, flights to MANWR are determined on an as-needed basis for the purposes of 

transporting support staff, scientists, volunteers, and restocking perishable foods. While the 

frequency of these flights varies, typically 2 flights occur per month, originating from Honolulu 

International Airport. A Gulfstream III jet aircraft is typically used, with a crew of 2 and a total 

capacity of 15 passengers. 
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3.2.2.2 Marine Transportation 

The only vessels permitted within MANWR are those that service activities and personnel within 

the monument, and those transiting through without stopping; as a consequence, very few vessels 

call at MANWR. Small craft typically enter the inner harbor and moor dockside, or in the harbor. 

Larger vessels used to resupply Sand Island and research vessels generally make their landing at 

the cargo pier, inside Midway’s lagoon but outside the inner harbor. Larger passenger vessels, 

when present, are required to remain outside the reef and shuttle passengers onto the atoll via 

launches or tending craft due to port security requirements. 

Annually, visits to MANWR by marine vessels generally include the following: (i) 1 barge, 

associated with construction projects, bringing construction materials as well as general 

operations material; (ii) 2 or more support barges; and (iii) between 3 and 5 NOAA research 

ships. 

3.2.3 CLIMATE

The climate of MANWR is influenced by the marine tropical and marine Pacific air masses, 

depending on the season. During the summer months, the Pacific High-Pressure System becomes 

dominant, with the ridgeline extending across the Pacific north of Kure and MANWR s. This 

places the region under the influence of easterly winds, with marine tropical and trade winds 

prevailing. During the winter, particularly between November and January, the Aleutian Low, a 

semi-permanent low-pressure system, moves south over the North Pacific, displacing the Pacific 

High before it. The Kure-Midway region is then affected by either the marine Pacific or marine 

tropical air masses, depending upon the intensity of the Aleutian Low or the Pacific HighPressure systems. 

The weather on Sand Island, MANWR is monitored at Henderson Field Airport (see Section 

3.2.2.1). Two seasons dominate the annual climate-cycle. During the warm season, which 

typically extends from late June through early October, the average high temperature is 85  ̊F (29 

 ̊C) and the average low temperature is 78  ̊F (25 ̊C). During the cool season, which typically 

spans from late December to mid-April, the average high temperature is 71  ̊F (21 ̊C) and the 

average low temperature is 63  ̊F (17 ̊C). The average annual rainfall is 41.3 in (104 cm), with 

January being the wettest month with an average of 5 in (13 cm) of rain. June is typically the 

driest month with 2.2 in. (5 cm) of rain (weatherbase.com). Dramatic variation in precipitation 

timing and volume is possible during El Niño and La Niña conditions. Sand Island is located at 

28 12 N, and daylight hours range from 10:22 and 13:55 hours per day, with the longest day 

occurring in June during the boreal summer. 

The typical seasonality of rainfall at MANWR is depicted in Table 3.3 below, showing higher 

monthly totals and number of days with precipitation in the winter months. During some 

exceptional years, such as 2015-2016, the pattern may be reversed. Precipitation normally occurs 

as rain, ranging from mist to moderately intense rainfall, with total monthly averages ranging up 

to 5 in (13 cm). Despite significant seasonal fluctuation, rainfall occurs throughout the year, 

generally in the form of light, intermittent showers. However, rainfall is generally lowest in 

April, May, June and July (Table 3.3). 
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Table 3.3 Average Rainfall on Sand Island, MANWR 

Average Precipitation 1974-2016 (in.)

Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Annual

5 3.8 3 2.5 2.3 2.2 3.3 4.3 3.5 3.5 3.8 4.1 41.3

Average No. of Days with Precipitation 1977-2016

Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Annual

16 14 12 11 9 9 15 15 15 14 14 16 160

Source: Weatherbase.com (2017)

3.2.4 VISUAL RESOURCES

Sand Island, MANWR is comprised of dunes, grasslands, forested areas, beaches, the protective 

barrier reef and lagoon, each with its own distinct character and visual appeal. It also 

encompasses several monuments to the Battle of Midway during the Second World War, as well 

as other points of human interest. However, none of these features has been formally designated 

as a protected vista or scenic viewpoint. In addition, because visitation to Sand Island is 

purposefully limited, there are very few individuals present to observe the natural and manmade 

environment present. 

3.2.5 FUEL FACILITIES

A new jet fuel tank farm was constructed in 2007 with a capacity of 450,000 gallons (1,703,435 

liters); the facility consists of 9 50,000-gallon (189,271-liter), aboveground storage tanks located 

on the southwest side of the Inner Harbor (see Figure 1.3). The tank farm stores a sufficient 

amount of fuel to operate electrical generators, vehicles, and aircraft for a year. The USCG and 

USFWS have an interagency agreement that covers this cooperative effort and outlines shared 

costs associated with fuel. 

3.2.6 ENERGY

Electrical power at MANWR is supplied by generators utilizing jet fuel. Two generators operate 

in automatic duplex mode such that, in most cases, only 1 generator is needed to meet Sand 

Island’s demand. If 1 generator exceeds capacity, the second generator automatically comes 

online and automatically shuts off when electrical demand reduces. The current system for 

generating electricity is sufficient for the existing population. Midway has 2 electrical 

distribution grids. A relatively new electrical distribution grid serves most of Sand Island, but 

portions of the older grid still provides power to the old airport hangar and the finger pier area. 

Finally, photovoltaic panels are used to power select energy demands, such as food storage 

refrigerated containers.

3.2.7 COMMUNICATIONS

Telecommunication is provided by satellite service and includes T-1 data and VOIP service. 

Communications are provided to the inhabited portions of Sand Island via a fiber optic 

distribution system. Radio communication is also widely used in place of cellular phone service; 

the service area extends throughout both Sand and Eastern Islands. 
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3.2.8 AIR QUALITY

Air quality at Midway is generally excellent. Sources of emissions on the atoll are minimal and 

include electrical generators, motor vessels, vehicles, tools, and occasional plane flights (U.S. 

Army Space and Missile Defense Command, 2003). 

3.2.9 GEOLOGIC RESOURCES

Midway is one of the northernmost coral atolls in the world and only one other atoll 90 mi. (145 

km) to the north of Midway, Kure Atoll, also has emergent land. MANWR is 28.7 million years 

old. It is the result of a classic geomorphological sequence along the Hawaiian ridge, ranging

from brand new volcanic basalt islands at the Southeastern end of the chain to true ring-shaped 

atolls at the Northwestern end of the chain and submerged seamounts even farther to the 

northwest. 

As its name implies, Sand Island is comprised of coral sand, as is Eastern Island and the 

relatively recently formed Spit Island. Despite the fact that the foundation of the atoll is volcanic, 

no in-situ volcanic rocks are found on the islands. The former volcanic island slowly eroded and 

sank to an elevation well below current sea level. As sea level rose and the island continued to 

sink, coral grew on top of the volcanic rock to form the atoll that is present today. 

Portions of both Sand and Eastern Islands are man-made fill. The fill is primarily believed to be 

coral sand from the dredging of the channel and harbor at MANWR. Other sources of fill are 

believed to be relatively minor and include: (i) large rocks from Hawai‘i and the US mainland, 

used to build shoreline revetments; and (ii) some organic material, such as soil from the US 

mainland, reportedly imported to help establish trees on the islands. Landfills, which are 

discussed in Section 3.3.5, also created landforms, most notably the “bulky dump” finger 

extending out from the south side of Sand Island (see Figure 1.3).

3.2.10 SOCIOECONOMIC AND ENVIRONMENTAL JUSTICE

Sand Island, MANWR does not have an established demographic or socioeconomic structure. 

The population of the Atoll fluctuates based on the needs of MANWR and PMNM; all 

inhabitants are on the Atoll strictly to operate, maintain, and address these two purposes. As all 

inhabitants are professionals employed in these undertakings, there are no environmental justice 

populations present there. 

The year-round community of people on MANWR includes USFWS staff and volunteers, base 

operations staff (mostly comprised of Thai nationals employed by Chugach Management) and 

temporary contractors or research scientists. Sand Island has extensive infrastructure, processes, 

and utilities in place (see Table 2.2) to support the approximately 60 people that live and work 

there, including housing, common eating spaces (known as the Clipper House), small scale 

agriculture, recreation facilities, transportation infrastructure, recycling, and liquid and solid 

waste disposal systems. In effect, Sand Island is a functioning, albeit small, municipality. 

Atoll residents live in renovated Navy housing, including single family homes, duplexes, and 

Bachelor Officer Quarters (BOQ). One BOQ, known as “Charlie Barracks,” which contains 36 

rooms, has been set aside for transient and visitor use. Almost all of the residents and transients 
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eat at the Clipper House, where 3 meals a day are served buffet style. Most supplies, particularly 

foodstuffs, are flown to the island on chartered aircraft. Approximately twice a year, a ship 

brings in equipment, additional food, and supplies too large or heavy for air transport. 

The typical complement of personnel present on Sand Island, MANWR is summarized in Table 

3.4 below. 

Table 3.4 Typical Personnel Present on Sand Island, MANWR

Type

Current 

Number Purpose

Refuge Staff 4 Full-time USFWS employees tasked with MANWR operations. 

Operations Contractors 37 Chugach Management Services employees responsible for the 

operation and maintenance of the active infrastructure on Sand 

Island.

Construction <30 During construction season, between August and October, 

additional workers responsible for construction and demolition 

operations on Sand Island.

FAA-Airport 4 Airport Maintenance and Management

Volunteers 1-4 Volunteers periodically assist the regular MANWR staff in 

biological and habitat management activities. 

Researchers Variable Sand Island, MANWR also hosts transient researchers, USFWS 

employees, and USCG personnel on an irregular and periodic 

basis. 

Transients Variable Refuge employees, Co-Trustee staff, USCG and other law 

enforcement entities, contractors, researchers, and other Federal 

and state employees. 

Source: USFWS (2017)

3.2.11 SOLID WASTE DISPOSAL

Solid waste generated in MANWR is disposed of via several methods. Most solid waste, such as 

household and food waste, is temporarily stored in open plastic trash bins with periodic trash 

collection via flatbed truck. Once collected, the solid waste is then burned in an oil-fired 

incinerator, dependent on the availability of waste fuel, or burned in an unlined open-air pit. 

Once burned, the ash is collected and disposed of at the existing landfill present on Sand Island. 

Aluminum cans are collected, compacted, stored, and then periodically sent to a recycling 

facility in the main Hawaiian Islands. Glass is collected, crushed, and buried in the landfill. 

Because the capacity of the existing landfill is limited both in capacity and in the types of waste 

which it can accommodate, it is only used for items which cannot be incinerated (e.g., some 

manmade marine debris). 

3.2.12 HISTORICAL AND CULTURAL RESOURCES AND VALUES

Study of Midway’s heritage resources was initiated in 1986 by the National Park Service when it 

conducted a survey of World War II-era properties eligible for designation as a National Historic 

Landmark. Nine structures, all defensive positions on the west side of Sand Island, were 

identified on Midway to convey a close association with the pivotal Battle of Midway, including 

ammunition magazines (ARMCO huts), a pillbox, and gun emplacements. Later that year, the 9 
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defensive positions on Sand Island identified as eligible by the National Park Service and 

surrounding buffer areas were designated as a landmark.

Between 1992 and 1994, the Navy sponsored studies of the Naval Air Facility on Midway, 

including archival research, interviews, and field surveys. The initial field effort consisted of an 

architectural history survey of the structures, buildings, and objects located on Sand and Eastern 

Islands. 

The study of Cold War Resources was conducted in 1993-94 by contractors hired by the 

Department of the Navy in order to identify the most important Cold War-era resources, even 

though they were less than 50 years old, as part of the Base Closure process. The historian hired 

to conduct the inventory, research, and make recommendations regarding the significance of the 

buildings on Midway was a specialist in the Cold War period. The Cold War-era buildings were 

constructed on Midway between 1957 and 1969. 

The recommendation accepted by the Navy was that the Cold War-era buildings and structures 

on Midway lacked architectural merit, were not directly associated with President Nixon’s visit, 

and do not convey a direct link to the events that occurred during the Cold War. The Navy 

subsequently demolished many of the Cold War-era buildings and structures prior to the transfer 

to the FWS. 

In addition to the landmark structures, 69 buildings, structures, and objects associated with the 

1903-1945 historic period on Sand and Eastern Islands were determined to be eligible according 

to criteria established for the National Register of Historic Places. The properties evaluated as 

significant are associated with 3 major themes: colonization, initial years of base construction 

and the Battle of Midway, and 1942-1945 base construction. 

In 1859, Captain N.C. Brooks was the first Westerner to “discover” Midway aboard the Gambia

from Honolulu. He claimed Midway for the U.S., based on the Guano Act of 1856, which 

authorized Americans to temporarily occupy uninhabited islands to obtain guano. Captain 

Brooks named the atoll “Middlebrooks,” reflecting its position between the U.S. west coast, 

Japan, and himself. The United States took formal possession of the unoccupied islands in 1867. 

Later, the name was changed to Midway. 

The Commercial Pacific Cable Company Site, which includes 5 buildings (Nos. 619, 623, 626, 

628, and 643) on Sand Island, has been determined by the Secretary of the Interior to be eligible 

for inclusion in the National Register of Historic Places. Originally constructed by the 

Commercial Pacific Cable Company, these buildings are the only remnants of the initial 

permanent colonization of the Midway Islands. 

Archaeological surveys of Sand and Eastern Islands were conducted in 1992 and 1994. Surface 

inspections, 68 subsurface core samples, and 5 shovel-test units were conducted in disturbed 

sediments with as much as 2 meters of fill in some areas. Heavy construction and military use 

since 1940 changed the island considerably. Prior to the military era, these islands were also 

periodically scoured by storms and high winds that may have removed or buried evidence of pre1900 use. A review of Hawaiian chants, genealogy, mythology, and oral histories found 

numerous references to distant low lying islands with abundant birds and marine life. Kuaihelani 

which translates to “back bone of heaven” is a name that is referenced often with these sources 
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and is potentially associated with Midway. This homeland of the gods is described as a floating 

island in the sky, which can derive from a lagoon’s refection in the clouds, such as at Midway 

Atoll. Pihemanu is a recent name that was given to the Atoll and means “loud din of birds” 

perfectly describing the current experience at MANWR. While no evidence of 

Polynesian/Hawaiian or pre-1900 historic period cultural remains have been found to date, there 

is still the potential for a buried discovery. In addition the chants, genealogies, mythologies and 

oral histories confirm that Hawaiians traveled to the islands and atolls within the Northwestern 

Hawaiian Islands over the span of several centuries. 

3.2.12.1 Programmatic Agreement and Treatment of Midway’s Historic Properties 

In 1996, the Navy’s Pacific Division, Naval Facilities Engineering Command, the Advisory 

Council on Historic Preservation, and USFWS signed a programmatic agreement directing how 

MANWR’s historic properties were to be treated during the closure of Naval Air Facility 

Midway. These properties were assigned to 1 of 6 categories of preservation treatment: reuse 

and maintain, secure and abandon in place, abandon in place and leave as is, fill or cover, 

relocate, or demolish. USFWS was required to prepare a long-term Historic Preservation Plan, 

which it completed in 1999. 

3.2.12.2 Historic Preservation Plan

The December 2010 Midway Atoll National Wildlife Refuge Historic Preservation Plan defines a 

program to integrate historic preservation planning with the wildlife conservation mission of 

USFWS at MANWR. The plan focuses on the long-term management conditions and goals for 

preserving and stabilizing historic properties. It also recommends procedures for treating new 

discoveries, caring for museum collections, and implementing a visitor program that includes 

historic preservation work. In the future, the Co-Trustees will incorporate submerged cultural 

resource protection into such plans. 

3.3 RESOURCES TOPICS ANALYZED IN DETAIL IN THIS EA

The resource categories in this section are those that have the potential to be affected by the 

proposed action. In the following subsections the existing condition of each resource is 

characterized, followed by a discussion of the potential for impacts resulting from the Preferred

or No Action Alternatives, including any mitigation activities which could avoid, minimize, or 

mitigate these potential impacts. 

3.3.1 AIRFIELD OPERATIONS

3.3.1.1 Existing Conditions 

As described previously in Section 3.2.1.3, the active airport on Sand Island, MANWR is 

Henderson Field Airport. Henderson Field has a 7,900-foot (2,405 m) runway, is fully certified 

as an airport maintained according to all applicable FAA standards, and is capable of handling 

virtually any type of aircraft. Because of its capacity, Henderson Field Airport is used as a 

required emergency landing site for ETOPS flights across the Pacific Ocean. It is staffed by air 

traffic control and ARFF personnel sufficient to operate as an ETOPS landing site. This airport is 
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one of the dominant features present on Sand Island and, along with the harbor, is the principal 

means of accessing MANWR. 

3.3.1.2 Probable Impacts 

No evidence suggests that the physical airfield, which consists primarily of hardtop asphalt and 

cement, support house mice. However, the proposed action does call for the treatment of 

potential mouse habitat in areas immediately surrounding the airport runway, including any 

subterranean utility access points. This treatment is particularly necessary in areas where 

vegetation has created significant ground cover and in the airfield utility access points, which 

create breaks in the otherwise uniformly sealed perimeter surfaces. 

A runway safety zone skirting, taxiway safety zone skirting, and 2 blast pads make up the area 

immediately adjacent to surfaces requiring Foreign Object Debris (FOD) management; these 

areas are delineated by large, conspicuous painted aircraft control lines on the tarmac. Baiting 

within these sites—up to but not within the aircraft control lines—and the airfield utility access 

points was assessed by airfield management and determined not to present a FOD hazard. 

Should bait pellets inadvertently drift onto the active airfield, pellets would be removed via an 

FOD-assessment following each bait distribution event. 

Additional flights and helicopter operations would be required to conduct the proposed action. 

Additional flights would include charter aircraft required to bring personnel, bait, and equipment 

to Midway. It is anticipated that these additional flights would not exceed an average of 6 

operations a day over the 3-week bait distribution period. Given airport staffing levels, the low 

level of other operations, and apron area size, which once supported frequent and numerous 

military operations, the increase in operations anticipated to occur during the proposed action 

would not adversely affect the airport’s ability to continue to serve its ETOPS emergency 

landing site function or other functions. 

3.3.2 WATER RESOURCES

Fresh water is defined as water having a sufficiently low salinity to allow for its consumption 

without ill effect. Salinity is a measure of the total amount of salt in water. Salinity and total 

dissolved solids are essentially synonymous. Water is considered “fresh” when its salinity is less 

than 0.5 parts per thousand (ppt). The salinity of ocean water is generally 35 ppt. Under the Safe 

Drinking Water Act, the EPA has established a Secondary Drinking Water Regulation

concentration limit of 0.5 ppt (which is the same as 500 milligrams per liter (mg/L) and 500 parts 

per million (ppm)) for total dissolved solids. 

3.3.2.1 Existing Conditions: Groundwater 

Midway Atoll’s subsurface geology and hydrogeology is similar to other atolls in the Northern 

Hawaiian chain and elsewhere. The atoll’s geology is discussed briefly in Section 3.2.9. There 

are no hydrogeology-specific publications publicly available regarding Sand Island’s 

groundwater resources. However, a hydrogeological study of Wake Island (AFCEE 2006), 

another atoll where bait has been used to eradicate rodents and annual rainfall is similar, provides 

insight into atoll hydrogeology. Numerous wells have been drilled into the uppermost saturated 
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zone of Sand Island to assess, remediate, and monitoring landfills and petroleum releases. The 

results of those investigations have yielded no evidence that Sand Island’s groundwater 

processes or conditions differ meaningfully from other atolls. 

Rainfall percolates through the coral sand and joins the underlying groundwater aquifer of Sand 

Island, MANWR. This unconfined (i.e., not confined under pressure beneath relatively 

impermeable rock) groundwater remains in contact with the atmosphere due to the porous nature 

of the coral sand soils. These porous soils at or below sea level—approximately 6 to 8 ft. (1.8-2.4 

m) below grade—also are infiltrated and saturated by sea water. As the freshwater encounters 

the sea water, a zone of brackish water of variable salinity develops as they intermix. The depth 

and thickness of this brackish layer varies with the magnitude of tidal fluctuations, the amount of 

rainfall, and the permeability of the sediments through which the tidal signal occurs. The 

shallowest and most interior portions of Sand Island’s aquifer are the freshest, due to saturation 

with percolating rainwater; this groundwater flows down and outward towards the shore, where 

it discharges into the ocean. The gradients and flux are small (GeoEngineers 2011); at Wake 

Island it was assessed that it would take 30 to 50 years for groundwater to migrate from the 

center of the island to either shore (a distance of approximately 1,000 ft. [305 m]) (AFCEE 

2006). Residence times at Sand Island could be as much as 3 times longer because it is roughly 

6,000 ft. (1,828 m) across. There are no wells used for potable drinking water on MANWR. 

3.3.2.2 Existing Conditions: Surface Water 

There are no streams or lakes on Sand Island, MANWR but there are several natural and manmade seeps present on the Atoll, which provide habitat for Laysan ducks, shorebirds, and 

migratory waterfowl. The seeps include small pools near the water tanks, in the area of former 

housing along Henderson Street, and west of the active dump (Figure 3.1). There are no 100-year 

floodplains on Sand Island, MANWR; however, the Atoll is surrounded on all sides by the 

Pacific Ocean and is periodically subjected to storm surges. 

The coral sand that makes up the island is sufficiently permeable that erosion and flowing 

surface water is not present except where storm water flows are concentrated by hardened 

surfaces. Storm water is discussed further in Section 3.3.4. 

3.3.2.3 Existing Conditions: Potable and Non-Potable Water Systems

Freshwater is a critical resource for people and wildlife present on Sand Island, MANWR. 

During substantial rain events, runoff from the airport runway is channeled into a pond adjacent 

to the runway and pumped into 3 large storage tanks for both potable and non-potable uses 

(Figure 3.2). Each of the 3 tanks has a 4.2 million-gallon (MG) (15,898,729 liters) capacity, for a 

total holding capacity of 12.6 MG (47,696,188 liters). Water is transferred from these 3 tanks to 

2 approximately 80,000-gallon (302,833-liter) tanks in town, as needed, and from there directed 

into either the potable or non-potable systems. 

The non-potable system was originally built by the Navy for its use, and is now used for fire 

suppression, watering plantings, and other non-potable uses. The potable system consists of a 

treatment facility and separate piping system that distributes potable water to inhabited buildings. 

The treatment system for potable water consists of sediment filtration to 5 microns and 

chlorination. In some of the older buildings, where the plumbing is aging, the water is also 
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filtered at the tap to address secondary particulate. The potable water in use on Sand Island is 

sampled and tested monthly, at randomly selected points in the system, to ensure the safety of the 

supply. 

Figure 3.2 Water Resources on Sand Island, MANWR

Source: USFWS (2017)

Typically water is transferred from the pond to the 3 large runway tanks once a year, following a 

heavy rainfall or storm event. As storm events are more frequent during the winter months, water 

is usually collected and transferred at these times. Total annual water use is approximately 5 MG

(18,927,058 liters) across all uses; thus, when the 3 large storage tanks are full they provide over 

2 years of water capacity.

3.3.2.4 Probable Impacts 

Evaluation criteria for effects on water resources are based on water availability, quality, and 

use, and the regulations associated with them. A proposed action can be characterized as having 

adverse impacts on water resources where it can be established that one or more of the following 

shall occur as a result of its implementation:

• Reduce water availability to supply to existing users;

• Overdraft groundwater basins;

• Exceed safe annual yield of water supply sources;
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• Affect water quality adversely;

• Endanger public health by creating or worsening a hazard to human health; 

• Threaten or damage unique hydrologic characteristics; or

• Violate established laws or regulations adopted to protect water resources. 

The proposed action would not reduce water availability or exceed the safe yield of water supply 

sources. The 3 water tanks on Sand Island would be filled during the winter rains so that they 

hold sufficient water to supply all island residents and visitors for a period of roughly 2 years. 

Because all the water is drawn from the pond that collects storm water runoff from the runways, 

there is no danger of groundwater basin overdraft when the 3 tanks are filled in the winter season 

prior to the proposed action. The watershed for the seep is at least 200 acres (81 ha), and is 

primarily new or aging asphalt pavement. At that size, less than 2 in (5 cm) of rain is necessary 

to provide sufficient runoff to completely fill the 3 tanks. Winter storms in December, January, 

and February commonly drop 4 to 5 in. (10-13 cm) of rain each month (Table 3.3).

Because all water for human consumption for a 2-year period would be collected in enclosed 

tanks prior to broadcasting the bait, no public health threat is anticipated associated with drinking 

water or other water use.

The effect of flood hazards on a proposed action may also be important if such an action is in an 

area with a high probability of flood or, with greater relevance to MANWR, storm surge. 

With regard to surface water quality, no adverse effects are anticipated as a result of the 

proposed action. Brodifacoum, the toxin proposed for the mouse eradication effort, has very low 

water solubility (Primus et al. 2005). Bait that enters any given water column, whether marine or 

fresh, would dissolve into individual grain particles, and the brodifacoum molecules would 

remain bonded to these grain particles. In addition, the bait proposed for use during the 

eradication operation would contain a poison concentration of approximately 0.0025% 

brodifacoum. At this concentration level, brodifacoum which if inadvertently introduced to 

surface water, groundwater, or the marine environment, would likely be below risk levels. 

Similarly, no groundwater quality adverse effects are anticipated as a result of the proposed 

action. Should brodifacoum dissolved at low concentrations (it is nearly insoluble) enter the 

groundwater aquifer, it would be degraded by bacteria in the subsurface, be diluted, and take 

years or decades for that water to discharge into the marine environment. Hydrogeological 

studies at Wake Island found that groundwater chemistry and temperature conducive to the 

biodegradation of organic compounds like brodifacoum, similar conditions are present at Sand 

Island. The Wake Island study also found that significant dilution, driven by vertical 

groundwater movement from tidal fluctuations, would occur (AFCEE 2006). Therefore, no 

short- or long-term discharge of brodifacoum-impacted groundwater into the marine 

environment is anticipated. 

If large pellet fragments containing brodifacoum do enter the marine environment, they could be 

ingested by organisms present there. However, the pellets would rapidly disintegrate into 

fragments too small to interest most consumers; these potential impacts are discussed further in 

Section 3.3.6. 
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In order to best address the potential for brodifacoum contamination of surface water, 

groundwater, or the marine environment, USFWS and Island Conservation have developed a 

series of Best Management Practices (BMPs) to minimize this potential. These measures would 

be used as needed and may include, but are not limited to, the following: 

• Hand broadcast in buffer zones around surface water, including seeps, and non-beach 

shorelines. 

• Directional deflectors mounted on the bait buckets during aerial broadcast in areas 

adjacent to the shoreline. 

• Pre and post application sampling of potable water sources using professional collection 

and lab processes consistent with procedures used at Palmyra by USDA, APHIS NWRC 

in 2012. (Pitt, et al. 2012) 

• Burying artificial seeps, temporarily avoiding or covering or avoiding natural seeps until 

at least ten days after broadcast operations are complete or pellets are no longer visible 

within 10 meters of seeps edge. Guzzlers will be inspected and cleaned before being 

refilled. 

3.3.3 NOISE

3.3.3.1 Existing Conditions 

Sound is measured with instruments that record instantaneous sound levels in decibels (dB). Aweighted sound level measurements (dBA) are used to characterize sound levels that can be 

sensed by the human ear. “A-weighted” denoted the adjustment of the frequency content of a 

noise event to represent the way in which the average human ear responds to the noise event. All 

sound levels analyzed in this EA are A-weighted. 

Noise levels, which result from multiple, single-events, are used to characterize community noise 

effects from aircraft operations and are measured in the Day-Night Average (DNL). The noise 

metric incorporates a “penalty” for nighttime noise events to account for increased annoyance. 

The DNL metric is the energy-averaged sound level measured over a 24-hour period, with a 10-

dB penalty assigned to noise events occurring between 10:00 p.m. and 7:00 a.m. DNL values are 

obtained by averaging sound exposure level values for a given 24-hour period. DNL is the 

preferred noise metric of the US Department of Housing and Urban Development, the FAA, the 

US Environmental Protection Agency, and the Department of Defense for modeling airport 

environs. Most people are exposed to sound levels of a DNL of 50 to 55 dBA or higher on a 

daily basis. Noise levels in residential areas vary depending on the housing density and location. 

As a frame of reference, a normal suburban area is exposed to approximately 55 dBA, increasing 

to 60 dBA for an urban residential area, and 80 dBA in the downtown section of a city. 

For Sand Island, MANWR, aircraft arrivals and departures are too infrequent to establish a 

reliable and accurate DNL metric. Noise impacts for this EA are calculated using Effective 

Perceived Noise Level (EPNdB). EPNdB is used by the FAA as the noise certification metric 

for large transport and turbojet aircraft and helicopters. Maximum sound level is important in 
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contrasting the interference caused by an aircraft noise event with conversation, sleep, or other 

common activities. 

As evidenced by the Hawaiian language name for MANWR —Pihemanu, which means “loud 

din of birds”—the dominant source of noise on Sand Island is the resident bird population. The 

extreme concentration of birds present on Sand Island combined with wind noise results in a 

natural, ambient noise level that exceeds 65 dBA during the day. At night seabirds remain active; 

thus, while reduced, the sound level remains higher than would normally be found in typical 

undeveloped areas. 

The density of human use on Sand Island, MANWR is very low. During normal operations on 

the Atoll, primary anthropogenic sources of noise include aircraft, engines used to generate 

power, air compressors, and refrigeration equipment. On relatively still nights when wind noise 

is limited, the power generation equipment can be heard throughout the inhabited portion of 

Sand Island when outside. Other sources of transient noise include construction and demolition 

activity, utility vehicles, and golf carts. 

3.3.3.2 Probable Impacts 

Noise impact analyses typically evaluate potential changes to the existing noise environment that 

would result from implementation of the proposed action. Potential changes in the acoustic 

environment can be:

• Beneficial, if they reduce the number of sensitive receptors exposed to unacceptable 

noise levels or reduce the ambient sound level; 

• Negligible, if the total number of sensitive receptors to unacceptable noise levels is 

essentially unchanged; or 

• Adverse, if they result in increased sound exposure to unacceptable noise levels or 

ultimately increase the ambient sound level.

Projected noise effects were evaluated quantitatively for the proposed action. 

Excessive noise can cause annoyance or irritation. Noise annoyance is defined by the EPA as any 

negative subjective reaction to noise by an individual or group. Aircraft noise effects can be 

described according to 2 categories: annoyance and human health concerns, such as hearing loss 

and sleep disturbance. Annoyance, which is based on perception, represents the primary effect 

associated with short-term aircraft noise. EPNdB is an acceptable unit for quantifying 

community annoyance to general environmental noise, including aircraft. 

Under the proposed action, 2 helicopters would be used to aerially disperse bait across Sand 

Island, MANWR. While no final decision has yet been made as to the type of helicopter which 

would be used, most helicopters of the size and range required for this project would present an 

EPNdB of between 85 and 91 dB in the vicinity of the aircraft. As a frame of reference, 2 models 

of helicopter that have been proposed for use in other rodent eradication projects on islands are 

the Bell 206B Jet Ranger and the Bell 206L4 Long Ranger. Table 3.5 below depicts effective 

perceived noise levels for these 2 aircraft. 
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Table 3.5 Effective Perceived Noise Level of Selected Aircraft 

Aircraft Model Flyover EPNdB Level Takeoff EPNdB Level

Approach EPNdB 

Level

Bell 206B Jet Ranger 85.4 88.7 90.6

Bell 206LR Long Ranger 85.2 88.4 90.7

Source: 15th Airlift Wing USAF (2009)

The use of 2 helicopters to disperse bait would be conducted during daylight hours and would 

only disperse bait for approximately 2 days per drop for 20 hours each drop. Three applications 

are planned, resulting in a total of 60 hours of helicopter time. The noise generated by the 

helicopter would present a noticeable, albeit short term annoyance to the human and animal 

populations present on Sand Island, MANWR. The contractors operating the helicopter and bait 

bucket would wear standard protective hearing devices in accordance with Occupational Safety 

and Health Administration (OSHA) standards. Other operational personnel carrying out the 

proposed action would wear standard issue ear plugs, to be used at their discretion when in 

proximity to the aircraft. Other than the aircraft used to transport personnel to and from Sand 

Island, MANWR and the operation of the helicopter itself, the other aspects of the proposed 

action such as bait stations and bait dispersal by hand would not produce elevated levels of 

sound. 

It is anticipated that the proposed action would cause temporary adverse noise impacts during the 

bait distribution procedure(s). Once those treatments are complete, there would be no significant 

or lasting effect on the existing acoustic environment on Sand Island, MANWR. The No Action 

Alternative would not produce any noise and would have no impact on the acoustic environment 

of the Atoll. 

3.3.4 WASTEWATER AND STORM WATER

3.3.4.1 Existing Conditions 

The potable water system (see Section 3.3.2.3) on Sand Island, MANWR incorporates 

collections points wherever potable water is used and conveyed to a septic system and leach field 

located in the central portion of the island between the runways and the housing (see Figure 1.3). 

The septic system and leach field was first installed in 1998, and is located in an elevated area 

with no threat of ponding during heavy rainfall. 

The previous Navy-built drainage system co-mingled wastewater and storm water, and the 

existing wastewater conveyance system utilizes portions of that older Navy system. Because of

this, some storm water continues to be mixed with wastewater. Steps have been taken to reduce 

the storm water component by disconnecting building downspouts from the system and reducing 

the hardened surface areas that collect rainfall, allowing for more natural percolation into the 

ground. 

There is no storm water drainage system of the type common in urban areas and military basis in 

Hawai‘i and the mainland. The coral sand that makes up the island is very permeable and storm 

water quickly infiltrates and becomes groundwater, resulting in essentially no storm water 

flowing into the ocean on the ground surface. The few exceptions to this are: 
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• At the few locations where hardscape extends to the shoreline, which is generally 

confined to the inner harbor and the eastern end of Runway 6-24. 

• There are a few catch basins and ditches that direct storm water to the pond and sump 

where fresh water is collected for potable and non-potable uses. This system 

primarily serves to concentrate storm water for collection, not discharge to the ocean. 

The system does include “overflow ditches” on the south side of Runway 6-24 so that 

in the event a storm event overwhelmed the pond and the ability for the coral sand to 

absorb storm water, excess storm water can flow to the Pacific Ocean. Overflow does 

not occur during typical years, suggesting that a 10-year or greater storm event is 

necessary to generate an overflow condition. 

3.3.4.2 Probable Impacts 

The proposed action would not have any direct effect on the wastewater and storm water 

infrastructure. The wastewater system was designed and built when many more people were 

present on Sand Island and is more than sufficient to handle the increased wastewater flow 

associated with the increased number of people that would be present on Sand Island during the 

eradication effort. Similar numbers of people are present on Sand Island during annual bird 

counts, and no adverse effects to the system have been experienced at those times. 

The few locations where storm water flow occurs are those areas where rodenticide application is 

not necessary (i.e., hardscape of runways and the inner harbor) or where rodenticide would be 

hand broadcast (i.e., non-beach shorelines and the water catchment system between the 

runways). Furthermore, the application would be conducted during the relatively dry portion of 

the year when storm events do not typically occur.

Based on these considerations, the potential effects to wastewater and storm water infrastructure, 

flows, and quality would be less than significant.

3.3.5 HAZARDOUS MATERIALS AND WASTES

3.3.5.1 Existing Conditions 

Hazardous material is defined by the Comprehensive Environmental Response, Compensation, 

and Liability Act (CERCLA), as amended by the Superfund Amendments and Reauthorization 

Act (SARA) and the Toxic Substances Control Act (TACA), as any substance with physical 

properties of ignitability, corrosivity, reactivity, or toxicity that might cause an increase in 

mortality, serious irreversible illness, or incapacitating reversible illness, or pose a substantial 

threat to human health or the environment. 

Hazardous waste is defined by the Resource Conservation and Recovery Act (RCRA), which 

was further amended by the Hazardous and Solid Waste Amendments, as any solid, liquid, 

contained gaseous, or semisolid waste, or any combination of wastes that poses a substantial 

present or potential hazard to human health or the environment. In general, hazardous materials 

and hazardous wastes include substances that, because of their quantity, concentration, physical, 

chemical, or infectious characteristics, might present substantial danger to public health or 

welfare or the environment when released or otherwise improperly managed. 
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Evaluation of hazardous materials and wastes in this EA focuses on the storage, transport, and 

use of pesticides, fuels, petroleum, oil, other lubricants, and other chemicals. Evaluation may 

also extend to generation, storage, transportation, and disposal of hazardous wastes when such 

activity occurs at or near the site of the proposed action. In addition to being a threat to humans, 

improper release of hazardous materials and wastes can threaten the health and wellbeing of 

wildlife, botanical habitats, soil systems, and water resources. In the event of a release of 

hazardous materials or wastes, the extent of contamination varies based on the type of soil, 

topography, and water resources. 

Sand Island, MANWR, as former Naval Air Facility (NAF) Midway, has undergone hazardous 

material removal operations, but still contains chemicals of potential concern (COPC). 

Therefore the Navy has implemented Land Use Controls (LUC) at the sites to limit exposure to 

contaminated material. These sites are listed in Table 3.6 below. 

Several different types of LUCs were established at 4 landfills and 1 asbestos disposal area 

located on the Atoll. The landfills contain either municipal or bulky solid waste (i.e., 

construction debris) and the asbestos disposal area contains asbestos roofing materials. The 

landfills and the disposal area have been closed and covered with 1.5 to 4 ft. (0.5 to 1.2 m) of 

clean soil. The following activities are prohibited at the landfills and asbestos disposal area: 

• Excavation or soil disturbance resulting from human activities that could compromise 

the integrity of the landfill or soil cover;

• Changing the intended land use of the landfill or disposal area; 

• Modifying or altering the landfill in any way that may adversely affect the landfill 

area or release or expose subsurface waste.

The USFWS does conduct some operations in the LUC areas on an ongoing basis, including 

Verbesina encelioides eradication and annual albatross counts. Any project work conducted on 

Sand Island, MANWR, including any earthmoving activities with the potential to disturb 

contaminated soils, require communication with USFWS’ onsite refuge managers and engineers 

based in Portland, Oregon. All work plans are reviewed and must be checked by the Refuge 

Manager, and all visitors are given a briefing related to hazardous materials and provided with a 

map indicated restricted areas, including LUC sites, as part of their orientation upon arrival. 
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Table 3.6 LUC Sites on Sand Island, MANWR

Site No. Site Name Description Prior to Remediation

01 Old Bulky Waste Landfill 

(OBWLF)

The OBWLF is an artificial peninsula extending from the south side of Sand Island, formed by the dumping 

of approximately 64,000 yd3 of bulky metal wastes, construction debris, vegetation waste, and scrap metal 

into the ocean. The ocean-exposed sides of the OBWLF are protected by concrete riprap. The marine and 

nearshore environment on the northeastern side of the OBWLF includes the location where a tug and a 

garbage barge were grounded next to the seawall, on the eastern side of the revetment (Ogden 1996).

02 Runway Landfill The Runway Landfill is located in a filled area beyond the east end of Runway 6-24. The landfill is 

surrounded by trees and is predominantly grass-covered (Ogden 1996). In operation from 1970 to 1997, the 

Runway Landfill received all non-hazardous, non-bulky municipal solid waste generated on Sand Island. To 

reduce the volume of debris, the waste placed in the landfill was burned and covered with soil.

04 New Asbestos Disposal Area The New Asbestos Disposal Area is located near the east end of Runway 6-24 on the east side of the Runway 

Landfill. The New Asbestos Disposal Area comprises approximately 18,000 ft.

2 and contains corrugated 

asbestos roofing material in plastic bags.

09 Pesticide Storage Area, Former 

Bldg. 629

The Pesticide Storage Area, Former Bldg. 629, is located near the corner of Morrell and Cannon Avenues. 

The building was destroyed by fire several years before the EBS (Ogden 1994) was conducted. Records of the 

types and quantities of pesticides stored in the building were reportedly lost in the fire (Ogden 1997). 

Pesticide contamination likely occurred at the site due to past pesticide handling practices and possible 

pesticide spillage during the fire.

20 Old Power Plant, Bldg. 354 The Old Power Plant, Bldg. 354, located in the Superblock Area bound by Nimitz, Branon, Cannon, and 

Morrell Avenues, was once the main diesel power plant for Sand Island. The Superblock Area consisted of 8 

centrally located maintenance and power generation facilities. Bldg. 354 housed diesel generators, oil-filled 

drums, sumps, switches, transformers, ASTs, and several USTs with evidence of leaks from multiple sources. 

Cable trenches, production distribution piping, and a storm drain leading to the Inner Harbor were also 

associated with the site.

34 Pesticide Shop, Bldg. 361 The Pesticide Shop, Bldg. 361, is located near the corner of Nimitz and Branon Avenues. It was formerly used 

as a transformer substation. Pesticides were mixed and stored at this site, and a sink in the building was 

reportedly used for pesticide mixing and washing. The facility contained numerous containers of pesticides 

and herbicides, which appeared to be properly labeled and stored (Ogden 1996).

53 Bldg. 348 Bldg. 348 is located at the southwest corner of the Superblock Area on Sand Island. Bldg. 348 was the former 

Public Works/Administration Building. Discarded electrical equipment parts observed behind the building 

were identified as potential PCB sources that may have impacted surface soil (Ogden 1996).

n/a New Bulky Waste Landfill, Sand 

Island

The New BWLF on Sand Island is located near the northern edge of Runway 15-33. Demolition- and 

removal-action-related debris, including concrete, metal debris, PCB-contaminated marine sediment, and 

asbestos, were placed in this landfill. This landfill also contains a CAMU where stabilized PCB- and 

pesticide-contaminated soil from various Midway removal actions was placed.

Source: Third Five Year CERCLA Review of 12 Sites, Dept of Navy, NAVFAC (2013)
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3.3.5.2 Probable Impacts 

Effects on hazardous materials or hazardous waste management may be considered adverse if the 

proposed action results in noncompliance with applicable Federal and state regulations, increases 

the amounts generated or present on Sand Island over current levels, or overwhelms existing 

hazardous waste management procedures and capacities. The effects of the proposed action may 

also be considered adverse if the proposed action disturbs or creates contaminated sites, resulting 

in adverse effects on human health or the environment. 

As noted in the previous section, as a former NAF (and battleground), the Atoll has several 

hazardous material, waste transfer, and storage areas. These existing conditions are the subject of 

other planning documents, including 5 Year CERCLA Reviews by the Naval Facilities 

Engineering Command. These project-related hazardous materials are summarized in Table 3.7

below. 

Table 3.7 Project Related Hazardous Materials, Waste, and Toxins 

Substance Use

Fuel(s) For use in all operational vehicles, including aircraft. 

Oils or Lubricants For use in all operational vehicles, including aircraft.

Brodifacoum Rodenticide toxin.

Source: Planning Solutions, Inc. (2017)

While vehicular fuel and lubricants are important to consider, the primary substance of concern 

is brodifacoum, a coumarin-based anticoagulant toxin. It is a vertebrate toxicant that acts by 

interfering with the blood’s ability to form clots, causing sites of even minor tissue damage to 

bleed continuously. Before brodifacoum can have a measurable physical effect, levels of the 

toxin in the liver must reach a toxic threshold, which varies widely by species. For a detailed 

discussion of the potential for adverse biological impacts related to the proposed broadcast of 

brodifacoum, see Section 3.3.6. Brodifacoum was the most commonly used rodenticide in the 

United States and was widely available for household use (Erickson and Urban 2004) until 2014 

when the EPA prohibited second-generation anticoagulant rodenticides for use in products 

geared toward consumers. Now they are only registered for the commercial pest control and 

structural pest control markets. Second-generation anticoagulants registered in the United States 

include brodificoulm, bromadiolone, difenacoum, and difethialone. 

It is anticipated that the proposed action of broadcasting brodifacoum bait across Sand Island, 

MANWR through a combination of aerial, hand, and bait station dispersal methods (see Section 

2.3) would have no long-term adverse impact on LUC sites or issues associated with the 

handling or management of hazardous waste. Operational staff carrying out the eradication 

project would adhere to all LUCs and other guidelines for vehicle refueling, disposing of 

hazardous wastes, and managing hazardous materials throughout its implementation. No aspect 

of the proposed action would require the alteration of the LUCs in force at the present time, or 

involve physical disturbance of contaminated sites, hazardous materials management, or 

hazardous waste disposal processes. 
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3.3.6 BIOLOGICAL RESOURCES

3.3.6.1 Evaluation Criteria for Effects on Biological Resources 

The significance of effects on biological resources is based on: (i) the importance (i.e., legal, 

commercial, recreational, ecological, or scientific) of the resource, (ii) the proportion of the 

resource that would be affected relative to its occurrence in the region, (iii) the sensitivity of the 

resource to proposed activities, and (iv) the duration of ecological effects. It is anticipated that 

the primary result of the Proposed Action to introduce a toxicant to achieve the purpose and need 

would be a shift in the plant and animal communities and ecosystem processes on MANWR

toward a state more representative of its ecosystem before mice were accidentally introduced. 

Using previous successful studies and similar applications of a toxin to remove mice from other

islands, it is anticipated that this shift would include an increase in the breeding success of 

several species of seabirds on the island. However, there are too many variables that would 

contribute to the post-eradication ecosystem responses for effective analysis within the scope of 

this document. The short-term impacts from exposure to brodifacoum or any other rodenticide to 

individual animals is determined by 2 factors as follows: 

1. The toxicity of the compound to that individual. 

2. The probability of that individual’s exposure to the compound (Erickson and Urban 

2004). 

The toxicity of a particular compound on an individual animal is often expressed as LD (Lethal 

Dose). A common value used to express toxicity is “LD50” which means that the dosage (D) of a 

toxin that is lethal (L) to 50 % of animals of the species in a laboratory test. The EPA has 

compiled laboratory data on the LD50 quantity of brodifacoum for a number of species. However, 

due to the difficulty and expense of obtaining extensive laboratory data, the LD50 values for most 

species remain unknown. Therefore, for the purpose of estimating impacts to wildlife, this 

document will use the following LD50 values to generalize potential toxicity for birds and 

mammals respectively using data from Erickson and Urban (2004) and USEPA (1991): 

For birds, an LD50 value of 4.1 x 10-6 ounces/pound (0.26 mg/kilogram) of body weight for bait 

containing brodifacoum at a concentration of 25 ppm will be used – this is the average LD50

value for the mallard (Anas platyrhynchos). 

For mammals, an LD50 value of 6.4 x 10-6 ounces/pound (0.4 mg/kilogram) of body weight for 

bait containing brodifacoum at a concentration of 25 ppm will be used – this is the average LD50

value for the laboratory rat (R. norvegicus). 

In comparison to real-world values that toxicologists have obtained from a wide class of species, 

these values are conservative. This toxicity model assumes that an animal’s body mass is the 

primary determinant of how much brodifacoum is required for that animal to reach an LD50

threshold, within each taxonomic category (in this case, birds and mammals). However, there are 

other variables that affect LD50 as well, but using conservative LD50 values such as those above 

decreases the possibility that the model would underestimate the risk or potential impact to each 

species considered. The LD50 value for mallards used for the assessment of toxicity to birds for 

the proposed action is 4.1 x 10-6 ounces/pound (0.26 mg/kg) (Ross et al. 1980, USEPA 1991). 
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Erickson and Urban (2004) use a similar model to determine the amount of bait needed to reach 

an LD50 threshold for birds with a mass of 0.88 ounces (25 grams), 3.53 ounces (100 grams), and 

35.3 ounces (1,000 grams), compared to the average daily food intakes for each of these size 

classes (Table 3.8). 

Table 3.8 Generalized proportion of daily food intake that must be bait for birds to reach 

an LD50 threshold where the dosage (D) of a toxin is lethal (L) to 50% of 

animals of the species in laboratory tests 

Body Size Class Amount of Bait for LD50 % of Daily Food Intake

0.88 oz. (25 grams) 0.0092 oz. (0.26 grams) 4.2

3.53 oz. (100 grams) 0.037 oz. (1.04 grams) 10.8

35.3 oz. (1,000 grams) 0.37 oz. (10.4 grams) 19.2

Source: Adapted from Erickson and Urban (2004), using a brodifacoum concentration of 25 ppm.

Erickson and Urban (2004) use a similar model to determine the amount of bait needed to reach 

an LD50 threshold for mammals, using the same size classes as Table 3.8 above. 

Toxicants are also evaluated by their sub-lethal effects on animals. These are represented by 

metrics, such as NOAEL (no observable adverse effect level) and LOAEL (lowest observable 

adverse effect level). NOAEL is a dose or exposure level of a toxicant that produces no 

measurable toxic effects on the test group of animals and LOAEL is the lowest dose or exposure 

level of a toxicant that produces a measurable toxic effect on the test group of animals. Sublethal effects observed from anticoagulant exposure may include a variety of mild adverse 

effects, including prolonged clotting time, internal bleeding, piloerection, lethargy, diarrhea, 

bloody diarrhea, and/or anorexia (Anderson et al. 2011). The NOAEL value for mallards is <3.2 

x 10-6 ounces/pound (<0.20 mg/kg) (EPA 1991). 

3.3.6.2 Non-Target Species

Implementation of the Midway Seabird Protection Project would pose inherent risks to nontarget species. These risks are summarized in Table 3.9 below. 

Table 3.9 Summary of Risks to Nontarget Species 

Risk Description

Primary Poisoning of nontarget species due to consumption of bait with rodenticide.

Secondary Poisoning of nontarget species from consuming primary-contaminated prey (e.g., 

contaminated mice, crabs, insects, fish, etc.).

Tertiary Poisoning of nontarget species from consuming secondary-contaminated prey.

Disturbance Risks to non-target species from personnel and equipment conducting eradication (e.g., 

disturbance to resting monk seals from overflight noise).

Crushed Burrows Risks of crushing the burrows of nesting seabirds as ground personnel walk into these 

areas during the baiting operation.

Bird Strike Collisions between flying birds and helicopter during aerial operations. 

Source: USFWS (2017)

From a toxicological perspective, the risk to nontarget species during an eradication project is a 

function of the species present on the island and their behavior. Specific factors which require 

consideration include: (i) toxicological properties, composition, and delivery method of bait; (ii) 

the susceptibility of those species to the toxin; and (iii) the probability of exposure to the 
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rodenticide by directly consuming it or indirectly by feeding on contaminated prey (Howald et 

al. 2007). Spatial and temporal risks should be eliminated, minimized, or mitigated to the 

maximum practicable extent, with due consideration to the species, their conservation status, and 

the population significance. 

On MANWR, although there is no single time of year during which all species with a potential 

nontarget concern are absent, there are times of the year when some species that have potential 

nontarget risks are present in very low numbers. Thus, examining the annual use of the island by 

each species can be used to identify the greatest risk periods so that they can be avoided (see 

Figure 3.3 below), along with using the latest population estimates of each species on the refuge. 

Rodenticide exposure, disturbance impacts, risk of crushing burrows, and bird strike hazards can 

be minimized by timing the eradication operation to avoid the seabird breeding season, and to 

target periods when migratory shorebirds are on breeding grounds in Alaska (Wegmann et al. 

2014, Howald et al. 2005). Careful timing of the project can also minimize risks to avoid specific 

behavior or key windows for some species, such as avoiding the monk seal pupping period and 

avoiding the time period when large numbers of albatross chicks are still present and exposed to 

bait pellets on the ground. Albatross chicks have been observed to occasionally swallow small 

items that they pick up and manipulate referred to as pica behavior. “Pica” means to display an 

indiscriminate preference for eating non-food items; in this case, albatross chicks pecking and 

ingesting rocks, sticks and other foreign objects (See “Pica” in Glossary of Terms). Other 

minimization and mitigation strategies may include captive holding and releasing animals after 

the risk period passes (e.g., Howald et al. 2005, Wegmann et al. 2014), hazing (scaring away 

from an area), as well as maintaining the antidote, Vitamin K, on hand if an individual animal is 

demonstrating signs of toxicosis and can be captured and held for treatment (e.g. Wegmann et al. 

2014). 

The Service will strive to implement all reasonable and prudent avoidance, minimization, and 

mitigation measures to reduce take of birds. 

The analysis of impacts, along with specific mitigation actions, will take into consideration the 

potential short-term impacts through mortality of individuals due to mouse eradication activities, 

and will weigh these against the benefits of long-term species recovery and protection afforded 

by mouse eradication. Mitigation activities can minimize overall impacts, but in some cases, may 

not eliminate risks completely.

The presence of wildlife on and around islands targeted for eradications present an inherent 

challenge. In essence, the operation must be able to deliver bait to every mouse on the island 

while minimizing availability of the rodenticide to other species. In addition to the toxicological 

risks, the operation may also impose disturbances and habitat alterations that could have negative 

impacts on the ecosystem.

Although impacts to native species are only ecologically significant if they pose a population 

level effect, as a principle, any risks to wildlife should be avoided, minimized, or mitigated 

whenever reasonably possible. The long-term benefits of the eradication must outweigh the 

short-term environmental impacts and mitigation strategies must be considered in the trade-off 

framework (Broome et al. 2014). 
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Figure 3.3 Monthly Species Abundance or Breeding Activity on Sand Island, MANWR

Source: USFWS (2017)

Although there are no species endemic to MANWR, the refuge is of high significance for several 

terrestrial and marine species, including:

• The critically endangered (non-migratory, resident) Laysan duck, extant on Sand and 

Eastern Island;

• The endangered short-tailed albatross that has bred in the recent past on Eastern Island 

and recently is represented by one pair of birds attending a site on Sand Island; 

• High density breeding populations of Laysan albatross and black-footed albatross present 

for about 8-9 months of the year; 

• Globally important populations of Bonin petrels and red-tailed tropicbirds; 

• A resident population of spinner dolphins (Stenella longirostris) in the lagoon; 
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• Overwintering shorebirds, such as the bristle-thighed curlew (Numenius tahitiensis), a 

species of special concern among the shorebirds at Midway due to its small world 

population size; 

• Threatened Hawaiian green sea turtles that use beaches for resting and nesting and 

Endangered hawksbill sea turtles; 

• Endangered monk seals that use the beaches and foreshore vegetation for resting and 

pupping, and can be found on the island year-round; 

• Two endangered plants present on Sand Island, the Pōpolo (Solanum nelsonii), a trailing 

shrub, and the Nihoa fan palm (Pritchardia remota), or Loulu. 

A general risk assessment to each species was developed to examine the likelihood of effects to 

the species from primary and secondary rodenticide exposure, risk of collision with the 

helicopter, risk of disturbance from the helicopter and ground personnel, risk of crushing 

burrows, and significance of the risk relative to the global population of the species (see Table 

3.10). 

3.3.6.3 Environmental Fate of Brodifacoum in Soil and Water 

The chemical compound brodifacoum, the active ingredient in the Brodifacoum-25D bait, has 

low or extremely low solubility in water and bind tightly to organic matter in soil where the 

rodenticide would be degraded by soil micro- organisms and exposure to oxygen and sunlight. 

The solubility in water at 20°C is 0.0038 mgl-1, which is considered low. The typical persistence 

time (DT50) is listed as 84 days which is considered moderately persistent. The half-life in soil is 

~84 to 175 days for brodifacoum. The rate of microbial degradation would be dependent on 

climatic factors such as temperature, light, humidity, and the presence of molds and soil 

microbes that potentiate degradation. Therefore, in general, degradation time would be more 

rapid in warm sunny places like NWHI than in colder climates (Eason and Wickstrom 2001, 

Eisemann and Swift 2006). Bait trials for the eradication of rats on the island of Lehua, Hawai’i 

indicated inert (placebo) pellets of a composition similar to the inert matrix of Brodificoum-25D, 

in the terrestrial environment would break down and be undetectable in 35-40 days when under 

vegetation and around 65 days on rock or bare ground (Mazurek 2015). The results of a 

degradation study in soil indicate that only minor metabolites are formed (<3.5% of parent 

compound). In rats, no toxicologically relevant metabolites have been identified which could be 

introduced in soil via urine or feces (European Parliament and Council 2010). Because of the 

rapid breakdown of the rodenticide, the Preferred Alternative would be unlikely to directly or 

indirectly cause persistent contamination of soil on Sand Island. The potential presence of 

brodifacoum in groundwater is discussed in Section 3.3.2. 
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Table 3.10 Preliminary Risk Assessment by Species, Consequence, and Potential Mitigation 

Species

Poisoning 

Risk

BASH Risk

Disturbance 

Risk

Global 

Population 

Significance

Mitigation Measures

PrimarySecondaryGroundAir

Laysan Albatross 

(adults) Low Low Med Low Low 64% n/a

Black-footed 

Albatross (adults) Low Low Med Low Low 22% n/a

Short-tailed 

Albatross (adults) Low Low Low Low Low 0.05% n/a

Albatross (chicks; 

all spp) Low Low Med Low Low - 

For Short-tailed albatross, and only if chick is present from single pair 

attempting to breed on Sand Island - Implement regimen of checking for 

and removing bait pellets from around the nest or use bait boxes.

Wedge-tailed 

shearwater Low Low Low High Low 0.20% Ground crews are: (i) to stay on established trails when possible; (ii) avoid walking close to nesting birds and exhibiting any actions that flush 

birds, especially those with eggs and young chicks; (iii) stay alert for bird 

burrows and avoid crushing them; (iv) if a burrow is crush in, gently dig 

out the bird.

Bonin petrel Low Low Low High Low < 0.01%

Black noddy Low Low Med Low Low < 0.01% n/a

Brown noddy Low Low Med Low Low 0.60% n/a

Gray-backed tern

Sooty tern Low Low Low Low Low - n/a

White tern Low Med High Low Low Low n/a

Great frigatebird Low Med Med Med Low 0.01% n/a

Red-tailed 

tropicbird Low Low High Med Low 19% n/a

Brown booby Low Low Low Low Low < 0.01% n/a

Small shorebirds High High Low Low Low 0.15 - 1.1% n/a
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Species

Poisoning 

Risk

BASH Risk

Disturbance 

Risk

Global 

Population 

Significance

Mitigation Measures

Primary

Secondary 

Ground

Air

Pacific golden 

plover High Med Low Low Low 0.15-0.83% Trap as many as is feasible; hold in pens; release after after the risk period has passed.

Bristle-thighed 

curlew High High Low Low Low 2.42%

Trap as many as is feasible with 2 options: (i) hold in aviary (as opposed 

to pens) and release after the risk period has passed; (ii) clip wing 

feathers and place on Eastern Island.

Laysan duck High High Low High Med > 50%

Live capture 100% of population (or a majority of the population) with: 

(i) hold in captivity on Sand Island and then Eastern Island after 

operation commences until the risk period passes; (ii) clip wing feathers 

of birds on Sand Island and translocate to Eastern Island; (iii) a 

combination of the above strategies.

Cattle egret 

Atlantic canary 

Common Myna

High High Low Low Low - 

Mitigation measures for the Atlantic canary due to its cultural 

significance. Trap and hold as many as is feasible; release after the risk 

period has passed.

Hawaiian Monk 

seal Low Low n/a Low Low 5%

Measures to reduce pellets entering water; ground crews maintain a 100 

ft. (30.5 m) buffer from Hawaiian monk seals; helicopters to avoid 

hovering near seal basking and pupping areas, and to minimize 

distribution of pellets over seals on the beaches.

Dolphin spp. Low Low n/a n/a Low - n/a

Green sea turtle Low Low Low Low Low - 

Measures to reduce pellets entering water; ground crews maintain a 100 

ft (30.5 m) buffer from sea turtles; helicopters to avoid hovering near 

turtle basking areas and to minimize distribution of pellets over turtles 

on the beaches.

Pōpolo and Nihoa 

fan palm (Loulu) n/a n/a n/a Low n/a - 

Staff will be trained to recognize the pōpolo and loulu and monitor their 

work areas at all times for the presence of these two species. They will 

exercise extreme care when hand broadcast of bait is necessary or when 

servicing bait stations to minimize any damage to listed plants.

Source: USFWS (2017)
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The amount of time bait pellets will be available on Sand Island plays a major role in risk of 

exposure to non-target species. Bait pellet longevity is influenced by many factors such as 

environmental conditions and bait uptake by mice and non-target species. Bait longevity may be 

high in some areas of Midway Atoll due to other factors (USFWS, Unpublished). Besides uptake 

by target species and exposure to environmental factors, bait pellet disappearance rates are also 

influenced by uptake by invertebrates like land crabs and cockroaches. Bait disappearance, in 

these cases, would vary depending upon the abundance and distribution of these invertebrates. 

While not driven by land crabs, the bait trials on Midway suggest that bait disappeared at high 

rates in some habitats (USFWS, Unpublished). Bait disappearance in some areas on Midway 

Atoll may be just as high as that found after bait operations for the eradication of rats on Palmyra 

Atoll, even though Midway Atoll has much lower populations of land crabs. The reasons for this 

occurring on Midway are unclear, but one possible explanation is that pellet disappearance on 

Midway was driven by cockroaches and other invertebrates. Moreover, the bait density proposed 

in this EA are based on data collected at Midway Atoll and tailored to Midway and its unique 

ecosystem.

Bait pellets may inadvertently fall into the ocean, but small amounts entering the ocean is not 

considered a great risk. This is illustrated from monitoring conducted on 2 rodent eradication 

projects using Brodifacoum-25D. On Anacapa Island, divers and land-based observers monitored 

bait for entry at 7 separate locations (Howald et al. 2009). Sites were selected based on their 

probability of bait entering the water (e.g., near or under steep cliffs). The application rate on the 

project was 13.4 lbs./ac. (15 kg/ha) and no bait was observed to directly enter the water, though 

small quantities indirectly entered at 3 locations, and densities were estimated at 0.15 pellets/10.8 

ft2 (1 m2

). On Isabel Island, Mexico, where the application rate was 18.4 lbs./ac. (20.6 kg/ ha), 

divers monitoring the operation documented bait in the sub-littoral zone at <1 pellet/108 ft2 (10 

m

2 or 0.1/m2

) (Samaniego-Herrera et al. 2014). Fisher et al. (2011) summarized the results of 

environmental monitoring for brodifacoum residues after rodent eradications in a fenced reserve 

at Maungatautari, New Zealand and on the offshore islands Little Barrier, Rangitoto and 

Motutapu, New Zealand. Brodifacoum was not detected in extensive fresh water monitoring at 

Maungatautari, or in fresh water samples from Little Barrier Island. Residual concentrations 

were present in soil samples from underneath degrading bait pellets on Little Barrier and 

decreased to near the limit of detection 100 days after application. No brodifacoum was detected 

in marine shellfish sampled from Little Barrier, Rangitoto or Motutapu. 

However, examples exist where large quantities of bait entered the marine environment. During 

the Palmyra rat eradication, where the documented bait application was extremely high, 75.6 

lbs./ac. (84.8 kg/ha) for the 1st application and 71.5 lbs./ac. (80.1 kg/ha) for the second 

application, the average density of bait entering the water was as high as 40 lbs./ac. (44.7 kg/ha) 

during the first application and 41 lbs./ac. (46.3 kg/ha) during the second (Engeman et al. 2013). 

A variety of factors are thought to have contributed to the high quantity of bait entering the 

marine environment at Palmyra, which include: an irregular coastline, baits drifting in the wind, 

pilot difficulty locating the shoreline due to overhanging palm trees, and an ineffective and 

broken bait deflector. The shoreline of Sand Island is much more regular, there are no trees 

overhanging shorelines or beaches with which the pilot must contend, some of the beaches are 

wide and bare of vegetation so that the pilot would not have to be near the high tide line, and the 

bait density would be less than at Palmyra, with an application rate on Sand Island at 65 lbs./ac. 
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(73 kg/ha). The application rate at Palmyra was 10-16% higher than that proposed for Sand 

Island. Complete breakdown of pellets in the water would be quick, especially for the exposed 

shorelines on the southern side of Sand Island. For the northern shorelines adjacent to the lagoon 

and protected by coral reefs, a channel was dredged by the military between Sand Island and 

Eastern Island into the lagoon, which allows a significantly larger tidal flux in and out of the 

lagoon and harbor than would otherwise occur. During the inert bait trials on Lehua in 2015, data 

collected show that pellets disintegrated within 30 minutes after application to seawater, and no 

pellets were found after 24 hours (Mazurek 2015). 

In trials on Kapiti Island, New Zealand, inert bait pellets were seen to disintegrate within 15 

minutes (Empson and Miskelly 1999) and on Isabel Island, pellets “sank immediately and 

disintegrated by wave action within a few minutes” (Samaniego-Herrera et al. 2014). During a 

rat eradication project on Anacapa Island in southern California, bait that entered the ocean 

completely dissolved within 5 hours (Howald et al. 2009). Sampling of seawater 24 and 48 hours 

post-application, conducted in conjunction with the Anacapa project, tested negative for 

brodifacoum residues. 

In the process of breaking down, pellets would consist of suspended cereal grain flocculants and 

dissolution of the active ingredients into seawater. The solubility of brodifacoum in water is 3.2 

x 10-5 oz./gallon (0.24 mg/l) (USEPA 1991). Any effect of salt water on solubility has not been 

reported. For the rat eradication on Mōkapu, Hawaiʻi and the first attempt on Lehua, seawater 

samples were collected 5 and 7 days after the last application of rodenticide baits. No 

diphacinone was detected in the seawater samples from either operation (Gale et al. 2008, Orazio 

et al. 2009). Because very little of the rodenticide is expected to enter the water, its low solubility 

in water, and the rapid breakdown in water, the Preferred Alternative would be unlikely to 

directly impact seawater on or around Sand Island. 

3.3.6.4 Terrestrial Environment 

3.3.6.4.1 Terrestrial Vegetation: Existing Conditions 

The first vascular plant inventory was conducted on Midway Atoll in 1904 by William Bryan

who documented 13 species (Bryan 1905). Since that time, over a dozen visits have been made 

by botanists to the remote islands for the purpose of investigating the plant life occurring there 

(e.g., Christophersen and Caum 1931, Apfelbaum et al. 1983, Bruegmann 1998, Conant et al. 

1983, Neff and DuMont 1955). In all, 389 species have been recorded, 350 of which are exotic 

(see Figure 3.4 below). Introductions of exotic species to Midway have occurred via a variety of 

means, beginning with the planting of gardens to provide food for residents of the Pacific 

Commercial Cable Station during the first decade of the 20th century. Other species were 

brought in accidentally. 

Not all plant species introduced to Midway have persisted or thrived. Less than half of the exotic 

plants once observed on Midway, 170 species, occur there today. Regular botanical inventories 

have been conducted at MANWR since 1999 (Starr and Martz 1999, Starr and Starr 2008, Starr 

and Starr 2015). As with earlier investigators, the bulk of the information produced has consisted 

of lists of the plant species observed, collection of voucher specimens for new occurrences, and 

locations of some of the plants observed with qualitative notes on distribution and abundance. 
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Figure 3.4 Map of Vegetative Cover on Sand Island, MANWR 

Source: USFWS, Draft Midway Atoll Habitat Management Plan (2014)

Annual weed monitoring has been conducted on MANWR since 2012, and has focused almost 

exclusively on detecting trends in cover of golden crown-beard (Verbesina encelioides), a highly 

invasive plant species that has been the subject of a refuge-wide eradication campaign. Past 

monitoring was conducted at 100 sites (50 sites each on Sand and Eastern islands) and entailed 

visually estimating the foliar cover of golden crown-beard within a 15.4 ft (4.7 m) radius plot. 

This monitoring effort served the refuge well in documenting the steep decline of golden crownbeard, which decreased from approximately 50% cover to <1% across a 5-year period. 

3.3.6.4.2 Dominant Vegetation Types 

The land cover classes from the Draft Midway Atoll Habitat Management Plan offer a snapshot 

of vegetation communities and plant associations on MANWR in December 2014 (see Figure 3.4

and Table 3.11 below). Spatially, the classification includes areas managed for human use, such 

as the “town” area, as well as areas primarily managed for habitat. The classes are arranged 

based on canopy type, starting with the highest tree canopy (forest) and ending with unvegetated 

classes. When more than 1 canopy layer is present, the highest layer determines the cover class. 

For example, woodland includes a sparse (<25%) tree canopy layer and a field layer, but in some 

areas a secondary tree canopy and shrub layer are also present. 
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Table 3.11 Vegetation Communities and Plant Associations on Sand Island, MANWR 

FOREST: Casuarina Forest Association with overall tree canopy cover >25%.

Tree canopy may range from open to closed. Casuarina seedlings are rarely present. The dominant species is 

Casuarina equisetifolia, although Casuarina glauca occurs in a few areas. Formerly, Pluchea carolinensis formed 

a sub-canopy in some areas, but P. carolinensis has largely been eliminated except for seedlings in areas where 

Casuarina has been removed. Adjacent to beaches, a thin shrub layer of Scaevola taccada may encroach a short 

distance into the forest. There is often no ground cover. When present, ground cover species include Verbesina 

encelioides and Euphorbia cyathophora. Euphorbia peplus, Coronopus didymus or Eustachys petraea may occur 

in forest openings. In areas underlain by pavement or cement, there are few petrel burrows; organic matter, needles 

and organic debris form the ground cover. Here, the trees are easily wind-thrown and there may be a tangle of 

downed trees. In dunes and sandy soils, petrel burrows abound and the soil shows weakly stratified layers of sand 

and organic duff. 

WOODLAND: Mixed Woodland Association with Casuarina tree canopy cover <25%.

Usually distinguished from forest by understory and/or ground cover composition, the mixed woodland association 

is dominated by large diameter, mature Casuarina equisetifolia or Casuarina glauca trees. Coccoloba uvifera, 

Hibiscus tiliaceus, Terminalia catappa and various other non-native trees may also occur, forming dense thickets. 

In combination with Casuarina, these other species may increase overall tree canopy above 25%. Behind beaches, 

Scaevola taccada may form a discontinuous subcanopy. A range of herbland communities may be present, but 

common ground cover includes Cynodon dactylon (around the town area), Stenotaphrum secundatum, Boerhavia 

repens and various other herbaceous species or bare ground. The sandy soil does not have a visible layer of tree 

detritus or needles. The south half of Sector 4 and many areas around “town” are mixed woodland. The Casuarina

forest also intergrades into woodland in some areas. 

SHRUBLAND: Scaevola Shrub Association with shrub canopy cover >25%.

Scaevola taccada dominates the shrub association except in areas bordering beaches, where Tournefortia argentea

may co-dominate. Both are considered widespread, halophytic, pioneer species, and they can be found in 

monotypic stands, or co-dominant and mixed forest (Niering 1963, Kepler and Kepler 1994). Below the canopy, 

very dense shrub stands eliminate most ground cover, resulting in bare ground covered with dead sticks. In Sector 

4, beachside Scaevola encroaches on the neighboring Casuarina forest and woodland. Casuarina seedlings are 

scattered throughout the shrubland backing North and West Beaches on Sand Island. Eustachys petraea, 

Verbesina encelioides and an occasional Bidens alba may climb up through the shrubs. Conyza spp. also occur. 

Scaevola shrub association is found in small patches inland, usually where it has been planted for soil stabilization 

or cover. A mosaic of shrub and herbaceous associations occurs on the northeastern portion of Eastern Island. On 

Spit Island, Solanum nelsonii grows in the shrubland. 

VINES: Viney Perennial Association with >50% cover of viney perennials in the field layer. For landcover 

mapping purposes, both the Tribulus-Boerhavia Association and the Ipomoea Association are combined into 

the viney perennial association.

Tribulus-Boerhavia Association: Tribulus-Boerhavia is the dominant cover class on Eastern Island. It intergrades 

with the Lobularia-Cynodon herbaceous association, making classification difficult depending on the season. The 

invasive mustard Brassica nigra is strongly associated with viney perennials on Eastern Island. Herbicide use in 

the fall and late winter significantly reduces Tribulus foliage, reducing competition with Lobularia maritima. 

During these times, the Lobularia-Cynodon association is prominent. Tribulus-Boerhavia vines persist from a 

woody base, and by early summer, account for >50% cover, masking underlying Lobularia plants. The vines also 

spread across abandoned runways, forming an important component of the partially vegetated runway class. 

Species common in this layer include Tribulus cistoides, Boerhavia repens, Lobularia maritima, Brassica nigra, 

Verbesina encelioides, Coronopus didymus, and occasional patches of Cynodon dactylon and other grasses. 

Ipomoea Association: >50% cover in the field layer; limited distribution on Sand and Eastern Islands. A few 

scattered patches of Ipomoea pes-caprae occur on or near beaches, often with Dactyloctenium aegyptium

encroachment. Ipomoea indica occurs inland on Sand Island. An aggressive vine, it is usually associated with and 

overruns the Lobularia-Cynodon association, also occasionally climbing onto Eragrostis variabilis and various 

trees or shrubs nearby.
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HERBLAND: Lobularia-Cynodon Herbaceous Association where herbaceous vegetation accounts for >75% 

of cover but may be less, as long as it exceeds woody plant cover.

The dominant non-forest cover class on Sand Island, this herbland is composed of forbs and low-growing grasses. 

Lobularia and Cynodon intergrade throughout the island, with up to 100% cover of Cynodon in the “town” area 

and 100% Lobularia in other locations. Predominant species include Lobularia maritima, Cynodon dactylon, 

Solanum americanum, Lepidium virginicum, Coronopus didymus, Eleusine indica and other low-growing nonnative forbs and grasses that may change throughout the year. Small patches of the tall grass Stenotaphrum 

secundatum are included when completely surrounded by herbland. These are generally remnants of former 

Casuarina forest or woodland that has been removed and converted to herbland. On Eastern Island, the LobulariaCynodon Herbaceous Association occurs in low-lying swales backing the beach and shrub zones along the north 

shore, and around the building foundations and previously developed areas near the pier. Herbs are also an 

important component of the Tribulus-Boerhavia viney association and seasonally appear to be the dominant cover 

class. Predominant species include Lobularia maritima, Cynodon dactylon, Tribulus cistoides, Boerhavia repens, 

Coronopus didymus, Brassica nigra, and Verbesina encelioides.

BUNCHGRASS: Eragrostis Bunchgrass Association is generally present in small patches spreading from 

out-planted nuclei on all 3 islands.

Eragrostis variabilis has been the primary species used for restoring native plant cover. In recent years, the grass 

started seeding and some Eragrostis patches are now expanding on their own. Near beaches, Eragrostis is 

occasionally overgrown by Scaevola taccada. Other species include Lobularia maritima, Coronopus didymus, 

Conyza spp, and other herbaceous species. On Eastern Island, Tribulus cistoides may occasionally overrun 

Eragrostis plantings. Chenopodium oahuense and other native shrubs and forbs are being restored to this 

community.

WETLAND: Wetland Cyperus Association with >50% cover of wetland-associated plants, primarily sedge.

Runway 24 east extension on Sand Island is the main expression of this association, but small patches occur in lowlying areas that intermittently flood. The main species is Cyperus polystachyos. Other species include Cyperus 

laevigatus, Cyperus involucratus, Andropogon virginicus, Sesuvium portulacastrum, Heliotropium procumbens, 

Phyla nodiflora and Portulaca oleracea. This category usually does not apply to the areas surrounding most of the 

ponds and former seeps since their soils do not support hydrophytic species. Some facultative wetland species 

occur at Catchment Pond shoreline and the former Sunrise and Mauka-Makai seeps on Sand Island. 

BEACH STRAND: Includes herbaceous cover and open beach from the mean tide mark to a shrub belt or 

herb-covered terrace above the beach.

While most of the beaches are unvegetated, a few species occur in patches or at low densities: Lepturus repens, 

Sesuvium portulacastrum, Ipomoea pes-caprae, and sparse Tournefortia argentea seedlings. Large, dense patches 

of Sesuvium portulacastrum surrounded by beach, such as the S. portulacastrum/Fimbristylis cymosa on Spit 

Island, are included in this class. 

BARREN: Where there is <5% vegetation due to management activities or erosion rather than artificially 

hardened substrate, excluding beaches.

The substrate and transitory nature of barren areas distinguishes this class from the unvegetated class. The barren 

substrate will support plant growth, whereas the hardened, artificial substrate in the unvegetated class will not until 

the surface is broken. Barren areas are not vegetated due to recent removal of plant cover, usually for restoration 

purposes or contaminants remediation. For example, large scale ironwood removal projects result in barren areas 

until restored to another land cover type, such as an herbaceous plant community. In future landcover maps, barren 

areas will be classified into the appropriate vegetation association. On Eastern Island, naturally-occurring barren 

areas occur on the tops of some revetments, however normal erosion processes will eventually result in plant 

growth. Barren areas also occur in erosive features behind sea walls where vegetative cover is destroyed by waves. 

Note that barren and unvegetated are somewhat arbitrary distinctions and could be combined into a single 

unvegetated cover class for mapping purposes. 

PARTIALLY VEGETATED: Partially Vegetated Former Runway/Pavement/Foundations which are 5-25% 

covered with vegetation.

On Sand Island, common species are Casuarina equisetifolia, Fimbristylis cymosa, Eustachys petraea, 

Andropogon virginicus, Dactyloctenium aegyptium, Sporobolus indica, Bidens alba, Pseudognaphalium 

sandwicensium and various herbaceous weeds. Many abandoned runways on Eastern Island are now nearly 

indistinguishable from off-runway vegetated areas and will usually contain a mix of species from the TribulusBoerhavia association as well as a number of incipient weeds. 
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UNVEGETATED: Unvegetated Structures/Runways with <5% vegetation.

Runways, concrete, asphalt, buildings, piers, structures.

Source: USFWS (2017)

Where noted, a few “orphan” plant types, generally remnants from previous land uses, are 

lumped into the cover class surrounding them or a structurally similar class. For example, the tall 

grass Andropogon virginicum, an upland species, intermixes with Cyperus polystachyos, the 

dominant wetland sedge, at the Catchment Pond area. In this case, it is classified as part of the 

wetland sedge association. Where A. virginicum has spread onto the adjacent abandoned runway, 

it is classified as “partially vegetated runway.” Some plant associations change dramatically with 

the seasons, such as viney associations and herblands on Eastern Island. These situations are 

noted and, while they may affect community composition at various times of the year, the overall 

effect on habitat structure is negligible. Because management activities and stochastic events 

create a dynamic system at MANWR, cover classes recognized in previous years have changed 

and, in some cases, disappeared. No longer is “Verbesina shrubland” a viable cover class, a 

testament to the success in controlling an invasive weed that caused significant degradation of 

seabird habitat.

3.3.6.4.3 Endangered Plants 

Kāmanomano is a short-lived rare perennial grass that has two recognized varieties: Cenchrus 

agrimonioides var. agrimonioides, found on the islands of O‘ahu, Lāna‘i, and Maui, and C. 

agrimonioides var. laysanensis, known historically from the Northwestern Hawaiian Islands of 

Laysan, Kure, and Midway (Service 2009). Populations of C. agrimonioides var. laysanensis

were last collected in 1973 on Kure Atoll, Midway Atoll, and Laysan (Wagner et al. 1999, 

Service 2009). The relatively isolated occurrences of kāmanomano in the northwestern Hawaiian 

Islands are negatively affected (on the low-lying islands) by nonnative plants and by stochastic 

events such as tsunami. An assessment by Fortini et al. (2013) concluded that kāmanomano is 

moderately vulnerable to the impacts of climate change. This plant was federally listed as 

endangered in 1996. Cenchrus agrimonioides var. laysanensis, a variety of this species endemic 

to the Northwestern Hawaiian Islands, became extinct in the 1980s (Bruegmann and Caraway 

2003). Therefore, the species has not been seen on MANWR for years, even though botanical 

surveys have been conducted on Sand Island, so it is very likely no longer present here and will 

not be addressed further. 

Pōpolo is a sprawling or trailing shrub up to 3 ft (1 m) tall, in the nightshade family 

(Solanaceae). Pōpolo is a plant species listed as endangered throughout all of its range (USFWS 

2016). No critical habitat has been designated. Typical habitat for this species is coral rubble or 

sand in coastal sites up to 490 ft (150 m), in the coastal ecosystem (Symon 1999, TNCH 2007, 

HBMP 2010). Historically, pōpolo was known from the island of Hawai‘i, the island of Ni‘ihau, 

Nihoa Island, Laysan Island, Pearl and Hermes Reef, and Kure Atoll (Lamoreaux 1963, Clapp et 

al. 1977, HBMP 2010). Currently, pōpolo occurs in the coastal ecosystem, on the islands of 

Hawai‘i and Moloka‘i, and on the northwestern Hawaiian Islands of Kure, Midway (on Sand, 

Eastern and Spit Islands) (Klavitter 2013), Laysan, Pearl, Hermes, and Nihoa (Aruch 2006, in 

litt.; Rehkemper 2006, in litt.; Tangalin 2006, in litt.; Bio 2008, in litt.; Vanderlip 2011, in litt.; 

Conry 2012, in litt.; PEPP 2013). 
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The relatively isolated occurrences of pōpolo in the northwestern Hawaiian Islands are 

negatively affected (on the low-lying islands) by nonnative plants and by stochastic events such 

as tsunami. Climate change may result in alteration of the environmental conditions and 

ecosystems that support this species. Pōpolo may be unable to tolerate or respond to changes in 

temperature and moisture, or may be unable to move to areas with more suitable climatic 

regimes (Fortini et al. 2013).

The Nihoa fan palm, or loulu, is a federally endangered species of palm (USFWS 1998) endemic 

on the island of Nihoa, Hawaiʻi, and later transplanted to the island of Laysan. It is listed as it is 

a smaller tree than most other species of Pritchardia, typically reaching only 13-16 ft. tall (4–5 

m) tall and with a trunk diameter of 5.9 in. (15 cm). The loulu is a long-lived perennial tree and 

is among three species endemic to the Island of Nihoa that were listed under ESA in 1996. At the 

time of listing, the plant was limited to two extant populations on Nihoa. Since then, seeds from 

the palm have been brought to MANWR, planted in the greenhouse, and outplanted within the 

atoll with a few surviving plants on both Sand and Eastern Island. 

3.3.6.4.4 Probable Impacts: No Action Alternative 

Under the no-action alternative, the mouse population would not be eradicated, and the 

population size would continue to fluctuate within an annual cycle. It is likely that population 

levels would increase during the rainy season and decline during the dry season. 

Anecdodal evidence suggests that native plant communities (including the pōpolo and loulu plant 

species) and vegetation restoration activities on Sand Island would continue to be limited in their 

productivity from herbivory of seeds and young plants by mice. When collecting seeds from 

species to plant and grow in the greenhouse for restoration purposes, biologists have noted that 

seeds from these species are much more abundant on Eastern Island where there are no mice. In 

addition, mice are eating the seeds and damaging young plants grown in the greenhouse, which 

are used for the restoration plantings. Adoption of the No Action Alternative would not meet the 

management objective of restoring the MANWR ecosystem. 

Under the no-action alternative, some vegetation would be exposed to the hand broadcasting of 

AGRID3 bait pellets for seabird and listed candidate plant protection, in areas where mouse 

predation of seabirds and mouse damage to listed or candidate plants is detected. (See Section 

2.4 “Alternative 2: No Action” detailing current control efforts). 

3.3.6.4.5 Probable Impacts: Preferred Alternative

Primary Exposure 

Plants are not known to be susceptible to toxic effects from rodenticides. Brodifacoum is 

strongly bound on soil particles and is not taken up by plants (WHO 1995). 

Operational Hazard (Noise Disturbance and Trampling) 

Helicopters would be taking off and landing from paved staging areas, which are clear of 

vegetation. Plants, including the two-listed species above, would not be affected by helicopter 

operations. There would be potential for trampling of some plants as a result of ground-based 

operations. However, ground-based operations are only expected to take approximately 240 
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personnel hours to complete over a 3-week period. Therefore, only minor effects would be likely 

to occur from the proposed operation. 

A biosecurity plan has been in place on MANWR for many years and any additional bio-security 

measures would only occur if there was a new incursion of a non-native species. There could 

also be some additional impact to terrestrial plants during implementation of the monitoring plan 

for the eradication project. New biosecurity measures enacted could include rapid response to an 

incursion by non-native invasive species and implementing the project monitoring plan would 

include follow-up observations and the collection of samples (see Appendix A and B). Potential 

impacts such as trampling of vegetation could occur with the additional monitoring activities. 

Given the minimization measures that will be in place to protect endangered plants, we expect 

any additional impacts to be minor and short-term. Implementing the biosecurity plan is only 

expected to have beneficial effects to listed plants. 

Positive indirect effects from the Preferred Alternative would be expected. Removal of mice may 

result in an increase in the number and diversity of native plants growing on Sand Island, a longterm indirect effect of eradicating mice. Positive effects of the action include the elimination of 

mice that might eat the seeds and parts of the pōpolo and loulu. The nature of the changes to the 

plant composition would be complex and it is uncertain how native plants would respond 

compared to non-native plants under potentially increased competition and reduced predation 

(Eijzenga 2011). It is possible that some species of plants being planted for vegetation restoration 

projects on Sand Island may spread faster without the negative effects of seed herbivory by mice. 

The most common invasive introduced taxa on MANWR include ironwood (Casuarina 

equisetifolia), golden crown-beard (Verbesina enceloides), wild poinsettia (Euphorbia 

cyanospora), haole koa (Leucaena leucocephala), sweet alyssum (Lobularia maritima), buffalo 

grass (Stenotaphrum secundatum), peppergrass (Lepidium virginicum), and Bermuda grass 

(Cynodon dactylon).

Mitigation 

Staff will be trained to recognize the pōpolo and loulu and monitor their work areas at all times 

for the presence of these two species. They will exercise extreme care when hand broadcast of 

bait is necessary or when servicing bait stations to minimize any damage to listed plants. By 

implementing these measures, the proposed project will avoid potential adverse effects to the 

pōpolo and loulu. 

As part of the project to restore plant communities on Sand Island and eliminate invasive weeds, 

vegetation restoration sites and invasive weed populations would be monitored post-mouse 

eradication. Annual weed monitoring has been conducted on Midway since 2012 and would 

continue, including detecting trends in the cover of golden crown-beard. Any significant changes 

to the success of these programs would be closely monitored and adaptive management actions 

taken if needed. All personnel visiting or working on MANWR would adhere to current 

biosecurity protocols to prevent any new botanical alien species from becoming introduced to 

Sand Island (Appendix A). In addition, the compressed grain bait pellets are manufactured to 

ensure that no active seeds are embedded into the baits, thereby preventing accidental 

introduction. The USFWS has a long-term commitment to successfully restore the MANWR 

ecosystem and monitor the results. 
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3.3.6.5 Seabirds 

MANWR provides a refuge for some 3 million seabirds (USFWS 2014). Twenty-one species 

are known to breed or roost on Sand Island (see Table 3.12 below). All species of seabirds at 

MANWR are protected under the MBTA. One species, the short-tailed albatross, is Federally 

listed as Endangered (Federal Register; July 31, 2000). 

Table 3.12 Breeding Seabirds of MANWR (n = 21 species)

Name

Common Scientific Hawaiian IUCN-list Federal Status

Laysan albatross Phoebastria immutabilis Mōlī Near Threatened -

black-footed 

albatross

Phoebastria nigripes ka'upu Near Threatened - 

short-tailed albatross Phoebastria albatrus - Vulnerable / 

Endangered Endangered

wedge-tailed 

shearwater

Puffinus pacificus ‘ua‘u kani Least Concern - 

Christmas shearwater Puffinus nativitatis - Least Concern -

Bulwer’s petrel Bulweria bulwerii ‘ou Least Concern -

Bonin petrel Pterodroma hypoleuca - Least Concern -

Tristram’s stormpetrelHydrobates tristrami - Near Threatened - 

black noddy Anous minutus Noio Least Concern -

brown noddy Anous stolidus noio kōhā Least Concern -

sooty tern Onychoprion fuscatus ‘ewa‘ewa Least Concern -

little tern Sternula albifrons - Least Concern -

least tern Sternula antillarum - Least Concern -

gray-backed tern Onychoprion lunatus pakalakala Least Concern -

white tern Gygis alba manu-o-ku Least Concern -

great frigatebird Fregata minor ‘iwa Least Concern -

white-tailed 

tropicbird

Phaethon lepturus koa‘e kea Least Concern - 

red-tailed tropicbird Phaethon rubricauda koa‘e ‘ula Least Concern -

red-footed booby Sula sula ‘ā Least Concern -

brown booby Sula leucogaster ‘ā Least Concern -

masked booby Sula dactylatra ‘ā Least Concern -

Source: USFWS (1983, 2014)

Details on the distribution, population status and trends, ecology, and conservation concerns for 

these 21 species can be found in the Regional Seabird Conservation Plan, Pacific Region 

(USFWS 2005) and the International Union on the Conservation of Nature (IUCN) Red List for 

Endangered Species (IUCN 2017a). The greatest threats to the seabirds of MANWR include 

introduced and invasive species, fisheries interactions, ocean contaminants, marine debris, and 

climate change (USFWS 2005).

3.3.6.5.1 Existing Conditions: Albatrosses 

Three albatross species are found at MANWR, (i) Laysan albatross, (ii) black-footed albatross, 

and (iii) short-tailed albatross. Adults forage offshore; their diet consists primarily of fish, squid, 

and crustaceans. Albatross pairs are philopatric and mate retention is high (USFWS 2005). 

Albatrosses are not agile flyers, due to their long wingspans and heavy body weight. Chicks 
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exhibit pica behavior and occasionally ingest soil, rocks, and paint chips when pecking the 

ground (Finkelstein et al. 2003). Adult albatross are subject to mortality at sea during interaction 

with commercial fishing operations. Adults and chicks are subject to mortality when on land 

during periods of low wind when birds die from overheating in the sun. Mortality can also occur 

from other causes like starvation or injury (USFWS, Unpublished b). 

Laysan albatross. The global population is estimated at 1.5 to 1.6 million individuals (Arata et 

al. 2009, 2017b, ACAP 2012b, USFWS, Unpublished b). Over 70% of the global population 

depends upon MANWR for breeding. Of MANWR’s population, over 60%, or approximately 

719,530 birds, nest on Sand Island (USFWS, Unpublished b). Individuals measure about 31.0-

32.0 in. (79-81 cm) in length, have wingspans of 76.8–79.9 in. (195–203 cm), and on average 

weigh about 5-8 lbs. (2,200-3,600 g) (Whittow 1993b). The species is present from November to 

July (USFWS, Unpublished b). Nests are built on bare ground and among vegetation; birds use 

surrounding grasses, shrubs, and dirt piled into large mounds as a nest cup into which a single 

egg is laid (USFWS 2005). 

Black-footed albatross. The global population of this albatross of the northern Pacific Ocean is 

estimated at 140,138 breeding individuals (Flint 2007, Naughton et al. 2007, ACAP 2012a). 

Thirty-seven percent of the global population or about 51,230 birds depend upon MANWR, with 

22% of the refuge’s population (approximately 30,168 birds) using Sand Island (USFWS, 

Unpublished b). Individuals measure about 25-29 in (64-74 cm) in length, have wingspans of 76-

85 in (193-216 cm), and on average weigh about 5-9.5 lbs. (2200-4300 g) (Whittow 1993a). The 

species is present on MANWR from November through June (USFWS 2005). Nests are similar 

to Laysan albatross nests in construction but occur in more open areas with sparse vegetation; 

primarily near coastal beach areas (Reynolds et al. 2017). 

Short-tailed albatross. Federally listed as Endangered, this species historically occurred 

throughout the North Pacific Ocean (USFWS 2005). Currently, 85% of the global population 

breeds on Torishima Island in Japan (USFWS 2005). At MANWR, two birds, representing 

0.05% of the global population of 4,200 birds (IUCN 2017a), arrived on Sand Island in recent 

years but have yet to successfully breed (USFWS, Unpublished b). Individuals measure about 

84- 33-37 in (94 cm) in length, have wingspans of 84-90 in (213-229 cm), and on average weigh 

about 8-14.5 lbs. (3,700-6,600 g) (USFWS 2008). The species is present November through June 

(USFWS 2008a, b). Nests are similar to Laysan albatross nests in both construction and 

placement (USFWS 2005). The primary threat to this species is from volcanic activity, which has 

the potential to destroy or disturb the Torishima Island colony. 

3.3.6.5.2 Existing Conditions: Nocturnal seabirds 

Nocturnal seabirds include: (i) wedge-tailed shearwater, (ii) Christmas shearwater, (iii) Bonin 

petrel, (iv) Bulwer’s petrel, and (v) Tristram’s storm-petrel. All 5 of these species nest in 

subterranean burrows or in cryptic rock crevices or rubble; Christmas shearwater also nest 

underneath trees, shrubs and dense bunch grasses on the ground (Reynolds et al. 2017). These 

species fly to and from their colonies at night. Impacts to Tristram’s storm-petrel would be low 

because birds are absent from MANWR during the proposed baiting operation. Impacts to 

Christmas shearwater and Bulwer’s petrel would be low given that nesting by these species on 

Sand Island has not been documented to date (USFWS, Unpublished b). Of the 5 nocturnal 
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species, only wedge-tailed shearwaters and Bonin petrels may be negatively affected by the 

operation. 

Wedge-tailed shearwater. This wide-ranging flyer is one of the most common seabirds in 

Hawai‘i. About 10,000 individuals nest on Sand Island (USFWS, Unpublished b), representing 

about 0.2% of the global population estimated at around 5,200,000 birds (Brooke 2004). 

Individuals measure about 16-18 in. (41-46 cm) in length, have wingspans of 38-41 in. (97-104 

cm), and on average weigh about 0.86-0.9 lb. (390-404 g) (USFWS 2015, Gross et al. 1963). 

Adult arrival is in late March and eggs are laid in June; hatching occurs from late July to late 

August and chicks fledge mid-October to mid-November (USFWS 2005). This species feeds 

mostly on fish, but also cephalopods, crustaceans and marine insects, catching prey mainly on 

the wing by dipping and surface-seizing or pursuit-plunging (IUCN 2017a). 

Bonin petrel. The Bonin petrel population at MANWR rebounded after rat eradication efforts 

from 1994-1997, but suffered a set-back from flooding caused by a 2011 tsunami (Pyle and Pyle 

2017). The global population of this species is not known, but estimated at around one million 

individuals (IUCN 2017a, Seto and O’Daniel 1999) with most of those occurring on Laysan, 

Lisianski and Sand Islands. These birds measure 11.8 in (30 cm) in length with wingspans of 

24.8-28 in (63-71 cm), and a mean body mass of 0.45 lb. (203.7 g) (Seto and O’Daniel 1999). 

The nest is a shallow sandy burrow where a single egg is laid in mid-January; chicks fledge by 

June (Mitchell et al. 2005). This species feeds offshore and surface dips for prey like fish, squid, 

marine insects, and crustaceans (Seto and O’Daniel 1999). Bonin petrel leave Sand Island in 

June but return again in August-September (Grant et al. 1983), resulting in a short absence 

window (USFWS 2005). The proposed eradication period coincides with this period when the 

lowest numbers of Bonin petrels are expected to be present.

3.3.6.5.3 Existing Conditions: Noddies 

Both black and brown noddies are present on Sand Island year-round (USFWS, Unpublished b). 

Both species may be negatively affected by the operation.

Black noddy. The global population of black noddy is estimated to be 3-4.5 million birds (IUCN 

2017a), of which, 0.003% or about 12,000 birds, occur on Sand Island. Black noddy measure 14-

16 in. (35–40 cm) in length, with a wingspan of 25-28 in. (65–72 cm), and a body mass ranging 

between 0.2-0.3 lbs. (85–140 g) (Gauger 1999). In Hawai‘i, this species is an asynchronous and 

aseasonal breeder, meaning that eggs are laid year-round, the synchronous timing of egg-laying 

among individuals varies, and peak egg-laying occurs in different seasons in different years 

(USFWS 2005). Nests are built in tree and shrub canopies and 1 egg is laid per breeding attempt 

(Gauger 1999). Black noddy forage in the surf along beach shoreline (USFWS, Unpublished b), 

in lagoons of atolls, and brackish water of coastal ponds; most feeding is <6.2 mi. (<10 km) from 

shore (Gauger 1999). Food items include small fish, squid, and crustaceans that are seized from 

the surface of the water or just below it. Birds tend to concentrate over nearshore waters.

Brown noddy. The global population of brown noddy is estimated to number 180,000-1,100,000 

individuals (Delany and Scott 2006), with approximately 7,200 birds occurring on Sand Island, 

or 0.6% of the global population (USFWS, Unpublished b). Adults are about 16-18 in. (40–45 

cm) in length with a body mass of about 0.35 lbs. (180 g) (Chardine and Morris 1996). Brown 

noddy breed synchronously, with peaks in breeding activity occurring in both the spring and 
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summer months (USFWS 2005). Eggs are present from March through August; a single egg is 

laid in a nest built on the ground or in a tree. Flight habit is to concentrate over nearshore waters, 

but mainly feeds offshore on small fish and squid it catches at the sea’s surface by dipping or 

seizing (Chardine and Morris 1996). 

3.3.6.5.4 Existing Conditions: Terns 

On MANWR, these species include the: (i) white tern, (ii) little tern, (iii) least tern, (iv) grayback tern, and (v) sooty tern. Population levels of all 5-tern species, except the white tern, are 

low on Sand Island, and the sooty tern only nests on Eastern Island. The operation would be 

unlikely to affect little, least and grey-backed terns because their flight behavior and nest 

locations make aircraft strikes unlikely. Of the 5 terns, only the white tern may be negatively 

affected by the operation. 

White Tern. The common white tern has a distribution across the tropics of the world, found 

year-round on islands in the south Atlantic Ocean, the Indian Ocean, and the western and central 

Pacific. This species is difficult to census accurately, because of the protracted breeding season, 

cryptic coloration of eggs and chicks, and inaccessibility of cliff nesting sites. The population at 

MANWR has increased greatly in past 50 years, owing to introduction of ironwood trees that 

have provided suitable nesting habitat (Niethammer and Patrick 1998). Population in 

Northwestern Hawaiian Islands was estimated at 80,700 individuals: 50,840 (63%) non-breeders 

and 29,860 (37%) breeders (USFWS 1983). The global population of white tern is not known but 

is thought to be stable (IUCN 2017a). Approximately 49,420 birds occur on Sand Island 

(USFWS, Unpublished b). 

As the name implies, this tern is all-white and is 11-13 in. (27.5–33 cm) in length, has a 

wingspan of 27.6-34.2 in (70–87 cm), and a body mass ranging between 0.17-0.35 lbs. (77–157 

g) (Niethammer and Patrick 1998). White tern on Sand Island breed year-round, and most nests 

are on branches of ironwood (Casuarina equisetifolia) trees or on buildings and other humanmade structures at MANWR (Howell 1978). No nest is made; instead, it lays its single egg, often 

delicately balanced, on a branch, building, or rock. Newly hatched chicks have well-developed 

feet and claws with which they cling to their perilous nest sites. Adults carry small fish and squid 

in their bills, often several at a time, to feed chicks. Adults seem tolerant of disturbance, often 

rearing their young near human activity (Niethammer and Patrick 1998). Most egg-laying occurs 

February to June (USFWS 2005). White terns forage primarily in the surf along the beach 

shoreline, along shoals and banks, and offshore for fish and squid (Niethammer and Patrick 

1998). 

3.3.6.5.5 Existing Conditions: Great Frigatebird 

The great frigatebird comes to Sand Island not to breed but to roost, and do so in relatively small 

numbers (USFWS, Unpublished b). The global population is estimated to be between 500,000-

1,000,000 individuals (Gauger et al. 2002, USFWS 2005), with approximately 0.01%, or 140 

birds occurring on Sand Island. Individuals are 33.5-41.3 in. (85–105 cm) in. length, have a 

wingspan of 81-90 in. (205–230 cm), and a body mass of 2.2-4 lbs. (1-1.8 kg) (Gauger et al. 

2002). The bird is an aerial acrobat, foraging for flying fish and squid at the ocean’s surface over 

deep, offshore waters (Gauger et al. 2002, USFWS 2005). The great frigatebird may be at some 

risk during the operation. 
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3.3.6.5.6 Existing Conditions: Tropicbirds 

Both red-tailed and white-tailed tropicbirds are present at MANWR. At MANWR, the whitetailed tropicbird is a rare breeder on Sand Island, and represented by only a few pairs (USFWS, 

Unpublished b). The red-tailed tropicbird is more numerous and would be breeding on Sand 

Island during the operation. Therefore, some negative impact on this species is possible. Both 

species behaviorally make showy aerial displays around midday at Sand Island, flying 98-164 ft. 

(30-50 m) in the air (Fleet 1974). Additionally, both species feed far offshore primarily on fish 

and squid (IUCN 2017a, USFWS 2016). 

Red-tailed tropicbird. The global population of the red-tailed tropicbird is estimated to number 

60,000-80,000 individuals (Schreiber and Schreiber 2009), with approximately 19%, or 15,000 

of birds occurring on Sand Island. The streaming red central rectrices are a striking characteristic 

for this species that is about 17-18.5 in. (44-47 cm) in body length and has a body mass ranging 

from 1.4-1.7 lbs. (650-780 g). Red-tailed tropicbirds are aseasonal breeders on Sand Island, and 

nests occur in a variety of available substrates. Eggs are typically laid on the ground in small 

depressions in the sand, soil, humus, or fine coral rubble under vegetation, or tucked into cliff 

crevices (Morrell and Aquilani 2000, USFWS 2005). 

3.3.6.5.7 Existing Conditions: Boobies 

Three booby species, red-footed, brown, and masked, are present at MANWR year-round. There 

are approximately 475 breeding pairs of red-footed booby on Eastern Island. Some red-footed 

booby individuals temporarily roost on Sand Island. The masked booby only nests in extremely 

low numbers on Eastern Island and are too few in number to be affected by the operation. There 

are generally fewer than 5 masked booby pairs nesting per year on Eastern Island, with no 

historical information indicating they were previously more numerous (USFWS, Unpublished b). 

The brown booby, once considered the most common booby at MANWR in the 1930s until rats 

were introduced, now number only 2 pair nesting on Eastern Island. This species is the only 1 of 

the 3 that forages in nearshore waters. Given that all 3-species nest on Eastern Island, with low 

numbers roosting on Sand Island, impacts would be minor. 

3.3.6.5.8 Probable Impacts: No Action Alternative 

Under the No Action Alternative, mice would not be eradicated on Sand Island and would 

continue to impact seabird colonies and the vegetation they use for nesting and cover. Over 3 

million seabirds, encompassing 21 different native species, nest on MANWR’s 3 islands and 

many of them are susceptible to predation by mice. If mice are able to prey upon adult Laysan 

albatrosses, one of the largest seabirds on Sand Island, then other ground nesting and burrowing 

seabirds, adults and chicks, are at risk from similar impacts. Introduced mice would continue to 

prey on nesting seabirds on the island, preventing them from reaching their full population 

potentials, and if the predatory behavior spreads at the rate observed in 2016/2017, then the 

predation would likely contribute to accelerated declines in affected seabird populations. Brooke 

et al. (2017), drawing on data regarding eradication of non-native mammals on islands from 

around the world, examined the population growth rates of 181 seabird populations (of 69 

seabird species) following successful mammal eradication projects. This analysis included the 

recovery of Bonin petrels following the eradication of the black rat at MANWR in 1996. After 

successful eradication, the median population growth rate (lambda) was 1.119 and seabird 
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populations, with positive growth rates greatly outnumbering those in decline. The study 

confirmed that invasive mammal eradication is usually followed by growth of seabird 

populations. 

Under the No Action Alternative, Sand Island’s mouse population would not be the subject of a 

targeted eradication project, but mouse control efforts to protect breeding albatross, which were 

started in 2016, would continue and expand as deemed appropriate. (See Section 2.4 “Alternative 

2: No Action” detailing current control efforts).

Eradication of the house mouse from MANWR would facilitate the protection and restoration of 

native plants present in the refuge. Beyond the predation of seabirds, mice likely have deleterious 

effects on many other components of the ecosystem of MANWR. No action would result in the 

continued presence of mice and a continuing long-term adverse impact on biological resources 

(see Section 1.2 and Section 1.3). Rodents are known to be a disease vector (de Bruyn et al. 

2008, Avenant and Smith 2003), feed opportunistically on plants, and alter the floral 

communities of island ecosystems (Campbell and Atkinson 2002). They also sometimes compete 

with native species and degrade the quality of nesting habitat for birds that depend on the 

vegetation (Wegmann 2009, Young et al. 2010). Rodents can also prey on intertidal invertebrates 

and reptiles and thus affect their abundance and age structure (Navarrete and Castilla 1993), 

along with negative effects to marine algae abundance (Kurle et al. 2008). The presence of 

rodents has also been shown to lower total soil carbon, nitrogen, phosphorous, mineral nitrogen, 

marine-derived nitrogen, and pH relative to rodent-free islands (Fukami et al. 2006). 

3.3.6.5.9 Probable Impacts: Preferred Alternative 

Primary Exposure 

The potential for exposure of adult seabirds to rodenticides on Sand Island would be limited. 

Consumption of bait pellets by adults would not be a risk, as all species are carnivorous, feeding 

on fish, squid, eggs, or crustaceans. Almost all of the 21 seabird species reported from MANWR 

(Table 3.12) typically forage many miles away from the island in deep water; the exceptions 

include black noddy, brown booby and white tern, which are assessed for secondary poisoning in 

the next section. 

Primary poisoning would be a potential risk for some species of seabird chicks. Ten species of 

seabirds have been documented to nest on Sand Island: Laysan albatross, black-footed albatross, 

short-tailed albatross, wedge-tailed shearwater, Bonin petrel, black noddy, brown noddy, white 

tern, white-tailed tropicbird, and red-tailed tropicbird. Of these, 4 nest on the surface of the 

ground and might have young in the nest during the period when bait would be on the ground. 

These species include the Laysan albatross, short-tailed albatross, brown noddy, and red-tailed 

tropicbird. The majority of black-footed albatross chicks fledge from Sand Island by late June, 

prior to when bait would be on the ground. However, only Laysan albatross and short-tailed 

albatross are at risk of ingesting non-food objects on land. These species nest on the ground, and 

their chicks are known to peck at or sometimes swallow objects found on the ground such as 

rocks, sticks, and foreign objects. This tendency is known as pica behavior. This behavior would 

only be detrimental to the young if they actually pick up a bait pellet and then ingest it. Both the 

red-tailed tropicbird and brown noddy were nesting on Palmyra during the 2011 rat eradication 

project and neither species was detected as having ingested brodifacoum after the operation. In 
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addition, there are no descriptions of the red-tailed tropicbird or brown noddy manipulating or 

swallowing foreign objects on land. In a study of the effects of chemical weapons incineration on 

a nesting colony of red-tailed tropicbirds on Johnston Atoll in the central Pacific, Schreiber et al. 

(2001) found that the ingestion of heavy metals from soil was not considered to be a problem 

since red-tailed tropicbirds did not feed on land and did not tend to pick up objects with their bill 

while on land. The method of feeding at sea by red-tailed tropicbirds is very different from that 

of albatross that do pick up and sometimes ingest items on land (chicks only) (Work and Smith 

1996). Albatross adults sit on the water and pick up potential food items and it is normal for 

chicks to do this on land instinctively as they learn to use their bill. However, red-tailed 

tropicbirds dive from the air to feed at sea and thus neither the adults or chicks appear to ingest 

particles on land and no soil is found in their stomach contents (Ashmole and Ashmole 1967, 

Schreiber and Schreiber 1993). 

The likely start date for the bait drop on Sand Island is early July. In a detailed study by Fisher 

and Fisher (1969) of the nesting chronology of Laysan albatross on MANWR, researchers using 

study plots found that the number of adult and juvenile Laysan albatross on June 11 was 19% of 

peak counts in April and only 7.1% of the peak population by June 29. Nestlings begin to leave 

the colony about June 20 and those that survived were essentially gone by August 2 or 3. In the 3 

years of study 10-26% left before July 1. The period of most rapid departure was July 5 to 25, 

but 50% of the young albatrosses were gone by July 15 in 1961, July 16 in 1962, and by July 9 in 

1963 (Fisher and Fisher 1969). Therefore, 50% of young Laysan albatross would likely be gone 

after the first 2 weeks of the bait drop. In addition, many of the young albatross that do not leave 

the island by late July often succumb to exposure to the heat and/or starvation, as the adults are 

no longer returning to feed them. 

For primary poisoning risks associated with pica behavior, objects within about 3 ft. (1 m) of the 

nest would be accessible to a Laysan albatross chick. At later ages, however, chicks wander even 

farther from the nest, to find shade for example. In an area with a 3-foot radius, which is 28 ft.2

(2.6 m2), about 0.67 oz. (19.2 g) of brodifacoum bait would be available under the proposed 

maximum application rate of 65 lbs./ac. (73 kg/ha). This represents 19 pellets since each pellet 

weighs 0.03 oz. (1 gram). For brodifacoum, an albatross chick would need to ingest about 0.73 

oz. (20.8 g), or 21 pellets, for a potential lethal dose (Table 3.13). This is 11.1% of its expected 

daily food intake. A chick would need to ingest about 0.07 oz. (2 g), or 2 pellets, for a sub-lethal 

dose. Therefore, for a Laysan albatross chick to receive a potential lethal dose, it would need to 

pick up and ingest every bait pellet (and more) within a 3 ft. (1 m) radius of its nest while the bait 

is still available and then range outside of this area and pick up and ingest another 2 pellets. This 

would be unlikely given that the bait is expected to be taken up rapidly by mice and invertebrates 

(e.g. cockroaches), and that the primary diet of albatross chicks is fish and squid brought by the 

parents. This latter point of primary diet also applies to chicks that wander further from their nest 

so that it would be unlikely for them to consume 21 pellets or more via pica behavior. 

For the short-tailed albatross, only 1 pair is present on Sand Island and they have not had an 

active nest to date. Therefore, it is unlikely an active nest with a chick would be present during 

the bait drop. However, the pair is monitored each year, and if a chick is present, all bait pellets 

within reach of this chick would be collected and removed as a mitigation strategy.
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The above risk of primary exposure for albatross is likely overestimated, primarily because most 

bait pellets from the first application would be rapidly consumed or cached by mice and 

cockroaches. Subsequent applications would occur after most albatross chicks have fledged. 

Also, not all birds would pick up the bait, and of those that do, not all would ingest significant 

amounts because of their main diet of fish and squid provided by the parents. Therefore, it would 

also be unlikely that any Laysan albatrosses would be killed or sub-lethally affected by primary 

poisoning from brodifacoum. 

Secondary Exposure 

While there would be potential for secondary poisoning of black noddy, brown booby, white tern 

and great frigatebird, that risk would be low. Of the 21 species of seabirds on Sand Island, only 

the black noddy, brown booby and white tern sometimes forage in the nearshore marine 

environment around Sand Island. This foraging habit puts these species at risk of potentially 

ingesting fish contaminated with brodifacoum, and potential exposure to persistent residues postoperation. The great frigatebird could be at risk of secondary poisoning from scavenging dead 

mice.

Table 3.13 Primary and Secondary Toxicity of Brodifacoum 

Primary toxicity presented as grams of bait and secondary as grams of fish. “N/A” indicates that there 

is no feeding behavior for this pathway and no risk from poisoning. The mg of active ingredient is 

abbreviated as a.i.; LD50 is that the dosage (D) of a toxin that is lethal (L) to 50% of animals of the 

species in laboratory tests.

Species

Body 

Wt (g)

Daily 

Food 

Intake 

(g)(1)

Brodifacoum

LD50

(2)

(mg/kg)

LD50 (mg 

of 

a.i./bird)

LD50

(3)

(g of bait)

LD50 2(4)

(g

of fish)

%(5) of 

Daily 

Food 

Intake

black noddy 110 26.9 0.26 0.029 N/A 24.7 91.7

brown noddy 180 37.4 0.26 0.047 N/A N/A N/A

brown booby 1,356 144.7 0.26 0.353 N/A 303.9 210.0

great frigatebird 1,400 147.8 0.26 0.364 N/A 56.4(6) 38.2

white tern 110 26.9 0.26 0.029 N/A 24.7 91.7

Laysan albatross 

chick

2000 187.7 0.26 0.520 20.8 N/A 11.1

black-footed 

albatross chick

3,400 267.9 0.26 0.884 35.4 N/A 13.2

short-tailed 

albatross chick

6,400 409.3 0.26 1.664 66.5 N/A 16.3

red-tailed 

tropicbird chick

660 89.3 0.26 0.172 6.9 N/A 7.7

Notes:

1. Daily food intake calculated from allometric equation (Bird Feeding Rate = 0.059 x (W 0.67) (USEPA 1995).

2. LD50 of brodifacoum based on mortality of mallard ducklings at the lowest dose, 0.26 mg/kg body weight = 0.00026 mg/g (Ross et al 1980, 

EPA 1991).

3. This is also the number of bait pellets that would need to be consumed to be lethal to 50% of the animals.

4. Based on mortality of fish at 1.16 mg/kg = 0.00116 mg/g (Pitt et al 2015).

5. Calculated as LD502 grams of bait or prey/daily food intake (g).

6. For the predatory great frigatebird, this is grams of whole rat. Contamination based on highest reported residues in rat carcasses (6.45 mg/kg 

liver = 0.00645 mg/g) (Pitt et al. 2015).
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Black noddy forage within a few yards of the shore and so could be at risk of secondary 

poisoning if they consume small intoxicated reef fish. Surveys indicate approximately 12,000 

birds could be present on Sand Island in July and August. However, black noddy feed on fish at 

the surface of the water, which are species less likely to consume any bait that falls in the water 

compared to bottom feeding fish (mullets, etc.). Although it is possible that black noddy could 

forage on fish exposed to rodenticide, the overall liklihood that this would occur is low. The 

relatively small quantity of bait that could enter the water and rapid degradation and dispersion 

of the rodenticide would combine to greatly reduce the probability of a noddy being exposed to 

an intoxicated marine fish or invertebrate. This is supported by results from post-application 

sampling of the near shore marine environment from 2 eradication projects in Hawaiʻi. The 

results showed no detectable levels of diphacinone in fish, invertebrates, or seawater (Gale et al. 

2008; Orazio et al. 2009). However, during the second 2017 Lehua rat eradication effort, fish 

were caught from shore and gut contents examined for signs of bait material and the pyranine 

biomarker fluorescence. Bait material and/or the biomarker were observed in some specimens of 

fish but not others (see details in Section 3.3.6.14.3). During rat eradication on Palmyra Atoll, 

the carcasses of 12 seabirds were recovered including 2 sooty terns, 6 red-footed boobies, and 1 

black noddy. None of these were confirmed to have died from ingesting brodifacoum, which is 

noteworthy considering the permitted application rate was 6 times higher than normal due to the 

rapid consumption of the bait by numerous land crabs (Pitt et al. 2015). In addition, an individual 

bird the size of a black noddy (110 g) would have to consume 0.9 oz. (24.7 g) of toxic fish to 

receive a potential lethal dose (Table 3.13) of rodenticide, which is 91.7% of its daily food 

intake. Because very little of the rodenticide is expected to enter the water, the rapid breakdown 

in water (see impacts to physical environment section), and the large % of a bird’s daily intake 

required for a potential lethal dose, the Preferred Alternative would be unlikely to result in the 

mortality of any black noddy adults or chicks.

Brown booby could also be at risk of secondary poisoning since they forage for a variety of fish 

and squid either at sea or in the surf along the beach shoreline (Schreiber and Norton 2002) and 

are often observed loafing atop the channel buoys on MANWR. However, only 2 pairs of birds 

nest on Eastern Island and no breeding occurs on Sand Island. In addition, an individual adult 

booby would have to consume 10.7 oz. (304.0 g) of toxic fish to receive a potential lethal dose 

(Table 3.13) of rodenticide, which is 210% of its daily food intake. Due to the low number of 

birds on MANWR, the large % of a bird’s daily intake required for a potential lethal dose, and 

the low likelihood of encountering toxic fish, the Preferred Alternative would be unlikely to 

result in the mortality of any brown booby adults or chicks. 

White tern could be at risk from secondary poisoning since they forage primarily in the surf 

along the beach shoreline and along shoals and banks as well as offshore for fish and squid 

(Niethammer and Patrick 1998). However, an individual adult white tern would have to consume 

0.87 oz. (24.7 g) of toxic fish to receive a potential lethal dose (Table 3.13) of rodenticide, which 

is 91.7% of its expected average daily food intake. Because very little of the rodenticide is 

expected to enter the water, the rapid breakdown of bait pellets in water (see impacts to physical 

environment section), and the large % of a bird’s daily intake required for a potential lethal dose, 

the Preferred Alternative would be unlikely to result in the mortality of any white tern adults or 

chicks.
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Frigatebird are at risk of secondary poisoning from scavenging dead mice and a maximum of 

140 birds have been reported on Sand and Eastern Islands. These birds are known to take 

unattended seabird chicks, thus there exists potential for scavenging or predation of mice that are 

dead or dying from ingestion of rodenticide. However, several factors reduce the risk of the 

frigatebird preying or scavenging on intoxicated mice. First, exposure risk would be relatively 

low, because most mice dying from anticoagulant rodenticide often do so in areas inaccessible to 

avian predators (Lindsey and Mosher 1994). Second, while the behavior of foraging on land (i.e, 

preying on chicks) is documented, it does not appear to be exhibited by all members of the 

population (Megyesi and Griffin 1996). In addition, based on the body weight of this species and 

the LD50 value, it would take the consumption of 2.0 oz. (56.4 g) of whole mice contaminated 

with brodifacoum for an individual bird to reach a potential lethal dose. This is 38% of its 

estimated daily food intake. Therefore, it is extremely unlikely that any individuals would be at 

risk from secondary poisoning. 

Based on the above analysis, it is unlikely that black noddy, brown booby, white tern, or great 

frigatebird would be killed or sub-lethally affected by secondary exposure to brodifacoum from 

the Preferred Alternative. 

Operational Hazard (Bird Strike and Noise/Human Disturbance) 

Crushed Burrows. There is a risk that ground crews that are hand broadcasting bait or 

conducting monitoring can accidentally collapse active seabird burrows containing adults, eggs, 

or chicks. There are 4 burrow-nesting seabirds on Sand Island: wedge-tailed shearwater, Bonin 

petrel, Bulwer’s petrel, and Tristram’s storm-petrel. All 4 species nest in subterranean burrows or 

cryptic rock crevices, and adults make flights to and from their nests at night. On Sand Island, 

nesting Tristram’s storm-petrels would not be present during the operation and no nests of 

Bulwer’s petrel have been documented (USFWS, Unpublished b). Bonin petrel are not expected 

to be impacted because a majority of these birds would have left Sand Island and few, if any, 

would be left during the operation. On MANWR, in 1993 and 1994, mean fledging dates for 

Bonin petrel was 6 Jun ± 5.2 d SD (range 24 May–17 Jun, n = 36) and 4 Jun ± 5.0 d SD (range 

26 May–15 Jun, n = 47), respectively (Seto 1994). 

The main species of concern is the wedge-tailed shearwater, which would be present and 

breeding during the operation. There are an estimated 5,000 pairs breeding on Sand Island 

(USFWS, Unpublished b). During the targeted period of July-August, the majority of birds 

would be at the egg stage and into the beginning of the chick rearing stage of breeding (USFWS 

2005, 2015). 

Hand broadcast application of bait and monitoring on Sand Island would be conducted by 

personnel skilled in recognizing seabird burrows and trained in mitigation measures. Hand 

broadcasting is being limited to a few sites including narrow shorelines, ponds and freshwater 

seeps, and around certain structures. Bait is typically distributed by a team who systematically 

walk on parallel transects stopping at predetermined intervals to distribute pellets as evenly as 

possible. For Sand Island, an estimated 240 total person-hours would be needed to hand 

broadcast for the entire operation (3 scheduled drops, 8-person team, working 10-hour days). 

However, after the initial hand broadcast operation, crews would be walking the exact same 

transect lines for the second and third bait applications. Therefore, it is less likely that any 

additional burrows would be crushed after the first walk-through. This initial hand broadcast 
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operation is expected to take a total of 80 personnel hours. The success rate of rescuing birds 

from a crushed burrow is high if mitigation protocols described below are followed. The 

exceptions are very deep sandy burrows for which it is difficult to find both passageways as a 

person digs or when a person actually steps on the chamber and crushes the egg or kills the bird. 

Regardless of whether an adult or chick is pulled out or a damaged burrow is repaired that has an 

occupant, it would still be counted as a “take” on project monitoring reporting forms. 

No data is available to gauge exactly how many burrows would be at risk. However, assuming a 

worst-case scenario, that 1 burrow is crushed for every 3 hours of personnel time, this would 

result in the risk of 26 burrows being damaged or crushed during the 1st bait drop. However, not 

all of these burrows would be active nest sites and may not be in use. In addition, for active nest 

burrows, some of the birds would be rescued by having personnel dig out the collapsed burrows. 

On Lehua, nocturnal shearwaters did not seem bothered by personnel on the ground and reacted 

by moving a few feet away from the person (USFWS and HDLNR 2017). Given the limited 

number of sites being hand treated, the low number of people on the ground, the few active 

shearwater burrows per acre, and the protocol and mitigation strategy in place, there would be a 

low risk of crushing a large number of wedge-tailed shearwater burrows with adults, eggs, or 

chicks. Ground crews have been very successful at minimizing impacts to surface and 

subterranean nests using the additional avoidance and mitigation protocols described below. By 

adhering to these protocols during ground operations, it is possible that up to 26 shearwater 

burrows could be collapsed containing an egg, chick, or adult resulting in injury or death. Due to 

the low number of anticipated mortalities relative to their population size on Sand Island, direct 

impacts would be minor. Effects would be detectable, but localized, small, and of little 

consequence shearwater populations on MANWR or globally. 

We expect there to be some additional impact to burrow nesting seabirds should the need arise to 

implement the rapid response portion of the refuge’s biosecurity plan and during implementation 

of the project monitoring plan. A biosecurity plan has been in place on MANWR for many years 

and any additional bio-security measures would only occur if there was a new incursion of a nonnative species. Biosecurity measures enacted would include rapid response to an incursion by 

non-native invasive species and implementing the monitoring plan would include follow-up 

observations and sample collecting (see Appendix A and B). Potential impacts such as trampling 

of burrows and crushing birds or eggs in the burrows could occur along with additional human 

disturbance. Given the minimization measures that will be in place to protect burrow nesting 

seabirds, we expect any additional impacts to be minor, localized, and short-term. Implementing 

the biosecurity plan is only expected to have beneficial effects to seabirds. 

Mitigation Measures for Burrow Nesting Seabirds 

Ground-based personnel would be instructed to avoid walking over known wedge-tailed 

shearwater burrows or other visible burrows. If a burrow is accidentally collapsed by personnel, 

it would be excavated to re-open the nest entrance to allow adults access to chicks. Burrows 

would be rebuilt as best as possible to provide chicks or eggs protection from the elements. To 

avoid impacting nest burrows, biologists would, whenever possible, stay on established trails. 

Airstrike Hazard
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Bird airstrike data from airplanes landing and taking off from Henderson Airfield on Sand Island 

were summarized from 2004 to 2010 (USFWS, Unpublished b). Albatross were the greatest 

hazard to aircraft movements at Midway because of their body sizes (wingspan approximately 

6.5 ft. or 2m), abundance, and lack of maneuverability. Albatross, frigatebird and booby would 

be the most dangerous to aircraft, because of their large body masses and wingspan. Birds with 

wingspans of 6.5 ft. (2 m) are large and may be difficult to avoid (Klavitter 2004). To minimize 

bird strikes, all aircraft are now required to land and takeoff during darkness when albatross are 

present at Midway from November to July. This can sometimes cause nocturnal seabirds to be 

struck and killed. However, the practice of landing at night has been an effective measure to 

mitigate albatross and other bird strikes, since albatross typically do not fly during hours of 

darkness. However, in emergencies, and at other times of the year, aircraft do sometimes land at 

Henderson Field during the day. In addition to albatross, approximately 900,000 Bonin petrel 

(wingspan about 18 in. or 46 cm) are found at Midway from August to May. The petrel is most 

active at night, but typically have lower numbers around the airfield (Klavitter 2004). All species 

of seabirds on MANWR are diurnal, except for those listed in Section 3.3.6.5.2 (Existing 

Conditions: Nocturnal seabirds).

From 2004 to 2010 there were a total of 59 bird strikes during 1,280 aircraft movements at 

Henderson Field. This is 1 strike for every 21.7 movements at Midway, or 460 strikes per 10,000 

aircraft movements. This strike rate is 81 times that of commercial airlines, which as of 2010 was 

5.7 strikes per 10,000 movements (Klavitter 2004). The higher strike rate at Henderson Field is 

due to the high populations of nesting seabirds on Midway compared to any other airfield in the 

nation. 

Sixty-three % of the strikes were from Laysan and black-footed albatrosses (Table 3.14). Species 

contributing to more than 10% of the total strikes also included Bonin petrel and brown noddy 

(Table 3.14). Two Department of Defense helicopter flights occurred on Midway during this 

period and no strikes were observed to these species. 

Table 3.14 Number and Species of Birds Reported Struck by Airplanes at Henderson 

Field, MANWR: 2004-2010 

Species Number Struck % of Total Reported Strikes

Black-footed albatross 7 11.9

Bonin petrel 6 10.2

brown noddy 6 10.2

great frigate 1 1.7

Laysan albatross 30 50.8

Unknown 3 5.1

white tern 5 8.5

yellow canary 1 1.7

Totals 59 100

Source: USFWS 2017, unpublished.

Timing of the eradication on Sand Island in the July-August period would place it outside of the 

peak breeding season for most seabirds, limiting collision risks to these species. Operations 

during the months of July and August would also occur before the majority of shorebirds arrive 

on MANWR, thus minimizing bird airstrike hazard (BASH) to the helicopters and risks to these 

species.
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The helicopters broadcasting the rodenticide would fly at speeds ranging from 29–58 mph (46-93 

km/hr.) and at an average expected altitude of approximately 164 ft. (50 m) above the ground. 

The bait hopper would be on a long-line 20-30 ft. (6-9 m) slung below the helicopters. Therefore, 

the bait hopper would be approximately 134-144 ft. (41-44 m) above the ground during the 

rodenticide drop. Consequently, except for landings and take-offs on the runway, the helicopters 

would fly at an average altitude of 164 ft. (50 m) and the bucket would be >134 ft. (41 m) above 

the ground most of the time. The height of the helicopters would likely be higher when above 

forested areas or buildings. These numbers are an estimate and may change as needed to 

complete the baiting operation safely and effectively. 

Due to the significantly lower air speed of the helicopters compared to planes and jets landing at 

Midway, the risk of bird collisions with a helicopter would be much lower. In addition, all 

helicopter operations would only occur during daylight, when visibility for birds and the pilot are 

optimal. Therefore, nocturnal seabirds would not be at risk, which include the wedge-tailed 

shearwater, Christmas shearwater, Bonin petrel, Bulwer’s petrel, and Tristam’s storm petrel. 

Further, impact to Tristram’s storm-petrel would be low because birds are mostly absent from 

MANWR from July to October, a period coinciding with the baiting operation; impacts to 

Christmas shearwater and Bulwer’s petrel would be low given that nesting by these species on 

Sand Island has not been documented to date (USFWS, Unpublished b). Although 6 Bonin 

petrels were struck by aircraft at Henderson Field on Sand Island (Table 3.14), the majority of 

these birds were struck after 8:00 p.m. or in the early morning hours during night landings. 

Black-footed albatross would have finished nesting and are unlikely to be present on Sand Island 

during the baiting operation. Population levels of all 5 tern species, except the white tern, are low 

on Sand Island, and sooty tern only nest on Eastern Island. Therefore, only the white tern is at a 

high risk during the operation. At MANWR, the white-tailed tropicbird is a rare breeder on Sand 

Island and only the red-tailed tropic bird would be at high risk of collisions. 

Three species of booby are present at MANWR year-round, red-footed booby, masked booby, 

and brown bobby. The red-footed booby does not nest on Sand Island and the number of total 

pairs is low, however some of the red-footed booby will temporarily roost on Sand Island. The 

masked booby and brown booby only nest in extremely low numbers on Eastern Island. 

Therefore, booby are unlikely to be at risk from the helicopter operations. In addition, with the 

helicopters flying at an average altitude of 164 ft. (50 m) and the bucket >134 ft. (41 m) above 

the ground, these heights would allow most birds to flush below the aircraft and temporarily 

disperse. Great frigatebird are expected to be at risk due to their large body size and habit of 

soaring above the island although their populations are small on Sand Island. 

Three bait drops are planned on Sand Island, using 2 helicopters to maximize the chance of 

completing each drop in a single day. These drops would be spaced 7 to 10 days apart. It is 

expected each drop would take a total of 20 flight hours or 60 total flight hours for the entire 

operation. Total flight times could be longer. Using helicopter strike data from the Palmyra rat 

eradication, and the number of hours of helicopter time used on Palmyra, we calculated the 

average number of small bodied <1.8 lbs. (<800 g) and large bodied >1.8 lbs. (>800 g) birds 

killed per hour on Palmyra. Small bodied birds (sooty tern and 2 unidentified birds) were struck 

at a rate of 0.085 birds per hour while large birds (red-footed booby) were struck at a higher rate 

of 0.119 birds per hour. We then applied these collision rates to each of the remaining species of 

seabirds at risk of strike hazard on Sand Island, but to be conservative, we assumed each species 
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in the 2 body size classes was at equal risk to the 2 species killed on Palmyra, thus likely 

overestimating risk. These included large seabirds (Laysan albatross and great frigatebird) and 

small seabirds (black noddy, brown noddy, red-tailed tropicbird, and white tern). After 

calculating the number of individuals at risk of a strike for each species based on the total 

helicopter time expected on Sand Island, we adjusted the numbers up or down based on the 

difference in total population numbers of each species of large or small bodied seabirds at 

Palmyra versus Sand Island. This adjustment thus accounted for the total number of birds 

expected to be in the air, based on their population size on Sand Island during the baiting period. 

For a small seabird, if the population of the white tern on Sand Island was 1/3 that of the sooty 

tern population on Palmyra, final mortality estimates were adjusted lower by 1/3. 

Although Laysan albatross populations are large on Sand Island and potentially a high strike 

hazard, in a detailed study by Fisher and Fisher (1969) of the nesting chronology of albatross on 

MANWR, researchers found that as the chicks mature in June and July, adults frequent the island 

even less often and for shorter periods of time. In the 60-day interval of mid-May to mid-July, 

when a number of the older young have already fledged, each parent probably visits the island at 

intervals of about 3 or 4 days, as indicated by the frequency of the feeding of the young. 

Therefore, after mid-May the parents may make 15 round trips to MANWR, and only spend 3% 

of the time in the colony. Over the entire year, males and females only spend 18% and 12% of 

their total time on land, respectively. To rear a chick successfully during the total nesting period 

of 230 days requires only 160 trips to the colony by both parents combined (Fisher and Fisher 

1969). In addition, adult breeding birds start to leave in mid-June, and by the first of August few 

of them may be seen in the colony. Adult albatross are also known for the brief duration of their 

visits to feed older chicks. In their study plots, Fisher and Fisher (1969) found the number of 

adult and juvenile Laysan albatross on June 29 was only 7.1% of the peak population. After 

August 7, adults of any category are seldom observed on Midway. Therefore, for Laysan 

albatross, we calculated that only 7.1% of adults would still be present on Sand Island at the start 

of the operation in early July. 

During the 2015 aerial bait trials on Lehua, field crews noted that seabirds were not disturbed 

(e.g., flushing) due to helicopter operations (Mazurek 2015). Seabirds and shorebirds are also 

somewhat conditioned to planes landing at Midway, with hundreds of landings and take-offs 

occurring per year. However, air operations would be expected to kill some seabirds. Using the 

results of our calculation above, based on the data from the eradication operation on Palmyra, 

there would be likelihood that 6 species of seabirds could be killed from air operations on Sand 

Island under the Preferred Alternative. This mortality includes a maximum of 15 Laysan 

albatross, 1 black noddy, 1 brown noddy, 1 red-tailed tropicbird, 2 white terns, and 1 great 

frigatebird. These numbers represent a worst-case scenario, based on maximum numbers of birds 

expected to be on Sand Island, and high probabilities of collision assumed with the helicopter.

Due to the low number of anticipated mortalities relative to their overall population levels (see 

Table 3.10), the Preferred Alternative could cause a direct impact, but those impacts would be

minor. Effects would be detectable but localized, small and of little consequence to their global 

populations. There are no specific mitigation measures that would be expected to reduce the 

amount of the impact from helicopter operations. Eradication of mice would be expected to 

directly benefit several species of seabirds, including the Laysan albatross, short-tailed albatross, 

black-footed albatross and other species. Elimination of risk from predatory mice would allow 
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these species to increase their population sizes. The eventual population-level benefits to 

seabirds from eradication of predatory mice on Sand Island outweigh the small number of 

potential mortalities that might occur through implementation of the Preferred Alternative.

3.3.6.6 Shorebirds 

3.3.6.6.1 Existing Conditions 

MANWR supports overwintering, year-round, and vagrant populations of shorebirds (Table 

3.15). Species include bristle-thighed curlew, Pacific golden-plover, wandering tattler, ruddy 

turnstone, and sanderling, and occasionally grey-tailed tattler, long-billed dowitcher, wood 

sandpiper and others. While some young birds stay at MANWR year-round, the bulk of 

shorebirds that had spent the summer breeding elsewhere arrive around August/September for 

the winter, and depart around April/May, making the preferred window to carry out the 

application of bait on Sand Island in the July/August period (Figure 3.3). Due to their habit of 

breeding elsewhere, the summer population of shorebirds on MANWR consists of juveniles and 

non-breeding birds. 

Table 3.15 Ducks, shorebirds, and wading birds of MANWR (n = 7 species)

Common Name Scientific Name Status, IUCN-list

Laysan duck Anas laysanensis Critically endangered

ruddy turnstone Arenaria interpres Least concern

wandering tattler Tringa incana Least concern

Pacific golden plover Pluvialis fulva Least concern

bristle-thighed curlew Numenius tahitiensis Vulnerable

sanderlings Calidris alba Least concern

cattle egret Bulbucus ibis Least concern

Source: USFWS (2017)

There are only 4 species of shorebirds present on MANWR in any significant numbers during 

the summer months of July and August, when the application of rodenticide is expected to occur. 

These include 4 species of concern, the bristle-thighed curlew, Pacific golden plover, wandering 

tattler, and ruddy turnstone. The bristle-thighed curlew and Pacific golden-plover are designated 

as species of high conservation concern in USFWS National and Regional Shorebird Plans, 

including the U.S. Pacific Islands Regional Shorebird Conservation Plan (Engilis Jr. and 

Naughton 2004). Both of these species overwinter at Midway, with low numbers of juvenile or 

non-breeding birds also present through the summer months. All of the shorebird species using 

MANWR demonstrate a pattern of greater abundance during the winter months, with very few or 

no individuals remaining throughout the summer when adult birds return to the breeding grounds 

in the Arctic (USFWS, Unpublished a). More details on the bristle-thighed curlew can be found 

in Section 3.3.6.7. 

3.3.6.6.2 Pacific golden plover 

This species has been sighted regularly on the shoreline of all 3 islets at MANWR, in the 

forested areas, and in open, grassy areas (USFWS, Unpublished b). This species has an 

extremely variable body mass range, about 0.2-0.4 lbs. (100-200+ g) within an annual cycle 

(Johnson and Connors 2010). These plovers spread out while foraging; they are visual foragers 
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that feed by running and seizing prey. At MANWR, they prefer open spaces, low vegetation 

fields, roadsides, sandy beaches, and mudflats. Their diet consists primarily of terrestrial 

invertebrates (and some freshwater and marine invertebrates), and includes berries, leaves, and 

seeds. Although these plovers do not nest in the tropical Pacific, they may return to the same 

winter foraging island each year (Pratt et al. 1987). Therefore, breeding birds are absent at 

MANWR from about May to August, but low numbers of juvenile and non-breeding birds are 

present throughout the summer months (USFWS, Unpublished b). 

The global population estimates range from 185,000 to 250,000 (Delaney and Scott 2006) with 

one estimate of 1,000,000 birds (Bamford et al. 2008, Johnson and Connors 2010). The highest 

documented count of this species on Sand Island from 1993 to 2001 was 1,540 birds, or 0.15-

0.83% of the global population. 

3.3.6.6.3 Ruddy turnstone 

Ruddy turnstone occurs on Sand Island, with a majority on Eastern Island. Breeding birds are 

absent at MANWR from about May to August, but low numbers of juvenile and non-breeding 

birds are present throughout the summer months (USFWS, Unpublished b). Individuals measure 

8-10 in. (21-26 cm) in length, have a wingspan of 20-22 in (50-57 cm), and a body mass ranging 

0.2-0.4 lbs. (84-190 g) (Nettleship 2000). This stocky, orange-legged shorebird forages on sandy 

and rocky beaches, coral reefs, tidal pools, and mudflats for marine insects, crabs, clams, and 

mussels.

Ruddy turnstone are common throughout the Pacific Islands, but the wintering population in this 

region is small compared to the global total (Engilis and Naughton 2004). Estimates of wintering 

populations range from 259,000 to 544,000 birds (Nettleship 2000, Van Gils and Wiersma 

1996). The highest documented count of this species on Sand Island from 1993 to 2001 was 880 

birds, or 0.16-0.34% of the global population. 

3.3.6.6.4 Wandering tattler 

Wandering tattler occur on Sand Island. Breeding birds are absent at MANWR from about May 

through July, but low numbers of juvenile and non-breeding birds are present throughout the 

summer months. Individuals measure 10-12 in. (26–30 cm) in length, with a wingspan of 19-21 

in. (50–55 cm), and a mean bill length 1.3-1.7 in. (3.4–4.2 cm) and an average body mass of 0.2-

0.3 lbs. (100–140 g). Wandering tattlers wade while they actively forage, making jerky bobbing 

movements, and repeatedly return back to the same spot over very short time intervals. They 

feed on rocky coasts, exposed reefs, sandy beaches, and mudflats (Gill et al. 2002), for 

crustaceans and marine worms, but they also eat insects (only when breeding) and small 

vertebrates.

The global population is estimated to range from 10,000 to 25,000 individuals (Engilis and 

Naughton 2004). The highest documented count of this species on Sand Island from 1993 to 

2001 was 108 birds, or 0.4-1.1% of the global population. 

3.3.6.6.5 Sanderling 

Sanderlings occur in very low numbers on Sand Island. No individuals of this species were 

recorded on MANWR during avian surveys conducted in June, July, August and September 
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2017. Breeding birds are absent at MANWR from about May to September, but low numbers of 

juvenile and non-breeding birds can be present throughout the summer months. Individuals 

measure 7-8 in. (18-20 cm) in length with a body mass of 0.09-0.22 lbs. (40–100 g) (Macwhirter 

et al. 2002). These plump shorebirds are faithful to mudflats, beaches, and open marshes, and are 

primarily found on sandy stretches of coast lines, the outer reaches of estuaries, and along rocky 

shores (Van Gils and Wiersma 1996). Sanderling feed on small mollusks, marine crustaceans, 

polychaete worms and insects in adult, larval and pupal stages (e.g. Diptera, Coleoptera, 

Lepidoptera, Hemiptera and Hymenoptera), as well as occasionally fish and carrion. This species 

is considered of “limited importance” in the Pacific Islands since the vast majority of birds 

winter in other parts of the world. The global population is unknown (Engilis and Naughton 

2004). 

Other shorebird species occasionally visit MANWR. These species can include the grey-tailed 

tattler, long billed dowitcher, black-bellied plover, wood sandpiper, and others. Such vagrants for 

example, can be birds that are blown off their normal migration routes. Vagrants do not breed at 

MANWR, nor do they use the refuge as annual wintering grounds. 

Because these 4 shorebird species do not breed at Midway, but use it as non-breeding habitat in 

the boreal winter, one simple method for reducing the risk to shorebirds during broadcast 

application of rodenticide bait is to time the dates of application to coincide with the period of 

lowest shorebird presence on Sand Island, specifically, the summer months of June, July, and 

August (see Figure 3.3 and Figure 3.5 below). This timing does not eliminate the exposure 

potential because in any given year, a certain proportion of the population may not migrate north. 

The subset of the population that remains on MANWR is made up of younger, non-breeding 

birds and those that may not be in good enough physical condition to make the journey north. 

Figure 3.5 Mean counts for years 1993-2001 and 2017 of bristle-thighed curlew, Pacific 

golden plover, wandering tattler, and ruddy turnstone combined by 

month on MANWR

Note: Data were sometimes influenced by pulses of greater numbers that may represent waves of birds coming from further south and 
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stopping to rest or forage on MANWR. 

Mean counts of bristle-thighed curlew, Pacific golden plover, wandering tattler, and ruddy 

turnstone at MANWR were derived from various sources. Data from 1993-2001 compiles counts 

gleaned from annual systematic surveying efforts, like the Christmas Bird Count, and from 

literature sources like MANWR trip reports and incidental counts by Refuge staff and visiting 

biologists. During 2017, monthly shorebird surveys were conducted simultaneously and 

systematically on all 3 islands (Sand, Eastern, and Spit) to count every shorebird and passerine 

for 3 hours in the morning (0700-1000); observers walk/bike assigned units to ensure complete 

coverage of each island, and to record time, species, location, and direction of travel if birds are 

in flight (Goodale 2017). The highest recorded numbers from 1993 to 2001 for each species 

during June, July, and August, respectively, were bristle-thighed curlew (12, 168, 242); Pacific 

golden plover (300, 202, 1,071), wandering tattler (12, 6, 67), and ruddy turnstone (186, 355, 

633). The average number of each species over June, July, and August during monthly 

systematic shorebird counts on Sand, Eastern, and Spit Islands in 2017 were 106 bristle-thighed 

curlew, 115 Pacific golden plover, 297 ruddy turnstone, and 8 wandering tattler (USFWS, 

Unpublished b). These numbers exclude surveys conducted on 8/30/17 when numbers for each 

of the 4 species increased significantly (see Figure 3.6 below) and outside of the time when the 

operation is scheduled to occur. 

Bristle-thighed curlew, Pacific golden plover, wandering tattler, and ruddy turnstone are a 

concern because of their numerical presence at MANWR, their foraging habits, and 

documentation of their vulnerability during similar operations at ecologically comparable sites 

(Engilis and Naughton 2004). The Pacific Islands function as an essential migratory habitat for 

maintaining many global shorebird populations. All of the shorebird species using MANWR 

demonstrate a seasonal pattern of greater abundance during the fall and winter months beginning 

in August/September, and very few individuals of some species remain throughout the summer 

when the breeders are elsewhere (Engilis and Naughton 2004). 
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Figure 3.6 Monthly counts on MANWR conducted in 2017 for bristle-thighed curlews 

(BTCU), Pacific golden plovers (PGPL), wandering tattlers (WATA), and 

ruddy turnstones (RUTU)

Source: USFWS (2017)

3.3.6.6.6 Probable Impacts: No Action Alternative 

Under the No Action Alternative, brodifacoum would not be used island-wide to eradicate mice 

on Sand Island, except for targeted control with the less toxic AGRID3. Since the rodenticide 

AGRID3 used under the no action alternate is not known to be harmful to shorebirds, there 

would be no effects to these species under the no-action alternative.

3.3.6.6.7 Probable Impacts: Preferred Alternative 

Primary and Secondary Exposure 

As summarized above, the Pacific golden-plover, wandering tattler, and ruddy turnstone are 

regularly seen on Sand Island. At MANWR during 2017, monthly shorebird surveys have been 

conducted simultaneously and systematically on all 3 islands (Sand, Eastern, and Spit) to count 

every shorebird and passerine for 3 hours in the morning (0700-1000); observers walk/bike 
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assigned units to ensure complete coverage of each island, and to record time, species, location, 

and direction of travel if birds are in flight (Goodale 2017). The highest recorded numbers for 

each of these species during July and August 2017 surveys (excluding surveys conducted on 

8/30/17 because the proposed action is not scheduled for this time) were 278 Pacific goldenplover, 351 ruddy turnstone, and 15 wandering tattler. Significantly higher numbers of each of 

these species were recorded on surveys conducted on August 30 and September 15, 2017 with 

maximum counts of 1,419 Pacific golden plover, 880 ruddy turnstone, and 84 wandering tattler 

(Figure 3.6) (USFWS, Unpublished b). 

These 3 species primarily consume a wide range of invertebrate and possibly vertebrate prey, 

which makes secondary poisoning a potential risk. Each is also documented to consume foods 

comprised of vegetable matter (natural and man-made); however, this is usually a minor 

component of the diet, making primary poisoning a relatively low risk. 

Table 3.16 indicates that to ingest a lethal dose of brodifacoum, any of these 3 shorebird species 

would only need to eat between 0.3 to 0.39 oz. (9-11 g) of contaminated invertebrates on a single 

day. This is only 35 to 37% of their estimated daily food intake. In addition, the ingestion of 2 

pellets of bait (0.07 oz. or 2 g) would constitute a potential lethal dose for an individual of each 

species. This would amount to only 7% or more of each species daily normal food intake of nonanimal matter (Table 3.16). 

Table 3.16 Primary and secondary toxicity of Brodifacoum to shorebirds on MANWR 

along with the Laysan duck and cattle egret

Primary toxicity presented as grams of bait and secondary as grams of invertebrate prey. Mg of 

active ingredient is abbreviated as a.i. LD50 is that the dosage (D) of a toxin that is lethal (L) to 50% 

of animals of the species in laboratory tests.

Species

Body 

Wt 

(g)

Daily Food 

Intake (g)(1)

Brodifacoum

LD50

(2)

(mg/kg)

LD50

(mg of 

a.i./bird)

LD50

(3)

(g of 

bait)

LD502(4)

(g of prey)

%(5) of Daily 

Food Intake 

(prey)

Pacific 

golden 

plover

110 29.9 0.26 0.029 1.14 9.4 34.9

ruddy 

turnstone

130 30.1 0.26 0.034 1.35 11.1 36.8

wandering 

tattler

120 28.5 0.26 0.031 1.25 10.2 35.9

bristlethighed 

curlew

497 73.9 0.26 0.129 5.17 42.4 57.4

cattle egret 370 60.6 0.26 0.096 3.85 14.9(6) 24.6

Laysan duck 500 74.2 0.26 0.130 5.20 42.6 57.5

Notes:

1. Daily food intake calculated from allometric equation (Bird Feeding Rate = 0.059 x (W 0.67) (USEPA 1995).

2. LD50 of brodifacoum based on mortality of mallard ducklings at the lowest dose, 0.26 mg/kg body weight = 0.00026 mg/g (Ross et al. 

1980, EPA 1991). 

3. This is also the number of bait pellets that would need to be consumed to be lethal to 50% of the animals.

4. Cockroach contamination based on highest reported value of 3.05 mg/kg = 0.00305 mg/g (Pitt et al. 2015).

5. Calculated as LD50 2 grams of prey/daily food intake (g).

6. For the predatory cattle egret, this is grams of whole rat. Contamination based on highest reported residues in rat carcasses (6.45 mg/kg 

liver = 0.00645 mg/g) (Pitt et al. 2015).
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In a study of mortality of shorebirds after the Palmyra rat eradication using brodifacoum, Pitt et 

al. (2015) found that all bristle-thighed curlew, Pacific golden plover, ruddy turnstone, and the 

wandering tattler mortalities collected had detectable brodifacoum residues. Six bristle-thighed 

curlew, 2 Pacific golden plover, 2 ruddy turnstone, and 1 wandering tattler were found dead after 

the rodenticide application. Bristle-thighed curlews had the highest average brodifacoum residue 

relative to the other birds analyzed. Results from Palmyra Atoll indicate that non-target deaths of 

shorebirds are a concern (Pitt et al. 2015). The number of shorebird mortalities from the 

eradication attempt were likely underestimated because some avian mortalities probably went 

undiscovered. Although the USFWS (2011) estimated that more than 20,000 rats were killed 

during the Palmyra eradication, only a few dozen rat carcasses were found during the project. To 

estimate the total maximum number of shorebirds that may have been killed due to poisoning, 

Pitt et al. (2015) used the low tide shorebird survey counts conducted prior to the operation (June 

3, 2011) and compared these counts to the numbers of birds counted after completion of the bait 

drop, but prior to the arrival (July 30, 2011) of post-breeding birds in autumn. Maximum 

estimates of mortality Pacific golden plover, ruddy turnstone, and the wandering tattler using this 

method were 28, 8 and 10 birds respectively. Using these data, we can calculate the minimum 

and maximum % mortality of shorebirds from the Palmyra operation. Using 2010 survey data, 

the maximum population estimates of these 3 species on Palmyra were 62 Pacific golden plover, 

35 ruddy turnstone, and 48 wandering tattler. The minimum and estimated maximum of the total 

population of each shorebird species sub-lethally impacted or killed was 3.2-45.2% for Pacific 

golden plover, 5.7-22.8% for ruddy turnstone and 2.1-20.8% for wandering tattler. 

Based on the above analysis, after the application of brodifacoum on Sand Island, it would be 

likely that 9-125 plovers, 20-80 turnstones, and 1-3 tattlers, would be sub-lethally impacted or 

killed by either primary or secondary poisoning from brodifacoum during the operational 

window. This estimate assumes that the maximum count of all shorebirds recorded from all 3 

islands would all be present on Sand Island, which is unlikely. Mortality estimates for bristlethighed curlew are presented in Section 3.3.6.7.3 below. 

Brodifacoum can persist in the environment for 6 months to a year and have impacts beyond the 

proposed operational window (Rueda et al. 2016; Pitt et al. 2015), such that any returning 

shorebirds would be at risk from secondary poisoning. Therefore, additional shorebirds could be 

killed in the months following the application of brodifacoum. Taking the estimated maximum % 

of each species killed on Palmyra and using the highest count of each species recorded on 

MANWR since 1993, we calculated the potential additional mortality of shorebirds over the fall 

and winter after the bait drop. There could be an additional 584 Pacific golden plover, 182 ruddy 

turnstone, and 17 wandering tattler at risk over the next 12 months after the baiting operation. 

This is a worst-case scenario based on conservative LD50 toxicity values, maximum expected 

number of birds on Sand Island, and maximum expected mortality rates. However, because of 

the high degree of site fidelity for birds on their wintering grounds, it would be likely that 

mortality of shorebirds from rodenticide poisoning would decline in subsequent months. In 

addition, some shorebirds would be expected to forage on Eastern Island and Spit Island, and 

therefore not experience primary or secondary exposure to the rodenticide. Combining the 

potential estimated mortality from the initial bait drop and over the subsequent year, the total 

estimated mortality of Pacific golden plover (709), ruddy turnstone (262), and wandering tattler 

(20) from primary or secondary poisoning is only 0.37%, 0.10%, and 0.2% of their estimated 
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minimum global populations and therefore would not have a measurable effect on those species’ 

populations. 

Operational Hazard (Bird Strike and Noise/Human Disturbance) 

It is unlikely ground operations associated with the Preferred Alternative would impact any 

shorebirds, as no nesting occurs on the island. Air operations have the potential to disturb 

shorebirds, but observations from field personnel during pre-project surveys indicate this 

disturbance would be minor and may cause birds to temporarily flush from their location. No 

shorebirds were known to be killed from collisions with the helicopter during the Palmyra 

operation, however, based on the data of small bodied birds (sooty terns and unidentified birds) 

killed from helicopter collisions on Palmyra (0.085 birds per hour), and using the estimated 

hours of helicopter time for the Sand Island operation and expected population of shorebirds 

during the drop, the estimated mortality is less than 1 bird for each of the 3 species of shorebirds. 

Calculations are based on the maximum number of birds observed in 2017 during the planned 

drop period. 

We expect there could be some additional impact to shorebirds should the need arise to 

implement the rapid response portion of the refuge’s biosecurity plan and during implementation 

of the project monitoring plan. A biosecurity plan has been in place on MANWR for many years 

and any additional bio-security measures would only occur if there was a new incursion of a nonnative species. Biosecurity measures enacted would include rapid response to an incursion by 

non-native invasive species and implementing the monitoring plan would include follow-up 

observations and sample collecting (see Appendix A and B). Potential impacts, such as causing 

shorebirds to flush, could occur from the additional human disturbance. However, we expect any 

additional impacts to be minor, localized, and short-term.

Mitigation

Several mitigation options have been proposed that could minimize exposure of shorebirds to 

bait containing the rodenticide during the eradication campaign on Sand Island. These include:

• Timing implementation of the eradication for when the population is lowest before 

the majority of birds arrive at MANWR from their breeding grounds (July/August); 

• Keeping bait pellets away from shorebird feeding areas to the extent possible by not 

broadcasting in intertidal zones; 

• Trapping as many individuals as possible and keeping them in captivity until risk of 

exposure is eliminated or greatly reduced.

As many shorebirds as possible would be trapped and either kept in captivity or their feathers 

would be clipped and they would be released on Eastern Island before the rodenticide is applied 

to Sand Island. The above estimates of mortality do not consider this mitigation action, as 

shorebirds can be very difficult to capture. 

Combined potential mortalities from primary and secondary poisoning, along with possible 

mortalities from airstrikes, represent insignificantly small numbers relative to overall global 

populations of these species, and represent a worst-case scenario based on maximum numbers of 

birds documented on Sand Island, upper extremes of toxicity, and high probabilities of collision 
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with the helicopter. Due to the low number of anticipated mortalities relative to their overall 

global population levels, the Preferred Alternative would be unlikely to adversely impact 

shorebird populations on MANWR. The impacts would be readily detectable and localized with 

likely measurable consequences to shorebirds, but not readily detectable or measurable beyond 

the immediate area of impact.

3.3.6.7 Bristle-thighed curlew 

3.3.6.7.1 Existing Conditions 

The bristle-thighed curlew is a medium-sized curlew with a wingspan of approximately 15.7-

17.3 in. (40-44 cm) and blue-gray legs (see Figure 3.7). The birds have a moderately long and 

decurved bill, which 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. 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. Mean weight of adults was 1.09 lbs. 

(497.4 g) and ranged from 0.84-1.29 lbs. (393-584 g) for 61 unsexed birds caught in the 

Northwestern Hawaiian Islands from October through November (Marks 1993). Juveniles are 

similar to adults except for the presence of larger cinnamon-buff spots on the upperparts, and 

virtually unstreaked underparts (Marks et al. 2002). 

Classified as Vulnerable on the IUCN Red List 

2012 (BirdLife International 2016a), bristlethighed curlew are considered species of high 

conservation concern because of their small 

population size and anthropogenic pressures on 

the wintering grounds, which include habitat loss, 

habitat degradation, and introduced mammalian 

predators. The bristle-thighed curlew has also 

been designated as a Bird of Conservation 

Concern by the USFWS at the regional and 

national scale (USFWS 2008a) due to limited 

breeding and non-breeding distributions, low 

relative abundance, and threats during the nonbreeding season. Although the birds’ tundra 

breeding grounds have remained largely 

undisturbed, some researchers believe that bristlethighed curlew are negatively impacted by 

introduced mammalian predators, including rats, 

on their wintering grounds and atolls, including 

Palmyra Atoll (Marks et al. 1990). The risk of a 

steep and sudden population decline is a serious 

threat because these birds are long-lived and sitefaithful. Bristle-thighed curlew occur on Sand 

Island. Breeding birds are absent at MANWR from about May through the end of July, but low 

numbers of juvenile and non-breeding birds are present throughout the summer months 

(USFWS, Unpublished b). 

Figure 3.7 Bristle-thighed curlew

Source: USFWS (2017)
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During the breeding season, bristle-thighed curlew 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 Jr. 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. Sub-adults may 

remain in the Pacific until they are nearly 3 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). Habitat preference in the Northwestern 

Hawaiian Islands includes beaches and shorelines with coral ledges, but birds are often found 

inland among grass- and forb-dominated areas (Woodward 1972, Ely and Clapp 1973, Amerson 

et al. 1974, Clapp and Wirtz II 1975, Marks et al. 2002). In fall of 1988, Laysan Island 

populations were predominantly inland (68% of 2,521 sightings), and only 1% on beaches 

(Marks et al. 2002). Birds walk as they pick up items from the ground, also probing in soil or 

mud with their long bills, to feed on crustaceans, small fish, insect grubs, and snails. This species 

has also been observed catching and eating mice. This species has been sighted regularly on the 

shoreline of all 3 islets at MANWR, in the forested areas, and in open, grassy areas (USFWS, 

Unpublished b).

Comprehensive surveys of known breeding range from 1988 to 1992 yielded about 3,200 

breeding pairs (Marks et al. 2002), while Engilis and Naughton (2004) estimate that the global 

population is 10,000 birds and is limited by restricted breeding and non-breeding distributions, a 

low relative abundance, and threats during the non-breeding season. Numbers may be declining, 

although data on population trends are not available (Marks et. al. 2002). In total, about 800 birds 

are thought to winter in the Northwestern Hawaiian Islands during the same period (1980 to 

1990), which included 300–350 birds on Laysan Island, 300–400 on Lisianski Island, and 100 on 

MANWR (Marks and Redmond 1994). 

A survey has been employed on MANWR to count shorebirds, including bristle-thighed curlew. 

The age of birds was not recorded because adult and sub-adult curlews can be somewhat difficult 

to distinguish. However, birds remaining through the boreal summer are most likely sub-adults, 

which do not migrate back north until they are approximately 34 months old (Marks 1993, Marks 

and Redmond 1996). Bristle-thighed curlew counts on MANWR from June to September 2017 

ranged from 11 to 242 birds, with the maximum number of birds counted on August 30 (Figure 

3.7). Although survey methods varied, using avian survey data collected from 1993 to 2001, 

along with the 2017 surveys, counts from January through December on MANWR ranged from 

12 to 242 birds with the lowest counts in June. The maximum counts on MANWR during the 

expected drop period in July/August was 168 birds in 2017. The highest documented count of 

this species on Sand Island from 1993 to 2001 was 242 birds, or 2.42% of the global population. 

Since there are no marked birds, it is not known how many of these birds are winter residents 

versus migrants stopping before they head further south. 

3.3.6.7.2 Probable Impacts: No Action Alternative 

Under the No Action Alternative, rodenticides would not be used island-wide to eradicate mice 

on Sand Island, except for targeted control with the less toxic AGRID3. Since the rodenticide 

AGRID3 used under the No Action Alternate is not known to be harmful to shorebirds, there 

would be no effects to the bristle-thighed curlew under the No Action Alternative.
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3.3.6.7.3 Probable Impacts: Preferred Alternative 

Primary and Secondary Exposure 

The mouse eradication project places non-resident migratory shorebirds, including bristlethighed curlew, at risk of both primary and/or secondary exposure to rodenticide bait that would 

be broadcast across the island. 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. In the non-breeding season, 

bristle-thighed curlew 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). 

Given the diverse diet of this species there are several potential secondary/tertiary exposure 

pathways for the bristle-thighed curlew including: 

• Feeding on crabs that have consumed bait or scavenged mice carcasses;

• Feeding on insects that have consumed bait or scavenged mice carcasses;

• Feeding on lizards/geckoes that have consumed insects that have ingested the bait; 

and/or 

• Feeding directly on live mice or mice carcasses that have consumed bait. 

Research conducted on Palmyra Atoll using remote cameras indicated bristle-thighed curlew 

showed little interest in the bait placed on the ground or in the carcasses of rats put out by the 

researchers (USFWS 2011). Curlew were ever-present 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, curlew, 

plover, wandering tattler, and booby 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. Although it was estimated that more 

than 20,000 rats were killed during the eradication project on Palmyra, only a few dozen rat 

carcasses were found during the project after the bait was applied (Pitt et. al. 2015). It is expected 

that this same result would occur on Sand Island. Thus, it is expected that there will be a few 

carcasses available for bristle-thighed curlew to find. 

A June 2011 rat eradication effort on Palmyra Atoll using brodifacoum reported 6 bristle-thighed 

curlew individuals found dead after the bait drop and Pitt et al. (2015) estimated as many as 68 

could have been killed after the application of rodenticide. Using these numbers, 3.3 to 37.4% of 

the islands population may have been sub-lethally impacted or killed by either primary or 

secondary poisoning from brodifacoum during the operational window. However, bait densities 

were very high for this effort and included 75.6 lbs./ac. (84.8 kg/ha) applied in the first drop and 

71.5 lbs./ac. (80.1 kg/ha) applied on the second drop, with a third application in some areas. This 

is 10-16% higher bait density than that proposed for the MANWR Preferred Alternative. Two of 

the curlew were confirmed to have been exposed to bait prior to capture and were successfully 

treated on Palmyra. Other eradication projects reported non-target mortality of bristle-thighed 

curlew (Pierce et al. 2008). Pierce et al. (2008) reported 2 dead curlew found 13 days after the 
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first spread of brodifacoum bait on Rawaki Island, Republic of Kiribati, in the Central Pacific, 

while 8 other live curlew were also recorded after the bait drop, which is a mortality rate of 25%. 

However, surveys for dead or dying shorebirds were not comprehensive for most eradication 

projects (USFWS 2011). It is also likely that most carcasses are rapidly consumed by scavengers, 

making estimations of mortalities resulting from rodenticide bait difficult to predict. Merton et 

al. (2002) showed high shorebird mortality in brodifacoum broadcast eradications on islands in 

the Seychelles. However, these eradications were timed to coincide with the lull in the tourist 

season rather than a seasonal low in shorebird numbers, so birds were present on the islands in 

great numbers during the eradication. For the Asiatic whimbrel, a related species of the bristlethighed curlew, 20% mortality was observed on one of the islands. For the ruddy turnstone, the 

mortality rates ranged from 20% to 90% on the 4 islands, with exceptional mortality rates 

possibly enhanced due to the birds being fed by people (Merton et al. 2002). The individuals 

over-summering on MANWR are the young non-breeders.

Using data from bristle-thighed curlew mortality rate on Palmyra in 2011 (3.3 to 37.4%), the 

mortality documented on the Seychelles for the closely related whimbrel (20%) and the bristlethighed curlew mortality reported from Rawaki Island (25%), and the number of birds expected 

to be on Sand Island during the July/August drop period, we calculated the minimum and 

maximum % mortality to bristle-thighed curlew from the Sand Island rodenticide application. It 

is anticipated that the bait application could sub-lethally affect or incidentally kill 5-52 bristlethighed curlew on MANWR without mitigation (trapping and holding birds in captivity or 

clipping wings and releasing birds on Eastern Island). Birds that remain on Eastern Island during 

the drop would be unlikely to experience any primary or secondary exposure. However, without 

trapping and clipping the wings of birds, individuals would be able to fly from Eastern to Sand 

Island. In addition, because it is not a closed population and because breeders would not be 

taken, it is unlikely there would be any negative long-term population-level effects to this species 

from this alternative. 

Brodifacoum could persist in the environment for 6 months to a year and have impacts beyond 

the proposed operational window if bait were available to foraging curlews (Rueda et al. 2016, 

Pitt et al. 2015), such that any returning shorebirds would be at risk from secondary poisoning. 

Therefore, additional bristle-thighed curlew could be killed in the months following the 

application of brodifacoum. Taking the estimated maximum % of bristle-thighed curlew killed 

on Palmrya (Pitt et al. 2015) and using the highest count of this species recorded on Sand Island 

since 1993, we calculated the potential additional mortality of bristle-thighed curlew over the fall 

and winter after the bait drop. There would be an additional 71 bristle-thighed curlew at risk over 

the next 12 months after the baiting operation. Combined with the estimated morality from the 

initial bait drop, this is 50% of the highest count of birds on MANWR. This is a worst-case 

scenario based on conservative LD50 toxicity values, maximum expected number of birds on 

MANWR, maximum expected mortality rates, and no mitigation. However, because of the high 

degree of site fidelity for birds on their wintering grounds it would be likely that mortality of 

shorebirds from rodenticide poisoning would decline in subsequent months. Combining the 

potential estimated mortality from the initial bait drop and over the subsequent year, the total 

estimated mortality of bristle-thighed curlew (n=123) from primary or secondary poisoning is 

1.23% of the estimated global population. 
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A population viability analysis (USFWS 2011) was completed for the Palmyra rat eradication 

project to explore the implications of incidental poisoning mortality and other mortalities of 

bristle-thighed curlew due to activities associated with the proposed application of brodifacoum. 

The model investigated the likely effects on global bristle-thighed curlew populations from the 

mortality of 10, 50, and 150 bristle-thighed curlew individuals on Palmyra Atoll. They assumed, 

given the timing of the rat eradication, that the majority of mortalities would be sub-adult birds 

remaining at MANWR during the breeding season, but they conservatively assume that 50% of 

the mortalities would be adults. For all scenarios, a second conservative assumption of an 

additional 50 bristle-thighed curlew lost due to a simultaneous but unrelated one-time event was 

added, again assumed to be 50% adults. They then modeled population trajectories over 50 years 

and reported the extinction risk and projected median and lower 90th percentile of population 

size. Therefore, the mortality scenarios they considered on Palmyra included 60 to 200 

individuals which represented a 3-8% increase in adult mortality and a 13-31% increase in subadult mortality of the global population for one year. They concluded that these one-time 

mortality events appeared to have a minor and diminishing effect on projected future 

populations. The one-time mortality events did not alter future population growth rate and did 

not appear to put the population in danger of increased risk of stochastic extinction over a 50-

year period. Therefore, extrapolating from that model, the expected mortality of 5-123 bristlethighed curlew from the MANWR mouse eradication project, even without the mitigation

described below, is not expected to have long-term adverse effects to the global population. 

Operational Hazard (Bird Strike and Noise/Human Disturbance) 

It would be unlikely ground operations associated with the bait drop would impact any bristlethighed curlew, since no nesting occurs on the island. Air operations have the potential to disturb 

bristle-thighed curlew but observations from field personnel during pre-project surveys on 

Palmyra indicate this disturbance would be minor and may cause birds to temporarily flush from 

their location (USFWS 2011). Bristle-thighed curlew could be at risk of collisions with the 

helicopter during bait drop operations. However, no shorebirds were known to be killed from 

collisions with the helicopter during the Palmyra operation, and no bristle-thighed curlew have 

been recorded killed by aircraft at Henderson Airfield on Sand Island. In addition, shorebirds 

including bristle-thighed curlew are not concentrated in locations on Sand Island but scattered 

across a larger area. Most are also fast and maneuverable, and thus better able to avoid 

helicopters, particularly as the helicopters will be flying at approximately 50 meters above 

ground. We know of no records of bristle-thighed curlew colliding with a helicopter (USFWS, 

Unpublished b), although the occasional plover may be hit. Therefore, the risk of bristle-thighed 

curlew colliding with a helicopter are very low. However, based on the data of small-bodied 

birds (sooty terns and unidentified birds) killed from helicopter collisions on Palmyra (0.085 

birds per hour), and using the estimated hours of helicopter time for the Sand Island operation 

and expected population of bristle-thighed curlew during the drop, the estimated mortality is less 

than 1 bird for the curlew. Calculations are based on the maximum number of birds observed in 

2017 during the planned drop period. 

We expect there could be some additional impact to bristle-thighed curlews should the need arise 

to implement the rapid response portion of the refuge’s biosecurity plan and during 

implementation of the project monitoring plan. A biosecurity plan has been in place on MANWR 

for many years and any additional bio-security measures would only occur if there was a new 
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incursion of a non-native species. Biosecurity measures enacted would include rapid response to 

an incursion by non-native invasive species and implementing the monitoring plan would include 

follow-up observations and sample collecting (see Appendix A and B). Potential impacts, such 

as causing birds to flush, could occur from the additional human disturbance. However, we 

expect any additional impacts to be minor, localized, and short-term. 

Mitigation 

Several mitigation options have been proposed that could minimize exposure of bristle-thighed 

curlew to bait containing the rodenticide during the proposed eradication campaign on Sand 

Island. These have been described above for other shorebirds but for the bristle-thighed curlew

these would also include: 

• Trapping as many individuals as possible and keeping them in captivity or clipping 

their flight feathers and moving them to Eastern Island until risk of exposure is 

eliminated or greatly reduced and the birds grow new feathers. Supplemental food 

and water would be supplied to ensure adequate carrying capacity on Eastern Island. 

For the Palmyra Atoll rat eradication feasibility study (Howald et. al. 2004), the assessment team 

concluded that the most effective mitigation for this species was to conduct the eradication 

between early June and mid-July, when most adult bristle-thighed curlew are still on their 

breeding grounds in Alaska. Similarly, the lowest counts of bristle-thighed curlew on MANWR 

are in June. Timing during the summer period would also minimize the risk of short-term 

rodenticide exposure to the majority of curlew overwintering on MANWR. 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. In addition, Pierce et. al. (2008) noted that it was easier 

for bristle-thighed curlew to ingest rodenticide bait after it had been softened by rainfall. 

However, the eradication on Sand Island will occur during the driest time of the year. In 

addition, the rodenticide bait used for Sand Island would be dyed a green color to reduce the 

likelihood of birds picking up the bait (Day and Matthews 1999, Oppel et al. 2016). The Palmyra 

Atoll eradication used blue-green dye, which was a color known to be least visible/preferred to 

non-target species including shorebirds (U.S. National Park Service 2000).

Live-trapping bristle-thighed curlew prior to the eradication of mice and holding the birds in 

captivity on Sand Island, or releasing birds with clipped wings on Eastern Island, would 

eliminate the risk of primary and secondary rodenticide exposure. Although feasible, it is 

unlikely that a significant portion of the summer population, the majority of which are likely subadult birds (1-3 years old), could be captured before the bait drop. Before the bait drop on 

Palmyra in 2011 for the rat eradication, biologists were able to trap 5-9% of the bristle-thighed 

curlew population present (USFWS 2011). If this same rate of capture were possible on 

MANWR, approximately 12 to 22 birds could be captured and held in captivity or released with 

clipped wings on eastern Island. However, there would also be additional risks associated with 

capturing birds, including physical injury and physiological stress that could result in the death 

of some individuals. Thirteen bristle-thighed curlew were caught and successfully held in 

captivity on Palmyra without any injuries or mortalities reported, but several different trapping 

methods would need to be employed on MANWR to maximize success, as bristle-thighed curlew 

tend to be extremely wary. 
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3.3.6.8 Laysan duck 

3.3.6.8.1 Existing Conditions 

The Laysan duck (Anas laysanensis) is currently on the Federal Endangered Species List due to 

its restricted distribution and small wild population. The Laysan duck was extirpated across the 

Hawaiian archipelago with one extant population persisting only on the island of Laysan. A 

second and third population were established via translocation of wild birds from Laysan Island 

to Midway and Kure Atolls, respectively (see Figure 3.8). The Laysan duck is largely nocturnal 

and sedentary. Body weight fluctuates significantly with season and reproductive status 

(Moulton and Weller 1984). In spring, females are heavier than males and can exceed 1.3 lbs. 

(600 g), while males are at less than optimum mass because of courtship activities. In summer, 

males are generally heavier than females. Females with young broods are lightest of all mature 

birds, often <0.88 lbs. (<400 g). Having evolved with avian rather than mammalian predators, 

Laysan ducks are more likely to walk than fly, and freeze rather than flush, when startled. 

Similar to other waterfowl, Laysan ducks molt all of their feathers at the same time, during 

which they become incapable of flight, and thus more vulnerable to predators at this time. On 

Laysan Island, molting typically occurs between July and August for males and between July 

and September for females. On MANWR, males start molting in June and the molt for females 

with brood may extend into October. 

The Laysan duck feeds almost solely on 

macroinvertebrates, primarily insects 

(Moulton et al. 1996). These include 

Dipteran brine fly, adults, larvae, and 

pupae taken in and around lakes and 

ponds, along with brine shrimp 

(Artemia spp.) They also eat the larvae

and pupae of noctuid moths (Agrotis 

dislocate) under low vegetation in 

upland areas. 

Habitat requirements of the Laysan 

duck include vegetative cover, an 

invertebrate prey base, a source of fresh 

water, and protection from mammalian 

predators (USFWS 2009). On Laysan 

and Midway, ducks use all available 

habitats: upland vegetation, ephemeral 

wetlands, freshwater seeps, mudflats, the hyper-saline lake, and coastal areas. Nests are on the 

ground and well-concealed, usually within a base of vegetation, especially bunchgrass 

(Eragrostis variabilis), but sometimes in Cyperus or Heliotropium, on vegetated portions of the 

island (Moulton and Weller 1984). Egg-laying can begin as early as February and occur as late 

as November, but typically occurs from April to August; initiation and duration of egg-laying 

varies from year to year. Duckling activities are concentrated near sources of fresh water with 

nearby food and cover. Extirpation of the Laysan duck from the main Hawaiian Islands most 

Figure 3.8 Laysan duck family

Source: USFWS (2017)
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likely was caused by a combination of predation by introduced mammals, especially rats, 

hunting by humans, and habitat destruction and degradation. 

Current threats include alien species (e.g., mice, and invasive weeds) that can alter the Laysan 

duck’s habitat. This was demonstrated on Laysan Island in the early 20th century, when 

introduced rabbits devegetated the island causing the accelerated filling of Laysan’s freshwater 

seeps and saline lake. High duckling mortality from 1999 through 2004 suggests a lack of 

sufficient brood rearing habitat on Laysan. 

Another threat to Laysan ducks is from on-going avian botulism outbreaks (Work et al. 2010). 

Dead mice and other dead non-target species could exacerbate the botulism issue by promoting a 

maggot cycle. Small population size and extremely limited distribution make the species highly 

vulnerable to demographic fluctuation and stochastic events, such as droughts, severe storms, 

epizootics, predators, and invasive species. Habitat degradation and loss within the Marine 

Monument may be intensified by increased storm severity and sea level rise associated with 

global climate change. The population at MANWR was founded with 42 wild birds from Laysan 

Island during 2004–2005 and grew to 661 adult and juvenile birds (95% CI 608–714) in 2010. A 

population decline of 38% was observed between 2010 and 2012 after the 2011 Tōhoku Japan 

earthquake-generated tsunami inundated 41% of the atoll and may have triggered an avian 

Botulism type C (Clostridium botulinum) outbreak. After another severe botulism outbreak 

during 2015, the population again experienced a 37% decline. Monitoring data indicate that the 

MANWR population, like the Laysan Island population, is susceptible to catastrophic population 

declines. 

In 2015, Reynolds estimated there were between 314 and 435 Laysan ducks (95% CI for 

population estimate). The point estimate was 375 individuals (Reynolds et al. in press). This 

estimate of Laysan ducks at MANWR is approximately 50% of the global population. In 

comparison, the most recent estimate on Laysan Island in 2012 was 339 individuals (95% CI: 

265–413). The model was then used to estimate the population of Laysan ducks on MANWR for 

2017. Using a maximum count of 116 ducks counted at the end of August 2017, the model 

returns an estimated population of 491 ducks with a range (95% CI) of 387 to 596 individuals. 

3.3.6.8.2 Probable Impacts: No Action Alternative 

Under the No Action Alternative, rodenticides would not be used island-wide to eradicate mice 

on Sand Island, except for targeted control with the less toxic AGRID3. Since the rodenticide 

AGRID3 used under the no action alternate is not known to be harmful to birds, there would be 

no adverse effects to Laysan ducks under the no-action alternative from the use of this 

rodenticide. However, any adverse impacts of predatory mice to nesting Laysan ducks, eggs, and 

their young would continue. Mice could also be competing with ducks for invertebrate food 

resources and mice are known to be a seed predator on Eragrastis spp., and important grass and 

plant cover for Laysan ducks. Therefore, any negative effects on Laysan ducks from the presence 

of the mice would continue under the no-action alternative. 
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3.3.6.8.3 Probable Impacts: Preferred Alternative 

Primary and Secondary Exposure 

Initial tests at sites on MANWR where non-toxic bait piles were put out and monitored, indicated 

that Laysan ducks would readily consume bait pellets. Thus, there is a clear primary route of 

exposure to the rodenticide as it is assumed they would consume bait. Since the ducks also 

consume invertebrates, there is a likely secondary exposure. The consequence of that exposure is 

presumed to be substantial and without mitigation, a large number of individual ducks present on 

the island during the eradication would very likely succumb to the toxic effects of the 

rodenticide. Therefore, reducing or eliminating the pathways of exposure would be a key 

mitigation strategy as described in the minimization and mitigation measures below. 

A female Laysan duck’s average weight during incubation is approximately 1.1 lbs. (500 g). The 

lethal dose (LD50) of brodifacoum for birds is 4.1 x 10-6 oz./lb. (0.26 mg/kg). This is the dose 

the dosage (D) of brodifacoum that is likely to be lethal (L) to 50% of birds ingesting the toxin. 

For primary exposure to the rodenticide, at an average weight of 1.1 lbs. (500 g), an individual 

duck would need to ingest only 5 bait pellets to receive a potential lethal dose of brodifacoum. 

For secondary exposure, an individual duck would need to ingest 1.5 oz. (42.6 g) of 

contaminated invertebrate prey, which would be 57.5% of a bird's daily food intake (Table 3.16). 

Therefore, based on Laysan duck feeding habits, primary and secondary exposure to the 

rodenticide are both likely sources of mortality. Thus, without mitigation, the impact could be 

very high to a significant proportion of the Laysan duck population. Without mitigation 

measures, the worst-case scenario is that the entire population on Sand Island could be at risk of 

mortality. However, birds that remain on Eastern Island would not be exposed to the bait and 

have little likelihood of being exposed to any contaminated invertebrate prey. Setting aside the 

worst-case scenario, using the maximum population estimate of 596 ducks for MANWR, it is 

possible that 20-80% (119-477 birds) of the population could be at risk from primary or 

secondary poisoning without mitigation. This range was derived from mortality data of 

shorebirds from the Palmyra rat eradication project (USFWS 2011, Pitt et al. 2015), other small 

mammal eradication projects documenting mortality to waterbirds (Pierce et al. 2008, Morton et 

al. 2002), and a worst-case mortality rate of 80% reported from a study of passerine mortality 

from an island rat eradication project using brodifacoum (McClelland 2002). Other instances of 

high avian mortality from rodent eradication projects include severe population impacts to ravens 

on Langara Island, British Columbia (Howald et al 1999), 80-90% mortality of Stewart Island 

weka, a flightless bird in New Zealand (Eason and Spurr 1995), and mortality to bald eagles on 

Rat Islands, Alaska, where forty six bald eagles died, which exceeded the known population of 

22 bald eagles on the island (The Ornithological Council 2010). 

With the mitigation strategy proposed below, these estimated mortality rates to Laysan ducks 

would be greatly reduced. However, even with the mitigation strategy outlined below, there is a 

possibility that birds will remain undetected and therefore not captured for protection. The worstcase scenario would be the rate of 33% (197 ducks) of the maximum population accessible for 

capture during the breeding and molting season from March through September (Reynolds et al. 

2017) would not be captured. If all these 197 ducks ingested more than 5 pellets or consumed 

prey with enough brodifacoum to deliver a lethal dose, a loss of 33% of the maximum population 

of Laysan ducks at Midway could occur. However, due to the extended period of planned 
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capture attempts, it is likely that individual birds would be detectable before or after breeding 

and molt in many cases, and capture rates would be higher than 33%. 

Operational Hazard and Disturbance (Bird Strike and Noise/Human Disturbance) 

Since Laysan ducks are more likely to walk than fly and freeze when disturbed rather than flush, 

they are at a very low risk for collision with the helicopter during bait drop operations. In 

addition, Laysan ducks molt all of their feathers at the same time and individuals are incapable of 

flight between July and August for males and between July and October for females. Therefore, 

many individuals would naturally be incapable of flight during the bait drop period in July and 

August. As part of the mitigation to protect this species, a significant number of birds would be 

captured and kept in captivity during the bait drop period, thus protecting them from possible 

helicopter collisions, disturbances from helicopter noise and humans distributing bait, and 

accidental trampling of eggs or chicks from distributing bait by hand broadcast methods. In 

addition, Laysan ducks are accustomed to human presence on MANWR and can be approached 

within a few feet before being disturbed. 

We expect there to be some additional impact to Laysan ducks should the need arise to 

implement the rapid response portion of the refuge’s biosecurity plan and during implementation 

of the project monitoring plan. A biosecurity plan has been in place on MANWR for many years 

and any additional bio-security measures would only occur if there was a new incursion of a nonnative species. Biosecurity measures enacted would include rapid response to an incursion by 

non-native invasive species and implementing the monitoring plan would include follow-up 

observations (cameras on nests, radio-telemetry) and sample collecting (see Appendix A and B). 

Potential impacts such as flushing ducks off their nest and trampling of vegetative cover could 

occur with the additional human disturbance. Given the mitigation measures that will be in place 

to protect Laysan ducks, we expect any additional impacts to be minor and short-term. 

Implementing the biosecurity plan is only expected to have beneficial effects to Laysan ducks. 

Mitigation

The Laysan duck presents a complex mitigation challenge for the Midway Seabird Protection 

Project. They are non-migratory, year-round resident species that are relatively abundant across 

MANWR, and regularly fly between Sand Island and Eastern Island. Thus, the only effective 

mitigation and minimization strategy is to prevent the exposure of the ducks to rodenticide either 

through live-capture and holding ducks on Sand Island or to capture and temporarily translocate 

the birds to another island such as Eastern Island, until the risk period passes. The population of 

Laysan ducks on MANWR is globally significant for the species, and a robust minimization 

strategy would need to be in place prior to implementation of the Midway Seabird Protection 

Project. The goal of the Laysan duck mitigation strategy is to ensure that Laysan ducks persist on 

MANWR after the mouse eradication. Thus, a robust and adaptive mitigation strategy with built 

in redundancy and monitoring to ensure that the mitigation is effective, and any uncertain or 

unexpected loss of ducks can be detected early, and before a significant portion of the population 

would be put at risk. 

With either risk minimization option, the ducks would then be released in a step-wise 

progression when bait pellets are no longer available (degraded), which is anticipated to be 

approximately 30 days (Pitt et al. 2015, Alifano et al. 2012), when primary exposure risk is 
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negligible. Duck release decisions would also be based on the testing of biological samples for 

rodenticide residues collected post-application when those residues are considered relatively 

non-toxic and low risk. A stepwise release would allow for an effective and adaptive approach to 

the mitigation and will not commit the entire population to inherent uncertainty with temporal 

secondary exposure risk – brodifacoum residues will persist well past the bait pellet degradation 

window and will likely enter the Laysan duck food web (invertebrates) leading to multiple and 

repeated exposures over time. The temporal exposure risk and consequence of exposure is 

difficult to quantify a priori but is likely to have high consequence to some individuals for a few 

to many months post-bait application. Thus, an adaptive mitigation strategy outlined here offers 

the highest probability of ensuring persistence of Laysan ducks on Midway. Effectively, each 

release group is a sentinel for the next group of released animals, and through monitoring for 

survivorship and other indicators, the mitigation team can either continue with the release of 

duck or halt the release and re-capture some individuals. 

Release of ducks from captivity in a step-wise progression would increase the probability of 

successfully limiting the exposure of all captive held ducks to remaining bait pellets (primary) 

and to rodenticide residues (secondary). The longevity of bait pellets among habitats can be 

markedly different, with the rate of pellet degradation dependent on many factors including air 

temperature, light, humidity, rainfall, and the presence of scavengers, molds, and soil microbes 

that potentiate degradation. For example, the bait proposed in this EA is formulated for use in 

dryer sites, therefore any significant rainfall will cause it to dissolve. Based on the Midway bait 

trials, pellets were still found on the ground by the monitoring team seven days post-application 

(USFWS unpublished). The detection time of brodifacoum residues in biological samples postapplication can vary; Pitt et al. (2015) detected residues at 30 days and Rueda et al. (2016) at 773 

days. For the purposes of this EA, the variability of pellet and residue persistence, and the 

possibility that residues may have consequences for Laysan ducks well past what we anticipate, 

is acknowledged.

Mitigation measures discussed in this EA to minimize rodenticide exposure to Laysan ducks 

include avoiding aerial broadcast near wetlands and open water bodies by hand broadcasting in 

these areas. The proposed approach for minimizing, reducing, and avoiding exposure is to 

capture as many adults and ducklings as possible starting in March of 2019 to allow more time 

for capture during the period of laying, incubation, brood rearing, and molt when the birds are 

much more difficult to find (Reynolds et al. 2017). Incubation varies from December to July 

(Reynolds et al. 2007); the location of nests with eggs will be marked and monitored for capturehold post-hatching. Mitigation measures include: 

• Live capture and hold 50 male and 50 female ducks in captivity on Sand Island to 

insure a local population survival against worst case scenario. Prior to initiation of 

bait application, these birds would be transferred to Eastern Island and held until they 

molt their flight feathers. Once new primaries and secondaries are grown and clipped, 

the birds will be released on Eastern Island. The size and number of holding pens and 

aviaries used on Sand and Eastern Islands will be dictated by the number of ducks 

caught. A holding pen for a pair of adult ducks might consist of a shade cloth 

enclosure that measures 100 square feet (9.3 square meters) (Reynolds and Klavitter 

2007). 
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• Once the aviary capacity of 100 ducks is reached all additional birds will be captured, 

marked with field readable bands, have their flight feathers clipped, and translocated 

to Eastern Island. Birds on Eastern Island would be monitored for flight feather 

regrowth and re-captured if their molt status indicates they will soon become flighted. 

Teams will also monitor behavior at the various artificial water sources and 

supplemental feeding stations necessary to support the free-range population. 

• Eastern Island birds will have access to supplemental food, water, and cover 

resources, spread widely enough across the island to minimize agonistic behavior and 

to ensure all birds have access to food. 

• Avicultural staff will camp on Eastern to care for the birds in the aviary and to 

monitor the free-living birds until all are released and flighted again and when it is 

safe for the birds to return to Sand Island based on monitoring of rodenticide pellet 

availability based on observations and biological samples collected post-application. 

• Capture efforts will continue on Sand Island throughout the bait application period 

and any ducks not captured for hold-release, subsequently exposed to the rodenticide, 

and demonstrating signs of toxicosis, would be captured and treated with the antidote 

Vitamin K by a veterinary professional to offset the negative effects of the 

rodenticide. Ducks would be held in temporary holding pens under observation and 

any decision-making would occur based on the duck’s on-going health prognosis. 

• Step-wise release of captive ducks after final bait application, whereby a few birds 

would be released back to Sand Island and observed for any signs of mortality or 

other signs of anticoagulant exposure (hunkered posture, puffed up wings, blood from 

nares, moribund). The first ducks would be released 30 days after the final bait 

application or when bait pellets are no longer available. Monitoring of released birds 

should include radio-tagging sentinels to aggressively track over time, using 

information gleaned for deciding when next batch of ducks should be released. 

• Invertebrate prey species on Sand will be collected at intervals after the final bait 

application and brodifacoum residues will be measured to assess when those residues 

are relatively non-toxic. The LD50 of brodifacoum for mallards is 4.1 x 10-6 oz./lb. 

(0.26 mg/kg) (Ross et al. 1980, USEPA 1991). Residue levels considered relatively 

non-toxic to the Laysan duck are approximately <0.12 ppm (Daniels 2013). 

An interdisciplinary team of scientist experienced with Laysan ducks has been formed to consult, 

test, and oversee the implementation of a robust minimization and mitigation plan. Based on 

capture success rates in 2017 on MANWR, it is likely that the majority of birds would be 

captured and held in captivity or released on Eastern island until risk of primary and secondary 

exposure to the rodenticide has passed, thus reducing the number of birds at risk on MANWR. 

Using a combination of captive care and wing clipping and release will increase the chances of 

survival for the greatest number of ducks. Laysan ducks are upland nesters, and subject to 

ground disturbance activities; if hand broadcasting of bait requires ground-based personnel to 

traverse across or apply bait in Laysan duck nesting habitat on Sand Island, they would be 

instructed to remain vigilant for Laysan duck nests and call in the capture team if one is detected. 

The location of nests with eggs will be marked and monitored for capture and hold posthatching. 
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To implement any of these mitigation strategies would require USFWS-Refuges to consult under 

Section 7 of the Endangered Species Act. Any proposal must have no net negative impact to this 

species. The overall goal would be to maintain a healthy population of ducks on MANWR 

during and after the mouse eradication. Since the Laysan duck is also a ground nesting species, 

the removal of mice would likely contribute to maintaining Laysan ducks on MANWR. 

However, short-term adverse impacts are likely even with minimization and mitigation measures 

in place. However, the founding population of Laysan ducks on MANWR was small and this 

species can reproduce quickly. The initial introduced population on MANWR in 2004 was 42 

birds and in 6 years this population grew more than 15-fold to 661 birds. In summary, with the 

implementation of the mitigation plan described above, there is likely to be short term adverse 

impacts to the population of ducks on Sand Island, but the population should recover quickly, 

and thus the action is not expected to have long-term adverse effects to the Pacific population. In 

addition, the populations on Laysan Island and Kure Atoll would not be affected. 

3.3.6.9 Land Birds 

3.3.6.9.1 Existing Conditions 

Three non-native landbird species are known to breed at MANWR: the Atlantic canary (Serinus 

canaria), the common myna (Acridotheres tristis), and the cattle egret (Bubulcus ibis) which is 

discussed in the next section. Both the Atlantic canary and the common myna are at risk of 

poisoning as they are present all year-round on Sand Island. Therefore, the timing of the 

rodenticide application is not a viable mitigation option. 

The Atlantic canary is known worldwide simply as wild canary and is a small passerine bird in 

the finch family, Fringillidae. It is also called the island canary, canary or common canary. It is 

native to the Canary Islands, the Azores, and Madeira. Wild birds are mostly yellow-green, with 

brownish streaking on the back. The wild Atlantic canary can range from 3.9 to 4.7 in (10 to 12 

cm) in length, with an average weight of around 0.53 oz. (15 g). The breeding population, which 

is confined to Europe, is estimated to number 1,500,000 to 2,520,000 pairs, which equates to 

3,000,000-5,050,000 mature individuals (BirdLife International 2016b). This species is often 

kept as a pet and is referred to as the domestic canary. Selective breeding has produced many 

varieties which differ in color and shape. The species is widely kept in captivity in most areas of 

the world and is also widely used in scientific research. There are no known significant threats to 

this species (BirdLife International 2016b).

Island-wide monthly avian surveys, conducted from June through September 2017, counted 502

to 3,985 canaries on Sand Island (Figure 3.9). Using the maximum count of 3,985 birds from 

July 2017, the MANWR Atlantic canary population represents less than 0.078% of the global 

wild population. 
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Figure 3.9 Results of island-wide monthly avian surveys conducted from June through 

September 2017 for land birds

Source: USFWS (2017)

For the Atlantic canary, a cup-shaped nest is built 3 to 20 feet (1–6 m) above the ground in trees 

or bushes. Nests are made of twigs, grass, moss and other plant material and lined with soft 

material. Eggs are laid between January and July in the Canary Islands. A clutch contains 3 to 4, 

or occasionally 5, eggs, and 2-3 broods are raised each year. The Atlantic canary typically feeds 

in flocks, foraging on the ground or amongst low vegetation. It mainly feeds on seeds such as 

those of weeds, grasses and figs. It also feeds on other plant material and small insects (Snow 

and Perrins 1998). 

In 1909, D. Morrison, superintendent in charge on Midway Island, purchased a mated pair of 

canaries from sailors on a ship in Honolulu Harbor. He brought them to Midway and kept them 

separate for 8 months until he put them in a breeding cage in January 1910. Soon after this, 

additional birds were brought from Hawaii and all birds were released on MANWR. By the end 

of 1910 they were breeding on Sand Island in the Casuarina trees and by 1922 there were 

approximately 1,000 canaries at Midway (Fisher 1949). 

The common mynas native range covers a large swath of south and central Asia, from 

Turkmenistan eastward through all countries of the Indian subcontinent, including India, 
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Pakistan, Nepal, Bangladesh, Bhutan, Sri Lanka, and Maldives. It also exists in much of 

southeast Asia south to Singapore. The species has been introduced and established in many 

other parts of the world (Kannan and James 2001). It is also abundant in urban areas of the 

Hawaiian Islands. It is one of the most common and most widespread avian species in all of the 

human-inhabited islands. Sexes alike, but male median weight of 4.5 oz. (126.5 g) is slightly 

larger than the female median weight of 4.0 oz. (113.5 g). Baker et al. (1999) estimated the 

population on MANWR in 1996 to be 750-850 individuals. Island-wide monthly avian surveys, 

conducted from June through September 2017, counted 278 to 490 birds for this species on Sand 

Island (see Figure 3.9). Using the maximum count of 490 birds from August 2017, the MANWR 

common myna population represents an insignificant proportion of the global population. 

In the Hawaiian Islands, the common myna nests in palms and trees. They are also known to nest 

in any place that will hold a large pile of leaves and twigs, including, air-conditioners, drain 

pipes, open-ended steel rafters, traffic lights, and under eaves of buildings, etc. (Kannan and 

James 2001). 

The common myna feeds while on ground and in trees and is omnivorous. The primary diet 

consists of fruits, grain, insects, and grubs. Its diet can also include kitchen scraps, tidbits from 

refuse dumps, bird eggs, small animals (young mice, frogs, lizards, crabs), and flower nectar. It 

has also been recorded to prey on seabird eggs including those of the wedge-tailed shearwaters in 

the Hawaiian Islands (Byrd 1979), terns (Sterna spp.) and noddies (Anous spp.) in Fiji and the 

Seychelles, and the eggs of gulls (Larus spp.) in New Zealand (Kannan and James 2001). 

3.3.6.9.2 Probable Impacts: No Action Alternative 

Under the No Action Alternative, limited mouse control would continue using the less toxic 

AGRID3 rodenticide. Therefore, there would be no effects to the Atlantic canary or common 

myna under the no-action alternative since there are no known adverse effects to birds from the 

use of AGRID3. Any potential predation of seabird eggs by the common myna would continue. 

3.3.6.9.3 Probable Impacts: Preferred Alternative 

Primary and Secondary Exposure. 

The data in Table 3.17 indicate that both the Atlantic canary and the common myna would be at 

risk of primary and secondary poisoning from brodifacoum, since birds would only need to eat a 

fraction of their normal daily food intake of bait to receive a lethal dose. For a primary pathway, 

1-2 pellets of bait (0.03 to 0.07 oz. [1 -2 g]) containing 0.025 mg of brodifacoum each, if 

ingested, would be enough to kill an individual canary or myna bird (Table 3.17). For secondary 

toxicity from consuming invertebrate prey, it would only take 18.1% and 36.5% of their daily 

food intake to reach a lowest lethal dose for the canary and myna bird respectively (Table 3.17). 

McClelland (2002) reported that 80% of fernbirds (Bowdleria punctata wilsoni), a warbler that 

forages on invertebrates, disappeared from a 74 ac (25ha) 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. 

In summary, brodifacoum would present a lethal risk to the Atlantic canary and common myna. 

Based on the above data, it would be possible that 996 to 3,188 (25-80% of the MANWR 
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population) Atlantic canaries and 122 to 392 (25-80% of the population) common mynas could 

be killed by either primary or secondary poisoning from brodifacoum without mitigation. These 

numbers represent worst-case scenarios, based on maximum numbers of birds documented on 

Sand Island during the drop window and upper extremes of toxicity. 

Table 3.17 Primary and secondary toxicity of Brodifacoum to Passerines on MANWR 

Primary toxicity presented as grams of bait and secondary as grams of invertebrate prey. Active 

ingredient (mg) of brodifacoum is abbreviated as a.i. LD50 is that the dosage (D) of a toxin that is 

lethal (L) to 50% of animals of the species in laboratory tests. 

Species

Body 

Wt. 

(g) 

Daily Food 

Intake 

(g)(1)

Brodifacoum

LD50

(2)

(mg/kg)

LD50

(mg of 

a.i./bird) 

LD50

(3) (g 

of bait) 

LD502(4) (g 

of prey) 

%(5) of Daily 

Food Intake 

Atlantic 

canary

15.0 7.1 0.26 0.0039 0.156 1.3 18.1

Common 

myna

126.5 29.5 0.26 0.0329 1.316 10.85 36.5

Notes: 

1. Daily food intake calculated from allometric equation (Bird Feeding Rate = 0.059 x (W 0.67) (EPA 1995).

2. LD50 of brodifacoum based on mortality of mallard ducklings at the lowest dose, 0.26 mg/kg body weight = 0.026 mg/g (Ross et al. 1980, 

EPA 1991).

3. This is also the number of bait pellets that would need to be consumed to be lethal to 50% of the animals.4. Cockroach contamination based 

on highest reported value of 3.05 mg/kg = 0.00305 mg/g (Pitt et al 2015).

5. Calculated as LD502 grams of prey/daily food intake (g).

Operational Hazard (Bird Strike and Noise/Human Disturbance) 

It would be unlikely ground operations associated with the Preferred Alternative would impact 

either the Atlantic canary and common myna. Both species either exclusively or preferentially 

nest in trees or shrubs, so trampling of nests would not be a concern. Helicopter operations have 

the potential to disturb passerines, but since planes land and take off from Sand Island regularly, 

this disturbance would be minor and might cause birds to temporarily flush from their locations. 

It would also be unlikely that helicopter operations would cause any collision hazard with these 2 

species. During the helicopter operations for the Palmyra rat eradication, all helicopter collisions 

were with seabirds and shorebirds. One canary was recorded killed by aircraft at Henderson 

Field from 2004-2010. 

The potential mortalities that would be expected to result from the Preferred Alternative 

represent insignificantly small numbers relative to overall global populations of both these 

species, but the Preferred Alternative would have a moderate negative affect for each of the Sand 

Island populations. Adverse effects would be readily detectable and localized with measurable 

consequences to the local population, but not readily detectable or measurable beyond the 

immediate area of impact. Mitigation measures would only be instituted for the Atlantic canary 

due to its cultural importance. Indirect effects from the Preferred Alternative would not be 

expected. 

We expect there to be no additional impacts to the Atlantic canary and common myna should the 

need arise to implement the rapid response portion of the refuge’s biosecurity plan and during 

implementation of the projects monitoring plan. A biosecurity plan has been in place on 

MANWR for many years and any additional bio-security measures would only occur if there was 
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a new incursion of a non-native species. Biosecurity measures enacted would include rapid 

response to an incursion by non-native invasive species and implementing the monitoring plan 

would include follow-up observations and sample collecting (see Appendix A and B). We expect 

such additional ground-based human activities would not impact tree-dwelling species like the 

Atlantic canary and common myna. 

Mitigation

Atlantic canaries on Sand Island would be caught and kept in aviaries during the bait drop 

period, and not released until post-monitoring of brodifacoum residues show decreased chance of 

primary or secondary exposure. A combination of mist-nets and walk in traps would be used to 

capture a subset of the resident flock adequate to protect the genetic variability of the population. 

However, this activity would receive a lower priority than protection of Laysan ducks or 

migratory shorebirds. In a capture test in 2017, 4 birds were caught in 2 morning hours of mistnetting. Walk-in traps have not been tested, but are known to be effective in trapping ground 

feeding passerines. The Atlantic canary is easy to hold in captivity, and any mortality of birds 

while being held should be minimal. After release, populations should grow quickly since this 

species can raise 2-3 broods each year, with the average nest containing 3 to 4 eggs. 

3.3.6.10 Cattle Egrets

3.3.6.10.1 Existing Conditions 

Invasive non-native cattle egrets (Bubulcus ibis) have colonized MANWR by island hopping 

through the Northwestern Hawaiian Islands. They have been documented breeding on Eastern 

Island, and the cattle egret regularly use both Eastern and Sand Island. Island-wide monthly 

avian surveys, conducted from June through September 2017, counted 0 to 83 birds for this 

species on MANWR (Figure 3.9). The European population is estimated at 76,100-92,300 pairs, 

which equates to 152,000-185,000 mature individuals (BirdLife International 2015). The global 

population is larger than this, although no estimate is available. Using the maximum count of 83 

birds from September 2017, and the estimate of the minimum number of individuals in Europe, 

the cattle egret population on MANWR represents 0.05% of the European population. 

The population of this species is actively managed on MANWR due to their predatory behavior 

on nesting seabirds. The USFWS has issued a federal migratory bird control order at 50 CFR 

21.55 which allows for the take of Cattle Egrets (and Barn Owls) on the main Hawaiian Islands, 

the Northwestern Hawaiian Islands, and on Midway, which authorizes the Service and personnel 

from certain other agencies to lethally take cattle egrets to protect native species without a permit 

(50 CFR 21.55 [or 82 FR 34419]). Prior to this Control Order, control operations were 

authorized by permit, and from March to August in 2017, MANWR staff destroyed 80 egret 

nests, treated 303 eggs, and dispatched 10 chicks. 

Since they only breed on Eastern Island, and a control program is already underway for this 

invasive species, helicopter disturbance or disturbance from ground personnel is not considered 

an issue. 
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3.3.6.10.2 Probable Impacts: No Action Alternative

Under the No Action Alternative, Sand Island’s mouse population would not be the subject of an 

island-wide eradication project, but limited mouse control efforts would continue using the less 

toxic AGRID3 to protect nesting seabirds and for human health and safety. Therefore, there 

would be no effects to the cattle egret under the no-action alternative. 

3.3.6.10.3 Probable Impacts: Preferred Alternative 

Primary and Secondary Exposure 

The likelihood of primary exposure to rodenticides would be very low. However, the egret is a 

predator species. These birds would be expected to consume small mammals, birds, lizards, and 

invertebrates. They would also likely scavenge mice or other animals that succumbed to 

rodenticide. Because of their diets, secondary exposure to the rodenticide could be a risk to these 

birds. This species would need to eat 52.0% or more of their normal daily food intake to receive 

a potential lethal dose of brodifacoum by consuming invertebrates. For mammalian prey, only 

0.52 oz. (14.9 g) of contaminated prey needs to be consumed for a potential lethal dose to an 

individual, which is only 24.6% of their estimated normal daily food intake (Table 3.16). 

Therefore, mortality from secondary exposure of this species could be high. However, although 

it was estimated that more than 20,000 rats were killed during the eradication project on 

Palmyra, only a few dozen rat carcasses were found during the project after the bait was applied 

because the animals often returned to their burrows before they died. (Pitt et. al. 2015). It is 

expected that this same result would occur on Sand Island, especially since mice are significantly 

smaller than rats and thus more difficult to detect. Thus, there may be few carcasses available for 

cattle egrets to find and consume. 

Based on the above data, it is possible that 20-80% of the egret population (17-67 birds) would 

be killed or receive sub-lethal doses by consuming brodifacoum intoxicated prey. There would 

also be a potential that brodifacoum would persist in the environment for at least a year and have 

impacts beyond the proposed operational window (Rueda et al. 2016; Pitt et al. 2015), such that 

any returning egrets to Sand Island would be at risk from secondary poisoning. 

Operational Hazard (Bird Strike and Noise/Human Disturbance) 

It would be unlikely ground or air operations would impact cattle egrets. Egrets are not known to 

breed on Sand Island and this species does not nest on the ground. Air operations have the 

potential to disturb roosting egrets, but observations from field personnel during pre-project 

surveys indicate this disturbance would be minor and could cause birds to temporarily flush from 

their location. In addition, egrets do not fly very high, and thus have a negligible risk for 

collision potential with the helicopter. Calculations of mortality are based on the maximum 

number of birds observed in 2017. The potential mortalities that would be expected to result 

from Preferred Alternative represent insignificantly small numbers relative to overall populations 

of this species. 

We expect there could be some additional impacts to cattle egrets should the need arise to 

implement the rapid response portion of the refuge’s biosecurity plan and during implementation 

of the projects monitoring plan. A biosecurity plan has been in place on MANWR for many 

years and any additional bio-security measures would only occur if there was a new incursion of 
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a non-native species. Biosecurity measures enacted would include rapid response to an incursion 

by non-native invasive species and implementing the monitoring plan would include follow-up 

observations and sample collecting (see Appendix A and B). Potential impacts such as causing 

birds to flush could occur from the additional human disturbance although this bird is a nonnative invasive species. However, we expect any additional impacts to be minor, localized, and 

short-term.

Mitigation

No mitigation measures are planned for this species since a lethal control program is in place on 

MANWR. 

3.3.6.11 Terrestrial Mammals

3.3.6.11.1 Existing Conditions 

No native terrestrial mammals are known from MANWR. No domestic animals or livestock are 

present on the island. Rats were previously documented on the 3 islands but were successfully 

removed and the islands were declared rat free in 1997 (USFWS, Unpublished b). Personnel 

from Island Conservation were unable to confirm the presence of rats using remote cameras and 

bait on either Sand or Eastern Island. If somehow rats have been re-introduced to Sand Island 

and are present in low numbers at the time of the eradication, the design of the mouse eradication 

would eliminate rats as well. House mice are presently the only known non-native mammal on 

the island. 

3.3.6.11.2 Probable Impacts: No Action Alternative 

Under the No Action Alternative, Sand Island’s mouse population would not be the subject of an 

island-wide eradication project, but limited mouse control efforts would continue using the less 

toxic AGRID3 to protect nesting seabirds and for human health and safety. Therefore, impacts to 

the islands ecosystem, including negative impacts to vegetation and seabird populations, would 

continue. 

3.3.6.11.3 Probable Impacts: Preferred Alternative 

Under Preferred Alternative, every mouse on the island would receive a primary or secondary 

exposure to the rodenticide brodifacoum and the house mouse would be eradicated from Sand 

Island. 

3.3.6.12 Herpetofauna 

3.3.6.12.1 Existing Conditions 

The only known terrestrial reptiles or amphibians present on Sand Island are non-native and 

include the House Gecko (Hemidactylus frenatus), Indo-Pacific Gecko (Hemidactylus garnotii), 

Mourning Gecko (Lepidodactylus lugubris), Penny Skink (Lampropholis delicata), and Blind 

Snake (Ramphotyphlops braminus). 
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3.3.6.12.2 Probable Impacts: No Action Alternative 

Under the No Action Alternative, Sand Island’s mouse population would not be the subject of an 

island-wide eradication project, but limited mouse control efforts would continue using the less 

toxic AGRID3 to protect nesting seabirds and for human health and safety. Therefore, there 

would be minor effects to any herpetofauna under the no-action alternative. Any negative effects 

of mice on herpetofauna populations on Sand Island would continue. 

3.3.6.12.3 Probable Impacts: Preferred Alternative 

Primary Exposure 

No mortality of herpetofauna associated with the use of brodificoum has been recorded to date, 

and one study indicates reptiles appear to be relatively insensitive to anticoagulant rodenticides 

(e.g., brodifacoum) compared to birds or mammals (Weir et al. 2015). This finding is supported 

by evidence from New Zealand, where brodifacoum has been extensively used in areas occupied 

by a wide range of herpetofauna, with no reports of reptiles or amphibians poisoned with 

brodifacoum (Eason and Spurr 1995). However, on Round Island Mauritius, Telfair’s skinks 

(Leiolopisma telfairii) that ate rain-softened brodifacoum pellets broadcast in an eradication 

project were found dead (Merton 1987 in Eason and Spurr 1995). Telfairs’s skinks are known to 

eat seeds and fruit. Analyses of the skink carcasses revealed brodifacoum concentrations in the 

liver of 9.6 x 10-6 oz./lb. (0.6 mg/kg). Neither the Penny skink nor the house gecko would be 

likely to consume pellets. Both species eat invertebrates and the gecko also consumes sap or 

nectar.

Because of the apparent relative insensitivity of reptiles to anticoagulants, it would be unlikely 

skinks, geckos or snakes would be killed by rodenticide poisoning. However, the situation with 

brodifacoum is less clear compared to diphacinone. However, when the above data are taken in 

total, the risk of killing skinks, geckos or snakes from brodifacoum poisoning would be low. If 

any mortality were to occur, population level effects are highly unlikely. 

Secondary and Tertiary Exposure 

While negative impacts to the skinks, geckos or snakes are unlikely, it is expected that these 

species would consume invertebrates that have fed on the pellets, which would then pose a 

tertiary poisoning risk to other animals that eat these animals as part of their diet. Because of 

reptiles’ relative insensitivity to anticoagulant rodenticide, they may be able to accumulate 

relatively high sub-lethal residues. On Pinzón Island, native lava lizards (Microlophus 

duncanensis) were found to maintain brodifacoum residues in their liver more than 800 days 

after the last application of a rat eradication project (Rueda et al. 2016). This resulted in the 

deaths of several raptors. 

The Preferred Alternative would be unlikely to affect the herpetofauna on the island, and there 

are no mitigation measures proposed to reduce this impact. Any impacts would likely be minor, 

localized, and of little consequence to the populations. 

We expect there to be some additional impact to herpetofauna should the need arise to 

implement the rapid response portion of the refuge’s biosecurity plan and during implementation 

of the projects monitoring plan. A biosecurity plan has been in place on MANWR for many 
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years and any additional bio-security measures would only occur if there was a new incursion of 

a non-native species. Biosecurity measures enacted would include rapid response to an incursion 

by non-native invasive species and implementing the monitoring plan would include follow-up 

observations and sample collecting (see Appendix A and B). Potential impacts such as trampling 

vegetation or the crushing of animals underfoot could occur with the additional human activities 

along with collection of some animals to test for brodifacoum residues; although these species 

are non-native. However, we expect any additional impacts to be minor, localized, and shortterm.

3.3.6.13 Terrestrial Invertebrates

3.3.6.13.1 Existing Conditions 

Midway’s terrestrial invertebrate fauna have been greatly altered by more than a century of 

human occupation. The majority of what we know about the terrestrial invertebrate community 

has focused on describing the species assemblage on Midway, and much of that assemblage 

work has focused on Arthropoda, and to a lesser extent Mollusca (Conant et al. 1983, Nishida 

and Beardsley 2002). Five hundred and fifty-two species of terrestrial invertebrates have been 

recorded thus far, of which 81% are introduced (Nishida and Beardsley 2002), and fill a wide 

range of habitat and functional niches in Midway’s terrestrial ecosystem, as well as food 

resources for some of the avifauna. 

The number of arthropod taxa observed on the atoll has grown rapidly over the past century and 

is speculated to have been aided by an increase in plant diversity and ease of migration (Nishida 

and Beardsley 2002). In the main Hawaiian Islands, Shiels et al. (2013) found that over half the 

diet of feral mice consisted of arthropods, with caterpillars making up the vast majority of the 

arthropod prey (~94%), followed by ants, fly larvae, burrowing bugs, and spiders. These results 

were in contrast with larger rodents (rats) at the same locations, which fed on a wider variety of 

arthropods, including cockroaches, Katydids, and honey bees (Shiels et al. 2013). 

3.3.6.13.2 Probable Impacts: No Action Alternative 

Under the No Action Alternative, Sand Island’s mouse population would not be the subject of an 

island-wide eradication project, but limited mouse control efforts would continue using the less 

toxic AGRID3 to protect nesting seabirds and for human health and safety. Therefore, there 

would be minor effects to terrestrial invertebrates under the no-action alternative. Any negative 

effects of mice on invertebrate populations on Sand Island would continue. 

3.3.6.13.3 Probable Impacts: Preferred Alternative 

Terrestrial invertebrates can accumulate anticoagulant rodenticide residues. It has been suggested 

that anticoagulant rodenticides, such as diphacinone and brodifacoum, are not likely to affect 

invertebrates, because their blood clotting mechanisms are different from those of vertebrates 

(Shirer 1992 in Eason and Spurr 1995). However, the toxicity of anticoagulants may differ across 

groups of invertebrates. Brodifacoum is highly toxic to Daphnia magna, an aquatic invertebrate, 

with an EC50 of 0.98 ppm after 48 hours (USEPA 1991). Most hard-bodied terrestrial 

invertebrates (e.g., crabs, cockroaches, beetles) appear to be relatively insensitive (Booth et al. 

2003, references therein; Morgan et al. 1996; but see Pitt et al. 2015). There is evidence that 
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brodifacoum may be more toxic to soft-bodied terrestrial invertebrates than hard-bodied species 

(Booth et al. 2003). In a laboratory study, 2 species of land snail (Pachnodus silhouettanus, 

Achatina fulica) died in 72 hours when exposed to doses ranging from 3.5 x 10-7 oz. to 1.1 x 10-6

oz. (0.01 to 0.04 mg) (Gerlach and Florens unpubl., Booth et al. 2003). In another lab study, 

brodifacoum equivalent to 8.0 x 10-5 to 1.6 x 10-4 oz./lb. (5 to 10 mg a.i./kg) was found to cause 

100% mortality of earthworms (Apporectodea calignosa) (Booth et al. 2003). 

However, causing this level of mortality required grinding pellets and mixing them with the soil, 

a scenario that would be unlikely to occur in the field. In general, most invertebrate species are 

not known to be susceptible to toxic effects from the use of brodifacoum in the field (Booth et al. 

2003, Hoare and Hare 2006). 

Preferred Alternative would be unlikely to directly affect any terrestrial invertebrates on the 

island and there are no mitigation measures planned to reduce impacts to invertebrates. Removal 

of mice from Sand Island would eliminate mice predation on invertebrates, and thus potentially 

could have a beneficial effect to these species. 

We expect there to be some minor additional impacts to terrestrial invertebrates should the need 

arise to implement the rapid response portion of the refuge’s biosecurity plan and during 

implementation of the projects monitoring plan. A biosecurity plan has been in place on 

MANWR for many years and any additional bio-security measures would only occur if there was 

a new incursion of a non-native species. Biosecurity measures enacted would include rapid 

response to an incursion by non-native invasive species and implementing the monitoring plan 

would include follow-up observations and sample collecting (see Appendix A and B). Potential 

impacts such trampling of vegetation and soil could occur from the additional human disturbance 

along with the collection of some animals to test for brodifacoum residues. However, over 80 

percent of terrestrial invertebrates on MANWR are non-native. In summary, we expect any 

additional impacts to invertebrates to be minor, localized, and short-term.

3.3.6.14 Marine Fish 

3.3.6.14.1 Existing Conditions 

A total of 266 species of fish, including 7 pelagic species, have been recorded at Midway. Some 

of these species are rare or absent from the main Hawaiian Islands. Despite its low species 

diversity, Midway’s reef fish biomass is higher than in the main Hawaiian Islands, largely due to 

lower fishing pressures. Midway and its neighboring atolls have the highest rates of endemic reef 

fishes within the archipelago, with up to 52% of all fish observed being endemic. Many Midway 

species grow to larger than average size. All trophic levels are well represented, including jacks 

and 4 species of sharks. Several species of fish found elsewhere only in deep waters are found at 

shallow diving depths at Midway, including the endemic Hawaiian black grouper (hapu‘upu‘u). 

One alien algae, one alien fish, the blueline snapper (Lutjanus kasmira), and 4 alien marine 

invertebrate species are established at Midway as found in 2000- 2003 surveys. Incidental 

observations of 2 other introduced species, blacktail snapper (Lutjanus fulvus) and bluespotted 

grouper (Cephalopholis argus), have occurred at Midway in the last decade.
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A total of 111 species of reef fish were observed during the 2008 surveys at Midway. Ten 

families represent the majority of the species of reef fish at Midway: Acanthuridae, Kyphosidae, 

Scareidae, Mullidae, Pomacentridae, labridae, Carcharhinidae, lutjanidae, Holocentridae and 

Oplegnathidae. The Kyphosids, or chubs, and the Acanthurids, or surgeon fish and tangs, are the 

most abundant and represent the highest biomass. Parrotfish (Scaridae) represented the third 

largest contributor to total fish biomass. Reef fish biomass density was higher in the forereef 

environment compared to the backreef and lagoon, and was slightly higher in the south and 

southeast quadrants of the atoll. Of the larger bodied reef fish greater than 50 cm in length, the 

parrot fishes (family scaridae) were the most abundant, composing 44% of the individual reef 

fish counted, and had the highest biomass density at 33%. Acanthurids represented the highest 

biomass in the backreef and lagoon habitats, and was third to sharks and chub, in the forereef 

habitat. Large jacks (Caranx ignobilis) are also known to frequent the forereef and reef crest 

environments. 

3.3.6.14.2 Probable Impacts: No Action Alternative 

Under the No Action Alternative, Sand Island’s mouse population would not be the subject of an 

island-wide eradication project, but limited mouse control efforts would continue using the less 

toxic AGRID3 to protect nesting seabirds and for human health and safety. No bait would be 

used in the vicinity of the marine environment; therefore, there would be no effects to marine 

fish or the marine ecosystem under the no-action alternative. 

3.3.6.14.3 Probable Impacts: Preferred Alternative 

Primary Exposure 

The likely pathways for contamination of fish would be through primary and secondary 

exposure. A potential, but unlikely, pathway would be absorption through skin or gills (Empson 

and Miskelly 1999). Bait pellets dissolve quickly in the near shore environment, often within 15 

to 30 minutes, and the concentration of rodenticide in sea water would be at undetectable levels 

and would pose very low, if any risk to fish. In a study on the Island of Lehua, Hawaiʻi, of the 48 

species of fish documented to occur around the island, 29 were found to consume inert bait 

pellets; another 7 species made contact with the bait, but did not consume it (Mazurek 2015). In 

this trial with inert baits, pellets were applied at a rate equivalent to 653 lb./ac. (733 kg/ha), 

which is more than 10 times higher than the maximum rate proposed for this eradication project. 

In a similar trial, in New Zealand, 3 species of fish were seen to eat non-toxic baits (Empson and 

Miskelly 1999). 

A recent laboratory study by the USGS showed that black triggerfish (Rhinecanthus aculeatus), 

smallmouth bass (Micropterus dolomieu) and fathead minnows (Pimephales promelas) refuse to 

eat bait pellets containing diphacinone (USGS Columbia Environmental Research Center). 

However, during the second 2017 Lehua rat eradication effort, fish were caught from shore by 

line and hook baited with shrimp on the day of each bait application; fish were euthanized, and 

gut contents examined for signs of bait material and the pyranine biomarker fluorescence. Bait 

material and/or the biomarker were observed in specimens of pinktail triggerfish (Melichthys 

vidua), black triggerfish, stocky hawkfish (Cirrhitus pinnulatus), and blue-lined snapper. No 

evidence of bait consumption was found in blacktail snapper or blotcheye soldierfish (Myripristis 

berndti) caught (S. Siers, personal communication, USDA NWRC 2016). 
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When diphacinone (bait or a.i.) is administered by gavage, the fish rapidly regurgitate the 

material (R. Riegerix, personal communication, USGS/University of Missouri-Columbia 2016), 

which indicates that some fish species can detect and avoid bait containing diphacinone. Results 

from aquarium trials associated with the Kapiti Island, New Zealand rat eradication found similar 

results using brodifacoum (Empson and Miskelly 1999). Three species of fish, variable triplefin 

(Forsterygion varium, 24 individuals), spotty (Notolabrus celidotus, 30), and blue cod 

(Parapercis colias, 6) were presented with bait pellets containing 0.002% brodifacoum. Of the 

60 total fish, only 6 spotties were seen to eat the bait, with one dying from brodifacoum 

poisoning. Several fish died that did not eat the bait, and no brodifacoum residues were found in 

their livers. The authors speculated the fish may have absorbed the chemical through their skins 

or gills. When small quantities of brodifacoum bait entered the marine environment during aerial 

application operations on Anacapa Island and Isabel Island, Mexico, no marine organisms (fish 

or invertebrates) were observed to consume the bait (Howald et al. 2009, Samaniego-Herrera et 

al. 2014). However, in the Kapiti Island trials, 3 species of fish were seen to eat the non-toxic 

bait within 15 minutes of entering the marine environment (Empson and Miskelly 1999). 

In summary, some species of fish may feed on pellets on the day of application. Whether the 

consumption is abundant or prolonged enough to cause illness or mortality to some fish remains 

unknown. The rapid dissolution of unconsumed pellets in water would prevent the prolonged 

feeding on pellets. Given the relatively small amount of bait that would be expected to enter the 

marine environment, the rapid dissolution of pellets, and the fact that some fish appear to avoid 

eating bait pellets with active rodenticide, it appears consumption of rodenticide baits for some 

species of fish would be minor and unlikely to have adverse affects on their populations. 

Secondary Exposure 

Secondary exposure of fish to brodifacoum around Sand Island would be a potential risk. 

However, on the Anacapa Island rat eradication project, 6 species of intertidal organisms (fish 

and invertebrates) were sampled 15, 30, and 90 days post-application, and all samples tested 

negative for brodifacoum residues (Howald et al. 2009). In addition, 2 studies conducted in 

conjunction with the 2008 Mōkapu and 2009 Lehua rat eradication projects using diphacinone 

indicate that the risk would be extremely low (Orazio et al. 2009, Gale et al. 2008). Within days 

of the last aerial broadcast of diphacinone pellets, samples were collected of fish, invertebrates, 

and seawater, and none of the species sampled showed detectable levels of diphacinone in their 

tissues. However, brodifacoum residues have been found in fish tissues after rat eradications. A 

review of rat eradication projects using brodifacoum found marine residue monitoring and 

analysis had been conducted in 10 applications between 1997 and 2011 (Masuda et al. 2015). Of 

the 10 applications, 1 detected brodifacoum residues in fish. Two of 65 fish sampled had 

residues, with concentrations 0.026 and 0.092 ppm in the liver, which exceeded the 96 hour 

LC50 for rainbow trout (Oncorhynchus mykiss) (0.015 ppm) and bluegill sunfish (Lepomis 

macrochirus) (0.026 ppm) (USEPA 1991). Following the rat eradication on Palmyra Atoll, 

rodenticide residues were detected in all fish samples collected from the lagoon which included 

mullet fishes (Moolgarda engeli and Liza vaigiensis) and one puffer fish. Fish were found dead 

and collected opportunistically for this study (Pitt et al. 2015). Mullet fish contamination ranged 

from 0.058–1.160 ppm (mean=0.337 ppm) and the single puffer fish (family Tetraodontidae) 

sample had 0.438 ppm of brodifacoum in homogenized tissue.
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However, a number of factors will reduce the likelihood of marine secondary exposure around 

Sand Island relative to Palmyra including: (i) the shape of Sand Island has less coastline per acre 

of treated area; (ii) the much broader beaches with a lack of vegetaton on Sand Island and few 

coastal trees to block the view of the coastline by the helicopter pilot; (iii) the use of hand 

broadcast of bait in areas without beaches or with armouring on the shoreline and; (iv) greater 

lagoon flushing at MANWR because land doesn’t protect the lagoon as it does on Palmyra. 

The above examples demonstrate that marine fish can be contaminated during an aerial 

application of brodifacoum. However, it also demonstrates that this occurs only infrequently. It is 

also noteworthy that the very large amount of brodifacoum used on Palmyra Atoll at 75.6 lb./ac. 

(84.8 kg/ha) and 71.5 lb./ac. (80.1 kg/ha), for the first and second application respectively, was 

unprecedented, which likely influenced the available brodifacoum residues consumed by nontarget species. The bait density used for Palmyra was 10-16% higher than that proposed for Sand 

Island. Following the accidental brodifacoum spill in New Zealand, fish samples were collected, 

and only one individual fish had detectable rodenticide residues (Primus et al. 2005). However, 

this site had a higher energy coastline with greater wave action than that on MANWR. In the 

above cases involving brodifacoum, it is unclear whether the fish exposure was primary or 

secondary.

In summary, the main secondary exposure risk from anticoagulant rodenticides would be from 

the consumption of fish that had died or had recently ingested toxicants, and therefore contained 

a high level of toxin, or from contaminated invertebrates. If any fish do die from primary 

exposure, those carcasses may pose secondary hazard to other species that may consume them. 

However, animals that survive direct ingestion would rapidly metabolize (24-48 hrs) the vast 

majority of the toxin, and residues in liver (and far lower in muscle tissue) are likely to be too 

low to be biologically significant. 

Based on the above data, it would be unlikely that a sufficient quantity of brodifacoum would 

enter the water, or that the pellets would remain intact, in the environment, long enough to 

present an absorption or primary poisoning risk to any fish populations. In addition, the bulk of 

the reef around MANWR Island is not in close proximity to Sand Island. Therefore, although 

some reef fish near the island may be affected, the majority of the populations around the atoll 

would unlikely to be affected. Some individual fish may be at risk if they were to ingest pellets. 

The low levels of residues found are not likely to be biologically significant with respect to 

secondary exposure or bioaccumulation, especially in such a diffuse environment. It also would 

be unlikely that the rodenticide would contaminate sufficient prey of fish to pose a secondary 

poisoning risk to any fish populations. Therefore, it would be unlikely that Preferred Alternative 

would directly or indirectly impact any fish populations. Minor direct and indirect impacts may 

occur to some individual fish. Besides the multiple steps being taken to minimize bait pellets 

entering the marine environment (see below), there are no other mitigation measures proposed 

for marine fish.

We expect there to be no additional impact to marine fish from the implementation of the 

projects monitoring plan. Implementing the monitoring plan would include follow-up 

observations and sample collecting. Some game fish may be collected for the sampling of 

brodifacoum residues. Additional impacts to marine fish are not expected from implementation 

of the bio-security plan or monitoring plan since these activities will mostly occur in the 
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terrestrial environment (see Appendix A and B). Therefore, we expect no potential impacts to 

marine fish from the additional terrestrial human disturbance and the number of fish collected 

will be small. 

Mitigation

To minimize bait from entering the marine environment, prior to the application of bait pellets 

with rodenticide, the bait delivery system (bait bucket, controller, GPS units, and helicopter) 

would be tested and calibrated to ensure an accurate application rate. An onboard computer 

linked to a GPS and light bar would guide the pilot along pre-programmed flight lines over the 

island at a prescribed airspeed, which would facilitate application of bait over the terrestrial 

environment only. Aerial application of bait pellets would not occur during wind speeds in 

excess of 35 mph, or when heavy rains are forecast to occur within 72 hours. In addition, for 

areas near the shoreline, the bait hopper would be fitted with a deflector that spreads bait out to 

only one side (approx. 120° angle) to minimize bait application directly into the water. For 

shorelines where armoring is present and the shoreline is very narrow, spreading bait using handbroadcast methods would be used to the maximum extent practicable. Every reasonable effort 

would be made to minimize the risk of bait drift into the water; however, it is expected that a 

small amount of bait will enter the ocean. The pilot and on-the-ground observers would visually 

monitor the application of bait, and if a malfunction were detected, operations would cease until 

the problem is corrected. Lastly, bait would be applied at the lowest rate possible to achieve 

eradication, and any bait spills above a defined threshold would be collected and disposed of 

according to label instructions.

3.3.6.15 Coral 

3.3.6.15.1 Existing Conditions 

MANWR is one of the northernmost coral atolls in the world, presenting a unique opportunity to 

study the effect of colder waters on the growth, development, and ecology of coral reefs. Its 

neighbor, Kure Atoll, is the northernmost atoll in the world. MANWR drops off steeply outside 

the barrier reefs, making it possible to observe in a relatively small area the different organisms 

and communities associated with pelagic, reef crest, ocean facing reef slope, deep reef, and 

lagoon habitats. 

The lagoon is filled with dense networks of linear reticulated and circular reefs that trap sand 

washed over the northeastern reef rim. As in many atoll lagoons, sediments limit coral growth on 

Midway, except in the deeper central lagoon, where a modest amount of finger coral gardens still 

exists. Meadows of seagrass are common in the lagoon, as are rock-boring urchins, calcareous 

green algae, and brown turban algae. The deep southern ship channel between the ocean and 

lagoon was dredged during the World War II era and has substantially modified circulation and 

lowered lagoon water levels. Together with lagoon reefs, these changes reduced or blocked water 

circulation in much of the lagoon and created higher levels of turbidity. In 2000 and 2004, coral 

bleaching episodes were reported at Midway, as well as at the neighboring atolls of Kure, Pearl, 

and Hermes. Lagoon lobe and finger corals have declined during the past decade, although blue 

encrusting coral continues to thrive. 
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Massive spurs and grooves consisting mostly of coralline algae face the open ocean along the 

northwest to southwest perimeter reefs and protect the atoll from heavy wave action common 

during the winter months. These massive reefs offer evidence of the importance of coralline 

algae as a major reef builder in the far end of the Northwestern Hawaiian Islands. Corals on 

ocean-facing reef habitats are generally not as abundant compared to neighboring atolls to the 

southeast, but are common in a few sheltered reefs and especially on shallow back-reefs and 

lagoon pinnacles. High concentrations of the rock-boring urchin Echinometra are presently 

eroding much of the shallow perimeter reef crests dominated by coralline algae. Although not 

grazing corals directly, the sea urchins are hollowing out the dead interior skeletons of living 

lobe corals, and undermining other attached corals. 

A total of 32 species of stony coral have been recorded at Midway, mostly Pocillopora, Porites, 

and Montipora, plus one zoanthid soft coral, Palythoa. Blue encrusting coral tentatively 

identified as Montipora cf. turgecens occurs in spectacular formations in the lagoon and back 

reef habitats, and may be endemic to the Northwestern Hawaiian Islands. 

Coral cover around MANWR varies with both habitat and within region of the atoll. Hard coral 

cover was generally low island-wide, averaging around 2.45% and never exceeding 20%. The 

highest coral cover was generally located along several sections of the northern and eastern 

backreef, where coral assemblage was primarily composed of Montipora, Pocillopora, and

Porites spp. Mean coral cover was low inside the lagoon (6.6 ± 3.0%) and on the forereef (4.0 ± 

1.5%), while mean cover was moderately high in the backreef (32.3 ±14.2%) (NOAA CREP 

2008). Coral community structure varied both between and within habitats. Two northern 

backreef sites consisted of large encrusting colonies of 3 Montipora species. The eastern 

backreef site was characterized by scattered Porites lobata and Pocillopora heads. On the 

forereef, the western area was scoured and corals were quite depauperate, most likely due to 

strong wave action. The southern forereef south of Sand Island is composed largely of Porites 

sp., while the forereef south of Eastern Island is composed of mostly Pocillopora sp. The coral 

communities at 2 lagoon patch reefs, one in the southeastern portion, and the other in the 

southwest (MID-03 and MID-H11, Figure 3.10), were quite different with one dominated by old 

Porites compressa mounds (MID-03, Figure 3.10) and the other (MID-H11, Figure 3.10) 

consisting of scarce Pocillopora heads. 

Figure 3.10 Spatial Distribution of Benthic Cover and Coral Composition at NOAA 

CREP Rapid Ecological Assessment Sites at Midway in 2008 

Source: NOAA (2008)
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3.3.6.15.2 Probable Impacts: No Action Alternative 

Under the No Action Alternative, Sand Island’s mouse population would not be the subject of an 

island-wide eradication project, but limited mouse control efforts would continue using the less 

toxic AGRID3 to protect nesting seabirds and for human health and safety. No bait would be 

used in the vicinity of the marine environment; therefore, there would be no effects to corals or 

the marine ecosystem under the no-action alternative. 

3.3.6.15.3 Probable Impacts: Preferred Alternative 

Primary and Secondary Exposure 

As described above, a variety of corals inhabit the waters around MANWR, and there would be 

potential for these organisms to be exposed to rodenticide that inadvertently reached the marine 

environmental and dissolved in the water. However, the level of bait entering the nearshore 

environment would be very low, pellets would dissolve quickly in the nearshore environment, 

often within 15-30 minutes, and the rodenticide would be diluted rapidly, disperse and sink to the 

ocean bottom and start decomposing (see Section 3.3.2). In addition, as described below under 

essential fish habitat, the nearshore, directly adjacent to Sand Island and the project area, is 

depauperate of corals. The benthic substrate, adjacent to the mouse eradication project area is 

categorized as sand, hardbottom-uncolonized, pavement, pavement with sparse algae, and 

pavement-uncolonized (see Figure 3.10). 

The only documented toxic effect of brodifacoum is that it prevents the production of vitamin K 

coagulating factors in mammals. These are “poisons” only due to the anticoagulant property and

invertebrates do not have the same blood clotting system as mammals. There are no data to 

indicate corals have been impacted by anticoagulant rodenticides from previous eradication 

projects. On Palmyra Atoll, no impact to corals was documented after the application of bait 

containing brodifacoum applied using 2 applications at the rate of 75.6 and 71.5 lbs./ac. (84.8 

and 80.1 kg/ha), which is 10-16% more than the application rate proposed for MANWR (65 

lbs./ac. or 73 kg/ha).

Based on the above data, it would be unlikely that a sufficient quantity of brodifacoum would 

enter the water, or that the pellets would remain intact, to present an absorption or primary 

poisoning risk to any corals. In addition, no short- or long-term discharge of brodifacoumimpacted groundwater into the marine environment is anticipated (see Section 3.3.2). Therefore, 

it would be unlikely that the Preferred Alternative would impact any corals. 

We expect there to be no additional impact to coral from the implementation of the projects 

monitoring plan. Implementing the monitoring plan would include follow-up observations and 

sample collecting. Additional impacts to coral are not expected from implementation of the biosecurity plan or monitoring plan (see Appendix A and B) since these activities will mostly occur 

in the terrestrial environment. 

Mitigation

The same minimization measures outlined under marine fish would also minimize the amount of

rodenticide entering the marine environment. 
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3.3.6.16 Essential Fish Habitat 

3.3.6.16.1 Existing Conditions 

The marine water column and seafloor of MANWR, adjacent to the proposed project area for the 

mouse eradication, is identified as Essential Fish Habitat (EFH). The EFH is said to support 

various life stages for Management Unit Species (MUS) identified under the Western Pacific 

Regional Fishery Management Council’s Pelagic and Hawaiʻi Archipelago Fishery Ecosystem 

Plans. Of key relevance to this project is the designation of EFH for Coral Reef Ecosystems, 

including the water column and all bottom down to 328 ft. (100 m) depth from the shoreline out 

to the exclusive economic zone (EEZ) boundary (NOAA 2013). 

The species composition, abundance and condition of the corals at MANWR vary depending on 

location within the atoll (see Figure 3.11). The nearshore, directly adjacent to Sand Island and 

the project area, is depauperate of corals. The benthic substrate, adjacent to the mouse 

eradication project area is categorized as sand, hardbottom-uncolonized, pavement, pavement 

with sparse algae, and pavement-uncolonized (see Figure 3.10). The benthic maps show only 2 

small areas in the marine environment, close to the project area, that are categorized as pavement 

with >10% live coral (see Figure 3.11). 

Figure 3.11 NOAA Midway Island Detailed Habitat Cover Image at 13m Resolution 

Source: National Centers for Coastal and Ocean Science (2017)

Sand Island is located in the southern portion of the atoll and is nearest to the southern forereef. 

The high level of wave energy on the southern shore of Sand Island makes the area adjacent to 

the project area poor coral habitat. The seawall area of the island was added by the Navy during 
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the Cold War (circa 1957-58) to lengthen the runway, and the nearshore environment was 

damaged by dredging and filling activities, and additional acres were added to the island (Figure 

3.12). The majority of the nearshore habitat is categorized as reef flat (semi-exposed area 

between the shoreline intertidal zone and the reef crest of a fringing zone), though the boundary 

between land and reef flat has become less obvious as the sheet pile has eroded and vegetation 

and seabird nesting areas have appeared. Debris is present in the majority of the benthic habitat 

adjacent to the sheet pile seawall (USFWS PIFWO 2016). The hard substrate of the seawall sheet 

pile walls and areas where riprap has been placed to control erosion are artificial habitat, and 

have more abundant coral colonization than the sand, and pavement environments (USFWS 

PIFWO 2016). 

A marine survey of the seawall portion of the adjacent marine environment was conducted by the 

Pacific Islands Fish and Wildlife Office and NOAA staff in February 2013, and again in April 

2016, to determine presence and density of protected species and sensitive habitat for the seawall 

repair project (Figure 3.13) (Godwin 2013, Klavitter 2013, USFWS PIFWO 2016). The 2016 

seawall survey covered nearshore areas, including the full length of seawall that may be included 

in future seawall repair efforts. Within the survey area, 97 reef fish, 9 coral, 32 non-coral macroinvertebrates, and 28 algae species were identified. The 9 coral species identified were from the 

families Acroporidae, Faviidae, Pocilloporidae, and Poritidae, with lobate, encrusting, and 

branching morphologies present. These species were found in low densities, with an average of 

0.77 colonies per 10.8 ft.

2

 (0.77/m2) and had a maximum diameter of approximately 19.7 in. (50 

cm). Corals were found on both benthic and artificial substrate. No ESA-listed coral species were 

found during this survey, and there are no reports of listed corals occurring at Midway or within 

the Hawaiian Archipelago. 

During a seawall site visit in June 2017, sites seaward of the repair areas were scouted and 

assessed for suitability as coral translocation sites (Figure 3.14). These sites are representative of 

the patch reefs in the area. Transplant site Y had a total of 93 corals from 3 species, 2 from the 

genus Pocillopora and one Porites, within a 2,152 ft.

2 (200 m2

) area. Transplant site Z had a total 

of 79 corals from 2 species in the genus Pocillopora within a 1,076 ft.2 (100 m2

) survey area. 

These sites are small areas of raised structure that are suitable for corals to persist. There is very 

little structure suitable to support live coral in the area, and what is colonized has a low 

abundance of live coral, as is represented by sites Y and Z. Sites Y and Z are over 500 ft. (157 

m) away from the seawall, and well outside of the mouse eradication project area. The area 

inshore from sites Y and Z, along the length of the seawall, were scouted for coral transplant 

suitability, and were categorized as unfit, due to the lack of appropriate structure and live coral. 
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Figure 3.12 Augmentation of Sand Island during the Cold War

An airfield was added to Sand Island and the coastline along the southern and southeastern shore was hardened with a seawall.

Source: National Centers for Coastal and Ocean Science (2017)
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Figure 3.13 Marine Survey Area for Seawall Repair Project

Areas of surveyed (orange) and interpolated (green) project area. “Target Area” identifies anticipated area of 

direct impact for the Seawall Repair Project. 

(USFWS PIFWO 2016)

Figure 3.14 Possible Coral Translocation Site for the Seawall Repair Project

Possible coral translocation site for the seawall repair project, located on the southern shore of Sand Island 

over 500 ft. (157 m) from the seawall.

Source: USFWS (2017)
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The back reef and reef crest habitat has a higher occurrence, abundance and species diversity of 

corals than the reef flat and lagoon habitats. On the southern shore of Sand Island, except for the 

area directly off of “Bulky Dump,” the closest back reef and reef crest habitat is over 600 ft. (180 

m) from shore. The area adjacent to the shoreline is sand or un-colonized pavement with few 

scattered coral heads. This area is subject to tidal exposure, further reducing the number of live 

coral present. The “Bulky Dump” area is categorized as pavement with sparse algae and is the 

closest point to the southern reef crest, at approximately 90 ft. (27 m). Excluding the seawall 

that has been addressed above, very few (if any) corals occur within a 30 ft. (10 m) zone along 

the southern shoreline of Sand Island. 

The northern shoreline of Sand Island is predominately sand, and the environment immediately 

adjacent to the shore is sandy lagoon habitat devoid of coral. Very few (if any) corals grow 

within the 33 ft. (10 m) marine zone. The high coral cover areas of the lagoon occur out at the 

northern reef crest and back reef at site such as MID-01, MID-H21 and MID-156 (Figure 3.10). 

The high coral cover areas of the back reef and reef crest on the Northern and Northwestern sides 

of the island are over 5,000 ft. (1.5 km) from shore. 

3.3.6.16.2 Probable Impacts: No Action Alternative 

Under the No Action Alternative, Sand Island’s mouse population would not be the subject of an 

island-wide eradication project, but limited mouse control efforts would continue using the less 

toxic AGRID3 to protect nesting seabirds and for human health and safety. No bait would be 

used in the vicinity of the marine environment; therefore, there would be no effects to essential 

fish habitat under the no-action alternative. 

3.3.6.16.3 Probable Impacts: Preferred Alternative 

Primary Exposure 

Based on the above data, it would be unlikely that a sufficient quantity of brodifacoum would 

enter the water, or that the pellets would remain intact, and in the environment, long enough to 

present a poisoning risk to essential fish habitat. Some dissolved particles of brodificoum would 

likely settle in the benthic marine environment and there is uncertainty how some organisms may 

be affected by trace amounts. However, since the toxic effect of brodifacoum is the prevention of 

the production of vitamin K coagulating factors in mammals, the effects would likely be 

negligible. Marine invertebrates do not have the same blood clotting systems as mammals and 

documented evidence show marine invertebrates such as crabs with no ill effects. As stated in the 

previous sections, the Preferred Alternative is unlikely to have any effects to coral, non-coral 

macro marine invertebrates (see Section 3.3.6.17), or algae (see Section 3.3.6.18) and only minor 

effects to individual reef fish. 

Since broadifacoum can stay active to ~6 months, there is a possibility that there could be

sufficient time for the toxin to percolate into the groundwater aquifer of Sand Island and possibly 

discharge active grains of ingrediant that settle on the benthic marine environment. However, as 

discussed in Section 3.3.2, should brodifacoum dissolved at low concentrations (it is nearly 

insoluble) enter the groundwater aquifer, it would be degraded by bacteria in the subsurface, be 

diluted, and take years or decades for that water to discharge into the marine environment. Due 

to saturation with percolating rainwater, groundwater flows down and outward towards the 
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shore, where it eventually discharges into the ocean. However, the gradients and flux are small 

(GeoEngineers 2011). At Wake Island it was assessed that it would take 30 to 50 years for 

groundwater to migrate from the center of the island to either shore (a distance of approximately 

1,000 ft. [305 m]) (AFCEE 2006). Residence times at Sand Island could be as much as 3 times 

longer because it is roughly 6,000 ft (1,828 m) across. Hydrogeological studies at Wake Island 

found that groundwater chemistry and temperature conducive to the biodegradation of organic 

compounds like brodifacoum, similar conditions are present at Sand Island. The Wake Island 

study also found that significant dilution, driven by vertical groundwater movement from tidal 

fluctuations, would occur (AFCEE 2006). Therefore, no short- or long-term discharge of 

brodifacoum-impacted groundwater into the marine environment is anticipated. 

Therefore, it would be unlikely that the Preferred Alternative would directly or indirectly impact 

essential fish habitat. Multiple steps are being taken to minimize the number of bait pellets 

entering the marine environment. Any impacts would likely be minor and localized. In summary, 

the Preferred Alternative would likely have some adverse effects on essential fish habitat, but 

those effects would be minor and temporary. 

We expect there to be no additional impact to essential fish habitat from the implementation of 

the projects monitoring plan. Implementing the monitoring plan would include follow-up 

observations and sample collecting. Additional impacts to essential fish habitat are not expected 

from implementation of the bio-security plan or monitoring plan since these activities will 

mostly occur in the terrestrial environment (see Appendix A and B). 

Mitigation

The same minimization measures outlined under marine fish would also minimize the amount of

rodenticide entering the marine environment. 

3.3.6.17 Marine Invertebrates

3.3.6.17.1 Existing Conditions 

The first systematic marine invertebrate survey was conducted at Midway in 1997. It 

documented 316 invertebrate species, 250 of which had not been previously recorded at Midway. 

Crustaceans were the dominant macroinvertebrates, composing 46% of the total species. 

The sea urchin, Echinostrephus aciculatus, Echinometra mathaei, and Heterocentrotus 

mammilatus, are the most abundant benthic invertebrate in all 3 habitats (forereef, backreef, and 

lagoon.) The boring sea urchin (Echinometra mathaei) is the most abundant non-coral 

invertebrate present on the forereef, with over 73,000 individuals observed during towed diver 

surveys, and has its highest densities along the southern shore. Free urchins were relatively 

uncommon, with all records noted within the lagoon and backreef environments. Trapezid crabs 

and holothuroids or sea cucumbers, Actinopyga obesa and Bohadaschia paradoxa, are abundant 

within the lagoon at Midway. Sea cucumbers the second most abundant group of mobile 

invertebrate present on the forereef, with approximately 1,000 individuals counted during towed 

diver surveys, with the highest abundance present on the northern and southern backreefs. 
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3.3.6.17.2 Probable Impacts: No Action Alternative 

Under the No Action Alternative, Sand Island’s mouse population would not be the subject of an 

island-wide eradication project, but limited mouse control efforts would continue using the less 

toxic AGRID3 to protect nesting seabirds and for human health and safety. No bait would be 

used in the vicinity of the marine environment; therefore, there would be no effects to marine 

invertebrates under the No Action Alternative. Any negative effects of mice on marine 

invertebrates or the intertidal and nearshore ecosystems would continue. 

3.3.6.17.3 Probable Impacts: Preferred Alternative 

Primary or Secondary Exposure 

Based on the above data, it would be unlikely that a sufficient quantity brodifacoum would enter 

the water, or that the pellets would remain intact long enough, to present an absorption or 

primary poisoning risk to any marine invertebrates. As noted above (see Section 3.3.6.14), 

samples of fish, invertebrates (crabs and limpets), and seawater collected days after aerial 

application of diphacinone on Mōkapu and Lehua showed no detectable levels of diphacinone in 

their tissues (Orazio et al. 2009, Gale et al. 2008). Brodifacoum residues have been found in 

invertebrate tissues after rat eradications. A review of rat eradication projects using brodifacoum 

found marine residue monitoring and analysis had been conducted in 10 applications between 

1997 and 2011 (Masuda et al. 2015). Of the 10 applications, 3 detected brodifacoum residues in 

invertebrates. Of the 196 invertebrates sampled, 11 had residues detected in their tissue, with 

concentrations ranging from 0.001 to 0.022 ppm (mean =0.008 ppm). After the rat eradication on 

Palmyra, brodifacoum residues were found in fiddler crabs (Uca tetragonon) (Pitt et al. 2015). 

In general, invertebrates appear to be relatively insensitive to anticoagulant rodenticides (Pain et 

al. 2000, Hoare and Hare 2006). However, on Palmyra Atoll, some fiddler crabs may have died 

from brodifacoum poisoning in conjunction with the rat eradication (Pitt et al. 2015). This would 

likely be an extreme situation given the application rate on Palmyra was 32-40% higher than that 

proposed for Sand Island. In addition, the lagoon environment on Palmyra is not analogous to the 

conditions on Sand Island, which experiences a higher level of water exchange due to how the 

channel was dredged into the atoll lagoon by the Navy to facilitate boat access.

Primus et al. (2005) suggest mortality of marine invertebrates may have occurred as a result of a 

large spill of rodenticide containing brodifacoum. However, this situation would not be 

representative of how bait might enter and interact with the nearshore environment in the 

Preferred Alternative. Therefore, it would be unlikely that the Preferred Alternative would 

impact any marine invertebrates. The minimization measures outlined for marine fish are not a 

factor in this determination. 

We expect there to be no additional impacts to marine invertebrates from the implementation of 

the projects monitoring plan. Implementing the monitoring plan would include follow-up 

observations and sample collecting. Some mollusks may be collected for the sampling of 

brodifacoum residues. Additional impacts to marine invertebrates are not expected from 

implementation of the bio-security plan or monitoring plan since these activities will mostly 

occur in the terrestrial environment (see Appendix A and B). In addition, the number of marine 

animals collected will be small.
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Mitigation

The same minimization measures outlined under marine fish would also minimize the amount of

rodenticide entering the marine environment. In addition, no short- or long-term discharge of 

brodifacoum-impacted groundwater into the marine environment is anticipated (see Section 

3.3.2).

3.3.6.18 Algae 

3.3.6.18.1 Existing Conditions 

More than 100 species of algae are known to exist on Midway, including 35 previously 

unrecorded species at Midway and 1 seaweed species new to science, Dudresnaya babbittiana. 

Algal communities contribute to the health of coral reef ecosystems, providing trophic resources 

for grazers and herbivorous fish (Gattuso et al. 1998), as well as contributing to coral reef 

productivity (Rowan 1998). The transfer of nutrients from algae to coral occurs when fish or 

invertebrates forage on primary producers and excrete on the coral reef (Birkeland and 

Grosenbaugh 1985). 

The Algae Benthic communities around MANWR are composed primarily of turf and 

macroalgal functional groups with a combined total of 23 species of macroalgae observed (7 

chlorophytes, 5 ochrophytes, 11 rhodophytes) from CREP sites surveyed (NOAA CREP 2008). 

Macroalgae cover averaged 21.1% island-wide and was generally highest along the eastern 

backreef areas (average 35.4%). In 2008, 2 towed-diver surveys approximately 5 mi (8 km) to 

the north of East Island encountered a boodlea algae bloom, with several segments recording 

100% cover of the benthos in a layer up to 1.5 ft. (0.5 m) thick. 

Coralline algae were generally low island-wide, recording 5.09% cover (range 0–40%). The 

highest coralline algae cover was generally noted along the northern forereef, reaching up to 

50.1–62.5% cover. In 2008, 9 benthic sites were surveyed and showed that Laurencia galtsoffii is 

the most prevalent species encountered, with cover varying from 0% to 35.2% of the substrate 

across all survey sites in the lagoon, backreef and forereef (Table 3.18). Dictyota ceylanica, 

Lobophora variegata, Stypopodium flabelliforme and a species of Padina are present on the atoll 

and can often be among the most dominant algal species. Overall, turf algae is abundant and was 

the dominant algal functional group at 6 of the 9 sites surveyed in 2009, with a % cover range of 

15.6% to 84.8% (NOAA CREP 2008). The lagoon habitat was characterized by high % cover of 

both turf and macroalgal communities, and very low presence and % cover (3.6 to 1.6%) of 

crustose coralline algae (CCA). Microdictyon setchellianum has been the most prevalent species 

documented at some lagoon sites, with 25.2% to 31.6% algal cover. The backreef habitat was 

characterized by high % cover of turf algae (34-40%) and a low presence of macroalgae (9%) at 

most sites, and little CCA cover. The forereef habitat was dominated by turf algae (50-84%) and 

also hade high cover of macro algae (36-44%). CCA cover on the forereef was less than 3%. 
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Table 3.18 Additional species recorded at each site at MANWR during roving diver survey 

Site Chlorophyta

MID-R20 Boodlea composita

MID-H11 Codium edule

MID-R7, MID-H10, MID-H11, MID-H21 Dictyosphaeria versluysii

MID-H11 Halimeda discoidea

MID-01, MID-02, MID-R3, MID-H21 Halimeda velasquezii

MID-H21 Microdictyon setchellianum

MID-01, MID-02, MID-H21 Neomeris sp.

Ochrophyta

MID-R20 Dictyota ceylanica

MID-02 Distromium flabellatum

MID-R20 Sargassum sp.

MID-H21 Stypopodium flabelliforme

MID-H21 Turbinaria ornate

Rhodophyta

MID-H11 Chondrophycus parvipapillatus

MID-H10, MID-H11 Galaxaura filamentosa

MID-02 Galaxaura sp.

MID-01 Halichrysis coalescens

MID-H11 Halymenia sp.

MID-02, MID-H10, MID-H11 Jania sp.

MID-02 Laurencia galtsoffii

MID-H11 Liagora sp.

MID-H10 Martensia sp.

MID-01 Peyssonnelia sp.

MID-R20 Portieria hornemannii

3.3.6.18.2 Probable Impacts: No Action Alternative 

Under the No Action Alternative, Sand Island’s mouse population would not be the subject of an 

island-wide eradication project, but limited mouse control efforts would continue using the less 

toxic AGRID3 to protect nesting seabirds and for human health and safety. No bait would be 

used in the vicinity of the marine environment; therefore, there would be no effects to marine 

algae or the marine ecosystem under the no-action alternative. 

3.3.6.18.3 Probable Impacts: Preferred Alternative 

Primary or Secondary Exposure 

There are no known effects (or pathways) of anticoagulant rodenticides on marine algae and 

operations would not extend into the marine environment. Therefore, the Preferred Alternative 

would be unlikely to directly or indirectly impact marine algae. 

We expect there to be no additional impacts to algae from the implementation of this projects 

monitoring plan. Implementing the monitoring plan would include follow-up observations and 

sample collecting. Additional impacts to algae are not expected from implementation of the biosecurity plan or monitoring plan since these activities will mostly occur in the terrestrial 

environment (see Appendix A and B). 
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Mitigation

The same minimization measures outlined under marine fish would also minimize the amount of

rodenticide entering the marine environment. In addition, no short- or long-term discharge of 

brodifacoum-impacted groundwater into the marine environment is anticipated (see Section 

3.3.2). 

3.3.6.19 Sea Turtles 

3.3.6.19.1 Existing Conditions 

The ranges of 5 species of marine turtles (all listed under the ESA) encompass the waters of 

Midway, including the loggerhead turtle (Caretta caretta), the olive ridley (Lepidochelys 

olivacea), and the leatherback (Dermochelys coriacea).

Worldwide populations of the green turtle (Chelonia mydas) have seriously declined as a direct 

result of overharvesting of turtles and eggs over the last centuries (Parsons 1962). In 1978, the 

Hawaiian subpopulation of the green turtle was listed as threatened under the Endangered 

Species Act of 1973. Additional protective regulations are enforced throughout all areas within 

U.S. jurisdiction, in an effort to conserve and restore marine turtle populations to their former 

levels of abundance. Inclusion of green turtles into the Convention on International Trade in 

Endangered Species of Wild Fauna and Flora (CITES), also known as the Washington 

Convention, made it illegal to trade any products made from this species in the U.S. and 130 

other countries. 

Threatened Hawaiian green turtles are frequently seen inside the MANWR lagoon and basking 

on beaches. They are present year round. No turtle nesting had been documented until 

successfully hatched eggs were discovered on Spit Islet in July 2006. High surf uncovered the 

eggs, which probably hatched in 2005. In 2007, a successful sea turtle nest was documented on 

Sand Island and in June 2017 several crawls and possible nests were observed but not confirmed 

on the beach to the west of Bulky Dump and North Beach. Adult green sea turtles are herbivores, 

feeding on seaweeds, seagrasses, and algae (NMFS and USFWS 1998). Juveniles are omnivores, 

eating a range of insects, crustaceans, worms, and seagrasses. Sea turtles are also reported to feed 

on marine debris (Schuyler et al. 2014). Green turtles of nearshore habitats in the Hawaiian 

Islands feed on benthic algae of the following genera: Codium, Amansia, Pterocladia, Ulva, 

Gelidium, and Caulerpa (NMFS 1998). Green turtles often nest on wide sandy beaches, and 

nesting has been documented at least once at Midway. 

Endangered hawksbill sea turtles (Eretmochelys imbricata) are infrequently seen in the lagoon, 

and other species of turtles have been observed foraging at MANWR. Hawksbill turtles are 

specialist sponge carnivores, selecting just a few genera of sponges for their principal diet 

(Vicente 1994). This feeding strategy is unique, as few vertebrates are capable of digesting 

sponges without being injured by the sponges' silicate spicules (i.e., needles). 

3.3.6.19.2 Probable Impacts: No Action Alternative 

Under the No Action Alternative, Sand Island’s mouse population would not be the subject of an 

island-wide eradication project, but limited mouse control efforts would continue using the less 
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toxic AGRID3 to protect nesting seabirds and for human health and safety. Therefore, there 

would be no effects to sea turtles under the no-action alternative.

3.3.6.19.3 Probable Impacts: Preferred Alternative 

Primary Exposure 

Little is known about the effect that brodifacoum may have on turtles. Rodenticide toxicity 

experiments have not been conducted in many turtle species and therefore the LD50 values are 

unknown for the Green sea turtles or other species of turtles present in the waters surrounding 

MANWR. However, an initial assessment from preliminary findings of a USDA National 

Wildlife Research Center (NWRC) turtle-anticoagulant hazards study indicates ornate wood 

turtles (Rhinoclemmys pulcherrima) were not negatively affected by brodifacoum consumption. 

Turtles that were fed high brodifacoum doses received 2.5 x 10-5 oz./lb. (1.6 mg/kg) of turtle 

body weight of brodifacoum, and none died or showed signs of ill health prior to being 

euthanized one week later. The turtle with the highest liver residue level (2.02 ppm) weighed 0.7 

lbs. (319 g), which means that it received about 500 ppm (0.5 mg) of brodifacoum. Since a 

Brodifacoum-25D pellet contains 25 ppm, the turtle essentially received the equivalent of 20 

pellets (USFWS 2011). Adult green sea turtles weigh on average 325 lbs. (147 kg) (NOAA 

Fisheries Service 2011a), thus, using similar metrics, one adult green turtle would have to 

consume approximately 9,200 pellets or 40.5 lbs. (18.4 kg) of pellets to receive a comparable 

exposure to that the ornate wood turtle received which showed no ill effects. Adult hawksbill 

turtles weigh on average 125 lbs. (57 kg) (NOAA Fisheries Service 2011b), thus one hawksbill 

turtle would have to consume approximately 3,500 pellets or 15.4 lbs. (7.0 kg) of pellets to 

receive a comparable exposure to that the ornate wood turtle received.

Green sea turtles could potentially eat baits that drift into the water. However, it would be very 

unlikely this would occur given the low probability of bait entering the water and the rapid 

decomposition of bait in water. Therefore, there would likely be no effect on sea turtles as a 

result of implementation of the Preferred Alternative. Secondary exposure or other indirect 

effects to sea turtles also would be very unlikely due to their diet. 

Operational Hazard (Noise/Human Disturbance) 

Turtles may be disturbed when loafing on the beach, but this occurs predominantly later in the 

day and thus disturbance should be minimal during the early morning and afternoon when the 

operation would take place. With a helicopter speed ranging from 29–58 mph (46-93 km/hr) 

during each bait drop, even at the slowest airspeed the helicopter would take only 16 seconds to 

travel 656 ft. (200 m). Thus, disturbance would only last a few seconds. The level of disturbance 

for individuals is likely to be low since the disturbance would only occur at each site once or 

twice during each baiting application. Therefore, these noise impacts would be short-lived and 

negligible. 

We expect there could be some additional impacts to sea turtles from the implementation of the 

projects monitoring plan (Appendix B). Implementing the monitoring plan would include followup observations and sample collecting. Potential impacts such as disturbing beach-basking turtles 

could occur from the additional human disturbances. Additional impacts to sea turtles are not 

expected from implementation of the bio-security plan since this will occur in the terrestrial 
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environment. Given the minimization measures that will be in place to protect the Hawaiian 

green sea turtle, we expect any additional impacts from disturbance to be minor, localized, and 

short-term.

Mitigation

The same minimization measures outlined under marine fish would reduce the likelihood that 

any rodenticide would enter the marine environment. In addition, all project personnel on the 

ground would maintain a 100 ft. (30.5 m) buffer from sea turtles during operations. During aerial 

bait broadcast, helicopters would avoid 

hovering near turtle basking areas and 

would avoid distributing pellets over 

turtles on the beaches to the extent 

possible without sacrificing the chance 

of project success. These mitigation 

measures would reduce any potential 

impacts on sea turtles. 

The USFWS will consult with the 

Protected Species Division of NOAA, 

under Section 7 of the Endangered 

Species Act, to identify the best course 

of action to ensure protection of sea 

turtles. This process will address 

monitoring protocols; bait application 

around turtles; and a response plan in 

the unlikely event of finding a turtle sick or dead during or following the operation. 

3.3.6.20 Marine mammals 

3.3.6.20.1 Existing Conditions 

Marine mammals of 2 orders, Cetacea and Pinnipedia, have been observed in the pelagic waters 

surrounding Midway. The most commonly sighted cetaceans are bottlenose dolphins (Tursiops 

truncatus) and spinner dolphins (Stenella longirostris). Although protected under the Marine 

Mammal Protection Act (MMPA) of 1972, none of the cetaceans mentioned here are listed under 

the ESA or otherwise considered threatened. Approximately 200-300 Hawaiian spinner dolphins 

rest within Midway’s lagoon and forage outside the atoll. Bottlenose, striped (Stenella 

coeruleoalba), spotted (Stenella attenuate), and rough-toothed dolphins (Steno bredanensis) may 

occasionally be seen in the open ocean, as well as beaked (family; Ziphiidae), pilot 

(Globicephala macrorhynchus), and the endangered humpback whales (Megaptera 

novaeangliae). 

Spinner dolphins frequently use inshore island and atoll habitat for day-time rest and social 

interactions, and forage over deep waters at night. The groups of spinner dolphins associated 

with Kure and Midway Atolls have been the subject of long-term research since 1998. Depth 

contours are used as vectors of movement within the atoll’s lagoon, while areas of extreme local

depth and shallows are generally avoided. Socially important behaviors, such as resting and 

Figure 3.15 Hawaiian monk seal

Source: USFWS (2017)
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socializing, occur over spatially restricted areas, contrary to behaviors such as travel and play 

that might occur over a considerably larger portion of the lagoon. 

Potential measurable impacts from mice eradication activities to cetaceans in the waters 

surrounding MANWR would be negligible, since all of the activities described in the proposed 

action are terrestrial and these marine mammals forage outside of the lagoon. 

The Hawaiian monk seal (Neomonachus schauinslandi) is one of the most endangered marine 

mammals in the world and the rarest pinniped in US waters (see Figure 3.15). Following decades 

of decline, Hawaiian monk seal abundance increased 3% annually from 2013-2016 and is 

estimated at about 1,400 individuals. This positive trend is largely due to multiple years of 

increased juvenile survival in the Northwestern Hawaiian Islands (NWHI). Weighing between 

400-600 lbs. (180-270 kg) and about 7-7.5 ft. (2.1-2.3 m) in length, females are slightly larger 

than males. Pups are approximately 24-33 pounds (11-15 kg) at birth and about 3 ft. (1 m) long. 

The Hawaiian monk seal’s entire range is within U.S. waters and the majority of seals reside in 

the NWHI within the Papahānaumokuākea Marine National Monument at 8 breeding 

subpopulations. These islands include; (i) Kure Atoll; (ii) Midway Islands; (iii) Pearl and Hermes 

Reef; (iv) Lisianski Island; (v) Laysan Island and; (vi) French Frigate Shoals, (vii) 

Mokumanamana (Necker) Island and (viii) Nihoa Island. A sub-population of about 300 seals is 

now also found on the main Hawaiian Islands where births have occurred on all major islands. 

Hawaiian monk seals live in warm subtropical waters and spend two-thirds of their time at sea. 

They use waters surrounding atolls, islands, and areas farther offshore on reefs and submerged 

banks. Hawaiian monk seals have also been found using deepwater coral beds as foraging 

habitat. Hawaiian monk seals sometimes spend days at sea before returning to the islands where 

they sleep and digest their food. Hawaiian monk seals are primarily benthic foragers, feeding on 

a variety of prey including fish, cephalopods, and crustaceans. Hawaiian monk seals generally 

hunt for food outside of the immediate shoreline areas in waters 60-300 ft. (18-90 m) deep and at 

depths of up to 1,600 ft. (500 m) where they prey on eels and other benthic organisms (NMFS 

and NOAA 2007). Hawaiian monk seals come ashore to rest, give birth and rear their pups, and 

during the molting period. They haul-out on sand, corals, volcanic rock, and other substrates. 

Sandy, protected beaches surrounded by shallow waters are preferred when pupping. Hawaiian 

monk seals are often seen resting on beaches on Sand Island (see Figure 3.16).

Females generally mature at age 7-10, the gestation period is believed to be about 10-11 months, 

and most births occur between February and July, with a peak in April to May. However, 

birthing has been recorded year-round. Nursing occurs for about 39 days, during which time the 

mother fasts and remains on land. After this period, the mother abandons her pup and returns to 

sea. 

The information below summarizes Hawaiian monk seal beach counts conducted on Sand Island, 

Midway from 2012 through 2016 (Johanos 2017). Data were collected on each hauled out seal 

during systematic whole-island beach surveys which began around 1300. In total, observers 

conducted 41 standardized beach surveys and recorded 486 Hawaiian monk seal sightings over 

this 5-year period. For the purpose of seal data collection, the perimeter of Sand Island is divided 

into 29 areas, or sectors, to describe the spatial properties of seal habitat use (Figure 3.16) (Table 

3.19 and Table 3.20). 
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Figure 3.16 Sand Island Hawaiian Monk Seal Sightings: 2012-2016 

Source: NOAA (2017)

Beach count data are summarized below by sector location (Table 3.19) and month (Table 3.20).

In 2016, the total number of endangered Hawaiian monk seals present at Midway was estimated 

to be 74 seals (12 pups and 62 non-pups). Pupping levels have increased significantly since 

1996, with a record number of 17 in 2004. These seals are present at all times of the year, 

generally hauling ashore to rest. The pupping season on Midway is predominantly February to 

July with only 3-4 animals typically having pups on Sand Island. However, as is common 

throughout the Hawaiian Islands, survivorship of juveniles is low and contributes to the 

endangered status of the species. In an effort to increase survivorship, NOAA-Fisheries 

established a captive care program on Sand Island in 2006. Six females were released in March 

2007. 
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Table 3.19 Hawaiian Monk Seal Beach Count Data Summarized by Sector

Average number of seals hauled out on Sand Island, MANWR, by sector, per standardized beach 

count, conducted during 2012 through 2016. This is the number of seals you would expect to 

encounter, on average, on one beach count.

Sector

Non-Pup Size Classes Totals

Adult Sub-Adult Juvenile Non-Pup Pup All Seals

1 0.3 0.1 0.1 0.5 0.0 0.5

2 0.4 0.0 0.0 0.5 0.0 0.5

3 0.2 0.2 0.1 0.4 0.0 0.4

4 0.2 0.0 0.0 0.2 0.2 0.4

5 0.1 0.0 0.0 0.4 0.2 0.6

6 0.2 0.1 0.0 0.3 0.0 0.3

7 0.5 0.2 0.0 0.7 0.0 0.7

8 0.7 0.3 0.0 1.0 0.0 1.0

9 0.7 0.3 0.2 1.1 0.0 1.1

10 0.9 0.2 0.1 1.2 0.1 1.3

11 0.5 0.7 0.3 1.5 0.1 1.7

12 0.0 0.2 0.1 0.3 0.0 0.3

13 0.0 0.0 0.0 0.1 0.0 0.1

14 0.0 0.1 0.0 0.2 0.0 0.2

15 0.1 0.0 0.0 0.1 0.0 0.1

16 0.0 0.0 0.0 0.0 0.1 0.1

17 0.0 0.0 0.0 0.0 0.0 0.1

18 0.1 0.0 0.0 0.1 0.0 0.1

19 0.6 0.1 0.0 0.7 0.0 0.7

20 0.0 0.0 0.0 0.0 0.0 0.0

21 0.0 0.0 0.0 0.0 0.0 0.0

22 0.0 0.0 0.0 0.0 0.0 0.0

23 0.0 0.0 0.0 0.0 0.0 0.0

24 0.1 0.0 0.0 0.2 0.0 0.2

25 0.0 0.0 0.0 0.0 0.0 0.0

26 0.0 0.0 0.0 0.0 0.0 0.0

27 0.0 0.0 0.0 0.0 0.0 0.0

28 0.1 0.1 0.0 0.1 0.0 0.1

29 0.6 0.1 0.0 0.6 0.0 0.7

Source: PIFSC 17-021 (Johanos2017)
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Table 3.20 Hawaiian Monk Seal Beach Count Data Summarized by Month

Average number of seals hauled out on Sand Island, MANWR, by month, during standardized beach 

counts conducted during 2012 through 2016.

Month

No. of 

Surveys Non-Pup Size Classes Totals

Adult

SubAdult Juvenile Non-Pup Pup All Seals Std.

March 1 5.0 3.0 6.0 14.0 0.0 14.0 -

April 2 5.0 2.5 3.0 10.5 0.5 11.0 1.41

May 2 5.5 2.0 3.5 11.0 1.0 12.0 4.24

June 11 7.1 4.4 1.1 12.6 2.6 15.1 5.82

July 9 6.6 3.6 0.1 10.2 0.8 11.0 3.12

August 6 6.2 1.7 0.8 8.7 0.5 9.2 2.64

September 7 7.9 1.9 0.9 10.6 0.6 11.1 1.68

October 2 6.0 2.0 1.5 9.5 0.0 9.5 3.54

November 1 5.0 1.0 3.0 9.0 0.0 9.0 -

Source: PIFSC17-021 (Johanos 2017)

3.3.6.20.2 Probable Impacts: No Action Alternative 

Under the No Action Alternative, Sand Island’s mouse population would not be the subject of an 

island-wide eradication project, but limited mouse control efforts would continue using the less 

toxic AGRID3 to protect nesting seabirds and for human health and safety. No bait would be 

used in the vicinity of the marine environment; therefore, there would be no effects to marine 

mammals under the no-action alternative.

3.3.6.20.3 Probable Impacts: Preferred Alternative 

Primary Exposure 

As many as 74 Hawaiian monk seals could be present on or around Sand Island during the 

proposed operation. Because they do not forage on land, direct consumption of bait pellets from 

the ground would not be a risk. Bait pellets that might drift into the water would fall close to the 

shoreline far from the typical offshore foraging areas of monk seals, however weaned pups often 

mouth and may consume sea cucumbers and other prey items in the wave wash and nearshore 

environment (NMFS unpublished data). Older Hawaiian monk seals were found not to interact 

with bait pellets during a placebo trial on the island of Lehua in 2015 for a rat eradication study 

(Mazurek 2015). 

Moreover, bait pellets degrade quickly in water and fragments sink to the bottom, and so would 

only be available to monk seals for a very short period of time. However, fish have been 

demonstrated to be intoxicated with anticoagulant rodenticide that has entered the ocean directly 

or indirectly from spills and eradication projects (Primus et al. 2005, Pitt et al. 2015). In a 2015 

placebo trial on the island of Lehua, 19 species of fish in the near shore environment consumed 

the baits (Mazurek 2015). However, post-application sampling of the near shore marine 

environment from 2 eradication projects in Hawaiʻi found no detectable levels of rodenticide in 

fish, invertebrates, or seawater (Orazio et al. 2009, Gale et al. 2008). Furthermore, because older 

Hawaiian monk seals typically forage in offshore areas, it would be unlikely they would prey on 
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any fish or invertebrates that may have consumed rodenticide pellets. In the unlikely event a nonpup seal did forage in the near shore environment there would be a low probability that it would 

encounter a prey item that had consumed rodenticide. 

Secondary Exposure 

Hawaiian monk seals would only be at risk of secondary exposure to brodifacoum in the unlikely 

event that a very large quantity of bait was accidently dropped into the ocean, and fish or other 

prey items were able to consume it before ocean currents dissipated the spilled bait. However, a 

220 lbs. (100 kg) juvenile seal would have to eat 22-88 lbs. (10-40 kg) of intoxicated fish to 

receive the calculated lethal doses. Hawaiian monk seals normally consume 5.8 to 12.9% of their 

body weight per day. For a 220 lbs. (100 kg) juvenile, that would correspond to around 13-28 

lbs./day (6 to 13 kg/day). It is not likely that a seal would consume more than their daily food 

intake of contaminated fish. Because nursing and newly weaned pups remain near shore for 

extended periods, there is some risk of exposure for this age class. 

Based on the above data, it would be unlikely that the Preferred Alternative would primarily or 

secondarily expose non-pup Hawaiian monk seals to a sufficient quantity of rodenticide to have 

any negative effects. There have been no documented cases of impacts to seals or sea lions after 

aerial bait application, including the 2009 rodenticide application on Lehua Island. 

Operational Hazard (Noise/Human Disturbance) 

Air and ground-based operations have the potential to cause Hawaiian monk seals to move or 

flush into the ocean. However, with a helicopter speed ranging from 29–58 mph (46-93 km/hr.) 

during each bait drop, even at the slowest airspeed the helicopter would take only 16 seconds to 

travel 656 ft. (200 m). Thus, disturbance would only last a few seconds. Therefore, these noise 

impacts would be short-lived and negligible, and have been determined as not likely to adversely 

affect. The level of disturbance for individuals is likely to be low since the disturbance would 

only occur at each site once or twice during each baiting application, which is believed not to 

pose a significant risk. The exception is during the pupping season. Although pups can be born at 

any month of the year, most pups are born between February and July, which is predominantly 

earlier than the proposed bait drop. There is little that can be done to mitigate this disturbance, 

but as only 3-4 animals pup on Sand Island each year, and most pupping would be completed 

before the baiting period, the disturbance would be short lived and minor. 

We expect there will be no additional impacts to bottlenose and spinner dolphins but some 

possible additional impacts to Hawaiian monk seals should the need arise to implement the rapid 

response portion of the refuge’s biosecurity plan and during implementation of this projects 

monitoring plan (see Appendix A and B). Biosecurity measures enacted would include rapid 

response to an incursion by non-native invasive terrestrial species and implementing the 

monitoring plan would include follow-up observations and sample collecting. Additional impacts 

to dolphins are not expected from implementation of the bio-security plan or from the additional 

human disturbance, since these will almost all occur in the terrestrial environment. However, 

some additional impacts such as disturbing basking seals and pupping activities could occur from 

these activities. Given the minimization measures that will be in place to protect the Hawaiian 

monk seal, we expect any additional impacts to be minor, localized, and short-term.
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Mitigation

The same minimization measures outlined under marine fish would also minimize the amount of

rodenticide entering the marine environment. In addition, all project personnel on the ground 

would maintain a 100 ft. (30.5 m) buffer from seals during operations. During aerial bait 

broadcast, helicopters would avoid hovering near Hawaiian monk seals and would avoid 

distributing pellets over seals on the shore. These mitigation measures would reduce impacts on 

Hawaiian monk seals. Indirect effects from the Preferred Alternative, particularly for non-pups, 

would be fairly unlikely. 

The USFWS will consult with the Protected Species Division of NOAA, under Section 7 of the 

Endangered Species Act, to identify the best course of action to ensure protection of Hawaiian 

monk seals. This process will address monitoring protocols; bait application around seals; and a 

response plan in the unlikely event of finding a monk seal sick or dead during or following the 

operation. 

3.3.6.21 Human Health and Safety 

3.3.6.21.1 Existing Environment 

A safe environment is one in which there is little or no potential for death or serious bodily injury 

or illness, or property damage. Human health and safety addresses: (i) workers’ health and 

safety during project operations, and (ii) public safety during project operations. Project safety is 

managed via adherence to regulatory requirements imposed for the benefit of worker and public 

safety, and implementation of operational practices that reduce the potential for illness, injury, 

death, and property damage. 

The health and safety of MANWR and PMNM workers are safeguarded by the numerous 

regulations designed to comply with standards promulgated by OSHA and the EPA. These 

standards specify the amount and type of training required for industrial workers, the use of 

protective equipment and clothing, engineering controls, and maximum exposure limits for 

workplace stressors. Compliance with OSHA and other applicable laws and regulations for the 

protection of employees is exclusively the obligation of the commercial contractor. 

On Sand Island, MANWR, the various agencies and contractors have health and safety 

managers, and all personnel are reminded to focus on workers safety on an ongoing basis. This 

focus on health and safety is particularly important given the Atoll’s remote and inaccessible 

location. There is a doctor and/or nurse practitioner on the Atoll at all times and that individual 

is on call 24-hours a day and 7 days a week in case of injury or illness. 

All fuel deliveries operate in compliance with USFWS regulations and the Midway Atoll Spill 

Prevention Control and Countermeasure Plan. 

Safety and accident hazards can often be anticipated, identified, and either reduced or eliminated. 

Necessary elements for an accident-prone situation or environment include: 

• The presence of one or more hazards;

• The presence of an exposed population; and 
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• The absence of appropriately-observed safety procedures. 

The degree of hazard is largely dependent on the proximity of the hazard to the exposed 

population. Activities that are innately hazardous include: (i) transportation; (ii) construction; 

(iii) maintenance and repair activities; (iv) training; and (v) noisy operations or environments. 

The proper operation, maintenance, and repair of vehicles and equipment are vital to creating a 

safe work environment. Extremely noisy environments can damage hearing and can also mask

verbal or mechanical warning signals such as sirens, bells, or horns. 

3.3.6.21.2 Aerial Operations Safety 

Aircraft safety is based on the physical risks associated with aircraft flight, as well as operational 

procedures related to aircraft and aircraft maintenance safety. Weather conditions at MANWR 

are generally clear, with light trade winds for most of the year, interrupted by periodic 

rainstorms. Adverse weather conditions of concern during the time of year proposed for the 

Midway Seabird Protection Project include: (i) thunderstorms, (ii) hail, (iii) severe turbulence, 

(iv) wind shear, and (v) hurricanes. There are no obstructions, such as towers or electrical 

transmission lines and poles, which would cause a safety concern for helicopter operations on 

Sand Island, MANWR. 

The extreme concentration of birds is also a concern for aircraft operations and would be taken 

into account in planning the exact timing of the eradication operation. In order to address this, 

MANWR has adopted a BASH Program that includes methods to reduce the risk of BASH using 

harassment techniques (such as pyrotechnics) under the terms of a USFWS permit. Per the terms 

of that permit, the airfield is inspected and the taxiway/runway area is cleared of birds prior to 

aircraft operations, which occur approximately twice per month. When needed based on the 

result of these inspections, a sweeper vehicle is used to prevent the accumulation of Foreign 

Object Debris (FOD) on the runway and taxiway. 

3.3.6.21.3 Ground Operations Safety 

Ground safety conditions on Sand Island, MANWR are subject to existing safety plans which 

incorporate and adhere to the requirements of OSHA and USFWS standards. All personnel 

working on Sand Island have attended a Basic Safety Course as part of their orientation when 

arriving on island, which includes lecture, discussion, and video materials intended to familiarize 

new arrivals with basic safety procedures and protocols. Periodically, a USFWS-designated 

Safety Officer will electronically disseminate messages, lessons, or other safety topics to all 

supervisors to be posted in work areas. 

Safety signs, instructions, and safety bulletin boards with required OSHA material are posted 

throughout the work spaces on the Atoll. Many accidents occur as a result of improper tool 

usage, foot injuries from rough coral present on the Atoll, and the typical lacerations and 

contusions resulting from construction and demolition work. Safety information and materials 

are available onsite for all hazardous materials used on Sand Island, MANWR, and there is an 

active industrial hygiene program. 

Emergency services such as police, fire, and emergency medical services are available on Sand 

Island, MANWR to allow for prompt response to emergencies, 24-hours per day. The Sand 
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Island Fire Station is located at Henderson Field Airport and is staffed by refuge workers 

qualified in firefighting. All firefighters are certified with 40-hour Hazardous Waste Operations 

and Emergency Response Standard training and serve as the MANWR Hazardous Materials 

Team. Available firefighting and emergency equipment include 2 crash trucks, a structure fire 

truck, a water tanker, a mini-pumper, a service truck, and an ambulance. One fire truck equipped 

with foam is on standby at the airfield. Fire hydrants are distributed across Sand Island to 

provide a firefighting water supply. 

Sand Island, MANWR has a Physician’s Assistant (PA) and a small clinic. The PA provides 

medical care to all personnel on the Atoll. In addition, the PA serves as the food inspector. In 

the event of a serious emergency, the patient would have to be airlifted off the island to 

Honolulu. Emergency medical evacuation services are provided by the U.S. Coast Guard. 

3.3.6.21.4 Probable Impacts 

If the implementation of the proposed action or alternatives were to substantially increase risks 

associated with the safety of personnel, contractors, or the contractor residences, or would 

substantially hinder the ability to respond to an emergency, it would represent a significant 

impact to safety on Sand Island, MANWR. 

Under the proposed action, short-term minor safety risks are anticipated as a result of: (i) 

conducting aerial broadcast operations; (ii) conducting hand broadcast operations in 

compromised structures; and (iii) broadcasting a toxicant, in this case brodifacoum. Specific 

risks could include handling the brodifacoum, loading the bait hopper, and flying the helicopter. 

To address this, a USFWS contractor would be required to establish and maintain safety 

programs and comply with all guidelines for handling bait pellets and operating or maintaining 

aircraft. In addition, the Contractor would comply with all existing aviation, airfield, and 

installation safety procedures and standards. 

Because the project involves the broadcast of a toxin, a potential short-term impact on safety on 

Sand Island, MANWR is the potential for accidental poisoning of staff and contractors. For the 

proposed action only USFWS and its Contractor would come in contact with brodifacoum. This 

contact with brodifacoum may occur in several ways, including: 

• Direct consumption of bait by personnel unfamiliar with its appearance. 

• Incidental consumption of bait through inadvertent contamination of food stocks with 

the toxin, whether through direct contact with bait or secondary transmission via 

rodent feces or urine. 

• Secondary ingestion of the toxin through consumption of animals that were primary 

consumers of the bait. 

While inadvertent consumption of brodifacoum by humans is unlikely, a small risk remains. The 

ingestion of 3.5 x 10-5 oz. (1 mg) of brodifacoum was reported to result in bleeding that 

persisted for more than 2 months. The average fatal dose for an adult man weighing 132 lbs. (60 

kg) is estimated to be approximately 5.3 x 10-4 oz. (15 mg) of brodifacoum, or approximately 

10.5 oz. (300 g) of bait (WHO, 1995). The brodifacoum concentration on the bait being proposed 

for use under the conservation label 0.0025 %, which would require that an adult ingest 1.3 lbs.
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(600 g) of bait to achieve an average fatal dose; this would be equivalent to ingesting 600 bait 

pellets. 

Symptoms of acute intoxication may be an increased tendency to bleed in less severe poisonings, 

to massive hemorrhages in more severe cases. The signs of poisoning develop with a delay of 1 

to several days after ingestion. Both intentional and unintentional poisonings have been 

reported. To reach the toxic or lethal does, the nontarget animals must consume comparatively 

large amounts of bait with a concentration of 0.0025% of the active ingredient (i.e., 

brodifacoum). Treatment of brodifacoum poisoning includes the use of Vitamin K1 to counter 

the effects. Physician-controlled Vitamin K1 supplements would be available for all Sand Island, 

MANWR residents during and after the eradication operation. 

Installation staff would be educated on the entire program and how to deal with operation 

mishaps, accidental release or poisoning, and transport of brodifacoum into non-target areas such 

as food stocks or drinking water. In addition, certain restrictions would be placed on residents 

during the proposed action, such as limiting the number of individuals authorized to come into 

contact with the bait to further mitigate the potential for inadvertent safety risks. Personnel 

would be advised to limit their outdoor activities on those days where bait is aerially applied 

along recommendations to wear long sleeves and long pants. 

Procedures would also be implemented to protect potable water supplies (see Section 3.3.2). 

Over the longer-term, the proposed action would have a beneficial effect on safety by 

eliminating an invasive pest species that can act as a disease vector, contaminate food supplies, 

and damage MANWR infrastructure. 

 

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CUMULATIVE IMPACTS

4-1 

CHAPTER 4: CUMULATIVE IMPACTS

4.1 CUMULATIVE IMPACTS

Federal agencies like the USFWS are required by NEPA to consider direct and indirect impacts 

of any actions taken, but also must consider the cumulative impacts of their actions. Cumulative 

impacts on environmental resources result from incremental effects of a proposed action, when 

combined with other past, present, and reasonably foreseeable future actions. Such impacts result 

from individually minor, but collectively substantial, actions undertaken over a period of time. 

Informed decision-making is elicited by consideration of cumulative impacts resulting from 

projects that are proposed, under construction, recently completed, or anticipated to be 

implemented. 

There are no future actions on Sand Island that are likely to negatively impact the environment 

because the atoll is managed in perpetuity as a National Wildlife Refuge. Additionally, it should 

be noted that many species of MANWR may be experiencing unrelated impacts elsewhere in 

their extensive ranges, or they may still be recovering from severe past impacts. In addition, the 

potential numbers of individuals of a species that could be killed from either rodenticide 

poisoning or aircraft collisions are not cumulative, since if an individual is killed by a collision it 

is taken out of the population and would not be exposed to the rodenticide. 

The following is a breakdown of the past, present, and foreseeable future actions that would 

likely contribute to the cumulative impacts associated with the 3 identified alternatives. Direct 

and indirect impacts from each alternative would be analyzed with the following list of activities 

to determine the cumulative impacts for a given alternative. 

4.2 PAST ACTIONS

Past actions are actions that occurred in the past but have lasting impacts that could contribute to 

the impacts associated with the proposed action. 

In the mid-1990s, the USFWS successfully eradicated black rats (Rattus rattus) from MANWR 

using bait stations with brodificoum and snap traps. In a study on brodifacoum bait residues 

before a rat eradication project on the island of Palmyra in 2011, residue concentrations 

decreased with time, and the toxicant was not detected in most of the 28, 36, and 50-day samples 

tested; and only trace amounts (≤0.2 ppm for brodifacoum) of the toxicant were detected in a few 

samples from these groupings. The results from the study show that following a broadcast of 

rodenticide across Palmyra’s emergent land area, only small amounts of brodifacoum remained 

in the islands topsoil for a short period of time. Given the short half-life of brodifacoum in soil, 

no cumulative effects from the previous attempt on MANWR are expected. Therefore, 

cumulative effects from this previous eradication are not expected and would not negatively 

contribute to the impacts from the proposed action. 

In addition, other small mammal eradications that have already been conducted on islands 

throughout the world to conserve and protect nesting birds will likely have a cumulative 
MIDWAY SEABIRD PROTECTION PROJECT DRAFT ENVIRONMENTAL ASSESSMENT

CUMULATIVE IMPACTS

4-2 

beneficial effect on global seabird populations (Brooke at al. 2017), including some of the 

seabird species present at MANWR. 

4.3 CURRENT ACTIONS

Current actions are actions that are occurring within the same timeframe as the proposed action, 

or within the planning and compliance phase of the proposed action and could contribute to the

impacts from the proposed action. 

4.3.1 PLANT RESTORATION AND INVASIVE WEED CONTROL 

The USFWS is conducting a project to restore native plants to MANWR, along with eradicating 

invasive plants, including the ironwood tree and invasive plant verbesina spp. These 2 actions 

could positively contribute to the cumulative impacts of the proposed action by improving 

habitat for native species and contributing to the overall restoration of the atoll. 

4.3.2 LEAD ABATEMENT 

Studies conducted by USFWS and others at Sand Island between the late 1980s and 2009 have 

shown that Laysan albatross chicks exhibited symptoms of lead toxicity, and that their exposure 

is likely related to ingestion of lead-based paint (LBP) chips and soil contaminated with LBP 

chips. Buildings and structures on Sand Island, some of which date back to the early 1900s, are 

the primary source of the paint chips that contaminate the soil where the albatross nest. From 

2005 to present, the USFWS has remediated all of the 95 buildings with LBP, with the total 

removal of all LBP from the interior, and the encapsulation of all lead-based paint on the 

exterior. This action contributes positively to the cumulative impacts of the proposed action by 

improving habitat for native species, decreasing mortality to seabirds, and contributing to the 

overall restoration of the atoll.

4.3.3 MARINE DEBRIS REMOVAL 

On a continuing basis, NOAA Coral Reef Ecosystem Program has sent their marine debris team 

to remove tens of thousands of pounds of debris from MANWR. Funded by the NOAA Marine 

Debris Program and the NOAA Papahānaumokuākea Marine National Monument, the mission of 

the NOAA Marine Debris Program is to investigate and prevent the adverse impacts of marine 

debris. In 2016, crews collected 15,206 lbs. (6,897 kg) of debris from Midway beaches. This 

action would positively contribute to the cumulative impacts of the proposed action by 

improving habitat for native species, decreasing mortality to seabirds, and contributing to the 

overall restoration of the atoll. 

4.3.4 MOUSE CONTROL/MANAGEMENT EFFORTS 

MANWR currently implements several ongoing measures on Sand Island to control/manage the 

spread and impact of invasive house mice. These efforts are in commensal areas to maintain 

human health standards and are around the nests of breeding albatross to prevent predation and 

mortality of adults and chicks. Control measures in commensal areas include bait stations and 

multi-catch live-traps deployed around habitations, food stores, and at the dining hall, and in 
DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

CUMULATIVE IMPACTS

4-3 

areas near buildings, man-made structures, at the airport, and on shipping docks receiving 

conveyances. To protect albatross, control measures are used in the winter months during the 

nesting season (November to February); these measures include bait stations and multi-catch live 

traps, as well as hand applications of rodenticide in areas where mouse attacks to albatross are 

documented. The Preferred Alternative of targeted mouse eradication on Sand Island would have 

a positive effect in that it would eliminate the need for these ongoing mouse control efforts. 

4.4 FUTURE ACTIONS

Future actions include actions that are reasonably foreseeable in the future, and that could 

contribute to the cumulative impacts from the proposed action. 

The U.S. Fish and Wildlife Service and the Federal Aviation Administration (FAA) propose to 

conduct repairs as needed over a ten year period (2018-2027) along a 5,720-foot-long seawall 

located on Midway Atoll’s Sand Island in order to protect Henderson Field and to control 

erosion of wildlife habitat along the southeast side of Sand Island. The proposed seawall repair 

project which is currently being planned would not contribute to additional, cumulative impacts 

when considered in combination with the proposed Midway Seabird Protection Project. There is 

not expected to be any persisting effects of the Midway Seabird Protection Project at the time 

that the seawall project is implemented and whatever impacts result from the seawall project will 

not “accumulate” with any impacts of the Midway Seabird Protection Project. 

Areas of impact linked to future global climate change, which may have the potential to affect 

MANWR, include warmer air temperatures and declines in rainfall (University of Hawaiʻi 2014). 

In addition, other small mammal eradications being planned on islands throughout the world to 

conserve and protect nesting birds will likely have a cumulative beneficial effect on global 

seabird populations as has been shown by Brooke at al. (2017). 

4.5 PROBABLE CUMULATIVE IMPACTS 

4.5.1 NO ACTION ALTERNATIVE

Under the no-action alternative, the current negative impacts of mice on MANWR’s seabird 

populations and terrestrial ecosystem would continue in perpetuity. These impacts could be 

additive to other, unrelated future impacts on the resources of MANWR. The minor impacts that 

ongoing projects (primarily conservation-related) would have on the biological, physical, and 

cultural resources of MANWR are not likely to contribute to mice-related impacts. If mice 

persist on Sand Island, the biological resources of the island would continue to be negatively 

affected.

Under the No Action Alternative, Sand Island’s mouse population would not be the subject of a 

targeted eradication project, but mouse control efforts to protect breeding albatross, which were 

started in 2016, would continue and expand as deemed appropriate. Mouse management on Sand 

Island currently consists of (i) trapping and rodenticide bait stations containing AGRID3 (active 

ingredient cholecalciferol) for human health and safety in commensal areas such as food storage 

and preparation areas, as well as in areas near buildings, man-made structures, at the airport, and 
MIDWAY SEABIRD PROTECTION PROJECT DRAFT ENVIRONMENTAL ASSESSMENT

CUMULATIVE IMPACTS

4-4 

on shipping docks receiving conveyances; and (ii) multi-catch live trapping, and rodenticide bait 

stations and hand broadcasting of AGRID3 for seabird and listed candidate plant protection in 

areas where mouse predation of seabirds and mouse damage to listed or candidate plants are 

detected. Trapping (i) includes multi-catch live traps and mechanical traps (snap-traps and glue 

boards) used in the commensal environment as deemed appropriate per the terms of each 

structure’s SMP (see Section 2.3.1). Hand broadcasting (ii), which is extremely labor and time 

intensive, involves 2 separate hand-broadcast applications of AGRID3 pellets approved for 

restricted use at MANWR under a supplemental label for mouse control. Per label instructions, a 

17 lbs./ac. (20 kg/ha) application rate is used over 27.2 ac. (11 ha) where evidence of mouse 

attacks occurred in 2016. The second application (same rate, same area) occurs in the month of 

November prior to the albatross’s main egg laying season, and then only as needed if and where 

there were mouse attacks throughout the incubation period, up until the following February. 

There were no observations of any non-target organism, such as shorebirds or Laysan ducks, 

interacting with bait pellets in the field, or being found sick or dead in the colony as a result of 

the baiting process (USFWS, Unpublished b). Both control measures, (i) and (ii), are ongoing. 

The proposed action of targeted mouse eradication on Sand Island would have a positive effect 

in that it would eliminate the need for these ongoing control efforts. 

4.5.2 PREFERRED ALTERNATIVE

There would be no major adverse impacts to the biological, physical, or cultural resources of 

Sand Island under the Preferred Alternative. The minor negative impacts to biological, physical, 

and cultural resources as a result of the Preferred Alternative would not contribute to the impacts 

related to any separate, current, or future projects. Similarly, the expected positive impacts of the 

Preferred Alternative to Sand Island’s biological resources could contribute to the cumulative, 

positive impacts from separate, current, or future projects. 
DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

LIST OF PREPARERS AND CONTRIBUTORS

5-1 

CHAPTER 5: LIST OF PREPARERS AND CONTRIBUTORS

5.1 PREPARERS 

Table 5.1 below identifies the principal agencies, organizations, and individuals that participated 

in the preparation of this report. 

Table 5.1 Principal Prepares of this Environmental Assessment

Agency or Organization Preparers

U.S. Fish and Wildlife Service, Pacific Islands 

Fish and Wildlife Office

Michael Marxen

Beth Flint

Hamer Environmental

Thomas Hamer

Kristin Murray

Cary Deringer

Planning Solutions, Inc. Jim Hayes

Mākena White

Source: Compiled by Hamer Environmental (2017)

5.2 CONTRIBUTORS

Table 5.2 below identifies the agencies, organizations, and individuals that contributed critical 

information for the development of this report. 

Table 5.2 Contributors to this Environmental Assessment

Agency or Organization Preparers

U.S. Fish and Wildlife Service

Susan Hunter

Kelly Goodale

Kauaoa Fraiola 

Amanda Pollock

Leila Nagatani

Michael Green

Jennifer Miller

Roberta Swift

Island Conservation

Patty Baiao

Gregg Howald

Wes Jolley

Source: Compiled by Hamer Environmental (2017)
5-2 

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Weatherbase.com. 2017. Average temperature and rainfall at Henderson Field Airport, Sand 

Island, Midway Atoll, NW Hawaiian Islands. Available from https://www.weatherbase.com. 
MIDWAY SEABIRD PROTECTION PROJECT DRAFT ENVIRONMENTAL ASSESSMENT

REFERENCES

6-14

Wegmann, A.S. 2009. Limitations to tree seedling recruitment at Palmyra Atoll. University of 

Hawai‘i: Honolulu, HI. 

Weir, S.M., S. Yu, A. Knox, L.G. Talent, J.M. Monk, and C.J. Salice. 2016. "Acute toxicity and 

risk to lizards of rodenticides and herbicides commonly used in New Zealand." New Zealand 

Journal of Ecology 40 (3):342-350. doi: 10.20417/nzjecol.40.43. 

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. 

Whittow, G.C. 1993a. “Black-footed Albatross (Diomedea nigripes).” In The Birds of North 

America, edited by A. Poole and F. Gill. Washington, D.C: The American Ornithologists' 

Union: Philadelphia: The Academy of Natural Sciences.

---. 1993b. “Laysan Albatross (Phoebastria immutabilis).” In The Birds of North America, edited 

by A. Poole and F. Gill. Washington, D.C.: The American Ornithologists' Union: 

Philadelphia: The Academy of Natural Sciences.

Woodward, P.W. 1972. "The natural history of Kure Atoll, Northwestern Hawaiian Islands." 

Atoll Res. Bull. 164:1-318. 

Work, T.M., and M.R. Smith. 1996. “Lead exposure in Laysan albatross adults and chicks in 

Hawaii: prevalence, risk factors, and biochemical effects.” Archives of Environmental 

contamination and Toxicology 31:115-119. 

Work, T. M., Klavitter, J. L., Reynolds, M. H. & Blehert, D. (2010). “Avian botulism: a case 

study in translocated endangered Laysan Ducks (Anas laysanensis) on midway atoll.” J. 

Wildl. Dis. 46: 499–506. 

Young, H., D. McCauley, R. Dunbar, and R. Dirzo. 2010. “Plants cause ecosystem nutrient 

depletion via the interruption of bird derived spatial subsidies.” Proceedings of the National 

Academy of Science. 107:2072-2077. 
DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

CONSULTATION & DISTRIBUTION

7-1 

CHAPTER 7: CONSULTATION & DISTRIBUTION

7.1 PRE-DRAFT SCOPING PROCESS 

The proposed mouse eradication action involves the aerial broadcast of bait pellets containing 

rodenticide into all potential mouse territories on Sand Island, MANWR. Mouse eradication 

would occur in the summer dry season (July to August) to maximize the probability of success, 

targeting the mice when their food resources are lowest and their abundance is declining. 

Conducting the operation during this period would also minimize the risk of exposure to both 

seabirds and shorebirds, as well as the risk of rain washing rodenticide pellets into the ocean. 

A Public Scoping effort by the USFWS was conducted to solicit input from the public, state and 

Federal regulatory agencies, and non-governmental organizations regarding the proposed 

Midway Seabird Protection Project on Sand Island, MANWR, and the Northwestern Hawaiian 

Islands. Prior to the preparation of the Draft Environmental Assessment for the proposed action, 

on August 7, 2017, a scoping letter describing the proposed action and interview questions were 

emailed to the individuals listed in Table 7.1: 

Table 7.1 Scoping Letter Recipients 

No. Recipient Agency or Role

1 Karen Vitulano Environmental Protection Agency

2 Thierry Work United States Geological Service, National Wildlife Health Center

3 Richard Hall National Oceanic and Atmospheric Administration, National Marine 

Fisheries Service

4 Thea Johanos-Kam National Oceanic and Atmospheric Administration, National Marine 

Fisheries Service

5 Gabrielle Fenix Grange Hawaii Department of Health, Hazard Evaluation and Emergency 

Response Office

6 Maggie Sergio Island Watch Conservation Science

7 Sydney Ross Singer Good Shepherd Foundation

8 Joshua Atwood Hawai‘i Department of Land and Natural Resources, Division of 

Forestry and Wildlife

9 Mark Rauzon Pacific Seabird Group/Laney College

10 Richard and Jenny Johnson former Midway resident and Midway volunteer

11 Jill McIntire Midway volunteer

Source: Hamer Environmental (2017)

These individuals, organizations, and agencies were contacted because they had previously 

expressed interest in similar island eradication projects or may have oversight or regulatory 

concerns about the project. All eleven responded to the interview questions either via email or 

by phone. 

7.2 INTERVIEW PROCESS 

A series of interview questions were prepared by Hamer Environmental, Inc., and Planning 

Solutions. Scoping participants were informed of the proposed project’s purpose, need, method, 

schedule, background and alternatives. The 16 questions were categorized into 4 parts as shown 

in Table 7.2: 
MIDWAY SEABIRD PROTECTION PROJECT DRAFT ENVIRONMENTAL ASSESSMENT

CONSULTATION & DISTRIBUTION

7-2 

Table 7.2 Summary of Scoping Interview 

Part I: Contact Information

No. Question

1 Please state your full name, preferred contact number, and email.

2 What is your occupation and/or affiliation?

3 How many people are in your organization?

4 How many days, week, months, or years have you spent on Midway?

5 When was your most recent trip to Midway?

6 What do you consider your particular areas of expertise related to the project purpose or location?

Part II: Survey

7 Do you have input on the purpose and need?

8 Do you believe that conservation of the native environment (seabirds, wildlife, and botanical resources) 

adequately justify the eradication of invasive mice?

Part III: Historical and Cultural Information

9 Is there anything you would like to say about the general history of the area, or past and present land use?

Questions only for people who have visited or lived on Midway:

10 Have you participated in or observed any cultural events or practices on Midway?

11 Do you know anything about the canaries and their potential historic or cultural significance?

Part IV: General Considerations

12 Have you encountered or are you aware of any facilities, areas, or resources on Midway that you believe 

require special consideration, either in terms of project implementation or potential project impacts?

13 What concerns would you have regarding the use of following rodenticide distribution methods on 

Midway: (a) aerial broadcast; (b) band broadcast; (c) bait stations? 

14 Are you aware of any human activities on Midway that may be impacted by or affect the efficacy of an 

eradication effort?

15 What factors, such as structures, topography, or human habits, do you feel represent the biggest challenges 

to the eradication effort? How would you approach them?

16 What impacts do you foresee (water or marine environment or others) from the action and how would you 

(a) avoid, (b) minimize, or (c) mitigation for them?

Source: Hamer Environmental (2017)

The USFWS compiled responses from the public scoping process, and prepared a list of 

environmental issues that warranted specific consideration in the EA analysis. The concerns that 

were identified are: (i) damage to seabird populations; (ii) secondary poisoning; (iii) poisoning of 

rodents and non-target species; (iv) disturbance; (v) cultural issues; (vi) project effectiveness; and 

(vii) the EA process and Alternatives. 
DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

STATEMENT OF COMPLIANCE

8-1 

CHAPTER 8: STATEMENT OF COMPLIANCE FOR 

IMPLEMENTATION OF THE PROPOSED ACTION AT MANWR 

The following Regulatory and Policy Compliance Requirements and Permit processes are 

currently underway and would be completed prior to implementing the proposed action. 

8.1 NATIONAL ENVIRONMENTAL POLICY ACT (1969) 

The Environmental Assessment development process has been conducted in accordance with 

NEPA Implementing Procedures, Department of the Interior and Service procedures, and has 

been performed in coordination with the affected public. 

8.2 NATIONAL HISTORIC PRESERVATION ACT (1966) 

The implementation of the proposed action is currently under review for its impacts on cultural 

resources. The proposed action does not meet the criteria of an effect or adverse effect as an 

undertaking defined in 36 CFR 800.9 and 614 FW 2. The Service would comply with the 

National Historic Preservation Act if any management actions have the potential to affect any 

historic properties which may be present. 

8.3 EO 12372 INTERGOVERNMENTAL REVIEW 

Coordination and consultation with affected State governments, and other Federal agencies has 

been completed through personal contact by Service planners, refuge managers, and supervisors. 

8.4 ENDANGERED SPECIES ACT OF 1973 

The Service has initiated consultation with the NOAA/National Marine Fishery Service and the 

U. S. Fish and Wildlife Service under Section 7 of the Endangered Species Act for all listed 

species at MANWR. A Biological Assessment will be written and used with this EA in the 

consultation process to identify mitigation actions to minimize impacts to all listed species.

8.5 MAGNUSON-STEVENS ACT ESSENTIAL FISH HABITAT 

The Service has initiated consultation with NOAA/National Marine Fishery Service for effects to 

Essential Fish Habitat from the Proposed Action. The Draft Environmental Assessment is 

serving as the primary document for the consultation process. 

8.6 MIGRATORY BIRD TREATY ACT AND EO 13186 FEDERAL 

PROTECTION OF MIGRATORY BIRDS 

The Draft NEPA analysis evaluates the effects of proposed action on migratory birds and 

outlines avoidance and minimization measures that will be implemented to reduce or eliminate 

incidental take of migratory birds. 
MIDWAY SEABIRD PROTECTION PROJECT DRAFT ENVIRONMENTAL ASSESSMENT

STATEMENT OF COMPLIANCE

8-2 

8.7 EO 13112 RESPONSIBILITIES OF FEDERAL AGENCIES

PERTAINING TO INVASIVE SPECIES 

EO 13112 requires Federal agencies to prevent the introduction of invasive species and provide 

for their control and to minimize the economic, ecological, and human health impacts that 

invasive species cause.

8.8 INTEGRATED PEST MANAGEMENT, 517 DM 1 AND 569 FW 1 

In accordance with 517 DM 1, and 569 FW1, an integrated pest management (IPM) approach 

has been adopted to eradicate, control, or contain pest and invasive species on the Refuge. In 

accordance with 517 DM 1, only pesticides registered with the Environmental Protection Agency 

(EPA) in full compliance with the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), 

and as provided in regulations, orders, or permits issued by EPA, may be applied on lands and 

waters under Refuge jurisdiction. Consistent with agency policy, a Pesticide Use Plan (PUP) 

would be prepared prior to implementing the proposed action. 

8.9 EPA-APPROVED RODENTICIDE LABEL 

The proposed action would be implemented using the product Brodifacoum-25D: Conservation 

(EPA Reg. No. 56228-37). A Supplemental label would be obtained prior to transporting the 

rodenticide, to account for the particularities of the mice eradication operation on Midway Atoll 

NWR. Field applications of the rodenticide would be made in full compliance with the EPA 

supplemental label. Alternate bait products of Brodifacoum 25ppm may be considered. Given 

that the concentration of the active ingredient, brodifacoum would be the same, this would not 

alter the environmental risk profile of the operation and all potential consequences discussed for 

Brodifacoum-25D: Conservation would apply. 

8.10 EPA – NATIONAL POLLUTION DISCHARGE ELIMINATION

(NPDES) SYSTEM GENERAL PERMIT

The proposed action requires a Pesticide General Permit under the NPDES Program. Once the 

application is submitted, there is a 30-day period for EPA to respond. No response means the 

Permit is approved. Permit application will be completed online at: epa.gov/NPDES/pesticidepermitting prior to implementing the proposed action. 

8.11 PAPAHĀNAUMOKUĀKEA MARINE NATIONAL MONUMENT 

(PMNM) PERMIT

The PMNM permitting program is designed to manage and minimize human impact, while 

increasing conservation protection for Papahānaumokuākea’s natural, cultural and historic 

resources. In accordance with Presidential Proclamation 8031 and codifying regulations in 50 

CFR Part 404, all activities in the Monument, with limited exceptions, require a permit. A 

Marine Monument permit would be obtained prior to implementation of the proposed action at 

Midway. Permit application deadline is February 1, 2018. 
DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

STATEMENT OF COMPLIANCE

8-3 

8.12 EO 12898. FEDERAL ACTIONS TO ADDRESS ENVIRONMENTAL 

JUSTICE IN MINORITY AND LOW-INCOME POPULATIONS

All Federal actions must address and identify, as appropriate, disproportionately high and 

adverse human health or environmental effects of its programs, policies, and activities on 

minority populations, low-income populations, and Indian Tribes in the United States. The 

proposed action was evaluated and no adverse human health or environmental effects were

identified for minority or low-income populations, Indian Tribes, or anyone else. 

8.13 PESTICIDE APPLICATOR CERTIFICATION

USFWS and Regional policy requires Pesticide Applicator certification for employees or 

volunteers who frequently apply pesticides or who supervise the application of pesticides by 

others (relevant policies include: Integrated Pest Management Policy 569 FW 1: and Pesticide 

Users Safety 242 FW 7:) 

DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

GLOSSARY OF TERMS

9-1 

CHAPTER 9: GLOSSARY OF TERMS

Anticoagulant - a class of drugs that work to prevent blood clotting. 

Atoll - a ring-shaped reef, island, or chain of islands formed of coral. 

Behaviorally plastic - change in an organism’s behaviors or habits that results from change in 

the environmental conditions, such as a shift to a new primary food source due to changes in 

food abundance. 

Biological Control - the control of a pest by the introduction of a natural enemy or predator. 

Broadcast – (of pesticide) the uniform treatment to a broad area using various procedures of 

application, such as hand and aerial broadcast methods.

Brodifacoum - a second-generation rodenticide that requires only one feeding for a rodent to 

receive a lethal dose.

Climate - how the atmosphere “behaves” over relatively long periods of time. 

Colony (of seabirds) - a large group of birds from one or more species that nest or roost (sleep) 

close to each other at a particular location. Most seabirds are social nesters and display 

extraordinary site fidelity.

Colonization - the process in biology by which a species successfully spreads to a new area. 

Commensal - (pertaining to humans) eating together at the same table; (in ecology, of an animal, 

plant, fungus, etc.) living with, on, or in another, without injury to either. 

Coumarin-based - (pertaining to anticoagulants) a class of vitamin K antagonist (VKA)

anticoagulant drug molecules derived from coumarin (4-hydroxycoumarin). 

Diphacinone - a first-generation rodenticide which requires multiple feedings over several days 

for a rodent to receive a lethal dose.

EC50 - Half Maximal Effective Concentration; the concentration of a toxicant that gives halfmaximal response; measured in ppm. 

Endemic - a species that is native to just one place.

Ephemeral (plants) - those which sprout, reproduce, and die back very quickly as an 

evolutionary adaptation to take advantage of brief wet periods in an otherwise dry climate.

Eradication - the complete removal of a damaging species from a specific location to enable 

ecosystem recovery.

Executive Order - presidential directives issued by United States presidents; generally directed 

towards officers and agencies of the Federal government. 

Extinction - when the last of a species dies and that species ceases to exist anywhere in the 

world. 
MIDWAY SEABIRD PROTECTION PROJECT DRAFT ENVIRONMENTAL ASSESSMENT

GLOSSARY OF TERMS

9-2 

Extirpation - the complete removal of an organism from a specific location but which continues 

to exist in other places; also known as local extinction. 

Federal Mandate - orders that induce “responsibility, action, procedure or anything else that is 

imposed by constitutional, administrative, executive, or judicial action” for state and local 

governments and/or the private sector. 

Federal Acts - laws, also known as statutes, passed by a legislature. 

Granivore - seed predators that feed on the seeds of plants as a main or exclusive food source, 

leaving seeds damaged and not viable. 

Groundwater - water held underground in the soil or in pores and crevices in rock. 

Half-life - the time it takes for a certain amount of a pesticide to be reduced by half as it 

dissipates or breaks down in the environment; a pesticide will break down to 50% of the original 

amount after a single half-life.

Hemorrhaging - the flow of blood out from a blood vessel; bleeding. 

Herpetofauna - amphibians (frogs, toads, salamanders and newts) and reptiles (snakes, lizards, 

turtles, tortoises and crocodilians). 

Hopper - a piece of equipment used in many types of industry to discharge products at a steady 

rate.

Immigration - the movement of an organism to a new area from elsewhere, assisted or 

unassisted. 

Insectivorous - an animal that eats insects as a primary or exclusive food source.

Invasive - a non-native species whose introduction causes or is likely to cause economic or 

environmental harm, or harm to human health. 

Ionic strength (of seawater) - a measure of the concentration of ions in a solution which affects 

important properties such as the dissociation or solubility of different salts. 

Island Biosecurity - The policies and protocols put in place to protect island ecosystems from 

non-native species by preventing, detecting and responding to introductions. 

Lambda - Rate of growth (lambda) is the ratio of population size at the end of one interval to 

population size at the end of the previous interval. When lambda = 1.0 the population density is 

stable while values >1.0 indicate increasing populations. 

LC50 - the concentration of the chemical in feed that kills 50% of test samples; usually 

administered over a multi-day period (e.g. 5 to 7 days). 

LD50 - the amount of an ingested substance that kills 50% of test samples; usually administered 

as a single dose.
DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

GLOSSARY OF TERMS

9-3 

LOAEL - the lowest dose or exposure level of a toxicant that produces a measurable toxic effect 

on the test group of animals. 

Mitigation - steps taken to reduce or avoid negative environmental impacts. 

Native - a species that occurs naturally (without human agency) in an area.

NOAEL - a dose or exposure level of a toxicant that produces no measurable toxic effects on the 

test group of animals.

Non-native (introduced, alien) - an organism that is not native to the place in which it occurs, 

having been accidentally or deliberately transported to the new location by human activity. 

pp_ - parts per thousand (ppt), parts per million (ppm), parts per billion (ppb) are units of 

concentration for extremely dilute solutions; for example, a concentration of 1 ppm means 1 mg 

of solute in 1,000,000 mg of solution, or 1 mg of solute in 1000 g of solution, or 1 mg of solute 

in 1 kg of solution. 

Palatability - having an agreeable or pleasant taste that is accepted by the target consumer.

Pesticide - any substance or mixture of substances intended for preventing, destroying, repelling, 

or mitigating any pest.

Pica - displaying an indiscriminate preference for eating non-food items; such as chicks pecking 

and eating rocks, sticks and other foreign objects. 

Pinnipeds - seals; a diverse group of carnivorous semi-aquatic marine mammals.

Potable - safe to drink; drinkable. 

Predation - the act of one organism killing and eating other organisms; can refer to both animals 

and plants. 

Pyranine - a fluorescent dye commonly found in highlighters and used as a biological stain to 

show ingestion pathways. 

Recruitment - the ability of juvenile organisms to survive and add to the population of that 

species.

Refuge - (pertaining to wildlife) a naturally occurring sanctuary, such as an island, that provides 

protection for species from hunting, predation, or competition; it is a protected area, a geographic 

territory within which wildlife is protected.

Rodenticide – a pesticide formulated to kill rodents.

Sublethal - having an effect less than lethal.

Threshold - the magnitude or intensity that must be exceeded for a certain reaction, 

phenomenon, result, or condition to occur or be manifested. 

Weather - conditions of the atmosphere over a short period. 
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GLOSSARY OF TERMS

9-4 

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DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

APPENDIX A 

A-1 

APPENDIX A. MIDWAY ATOLL NATIONAL WILDLIFE REFUGE BIOSECURITY PLAN 

Island biosecurity results from policies and protocols put in place to protect island ecosystems 

from non-native species by preventing, detecting and responding to introductions Non-native 

species (sometimes referred to as non-indigenous, alien, or exotic species) are plants, animals, 

and micro-organisms (PAMs) transported or established outside of their natural range due to the 

activities of humans, regardless of whether these actions are intentional or not. Non-native 

invasive species (NISs) have the potential to establish populations and cause unacceptable harm. 

The main points found within the Midway Atoll Wildlife Refuge Biosecurity Plan are briefly 

summarized in this appendix. They address prevention measures, reporting protocol, education, 

and rapid response. Preventing the introduction of NISs is the most time- and cost-effective way 

to protect island ecosystems. The focus of this summary is rodents, particularly mice and rats.

I. Prevention Measures

Use a rodent-proof facility to hold supplies and equipment prior to shipping. Pack consumable 

goods in rodent-proof containers, and check non-food items carefully. Do not leave cargo outside 

over-night. On-island preparation includes setting traps/bait stations in key areas like the dock, 

airport, and cargo staging/storage areas, elevating them to avoid interference with crabs. Check 

all detection devices regularly and maintain them; have spare traps/bait on hand and replace as 

needed. Train personnel handling cargo to identify rodent signs, e.g., feces in containers, holes 

chewed in packaging, etc.

a. Boat Arrival 

All docking vessels must: (i) have rodent inspections prior to off-loading, (ii) deploy collared ratguards to all dock lines, and (iii) have pest detection and control devices in use on board, e.g., 

snap-traps and glue-traps. Carry out rodent control measures 2 weeks before departure, 2 weeks 

prior to estimated arrival, and for the duration of stay. 

b. Plane Arrival 

All planes must have rodent traps/bait stations deployed near the wheels. Those planes stored 

inside (e.g., hangers) must additionally deploy control devices around the edges of each 

structure.

II. Reporting Protocol

Report any detections or suspicions of NIS presence immediately to the Refuge Manager who 

will coordinate appropriate follow-up. 

III. Education 

Update residents and educate visitors on refuge biosecurity measures. Provide guidelines, signs, 

and brochures containing the basic protocols and procedures, e.g., how to detect, identify, and 

report NISs.
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APPENDIX A 

A-2 

IV. Rapid Response if Animals Are Detected 

a. Rodents

i. Use a variety and combination of removal methods, e.g., snap traps, bait 

stations, flavored sticky traps, rodenticides, and cage traps. Exact types of 

devices and methods will be determined by target rodent. 

ii. Bait station grid should cover all habitat types across the island. Bait 

stations and traps should be placed at a higher density around key habitat 

and detection sites.

iii. All trap and bait station locations should be numbered, visibly marked, 

and mapped. Any member of the response team should be able to easily 

locate every location.

iv. Place traps in locations with plenty of natural cover, and where animals 

are likely to be active. Place additional traps near any footprints or scat.

v. Traps should be covered and/or placed in locations (e.g. attached to tree 

limbs) that reduce the chance of interference by non-targets.

vi. Bait traps with known attractants. Check all traps daily and bait stations 

daily or every other day. Peanut butter mixed with rolled oats makes good 

rodent bait. 

vii. Keep detailed records. Any sign should be recorded and analyzed. 

viii. Any specimens caught are to be aged, sexed, breeding status obtained and 

have samples collected for DNA. DNA analysis may help determine 

source population. The specimen is then to be frozen (well labeled) in case 

required for later analysis.

ix. Staff should continually search for signs and new trap locations. 

b. Mammalian Predators 

i. A variety of trap types should be used. Possibilities include snares, 

foothold traps, conibear traps, and box traps. Exact size and trapping 

techniques will be dictated by the target animal.

ii. Bait traps with known attractants. Check all traps daily and bait stations 

daily or every other day. Peanut butter mixed with rolled oats makes good 

rodent bait. 

c. Reptiles and Amphibians 

i. Active search and capture of individuals by hand, with sniffer dogs, or 

using nets or nooses. 

ii. Drift fences with funnel traps 
DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

APPENDIX A 

A-3 

d. Post-Animal Review 

i. Monitor island-wide to verify that all individuals have been removed and a 

population was not established. During and after an introduction, review 

the current biosecurity practices and identify how the animal arrived on 

island. Any failures identified in the biosecurity protocols must be reevaluated to prevent similar situations from occurring. 

DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

APPENDIX B

B-1 

APPENDIX B.SUMMARY OF PROPOSED MONITORING

Documentation of the best operational approach, the efficacy of the operation, the environmental

and ecological effects of the proposed action requires monitoring of a number of parameters 

before, during, and after the implementation of an eradication operation will be undertaken by 

the Restoration partners. 

I. Eradication Planning 

To inform eradication planning efforts where possible (e.g., baiting methods, evaluation of 

methods to reduce non-target impacts of the eradication procedure) we will evaluate bait uptake 

rates and persistence in representative habitats and use DNA Metabarcoding to provide direct 

evidence for mice diet components. We will collect mouse diet samples via stomach contents 

and mouse feces in stratified habitat types; collect samples of diet items if DNA hasn’t been 

previously characterized. These data can directly inform eradication planning and baiting 

strategy. We will monitor phenology of plants suspected of being important in mouse diets. 

II. Conservation Measures

To measure recovery of target conservation species and ecosystems and the unintended 

consequences of the removal of a ubiquitous species, a number of ecosystem components will be

characterized prior to and at 1, 3, 5 and 10 years post-eradication. Good monitoring will enable 

land managers to predict and prepare for positive and negative impacts of the eradication action 

(pre-eradication) and clearly document conservation gains (post-eradication).

Taxa identified for monitoring, parameters to be measured, and methods include: 

1. Seabirds, especially those burrow nesters and ground-nesters particularly vulnerable 

torodent predation such as Laysan Albatross, Tristram’s Storm-petrel, Bulwer’s 

Petrel, and Bonin Petrel for which we will measure breeding population size using 

counts and acoustic activity and reproductive performance and impacts of mice to 

Bonin petrels by using camera traps and tracking cards to document mouse-seabird 

interactions. We will deploy 10-13 Songmeters across Sand and Eastern (control) at 

known and potential breeding locations to record call activity to record population 

densities of cryptic burrow nesting species such as Tristram’s Storm-petrels and 

Bulwer’s Petrels. We will observe and quantify impacts of mice on Laysan and 

Black-footed Albatross mice and chicks within and outside of mouse control 

treatment areas by monitoring albatross nest density and reproductive success within 

a subset of existing albatross demography 20 x 20m plots as well as additional plots 

(e.g., zones where no baiting is being conducted as well as Eastern Island as a 

control). 

2. Laysan Duck, for which we will monitor population size, reproductive performance, 

and behavior. We will quantify direct and indirect impacts of mice on duck 

population by the use of camera traps on nests and conducting measures of 

reproductive performance and foraging behavior before and after implementation. 

After live-capture and holding ducks on Sand or Eastern Island, birds will be released 

in a step-wise progression beginning 30 days after the final bait application or until 

bait pellets are no longer available to be consumed or biological samples collected 
DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

APPENDIX B 

B-2 

post-application indicate low risk. Monitoring will also include recapture of ducks 

demonstrating signs of toxicosis, radio-tagging and aggressive tracking of sentinel 

ducks released post-bait application.

3. Arthropod community, for which we will document changes in population densities 

of land crabs, insects, and spiders. We will confirm extant land crab species for 

Midway Atoll and document density and demography of land crab population by 

conducting opportunistic searches and observations of crabs and potential crab holes 

that are not obviously the known species, Ocypode pallidul, and surveying quadrats 

across potential crab habitat, counting burrows and measuring width of burrows. We 

will monitor arthropod abundance and richness by deploying pitfall traps in stratified 

habitats and count sample and identify them to families.

4. Plant community and seed production, especially species known to provide 

important forage for native species in order to understand the extent of competition 

between introduced house mouse and native birds and insects. We will quantify 

native seed availability (potential food resource for both mice and ducks) before and 

after mouse removal by counting seeds and looking at plant recruitment rates for 

selected species. DNA Metabarcoding will help to predict where land managers can 

expect to see changes in flora and fauna and identify areas of focus for preeradication monitoring efforts. 

III. Efficacy Monitoring 

Documentation of bait persistence and availability during the implementation period over all 

habitat types will inform practitioners of appropriateness of application rates. Telemetry of radiotagged mice during the implementation will allow us to track fates of a sample of individuals. 

Post eradication detection methods including chew blocks, trail cameras, and other techniques 

will evaluate successful removal of all mice from Sand Island.

IV. Environmental Impact and Residue Monitoring

1. Brodifacoum residue monitoring: Environmental brodifacoum residues will be 

evaluated by testing of soil and seawater samples before and after baiting operations. 

Brodifacoum residues in living tissues (e.g., food web compartments) will be assessed 

by collection and euthanasia of appropriate invertebrates, lizards, fishes and birds, 

with liver tissues (site of greatest accumulation) harvested and submitted for 

chemistry (whole-body samples will be shipped for processing, with tissue harvest 

occurring under residue-sanitary conditions). Any tissues representative of items for 

human food consumption (mollusks, game fish) will have whole-body or muscle 

tissues analyzed as well. Cockroaches, which are demonstrated to be a significant 

consumer of rodenticide baits and in turn are heavily consumed by Laysan Ducks, 

will be a particular focus of sampling, with diminishment of brodifacoum levels to be 

confirmed before ducks are returned to Midway Island. 

2. Mortality of all non-target organisms associated with the baiting operations will be 

assessed by active searching for non-target carcasses on terrestrial and near-shore 

marine environments (including recording of data on search effort), and by 

opportunistic sampling during other aspects of operational activities. Carcasses that 

appear to be within approximately three days of time of death, for which cause of 
DRAFT ENVIRONMENTAL ASSESSMENT MIDWAY SEABIRD PROTECTION PROJECT

APPENDIX B

B-3 

death is not obvious (e.g., aircraft strike), will be collected and submitted for 

brodifacoum residue testing. 

3. Sampling of prey species important to terrestrial vertebrates vulnerable to 

brodifacoum will continue periodically until residue levels become undetectable or 

until the levels are deemed not harmful to Laysan ducks and other migratory bird 

species foraging in the terrestrial environment on Sand Island. 

Chemical analyses (assay and quantification by liquid chromatography and tandem mass 

spectrometry, “LC-MS/MS”) will be conducted by the USDA NWRC Chemistry Lab Unit in 

Fort Collins, Colorado. Detection and quantitation limits for each sample type will be established 

during analysis. Remaining tissues or homogenates may be made available for confirmatory 

testing by external agencies.

Given that brodifacoum has higher toxicity and a longer half-life (compared to first-generation 

anticoagulants), and therefore an increased risk of bioaccumulation in the food web, sampling 

will continue over a long enough timeframe to ensure that appropriate environmental thresholds 

have been met for actions such as the release of Laysan Ducks from protective captivity.

V. Mitigation Measures and Effectiveness Monitoring 

Mitigation measures and actions identified for multiple species in Chapter 3 would be carried out 

and monitored for their effectiveness. Effectiveness monitoring tracks the success in achieving 

desired outcomes and evaluating environmental effects. Mitigation includes specific measures or 

practices that would reduce, avoid or eliminate the effect of the proposed action on non-target 

species. In this EA, the identified mitigation measures are part of the proposed action (project) 

and necessary to support a FONSI. Examples of mitigation measures in Chapter 3 include: 

training ground-based staff to identify endangered plants and how to avoid stepping on seabird 

burrows; capturing and moving vulnerable species to avoid rodenticide exposure; measures to 

minimize bait entering the marine environment; and measures to reduce impacts to sea turtles 

and monk seals. For detailed descriptions see the mitigation section for each species in Chapter 

3. 
U.S. Fish & Wildlife Service National

Wildlife Refuge System Pacific

Marine National Monuments

300 Ala Moana Blvd. 

Honolulu, HI 96850

808/792 9484

March 2018

Front cover: Wisdom’s mate and their chick

Kiah Walker/USFWS Volunteer

Back cover: Albatross nesting at Midway Atoll

© L. Young/Pacific Rim Conservation