Restoring Wildlife Habitat on Rat Island 

Alaska Maritime National Wildlife Refuge 

Aleutian Islands Unit 

Environmental Assessment 

 U.S. Fish and Wildlife Service 

Alaska Maritime National Wildlife Refuge 

December 2007 
Executive Summary 

Restoration of natural ecosystem function on Rat Island promises to re-establish native seabirds 

and other native species, thus returning this wilderness island to a healthy natural community. 

This restoration cannot occur until the island is cleared of the invasive non-native rats that now 

dominate the living community. 

Introduced non-native species are a leading cause of extinctions in island communities 

worldwide. Increasingly, land managers are removing introduced species to aid in the restoration 

of native ecosystems. Rats are responsible for 40-60% of all recorded bird and reptile extinctions 

worldwide. Given their widespread successful colonization on islands and the resulting impact to 

native species, introduced rats are identified as key species for eradication. 

Most of the Aleutian Islands lying within the Alaska Maritime National Wildlife Refuge (NWR) 

provide important breeding habitat for seabirds, including many for which the Aleutians provide 

a substantial portion of their worldwide range. Norway rats are established on at least 10 

Aleutian islands or island groups, and the diversity and numbers of breeding seabirds occurring 

on those islands are now conspicuously low. Rat-caused modifications to other components of 

the island ecosystems (e.g., other birds, plants, and invertebrates) are also evident. 

The restoration of Aleutian ecosystems through introduced predator eradications has long been 

identified as a priority for Alaska Maritime NWR, and the initial efforts have been directed to 

removing introduced foxes. The focus now has turned to rats. This Environmental Assessment 

evaluates the environmental effects of eradicating introduced non-native rats from Rat Island, 

located in the central Aleutians within Alaska Maritime NWR. The consequences of the No 

Action alternative are addressed along with the Preferred Alternative (Proposed Action hereafter) 

which is to eradicate rats from Rat Island employing an aerial broadcast of rodenticide, and 

subsequently maintaining the island in rodent-free status. The intent of the Proposed Action is to 

facilitate the restoration of the natural island ecosystem by improving habitat quality for native 

species. 

Figure 1. Rat Island is located in the central Aleutian Islands. 

ii
Public Comment Period:

December 12, 2007 through January 11, 2008

The Alaska Maritime National Wildlife Refuge is seeking public comment on this 

Environmental Assessment which proposes the restoration of native species and natural 

ecosystem function on Rat Island through the eradication of invasive rats. A 30 day comment 

period opens December 12, 2007. Written comments via fax, mail or email are requested by the 

close of business January 11, 2008. 

The document is available online at http://alaskamaritime.fws.gov/news.htm. Reading copies 

have been placed in the public libraries of the communities of Unalaska, Homer and at the US 

Fish and Wildlife Service Alaska Regional Office reception desk located at 1011 E. Tudor Road 

in midtown Anchorage. If you need a paper copy please contact the Refuge. 

Following the closing of the comment period, the Service will examine the comments and 

determine whether the Environmental Assessment action warrants a “Finding of No Significant 

Impact”. If a Finding of No Significant Impact is warranted, plans will proceed for rat 

eradication on Rat Island. 

Contact Person: 

Will Meeks, Deputy Refuge Manager 

Alaska Maritime National Wildlife Refuge 

95 Sterling Highway, Suite 1. Homer, AK 99603 

FAX: (907) 235-7783 email: rat_island@fws.gov 

iii
Table of Contents 

Executive Summary........................................................................................................................ ii 

Public Comment Period:................................................................................................................iii 

Table of Contents........................................................................................................................... iv 

1. Purpose & Need .......................................................................................................................... 1 

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

1.2. Purpose of Action .................................................................................................................... 1 

1.3. Need for Action........................................................................................................................ 1 

1.3.1. Introduced Rats on the Alaska Maritime National Wildlife Refuge............................. 2 

1.3.2. Impacts of Introduced Rats on Island Ecosystems in General...................................... 3 

1.3.3. Eradication of Rats from Islands................................................................................... 5 

1.4. Scope of Analysis .................................................................................................................... 5 

1.5. Authority for Action & Regulations Governing Action .......................................................... 6 

1.5.1. Authorities for Taking Action....................................................................................... 6 

1.5.1.1. U.S. Fish and Wildlife Service statutes, policies, and plans.................................. 6 

1.5.1.2. Executive Orders.................................................................................................... 7 

1.5.2. Regulatory Framework ................................................................................................. 7 

1.5.2.1. Federal laws........................................................................................................... 8 

1.5.2.2 Alaska state laws and policies................................................................................. 8 

1.5.2.2.1 Alaska Board of Game..................................................................................... 8 

1.5.2.2.2. Alaska Department of Fish and Game (ADF&G) .......................................... 9 

1.5.2.2.3. Alaska Department of Health and Social Services, Division of Public Health, 

Section of Epidemiology............................................................................................... 10 

1.5.2.2.4. Alaska pesticide-related laws and responsible entities................................. 10 

1.6. Purpose of This Analysis ....................................................................................................... 11 

2. Alternatives............................................................................................................................... 12 

2.1. Alternative A: No Action....................................................................................................... 12 

2.2. Alternative B (Proposed Action): Introduced Rat Eradication from Rat Island, Aerial Bait 

Broadcast Technique..................................................................................................................... 12 

2.2.1. Summary of Actions................................................................................................... 12 

2.2.2. Description of Action Operations ............................................................................... 13 

2.2.2..1 Timing.................................................................................................................. 13 

2.2.2.2. Project staging...................................................................................................... 15 

2.2.2.3. Introduction to broadcast bait application............................................................ 16 

2.2.2.4. Bait pellet composition ........................................................................................ 17 

2.2.2.5. Determining application rate................................................................................ 18 

2.2.2.6. Number of bait applications................................................................................. 18 

2.2.2.7. Bait hopper........................................................................................................... 18 

2.2.2.8. Equipment calibration.......................................................................................... 19 

2.2.2.9. Flight plan ............................................................................................................ 19 

2.2.2.10. Monitoring bait application................................................................................ 19 

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2.2.2.11. Preventing bait spread into the marine environment ......................................... 20 

2.2.2.12. Preventing bait spread into the freshwater environment.................................... 20 

2.2.2.13. Supplemental bait broadcast .............................................................................. 21 

2.2.2.14. Special treatment of the islet off Ayugadak Point ............................................. 22 

2.2.2.15. Personal protective equipment........................................................................... 22 

2.2.2.16. Training and supervision.................................................................................... 23 

2.2.3. Rodenticide (Brodifacoum) ........................................................................................ 23 

2.2.3.1. Introduction to brodifacoum ................................................................................ 23 

2.2.4. Impact Mitigation........................................................................................................ 23 

2.2.4.1. Archaeological site impact mitigation ................................................................. 23 

2.2.4.2. Wildlife impact mitigation measures................................................................... 24 

2.2.4.2.1. Mitigating for rodenticide risks .................................................................... 24 

2.2.4.2.2. Mitigating for disturbance risk...................................................................... 25 

2.2.5. Public Information ...................................................................................................... 25 

2.2.6. Monitoring Eradication Efficacy and Ecosystem Response....................................... 25 

2.2.7. Rodent Prevention and Response to New Introductions............................................. 26 

2.2.7.1. Prevention ............................................................................................................ 26 

2.2.7.2. Response .............................................................................................................. 27 

2.3. Alternatives Dismissed from Detailed Consideration............................................................ 27 

2.3.1. Widespread Use of Bait Stations for Bait Delivery.................................................... 27 

2.3.2. Use of a First-Generation Anticoagulant (Diphacinone)............................................ 28 

2.3.2.1. Toxicology comparison: brodifacoum vs. diphacinone....................................... 28 

2.3.2.2. Pros and cons of diphacinone in comparison to brodifacoum............................. 28 

2.3.2.3. Diphacinone and eradication efficacy.................................................................. 29 

2.3.2.4. Diphacinone and operational considerations....................................................... 29 

2.3.2.5. Weighing the costs and benefits of rat eradication .............................................. 30 

2.3.3. Other Toxins ............................................................................................................... 30 

2.3.4. Use of Disease............................................................................................................. 31 

2.3.5. Trapping...................................................................................................................... 31 

2.3.6. Biological Control....................................................................................................... 32 

2.3.7. Fertility Control .......................................................................................................... 32 

2.3.8. Rat Removal with the Goal of “Control”.................................................................... 32 

3. Affected Environment............................................................................................................... 34 

3.1. Introduction............................................................................................................................ 34 

3.2. Physical Description .............................................................................................................. 35 

3.3. Climate................................................................................................................................... 37 

3.4. Biological Description ........................................................................................................... 37 

3.4.1. Marine Waters............................................................................................................. 37 

3.4.2. Intertidal...................................................................................................................... 38 

3.4.3. Terrestrial Vegetation ................................................................................................. 38 

3.4.4. Freshwater Wetlands................................................................................................... 39 

3.4.5. Marine Mammals........................................................................................................ 39 

3.4.6. Birds............................................................................................................................ 41 

3.4.6.1. ESA-listed bird species........................................................................................ 41 

3.4.6.2. Non-ESA-listed bird species................................................................................ 41 

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3.4.7. Terrestrial Mammals................................................................................................... 46 

3.4.8. Freshwater Fish........................................................................................................... 46 

3.5. Cultural Resources................................................................................................................. 46 

3.6. Current Human Uses of the Area........................................................................................... 47 

4. Environmental Consequences................................................................................................... 48 

4.1. Introduction............................................................................................................................ 48 

4.2. Categories Analyzed (Descriptions) ...................................................................................... 48 

4.2.1. Restoration Efficacy.................................................................................................... 48 

4.2.2. Assessing Impacts to Biological Resources................................................................ 49 

4.2.2.1. Assessing risks to biological resources from rodenticide use.............................. 49 

4.2.2.1.1. Toxicity......................................................................................................... 49 

4.2.2.1.2. Exposure ....................................................................................................... 51 

4.2.2.1.3. Assessing overall risk from brodifacoum use............................................... 53 

4.2.2.2. Assessing risk to biological resources from disturbance ..................................... 54 

4.2.2.3. Assessing cumulative impacts to biological resources........................................ 54 

4.2.2.4. Limited analysis of invertebrates......................................................................... 55 

4.2.2.5. Limited analysis of vegetation............................................................................. 55 

4.2.2.6. Assessing significance of impacts to biological resources.................................. 55 

4.2.2.7. Special considerations for ESA-listed species..................................................... 56 

4.2.2.8. Special considerations for marine mammals ....................................................... 56 

4.2.2.9. Special considerations for migratory birds.......................................................... 57 

4.2.2.10. Special considerations for bald eagles............................................................... 57 

4.2.3. Assessing Impacts to Water Resources....................................................................... 58 

4.2.4. Assessing Impacts to Wilderness Character............................................................... 58 

4.2.5. Assessing Impacts to Historical and Cultural Resources............................................ 59 

4.2.6. Assessing Impacts to Social and Economic Values.................................................... 59 

4.3. Aspects of the Environment Excluded from Detailed Analysis (with rationale)................... 59 

4.3.1. Marine Fish ................................................................................................................. 59 

4.3.2. Cetaceans .................................................................................................................... 60 

4.3.3. Air Quality .................................................................................................................. 60 

4.4. Alternative A: No Action....................................................................................................... 60 

4.4.1. Introduction................................................................................................................. 60 

4.4.2. Restoration Efficacy.................................................................................................... 61 

4.4.3. Impacts to Species Listed Under the Endangered Species Act................................... 61 

4.4.3.1. Steller sea lion...................................................................................................... 61 

4.4.3.2. Northern sea otter................................................................................................. 61 

4.4.3.3. Steller’s eider....................................................................................................... 61 

4.4.4. Impacts to Species Listed Under the Marine Mammal Protection Act ...................... 61 

4.4.4.1. Species also listed under ESA.............................................................................. 61 

4.4.4.2. Harbor seal........................................................................................................... 62 

4.4.5. Impact on Species Listed Under the Migratory Bird Treaty Act................................ 62 

4.4.5.1. Waterfowl ............................................................................................................ 62 

4.4.5.2. Birds of prey ........................................................................................................ 62 

4.4.5.3. Passerines and other landbirds............................................................................. 62 

4.4.5.4. Seabirds and shorebirds ....................................................................................... 63 

vi
4.4.6. Impacts to Other Species On and Around Rat Island ................................................. 63 

4.4.6.1. Terrestrial invertebrates....................................................................................... 63 

4.4.6.2. Freshwater organisms .......................................................................................... 63 

4.4.6.3. Intertidal organisms ............................................................................................. 64 

4.4.6.4. Vegetation............................................................................................................ 64 

4.4.6.5. Multi-trophic cascading effects............................................................................ 64 

4.4.7. Impacts to Water Quality............................................................................................ 64 

4.4.8. Impacts to Wilderness Character................................................................................ 64 

4.4.9. Impacts to Historical and Cultural Resources............................................................. 65 

4.4.10. Impacts to Social and Economic Values................................................................... 65 

4.4.10.1. Fishery resources ............................................................................................... 65 

4.4.10.2. Refuge visitors................................................................................................... 65 

4.4.10.3 Subsistence uses.................................................................................................. 65 

4.5. Alternative B: Rat Eradication from Rat Island, Aerial Broadcast Technique...................... 66 

4.5.1. Restoration Efficacy.................................................................................................... 66 

4.5.2. Impacts to Species Listed Under the Endangered Species Act................................... 67 

4.5.2.1. Steller sea lion...................................................................................................... 67 

4.5.2.2. Northern sea otter................................................................................................. 70 

4.5.2.3. Steller’s eider....................................................................................................... 72 

4.5.3. Impacts to Species Listed Under the Marine Mammal Protection Act ...................... 74 

4.5.3.1. Species also listed under ESA.............................................................................. 74 

4.5.3.2. Harbor seal........................................................................................................... 74 

4.5.4. Impact on Species Listed Under the Migratory Bird Treaty Act................................ 76 

4.5.4.1. Waterfowl ............................................................................................................ 76 

4.5.4.2. Birds of prey ........................................................................................................ 79 

4.5.4.3. Shorebirds............................................................................................................ 82 

4.5.4.4. Marine birds except gulls and jaegers.................................................................. 84 

4.5.4.5. Scavenging and predatory seabirds...................................................................... 88 

4.5.4.6. Common raven..................................................................................................... 90 

4.5.4.7. Small and medium-sized passerines (other than ravens)..................................... 92 

4.5.5. Impacts to Bald Eagles................................................................................................ 95 

4.5.6. Impacts to Other Species On and Around Rat Island ................................................. 98 

4.5.6.1. Rock ptarmigan.................................................................................................... 98 

4.5.6.2. Freshwater fish..................................................................................................... 99 

4.5.6.3. Terrestrial Vegetation ........................................................................................ 100 

4.5.7. Impacts to Water Resources...................................................................................... 101 

4.5.8. Impacts to Designated Wilderness............................................................................ 102 

4.5.9. Impacts to Historical and Cultural Resources........................................................... 102 

4.5.10. Impacts to Social and Economic Values................................................................. 103 

4.5.10.1. Refuge visitors................................................................................................. 103 

4.5.10.2. Fishery resources ............................................................................................. 103 

4.5.10.3. Subsistence resources....................................................................................... 103 

5. Consultation and Coordination ............................................................................................... 106 

5.1. Preparers .............................................................................................................................. 106 

5.2. Contributors......................................................................................................................... 106 

vii
5.3. Agencies, Organizations, and Persons Consulted................................................................ 106 

6. References............................................................................................................................... 108 

Appendix 1: The status of birds that are likely to be present at Rat Island in fall...................... 124 

Appendix 2: Historical observations of Wildlife at Rat Island (1937 – 2004)...Error! Bookmark 

not defined.

Appendix 3: Minimum Requirements Decision Guide .............................................................. 129 

Appendix 4: ANILCA 810 Evaluation ....................................................................................... 139 

viii
List of Figures and Tables

FIGURES

Figure 1. Rat Island is located in the central Aleutian Islands........................................................ ii 

Figure 2. Rat Island, Alaska Google Earth Satellite Image ......................................................... 1 

Figure 3. Map of Alaska Maritime National Wildlife Refuge........................................................ 3 

Figure 4: Norway rat on Rat Island 2007 Island Conservation ................................................... 4 

Figure 5. Coastal environment on Rat Island Ebbert 2001...................................................... 12 

Figure 6. Proposed Rat Island field camp and staging areas ........................................................ 16 

Figure 7. Aerial broadcast of rat rodenticide on Anacapa Is., CA. S. Ebbert 2002................... 17 

Figure 8. Bait hopper loaded for broadcast, Anacapa Is. rat eradication S. Ebbert 2002.......... 19 

Figure 9. Map of Rat Island showing lake clusters....................................................................... 21 

Figures 10a & b. Coastal cliffs on Rat Island. .............................................................................. 22 

Figure 11. Location map of Rat Island in Alaska ......................................................................... 34 

Figure 12. Rat Island, Alaska Maritime NWR S. Ebbert 2001.................................................. 35 

Figure 13. Map of Rat Island, Alaska Maritime NWR, including The Aleut Corporation 

selections (red).............................................................................................................................. 37 

Figure 14. Overlooking upland plateau on Rat Island, showing a lake cluster. .......................... 39 

Figure 15. Norway rat survey on Rat Island 2002 AMNWR .................................................... 48 

Figure 16. Field camp in Gunner’s Cove on Rat Island, 2007. .................................................. 104 

TABLES

Table 3.1. Recent survey results for marine mammals that haul-out on Rat Island.................40 

Table 3.2. Birds expected to occur at Rat Island in fall (Sept.-October)..............................43 

Table 4.1. Generalized proportion of daily food intake that must be bait for birds to reach an 

LD50 threshold...............................................................................................50 

Table 4.2. Likelihood of exposure to brodifacoum based on food habits and other 

characteristics.................................................................................................53 

Table 4.3. Summary: Impacts of the Proposed Action, by issue.....................................105 

ix
List of Acronyms used in this document

AAC Alaska Administrative Code 

ACMP Alaska Coastal Management Program 

ADF&G Alaska Dept of Fish and Game 

AIU Aleutian Islands Unit (of the Alaska Maritime NWR) 

AMNWR Alaska Maritime National Wildlife Refuge (Alaska Maritime NWR) 

ANCSA Alaska Native Claims Settlement Act 

ANILCA Alaska National Interest Lands Conservation Act 

APHIS Animal Plant Health Inspection Service, USDA 

AS Alaska Statutes 

BGEPA Bald and Golden Eagle Protection Act 

BIA Bureau of Indian Affairs 

CCP Comprehensive Conservation Plan 

CEQ US Council on Environmental Quality 

CFR Code of Federal Regulations 

CWA Clean Water Act 

CZMA Coastal Zone Management Act 

DEC Alaska Dept. of Environmental Conservation 

DCED Alaska Dept. of Commerce, Community and Econ. Development 

DGPS Differential global positioning system 

DNR Alaska Dept. of Natural Resources 

DOI Department of Interior 

DOT Alaska Dept. of Transportation and Public Facilities 

DPS Distinct population segment 

EA Environmental Assessment 

EIS Environmental Impact Statement 

EO Executive Order 

EPA US Environmental Protection Agency 

ESA Endangered Species Act 

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act 

FONSI Finding of No Significant Impact 

FWS US Fish and Wildlife Service 

GPS Global positioning system 

LD50 Dosage of a toxin that is lethal to 50% of animals in a laboratory test 

MBTA Migratory Bird Treaty Act 

MMPA Marine Mammal Protection Act 

NEPA National Environmental Policy Act 

NHPA National Historic Preservation Act 

NMFS National Marine Fisheries Service 

NOAA National Oceanic and Atmospheric Administration 

NWR National Wildlife Refuge (as in Alaska Maritime NWR) 

OPMP Alaska DNR, Office of Project Management and Permitting 

UNESCO United Nations Educational, Scientific, and Cultural Organization 

USC United States Code 

USDA United States Department of Agriculture 

WWII World War II 

x
1. Purpose & Need 

Figure 2. Rat Island, Alaska Google Earth Satellite Image 

1.1. INTRODUCTION

This environmental assessment (EA) evaluates the environmental effects of one alternative other 

than the No Action alternative for rat eradication on Rat Island, a wilderness area, within the 

Alaska Maritime National Wildlife Refuge (Alaska Maritime NWR or Refuge). The EA will be 

used by the U.S. Fish and Wildlife Service (FWS) to solicit public involvement and to determine 

whether the implementation of the alternatives would have a significant impact on the quality of 

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

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

1.2. PURPOSE OF ACTION

The purpose of the Proposed Action is to eradicate introduced non-native rats from Rat Island 

and maintain its rodent-free status, which will facilitate the restoration of the natural island 

ecosystem and improve habitat quality for native species. 

1.3. NEED FOR ACTION

 
Chapter 1: Purpose & Need 

1.3.1. Introduced Rats on the Alaska Maritime National Wildlife Refuge 

Introduced non-native species are a leading cause of extinctions in island communities 

worldwide (World Conservation Monitoring Centre 1992). Increasingly, land managers are 

developing and implementing techniques for removing introduced species to aid in the 

restoration of native ecosystems. Rats living in close association, or commensally, with humans 

(the Norway rat Rattus norvegicus, black rat R. rattus, and Polynesian rat R. exulans) have been 

introduced to about 90% of the world’s islands (Towns et al. 2006), and are responsible for 40-

60% of all recorded bird and reptile extinctions globally (Atkinson 1985; Island Conservation 

analysis of World Conservation Monitoring Centre data). Given the widespread successful 

colonization of rats on islands and their impact on native species, rats are identified as key 

species for eradication (Howald et al. 2007). 

Norway rats (and in one recorded case, the black rat) are established on at least 10 independent 

Aleutian islands or island groups within the Aleutian archipelago. The Aleutians, including many 

of the islands in Alaska Maritime NWR, provide breeding habitat for 26 species of seabirds 

(Gibson and Byrd 2007) including species and subspecies for which the Aleutians provide a 

substantial portion of their worldwide range. However, the diversity and numbers of breeding 

seabirds are conspicuously low on islands with an established population of introduced rats 

(Atkinson 1985; Ebbert and Byrd 2002; Major and Jones 2005). This phenomenon is consistent 

with worldwide observations of the devastating direct impacts of introduced rats on seabirds 

(Atkinson 1985; Towns et al. 2006; and see below for examples). 

In the Aleutians, besides the indirect evidence of rat impacts cited above (i.e., absence of 

otherwise widespread species), there is direct observational and experimental evidence of rat 

predation on seabirds. For example, rat impacts on seabirds are documented for Kiska Island, 

where rats are preying on least (Aethia pusilla) and crested auklets (A. cristatella) (Major and 

Jones 2005). Food caches from rats near the Kiska auklet colony have been found to contain up 

to 150 auklet carcasses in a single cache (I.L. Jones, pers. comm.). Experiments in the Bay of 

Islands, located off Adak Island, indicated very high egg predation rates on artificial alcid nests, 

demonstrating that invasive rat impact to nesting seabirds can be severe and that the removal of 

the rat population has the potential to provide measurable increases in the nesting success of 

impacted seabirds (Buckelew et al. 2007a). Furthermore, recent research suggests that rat 

predation on nesting marine birds such as glaucous-winged gulls (Larus glaucescens) and black 

oystercatchers (Haematopus bachmani) might also indirectly alter intertidal community structure 

(Kurle 2005). Shorebirds and some seabirds forage heavily on intertidal invertebrate grazers, and 

are capable of significantly altering both the species assemblage and algal abundance of 

intertidal communities. Significant predation by rats on intermediate marine predators has shifted 

the intertidal community structure of islands with introduced rats (Kurle 2005; C. Kurle, pers. 

comm.). Other research on the Aleutians, which addressed the impacts of another seabird 

predator, arctic fox (Alopex lagopus), suggests that predation on seabirds also has the potential to 

broadly impact the terrestrial ecosystem through removal of marine-derived nutrients formerly 

supplied by seabirds (see Croll et al. 2005; Maron et al. 2006). 

Rats are thought to have been introduced to Rat Island by shipwreck in the late 1700s (Black 

1983). Other than these non-native invasive rats and non-native introduced fox, which were 

2
Chapter 1: Purpose & Need 

removed from the island in 1984, no terrestrial mammals occur on Rat Island. Because the initial 

rat introduction was so long ago, the lack of baseline biological data from Rat Island before rats 

were introduced makes it difficult to determine the previous ecological condition of the island 

with great precision. Consequently, it is also difficult to precisely infer the ecological impacts of 

introduced rats on Rat Island specifically. The ecological impacts that rats have caused on Rat 

Island may have largely occurred soon after they were introduced, leaving the island ecosystem 

in an altered state for an extended period. However, the relative ecological similarity between 

neighboring islands in the Aleutians gives us clues to the former ecological state on Rat Island. 

Such a comparison reveals that Rat Island has a much lower abundance and diversity of breeding 

seabirds than other apparently similar Aleutian islands that are rat-free. Furthermore, the 

terrestrial vegetation on Rat Island is quite different than neighboring islands that have large 

seabird colonies and no rats (Byrd 1984, 1989; Croll et al. 2005). This evidence, when combined 

with the preponderance of evidence implicating rats in serious ecological damage on other 

temperate-climate and sub-polar islands worldwide, cast the presence of introduced rats on Rat 

Island as a serious threat to native species and natural ecosystem processes. 

Figure 3. Map of Alaska Maritime National Wildlife Refuge 

1.3.2. Impacts of Introduced Rats on Island Ecosystems in General 

The most pronounced impact of introduced rats on island ecosystems is the extinction of 

endemic species of mammals, birds and invertebrates on islands throughout the world’s oceans 

(Andrews 1909; Daniel and Williams 1984; Meads et al. 1984; Atkinson 1985; Hindwood 1940; 

Tomich 1986). 

Even if species are not completely extirpated, rats can have negative direct and indirect effects 

on native species and ecosystem function. For example, comparisons of rat-infested and rodentfree islands, and pre- and post-rat eradication experiments, have shown that rats depressed the 

population size and recruitment of birds (Thibault 1995; Campbell 1991; Jouventin et al. 2003), 

reptiles (Bullock 1986; Cree et al. 1995; Whitaker 1973; Towns 1991), plants (Campbell et al. 

1984; Pye et al. 1999) and terrestrial invertebrates (Ramsey 1978; Bremner et al. 1984). Rats are 

3
Chapter 1: Purpose & Need 

known to cause disturbance to sensitive breeding seabirds, resulting in failed breeding attempts 

and higher susceptibility to predation by other species (Jouventin et al. 2003; Tomkins 1985). 

Rats also affect the abundance and age structure of intertidal invertebrates (Navarrete and 

Castilla 1993). Rats alter key ecosystem properties; for example, total soil carbon, nitrogen, 

phosphorous, mineral nitrogen, marine-derived nitrogen and pH are lower on invaded islands 

relative to rat-free controls (Fukami et al. 2006). Such changes are a result of indirect negative 

effects of rats mediated by the reduction in seabird populations – rat predation often drives 

seabird colonies to near-extirpation (Moller 1983; Atkinson 1985; McChesney and Tershy 1998), 

resulting in the loss of seabird-derived nutrients on islands (Fukami et al. 2006). Where rats coexist with other predators (such as cats or predatory birds) the collective direct impact of 

introduced predators on seabirds is greater than the sum of the individual impacts because rats 

also act as a food resource to higher level predators when seabirds are absent from the islands 

(Atkinson 1985; Moors and Atkinson 1984). 

In addition to preying on local seabird colonies, introduced rats feed opportunistically on plants, 

and alter the floral communities of island ecosystems (Campbell and Atkinson 2002), in some 

cases degrading the quality of nesting habitat for birds that depend on the vegetation. On Tiritiri 

Matangi Island, New Zealand, ripe fruits, seeds, and understory vegetation cover underwent 

significant increases after rats were eradicated from the island, indicating their previous impacts 

on the vegetation (Graham and Veitch 2002). 

Each of the three species of introduced rats has been implicated in extinctions and changes in 

prey population structure. Although all rat species affect insular biota, due to their different 

natural histories each species has slightly different impacts. For example, of the three introduced 

rat species, the Norway rat tends to have the greatest impact on burrow-nesting seabirds, the 

black rat tends to prefer preying on tree-nesting birds, and the Polynesian rat appears to impact 

both types of nesters (Atkinson 1985). Consequently, the introduction of new Rattus species 

should be avoided, even to islands that already have introduced rats (Moors et al. 1992). 

Figure 4: Norway rat on Rat Island 2007 Island Conservation 

4
Chapter 1: Purpose & Need 

1.3.3. Eradication of Rats from Islands 

Removal of introduced apex predators such as foxes and rats from islands can reverse the 

cascading detrimental ecosystem effects initiated by these species and allow for the recovery of 

seabirds and other impacted species (e.g. the Aleutian cackling goose, Branta canadensis 

leucoparia, which was removed from the Endangered Species list in 2001 after introduced foxes 

were removed from critical habitat in the Aleutian Islands). The restoration of Aleutian 

ecosystems through introduced predator eradications has long been identified as a priority for 

Alaska Maritime NWR in its Comprehensive Conservation Plan (USFWS1988) and management 

efforts (Murie 1959; Bailey 1993). 

There have been at least 318 successful island rat eradications worldwide, from the deep tropics 

to high latitudes (Howald et al. 2007). The fundamental methodology that all but one of these 

eradications used was the delivery of bait containing a rodenticide into every potential rat 

territory on the island. Bait was typically delivered during the time of year when rats were 

relatively food deprived, as indicated by annual resource-dependent population declines. 

Depending on island topography and size, climate, native species assemblages, operational 

logistics and other factors, these eradication projects applied bait using broadcast or bait stations 

or both. Bait stations were typically laid out on a grid pattern. Bait broadcast was by hand or 

using spreaders suspended under a helicopter (Howald et al. 2007). 

Island ecosystems worldwide have repeatedly demonstrated major positive changes as a result of 

rat eradication. Some examples include: 

• Whale Island in New Zealand, where the breeding success of grey-faced petrels 

(Pterodroma macroptera ssp. gouldi) increased after rat eradication (Imber et al. 2000) 

• Mokoli’i Islet, offshore of the Hawai’ian island of Oahu, where breeding success in 

wedge-tailed shearwaters (Puffinus pacificus) increased after rat eradication (D. Smith, 

pers. comm.) 

• Anacapa Island, off the coast of southern California, where the number of breeding 

attempts and proportion of successful breeding attempts in Xantus’s murrelets 

(Synthliboramphus hypoleucus) have both increased since rats were eradicated 

(Whitworth et al. 2005) 

• Breaksea Island in New Zealand, where seedling numbers of numerous native plants 

increased after rat eradication (Allen et al. 1994) 

1.4. SCOPE OF ANALYSIS

The Proposed Action is focused on methods for the eradication of introduced rats from Rat 

Island. Other actions that may occur in the future as a result of the Proposed Action will not be 

analyzed in detail in this document. The potential implications of the Proposed Action in relation 

to future actions will be discussed in the Cumulative Impacts sections of the Environmental 

Consequences section (Chapter 4). This analysis will not focus on restoration actions on Rat 

Island other than the eradication of introduced rats. 

5
Chapter 1: Purpose & Need 

1.5. AUTHORITY FOR ACTION & REGULATIONS GOVERNING ACTION

1.5.1. Authorities for Taking Action 

The Proposed Action is authorized by the Federal laws, regulations, guidelines, and Presidential 

Executive Orders listed below. 

1.5.1.1. U.S. Fish and Wildlife Service statutes, policies, and plans 

When the Alaska National Interest Lands Conservation Act (ANILCA) of 1980 established 

Alaska Maritime NWR in its current form, Section 303 (1)(b) established the following purposes 

(among others) for the establishment and future management of the Refuge: 

• “To conserve fish and wildlife populations and habitats in their natural diversity 

including, but not limited to marine mammals, marine birds and other migratory birds, 

[and] the marine resources upon which they rely...; [and] 

• “To fulfill the international treaty obligations of the United States with respect to fish and 

wildlife and their habitats.” 

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

amended, directs the FWS to conserve ecosystems upon which threatened and endangered 

species depend. Under the Act, the National Marine Fisheries Service (NMFS) and the FWS 

publish lists of endangered and threatened species. Section 7 of the Act requires that Federal 

agencies consult with these two agencies to minimize the effects of Federal actions on 

endangered and threatened species. The Refuge will conduct Section 7 consultations with the 

appropriate entities. 

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

1119), as amended, gives general guidance which can be interpreted to include alien species 

control, that requires the Secretary of the Interior take steps "required for the development, 

management, advancement, conservation, and protection of fish and wildlife resources." 

National Wildlife Refuge System Improvement Act of 1997. The Improvement Act which 

amends the National Wildlife Refuge System Administration Act of 1966, serves as an “Organic 

Act for the Refuge System” and provides comprehensive legislation on how the Refuge System 

should be managed and used by the public. The Improvement Act: 

• Identified a new mission statement for the Refuge System. 

• Established six priority public uses (hunting, fishing, wildlife observation and 

photography, environmental education and interpretation). 

• Emphasized conservation and enhancement of the quality and diversity of fish and 

wildlife habitat. 

• Stressed the importance of partnerships with Federal and State agencies, other 

organizations, and the general public. 

• Mandated public involvement in decisions on the acquisition and management of refuges. 

6
Chapter 1: Purpose & Need 

• Required, prior to acquisition of new refuge lands, identification of existing compatible 

wildlife-dependent uses that would be permitted to continue on an interim basis pending 

completion of comprehensive conservation planning. 

The Improvement Act establishes the responsibilities of the Secretary of the Interior for 

managing and protecting the Refuge System; requires a Comprehensive Conservation Plan for 

each refuge by the year 2012; and provides guidelines and directives for the administration and 

management of all areas in the Refuge System, including wildlife refuges, areas for the 

protection and conservation of fish and wildlife threatened with extinction, wildlife ranges, game 

ranges, wildlife management areas, or waterfowl production areas. 

Comprehensive Conservation Plan/Environmental Impact Statement/Wilderness Review 

for the Alaska Maritime National Wildlife Refuge. This congressionally mandated plan was 

completed in 1988 and provides the overall general guidance for managing the Alaska Maritime 

National Wildlife Refuge. 

The USFWS policy for maintaining biological integrity and diversity and environmental 

health (601 FW 3, 2001), directs refuges to “prevent the introduction of invasive species, detect 

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

habitat conditions in invaded ecosystems.” 601 FW 3 further directs refuge managers to “develop 

integrated pest management strategies that incorporate the most effective combination of 

mechanical, chemical, biological, and cultural controls while considering the effects on 

environmental health.” 

1.5.1.2. Executive Orders 

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

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

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

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

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

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

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

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

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

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

invasive species and the means to address them.” 

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

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

environmental harm or harm to human health.” 

1.5.2. Regulatory Framework 

7
Chapter 1: Purpose & Need 

The Proposed Action would be carried out in compliance with the Federal and state laws and 

regulations listed below. 

1.5.2.1. Federal laws 

National Environmental Policy Act (NEPA) of 1969, as amended, and including all relevant 

subsequent guidelines and regulations 

Endangered Species Act (ESA) of 1973, as amended 

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

Migratory Bird Treaty Act (MBTA) of 1918, as amended 

Bald and Golden Eagle Protection Act (BGEPA) of 1940 

National Historic Preservation Act (NHPA) of 1966, as amended) 

Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) of 1947, as amended 

Clean Water Act (CWA), as amended (formally, the Water Pollution Control Act, USC 33 1251 

et seq.) 

Coastal Zone Management Act (CZMA) of 1972, as amended 

Archaeological Resources Protection Act of 1979, as amended, 16 USC 470 

Wilderness Act of 1964 

Alaska National Interest Lands Conservation Act (ANILCA), 1980 

1.5.2.2 Alaska state laws and policies 

1.5.2.2.1 Alaska Board of Game 

Alaska Statute (AS) 16.05.255 authorizes the Board of Game to adopt regulations it considers 

advisable in accordance with AS 44.62 (Administrative Procedure Act) for the following actions 

relating to game including rats and other rodents: 

(2) establishing open and closed seasons and areas for the taking of game; 

(3) establishing the means and methods employed in the pursuit, capture, taking, and 

transport of game;... 

(5) classifying game as . . . big game animals, fur bearing animals, predators, or other 

categories; 

(6) methods, means, and harvest levels necessary to control predation and competition 

among game in the state; 

8
Chapter 1: Purpose & Need 

(7) watershed and habitat improvement, and management, conservation, protection, use, 

disposal, propagation, and stocking of game; 

(8) prohibiting the live capture, possession, transport, or release of native or exotic game 

or their eggs;... 

(11) taking game to ensure public safety; and 

(12) regulating the activities of persons licensed to control nuisance wild birds and 

nuisance wild small mammals. 

1.5.2.2.2. Alaska Department of Fish and Game (ADF&G) 

AS 16.05.940(19) defines rats as “game,” and AS 16.05.330 requires a hunting license for the 

taking of game. This means a person killing rats by any means (poison, traps, shooting, sticky 

boards, etc.) needs a hunting license. Other provisions relating to rats are found in the following 

state wildlife regulations. 

5 Alaska Administrative Code (AAC) 92.990(a)(52) – Defines as Deleterious Exotic Wildlife 

any Muridae rodent that is “unconfined or unrestrained.” 

5 AAC 92.990(a)(73) – Effective September 13, 2007, defines as Nuisance Wildlife any 

Deleterious Exotic Wildlife that is feral, and any animal that invades or comes to occupy a 

dwelling, vessel, vehicle, structure, or storage container; causes property damage, or is an 

invasive or introduced nonnative species that poses immediate or long-term threats to human 

health, safety, or property or to native wildlife, wildlife health, or habitat. 

5 AAC 92.990(a)(76) – Effective September 13, 2007, defines: “invasive species” as a 

nonnative species whose introduction does or is likely to cause economic or environmental harm 

or harm to human health; this includes all of the species listed in 5 AAC 92.990(52); and 

“Muridae rodent” as including true mice and rats, gerbils, and their relatives. 

5 AAC 85.075 – Establishes no bag limits/no closed season for Deleterious Exotic Wildlife. 

5 AAC 85.075 (b) – Allows take by any means (except those prohibited in 5 AAC 92.080) for 

Deleterious Exotic Wildlife. 

5 AAC 92.080(2) – Requires written consent from the Board of Game to take wildlife using 

poisons; effective September 13, 2007, the use of poisons for taking deleterious exotic wildlife 

within a building, vessel, port, vehicle, or aircraft, is authorized without board approval when 

using Alaska Department of Environmental Conservation registered pesticides in their approved 

manner. 

5 AAC 92.029 – Allows possession of specifically listed animals without a permit but prohibits 

their release into the wild; requires a permit for possessing all other rodent species/subspecies. 

[Note: Rodents that are allowed with a permit include white rats (R. norvegicus var. albinus); 

white, waltzing, singing, shaker, and piebald mice (Mus musculus vars.); fat-tailed gerbil 

(Pachyuromys duprasi); gerbil (Gerbillus spp.); hamster (golden) (Mesocricetus auratus); 

chinchilla (Chinchilla laniger); cavy (Cavia aperea); and guinea pig (Cavia porcellus)]. As of 

9
Chapter 1: Purpose & Need 

September 13, 2007, includes rats and mice in the list of Deleterious Exotic Wildlife that can be 

captured or destroyed if found feral or unrestrained by an owner. 

5 AAC 92.230 – Effective September 13, 2007, a person may not intentionally feed deleterious 

exotic wildlife (including rats and mice), or negligently leave human food, pet food, or garbage 

in a manner that attracts these animals. However, this prohibition does not apply to use of bait 

for trapping Deleterious Exotic Wildlife. 

5 AAC 92.141 – (a) Effective September 13, 2007, it is unlawful for the owner or operator of a 

vessel, vehicle, aircraft, structure being translocated, or other means of conveyance to knowingly 

or unknowingly harbor live Muridae rodents, or to enter Alaska (including Alaskan waters) while 

knowingly or unknowingly harboring live Muridae rodents. (b) It is unlawful for an individual to 

release to the wild any live Muridae rodent. (c) It is unlawful for the owner or operator of a 

facility to knowingly or unknowingly harbor live Muridae rodents. The owner or operator of a 

harbor, port, airport, or food processing facility in which live Muridae rodents have been found 

shall develop and implement an ongoing rodent response and eradication or control plan. 

5 AAC 92.210 – Allows Deleterious Exotic Wildlife to be used as food for dogs or furbearers or 

for bait. 

ADF&G Invasive Species Program released an invasive rodent management plan in October 

2007 aimed at preventing and removing rat infestations in the state: Wildlife and People at Risk: 

A Plan to Keep Rats Out of Alaska (Fritts 2007). 

1.5.2.2.3. Alaska Department of Health and Social Services, Division of Public Health, Section 

of Epidemiology 

Under 7 AAC 27.020, the Department of Health and Social Services can take actions to control 

rodents or other animals found to carry diseases transmissible to humans. The Department may, 

alone or in cooperation with federal or other state agencies, investigate the circumstances and 

extent of the threat, and quarantine or euthanize the diseased animals to protect human health. 

1.5.2.2.4. Alaska pesticide-related laws and responsible entities 

A suite of other state laws is designed to protect humans and non-target organisms against the 

adverse effects of pesticides (Alaska State Pesticide Laws 18 AAC 90). Agencies with 

responsibility for administering these laws in Alaska include: the Alaska Department of 

Environmental Conservation; Alaska Department of Transportation and Public Facilities; Alaska 

Department of Commerce, Community, and Economic Development; and the Alaska 

Department of Natural Resources, Office of Project Management and Permitting, Coastal Zone 

Management Program. For more information on Alaska pesticide terminology and laws, see: 

http://www.dec.state.ak.us/eh/pest/index.htm (state laws); and 

http://www.dec.state.ak.us/regulations/pdfs/90mas.pdf (state pesticide regulations). 

Specific state permitting requirements for Alaska Coastal Zone Management Act consistency 

determination and State Historic Preservation Act consultation will be conducted simultaneous 

10
Chapter 1: Purpose & Need 

with the public comment period on this EA. Prior to implementing the Proposed Action, Alaska 

Maritime NWR will request a state permit for aerial application of rodenticide from ADEC, as 

well as renew our Collections and Wildlife Nuisance permits with ADF&G. 

1.6. PURPOSE OF THIS ANALYSIS

The analysis is composed of four parts: 

1. The purpose of the Proposed Action and the need for action are described; 

2. The reasonable ways to meet the purpose of the action are discussed, including a 

description of the Proposed Action as well as a description of the No Action alternative 

for comparison purposes; 

3. The natural and physical environment potentially affected by the action is described; and 

4. The potential for a range of environmental impacts as a result of the action is analyzed, 

quantified as much as possible, and described. 

Using this document, the decision maker who has authority to approve the Proposed Action 

should be able to make an informed decision as to how best to meet the purpose of the action, 

which action is environmentally preferable, whether or not the Proposed Action may have 

significant environmental impacts, and to address any unresolved environmental issues. 

11
2. Alternatives 

Figure 5. Coastal environment on Rat Island Ebbert 2001 

2.1. ALTERNATIVE A: NO ACTION

Analysis of the No Action alternative is required under NEPA. Rats will not be eradicated from 

Rat Island under this alternative. The other ongoing invasive species management programs in 

the Aleutians, including a response program for rodents escaping from grounded ships and the 

Aleutians-wide introduced fox eradication program, will be maintained based on previous 

agency decision documents. Any other related programs or projects, now or in the future, 

decided and implemented under different authority will also be maintained. However, the 

presence and negative ecosystem impacts of rats is counter to the establishing purpose of Alaska 

Maritime NWR and other FWS policies for conservation and restoration of natural biodiversity; 

these negative ecosystem impacts will continue under the No Action alternative. Removal of 

introduced foxes from some of the islands with rats will have only limited effectiveness as long 

as rats remain. Additionally, the value of Rat Island to wildlife and its character as a wilderness 

area will continue to be compromised. 

2.2. ALTERNATIVE B (PROPOSED ACTION): INTRODUCED RAT ERADICATION FROM RAT 

ISLAND, AERIAL BAIT BROADCAST TECHNIQUE

2.2.1. Summary of Actions 

• Eradication of rats from Rat Island to facilitate restoration of the island ecosystem; 

 
Chapter 2: Alternatives 

• Removal techniques based on successful island rat eradications elsewhere in the US and 

globally; 

• Pressed-grain bait pellets (1 – 5 g [0.04 – 0.1 oz]), containing 25 ppm brodifacoum 

applied at the minimum quantity necessary to achieve rat eradication, according to 

Environmental Protection Agency (EPA) approved pesticide label instructions; 

• Bait applied to every potential rat territory on Rat Island and all vegetated offshore rocks 

and islets within 2000 m (6562 ft); 

• Whole-island coverage attempted using helicopters and specialized bait-spreading 

buckets; 

• Supplemental hand application of bait pellets on land adjacent to coastal areas and 

overhanging cliffs, where automated helicopter spreading will be limited or is not 

feasible; 

• Limited supplemental installation of bait stations; 

• All bait application activities to be conducted under the supervision of a Pesticide 

Applicator certified by the State of Alaska. 

2.2.2. Description of Action Operations 

The purpose of eradicating rats from Rat Island is to conserve, protect and enhance habitat for 

native wildlife species, especially nesting habitat for seabirds, and to restore the biotic integrity 

of the island. The overarching goal in a successful rodent eradication is to ensure the delivery of 

a lethal dose of toxicant to every rodent on the island. This Proposed Action presents a detailed 

analysis of a rodenticide, delivered by aerial broadcast, as the primary method for eradicating 

rats from Rat Island. A list of other methods of rat removal that have been used elsewhere or 

suggested in the past, but are considered to be ineffective or inappropriate for Rat Island, are 

discussed in Section 2.3 below. 

2.2.2..1 Timing 

The timing of an aerial broadcast rodent eradication is a critical factor in its ultimate success. 

Timing an aerial broadcast to maximize the probability of eradication success is dependent on 

three major factors: 1) the local population biology of rats; 2) the local population biology and 

migratory patterns of animals other than rats that may be vulnerable to rodenticide exposure; and 

3) local weather conditions and seasonal patterns that would affect the feasibility of conducting 

operations. 

Biology of rats: Rat eradications from islands are more likely to be successful if they take place 

when the rat population is declining in response to annual resource declines. At this time, rodents 

are typically more food stressed and therefore more likely to eat the bait presented. The 

probability of success is also increased if bait application takes place when rats are not breeding. 

During peak breeding season, it is more likely that juvenile rats exist that are too young to leave 

the nest during bait application. These juvenile rats could mature and emerge from the nest after 

bait becomes scarce, and survive the eradication attempt. Population monitoring of rats on the 

Aleutian Islands indicates that the most favorable time window for eradication is between late 

fall and early spring: 

13
Chapter 2: Alternatives 

• No pregnant female rats have been detected between November and March (Dunlevy and 

Scharf 2006), indicating the lowest probability that juvenile rats would be in burrows, 

thereby avoiding exposure and compromising efficacy, during any bait application in that 

timeframe (USFWS unpubl. data; Witmer 2005). 

• Rat populations in the Aleutians are at their lowest point between February and April, 

and at their highest in June and July (Dunlevy and Scharf 2006). 

• The lowest diversity and abundance of alternative foods for rats occurs between 

December and March (Dunlevy and Scharf 2006). 

Seasonal sensitivities of native wildlife: Effects of the activities associated with rat eradication 

(e.g., helicopter operations, non-target impacts associated with rodenticide application) on birds, 

marine mammals and potentially on anadromous fish would be reduced by avoiding the breeding 

seasons. 

For birds, most nesting occurs between April and September and all nesting is over by early to 

mid-September (see Gibson and Byrd 2007). 

Specific timing considerations for marine mammals follow: 

• The reproductive period (when pups are born) for Steller sea lions (Eumetopias jubatus) 

is generally late May through early July, with a peak in the second and third weeks of 

June (Pitcher and Calkins 1981; Gisiner 1985). Pups stay on land for about 2 weeks after 

which they spend increasing time in nearshore marine waters until they begin to disperse 

from rookeries to haul-outs with females at about 2.5 months of age (Raum-Suryan et al. 

2004; Maniscalco et al. 2002, 2006). Therefore, in the Aleutian Island area, assuming 

most pupping is done by the last week of June, dispersal should occur by mid-September. 

• For harbor seals (Phoca vitulina), there are two periods of relatively high activity on 

islands; pupping occurs on land during May-June and molting occurs on land AugustSeptember (Jemison and Kelly 2001; Daniel et al. 2003). 

• Although northern sea otters (Enhydra lutris kenyoni) may have pups at any time of the 

year, their peak period of production is spring and summer (Kenyon 1969). 

Consequently, the number of small pups in the population would be relatively low in fall 

and winter (Pitcher and Calkins 1981; Kurle and Worthy 2001, Burns 1970; Estes 1990). 

Conducting aerial bait application operations after marine mammal breeding and molting is 

complete reduces the potential for disturbance to these species during the sensitive periods of 

breeding, pup rearing, and molting. 

No anadromous fish streams were identified on Rat Island during statewide surveys (Johnson 

and Weiss 2007), and no anadromous fish were found in the small island streams in 2007 (S. 

Buckelew, pers. comm.). Where anadromous salmonid species occur elsewhere in the Aleutian 

Islands, their entrance into freshwater bodies for spawning typically occurs between late summer 

and late fall (Palmer 1995; National Marine Fisheries Service 2005), depending on the species. 

Seasonal logistics considerations: Winter working conditions in the central Aleutians introduce 

safety issues for the field crews and project efficiency. Also winter adds potential complications 

of snow and freezing temperatures which could affect bait availability. Starting in late fall, the 

strengthening of the Aleutian low pressure system begins to generate frequent severe storm 

14
Chapter 2: Alternatives 

events. By November, temperatures can fall below freezing causing “white-out” conditions and 

snow accumulation during storms, and these conditions can continue throughout the winter (see 

Armstrong 1971; Alaska Ocean Observing System website). Although it is possible that 

persistent ground-covering snow may begin on Rat Island in some years as early as October, it is 

more likely that a major portion of Rat Island will be covered by snow in March and April. The 

effectiveness of aerial application of brodifacoum on top of snow cover to eradicate island rats is 

unknown (J. Parkes, pers. comm.). 

Synthesis of timing considerations: No specific range of dates for the eradication is ideal from all 

standpoints. For personnel safety and project efficiency, the ideal operational window would 

likely be spring or summer. However, it is unreasonable to plan aerial bait application operations 

at this time because rat populations are growing rapidly, and alternative food sources are widely 

available. Furthermore, spring and summer are the periods when disturbance to native wildlife 

would likely be highest. We conclude that the most reasonable time period to conduct bait 

application operations on Rat Island is outside the breeding period for most species (April to 

mid-September), but before the onset of winter storms and snow accumulation on the ground. 

The actual dates of the application window for the Proposed Action will not be determined until 

project leaders can ascertain, with reasonable certainty, the anticipated seasonal patterns 

discussed above for that particular year. Bait broadcast will be completed within a 45-day 

window, allowing for anticipated weather contingencies. 

2.2.2.2. Project staging 

Field personnel will visit Rat Island during the summer and will install temporary infrastructure 

and storage sites. These will include: 

• A camp site capable of supporting 20 people for up to seven weeks; 

• Three bait staging areas, where bait will be contained in up to 200 wooden storage units 

at each staging area; and 

• A fuel storage site that will comply with all appropriate safety standards and regulations. 

15
Chapter 2: Alternatives 

Figure 6. Proposed Rat Island field camp and staging areas 

Additional material may be brought to the island at that time and staged for the fall application of 

bait. Helicopters will deliver most of the necessary materials to each site on the island. Staging 

procedures in summer will be conducted using a helicopter capable of lifting a 700 kg (1,543 lb) 

payload. Helicopter operations during project staging will be localized to discrete flight paths 

and landing sites, servicing the camp, three bait staging locations, and a fuel storage site. All of 

these flight paths will be routed to avoid or minimize helicopter disturbance to sensitive species 

such as hauled-out marine mammals and nesting waterfowl. 

2.2.2.3. Introduction to broadcast bait application 

Aerial broadcast of pelletized bait across an entire island in one or two concerted applications is 

becoming the common method of rodenticide delivery on large islands (Howald et al. 2007; 

Towns and Broome 2003). Aerially broadcasting bait is operationally preferable to bait stations 

when sections of a large target island are very steep or otherwise inaccessible to foot traffic (i.e., 

unsafe to hand-deliver bait), if the island is very large (reducing the practicality of hand 

broadcasting or the use of bait stations [Howald et al. 2007]), and/or if a regimen of regular foot 

traffic on the island would likely cause substantial ecosystem damage (through permanent trails, 

repeated disturbance to sensitive animals, and trampling of sensitive vegetation). 

Bait application operations will be conducted using a single-primary-rotor/single tail-rotor 

helicopter. Helicopter models that will be used for the operations are small, 2-4 passenger 

aircraft. Models considered for use in the operations will include Bell 206B Jet Ranger, Bell 

206L4 Long Ranger, or other small-medium sized aircraft. Bait will be applied from a 

specialized bait hopper (see Section 2.2.2.7) slung beneath the helicopter by 15 – 20 m (49 – 66 

ft). Helicopter operations for the bait application will necessitate low-altitude overflights of the 

entire land area of Rat Island and adjacent vegetated islets. The helicopter will fly at a speed 

16
Chapter 2: Alternatives 

ranging from 25 – 50 knots (46 – 93 km/hr or 29 – 58 mph) at an average altitude of 

approximately 50 m (164 ft.) above the ground. 

To make bait available to all possible rat home ranges on the island, bait will need to be applied 

evenly across emergent land area, with every reasonable effort made to prevent bait spread into 

the marine environment (see section 2.2.2.11). The baiting regime will follow common practice 

in which parallel, overlapping flight swaths are flown across the interior island area and 

overlapping swaths with a deflector attached to the hopper (to prevent bait spread into the marine 

environment) flown around the coastal perimeter. Flight swaths will be defined by the uniform 

distance of bait broadcast from the hopper, ranging from 50 – 75 m (164 – 246 ft). Flight swaths 

will be flown in a parallel pattern, with subsequent flight swaths overlapping the previous by 

approximately 25-50% to ensure no gaps in bait coverage. 

During one application all points on Rat Island may be subject to up to three helicopter passes. 

Within each bait application, there should be no more than three consecutive operating days, and 

it is likely that there will be two separate applications. The entire helicopter operations window 

for bait application will be no longer than seven weeks and could be as short as half that time. 

Figure 7. Aerial broadcast of rat rodenticide on Anacapa Is., CA. S. Ebbert 2002 

2.2.2.4. Bait pellet composition 

The bait used will be registered with EPA in compliance with the Federal Insecticide, Fungicide 

and Rodenticide Act (FIFRA). The bait product will be designed to be highly attractive to rats, 

and colored blue to minimize attractiveness as a food item for granivorous birds (Pank 1976; 

Tershy et al. 1992; Tershy & Breese 1994; Buckle 1994; Island Conservation, unpubl. data). The 

17
Chapter 2: Alternatives 

bait will be a compressed grain pellet, 1 – 5 g in weight (0.04 – 0.1 oz), containing 25 ppm 

brodifacoum. All ingredients in bait pellets will be non-germinating grains (either sterile or 

crushed). The bait pellets are designed to withstand the wet maritime environment of the 

Aleutians. Any bait not initially consumed will likely remain attractive to rats, including 

juveniles that newly emerged from the nest (typically, emergence is between 21 and 28 days 

post-parturition). However, frequent, heavy rainfall of the late fall and winter will cause bait 

degradation before winter is over (Buckelew et al. 2007a). 

2.2.2.5. Determining application rate 

Bait will be applied strictly according to the instructions given on the product’s EPA-approved 

label. If the label instructions provide an acceptable range of application rates, the precise 

application rate will be determined based on experiments conducted in similar habitat in the 

Aleutians (see Buckelew et al. 2007a). These experiments will use a non-toxic placebo bait 

replica to measure the rate of bait uptake (i.e., includes both consumption and breakdown) on Rat 

Island. Soon after application, baits are consumed and cached by rats and other wildlife, 

including invertebrates. Baits exposed to heavy moisture will degrade faster than baits which fall 

in drier locations. Application rate will stay within the rate legally allowed on the EPA pesticide 

label of the bait. The proposed label allows for more than one aerial broadcast application if 

rodent sign persists. The application rate will be calculated so an adequate amount of bait is 

available for consumption by rats for a period of at least 4 days. 

2.2.2.6. Number of bait applications 

Rat eradication has been successful with a single island-wide broadcast application (Howald et 

al. 2007). On Rat Island, we propose a second application, begun approximately 7-10 days after 

the initial treatment, to minimize the likelihood of juvenile rats surviving the initial broadcast. 

However, trial bait broadcasts conducted in the Aleutians in 2006 (see Buckelew et al. 2007a) 

showed that palatable bait may be available for rat consumption for longer than 10 days after an 

initial application. The environmental impacts analysis in Chapter 4 of this document is based 

upon two applications of brodifacoum, with the second application conducted at a lower 

application rate than the first. 

2.2.2.7. Bait hopper 

Bait will be applied across Rat Island through the use of a commercial bait hopper suspended 

from a helicopter. The hopper is composed of a bait storage compartment, a remotely-triggered 

adjustable gate to regulate bait flow out of the storage compartment, and a motor-driven 

broadcast device that can be turned on and off remotely and independently of the outflow gate. 

The broadcast device will include a deflector that can be easily installed when directional (rather 

than 360°) broadcast is necessary, such as on the coastline or near significant freshwater lakes or 

streams (deflector use is discussed in greater detail below). 

18
Chapter 2: Alternatives 

Figure 8. Bait hopper loaded for broadcast, Anacapa Is. rat eradication S. Ebbert 2002 

2.2.2.8. Equipment calibration 

Before bait application, the pilot, helicopter, and hopper combination to be used in the 

application will be calibrated and tested for consistency and accuracy of application using a 

placebo bait broadcast. The calibration will occur over a test site off-island, in Aleutian 

conditions similar to those on Rat Island. 

2.2.2.9. Flight plan 

The bait will be applied according to a flight plan that will take into account: 

• The need to apply bait relatively evenly and to prevent any gaps in coverage or excessive 

overlap; 

• Island topography; 

• The need to avoid bait spread into the marine and freshwater environments; 

• The need to minimize disturbance to native wildlife, especially any marine mammals 

hauled-out on land and resting in nearshore waters; and 

• The need to minimize the substantial costs associated with helicopter flight time. 

2.2.2.10. Monitoring bait application 

To ensure complete and uniform application: 

19
Chapter 2: Alternatives 

• The actual application path will be monitored onboard the helicopter using an onboard 

differential global positioning system (DGPS) and computer to guide the application in 

order to avoid gaps and unanticipated overlaps in application coverage. 

• The application rate will be calculated using the known rate of bait flow from the hopper, 

the helicopter’s reported velocity, and overlaps in the bait swath reported by the onboard 

DGPS tracking system. 

Adjustments in bait flow rates, helicopter speed, and flight lines will be made as necessary to 

meet the optimal application rate, stay within limits legally required on the EPA pesticide label, 

and comply with FIFRA. 

2.2.2.11. Preventing bait spread into the marine environment 

Every reasonable effort will be made to minimize the risk of bait being broadcast into the marine 

ecosystem. The broadcast deflector will be attached to the hopper for all treatment passes of 

coastal bluffs and cliffs. The deflector directs bait within approximately 120° of the onshore side 

of the helicopter, to minimize the risk of bait entering the ocean on the opposite, or seaward, 

side. 

2.2.2.12. Preventing bait spread into the freshwater environment 

The freshwater bodies on Rat Island can be broken roughly into two categories, streams and 

lakes. The “stream” category consists of all moving water bodies on the island, whether or not 

they are continuous or run all the way to the ocean. The “lake” category consists of all standing 

bodies of fresh water on the island, regardless of depth. On Rat Island, the lakes occur almost 

entirely in clusters, rather than being evenly distributed (Buckelew et al. 2007b). Project 

managers will plan flight paths for aerial bait application that leave a buffer around the perimeter 

of each lake cluster to minimize bait entry into freshwater bodies. 

20
Chapter 2: Alternatives 

Figure 9. Map of Rat Island showing lake clusters 

2.2.2.13. Supplemental bait broadcast 

As a result of the need for caution near the marine and freshwater environments, the coastline of 

the main island, offshore islets, and the land areas within the lake clusters that are omitted from 

aerial treatment, all of which are potential rat habitat, may not receive the optimal bait coverage 

with helicopter broadcast. In cases where it is evident or suspected that any land area on Rat 

Island or offshore islets did not receive full coverage, there will be supplemental systematic hand 

broadcast either by foot, boat, helicopter, or any combination of the above. All personnel who 

may participate in supplemental hand broadcasts will be trained and tested in systematic bait 

application at a target application rate (as described in Buckelew et al. 2005). 

21
Chapter 2: Alternatives 

Figures 10a & b. Coastal cliffs on Rat Island. 

2.2.2.14. Special treatment of the islet off Ayugadak Point 

The islet located 1.6 km (1 mi) off Ayugadak Point is a Steller sea lion rookery, qualifying as 

Critical Habitat under the Endangered Species Act (ESA). However, the islet is nevertheless 

potential rat habitat and the thick kelp beds between the main island and this islet make rat 

migration to and from the islet theoretically possible. Bait will be delivered to the islet off 

Ayugadak Point with an adaptive alternative-baiting strategy designed to mitigate helicopter 

disturbance. 

During staging operations in early summer, project crews will attempt to access the islet by boat, 

landing on a beach that is out of view of hauled-out sea lions. Personnel will install multiple 

enclosed bait stations on the islet, which will be designed to provide rats easy access to the bait 

inside while minimizing bait access by non-target species that may be present on the islet, 

including a relict song sparrow population. Stations will be anchored securely in place, and filled 

with enough bait to ensure that any rats on the island will have bait available for many weeks. 

During the major bait application operations in the fall, project crews will attempt to access the 

islet by boat again, although the likely sea state during this season may make access more 

difficult than the previous attempt. If personnel can access the island by boat, they will check the 

bait stations installed earlier for signs of bait consumption or other rat activity. Bait stations will 

be refilled as necessary during this visit. If rats are detected or suspected, personnel may 

additionally hand-broadcast bait pellets on the islet. 

If project crews are unable to access the islet by boat at any time during fall operations, it will be 

necessary to aerially treat the island. 

2.2.2.15. Personal protective equipment 

22
Chapter 2: Alternatives 

All personnel that handle bait or monitor bait application in the field will meet or exceed all 

requirements for personal protective equipment described on the bait’s EPA pesticide label. 

2.2.2.16. Training and supervision 

All bait application activities (aerial broadcast, hand broadcast, and bait station filling) will be 

supervised by personnel certified by the state of Alaska as pesticide applicators. 

2.2.3. Rodenticide (Brodifacoum) 

2.2.3.1. Introduction to brodifacoum 

Brodifacoum is a coumarin-based anticoagulant. 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. Brodifacoum is the most commonly-used rodenticide in the United States, and it is 

widely available for household consumers (Erickson and Urban 2002), although the EPA is 

currently considering restricting its use to professional pest control operations (72 FR 10 pp. 

1992-3, 2007). 

Before the toxin can have any measurable physical effects, brodifacoum levels in the liver must 

reach a toxic threshold; this level can vary widely between species. Most vertebrates (e.g. mice, 

cats, ducks) are less susceptible to brodifacoum than are rats, and would have to consume a 

higher dose, relative to body mass, before reaching a toxicity risk threshold. A few species are 

more sensitive to brodifacoum, such as dogs and pigs. 

The effects of sublethal exposure are becoming an interest of study; however, there has been 

nothing identified to date that would warrant concern over sublethal effects of exposure to 

brodifacoum, especially for those species that could be considered even slightly at risk of 

exposure. 

2.2.4. Impact Mitigation 

2.2.4.1. Archaeological site impact mitigation 

There are four “cemetery sites or historical places,” on Rat Island that are selected by The Aleut 

Corporation in accordance with the Alaska Native Claims Settlement Act (ANCSA), Section 

14(h)(1). The precise archaeological contents of these parcels have yet to be determined, but they 

are likely to include barabara (house) pits and midden sites. Project personnel will be briefed on 

the locations and identification of archaeological and cultural resources that may be present on 

the island. Further, they will be instructed in how to avoid disturbing any sites of archeological 

or cultural importance within these parcels and anywhere else on the island where sites of 

significance have been identified (such as artifacts from the WWII era). 

23
Chapter 2: Alternatives 

2.2.4.2. Wildlife impact mitigation measures 

There are no known endemic animal species or subspecies unique to Rat Island. Most of the 

native species on Rat Island are highly mobile and known to travel between nearby islands or 

their populations are relatively wide-spread in the Aleutians. These facts will be taken into 

consideration in Chapter 4, which analyzes the environmental consequences of the action 

proposed in this chapter. 

This environmental analysis focuses on determining whether or not any impacts to wildlife on 

Rat Island may be significant. Regardless of the determination made, the FWS and refuge 

manager of Alaska Maritime NWR recognize the need to minimize disturbance and loss of 

individual animals during this operation to ultimately restore native populations. The eradication 

project is designed to ensure the protection of native wildlife. The seasonal timing chosen for the 

application (post breeding seasons for birds and marine mammals), the use of only enough bait to 

achieve success, the use of a bait that biodegrades and becomes unattractive to non-targets 

quickly in the fall Aleutian environment, and the use a grain-based bait to minimize primary 

hazard to scavengers are all examples of ways the project is designed to minimize impacting 

native wildlife. Other mitigation measures will depend on the final interpretation of this analysis 

in the decision document for this action, further consultation among project planners, the results 

of further studies of the Rat Island ecosystem especially in the months leading up to 

implementation, and the advice of scientific and technical experts. 

In this analysis of the potential impacts of the Proposed Action on each species addressed in the 

mitigations described below, impacts both with and without these mitigation measures will be 

examined. 

2.2.4.2.1. Mitigating for rodenticide risks 

Mitigation considerations as part of the planning to minimize non-target wildlife exposure to bait 

pellets will include the following: 

• Temporal considerations: As discussed above, aerial bait application operations will 

avoid seasons when the greatest number of migratory wildlife species, especially 

breeding seasons when more species of birds and individuals of those species, would 

potentially be exposed to rodenticides. 

• Pellet size: Pellets are designed to be too large for small passerines such as sparrows to 

easily consume, but too small to be an object of interest for larger scavengers. 

• Inert ingredients: The grain base of the bait pellets is attractive as a food item only to 

granivorous and opportunistic omnivorous animals. Pellets may be attractive to highly 

curious birds such as gulls, but this would occur regardless of the inert “matrix” of the 

bait. 

• Bait color: Pellets will be dyed blue, which has been suggested to make pellets less 

attractive to some birds (Pank 1976; Tershy et al. 1992; Tershy and Breese 1994; Buckle 

1994; Island Conservation, unpubl. data). 

• Operational aspects: Use of a bait deflector when making helicopter passes along the 

coastline of Rat Island, avoiding bait application to the upland lake clusters and 

significant freshwater streams, and meeting the target application rate by supplemental 

24
Chapter 2: Alternatives 

hand-broadcasting in areas where aerial application must be limited to minimize 

accidental bait drift into the marine and freshwater environments. 

Mitigation measures described above are designed to protect individual animals even if expected 

impacts are not considered significant to the population. Eradication of rats from Rat Island is 

anticipated to have long term positive impacts for non-target species, even those populations that 

may experience some level of mortality as a result of bait application. 

Rat Island birds will be monitored before and during bait application to determine if management 

actions may be necessary. When on the island, crews will collect and remove non-target bird 

remains and any dead rats found. Rat Island monitoring is planned for subsequent years to 

monitor recovery of native wildlife and determine if further habitat improvement or translocation 

is warranted. 

2.2.4.2.2. Mitigating for disturbance risk 

The primary mitigation that will be incorporated into planning is timing the eradication activities 

to occur after the Aleutian summer breeding season. Outside of the breeding season, species that 

inhabit Rat Island are comparatively less sensitive to disturbance. Before eradication operations 

begin, personnel will be briefed on strategies and techniques for avoiding wildlife disturbance 

whenever possible and these techniques will be implemented during actual eradication 

operations. 

2.2.5. Public Information 

Informational posters will be distributed to community centers in the Aleutians from which ships 

might embark for the vicinity of Rat Island. Researchers with an interest in the Rat Islands group 

will also be updated about eradication activities and timing. 

Signs stating brodifacoum is present on the island, pellet description, and project purpose will be 

posted just before bait application. The signs will remain until spring after bait application, and 

long after baits remaining on the ground have deteriorated. 

2.2.6. Monitoring Eradication Efficacy and Ecosystem Response 

We will monitor rats on Rat Island during and immediately after bait application to assess 

effectiveness of eradication effort. Pre-eradication surveys were conducted on Rat Island in 

2007, and will continue in 2008 up until the eradication. Monitoring will likely continue in 

2009. 

Monitoring activities may include: 

• Rat detection devices such as traps, chew indicators, and special tracking surfaces to 

capture rat tracks and bite marks; 

25
Chapter 2: Alternatives 

• Radio transmitters attached to individual rats, which will allow project personnel to track 

rat activity and confirm 100% mortality within a sample of rats on the island. 

The impacts of monitoring are not expected to be significant to any aspect of the Rat Island 

environment. Monitoring activities on Rat Island are described as appropriate Alaska Maritime 

NWR activities for the collection of scientific data, general management and conservation of the 

natural resources on the refuge, and other approved FWS actions (Byrd 1995; USFWS 1988). 

The potential environmental impacts of post-eradication monitoring activities will not be 

analyzed in this document. 

2.2.7. Rodent Prevention and Response to New Introductions 

The benefits of a successful eradication could be lost with introduction of just one pregnant 

female rodent. Rodents can be accidentally transported to islands and escape from: 

• Watercraft moored onshore or anchored near islands 

• Watercraft pulled up on shore 

• Cargo containers such as food boxes, fishing gear or other bulk materials 

• Debris washed ashore from other rat-infested places 

• Sinking or disabled vessels 

• Aircraft 

2.2.7.1. Prevention 

Alaska Maritime NWR currently works to prevent new rodent introduction onto rat-free refuge 

islands. The program includes shore- and ship-based rodent prevention and shipwreck response. 

The prevention program is designed to reduce the number of rats traveling on ships between 

ports in Alaska. The goal is to reduce the likelihood of a disabled ship to “spill” rats onto islands, 

including Rat Island. 

Alaska Maritime NWR has adopted procedures to prevent transport of invasive rodents between 

Homer, Adak, and other ports to refuge islands, and between refuge field camps, including Rat 

Island. These measures are briefly described below: 

• Inspection of gear supplies delivered and stored at the Alaska Maritime NWR Homer and 

Adak warehouses for rodent sign; infested gear is discarded and replaced. Inspection 

continues during gear preparation and staging for loading onto a ship. The gear for the 

planned action will be inspected according to these standard procedures as it is loaded 

onto vessels for transport to Rat Island. 

• Some gear and supplies may be loaded from ports that have rats and are out of FWS 

control and inspection. In those cases, gear is inspected before and during loading for 

signs of infestation. Rodent control devices are maintained on the Alaska Maritime NWR 

research vessel, M/V Tiˆglaˆx, and will also be installed on other vessels used to transport 

gear to Rat Island. 

26
Chapter 2: Alternatives 

• Another opportunity to inspect gear and supplies is during handling on the ship prior to 

sending it to camp ashore. Again, the gear is inspected for rodent sign, and if gear is 

infested, it is not taken ashore until sanitized. 

• The last opportunity to capture a rodent that might have gotten aboard, or escaped 

undetected from other camp gear on the ship, is during unpacking in camp. If rodent sign 

is detected in gear or supplies brought ashore, rodent control measures are implemented 

as soon as possible. 

The Rat Island project will pose additional challenges because of the number of participants 

traveling to and from the island, the amount of gear being transported and stored on the island, 

and the utilization of aircraft in addition to watercraft to transport supplies to the island. A 

combination of rodent traps and poison bait will be maintained at arrival points on Rat Island 

after the eradication and during monitoring phases. There is currently no formal infrastructure to 

support vessel arrivals on the island, and none is planned. 

2.2.7.2. Response 

Eradication protocols include the possibility of multiple (two) bait applications to ensure that all 

rats have been removed from Rat Island. After it has been determined that the eradication 

operation has concluded, efforts will be re-focused on monitoring the island for new rodent 

introductions or the possibility that some rats remained after eradication operations. In the event 

that rodents are detected on Rat Island after FWS has declared the end of the eradication 

operation, a rodent response plan will be implemented immediately. The response plan will be 

based on the FWS emergency rodent eradication response plan for shipwrecks and grounded 

vessels on Alaska Maritime NWR. 

2.3. ALTERNATIVES DISMISSED FROM DETAILED CONSIDERATION

2.3.1. Widespread Use of Bait Stations for Bait Delivery 

Bait stations are box-like enclosures with small entryways designed to be attractive to rodents 

but difficult to navigate for other animals such as birds. On Rat Island, bait stations would 

prevent bait exposure to some species that would be attracted to bait pellets (e.g. granivorous, 

omnivorous and/or curious birds). However, their installation and maintenance to completely 

cover Rat Island would require a very large crew (>50 people) to be present on the island 

continuously for a period of up to two months. Furthermore, the installation and maintenance of 

bait stations would result in a network of trails across the island. While much of Rat Island is 

hikeable, some island sections would require ropes, anchors bolted to rocks, and construction of 

pathways or crude stairways. Rat eradication requires placement of rodenticide into every 

potential rat territory or foraging area. Station placement may be as close together as every 25 m 

(82 ft) (Howald et al. 2004). After placement, stations are monitored for a period of up to two 

years, with near-daily visits for the first six to eight weeks of the bait application period. Bait 

station placement and maintenance, including bait replacement, could at times be dangerous for 

field personnel, especially stations placed on and near cliffs which pose a serious safety risk. 

27
Chapter 2: Alternatives 

The remoteness of Rat Island increases the seriousness of field injuries because of the time and 

difficulty to obtain medical attention and treatment. 

2.3.2. Use of a First-Generation Anticoagulant (Diphacinone) 

The vast majority of island rodent eradications have used the rodenticide brodifacoum, which is 

classified as a “second-generation” anticoagulant. Due to the potency of brodifacoum, there is 

interest in the conservation community for the examination of less toxic alternative compounds 

for rodent eradication purposes (Brakes and Smith 2005; Donlan et al. 2003; DuVall et al. 1989; 

Fishel 2005; O’Connor and Eason 2000). Diphacinone, a “first-generation” anticoagulant, is the 

most commonly considered alternative compound. The comparisons below will focus on these 

two compounds. 

2.3.2.1. Toxicology comparison: brodifacoum vs. diphacinone 

The anticoagulants brodifacoum and diphacinone both bind to the same molecular site in the 

liver. Ingestion of these compounds will 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, in order 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 a few 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 multiple times over a few days. 

2.3.2.2. Pros and cons of diphacinone in comparison 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 diphacinone 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. 

The successful eradication of rats on islands using baits is partly dependent upon overcoming 

bait avoidance by rats and inadequate bait consumption. While diphacinone generally presents 

28
Chapter 2: Alternatives 

less risk to non-target species than brodifacoum, its low retention in body tissues and its 

multiple-feeding requirement makes rodent eradication efforts using diphacinone at increased 

risk of failure (Donlan et al. 2003). Rats are naturally wary and initially eat only very small 

amounts of unfamiliar food encountered in their environment. Ill effects typically cause the rats 

to associate the food with the effect and result in avoidance, even transferring this learned 

avoidance to other rats (Jackson 1982). This characteristic “bait shyness” renders diphacinone 

more problematic as a toxicant than brodifacoum. All other operational considerations being 

equal, the task of delivering enough bait to all rats on the island to ensure 100% mortality is less 

certain to succeed when using diphacinone than when using brodifacoum. Rats that survive a 

diphacinone bait application could be resistant to first generation anticoagulants (e.g. 

diphacinone), or unable to find adequate bait to maintain lethal effects of diphacinone dose, or 

avoid bait after a single feeding, or combination of these. These rats, and possibly their offspring, 

could consequently be more difficult to eradicate from the island in subsequent attempts. 

2.3.2.3. Diphacinone and eradication efficacy 

Rat eradications are highly complex and require the consideration of a large number of variables. 

While the likelihood of success of a proposed eradication program cannot be precisely 

quantified, there are certain variables that are critical to the success of an eradication attempt. 

Likewise, there are certain variables that can independently influence the necessary balance 

between ensuring eradication success and minimizing non-target impacts. 

In the case of Rat Island, while both sides of this balancing equation are important, the need to 

ensure eradication success is particularly acute. Targeted control efforts, or an incomplete 

eradication attempt, will provide few conservation returns in the long term, since rats at low 

densities have the ability to reproduce at high rates and quickly re-occupy vacant territories 

throughout the island. If FWS decides to invest in rat removal from Rat Island, the only way to 

attain cost-effective, and ecologically secure, long-term conservation returns on this investment 

is through a successful eradication on the first attempt. 

2.3.2.4. Diphacinone and operational considerations 

From an operational perspective, there are a number of variables that increase the complexity of 

the proposed eradication. At 2800 ha (6919 ac), Rat Island will be one of the largest islands 

worldwide on which rat eradication is conducted, and its large size will require careful logistical 

coordination, a competent staff, and a lengthy implementation period. Even with careful 

planning, the chance that bait will be applied unevenly, or that there will be coverage gaps, 

increases with each additional pass the helicopter must make to cover the island. Multiple passes 

also increases the risk of excess bait being spread in other places, consequently increasing the 

hazard for non-target species. The unsettled fall and winter weather of the Aleutians (the 

proposed time of action) makes operating a helicopter for long periods of time exceptionally 

risky. When planning helicopter operations in the Aleutians, experts recommend bracketing 

several additional flight days on either side of a target operation day, because unexpected 

weather can prevent helicopter flights for days at a time. Each additional day on which helicopter 

operations are required increases the chance of serious project delays, which can make the 

difference between a successful eradication and an unsuccessful (incomplete) one. 

29
Chapter 2: Alternatives 

An analysis of these operational variables leads to the conclusion that, for the sake of safety and 

the effectiveness of the operation, the number of helicopter flights and amount of flight time 

must be minimized to the greatest extent possible. At the same time, however, the large size of 

Rat Island increases the chances that a full-island application will have coverage gaps. 

If diphacinone were used as the primary toxin for rat eradication from Rat Island, every potential 

rat territory on the island would need to have bait available for consumption continuously for a 

period of up to four days. If any of the scheduled application sessions are delayed due to 

weather, the risk of less than 100% mortality of rats increases dramatically. If even only a few 

rats survive exposure to diphacinone, for example juvenile rats that emerge from the nest 

midway through a diphacinone application, the long-term conservation returns of rat eradication 

will be lost. 

2.3.2.5. Weighing the costs and benefits of rat eradication 

Conservation practitioners in general, and FWS in particular, seek to avoid causing harm to 

biological resources whenever practical. However, in the case of conservation projects that have 

a high likelihood of success and the achievement of measurable results, harm to individual 

animals or plants that is incidental to the conservation action may prove necessary in the balance. 

Furthermore, FWS policies and other government regulations, some of which are discussed in 

more detail elsewhere in this document (Section 1.5.1.1), acknowledge that there are 

circumstances in which the responsible management of refuge lands necessitates actions that 

may incidentally harm individual animals or plants. Alaska Maritime NWR staff believes that rat 

eradication from Rat Island is a highly valuable conservation project, and using brodifacoum 

offers the highest probability of a successful rat eradication operation and thus the highest 

probability of successful restoration of Rat Island ecosystems. Therefore, the staff is prepared to 

accept the potential for harm to some individual animals incidental to the use of brodifacoum on 

Rat Island as long as these individual negative effects are outweighed by the expected beneficial 

effects of rat eradication. 

2.3.3. Other Toxins 

The use of other rodenticides registered with the EPA was dismissed from further consideration, 

for one or more of the following reasons: 1) lack of proven effectiveness in island rat 

eradications; 2) potential for development of bait shyness in the rat population; and 3) the 

unavailability of an antidote in case of human exposure. Each of these issues and the associated 

rodenticides are discussed below. 

The vast majority of island-wide rat eradication projects (at least 226) have used brodifacoum or 

similar so-called “second-generation” anticoagulants, while only 29 have used “first-generation” 

anticoagulants such as diphacinone. Of the nine eradications that have used non-anticoagulant 

toxins (such as zinc phosphide, strychnine, and cholecalciferol), none have been on islands larger 

than 22 ha (~54 ac), making them untested as effective toxins for large-island eradications 

(Howald et al. 2007). 

30
Chapter 2: Alternatives 

Acute rodenticides, such as zinc phosphide and strychnine, have the ability to kill rats quickly 

after a single feeding. However, because poisoning symptoms appear rapidly, the acute 

rodenticides can induce future bait avoidance if animals consume a sub-lethal dose. Studies with 

zinc phosphide have demonstrated that rodents associate toxic symptoms with a novel bait 

consumed earlier if the onset of symptoms occur even 6 – 7 hours after consumption (see Lund 

1988). Thus, any individual consuming a sub-lethal dose is likely to avoid the bait in the future 

(Record and Marsh 1988). Also, acute rodenticides are often extremely toxic to humans and 

there are not always effective antidotes. The combination of these factors disqualifies the acute 

rodenticides from detailed consideration. 

Cholecalciferol, which is classified as a “subacute” rodenticide, has the ability to kill rats more 

quickly than the anticoagulant rodenticides, but most often more slowly than the acute 

rodenticides. Cholecalciferol has a lower level of toxicity to birds. It has been used successfully 

to eradicate rats from very small islands. While these characteristics show potential as a 

candidate for eradications, cholecalciferol has not been tested on a large island such as Rat 

Island. Additionally, its potential effects on non-target organisms is not well-understood in the 

Aleutian environment. The lack of field-testing of cholecalciferol disqualifies it from detailed 

consideration for use in Rat Island rat eradication. 

2.3.4. Use of Disease 

While there is ongoing research focused on the development of taxon-specific diseases that can 

control populations of exotic species (such as by the Australian agency CSIRO, 

http://www.cse.csiro.au/research/rodents/publications.htm), there are no pathogens with proven 

effectiveness at eradicating rats (Howald et al. 2007). In any event, the use of lethal disease 

would be ineffective at eradicating rats from Rat Island, because if the rat population rapidly 

declined, the introduced disease would likely disappear before being able to affect the few 

remaining individuals. Furthermore, the introduction of novel diseases into the environment 

carries tremendous potential risks to non-target species. 

2.3.5. Trapping 

This alternative would call for the use of live traps and/or lethal (“snap”) traps to eradicate rats. 

This action is highly unlikely to succeed on Rat Island. The use of live traps and/or kill traps to 

remove rats from an area is a strong selection agent in favor of rats that are “trap shy.” Thus, 

after extensive trapping the only rats that will remain will be those that are behaviorally less 

likely to enter a trap, and these rats will be very difficult to remove without the introduction of 

alternate methods such as toxins. Given the large size of Rat Island, the widespread use of traps 

is not feasible because of the extensive effort and considerable personnel risk required to set and 

monitor traps in sometimes steep and rough terrain. Additionally, trapping would put a range of 

non-target animals at risk for the entire length of the trapping program. Therefore, this alternative 

is considered infeasible to implement. 

31
Chapter 2: Alternatives 

2.3.6. Biological Control 

The introduction of predators on rats, such as snakes and cats, was dismissed because biological 

control most often only reduces, rather than fully eliminates the target species and thus fails to 

achieve the desired ecological benefit gained through complete rat removal. There is no known 

effective biological control agent for rats on large islands, and some forms of biological control 

would result in unreasonable damage to the environment. The introduction of cats to islands in 

order to control introduced rats has been attempted numerous times since European explorers 

began crossing the Atlantic and Pacific Oceans. The introduction of a rat predator, such as cats, 

generally results in a greater impact on birds than if one or the other were present alone. When 

seabirds are present, cats have been known to prey heavily on seabirds (Keitt 1998; Atkinson 

1985), consuming fewer rats during these times. When seabirds migrate off the islands following 

the breeding season, cats switch prey to rats which allows the island cat population to remain 

stable at a higher level than if no rats were present on the island (Atkinson 1985). Thus, birds are 

impacted not only by rats but the larger number of cats that are sustained by rat presence on the 

island. Introduction of another species onto an island can have severe and permanent 

consequences to the ecosystem (see Quammen 1996). 

2.3.7. Fertility Control 

Fertility control has been used with limited success as a method of pest management in a few 

species. Fertility control for male rats was developed in the 1980’s. Oral fertility control is 

temporary and variable in its effectiveness between individual rats, and multiple applications of 

anti-fertility baits on a remote island is impractical and risky. Because of their mating strategies, 

birth control is not effective for wild populations of highly prolific rodents. Only some members 

of a population need to be fertile to maintain a rat colony or population. There is no method of 

rodent sterilization developed that has demonstrated success to a wild rat population. Impacts of 

experimental fertility control substances for rodents on non-target animals are unknown. Other 

reproductive inhibiters are chemicals or proteins delivered by vaccine or a genetically modified 

viral pathogen. Aerial application of rodenticide is a more practical, effective, and safer method 

to eradicate rats than repeated baiting of oral contraceptives on a remote island across seasons or 

capturing, vaccinating, and releasing every member of one gender of a 6900-acre island rat 

population. This lack of data and tools disqualifies the use of fertility control from detailed 

consideration (see Tobin and Fall 2005). 

2.3.8. Rat Removal with the Goal of “Control” 

The net conservation gain achieved by rat control (i.e., reducing rat populations to extremely low 

levels), rather than complete eradication, is slight, yet the risks to non-target wildlife are nearly 

the same. Rats can reproduce rapidly and recolonize areas from which they were previously 

eliminated. The benefits to nesting seabirds last only as long as population control. In fact, even 

a low density of rats in high-quality nesting habitat of some seabirds result in complete nesting 

failure. The constant maintenance of an ecologically beneficial rat control program on Rat Island 

32
Chapter 2: Alternatives 

is far less cost effective and does not result in the permanent conservation benefits of entireisland eradication. 

33
3. Affected Environment 

Figure 11. Location map of Rat Island in Alaska 

3.1. INTRODUCTION

Rat Island is located in the Rat Islands group of the Aleutian Islands and is part of the Aleutian 

Islands Unit of Alaska Maritime NWR. The Aleutian Islands Unit (formerly known as the 

Aleutian Islands NWR) has been part of the National Wildlife Refuge System since 1913. See 

also Figure 3 for a map of the Alaska Maritime NWR showing Rat Island. 

In 1980, most of the islands in Alaska Maritime NWR, including Rat Island, were designated as 

Wilderness under the Wilderness Act and ANILCA. 

The Aleutian Islands are also designated as an International Biosphere Reserve by the United 

Nations UNESCO Man and the Biosphere program, which recognizes areas worldwide whose 

management strategies promote solutions to reconcile the conservation of biodiversity with its 

sustainable use (UNESCO 2007). 

Rat Island, and subsequently the Rat Islands group, was named after shipboard Norway rats that 

escaped from a shipwreck about 1780 (Black 1983). An Aleut name reported for the island is 

Hawadax (or Howadak) Island, an Aleut word possibly meaning “entry,” (see Bergsland 1994). 

No accounts of Rat Island are known that were written before this first known rat introduction. 

However, Rat Island was probably more similar then to nearby rat-free islands than it is today, 

and supported a richer diversity of bird life prior to rat introduction. 

 
Chapter 3: Affected Environment 

One of the goals of Alaska Maritime NWR is to restore native ecosystems by removing 

introduced non-native animals, and a program has been underway for decades to remove 

introduced foxes (Ebbert and Byrd 2002). Eradication of non-native arctic foxes was completed 

on Rat Island in 1984 (Hanson et al. 1984). The Proposed Action is to continue the restoration of 

native biodiversity by removing Norway rats. 

To determine the feasibility and most appropriate strategy of eradicating rats from islands in the 

Aleutians, several field studies were conducted between 2003 and 2006 in order to: 

• assess the efficacy of two different rodenticides; 

• test different delivery methods (bait stations and aerial broadcasts); 

• evaluate the effects of rodenticides on non-target species (animals other than rats); and 

• describe various aspects of rat biology and effects on native ecosystems in the Aleutians 

(Dunlevy and Scharf 2006; Kurle 2005; Howald et al. 2007). 

Additionally, we conducted studies on Rat Island in June and August 2007 to establish a baseline 

inventory, develop and update descriptions of wildlife habitat and abundance, and examine the 

topography and water resources of the island (Buckelew et al. 2007b). 

Prior to 2007, wildlife studies at Rat Island included: evaluation of fox populations (Berns 1969), 

general wildlife surveys (Murie 1940; Dragoo and Deines 1983; Byrd et al. 2006), the Aleutian 

Goose Recovery Program research (Byrd 1989), and preliminary rat population studies 

(Williams and Howald 2007). 

3.2. PHYSICAL DESCRIPTION

Figure 12. Rat Island, Alaska Maritime NWR S. Ebbert 2001 

35
Chapter 3: Affected Environment 

Rat Island is about a 2800 ha (6861 ac) volcanic island. The coastline is mostly surrounded by 

steep, vegetated, 50-m high (164 ft) cliffs and slopes. Rolling plateaus stretch 1 km (.6 mi) inland 

to the base of a small range of mountains with a peak elevation of 343.5 m (1127 ft). Much of the 

island is accessible by foot. Shallow freshwater lakes occur in seven separate clusters (Figure 9), 

and scattered small drainages carry water during spring melt and heavy rains. The majority of 

these narrow, shallow streams end in a waterfall or closed terminus, thereby precluding fish 

passage (Buckelew et al. 2007b). 

Nearshore pelagic marine waters surrounding Rat Island are influenced by the Alaska Stream on 

the south side in the North Pacific Ocean (Favorite 1974) and by the Aleutian North Slope 

Current on the north side in the Bering Sea (Reed and Stabeno 1999). Net flow of water through 

passes in the Rat Islands is northerly and there are strong currents (Ladd et al. 2005). A narrow 

band of shallow water (<50 m (<164 ft) deep) extends out to 1 km (.6 mi) from Rat Island, but 

beyond that, depths rapidly increase to >100 m (328 ft) within 2 km (1.2 mi) of the island, and 

then to depths of more than 250 m (820 ft) at 5 to 15 km (3.1 to 9.3 mi) offshore (see Lewis et al. 

1960). 

The nearshore marine environment adjacent to Rat Island’s 32 km-long (20 mi) coastline 

includes several shallow coves, but no protected bays. Shallow reefs and rocks abound in the 

nearshore marine waters of the south side of the island, making the area extremely challenging 

for boating. 

Several offshore islets occur along the coastline. The largest, 1.6 km (1 mi) off Ayugadak Point 

on Rat Island’s southeast end, is approximately 4 ha (10 ac) in area. 

36
Chapter 3: Affected Environment 

Figure 13. Map of Rat Island, Alaska Maritime NWR, including The Aleut Corporation selections (red). 

3.3. CLIMATE

The Aleutian climate is primarily marine-influenced and is characterized by generally overcast 

skies, frequent and often severe storm events driven by the Aleutian low pressure system (see 

Rodionov et al. 2005), and high winds. Year-round, the average air temperature is cool but not 

cold – summer temperatures average 9° C (48.2° F) and winter temperatures average 1° C (33.8° 

F). Although minimum temperatures seldom reach below -12° C (10.4° F), the effect of wind 

chill often pushes them lower in winter. Rain falls frequently throughout the year, with snow, 

often slushy, falling throughout the colder months. Snow accumulations are highly variable 

among years, but blowing snow causing “white-out” conditions occurs periodically from 

November through February and sometimes into March. This also is the period when daily 

minimum temperatures most frequently fall below freezing. There is frequent gusty wind yearround, but most particularly during the fall and early winter seasons, with an average daily wind 

speed of 25 km/hr (15.5 mph or 13.4 knots). 

3.4. BIOLOGICAL DESCRIPTION

3.4.1. Marine Waters 

37
Chapter 3: Affected Environment 

Deep pelagic marine waters near the Rat Islands group are foraging areas for whales, porpoises, 

miscellaneous groundfish species, and numerous seabird species. Kelp forests are the dominant 

plant community in the shallow subtidal zone, and they extend around Rat Island typically up to 

0.5 km from shore. The kelp forest’s food web includes marine mammals, marine birds and a 

diverse suite of fishes (e.g., greenling [family Hexagrammidae], blennies and pricklebacks 

[family Stichaeidae], and sculpins [family Cottidae]) (Simenstad et al. 1977). 

3.4.2. Intertidal 

Introduced rats are significantly affecting the intertidal ecosystem on Rat Island (Kurle 2005). 

Rats prey directly on intertidal invertebrates, but also on shorebirds that depend on Rat Island as 

nesting habitat. Due to reduced shorebird (and seabird/marine bird) populations, the abundance 

of intertidal organisms, such as sea urchins and sea stars (phylum Echinodermata); barnacles, 

mussels, limpets, and herbivorous snails (phylum Mollusca); sea anemones (phylum Cnidaria); 

tunicates or sea squirts (phylum Urochordata); and sponges (phylum Porifera) (O’Clair 1977) – 

all common prey items for shorebirds – is much higher on Rat Island than on nearby rat-free 

islands (Kurle 2005). At the same time, the relative abundance of fleshy algae, which is 

consumed by grazing invertebrates such as those mentioned above, is much lower on Rat Island 

as a result of the increased numbers of grazers, and the abundance of less-palatable coralline 

algae is much higher than expected. 

3.4.3. Terrestrial Vegetation 

Terrestrial plant communities in the Aleutians are classified as “maritime tundra” (Amundsen 

1977) or, more recently, “oceanic boreal heath” (Talbot et al. 1999). Aleutian vegetation lacks 

trees, instead being characterized by <2 m tall plant communities dominated by grasses, forbs, 

and dwarf shrubs. The only studies of terrestrial vegetation specifically on Rat Island were part 

of an effort to map potential Aleutian cackling goose nesting habitat (Byrd 1989) and several 

vegetation plots (relevés) surveyed in August 2002 to classify plant communities (S.S. Talbot 

unpubl. data). Rat Island is dominated by short grasses (e.g., Calamagrostis nutkaensis), sedges 

(e.g., Carex macrochaeta, C. pluriflora), dwarf shrubs (e.g., Empetrum nigrum) and nonvascular plants (e.g., Cladina spp., Cladonia spp.). Tall-plant communities, which are fairly 

extensive on islands in the Aleutians with dense breeding birds (e.g., Byrd 1984; Croll et al. 

2005), are uncommon on Rat Island (Byrd 1989). The presence of rats on Rat Island is likely 

suppressing seabird numbers, and rat eradication may ultimately lead to an increase in tall-plant 

abundance as seabirds recolonize the island and again deposit nutrients into the soil (see Croll et 

al. 2005). 

The only plant currently listed as Endangered in Alaska, the Aleutian shield fern (Polystichum 

aleuticum), has not been found on Rat Island and is unlikely to be present, based on its habitat 

requirements (S.S. Talbot, pers. comm.). However, Rat Island is one of only two known 

locations for Aleutian wormwood (Artemisia aleutica), which is not federally listed under ESA 

but is listed in the Atlas of Rare Endemic Vascular Plants of the Arctic (Talbot et al. 1999) and in 

the Alaska Rare Plant Field Guide (Lipkin and Murray, 1997). 

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Chapter 3: Affected Environment 

3.4.4. Freshwater Wetlands 

The freshwater bodies on Rat Island can be broken roughly into two categories, streams and 

lakes. The “stream” category consists of all moving water bodies on the island, whether or not 

they are continuous or run all the way to the ocean. The “lake” category consists of all standing 

bodies of fresh water on the island, regardless of depth. On Rat Island, the lakes occur almost 

entirely in clusters predominantly across the rolling upland plateau (Buckelew et al. 2007b). The 

largest lakes are <200 m (<656 ft) across. No fish species were observed in any of these lakes 

during surveys in August 2007 (Buckelew et al. 2007b). The majority of lakes do not have 

associated wet meadows, and those that do have only very narrow bands of meadow habitat. The 

two largest streams on Rat Island flow into Gunner’s Cove, on the northern side of the island. 

The streams are on average less than 2 m (6.6 ft) wide. Numerous runoff drainages are active 

during spring melt and heavy rains, but most do not contain water perennially. 

Figure 14. Overlooking upland plateau on Rat Island, showing a lake cluster. 

3.4.5. Marine Mammals 

Three species of marine mammals haul-out on Rat Island and forage in nearshore waters: harbor 

seals, sea otters, and Steller sea lions. All three species are protected by the Marine Mammal 

Protection Act (MMPA), and the latter two are also listed under the ESA. The sea otter is listed 

as Threatened throughout southwest Alaska, including the Aleutians. The Steller sea lion is listed 

39
Chapter 3: Affected Environment 

as Endangered in the Aleutians. The most recent surveys for these species on Rat Island are 

summarized in Table 3.1. 

Steller sea lions have an exclusively piscivorous diet, which includes walleye pollock, Pacific 

cod, herring, sculpins, octopus, and squid (National Marine Fisheries Service 2007). Like many 

other species in the Aleutians, Steller sea lions generally breed and give birth during the summer 

months (Pitcher and Calkins 1981), and pups remain at rookeries until about early to midSeptember (Calkins et al. 1999). The western Distinct Population Segment (DPS) of Steller sea 

lions has recently experienced a major decline: a reduction of 75% over 20 years (Calkins et al. 

1999; USFWS 1997a; NMFS 2007). The reasons for this decline are unknown and currently 

under investigation. At Rat Island, a persistent haul-out site is known from near Krysi Point and 

a rookery is known from the islet off Ayugadak Point (NMFS database, Table 3.1). Both sites 

were active in 2007 (Buckelew et al. 2007b). 

Sea otters have an exclusively carnivorous diet, consisting primarily of benthic invertebrates 

such as sea urchins, bivalves, crustaceans, and molluscs (Estes 1990). Sea otters inhabit waters 

within 1 – 2 km (0.6 – 1.2 mi.) of land and can reproduce throughout the year, but are assumed to 

have peak breeding seasons in early summer (Estes 1990). Although they spend most of their 

lives at sea and typically give birth at sea, sea otters have been found to occasionally haul-out 

and give birth onshore (Barabash-Nikiforov et al. 1968). However, they tend to haul-out more in 

the winter months in the intertidal zone, and as high as about the storm tide line, in the Aleutian 

Islands (T. Tinker, pers. comm.). Sea otters were nearly extirpated from Alaska in the 18th and 

19th centuries due to over-hunting (Kenyon 1969). As a result, sea otter hunting was banned in 

1919 (Estes 1990). The Alaskan sea otter population rebounded quickly following the hunting 

ban (Estes 1990); however, since the mid-1980s sea otters in Alaska have undergone a 55-67% 

decline (Doroff et al. 2003; Burn et al. 2003; Burn and Doroff 2005; Estes et al. 2005; USFWS 

2005). More specifically, the population decline in the Rat Islands group was about 94%; Rat 

Island decreased from a count of 270 in 1959 to 11 in 2000 (Kenyon 1969; Doroff et al. 2003). 

The reasons for this decline are unknown with certainty, and are under investigation. Twentytwo sea otters were noted at Rat Island during boat surveys in 2007 (Buckelew et al. 2007b) (see 

Table 3.1). 

Table 3.1. Recent survey results for marine mammals that haul-out on Rat Island. 

Species Number Year Source Comments 

Harbor seal 93 

“Fairly 

common” 

1999 

2007 

Small et al. in press 

Buckelew et al. 2007b 

Aerial survey 

Often seen in water, not seen 

Hauled-out 

Sea otter 11 2000 Doroff et al. 2003 

22 2007 Buckelew et al. 2007b 

Steller sea lion 45 

171* 

present 

2004 

2005 

2007 

NMFS database 

NMFS database 

Buckelew et al. 2007b 

Buckelew et al. 2007b 

Aerial survey for Rat I. 

Aerial survey for islet off Ayugadak 

Point (plus 5 pups) 

Seen from boat offshore at Rat I. and 

Ayugadak Point 

*Survey numbers for islet off Ayugadak Point, which is a Steller sea lion rookery 

40
Chapter 3: Affected Environment 

3.4.6. Birds 

Knowledge of the status of birds at Rat Island is based largely on incidental observations made 

during periodic short visits, largely by refuge staff, in summer (e.g., Dragoo and Deines 1983; 

Byrd 1989; Williams and Howald et al. 2007; Byrd et al. 2004; Buckelew et al. 2007b). These 

observations and general knowledge about the seasonal distribution of birds in the central 

Aleutians (Gibson and Byrd 2007) may be used to characterize the avifauna that is likely to be 

present at Rat Island in fall (Table 3.2, Appendices 2 and 3). 

3.4.6.1. ESA-listed bird species 

Short-tailed albatross (Phoebastria albatrus), listed as Endangered, is considered rare May – 

September in the Aleutians in offshore marine waters (Gibson and Byrd 2007). The species does 

not occur on land anywhere in the Aleutians, and it is unlikely to occur in nearshore waters at 

Rat Island. The Threatened seaduck Steller’s eider (Polysticta stelleri) is considered rare in fall, 

winter, and spring in the central Aleutians, where it occupies nearshore marine waters. 

Nevertheless, most records in the central Aleutians are east of Rat Island (Gibson and Byrd 

2007). Few records exist for Amchitka, the island closest to Rat Island where observers have 

been present during the winter. In fact, the species was never recorded at Amchitka during the 

extensive studies 1967 – 1973 (White et al. 1977). Therefore, it is unlikely the species will occur 

at Rat Island during the proposed eradication project. 

3.4.6.2. Non-ESA-listed bird species 

At least five species of waterfowl are likely present annually at Rat Island in fall (Table 3.2). 

Emperor goose (Chan canagica) may begin to arrive in September, although most probably are 

not present until late November or December (Gibson and Byrd 2007) when at least several tens 

of individuals may remain until at least March. A few pairs of Aleutian cackling goose (Branta 

hutchinsii leucopareia) have recently been found nesting on Rat Island (Buckelew 2007b), but 

most of the fall use is expected to be flocks of at least several tens of birds making brief 

stopovers during their migration from western Aleutian breeding areas to wintering areas in 

California. Aleutian green-winged teal (Anas crecca crecca [nimia]), and Pacific common eiders 

(Somateria mollissima v-nigrum) probably nest on Rat Island, but by fall both species would be 

using inshore marine waters for foraging and roosting. Teal also use island wetlands. Nonbreeding harlequin ducks (Histrionicus histrionicus) summer near Rat Island using inshore 

marine waters, and they are joined in late fall by harlequins that nest in mainland of Alaska. 

Small numbers of other species of seaducks like black scoter (Melanitta nigra) also may occur 

after mid-September in some years. 

One of the Aleutian endemic birds that is resident on Rat Island is Townsend’s rock ptarmigan 

(Lagopus muta townsendi). This form occurs throughout the Rat Island group, and is one of the 

species that seems to have begun to partially recover after removal of introduced arctic foxes 

(Alaska Maritime NWR, unpubl. data). Recently at least 50 birds were seen on the island during 

a September survey (Williams and Howald 2007). The species tends to assemble in flocks in the 

41
Chapter 3: Affected Environment 

42

fall where, at least in some locations in the Aleutians, they feed on Empetrum berries and other 

vegetation. 

Few, if any, burrow-nesting seabirds still breed on Rat Island, because these species are probably 

particularly susceptible to extirpation by introduced rats, but analysis of faunal remains from 

Aleutian midden sites on the island indicate the likelihood that puffins (species not specified) and 

possibly other burrow-nesting species in the family Alcidae were common prior to rat 

introductions (D.G. Corbett and C.L. Funk, unpubl. data). Also found fairly frequently were 

bones of species within the order Procellariidae which includes storm-petrels (Oceanodroma

spp.). Interestingly, on the islet about 1.6 km east of Ayugadak Point on Rat Island, Dragoo and 

Deines (1983) discovered a diverse colony of burrow-nesting species including fork-tailed and 

Leach’s storm-petrels (Oceanodroma furcata and O. leucorhoa), ancient murrelet 

(Synthliboramphus antiquus), Cassin’s auklet (Ptychoramphus aleuticus), and tufted puffin 

(Fratercula cirrhata). The presence of these species suggest rats were not present on the islet at 

least as recently as the early 1980s, and if these species remain today (and numbers of some of 

the species seen in the water near the islet suggest they have persisted) they may provide a 

nearby source for eventual repopulation of Rat Island after it is rat-free. Seasonal timing of 

breeding among these species varies; ancient murrelets and Cassin’s auklets departing the 

colonies in the Aleutians by early to mid-August (Gibson and Byrd 2007), and therefore, they are 

not shown in the Table 3.2 of birds likely to be present at Rat Island in fall. Fork-tailed stormpetrels and tufted puffins usually depart after chicks fledge by mid or late September, but some 

late chicks of Leach’s storm-petrels are not fledged until late October or early November in 

extremely late years. Although some individuals of some of these species may continue to be in 

the vicinity of the Rat Islands in fall and winter, these plankton and fish feeders typically occupy 

offshore marine waters. 
Chapter 3: Affected Environment 

Table 3.2. Birds expected to occur at Rat Island in fall (Sept.-October)a 

Species Rat Island 

Abundanceb Primary Foraging Habitat on Rat Islandc Rat Islands Group Abundanced Source for 

Emperor goose <10 Beach and Reefs low hundreds Byrd pers. Cackling goose <50 Dwarf Shrub Meadow ten thousands Byrd pers. Green-winged teal 15+ Ponds, Inshore Marine low thousands Williams anCommon eider mid hundreds Inshore Marine Waters mid thousands Williams an

Buckelew e

Harlequin duck mid hundreds Inshore Marine Waters mid thousands Buckelew eRock ptarmigan 50+ Dwarf Shrub Meadow mid thousands Williams anFork-tailed storm-petrel hundreds Offshore Marine Waters ten thousands Dragoo and Leach’s storm-petrel hundreds Offshore Marine Waters ten thousands Dragoo and Red-faced cormorant low hundreds Inshore Marine Waters mid thousands Byrd et al. Pelagic cormorant low hundreds Inshore Marine Waters mid thousands Byrd et al. Bald eagle 6 nesting prs Various habitats mid hundreds Buckelew ePeregrine falcon 2 pairs Inshore Marine Waters low hundreds Dragoo and Pacific golden-plover <20 Grass and Shrub Meadows low hundreds Byrd pers. Black oystercatcher 30-40 Beach and Reefs mid hundreds Byrd et al. Wandering tattler 1-3 Beach and Reefs mid tens Buckelew eRuddy turnstone <10 Beach and Reefs, Dwarf Shrub 

Mat 

low hundreds Byrd pers. 

Pectoral sandpiper <20 Wet Meadow low hundreds Byrd pers. Sharp-tailed sandpiper <10 Wet Meadow low hundreds Byrd pers. Rock sandpiper 20+ Beach and Reefs mid-thousands Williams anGlaucous-winged gull 500+ Beach and Reefs high thousands Buckelew eParasitic jaeger <10 Dwarf Shrub Mat mid hundreds Byrd et al 2Pigeon guillemot 200 Inshore Marine Waters low thousands Byrd et al 2Whiskered auklet low tens Inshore Marine Waters ten thousands Byrd pers. Horned puffin <150 Inshore Marine Waters ten thousands Buckelew e

2004 
Chapter 3: Affected Environment 

Species Rat Island 

Abundanceb Primary Foraging Habitat on Rat Islandc Rat Islands Group Abundanced Source for 

Tufted puffin <300 Inshore Marine Waters ten thousands Buckelew e

2004 

Short-eared owl 1-2 Grass Meadow low tens Byrd pers. Common raven 2-4 various high tens Buckelew e

al. 1984 

Winter wren low hundreds Beach and Reefs low thousands Buckelew eSong sparrow 2-5f Tall Forb Meadow mid hundreds Buckelew eLapland longspur mid hundreds Grass Meadow ten thousands Buckelew eSnow bunting <20 Grass Meadow high hundreds Byrd pers. Gray-crowned rosy-finch 50-100 Cliffs and Beaches high hundreds Buckelew ea These are species very likely to occur at Rat Island in fall. Other migrating species (e.g. waterfowl, shorebirds, and passerines) could 

numbers in some years, but effects of the proposed project would be similar to those discussed for similar taxa listed here; 

b Approximate estimates based on the listed source; c Habitats from Gibson and Byrd 2007; d Approximate estimates for the Rat Islands group are from Gibson and Byrd 2007 and Alaska Maritime NWR unpubl. data (see Appene Low thousands = 1-3 thousands, medium thousands = 4-6 thousands, high thousands = 7-10 thousand; estimates based on information 

and Alaska Maritime NWR unpubl. data for fall populations in the Rat Islands group; 

e Subjective estimate based on knowledge of the status of birds in the area; f 15 additional birds were seen on the islet off Ayudagak Pt. (Buckelew et al. 2007b) 

.
Chapter 3: Affected Environment 

Ledge-nesting seabirds like cormorants (Phalacrocorax spp.) and crevice-nesting seabirds like 

pigeon guillemot (Cepphus columba), whiskered auklet (Aethia pygmaea), and horned puffin 

(Fratercula corniculata) apparently still nest on Rat Island or on the islet off Ayugadak Point, 

because numbers were seen in marine waters, where they forage on fish or plankton, near the 

island (Table 3.2). The former two species likely are resident in the area, but horned puffins 

probably depart after young fledge by mid- September. 

Inland, surface-nesting seabirds at Rat Island include glaucous-winged gull (Larus glaucescens) 

and parasitic jaeger (Stercorarius parasiticus), the former a scavenger and the latter a 

kleptoparasite on seabirds. Gulls congregate on beaches and rocky reefs in fall and winter, 

whereas jaegers depart the Aleutians usually by early to mid-September (Gibson and Byrd 2007). 

Rat Island could possibly have saturated breeding densities of bald eagle (Haliaeetus 

leucocephalus) with an estimated 4-5 breeding pairs. Additionally, numbers of subadult eagles 

have been recorded on the island on one visit when a dead whale was present (see Appendix 2). 

As predators and scavengers, eagles congregate, particularly after breeding is done by late 

August, at food sources such as beach-cast whales, concentrations of spawning salmon, or 

artificial sources of food like refuse at dumps and associated with seafood processing in the 

Aleutians (Gibson and Byrd 2007). Peregrine falcon (Falco peregrinus pealei) also breeds on 

Rat Island, and this species is primarily a predator and not a scavenger. 

The only breeding shorebirds on Rat Island are black oystercatcher (Haematopus bachmani) and 

rock sandpiper (Calidris ptilocnemis), and both are resident in the region. In fall, rock 

sandpipers join oystercatchers on beaches and rocky reefs where they both winter, feeding on 

invertebrates the intertidal. During fall migration at least five additional species of shorebirds 

probably stop at least briefly at Rat Island annually (see Table 3.2). Numbers of these migrants 

typically are low (typically fewer than 20 individuals at any one time). Some of these species 

such as Pacific golden-plover (Pluvialis fulva) use grass and shrub meadows, whereas others like 

pectoral and sharp-tailed sandpipers (Calidris melanotos and C. acuminata, respectively) 

primarily are found in wet meadows. Wandering tattler (Heteroscelus incanus) and ruddy 

turnstone (Arenaria interpres) tend to use beaches and rocky shores, but tattlers are sometimes 

found at stream edges as well. 

It is likely that a few migrant short-eared owls (Asio flammeus) stop at Rat Island each fall where 

they probably take some rats. Most records of migrating short-eared owls in the central Aleutians 

are for the period September 17 to the end of October. 

Breeding Lapland longspurs (Calcarius lapponicus) are flocking by late August and moving 

around the island, primarily feeding on seeds. Most depart by the end of September. Resident 

perching birds known to be present at Rat Island include: common raven (Corvus corax), winter 

wren (Troglodytes troglodytes), song sparrow (Melospiza melodia), snow bunting 

(Plectrophenax nivalis), and gray-crowned rosy-finch (Leucosticte tephrocotus griseonucha) 

(Table 3.2). Wrens and rosy-finches are common along the coast on beaches, cliffs, and reefs. 

Wrens appear to feed on invertebrates in fall, but rosy-finches probably also take seeds. Snow 

buntings probably are not very common in fall, but these seed-eaters can be found from sea level 

to uplands. Very few ravens have been seen on Rat Island during past surveys. These scavengers 

45
Chapter 3: Affected Environment 

and predators take a wide variety of food. Likewise, very few sightings have been recorded of 

song sparrow on Rat Island, and it is possible rats have all but extirpated them from the main 

island. Evidence for this is the presence of 15 sparrows on the islet off Ayugadak Point, which 

may be rat-free, during a brief survey in August (Buckelew 2007b). 

All of the bird species listed above are protected under the Migratory Bird Treaty Act except 

rock ptarmigan which are protected as a game bird by the State of Alaska. Bald eagles have 

added protection from the Bald and Golden Eagle Protection Act. 

3.4.7. Terrestrial Mammals 

There are no terrestrial mammals on Rat Island other than the Norway rats. At one time, 

introduced arctic foxes occurred on the island, but were eradicated (Hanson et al. 1984). 

Norway rats are the largest of the three species of commensal rats, with large males weighing up 

to 450 g (1 lb). Norway rats are generally highly secretive, remaining hidden whenever possible 

and preferring to travel along edges rather than entering open spaces. Norway rats are 

omnivorous generalists, adapting their feeding habits constantly to exploit the most nutrient-rich 

and easiest to obtain food items in their environment. However, Norway rats are also considered 

“neophobic,” or wary of novel objects in their environment including potential food items. Rats 

will often avoid novel food items completely at first, then sample small tastes, and only wholly 

consume new food items after multiple exposure events (information above adapted from 

Jackson 1982). Norway rats in the Aleutians have been documented consuming a very wide 

variety of food items, including plant matter, invertebrates (both terrestrial and intertidal marine 

species), and vertebrates such as birds, fish, sea otter, and even other rats (Brechbill 1977, 

Dunlevy and Scharf 2007). Rats in the Aleutians have been shown to actively breed from midspring through late fall, with a population peak in late summer and a crash in early spring 

(Dunlevy and Scharf 2006). 

3.4.8. Freshwater Fish 

Anadromous stream surveys have been conducted by ADF&G throughout the Aleutians and 

none have been found to occur on Rat Island (Johnson and Weiss 2007). Previous reports 

indicate that two of the perennial streams flowing into Gunner’s Cove may support Dolly varden 

(Salvelinus malma) and pink salmon (Oncorhyncus gorbuscha) in their lower reaches. However, 

no fish of either species were recorded in streams or intertidally during surveys in August 2007 

(Buckelew et al. 2007b). During these surveys, observers recorded stickleback (Gasterosteus 

aculeatus or Pungitius pungitius) in some of Rat Island’s coastal streams. 

3.5. CULTURAL RESOURCES

Rat Island is presently uninhabited and the most recent residents (other than visiting Refuge 

personnel and other researchers) were probably fox trappers in the 1920s. There are four sites 

46
Chapter 3: Affected Environment 

which have been certified by the Bureau of Indian Affairs (BIA) as cemetery and historical sites 

eligible for conveyance to The Aleut Corporation under section 14(h)(1) of ANCSA. These areas 

have been selected by The Aleut Corporation under that entitlement, but have not yet been 

conveyed. 

Recent archeological work to identify faunal remains in a midden site is not yet published, but 

ultimately will provide information on relative abundance of species used by the Aleuts for food 

prior to the introduction of rats on the island (Corbett et al. 2003). 

3.6. CURRENT HUMAN USES OF THE AREA

Some commercial fishing occurs in the vicinity of the Rat Islands. For instance golden king crab 

(Lithodes aequispinus) are harvested in nearby Oglala Pass and there is some fishing for halibut 

(Hippoglossus stenolepsis), cod (Gadus morhua), sablefish (Anoplopoma fimbria) and Atka 

mackerel (Pleurogrammus monopterygius) in the Rat Islands group and probably occasionally 

near Rat Island (F. Bowers, pers. comm.). 

Due to its extreme isolation, Rat Island is rarely, if ever, visited by the public. In fact, the Refuge 

has no records of known recreational visitors, although the island may be visited occasionally by 

commercial fishermen. Smaller cruise ships (~120-passenger) visit the Aleutian Islands in 

summer, and up to four might pass in the vicinity of Rat Island during June and July in a typical 

year. The Refuge has not had any requests from tour companies to go ashore on Rat Island. 

Probably the most frequent visitors have been Refuge personnel, as well as other researchers 

with special use permits from FWS. 

Little, if any, subsistence activity is known to occur near Rat Island because the nearest 

community, Adak is about 322 km (200 mi) away. In the Aleutians, residents have traditionally 

made use of the following types of resources: marine resources, including fish, (salmon, halibut, 

cod, etc.); marine mammals (Steller sea lions, sea otters, harbor seals, and northern fur seals 

(Callorhinus ursinus) in the Pribilofs); and intertidal invertebrate resources such as sea urchins, 

razor clams, butter clams, cockles, mussels, and chitons, crab and shrimp. Plants harvested 

include berries (blueberries, salmonberries, mossberries, strawberries, and lingonberries), wild 

celery (Angelica lucida), wild rice (Fritillaria camschatcensis) giant kelp, and fiddlehead ferns. 

Birds are harvested, including ducks, geese, and ptarmigan. Eggs are collected primarily from 

gull colonies, although mallard, merganser, puffin, and murre eggs are also collected, depending 

on the location (above data from BIA 1992; Fall et al. 1998; Veltre and Veltre 1981, 1983; and 

Wolfe et al. 1990). 

47
4. Environmental Consequences 

Figure 15. Norway rat survey on Rat Island 2002 AMNWR 

4.1. INTRODUCTION

The purpose of this chapter of the EA is to determine whether or not any significant impacts to 

the environment of Rat Island should be expected from either of the Alternatives. According to 

federal Council on Environmental Quality (CEQ) regulations (40 CFR 1508.27), significance is 

determined by considering both the context in which the action will occur and the intensity of the 

action. “Context” is the setting within which an impact is analyzed, such as a particular locality, 

the affected region, or society as a whole. “Intensity” is a measure of the severity of an impact. 

Determining the intensity of an impact requires consideration of the appropriate context of that 

impact as well as a number of other factors. 

In the analysis below, the potential significance of impacts of the Proposed Action and the No 

Action alternative will be discussed on a case-by-case basis for each impact topic, with an 

identification of both the context used for the analysis and the considerations included for a 

determination of the intensity of the impact. 

4.2. CATEGORIES ANALYZED (DESCRIPTIONS) 

4.2.1. Restoration Efficacy 

The Proposed Action has a stated purpose of benefiting Rat Island’s local environment. The 

impacts analysis in this chapter will examine the extent of this benefit – the efficacy of the 

Proposed Action in meeting restoration objectives. As stated in Section 1.2, the specific 

objectives of this project are to 1) eradicate non-native rats from Rat Island, and 2) keep Rat 

Island rodent-free through an introduction-prevention program. Both of these objectives are 

 
Chapter 4: Environmental Consequences 

necessary conditions for successful restoration. Restoration efficacy as defined by these two 

objectives will be evaluated according to simple yes-or-no answers to the questions “does the 

action have a high probability of eradicating rats from Rat Island?” and “do the appropriate 

elements of the action have a high probability of preventing the reintroduction of rodents to Rat 

Island in the future?” We believe that the established record of successes (as well as failures) in 

previous island rat eradication attempts is the best predictor available of this project’s probability 

of success. 

We anticipate that the primary result of the Proposed Action will be a shift in the plant and 

animal communities and ecosystem processes on Rat Island toward a state more representative of 

it’s ecosystem before rats were introduced. We anticipate this shift to include, among other 

things, an increase in the number of breeding seabirds on the island, especially burrow- and 

crevice-nesting species. However, there are too many variables that will contribute to the posteradication ecosystem responses to effectively analyze all of them within the scope of this 

document. 

4.2.2. Assessing Impacts to Biological Resources 

The impacts of the Proposed Action on the biological resources of Rat Island, including the 

condition of the ecosystem in general, will be examined in two different contexts. First, this 

document will analyze the risks as well as the benefits that the Proposed Action will bring to 

individual animals that utilize Rat Island. Second, and most critical from the perspective of 

environmental analysis under NEPA regulations, this document will analyze whether impacts to 

a particular resource could be considered significant as described in Section 4.1. The concept of 

“significance” will be defined separately for each topic analyzed below. In some cases, impacts 

at the individual level (e.g. causing mortality or behavior changes to individual animals) must be 

considered significant. However, in the case of many of the species (see Sections 4.5.2.1 - 

4.5.6.3), impacts to individual organisms, however major, may not qualify as significant impacts 

in the context of population-level impacts to species utilizing Rat Island. Risk analyses for 

individual animals will contribute to the overall analysis of significance for each biological taxon 

considered, but should not be used independent of, or interchangeably with, the significance 

determination for each impact topic considered. 

4.2.2.1. Assessing risks to biological resources from rodenticide use 

The risk of impacts from brodifacoum or any other rodenticide to individual animals is 

determined by two factors: 

• the toxicity of the compound to that individual; and 

• the probability of that individual’s exposure to the compound (Erickson and Urban 2002). 

4.2.2.1.1. Toxicity 

The toxicity of a particular compound on an individual animal is often expressed in a value 

known as the “LD50” – the dosage (D) of a toxin that is lethal (L) to 50% of animals in a 

laboratory test. The EPA has compiled laboratory data on the LD50 quantity of brodifacoum for 

49
Chapter 4: Environmental Consequences 

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 individual impacts, this document will use the following LD50 values to generalize 

potential toxicity for birds and mammals respectively (adapted from Erickson and Urban 2002): 

• For birds, an LD50 value of 0.26 mg/kg will be used – this is the average LD50 value for 

the mallard (Anas platyrhynchos) 

• For mammals, an LD50 value of 0.4 mg/kg will be used – this is the average LD50 value 

for the laboratory rat (Rattus 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). In reality, there are 

other variables that affect LD50 as well, but using conservative LD50 values such as those above 

decreases the possibility that the model will under-estimate the risk to individual animals. 

Erickson and Urban (2002) use another general model to determine the amount of bait needed to 

reach an LD50 threshold for birds at a mass of 25 g, 100 g, and 1000 g, compared to average 

daily food intakes for each of these size classes. See Table 4.1. 

Table 4.1. Generalized proportion of daily food intake that must be bait for birds to reach an 

LD50 threshold (adapted from Erickson and Urban 2002, using a brodifacoum concentration of 

25 ppm) 

Size class: Amt of bait for LD50: % of daily food intake: 

25 g 0.26 g 4.2 

100 g 1.04 g 10.8 

1000 g 10.4 g 19.2 

Erickson and Urban 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 4.1 above. However, Steller 

sea lions, sea otters, and harbor seals are the only mammals, other than rats (and project 

personnel), that may be present in baited areas, and the large size of each of these animals 

(orders of magnitude larger than 1000 g) makes it difficult to apply this particular model. 

Therefore, marine mammal toxicity will be analyzed primarily using the generalized mammal 

LD50 of 0.4 mg/kg, described earlier, with an extrapolation of the number of bait pellets needed 

to reach an LD50 threshold. For these estimates, as well as elsewhere in the impacts analysis of 

this document, there will be an assumption that bait pellets will weigh 2.4 g each, the mid-range 

of expected pellet size. 

Besides lethal toxicity, there are other effects from ingestion of anticoagulants. Erickson and 

Urban (2004) report that individual birds and mammals surviving toxicity tests may experience 

internal hemorrhaging, external bleeding, etc. In rabbits dosed at the time of gestation, internal 

hemorrhaging was reported at concentrations two orders of magnitude less than the LD50. 

Further, the authors suggest fetuses may be more susceptible to brodifacoum effects than adults. 

Erickson and Urban (2004) also note that rat two-generation reproduction tests are not available 

for the nine rodenticides they evaluated. 

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Chapter 4: Environmental Consequences 

The EPA 1998 Reregistration Eligibility Decision (RED) Rodenticide Cluster report discusses 

developmental toxicity studies in rats and rabbits. The no effects level (NOEL) for rabbits was 

set at 0.002 mg/kg and the lowest effects level (LOEL) was determined to be 0.005 mg/kg. 

4.2.2.1.2. Exposure 

Exposure to brodifacoum is essentially dependent on two factors: 

1. The availability of rodenticide in the local environment; and 

2. Any food habits, behavior patterns, and other specific characteristics that increase or 

decrease an animal’s exposure to the rodenticide. 

Bait will be applied according to EPA-approved label instructions, which will set application rate 

values, ranges, and/or limits for the bait product used. As permitted by FIFRA, different 

application rates may be considered for different habitat types. For the purpose of risk modeling 

in this document, application rates will be used based on data collected in 2006 during a trial bait 

broadcast at the Bay of Islands on Adak Island, 322 km (200 mi) east of Rat Island (Buckelew et 

al. 2007a). There were two target application rates calculated during this trial: 17 kg/ha for 

coastal areas with a higher density of rats, and 8 kg/ha for upland areas where rat density is 

lower. Given an estimated individual pellet weight of 2.4 g (.08 oz), these application rates 

equate to a target application rate of 0.7 pellets/m2

 (or 1 pellet every 1.4 square meters) for 

coastal areas, and a target of 0.33 pellets/m2

 (or 1 pellet every 3 square meters) for upland areas 

(Buckelew et al. 2007a). 

Bait will not be broadcast directly into the marine environment, and precautions will be taken to 

reduce the likelihood of incidental or unintentional application. Application of pellets will not 

occur above the wind speed specified on the product label. A deflector will be used on the bait 

spreader for all flight paths that come near the coast in order to direct bait away from the ocean, 

but a limited number of pellets are likely to drift into the intertidal or nearshore zones. On 

Anacapa Island, project personnel monitoring bait drift into the intertidal environment reported 

72 bait pellets in the water over a 500 m2

 (598 sq yd) area, which equates to 0.14 pellets/m2

(Howald et al. 2005). Bait pellets that enter the water will be available for consumption for a 

short period of time after entry. In bait disintegration experiments and observations in New 

Zealand (Empson and Miskelly 1999) and California (Howald et al. 2005), observers found that 

pellets similar to those planned for use on Rat Island sank almost immediately and disintegrated 

completely in as little as fifteen minutes. Although the bait that will be used on Rat Island has 

been engineered to withstand moisture better than the baits in the observations mentioned above, 

the frequent turbulence of the waters surrounding Rat Island, especially in the intertidal and 

nearshore areas, will accelerate the bait’s disintegration. Brodifacoum’s water solubility is very 

low (Primus et al. 2005; US EPA 1998), making the risk of brodifacoum contaminating the water 

column also very low. Hypothetically, even if brodifacoum was highly water soluble, and bait 

was broadcast at the full application rate of 17 kg/ha into water only 1 m (3.3 ft) deep, the 

resultant brodifacoum concentration in the water – about 0.04 parts per billion – would still be 

nearly 1000 times less than the measured LC50 value for trout (0.04 parts per million) (Syngenta 

2003). Similar in concept to an LD50 value, this LC50 value represents the concentration of 

brodifacoum dissolved in water that will be lethal to 50% of the trout within 96 continuous hours 

of exposure in a laboratory test. While dissolution of brodifacoum into the water-column is 

51
Chapter 4: Environmental Consequences 

expected to be low given its solubility, it is likely that as pellets break apart, some particles 

containing brodifacoum residues may be available to filter-feeders such as mussels and clams. 

Post-application sampling during the 2006 bait trial study in the Bay of Islands off Adak did not 

detect brodifacoum in the water (Buckelew et al. 2007a; Island Conservation, unpubl. data), and 

post application sampling in the Anacapa Island rat eradication did not detect any brodifacoum 

residue in intertidal mussels or shore crabs (Howald et al. 2005). Further, an estimated 360 g of 

brodifacoum (from 17.7 tons of bait) was accidentally spilled in the tidal environment in New 

Zealand (Primus et al. 2005). The brodifacoum was measurable in the water at the spill location 

for only 36 hours and was undetectable afterwards (measuring less than .020 ppb). Additionally, 

brodifacoum was undetectable in sediment samples taken from the ocean floor nine days after 

the spill. In terms of intertidal invertebrates, brodifacoum concentrations peaked in mussels one 

day after the spill but averaged just above detectible after Day 29 and lasted in limpets for up to 

80 days. The similar sampling results of the Bay of Islands trial and the Anacapa eradication, in 

concert with the results of the accidental spill event in New Zealand, demonstrate the low 

solubility of brodifacoum in water and its lack of accumulation or persistence in filter feeders 

such as mussels. Nevertheless, uptake by these filter feeders may be a potential exposure 

pathway over the short term, and will be considered in this EA. 

Bait will not be broadcast within the freshwater lake clusters identified on Rat Island (see Figure 

6), and the planned helicopter flight paths will leave a 1.5 m (5 ft) minimum buffer around the 

outer perimeter of each lake cluster. Within this buffer and between lakes in each cluster, 

personnel will hand broadcast bait pellets at the same target application rate applied by the 

helicopter. When possible, the helicopter will also avoid flight paths over the largest streams on 

the island. 

These mitigation measures will result in there being a low likelihood of bait entering lakes 

(similar to the likelihood of bait entering the marine environment) and a somewhat higher 

likelihood of bait entering streams. Any bait that does enter the water will sink to the bottom and 

disintegrate quickly. In rapidly flowing water, bait pellets will disintegrate and become 

unavailable for consumption nearly as quickly as in the marine environment. In standing or 

slowly flowing water, bait disintegration will be slower, but much more rapid than bait 

disintegration on land. 

In the form used for rodent control or eradication, brodifacoum can only effectively be delivered 

through oral ingestion; animals can either ingest brodifacoum by consuming bait pellets (known 

as “primary exposure”), or by preying or scavenging on other animals that have previously 

consumed bait pellets (known as “secondary exposure”). Because the bait is composed primarily 

of grains, herbivorous and omnivorous species are more likely to consume bait (primary 

exposure) than carnivorous species, including insectivores (see Table 4.2 below). Bait 

persistence in the Aleutian environment is variable and dependent on the rate of application, 

density of rats in a given location and ambient weather conditions (rainfall, early or late onset of 

freezing conditions), as well as on consumption by rats, non-target animals. Previous 

observations have determined that bait not taken by rats or non-target species could persist for 2 

– 8 months, depending on exposure to rain and/or snow conditions (S. Buckelew, pers. comm.). 

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Chapter 4: Environmental Consequences 

The low application rate and high bait consumption by rats should reduce the likelihood of bait 

persistence in the environment. 

Once consumed, brodifacoum is retained in the body of the consumer for an amount of time that 

varies considerably between taxa. The exact mechanisms of brodifacoum retention in 

invertebrates are unclear. In vertebrates, ingested brodifacoum exits the body (primarily through 

feces) in a bi-phasic pattern over time: Most of the compound is flushed soon after ingestion, but 

the brodifacoum that is retained after this initial flush exits the body much more slowly. In 

mammals (the only vertebrate taxon for which extensive data are available), the half-life of 

brodifacoum in the blood has been measured at no more than 30 days; brodifacoum half-life in 

the bloodstream of rats has been measured at 6.5 days (Erickson and Urban 2002). The amount 

of brodifacoum that is retained in the liver and other tissues may remain present for much longer. 

In rats, the half-life of a sub-lethal brodifacoum dose in the liver has been measured at 350 days 

(Erickson and Urban 2002). Because the likelihood of all rats consuming a lethal brodifacoum 

dose is very high, it is unlikely that animals feeding on rats will be at risk of brodifacoum 

exposure for this long – rat carcasses are not likely to be available for longer than 30 days before 

decomposing to the point of becoming unavailable as a food item. The majority (88%) of rat 

carcasses recovered after bait application on islets within the Bay of Islands off Adak were found 

underground or in burrows, reducing the probability of secondary poisoning to avian predators or 

scavengers (Buckelew et al. 2007a). However, as long as some bait pellets remain in the 

environment there will be a low risk of secondary exposure to predators or scavengers of birds 

killed as non-targets. 

Table 4.2. Likelihood of exposure to brodifacoum based on food habits and other characteristics 

Food habits/habitat Likelihood of 

primary 

exposure 

Likelihood of 

secondary 

exposure 

Taxon example(s) (not a 

comprehensive list) 

Largely granivorous 

(terrestrial) 

High Very low Some passerines; some waterfowl 

Omnivorous (terrestrial) Probably high High Rats; ravens; gulls; bald eagles; others 

Largely carnivorous 

(terrestrial) - 

Rat consumption Very low High Ravens; bald eagles 

Bird consumption Very low Low Peregrine falcons, bald eagles 

Largely insectivorous 

(terrestrial) 

Low Low Some passerines 

Scavenger (terrestrial) High High Ravens; gulls; eagles; rats 

Intertidal invertebrates* Very low to low Very low Mussels; limpets; sponges 

Marine mammals** Very low to low Very low Steller sea lions; harbor seals; 

sea otters 

*Invertebrate exposure data is only relevant for extrapolations of secondary exposure likelihood for predators on 

intertidal invertebrates 

**Only pinnipeds and sea otters are considered in detail due to their occasional use of terrestrial habitat 

4.2.2.1.3. Assessing overall risk from brodifacoum use 

The risk of brodifacoum poisoning is a function of both exposure and toxicity. In other words, 

the theoretical toxicity of a compound is only relevant if the species of concern has an actual risk 

of exposure. The toxicity of brodifacoum to each species analyzed here, as well as that species’ 

53
Chapter 4: Environmental Consequences 

likelihood of exposure (Table 4.2), will be considered together. For example: A 300 g (.7 lb) 

Norway rat (average adult size) will need to consume only 2 bait pellets to have a 50% risk of 

mortality. Because Norway rats have a high likelihood of primary exposure to the rodenticide (as 

opportunistic omnivores in concert with the design of the bait to be a rat attractant), rats are very 

likely to be at risk of brodifacoum poisoning. 

4.2.2.2. Assessing risk to biological resources from disturbance 

The operation of low-flying aircraft throughout Rat Island is likely to result in disturbance to 

wildlife from sound, the sudden appearance of an aircraft, or a combination of both (Efroymson 

et al. 2001). Wildlife on Rat Island will be exposed to noises that exceed background levels. 

Helicopters will be used both during staging procedures in summer and during bait application in 

fall. There are, therefore, two opportunities for sound disturbance to wildlife. The relatively low 

altitude at which helicopters will fly will result in a narrow focus of the narrow cone of highest 

noise underneath the helicopter, minimizing disturbance of marine mammals or birds in 

nearshore marine waters or on offshore rocks. 

Pinniped responses to aircraft overflights vary from no reaction to completely vacating haul-outs 

in response to a single overflight (Efroymson and Suter 2001). In general, pinnipeds hauled-out 

for molting or pupping are most responsive to aircraft (Richardson et al. 1995). In order to 

estimate the risk of disturbance for each taxon of concern, the anticipated helicopter operations 

pattern described above will be compared against observational evidence of effects displayed 

elsewhere in that taxon or a sufficiently similar group (based on literature reviewed in US Air 

Force and US Fish and Wildlife Service 1988). 

Wildlife could be disturbed or harmed as a result of installing the temporary field camp, staging 

areas, fuel storage site, and bait stations (on the islet off Ayugadak Point). Additional wildlife 

disturbance could result from personnel traveling by foot across the island (e.g., when hand 

broadcasting bait, surveying for non-target mortality, and collecting rat carcasses). Personnel will 

be based on Rat Island in the summer for staging and continuing pre-eradication surveys and 

then for at least a seven-week period in the mid-to-late fall, including the bait application 

operation. Following eradication, there will be monitoring visits to the island for at least two 

years. Personnel will be briefed on strategies and techniques to reduce wildlife disturbance 

whenever possible, but some level of disturbance is still likely to occur. Anthropogenic 

disturbance to marine mammals has been described many times by behavioral researchers 

(Richardson et al. 1995). Although most of these descriptions are anecdotal, they do provide 

information about the level of reaction in specific situations. Almost all descriptions of 

disturbance reactions involved short-term behavioral reactions such as movement from haul-out 

sites to water. The significance of these short-term behavioral responses to individual fitness of 

individuals and populations are generally not known, although such brief interruptions likely 

have little effect on overall energy balance or reproductive performance (Richardson et al. 1995). 

Disturbance from personnel movements and activities is anticipated to be much lower than that 

caused by helicopter operations. 

4.2.2.3. Assessing cumulative impacts to biological resources 

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Chapter 4: Environmental Consequences 

Impacts to a biological resource that occur as a result of rat eradication on Rat Island, even if 

they are individually minor, could potentially contribute to cumulative effects when combined 

with other unrelated impacts. The following is a brief description of the major impacts that have 

occurred on Rat Island in the past, as well as an assessment of unrelated impacts to biological 

resources that are occurring today or could occur in the foreseeable future. 

Rat Island is currently uninhabited and there probably have not been year-round residents on the 

island since the fox farming era, prior to WWII. Evidence of human habitation, including Alaska 

Natives, prior to the fox trapping era exists as well. Human habitation itself did not likely have 

much impact on the biological resources of Rat Island, but island residents and traveling vessels 

likely harvested large numbers of pinnipeds and sea otters from its shores, which probably 

reduced populations locally. Additionally, non-native foxes, which were introduced specifically 

for trappers to harvest, preyed heavily on the island’s bird populations for decades until the foxes 

were eradicated in 1984 (Hanson et al. 1984). Last but not least, non-native rats have impacted 

many of the species on the island, as described in detail in Chapter 1. Because Rat Island is now 

being managed in perpetuity as a National Wildlife Refuge, the biological resources on and 

around the island are unlikely to be affected by anything other than natural forces in the 

foreseeable future. However, many of the species that use Rat Island have large ranges and may 

be currently experiencing unrelated impacts elsewhere in their ranges. Additionally, many of 

these far-ranging species have experienced impacts in the past that are still affecting their 

populations. These unrelated impacts will be considered for each biological resource analyzed. 

4.2.2.4. Limited analysis of invertebrates 

Most invertebrate species are not known to be susceptible to toxic effects from the use of 

brodifacoum in the field (Hoare and Hare 2006), nor are they anticipated to be measurably 

affected by helicopter operations or personnel activities. However, both marine and terrestrial 

invertebrates are known to consume bait pellets. Therefore, they will be considered in this 

document only in reference to their function as intermediate carriers of brodifacoum. As 

referenced in Section 4.5.7, during a catastrophic accidental spill of 20 tons of brodifacoum into 

nearshore waters in New Zealand (Primus et al. 2005), a peak concentration of the toxicant 

measured in mussels occurring at the spill site was 0.41 ppm one day after the spill; this equates 

to 1/60th of the brodifacoum found in one bait pellet. Within 30 days, the concentration had 

dropped to just above 0.002 ppm or 200 times less than the peak. 

4.2.2.5. Limited analysis of vegetation 

Plants are not known to be susceptible to toxic effects from brodifacoum, nor are they anticipated 

to be significantly affected by helicopter operations. However, the impact of personnel activities 

and temporary infrastructure installation related to the Proposed Action on the vegetative 

communities occurring on Rat Island will be analyzed. 

4.2.2.6. Assessing significance of impacts to biological resources 

The purpose of the Proposed Action is to restore the biological diversity and environmental 

health of Rat Island through rat eradication. While the precise responses of Rat Island’s species 

55
Chapter 4: Environmental Consequences 

to rat eradication are unknown, data from elsewhere in the Aleutians and from islands around the 

world indicate that rat eradication has the potential to contribute to beneficial effects in a wide 

variety of birds, among other species. At the same time, the Proposed Action has the potential to 

cause short-term negative impacts to individual animals. Therefore, the relationship between 

potential short-term risks to individual animals and the long-term benefits to animal species must 

be examined. For the Proposed Action to be considered a successful conservation effort, the 

long-term benefits to the island ecosystem must outweigh the potential risks to individual 

animals. 

For biological resources analyzed below, except those identified in the “special considerations” 

described later in this section, the potential for significance will be determined using the 

following guidelines: 

1. Is there a high likelihood that the Rat Island population of a species will experience 

noticeable changes that will not be counteracted by inter-island migration? 

2. Is there a high likelihood that impacts on animals at Rat Island will have global 

population-level impacts for the species? 

3. Is the species in question protected by special legislation such as ESA, MMPA, MBTA, 

or BGEPA? 

4.2.2.7. Special considerations for ESA-listed species 

There are three species known or suspected (based on their known range) from Rat Island that 

have been listed under ESA: the southwestern Alaska DPS of northern sea otter (Threatened), the 

western DPS of the Steller sea lion (Endangered), and the Alaska breeding population of 

Steller’s eider (Threatened). Listing under ESA provides a context for impacts analysis which 

lowers the threshold of significance. The ESA regulations require any federal agency that 

believes an action it is planning may affect a species listed under ESA to initiate a formal process 

of consultation with either the FWS Ecological Services division or NMFS, depending on the 

species potentially affected. Through this consultation, the agencies determine whether or not the 

action will put the potentially affected species in jeopardy of continued survival. The impacts 

analysis for biological resources in this document will identify any ESA-listed species and any 

ESA-designated critical habitat that may be affected by the Proposed Action. 

The significance of these impacts will be determined separately, but the ESA-listed status of the 

species affected will be given special weight. For marine mammals (Steller sea lions and 

northern sea otters), the significance threshold will be set according to the MMPA’s definition of 

Level A Harassment: “any act which injures or has the significant potential to injure a marine 

mammal or marine mammal stock in the wild” (MMPA 515.18(A)). For Steller’s eiders, the 

significance threshold will be set as the likely take (which includes harassment or harm) of one 

or more Steller’s eiders as a result of the Proposed Action as defined under the ESA (16 U.S.C. 

1532(19)). 

4.2.2.8. Special considerations for marine mammals 

Listing under MMPA also provides a context for impacts analysis which lowers the threshold of 

significance. Except for the case of subsistence harvesting activities, the MMPA regulations 

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Chapter 4: Environmental Consequences 

generally prohibit the killing, injury or disturbance of marine mammals. However, permits can 

be granted allowing exceptions to this prohibition for actions that may impact a marine mammal 

if the impact is incidental to, rather than the intention of, the action. This analysis will identify 

the potential for impacts to marine mammals that may require additional permits under MMPA. 

The significance of these impacts will be determined separately, but the MMPA-listed status of 

the species affected will be given special consideration. For marine mammals, the significance 

threshold will be set according to the MMPA’s definition of Level A Harassment: “any act 

which injures or has the significant potential to injure a marine mammal or marine mammal 

stock in the wild” (MMPA 515.18(A)). The lesser MMPA category, Level B Harassment, will 

not alone constitute a significant impact, but other potential circumstances (including cumulative 

impacts analysis) may nevertheless contribute to an overall determination of significant impacts. 

4.2.2.9. Special considerations for migratory birds 

The regulations of the MBTA generally prohibit the intentional killing of migratory birds except 

by permit and other special exceptions. However, the MBTA has been interpreted not to apply to 

invasive species management actions in which migratory birds are killed incidental to the 

management action (Humane Society of the United States v. Glickman, Case No. 99-5309, 

decided 18 July 2000). 

The potential impacts to these species will be determined using the following guidelines: 

1. Is there a high likelihood that the Rat Island population of a species will experience 

noticeable changes that will not be counteracted by inter-island migration? 

2. Is there a high likelihood that impacts on animals at Rat Island will be measurable 

elsewhere in the region (i.e. will impacts on individual animals on Rat Island have global 

population-level impacts for the species)? 

4.2.2.10. Special considerations for bald eagles 

Bald eagles in the lower 48 states were removed from the Endangered Species list in June 2007 

(eagles in Alaska were never listed under ESA). Eagles remain protected under BGEPA, but 

FWS is currently in the process of reviewing and revising the regulations of the BGEPA. In the 

meantime, FWS is strongly recommending that all agencies and non-federal entities follow the 

recommendations of the Bald Eagle Management Guidelines issued by FWS in May 2007. The 

management guidelines’ recommendations include (in part): 

• Avoiding operating aircraft within 1000 feet of the nest during breeding season; and 

• Using pesticides only in accordance with federal and state laws. 

Because bald eagles are also protected under MBTA any permits that must be granted under 

MBTA will include any anticipated bald eagle take. The FWS will adhere to the 

recommendations of the Bald Eagle Management Guidelines in implementing the Proposed 

Action, as well as any additional permitting or compliance requirements that are implemented or 

clarified at any time before project implementation begins. 

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Chapter 4: Environmental Consequences 

The potential significance of impacts to bald eagles will be determined using the following 

guidelines: 

1. Is there a high likelihood that the Rat Island population of eagles will experience 

noticeable changes that will not be counteracted by inter-island migration? 

2. Is there a high likelihood that impacts on eagles at Rat Island will have population-level 

impacts for central Aleutian bald eagles? 

4.2.3. Assessing Impacts to Water Resources 

Water quality in the State of Alaska is regulated by the Alaska Department of Environmental 

Conservation (DEC), Division of Water Quality, which requires all state waters to meet 

minimum criteria for a number of designated uses. The only reasonably foreseeable potential 

impact to water quality on or around Rat Island would involve the incidental introduction of 

rodenticide into the water column. There are no specific criteria set by the State of Alaska for 

maximum allowable quantities of brodifacoum or other rodenticides. While the federal Clean 

Water Act (CWA) prohibits the discharge of “pollutants” into waters of the United States, the 

EPA recently clarified its interpretation of this term to exclude pesticides that may unavoidably 

enter the water while being applied to control pests that occur “over, including near” water 

bodies (71 CFR 227 pp. 68483-68492). As rats on Rat Island are known to frequently live at the 

shoreline and feed near and/or in bodies of water, the application of a rodenticide to eliminate 

rats according to the techniques described in the Proposed Action and as permitted by 

rodenticide label requirements under FIFRA may include areas immediately adjacent to water 

bodies without additional compliance requirements under CWA. The potential for significant 

environmental impacts of the Proposed Action on water quality, irrespective of other water 

quality regulations, will be analyzed as an examination of the potential for biologically adverse 

quantities of brodifacoum to be introduced into Rat Island’s associated water bodies. 

4.2.4. Assessing Impacts to Wilderness Character 

All of Rat Island is designated Wilderness as regulated by the Wilderness Act (PL 88-577), as 

well as being part of Alaska Maritime NWR as established in ANILCA (PL 96-487). In some 

instances the use of mechanized tools or equipment is necessary for the managing agency to 

effectively administer designated wilderness areas. Section 4(c) of the Wilderness Act provides 

for an administrative exception for some specific uses. When the use of tools otherwise 

prohibited by the Wilderness Act is necessary for an agency to administer a wilderness area, a 

Minimum Requirements Analysis (MRA) is completed. The MRA process determines whether 

or not the proposed activity is necessary within the wilderness area and if so, which least 

intrusive action or “minimum tool” is needed to achieve the objective. The MRA is documented 

through the Minimum Requirements Decision Guide, which demonstrates how the agency 

arrived at the decision to conduct a specific administrative action. The completed Minimum 

Requirements Decision Guide worksheet associated with the Proposed Action is included in this 

EA as Appendix 3. 

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Chapter 4: Environmental Consequences 

Preservation of wilderness character is not a category of analysis required under NEPA 

regulations, but the special designation of Rat Island as Wilderness will be considered through an 

analysis of the impacts of the Proposed Action. Under the Wilderness Act, an area’s wilderness 

character is defined by the following qualities: 

1. Untrammeled by human impacts; 

2. Undeveloped, without permanent structures or habitations; 

3. Influenced primarily by natural forces; and 

4. “Has outstanding opportunities for solitude or a primitive and unconfined type of 

recreation.” 

The impacts of the Proposed Action that relate to Wilderness Act and ANILCA will be discussed 

according to their benefit or harm to each of the above four qualities that characterize wilderness. 

4.2.5. Assessing Impacts to Historical and Cultural Resources 

The categories of historical and cultural resources are broad and impacts to these resources are 

usually difficult to quantify, especially in the context of NEPA’s requirement to identify 

“significant” impacts. The National Historic Preservation Act (NHPA) defines the concept of an 

“adverse impact” to historical resources, but the regulations make clear that “a finding of adverse 

effect on a historic property does not necessarily require an EIS under NEPA” (36 CFR 

800.8(a)(1)). Regardless, Section 106 of the NHPA requires agencies to consult with the 

appointed regional Historic Preservation Officer(s) if adverse impacts to historical or cultural 

resources are possible. This analysis will describe the potential impacts to historical and cultural 

resources on Rat Island as a reference for consultation with the appropriate Historic Preservation 

Officers. 

4.2.6. Assessing Impacts to Social and Economic Values 

The CEQ guidelines at 40 CFR 1508.14 include the human relationship with the natural 

environment as a category of potential impacts that should be considered in a NEPA analysis. 

This is interpreted to mean that a NEPA analysis examine potential effects on any economic 

and/or social values. In the case of Rat Island, the issues of concern identified were: 

• Impacts to visitors of the Refuge in the vicinity of Rat Island; 

• Impacts to commercial fishing activities in the vicinity of Rat Island; and 

• Impacts to subsistence harvests by rural Alaskans in the vicinity of Rat Island. 

The potential for significant impacts to human uses of the Rat Island environment will be 

analyzed based on input from any potentially affected parties during the circulation of the draft 

of this EA. 

4.3. ASPECTS OF THE ENVIRONMENT EXCLUDED FROM DETAILED ANALYSIS (WITH 

RATIONALE) 

4.3.1. Marine Fish 

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Chapter 4: Environmental Consequences 

Potential impacts of rat eradication activities to marine fish in the waters surrounding Rat Island 

will not be analyzed in this EA, because the likelihood of the Proposed Action having 

measurable impacts on marine fish populations is negligible. 

• The number of bait pellets that will enter the marine environment as a result of bait 

application activities will be low as a result of the mitigation measures described in the 

Alternatives chapter for avoiding bait application into the ocean; 

• The probability that fish will consume bait pellets is considered to be very low; 

• The bait pellets will disintegrate rapidly upon contact with the water; 

• In tests conducted by researchers in the Aleutians, as well as in California, Hawai’i, and 

the equatorial Pacific, marine fish species demonstrated almost no interest in placebo bait 

pellets that entered the water nearby (Buckelew et al. 2007a; Howald et al. 2005; USFWS 

2005; A. Wegmann, pers. obs.). 

4.3.2. Cetaceans 

Potential impacts of rat eradication activities to cetaceans (whales, dolphins, and their close 

relatives) in the waters surrounding Rat Island will not be analyzed in this EA. Except for small 

boat traffic, which will be limited in duration and concentrated immediately offshore of the 

island, all of the activities described in the Proposed Action are terrestrial, and the likelihood of 

the Proposed Action having measurable impacts on cetaceans is negligible. 

4.3.3. Air Quality 

Air quality in the region of Rat Island is not an issue of concern. Rat Island is 322 km (200 mi) 

away from the nearest permanent human settlements, the town of Adak and the Air Station at 

Shemya, which are themselves extremely isolated from any major sources of air pollution. The 

helicopter operations described in the Proposed Action will not generate measurable levels of 

pollutants or contribute to air quality thresholds being reached. 

4.4. ALTERNATIVE A: NO ACTION

4.4.1. Introduction 

Under the No Action alternative, rats will be allowed to persist on Rat Island, subject to the 

natural processes of the island ecosystem. There will be no use of rodenticide to control rats. 

With No Action on the island, the rat population will not be controlled, and population sizes will 

fluctuate within an annual cycle. Rat population levels on Aleutian islands typically increase 

during the summer, and decline during the winter (Dunlevy and Scharf 2006; Major et al. 2006). 

As a direct result of rats remaining on the island, habitat quality for native species has been 

altered. Restoration of natural biodiversity and habitat may only occur after the eradication of 

invasive rats on Rat Island. The direct impacts invasive rats have on the island’s native species, 

for which the Refuge was established, will continue under the No Action alternative. 

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Chapter 4: Environmental Consequences 

4.4.2. Restoration Efficacy 

Adoption of the No Action alternative will not meet the purpose and need of the Proposed Action 

– rats will remain and impacts on Rat Island’s habitats and ecosystem will go unaddressed. The 

continued presence of rats on Rat Island is inconsistent with FWS policy for land management. 

The agency’s policy for maintaining biological integrity, diversity and environmental health (601 

FW 3, 2001) guides refuge management priorities. It directs managers to: 

• “Restore lost or severely degraded elements of integrity, diversity, [and] environmental 

health...; 

• “Favor management that restores or mimics natural ecosystem processes or functions to 

achieve refuge purpose(s)...”; and 

• “Strive to prevent the further loss of natural biological features and processes; i.e., 

biological integrity.” 

The ongoing negative impacts of rats on the environmental health and natural biological 

processes of Rat Island make them a candidate for FWS action under 601 FW 3. 

4.4.3. Impacts to Species Listed Under the Endangered Species Act 

4.4.3.1. Steller sea lion 

Rats are not known to impact Steller sea lions. Steller sea lions on and around Rat Island are not 

expected to be affected if the No Action alternative is adopted. 

4.4.3.2. Northern sea otter 

Rats are not known to impact northern sea otters. However, there is evidence that rats directly or 

indirectly affect nearshore environments (Navarrete and Castilla 1993, Drummond 1960). This 

may have an unknown indirect impact on sea otters. Nonetheless, sea otters on and around Rat 

Island are not expected to be affected if the No Action alternative is adopted. 

4.4.3.3. Steller’s eider 

Steller’s eiders do not breed in the Aleutians (Fredrickson 2001) and are considered rare in the 

central Aleutian Islands in winter (Gibson and Byrd 2007; Kenyon 1969). There is no reasonable 

likelihood that Steller’s eiders will be affected by the continued presence of rats on Rat Island, as 

will be the case if the No Action alternative is adopted. 

4.4.4. Impacts to Species Listed Under the Marine Mammal Protection Act 

4.4.4.1. Species also listed under ESA 

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Chapter 4: Environmental Consequences 

Steller sea lions and northern sea otters are protected by the MMPA regulations as well as the 

ESA. See Section 4.4.3 above for impacts analysis for both of these ESA-listed species. 

4.4.4.2. Harbor seal 

Rats are not known to directly impact harbor seals. There is some concern that diseases could be 

transferred from rats to pinnipeds, and from there to subsistence users (M. Williams, pers. 

comm.). Even so, harbor seals on and around Rat Island are not expected to be affected if the No 

Action alternative is adopted. 

4.4.5. Impact on Species Listed Under the Migratory Bird Treaty Act 

4.4.5.1. Waterfowl 

Rats are known predators of ground-nesting birds including waterfowl. Additionally, rats are 

known to crop vegetation and thereby reduce waterfowl nesting habitat. The combined impacts 

of threats such as predation and habitat destruction have led to severe population declines and 

species endangerment in some waterfowl, such as the Laysan duck (Anas laysanensis) in Hawai`i 

(Reynolds 2004; Moulton and Marshall 1996). Adoption of the No Action alternative will leave 

waterfowl on Rat Island, including the Aleutian green-winged teal and Pacific common eider, 

vulnerable to the impacts of rat predation and disturbance. 

4.4.5.2. Birds of prey 

Rats may present a direct threat to breeding raptors on Rat Island; rats are known predators of 

peregrine falcon chicks in the Aleutians (Jones and Byrd 1979). Furthermore, peregrine falcons 

in the Aleutians depend heavily on seabirds for prey (White et al. 2002). The negative impacts 

that rats have on seabird colonies may indirectly reduce food availability to the peregrine falcon 

population on Rat Island, and the historical impacts that rats had on Rat Island’s seabird colonies 

may have led to a long-term decrease in the island’s habitat quality for peregrine falcons. 

Adoption of the No Action alternative will prevent any major seabird recovery on Rat Island and 

continue to suppress the potential habitat quality of the island for peregrine falcons. 

On average, rats accounted for 13% of bald eagles’ diet in a two-year study on nearby Kiska and 

Amchitka Islands (Anthony et al. 1999). However, bald eagles are opportunistic feeders and 

consume a range of food items, both in the marine and terrestrial environments. Due to the 

abundance of alternative eagle prey in the region, it is unlikely that changes in Rat Island’s rat 

population have noticeable effects on local eagle populations. 

4.4.5.3. Passerines and other landbirds 

Rats are known predators of landbirds in all life stages in the Aleutians (Atkinson 1985; I. Jones, 

pers. obs.). Landbirds will continue to be vulnerable to rat predation under the No Action 

alternative. Upon introduction, rats caused a major decline in winter wren and song sparrow 

populations on Amchitka Island (White et al. 1977), and it is likely that landbird populations on 

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Chapter 4: Environmental Consequences 

Rat Island continue to be suppressed. There are no trees on Rat Island, forcing all birds to nest on 

or near the ground. Ground-nesting landbirds are particularly vulnerable to disastrous population 

reduction from rat predation (Atkinson 1985), and adoption of the No Action alternative will 

allow negative impacts to landbirds on Rat Island to continue. 

The continued presence of rats will provide a potential food source for ravens that visit or reside 

on Rat Island. However, the abundance of alternative food sources for ravens on Rat Island 

makes the continued presence of rats unlikely to influence the local raven populations. The 

continued presence of rats may also provide a food source for migrant short-eared owls, which 

appear uncommonly on Rat Island but likely feed on rats during their stay on the island. 

4.4.5.4. Seabirds and shorebirds 

Predation and loss of nesting habitat caused by invasive rats is the leading cause of the decline of 

seabirds on islands (Towns et al. 2006). Rats are known to significantly reduce breeding success 

of some species of seabirds in the Aleutian Islands (Major et al. 2006) and worldwide (Atkinson 

1985; Jones et al. in review), both through predation and through repeated disturbances that lead 

to higher abandonment of nests and of breeding partners (Jouventin et al. 2003). On Kiska 

Island, rat predation on auklets is considered intense enough to potentially cause the future 

extirpation of the millions of auklets that now use this island (Major et al. 2006). Cumulatively, 

rat impacts can cause complete extirpation of insular breeding seabirds in some cases (Jones et 

al. in review). Thus, the No Action alternative will continue to preclude recovery of seabirds that 

are attempting to breed on Rat Island. 

Shorebirds are also susceptible to rat predation. Densities of black oystercatchers on rat-free 

islands in the Aleutians are more than an order of magnitude higher than on rat-invaded islands 

(Kurle et al. in review). The No Action alternative will allow rats to continue negatively 

affecting shorebird communities on Rat Island, with a consequent effect on the intertidal 

community. 

4.4.6. Impacts to Other Species On and Around Rat Island 

4.4.6.1. Terrestrial invertebrates 

Rats are omnivores and invertebrates make up a portion of their diet in the Aleutians (Major et 

al. 2007). The impacts of rats on each species of invertebrates on and around Rat Island are 

unknown. Some invertebrate species can be critical components of a food web. The impacts of 

rat predation on one particular insect species potentially could have widespread ecological 

consequences (Schmitz 2006). In some cases, direct rat predation coupled with other indirect 

impacts from rats can cause the complete elimination of an invertebrate species from an island 

(e.g. weta in New Zealand [Rufaut and Gibbs 2003]). Adoption of the No Action alternative will 

continue to leave the invertebrates that inhabit Rat Island vulnerable to rat impacts. 

4.4.6.2. Freshwater organisms 

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Chapter 4: Environmental Consequences 

Rats are known to prey on Dolly varden and freshwater algae in the Aleutians (Major et al. 

2007). Adoption of the No Action alternative will allow this predation to continue and may alter 

natural ecological processes in freshwater habitats. 

4.4.6.3. Intertidal organisms 

A study of intertidal communities in the Aleutian Islands found that rats prey on intertidal algae 

and invertebrates (Kurle et al. in review). This study suggested the largest effects of rats in the 

intertidal could be a result of predation on shorebirds. Rat predation on black oystercatchers and 

glaucous-winged gulls releases their intertidal herbivorous snail prey from predation and may 

noticeably alter intertidal communities. Adoption of the No Action alternative will allow rats to 

continue to directly prey on intertidal organisms and to continue depressing shorebird 

populations, both of which may affect the trophic structure of intertidal communities. 

4.4.6.4. Vegetation 

Vegetation can comprise up to 80% of rat diet on some Aleutian Islands (Major et al. 2006). The 

reduction of nutrient availability in the environment through predation-driven seabird declines 

has been shown to indirectly affect Aleutian Island vegetative communities (Croll et al. 2005). 

Introduced foxes drove seabirds to such low levels that without the nutrient subsidy provided by 

their guano, vegetation changed from grassland to tundra, resulting in long-term cumulative 

impacts (Croll et al. 2005). Vegetation may be indirectly impacted by rats through impacts on the 

invertebrate community. As discussed above (Section 4.4.6.1), predation of invertebrates may 

lead to major impacts on the local vegetative community. Under the No Action alternative, 

vegetative communities on Rat Island will continue to be shaped by direct and indirect rat 

effects. See more detail in Section 4.4.6.5 below. 

4.4.6.5. Multi-trophic cascading effects 

As a result of impacts from invasive species (such as rats), island ecosystems can experience 

effects that cascade through multiple trophic levels, leading to major changes in ecosystem 

functioning (Fukami et al. 2006). As described in Section 4.4.6.4 above, the No Action 

alternative will leave the Rat Island ecosystem in a modified state as a result of reduced input 

from marine derived nutrients formerly supplied by nesting seabirds (Croll et al. 2005; Maron et 

al. 2006). 

4.4.7. Impacts to Water Quality 

There is no evidence that rats currently have a perceptible impact on water quality on or around 

Rat Island. Therefore, there is no reasonable risk that adopting the No Action alternative will 

affect the island’s water quality. 

4.4.8. Impacts to Wilderness Character 

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Chapter 4: Environmental Consequences 

After their introduction more than 200 years ago, rats have dramatically changed ecological 

processes on Rat Island. Prior to this introduction, the island likely supported significant 

populations of breeding seabirds and other ground-nesting birds that evolved in the absence of 

mammalian predators, similar to the other islands in the Rat Islands group. In addition to 

extirpating seabirds, rats have changed the vegetative community structure and possibly 

intertidal life of the island. As a result, their presence has altered the natural character of the 

island, and adoption of the No Action alternative will allow this unnatural state to continue. 

4.4.9. Impacts to Historical and Cultural Resources 

While Rat Island is uninhabited today, there is evidence of multiple former Aleut village sites. 

Within these sites, there are items of archaeological value. The Aleut Corporation has selected 

four of these sites for eventual incorporation as ANCSA 14(h)(1) cemetery sites and historical 

places. Norway rats excavate large and extensive burrows and increase erosion that may harm or 

destroy sensitive archaeological resources within these and other archaeological and cultural 

sites on the island. If the No Action alternative is adopted, this risk to Rat Island’s Aleut cultural 

resources will continue. 

4.4.10. Impacts to Social and Economic Values 

4.4.10.1. Fishery resources 

Fishery resources around Rat Island will not be affected if the No Action alternative is adopted. 

4.4.10.2. Refuge visitors 

Visitation to Rat Island by the general public is very low. Most visits are by researchers and 

government personnel. However, tour boats occasionally pass within view. With the adoption of 

the No Action alternative, these visitors will continue to experience Rat Island as a compromised 

ecosystem that is not meeting its potential as a unique refuge for wildlife, especially birds that 

could be viewed from passing boats. 

4.4.10.3 Subsistence uses 

Subsistence harvest of animals and plants occurs almost exclusively in the areas immediately 

surrounding communities in the Aleutians. The closest settlement to Rat Island, on Adak Island, 

is over 322 km (200 mi) away. For that reason, it is very unlikely that Rat Island is used for 

subsistence harvest activities. Regardless, if the No Action alternative is adopted, rats will 

continue to degrade habitat quality on Rat Island for waterfowl, through damage to vegetation 

used for nesting, and possibly through predation. Rural Alaskan subsistence harvests often 

include waterfowl, which eventually migrate over inhabited islands. Therefore, the continued 

presence of rats on Rat Island will affect potential subsistence resources on the island into the 

future. 

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Chapter 4: Environmental Consequences 

4.5. ALTERNATIVE B: RAT ERADICATION FROM RAT ISLAND, AERIAL BROADCAST 

TECHNIQUE

4.5.1. Restoration Efficacy 

Rat eradication has been conducted successfully on more than 300 islands worldwide (Howald et 

al. 2007). The largest successful rat eradication, an aerial broadcast of brodifacoum to eradicate 

Norway rats, was from 11,500 ha (28,417 ac) Campbell Island in the Southern Ocean south of 

New Zealand. With effective implementation of this similar aerial broadcast technique, 

according to the specifications described in the Proposed Action (Section 2.2), there is a high 

probability of successful rat eradication from Rat Island. 

Rat eradication must be followed by an ongoing reintroduction prevention plan that will keep Rat 

Island free of rodents and allow the ecosystem to respond and recover. Such a program will be 

implemented under the Proposed Action, which will allow rat eradication to have lasting 

conservation benefits. 

Island ecosystems have a demonstrated history of responding quickly and dramatically as a result 

of rat eradication. On Anacapa Island in Southern California, breeding success and number of 

nests found for Xantus’ murrelets (Synthliboramphus hypoleucus), small crevice-nesting 

seabirds, began increasing immediately after rat eradication and within three years hatching 

success in monitored murrelet nests nearly doubled (Whitworth et al. 2005). Almost immediately 

after rats were eradicated on Campbell Island, the Campbell Island snipe began successfully 

recolonizing the island from an offshore islet where it had persisted in low numbers for decades 

after being extirpated from the main island (Miskelly and Fraser 2006). 

In the Aleutians, the removal of introduced foxes has led to major recovery in island bird 

populations (see Ebbert and Byrd 2002). Seabird colonies on some islands grew four- to fivefold after foxes were removed (Byrd et al. 2004), and the Aleutian cackling goose recovered 

from an estimated population of 1000 total birds to a population of well over 100,000 throughout 

the Aleutians (V. Byrd, pers. comm.). In fact, fox removal and subsequent goose re-introduction 

allowed the Aleutian cackling goose to recover sufficiently to be removed from the Endangered 

Species list in 2001. Rats have been conclusively shown to prey heavily on seabirds within 

nesting colonies. While islands throughout the Aleutians that are ecologically similar to Rat 

Island have large seabird colonies, Rat Island has comparatively few nesting birds of any kind, 

which strongly suggests that the presence of rats is preventing certain species of seabirds from 

nesting on the island. The removal of rats will therefore likely be followed by an influx of new 

breeding seabirds. Rat eradication will also restore Rat Island’s native vegetation, which rats 

consume as a major part of their diet in the Aleutians at certain times of the year (Dunlevy and 

Scharf 2006). It will also be beneficial to ecological balance of the island’s intertidal community, 

which is currently heavily influenced by rat predation. This benefit will extend to Rat Island’s 

shorebird population, which depends on intertidal organisms as a major food source. 

One of the critical aspects of a NEPA analysis (Sec. 102(I)(iv)) is addressing “the relationship 

between local short-term uses of man’s environment and the maintenance and enhancement of 

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Chapter 4: Environmental Consequences 

long-term productivity.” The restoration benefits described above make the Proposed Action 

beneficial to the long-term productivity of Rat Island as a refuge for plants and wildlife. 

4.5.2. Impacts to Species Listed Under the Endangered Species Act 

4.5.2.1. Steller sea lion 

Brodifacoum toxicity risk – The brodifacoum LD50 value for Steller sea lions has not been 

established. Using a conservative LD50 figure of 0.4 mg/kg, a small juvenile sea lion weighing 

45 kg (100 lbs) will need to ingest the equivalent of approximately 300 bait pellets to be at a 

50% risk of mortality. A large male adult, weighing 1088 kg (2400 lbs; National Marine 

Mammals Laboratory 2006), will need to ingest more than 7500 pellets. Steller sea lions are 

carnivorous (almost exclusively piscivorous), so brodifacoum ingestion will need to occur either 

accidentally or through an intermediate prey species (fish) that previously consumed bait pellets. 

However, fish are extremely unlikely to consume the bait themselves (Section 4.3.1 and 4.5.6.2). 

Brodifacoum exposure risk – Steller sea lions are marine mammals, but they also use terrestrial 

habitat year-round. Sea lions are likely to be present in the waters surrounding Rat Island, and 

are likely to be hauled-out on offshore rocks off Krysi Point, on the islet off Ayugadak Point, and 

perhaps elsewhere on Rat Island or surrounding offshore stacks and islets at any given time 

during rat eradication operations. Sea lions may encounter stray bait pellets, at low densities, if 

they are hauled-out on Rat Island or surrounding islets during bait application. Nevertheless, the 

majority of stray pellets will be consumed by rats within 4 days of the final bait application. 

Most of the remaining stray pellets within the sea lions’ normal terrestrial ranges, particularly the 

low intertidal zone, will be washed away with the first high tide after each bait application. A 

scattered few pellets may remain present in areas that are above the high-water line for up to a 

few months after the application, but these are outside the sea lions normal terrestrial range. Sea 

lions in the water may encounter bait pellets in the ocean or intertidal zones, but this is unlikely 

because of the mitigation measures that will be implemented to minimize bait entry into the 

marine ecosystem. If bait does enter the water, it will be available immediately after entry but 

will disintegrate and disperse within hours. 

The offshore islet off Ayugadak Point is listed by NMFS as a Steller sea lion rookery (50 CFR 

226.202). The bait that will be applied to this islet during early summer staging operations will 

be enclosed in bait stations, which will prevent sea lions from being exposed. If bait is later 

broadcast onto the islet during bait application operations in the fall (according to the criteria 

described in the Proposed Action, Section 2.2), hauled-out sea lions will encounter bait pellets 

according to the same conditions described in the previous paragraph. 

Steller sea lions are exclusively carnivorous (almost exclusively piscivorous) and do not feed 

while on land, so the only possible routes for bait ingestion are accidental. The likelihood of 

primary exposure is therefore very low, and the likelihood of secondary exposure through fish or 

other prey species is negligible (as discussed above in Section 4.3.1). 

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Chapter 4: Environmental Consequences 

Overall risks from brodifacoum use – The toxicity of brodifacoum to Steller sea lions is high, 

however due to their large size, it would require a high dose for any toxic effect to be measured. 

Further, the likelihood of sea lions experiencing either primary or secondary exposure is very 

low to negligible; under the proposed baiting regime, sea lions will not be exposed to a high 

enough dose to experience measurable effects. Therefore, the overall risk of sea lion mortality or 

sub-lethal effects as a result of brodifacoum use is negligible. 

Risks from aircraft disturbance on Rat Island –The response of pinnipeds like Steller sea lions to 

aircraft overflights varies from no discernable reaction to completely vacating haul-outs after a 

single overflight (Calkins 1979;Efroymson and Suter 2001). Approaching aircraft generally flush 

animals into the water. In one case, Withrow et al. (1985 in Richardson et al. 1995) reported 

Steller sea lions left a beach in response to a Bell 205 helicopter >1.6 km away, but the noise 

from a helicopter is typically directed down in a “cone” underneath (Richardson et al. 1995) so 

disturbance at such great distance is probably uncommon. 

At Rat Island there is a known persistent haul site on rocks off Krysi Pt. and a rookery on the 

islet off Ayugadak Point. Occasionally sea lions probably also haul-out elsewhere on Rat Island. 

During staging operations, helicopter flight lines will avoid the rookery, the known haul site and 

any other haul sites discovered prior to helicopter operations. However, in spite of these 

precautions, sea lions encountered unexpectedly during helicopter operations could be flushed 

from land temporarily. An individual sea lion’s exposure to peak noise from the helicopter will 

be limited to animals that remain ashore, and is likely to be of short duration, as the elevation and 

speed of the helicopter (see Section 2.2.2.3) will limit the time that any single location is exposed 

to maximum noise. 

Unlike during staging, it will be more difficult to avoid known haul sites on Rat Island with the 

helicopter during bait application because of the need for thorough coverage. No pups are 

expected on Rat Island, but the impacts of disturbance to sea lions during molting (a sensitive 

period to disturbance, Richardson et al. 1995) will be minimized by timing overflights after the 

peak molting period is over. 

Risks from disturbance on the islet off Ayugadak Point – Installation of bait stations on the islet 

off Ayugadak Point is likely to result in short-term flushing of some animals off the land. This 

disturbance is likely to be limited to the few-hour period when personnel are present on the 

island. Sea lion pups could potentially be present on the islet during installation of bait stations, 

depending upon the exact timing of the operation (e.g., a summer effort occurring after pups are 

born or a fall effort occurring while pups are still being nursed on land). To minimize 

disturbance to the rookery, the islet will be approached slowly in a small boat, from the side of 

the island opposite and out of sight of the rookery. This is expected to reduce the tendency of 

animals to stampede, thereby reducing the possibility of pup injury. While on the islet personnel 

will remain out of sight of the rookery as much as possible. 

In late summer or fall, the bait stations on the islet will need to be replenished. Again, the 

approach to the island will be slow, and opposite the haul-out. This may result in flushing the 

haul-out and short-term displacement for the few hour period that personnel are present on the 

islet. If it is not possible to land a skiff on the islet, the island will be baited with the helicopter as 

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Chapter 4: Environmental Consequences 

described in Section 2.2.2.3, in the fall after the pupping and primary molting season. 

Nevertheless, this is likely to result in flushing sea lions from the islet resulting in short-term 

displacement. However, as helicopter baiting will be a very short process (approximately 10 

min), disturbance to Steller sea lions is likely to be very short-term. 

Risks from camps on Rat Island-Impacts to Steller sea lions from camps on Rat Island will be 

minimal as camps and storage sites will be installed well inland. 

Overall, the effects of the operations described in the Proposed Action on Steller sea lions will 

vary depending on the number of disturbance events. However, the short-term displacement from 

haul-outs that is likely to occur as a result of helicopter noise and personnel is not anticipated to 

have any effect on overall energy balance or fitness of any individual animals. 

Indirect effects – There is no reason to believe that the Proposed Action will lead to any effects 

in the habitat, prey base, or other ecological interactions of Steller sea lions that will indirectly 

affect them. 

Cumulative effects – Steller sea lions in the Aleutians have undergone a major population 

decline over the last 20 years, but the reasons for this decline are poorly understood. The two 

potentially greatest threats to sea lions that have been identified are competition with fisheries for 

food resources, and variability in environmental conditions that affect the availability of food for 

sea lions (NMFS 2007). Both of these ongoing effects lead to malnutrition and a corresponding 

decrease in the fitness of individual animals. Although there is no known evidence of 

malnourishment in sea lions using Rat Island, there is a possibility that some of the sea lions on 

and around the island could be malnourished. If that were the case, the disturbance effects from 

the Proposed Action may disproportionately affect these animals. However, if disturbance from 

operations is minimized by planning flight paths and helicopter activity to coincide as little as 

possible with the known locations of sea lions, disturbance effects from bait application 

operations are not likely to contribute measurably to negative cumulative effects on sea lions. 

In the foreseeable future, there is the possibility for rat eradication efforts on additional Aleutian 

Islands. These eradications are unlikely to occur soon enough after the Rat Island project to 

contribute to cumulative effects on any sea lions affected by the eradication on Rat Island. Thus, 

especially if helicopter activity is adjusted to minimize the amount of necessary sea lion 

disturbance while still ensuring a successful rat eradication, there is no reasonable risk for 

measurable cumulative effects on Steller sea lions. 

Significance of effects to Steller sea lions on and around Rat Island – It is not likely that any 

Steller sea lions will suffer injury or the significant potential for injury as a result of the activities 

described in the Proposed Action. Therefore, this analysis concludes that implementation of rat 

eradication activities as described in the Proposed Action is not likely to adversely affect 

individual Steller sea lions on an individual or population level. 

Special considerations under ESA – The ESA regulations obligate federal agencies to ensure that 

the actions they take are not likely to “jeopardize the continued existence of a listed species or 

result in the destruction or adverse modification of designated critical habitat” (ESA Section 

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Chapter 4: Environmental Consequences 

7(a)2). If a federal action may adversely affect an ESA-listed species or its designated critical 

habitat, the action agency must enter a process of formal consultation with either FWS or NMFS, 

depending on the species in question. Based on the impacts analysis above, the possibility of 

adverse effects to individual Steller sea lions cannot be reasonably eliminated, although adverse 

effects are unlikely to occur. Furthermore, helicopter and personnel operations will occasionally 

need to occur within the “no-entry zones” established by 50 CFR 223.202. Agency personnel 

acting in the course of official “legitimate governmental activities” are exempted from the noentry zones, but appropriate consultation with NMFS will be conducted to ensure compliance 

with Sections 7 and 9 of the ESA. 

4.5.2.2. Northern sea otter 

Brodifacoum toxicity risk – The brodifacoum LD50 value for sea otters has not been established. 

Toxicity testing with a related species, the American mink (Mustela vison) suggests that mink 

are relatively insensitive to brodifacoum, with an LD50 of 9.2 mg/kg (cited in FournierChambrillon et al., 2004). Young of the year are the most sensitive indicator of toxicant exposure 

(P. Johnson, pers. comm.) as well as of the northern sea otter population overall (Ballachey et al. 

2003; A. Doroff, pers. comm.). Therefore, using a conservative LD50 figure of 0.4 mg/kg, a 

juvenile sea otter of average mass, 9.1 kg (20 lb) (A. Doroff, pers. comm.), will need to ingest 

the equivalent of approximately 61 bait pellets to be at a 50% risk of mortality. Sea otters are 

exclusively carnivorous, so brodifacoum ingestion will need to occur either accidentally (i.e., by 

sticking in the fur and being accidentally ingested when grooming) or through an intermediate 

prey species that previously consumed bait pellets or particulate-bound residues. However, based 

on studies from California and New Zealand, there is no reasonable likelihood that intertidal 

invertebrates will register biologically harmful, or even detectable, levels of brodifacoum as a 

result of bait application to Rat Island (see Section 4.5.7). 

Brodifacoum exposure risk – Northern sea otters are primarily marine organisms, but they also 

haul-out on beaches and offshore rocks year-round. Sea otters are likely to be present in the 

waters surrounding Rat Island during the rat eradication effort, and a few could be hauled-out on 

beaches. Although the intent is to keep rodenticide pellets out of the intertidal zone and 

nearshore marine waters, stray pellets may be present in the vicinity of a few sea otters. The 

majority of this bait will be consumed by rats within 4 days of the final application. Most of the 

unconsumed stray pellets within the lower intertidal zone, where sea otters are likely to haul-out, 

will be dispersed in marine waters at the first high tide after each bait application. A scattered 

few pellets may remain in areas that are above the high-water line for up to one month after the 

last application. Bait pellets quickly began to soften and disintegrate in the water after a major 

spill in New Zealand (Primus et al. 2005). If bait does enter the water, it will be available 

immediately after entry but will dissolve within hours. Sea otters may encounter an occasional 

bait pellet in the nearshore or intertidal zones, but it is unlikely because of the mitigation 

measures to minimize bait entry into the marine ecosystem (Section 2.2.2.11). 

Northern sea otters are exclusively carnivorous, feeding on benthic invertebrates such as sea 

urchins, crabs, and octopus (USFWS 2005) and do not feed while on land. As a result, the only 

possible route for bait ingestion on land is accidental. Sea otters are known to groom themselves 

and each other while on land, and although possible it is not likely that grooming behavior will 

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lead to accidental bait ingestion (i.e., bait pellet dust). Little is known about sub-lethal effects of 

bait ingestion in sea otters. However, the likelihood of primary exposure is low to begin with and 

the chance that enough pellets would be ingested to negatively impact an individual sea otter is 

very low. Further, the chance of secondary exposure through consuming prey is negligible. Any 

stray pellets in the intertidal or nearshore zone would be in such low density and viable for such 

a short time, that the brodifacoum level would not be detectable in the invertebrate prey the sea 

otters feed upon. 

On Anacapa Island, Howald et al. (2005) collected mussels and crabs at Day 15 and 30, and 

tidepool sculpins at Days 15, 30 and 90 post-application. They reported that no brodifacoum 

residues were detected in the invertebrate and fish samples. 

Overall risks from brodifacoum use – Due to the relatively large size of sea otters, the toxicity of 

brodifacoum to them is very low, enough to be discountable. Furthermore, the likelihood of sea 

otters experiencing either primary or secondary exposure to brodifacoum is low to very low. A 

sublethal dose of brodifacoum can result in clotting abnormalities and hemorrhaging in animals 

(Erickson and Urban 2002), but in the case of a sea otter, the dose is unlikely to be sufficient to 

predispose an otter to other causes of death. However, there is no data available on the potential 

for subclinical affects from low levels of exposure, particularly for young of the year. 

Nonetheless, the overall risk of sea otter mortality or noticeable sub-lethal effects as a result of 

brodifacoum use is very low (see Sections 2.2.3.1 and 4.5.7). 

Risks from the operation – Sea otters have not been reported as particularly sensitive to sound 

and/or movement disturbance, especially in comparison to other marine mammals such as 

pinnipeds (US Air Force and US Fish and Wildlife Service 1988; Efroymson and Suter 2001). 

However, observations of sea otters indicate their responses to disturbance are highly variable 

(A. Doroff, pers. comm.). If any sea otters are present during the eradication project, some of 

them may be temporarily disturbed by helicopter noise or boats operating in the area; however, it 

is unlikely that the Proposed Action will result in measurable effects to sea otters at Rat Island. 

Indirect effects – Persistent rat predation on shorebirds in the Aleutians has contributed to 

inflated populations of some intertidal invertebrates that would normally be controlled by 

shorebird predation. A possible increase in the abundance of shorebirds after rat removal may 

facilitate a transformation in the intertidal ecosystem from invertebrate-dominated to algaedominated, as are many of the intertidal ecosystems on rat-free Aleutian islands (Kurle et al. in 

review). Sea otters feed in the intertidal zone and adjacent nearshore waters but it is unlikely that 

intertidal community shifts after rat eradication will measurably affect their feeding success 

because of the local availability of a variety of food sources. 

There is no reason to believe that the Proposed Action will lead to any other effects in the 

habitat, prey base, or other ecological interactions of sea otters that will indirectly affect them. 

Cumulative effects – Sea otter hunting for pelts in the 18th through the early 20th centuries 

essentially extirpated the Aleutian sea otter population. Sea otter populations recovered after 

hunting was banned in 1911, but after an initial recovery the sea otter population in the Aleutians 

began declining sharply in the 1980s. The Rat Islands region posted one of the largest declines of 

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the archipelago. The reasons for this decline are unclear, but the implication is that at present, the 

sea otter population at Rat Island is very vulnerable. However, effects from bait application 

operations are not likely to contribute measurably to negative cumulative effects in individual 

sea otters or the sea otter population. 

In the foreseeable future, there is the possibility for rat eradication efforts on additional Aleutian 

Islands. These eradications are unlikely to occur soon enough after the Rat Island project or close 

enough to Rat Island to contribute to cumulative effects on sea otters that were affected by the 

eradication on Rat Island. Thus, there is no reasonable risk for measurable cumulative effects on 

northern sea otters. 

Significance of effects to sea otters on and around Rat Island – There will likely be no acute 

mortality to sea otters that will result from this operation. Further, it is not likely that any sea 

otters will experience injury or the significant potential for injury as a result of the activities 

described in the Proposed Action. Therefore this analysis concludes that implementation of rat 

eradication activities as described in the Proposed Action is not likely to adversely affect 

northern sea otters on an individual or population level. 

Special considerations under ESA – Appropriate consultation will occur to ensure compliance 

with Section 7 of the ESA.with regard to Threatened sea otters. 

4.5.2.3. Steller’s eider 

As indicated in the Affected Environment section (Section 3.4.6.1), Steller’s eiders are unlikely 

to be present near Rat Island. Nevertheless, since they are listed under the ESA, analysis is 

completed below. 

Brodifacoum toxicity risk – The Steller’s eider is in the same taxonomic family as the mallard, 

which has an LD50 of 0.26 mg/kg. Steller’s eiders average about 850 g (1.9 lb) in mass 

(Fredrickson 2001). However, the estimates of bait intake needed to reach an LD50 threshold 

illustrated in Table 4.1 are not informative for Steller’s eiders, as eiders are almost exclusively 

carnivorous. Given an eider’s average mass and an LD50 assumption of 0.26 mg/kg, one bird 

will need to eat enough primarily-exposed prey animals to ingest the equivalent of only four full 

bait pellets to be at a 50% risk of mortality. 

Brodifacoum exposure risk – Steller’s eiders are not likely to be present during application 

activities, since the few birds that occur in the central Aleutians do not typically arrive until early 

winter, after the operations window will likely be closed by weather (Gibson and Byrd 2007). No 

Steller’s eiders have been reported at Rat Island in the record of historical observations (see 

Appendix 2). Nevertheless, if there are Steller’s eiders present in the Rat Island area during bait 

application activities, they would be on the water offshore. Birds in the water may encounter 

some bait pellets in the nearshore or intertidal zones immediately after bait application, but the 

planned mitigation measures to minimize bait entry into the marine ecosystem reduce this 

likelihood. However, if bait does enter the water, it will dissolve within hours. Typically, 

Steller’s eiders are carnivorous feeders and not expected to deliberately ingest bait pellets when 

their natural prey is readily available. Bait pellets entering the water will disintegrate, but the 

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active ingredient is mostly insoluble in the water. Grain particles will either be suspended in the 

nearshore turbulence or settle to the bottom. Small particles, each only 25 parts per million or 

less active ingredient that reach benthic filter feeders could be ingested. In the New Zealand 

brodifacoum spill (Primus et al. 2005) brodifacoum concentration peaked one day after the spill. 

Although Steller’s eiders prey on intertidal and subtidal invertebrates, they will be at very low 

risk of secondary brodifacoum exposure. 

Overall, based on the availability of brodifacoum in the environment over time, and their food 

habits and distribution patterns, Steller’s eiders are very unlikely to be exposed to brodifacoum. 

Overall risks from brodifacoum use – The toxicity of brodifacoum to Steller’s eiders is high. 

However, they are very unlikely to be exposed to the toxin. Overall, therefore, Steller’s eiders 

are very unlikely to suffer lethal or sublethal effects as a result of the Proposed Action because 

so little bait, and therefore active ingredient, is likely to enter the water column. 

Risks from the operation – While there are no data on the sensitivity of Steller’s eiders to 

helicopter noise, waterbirds in general have been reported to flush from roosts and nests in 

response to noise from low-flying helicopters (US Air Force and US Fish and Wildlife 

Service1988). Steller’s eiders are also likely to flush (or swim away) when approached by 

personnel. Birds are generally more vulnerable to disturbance during the breeding season, but 

Steller’s eiders do not breed on Rat Island or anywhere in the Aleutians. There is no reason to 

believe that disturbances over the temporal scale described in the Proposed Action will result in 

measurable effects to Steller’s eiders on Rat Island, if they are present. 

Indirect effects – Persistent rat predation on shorebirds in the Aleutians has contributed to 

inflated populations of some intertidal invertebrates that would normally be controlled by 

shorebird predation. A possible increase in the abundance of shorebirds after rat removal may 

facilitate a transformation in the intertidal ecosystem from invertebrate-dominated to algaedominated, as are many of the intertidal ecosystems on rat-free Aleutian islands (Kurle et al., in 

review). Steller’s eiders depend on the intertidal zone for food resources, but it is unlikely that 

intertidal community shifts after rat eradication will measurably affect the feeding success of 

eiders. 

Cumulative effects – Steller’s eiders are listed as Threatened under the ESA, due to an ongoing 

contraction in their breeding range. However, the causes of this contraction are unclear and 

possibly due to a number of different factors (USFWS 2002). Regardless, there are no impacts 

anticipated as a result of the Proposed Action that could be considered additive to any external 

impacts that eiders may be facing. 

In the foreseeable future, there is the possibility for rat eradication efforts on additional Aleutian 

Islands. These eradications are unlikely to occur soon enough after the Rat Island project to 

contribute to cumulative effects on eiders that were affected by the eradication on Rat Island. 

Thus, there is no reasonable risk for measurable cumulative effects on Steller’s eiders that can be 

linked to the Proposed Action. 

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Significance of effects to Steller’s eiders on and around Rat Island – There is no reasonable risk 

that the Proposed Action will lead to the harassment, harm, or mortality of any Steller’s eiders, 

and therefore no risk of significant effects at the individual or population level. 

Special considerations under ESA – Based on the analysis above it is unlikely that a formal 

consultation will be conducted under Section 7 of the ESA will be necessary for Steller’s eiders. 

4.5.3. Impacts to Species Listed Under the Marine Mammal Protection Act 

4.5.3.1. Species also listed under ESA 

As previously stated, two marine mammal species on Rat Island, Steller sea lions and northern 

sea otters, are protected by the ESA as well as the MMPA. Any compliance requirements 

required by NMFS for the Proposed Action will be relevant to these species. See Section 4.5.2 

above for impacts analysis for both of these ESA-listed species. 

4.5.3.2. Harbor seal 

Brodifacoum toxicity risk – The brodifacoum LD50 value for harbor seals has not been 

established. Using a conservative LD50 figure of 0.4 mg/kg, a harbor seal of average mass, 80 kg 

(176 lb) (Kinkhart and Pitcher 1994), will need to ingest the equivalent of more than 500 bait 

pellets to be at a 50% risk of mortality. Harbor seals are exclusively carnivorous, so brodifacoum 

ingestion will need to occur either accidentally or through an intermediate prey species that 

previously consumed bait pellets. 

Brodifacoum exposure risk – Harbor seals are primarily marine organisms, but they also utilize 

beaches year-round. Seals are likely to be present in the waters surrounding Rat Island, and are 

likely to be hauled-out somewhere on the island or surrounding offshore stacks and islets at any 

given time during rat eradication operations. Seals could conceivably encounter stray bait pellets, 

if they are hauled-out on Rat Island during bait application. Most of this bait will be consumed 

by rats within 4 days of the final bait application, and most of the stray bait in the lower intertidal 

zone where seals tend to be, will be carried away with the first high tide after each bait 

application. A scattered few pellets may remain present in areas that are above the high-water 

line for up to a few months after the application, but these are outside seals’ normal terrestrial 

range. Seals in the water may encounter occasional bait pellets in ocean or intertidal zones, but 

this is unlikely because the few pellets that might inadvertently enter the nearshore marine waters 

will dissolve within hours. 

Harbor seals are exclusively carnivorous (almost exclusively piscivorous) and do not feed while 

on land, so the only possible routes for bait ingestion are accidental. The likelihood of primary 

exposure is therefore very low. The likelihood of marine fish ingesting bait pellets is very low 

(as discussed in Section 4.3.1) and therefore the likelihood of secondary exposure in seals is 

negligible. 

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Chapter 4: Environmental Consequences 

Overall risks from brodifacoum use – Due to their large size, the probability that an individual 

would consume enough bait to achieve toxic levels of brodifacoum is, in practice, low. 

Furthermore, the likelihood of harbor seals experiencing either primary or secondary exposure is 

very low to negligible. Overall, the overall risk of harbor seal mortality or noticeable sub-lethal 

effects as a result of brodifacoum use is negligible. 

Risks from the operation – The response of pinnipeds like Steller sea lions to aircraft overflights 

varies from no discernable reaction to completely vacating haul-outs after a single overflight 

(Calkins 1979;Efroymson and Suter 2001). Approaching aircraft generally flush animals into the 

water. 

During staging operations, project managers will plan helicopter flight lines and boat travel to 

minimize the potential for disturbance to harbor seal haul-outs known from existing databases 

and surveys conducted prior to the operations. However, in spite of these precautions, seals 

encountered unexpectedly during helicopter operations could be flushed from land temporarily. 

An individual seal’s exposure to peak noise from the helicopter will be limited to animals that 

remain ashore, and is likely to be of short duration, as the elevation and speed of the helicopter 

(see Section 2.2.2.3) will limit the time that any single location is exposed to maximum noise. 

Unlike during staging, it will be more difficult to avoid known haul sites on Rat Island with the 

helicopter during bait application because of the need for thorough coverage of the entire island. 

No young pups are expected on Rat Island during fall but the impacts of disturbance to seals 

during molting (another sensitive period) will be minimized by timing overflights after the peak 

molting period is over. 

The sporadic personnel presence and temporary infrastructure installations that may be necessary 

near seal haul-outs during both staging and bait application operations may result in localized 

disturbances, although this is much less likely to disturb animals than helicopter overflights. The 

camps and staging areas themselves will be well inland and will have negligible impacts on seals 

hauled out on the coastline. 

Overall, the effects of the operations described in the Proposed Action on harbor seals will vary 

depending on the number of disturbance events. However, the short-term displacement from 

haul-sites that is likely to occur as a result of helicopter noise and personnel is not anticipated to 

have any significant effect on overall energy balance or fitness of any individual animals. 

Indirect effects – There is no reason to believe that the Proposed Action will lead to any effects 

in the habitat, prey base, or other ecological interactions of harbor seals that will indirectly affect 

them. Any pellets unintentionally deposited into nearshore marine waters will dissolve quickly; 

they are not likely to enter the food web by being ingested by fish that are then eaten by harbor 

seals. Nevertheless, even if a harbor seal eats a fish that has ingested a bait pellet, the likelihood 

of negative effects on the seal is negligible. 

Cumulative effects – Harbor seals in Alaska were hunted in the 19th and early 20th centuries, 

and Alaska Natives continue to harvest them for subsistence. However, harbor seals are not 

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Chapter 4: Environmental Consequences 

currently listed as depleted under the MMPA. Any effects from bait application operations are 

not likely to contribute measurably to negative cumulative effects in seals. 

In the foreseeable future, there is the possibility for rat eradication efforts on additional Aleutian 

Islands. These eradications are unlikely to occur soon enough after the Rat Island project or close 

enough to the island to contribute to cumulative effects on seals that were affected by the Rat 

Island eradication. Thus, especially if helicopter activity is adjusted to minimize the amount of 

seal disturbance – within the constraints of ensuring a successful rat eradication – there is no 

reasonable risk for measurable cumulative effects on harbor seals. 

Significance of effects to harbor seals on and around Rat Island – It is not likely that any harbor 

seals will suffer injury or the significant potential for injury as a result of the activities described 

in the Proposed Action. Therefore this analysis concludes that implementation of rat eradication 

activities as described in the Proposed Action is not likely to result in significant effects to harbor 

seals at an individual or population level. 

Special considerations under MMPA – With the exception of subsistence harvests, the MMPA 

regulations generally prohibit the killing, injury or disturbance of marine mammals. However, 

permits can be granted allowing exceptions to this prohibition for actions that may impact a 

marine mammal if the impact is incidental to rather than the intention of the action. Carrying out 

an action that is likely to lead to the disturbance of hauled-out harbor seals to the point that they 

enter the water may be considered “harassment” under the MMPA, but the precedent for this 

determination is unclear. On Anacapa Island in southern California, where harbor seals are 

known to haul-out, aerial broadcast of rodenticide bait pellets for a rat eradication operation 

required no special permits from NMFS. 

4.5.4. Impact on Species Listed Under the Migratory Bird Treaty Act 

No endemic species or subspecies of birds are restricted to Rat Island (see Gibson and Byrd 

2007). Of the Aleutian endemics that occur on Rat Island (e.g., rock ptarmigan, winter wren, 

song sparrow), Townsend’s rock ptarmigan is the only taxon restricted to the Rat Island group 

(Kiska to Amchitka), but it occurs on most of the islands in the group being particularly 

abundant on nearby Amchitka Island. 

4.5.4.1. Waterfowl 

As indicated in section 3.4.6, the following five species of waterfowl are likely to be present at 

Rat Island in fall. Other species of migrant waterfowl could also occur in some years, but risks 

would be similar to appropriate taxa analyzed here (e.g. data for mallards and Canada geese 

could be applied to other species of ducks and geese respectively). 

• Emperor goose 

• Aleutian cackling goose 

• Aleutian green-winged teal 

• Common eider 

• Harlequin duck 

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Chapter 4: Environmental Consequences 

Emperor geese occur on beaches and rocky shores, migrant cackling geese are typically found in 

grass and dwarf shrub meadows, teal are in freshwater wetlands or inshore marine waters, and 

eiders and harlequins occur in inshore marine waters primarily. In the section immediately 

following, only geese and teal are treated because their exposure risk is different than the risk for 

eiders and harlequin ducks (seaducks) occupying marine waters. Environmental consequences 

for seaducks are discussed later with other marine birds (section 4.5.4.6). Geese and teal are 

unlikely to eat whole bait pellets, but pieces of pellets after baits begin to breakdown, could 

potentially be ingested. 

Brodifacoum toxicity risk – There are multiple LD50 data points for waterfowl. For greenwinged teal, use of the known LD50 for mallards (0.26 mg/kg) is appropriate. For Aleutian 

cackling geese and emperor geese, the LD50 value measured for Canada geese of <0.75 mg/kg 

(Godfrey 1985, as cited in Erickson and Urban 2002) would be most accurate. However, for the 

sake of consistency and caution, mallards appear to be one of the more sensitive avian species 

based on the literature (P. Johnson, pers. comm.), the lower value of 0.26 mg/kg will be used for 

all waterfowl. The average mass range for a small adult of these species is between 270 g (.6lb) 

(for green-winged teal) and almost 2 kg (4.4 lb) (for emperor geese) (Mowbray et al. 2002; 

Petersen et al. 1994; Johnson 1995). Based on this size range (which falls between the 100 g and 

1000 g (.2 and 2.2 lb) size classes in Table 4.1), the estimated portion of daily food intake that 

must be bait for these species to be at a 50% risk of mortality is between 10% and 20%. 

However, because some of these waterfowl may be at risk of both primary and secondary 

exposure (see further analysis below), an actual bait pellet intake less than this may still 

contribute to some birds reaching a 50% risk of mortality, if these individuals also consume 

invertebrates that were previously exposed to brodifacoum and have stored the chemical their 

gut. 

Brodifacoum exposure risk – Any waterfowl that are present on Rat Island during bait 

application activities will be likely to encounter bait pellets in both upland (0.33 pellets/m2 or 

0.28 pellets/sq yd) and coastal (0.7 pellets/m2

 or 0.6 pellets/sq yd) areas. Waterfowl are unlikely 

to encounter bait pellets in marine or freshwater habitat because large waterbodies will be 

avoided to prevent applying bait directly to water and a directional shield will minimize the 

amount of bait that drifts towards water. Some bait will inadvertently fall into water where steepsided cliffs with hard (rock) faces are adjacent to the coastline. If bait does enter the water, it will 

be available immediately after entry but will dissolve within hours. Most of the bait on land will 

be consumed, primarily by rats within 10 days of the final bait application, but a scattered few 

pellets may remain present for up to a few months after the application. Some invertebrates on 

the island may continue to register measurable levels of brodifacoum for as long as bait pellets 

are available in the environment (Howald et al. 2005), but the actual risk of waterfowl 

experiencing secondary exposure through the consumption of invertebrates will decline from low 

(immediately after bait application) to negligible (within 30 days of bait application). 

Animals on Rat Island are only at risk of exposure to brodifacoum if they are likely to consume 

bait pellets and/or if they are likely to prey or scavenge on animals that have consumed the bait 

pellets. Emperor geese and green-winged teal can be generally characterized by omnivorous food 

habits (Petersen et al. 1994; Johnson 1995). Aleutian cackling geese are almost exclusively 

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Chapter 4: Environmental Consequences 

herbivorous (Mowbray et al. 2002). While there are no specific field data to demonstrate this, a 

general diet analysis indicates that emperor geese and teal are likely to experience primary 

exposure to brodifacoum. In an observational trial conducted on Shemya Island (western 

Aleutians) in September 2007, Aleutian cackling geese did not recognize a non-toxic bait replica 

spread in their foraging area as food (Schwitters 2007). This study suggests that Aleutian 

cackling geese on Rat Island are unlikely to experience primary exposure to brodifacoum as a 

result of the Proposed Action. 

It is possible emperor geese and green-winged teal could be exposed to low levels of 

brodifacoum by consuming invertebrates that have fed upon bait. Because they are herbivorous, 

Aleutian cackling geese are very unlikely to experience secondary exposure through 

invertebrates. 

Regardless of food habits, waterfowl will only be at risk of exposure to brodifacoum if they are 

present on Rat Island for the period of time during and soon after bait is applied to the island 

(likely to be in mid- to late fall, and for a few months afterward). As indicated in Section 3.4.6, 

up to 15 – 20 green-winged teal could be present on Rat Island in fall, mostly associated with 

wetlands and inshore marine waters where they are not likely to encounter baits. Emperor geese 

winter in the Aleutians. A few birds arrive by September, but numbers typically do not reach a 

peak until December (Gibson and Byrd 2007; Petersen et al. 1994). Emperors feed almost 

exclusively in the intertidal zone so they will be exposed to relatively low densities of baits for a 

relatively short period of time. The few pairs of Aleutian cackling geese that have recently been 

found breeding on Rat Island (Buckelew et al. 2007b), will be feeding in dwarf shrub and grass 

meadows in fall, where they could be joined in September or early October by passing flocks of 

migrant birds from western Aleutian breeding sites. Most geese have left the Aleutians for 

wintering grounds by early to mid-October (Gibson and Byrd 2007). 

Overall, based on the availability of brodifacoum in the environment over time, and the food 

habits and migratory patterns of the waterfowl on Rat Island: 

• Emperor geese and green-winged teal may be exposed to brodifacoum as a result of the 

Proposed Action, although it is somewhat unlikely; and 

• Aleutian cackling geese are unlikely to be exposed to brodifacoum. 

Overall risks from brodifacoum use – The toxicity of brodifacoum to the waterfowl analyzed 

here is probably high. Exposure to brodifacoum is possible. Therefore, as a result of brodifacoum 

use as described in the Proposed Action: 

• Some individual green-winged teal and/or emperor geese may die or experience sublethal effects, although it is somewhat unlikely; and 

• Aleutian cackling geese are unlikely to die or be exposed sub-lethally. 

Risks from the operation – Waterfowl have been reported to flush in response to noise from lowflying helicopters (US Air Force and US Fish and Wildlife Service 1988). Waterfowl are also 

likely to flush when approached by personnel. Birds are generally considered to be particularly 

sensitive to disturbance during breeding activities, and altered breeding behaviors have been 

noted as a result of aircraft disturbance (US Air Force and US Fish and Wildlife Service 1988). 

Summer staging operations may result in localized disturbances to nesting waterfowl, but the 

78
Chapter 4: Environmental Consequences 

FWS will conduct island-wide nest surveys during staging operations, and project managers will 

take every reasonable measure to avoid placing helicopter flight lines or temporary infrastructure 

in the immediate vicinity of any known waterfowl nest sites. Bait application operations will not 

take place until after breeding seasons are over for the waterfowl species analyzed here. There is 

no reason to believe that disturbance over the temporal scale described in the Proposed Action 

will result in measurable effects to any of the waterfowl on Rat Island. 

Indirect effects – Rats are known predators of ground-nesting birds, chicks, and eggs, including 

waterfowl. A successful rat eradication will remove the risk of predation from rats and may lead 

to an increase in waterfowl numbers. 

Cumulative effects – When foxes were present on Rat Island, there were likely few breeding 

waterfowl on the island. Aleutian cackling geese were driven to near extinction in the 19th and 

20th centuries by introduced foxes, and they were listed as an endangered species in 1967 

(USFWS 1999). Fox removal from many Aleutian Islands, and other protective measures in 

wintering grounds, led to the Aleutian cackling goose being removed from the Endangered 

Species list in 2001, and a few breeding pairs have recently reoccupied Rat Island (Buckelew et 

al. 2007b). Green-winged teal were undoubtedly also prey items for foxes, and since fox 

eradication the teal population on Rat Island has likely increased. 

In the future, there is the possibility for rat eradication efforts on additional Aleutian Islands. 

These eradications are unlikely to occur soon enough after the Rat Island project to contribute to 

cumulative effects on waterfowl that were affected by the eradication on Rat Island. 

Thus, there is no reasonable risk for measurable cumulative effects on waterfowl that can be 

linked to the Proposed Action. 

Significance of effects to waterfowl on Rat Island – The three species of waterfowl analyzed 

here are present on the islands surrounding Rat Island (Table 3.2), and there is likely gene flow 

between these islands. There is no reason to believe that the impacts to individual birds that are 

predicted above as a result of brodifacoum use will lead to noticeable changes in Rat Island’s 

waterfowl community over the long term. There is likewise no reason to believe that impacts to 

individual birds on Rat Island will be measurable elsewhere in the region. This analysis 

concludes that implementation of the Proposed Action will not result in significant negative 

effects to waterfowl, but will likely produce positive long-term benefits for waterfowl 

populations and their recovery on Rat Island. 

4.5.4.2. Birds of prey 

Effects of the Proposed Action on the following birds of prey will be analyzed here: 

• Peregrine falcon 

• Short-eared owl 

Effects of the Proposed Action on Bald eagles will be analyzed separately in Section 4.5.5. 

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Chapter 4: Environmental Consequences 

As indicated in Table 3.2, typically two pairs of peregrine falcons nests on Rat Island, and with 

normal reproductive success there could be up to 10 falcons (including fledglings) associated 

with the island in fall. Furthermore, one or two short-eared owls could be present during fall 

migration. 

Brodifacoum toxicity risk – There are studies that have established an average LD50 for a raptor 

(the Australasian harrier Circus approximans) at 10 mg/kg (Godfrey 1985, as cited in Erickson 

and Urban 2002). However, for the sake of consistency and caution, the much lower value of 

0.26 mg/kg will be used as with the other birds analyzed in this document. The average mass for 

a peregrine falcon is between 900 and 1000 g (2 and 2.2 lb) (White et al. 2002), while the 

average mass for short-eared owls is between 300 and 400 g (.6 and .9 lb) (Wiggins et al. 2006). 

The estimates of bait intake needed to reach an LD50 threshold illustrated in Table 4.1 are not 

informative for animals such as birds of prey, which are exclusively carnivorous. However, 

given the average mass for each bird, and using the reported LD50 range of between 0.26 mg/kg 

and 10 mg/kg: 

• A peregrine falcon will need to eat enough primarily-exposed prey animals to ingest the 

equivalent of at least 4 full bait pellets to be at a 50% risk of mortality. 

• A short-eared owl will need to eat the enough primarily-exposed prey animals to ingest 

the equivalent of at least 2 full bait pellets to be at a 50% risk of mortality. 

Brodifacoum exposure risk – Peregrine falcons and short-eared owls are exclusively carnivorous, 

and therefore they have a very low likelihood of primary exposure to brodifacoum. Peregrine 

falcons are specialist predators that almost exclusively feed on birds, and some birds on Rat 

Island are likely to consume bait pellets, which means that falcons may experience secondary 

exposure to brodifacoum. 

Peregrine falcon diet on Amchitka Island (White et al 1973) largely consisted of seabirds and 

waterfowl, but rats were also taken (1.3% of diet). Ptarmigan, a potentially affected species from 

bait application, comprised 11.6% of the diet, and passerines were also taken at low percentages 

(total about 1% of diet). Non-target birds exposed to brodifacoum may be more susceptible to 

predation by peregrines and owls. American kestrels have been reported killed by secondary 

exposure to brodifacoum (Erickson and Urban 2004). 

The anticipated risk of falcons experiencing secondary exposure through the consumption of 

birds will decline from low (immediately after bait application) to negligible (within 30 days of 

bait application). 

Short-eared owls are known to prey on rats as well as birds, and therefore the likelihood of owls 

experiencing secondary exposure will be initially high (immediately after bait application) and 

will decline to negligible (within 30 days of bait application). Barn owls have been reported 

killed by secondary exposure to brodifacoum (Erickson and Urban 2004). 

Through secondary exposure, both peregrine falcons and short-eared owls are likely to be 

exposed to brodifacoum. 

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Chapter 4: Environmental Consequences 

Overall risks from brodifacoum use – While precise figures are unavailable, a conservative 

analysis must assume that the toxicity of brodifacoum to both peregrine falcons and short-eared 

owls is high. Because rats might be targeted as prey by owls, they are more likely to be exposed 

to the toxin than peregrines, but both could be exposed with at least sub-lethal effects and some 

birds might be killed by secondary exposure. Birds of prey exposed to brodifacoum-poisoned 

prey died (42%) and 1/3 of the surviving individuals showed signs of toxicosis (Erickson and 

Urban 2004). However, on Langara Island in British Columbia, the population of breeding 

peregrine falcons in fact increased one year after rat eradication efforts (W. Nelson, pers. 

comm.). 

In summary, the relatively few birds of prey occurring on Rat Island during or soon after the 

proposed time of application may be exposed to brodifacoum, and there is risk of some mortality 

as a result. 

Risks from the operation – Raptors have been reported to flush in response to noise from lowflying helicopters (US Air Force and US Fish and Wildlife Service 1988). Raptors are also likely 

to flush when approached by personnel. Birds are generally considered to be particularly 

sensitive to disturbance during breeding activities, and altered breeding behaviors have been 

noted as a result of aircraft disturbance (US Air Force and US Fish and Wildlife Service 1988). 

Peregrine falcons are known to breed on Rat Island, but short-eared owls are not. Helicopter 

operations during summer staging activities will be localized to discrete flight paths, making 

disturbance to nesting peregrines unlikely but possible. Bait application operations will not begin 

until after the breeding season is over for peregrines (White et al. 2002). There is no reason to 

believe that disturbance over the temporal scale described in the Proposed Action will result in 

measurable effects to peregrine falcons or short-eared owls. 

Indirect effects – Peregrine falcons in the Aleutians depend largely on seabirds for prey. The 

negative impacts that rats have on seabird colonies may be indirectly reducing food availability 

to the peregrine population on Rat Island. Furthermore, rats are known predators of peregrine 

chicks in the Aleutians (Jones and Byrd 1979). The Proposed Action may result in an increase in 

food abundance (seabirds) for peregrines on Rat Island, and will eliminate rat predation. 

Short-eared owls that arrive on Rat Island during migration likely prey on rats, and rat removal 

may negatively affect food availability for owls on the island. However, it is unlikely that this 

will have measurable effects on the migratory population of owls in the Rat Island region. 

Cumulative effects – Owls and falcons can have large ranges, and it is possible that individual 

birds present on Rat Island are presently experiencing harm elsewhere in their ranges. However, 

there are no impacts anticipated as a result of the Proposed Action that could be considered 

additive to any external impacts that these birds may be facing. 

In the foreseeable future, there is the possibility for rat eradication efforts on additional Aleutian 

Islands. These eradications are unlikely to occur soon enough after the Rat Island project to 

contribute to cumulative effects on birds of prey that were affected by the eradication on Rat 

Island. 

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Chapter 4: Environmental Consequences 

Thus, there is no reasonable risk for measurable cumulative effects on either of the birds of prey 

analyzed here that can be linked to the Proposed Action. 

Significance of effects to birds of prey on and around Rat Island – Peregrine falcons and shorteared owls are both present on the islands surrounding Rat Island (Table 3.2), and there is likely 

gene flow between birds on Rat Island and birds on surrounding islands. Furthermore, shorteared owls are considered uncommon on Rat Island and there are not likely to be more than a 

few, if any, owls present during or shortly after bait application operations (Gibson and Byrd 

2007). There is no reason to believe that the impacts to individual birds predicted above as a 

result of brodifacoum use will lead to noticeable changes in Rat Island’s peregrine or owl 

populations over the long term. There is likewise no reason to believe that impacts to individual 

birds on Rat Island will be measurable elsewhere in the region, such as through changes in 

regional populations. Therefore this analysis concludes that implementation of the Proposed 

Action will not result in significant effects to peregrine falcon or short-eared owl populations. 

4.5.4.3. Shorebirds 

Effects of the Proposed Action on the following shorebird species will be analyzed: 

• Pacific golden-plover (fall migrant) 

• Black oystercatcher (resident) 

• Wandering tattler (fall migrant) 

• Ruddy turnstone (fall migrant) 

• Pectoral sandpiper (fall migrant) 

• Sharp-tailed sandpiper (fall migrant) 

• Rock sandpiper (resident) 

Numbers of migrant shorebirds that are likely to be present in fall at Rat Island probably will not 

exceed 20 birds for any of the species (Table 3.2). The resident species, black oystercatcher and 

rock sandpiper could occur in numbers up to 40 or so. These latter two species will be primarily 

confined to intertidal areas in fall, but some of the migrants will likely occur in the uplands. The 

bait pellets are too large to be consumed whole by shorebirds, but particularly omnivorous 

migrant shorebirds foraging inland, where pellet density is higher, might ingest pieces of pellets 

by pecking at them or by picking up pieces after baits not consumed by rats begin to disintegrate. 

Brodifacoum toxicity risk – The conservative LD50 value of 0.26 mg/kg will be used to estimate 

brodifacoum toxicity to shorebirds, as with the other birds analyzed in this document. The 

average mass range for a small adult of these species is between around 70 g (2.5 oz) (for 

wandering tattlers) (Gill et al. 2002b) and over 500 g (17.6 oz) (for black oystercatchers) (Andres 

and Falxa 1995). This places the shorebirds analyzed here between the 100 g and 1000 g (.2 and 

2.2 lb) size classes on Table 4.1. According to this table, the estimated portion of daily food 

intake that must be bait for these birds to be at a 50% risk of mortality is between around 10% 

and 20%. Because some of these birds may be at risk of both primary and secondary exposure 

(see further analysis below), an actual bait pellet intake of a lower proportion of their diet may 

still contribute to some birds reaching a 50% risk of mortality, if they also consume invertebrates 

that were previously exposed to brodifacoum. 

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Chapter 4: Environmental Consequences 

Brodifacoum exposure risk – Shorebirds that are present on Rat Island during bait application 

activities will likely encounter bait pellets on the ground in both upland (0.33 pellets/m2

 or 0.28 

pellets/sq yd) and coastal (0.7 pellets/m2 or 0.6 pellets/sq yd) areas. If bait does enter the water, it 

will be available immediately after entry but will dissolve within hours. Most of the bait on land 

will be consumed by rats within 10 days of the final bait application, but a scattered few pellets 

may remain present for up to a few months after the application. Some invertebrates on the 

island may continue to register measurable levels of brodifacoum for as long as bait pellets are 

available in the environment (Howald et al. 2005). Brodifacoum does not persist in invertebrate 

tissue (e.g., land crabs see Pain et al. 2000) after one month following exposure to brodifacoum 

bait. The actual risk of birds experiencing secondary exposure through the consumption of 

invertebrates will decline from low (immediately after bait application) to negligible (within 30 

days of bait application). 

Animals on Rat Island are only at risk of exposure to brodifacoum if they are likely to consume 

bait pellets and/or if they are likely to prey or scavenge on animals that have consumed the bait 

pellets. All shorebirds analyzed here except the black oystercatcher and rock sandpiper are likely 

to occur in inland areas where bait density is relatively high. Ruddy turnstones are omnivorous 

during the fall (Nettleship 2000) and due to their highly-variable diet this species might peck at 

bait pellets and ingest some of the rodenticide directly. Golden plovers tend to feed on berries or 

insects in fall, and the other migrant shorebirds tend to feed on insects and are not likely to 

directly ingest baits (Gill et al. 2002a; Johnson and Connors 1996; Gill et al. 2002b), but would 

have at least a low likelihood of at least sub-lethal effects from secondary exposure. Black 

oystercatchers are carnivorous, and they specialize in intertidal invertebrates (Andres and Falxa 

1995). During the fall and winter months, rock sandpipers also feed largely on intertidal 

invertebrates. The likelihood of primary exposure in these two species is thus very low, and their 

likelihood of secondary exposure through invertebrate consumption is somewhat higher but still 

low because bait densities in intertidal zones will be low and generally temporary (between high 

tides). 

Regardless of food habits, shorebirds will only be at risk of exposure to brodifacoum if they are 

present on Rat Island for the period of time during and soon after bait is applied to the island 

(likely to be in mid- to late fall, and for a few months afterward). Black oystercatchers and rock 

sandpipers are both considered resident to Rat Island and are likely to be present during and after 

bait application. Pacific golden plovers, wandering tattlers, ruddy turnstones, and pectoral and 

sharp-tailed sandpipers are all long-migrating species that could be present in small numbers on 

Rat Island temporarily during fall migration. 

Overall risks from brodifacoum use – While precise figures are unavailable, a conservative 

analysis must assume that the toxicity of brodifacoum to the shorebirds on Rat Island is more or 

less uniformly high. However, most are unlikely to be directly exposed to the toxin. Overall, 

therefore, as a result of the Proposed Action: 

• Given their particularly broad dietary habits (Nettleship 2000), ruddy turnstones are the 

most likely shorebirds to directly ingest portions of bait pellets and therefore get primary 

exposure that could potentially cause mortality or sub-lethal effects; 

• Because they primarily are feeding on berries and insects in fall, the other migrant 

shorebirds have a very low risk of primary exposure because they are not likely to 

83
Chapter 4: Environmental Consequences 

directly ingest parts of bait pellets, but there is a low risk of secondary exposure in 

quantities sufficient to cause at least sub-lethal effects in some of the relatively few 

individuals that could be present at Rat Island; 

• Black oystercatchers and rock sandpipers are unlikely to experience primary exposure, 

but there is a low likelihood of secondary exposure that could cause at least sub-lethally 

effects in some individuals. 

Risks from the operation – Waterbirds, including shorebirds, have been reported to flush in 

response to noise from low-flying helicopters (US Air Force and US Fish and Wildlife Service 

1988). Shorebirds are also likely to flush when approached by personnel. Shorebirds, especially 

black oystercatchers, are considered to be particularly sensitive to disturbance during breeding 

activities. Helicopter operations during summer staging activities will be localized to discrete 

flight paths, making disturbance to nesting oystercatchers and rock sandpipers unlikely but 

possible. Aerial bait application operations will not begin until after Rat Island’s shorebird 

breeding season is over. Ruddy turnstones, Pacific golden plovers, and wandering tattlers are 

unlikely to be present during either staging or bait application activities, although their presence 

is possible. There is no reason to believe that disturbance over the temporal scale described in the 

Proposed Action will result in measurable effects to any of the shorebirds on Rat Island. 

Indirect effects – Rats are known predators of ground-nesting birds including shorebirds. A 

successful rat eradication will release breeding oystercatchers and sandpipers from rat predation 

and may lead to an increase in their numbers. 

Cumulative effects – When foxes were present on Rat Island, there were likely few or no 

breeding rock sandpipers or black oystercatchers on the island. Fox eradication from Rat Island 

released shorebirds from one predation threat, but rats remained. Today, rat predation may be 

keeping populations of oystercatchers or sandpipers on Rat Island smaller than they would be in 

a rat-free state. This current persistent downward population pressure is likely more substantial 

than any short-term negative impacts that may occur as a result of the Proposed Action. 

In the foreseeable future, there is the possibility for rat eradication efforts on additional Aleutian 

Islands. These eradications are unlikely to occur soon enough after the Rat Island project to 

contribute to cumulative effects on shorebirds that were affected by the eradication on Rat 

Island. 

Significance of effects to shorebirds on Rat Island – The shorebirds analyzed here are present on 

the islands surrounding Rat Island and there is likely gene flow between these islands among all 

breeding species. There is no reason to believe that the impacts to individual birds that are 

predicted above as a result of brodifacoum use will lead to noticeable changes in Rat Island’s 

shorebird community over the long term. There is likewise no reason to believe that impacts to 

individual birds on Rat Island will result in measurable population-level changes for the species 

elsewhere. Therefore this analysis concludes that implementation of the Proposed Action will not 

result in significant effects to shorebird populations on Rat Island. 

4.5.4.4. Marine birds except gulls and jaegers 

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Chapter 4: Environmental Consequences 

Effects of the Proposed Action on the following marine birds will be analyzed. Foraging 

strategies vary and therefore potential to exposure varies among species groups accordingly. 

Marine birds most likely to be exposed directly (primary exposure) or indirectly (secondary 

exposure) to brodifacoum are scavengers like gulls and predators like jaegers, so these species 

are dealt with separately in the next section (4.5.4.5). 

• Seaducks (inshore marine waters) 

o Pacific common eider 

o Harlequin duck 

• Pelagic Seabirds (inshore marine waters) 

o Red-faced cormorant 

o Pelagic cormorant 

o Pigeon guillemot 

o Whiskered auklet 

• Pelagic Seabirds (offshore marine waters) 

o Fork-tailed storm-petrel 

o Leach’s storm-petrel 

o Horned puffin 

o Tufted puffin 

Brodifacoum toxicity risk – There are studies that have established an average LD50 for the 

Southern black-backed gull (Larus dominicanus) at <0.75 mg/kg (Godfrey 1985, as cited in 

Erickson and Urban 2002). However, for the sake of consistency and caution, the lower value of 

0.26 mg/kg will be used, as with the other birds analyzed in this document. The average mass 

range for a small adult of these various marine bird species is between only 45 g (1.6 oz) (for 

Leach’s storm-petrel) and 1600 g (3.5 lb) (for common eiders) (Huntington et al. 1996; 

Robertson and Goudie 1999; Goudie et al. 2000; Causey 2002; Hobson 1997; Ewins 1993; Piatt 

and Kitaysky 2002a; Piatt and Kitaysky 2002b). The estimates of bait intake needed to reach an 

LD50 threshold illustrated in Table 4.1 is not informative for most of the marine birds, which are 

exclusively carnivorous. However, common eiders may occasionally consume plant matter, 

making Table 4.1 applicable to them. Average common eider mass is 1600 g (3.5 lb) (Goudie et 

al. 2000), putting them closest to the 1000 g (2.2 lb) size class. Consequently, Table 4.1 

estimates the portion of daily food intake that must be bait for these birds to be at 50% risk of 

mortality as around 20% (a little more than 4 pellets for a 1000 g bird). Because common eiders 

may be at risk of both primary and secondary exposure (see further analysis below), an actual 

bait pellet intake of a lower proportion of their diet may still contribute to some birds reaching a 

50% risk of mortality if they also consume intertidal invertebrates that were previously exposed 

to brodifacoum. 

Potential brodifacoum toxicity in the carnivorous marine birds is more informative for decisionmaking when considered, similar to other predatory birds in this analysis, as the quantity of bait 

pellets that would contain an LD50 threshold. Given the mass range of these birds and a very 

conservative LD50 assumption of 0.26 mg/kg, marine birds on Rat Island will need to consume 

enough primarily-exposed prey animals to ingest the equivalent of between 1 and 7 full bait 

pellets to be at a 50% risk of mortality. 

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Chapter 4: Environmental Consequences 

Brodifacoum exposure risk – Marine birds that are present on or around Rat Island during bait 

application activities will be likely to encounter bait pellets in coastal areas at a density of about 

0.7 pellets/m2

 (0.6 pellets/sq yd). Marine birds may encounter bait pellets in ocean or intertidal 

zones, but this is unlikely because of the mitigation measures that will be implemented to 

minimize bait entry into the marine ecosystem. If bait does enter the water, it will be available 

immediately after entry but will dissolve within hours. Most of the bait on land will be 

consumed, primarily by rats, within 10 days of the final bait application, but a scattered few 

pellets may remain present for up to a few months after the application. 

Animals on Rat Island are only at risk of exposure to brodifacoum if they are likely to consume 

bait pellets and/or if they are likely to prey or scavenge on animals that have consumed the bait 

pellets. Seaducks feeding in shallow inshore marine waters could conceivably come into contact 

with stray bait pellets, in spite of mitigation to keep pellets out of the marine waters. However, it 

is unlikely that pellets would be ingested. If seaducks are exposed at all, it would likely be an 

indirect exposure through diets. Eiders (and harlequins to a lesser degree) eat sessile marine 

invertebrates, particularly molloscs, in the intertidal zone and nearshore subtidal zones 

(Robertson and Goudie 1999; Goudie et al. 2000). These are areas that likely will have low 

densities of bait pellets, but a few seaducks could possible ingest invertebrates that have some 

level of brodifacoum, there is a remote possibility of primary exposure if they encounter a pellet 

and ingest it and a slightly higher, but still low, due to secondary exposure from eating 

invertebrates which themselves have a low likelihood of consuming baits before they 

disintegrated. The small amount of bait which inadvertently entered the water during the baiting 

at Anacapa Island (Howald et al. 2007) began to degrade after 1.5 hrs in the water. No 

brodifacoum was detected in the water or mussel samples collected. Pelagic seabirds, which feed 

on plankton (whiskered auklets and storm-petrels) or fish (cormorants, guillemots, and puffins) 

are not subject to primary exposure, and are there is negligible likelihood of secondary exposure. 

Regardless of food habits, marine birds will only be at risk of exposure to brodifacoum if they 

are present on Rat Island for the period of time during and soon after bait is applied to the island. 

As shown in Table 3.2, hundreds of common eiders and harlequin ducks will be present in fall at 

Rat Island, where they will forage in inshore marine waters and roost on offshore rocks, reefs, or 

on the water (Robertson and Goudie 1999; Goudie et al. 2000). Cormorants, gulls, pigeon 

guillemots, and whiskered auklets are generally resident in the region (Causey 2002; Hobson 

1997; Ewins 1993, Gibson and Byrd 2007), and all feed nearshore in marine waters. Stormpetrels and puffins will be completing nesting mostly in September and departing the area until 

spring. While still present, these species are feeding mainly well offshore in marine waters (e.g., 

Piatt and Kitaysky 2002a, b). 

The bait applied to the islet off Ayugadak Point in early summer will be enclosed in bait stations 

and will not be available to gulls that might tend to scavenge them. 

Overall risks from brodifacoum use – While precise figures are unavailable, a conservative 

analysis must assume that the toxicity of brodifacoum to the marine birds on Rat Island is 

generally high. However, they are very unlikely to be exposed to the toxin. Overall, therefore, all 

of the marine birds are very unlikely to die or be exposed sub-lethally as a result of brodifacoum 

use as described in the Proposed Action. 

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Chapter 4: Environmental Consequences 

Risks from the operation – Marine birds have been reported to flush from roosts and nests in 

response to noise from low-flying helicopters (US Air Force and US Fish and Wildlife Service 

1988). Some, particularly seabirds, are also likely to flush when approached by personnel. Of all 

the marine birds analyzed here, ledge-nesting cormorants would be the most susceptible to 

disturbance from helicopter overflights or ground personnel during staging operations if they 

occur during the nesting season, particularly before young in nests are feathered and can 

thermoregulate (usually by early August in the Aleutians, Alaska Maritime NWR, unpubl. data). 

Altered breeding behaviors have been noted in other marine bird species specifically as a result 

of aircraft disturbance (US Air Force and US Fish and Wildlife Service 1988). Helicopter 

operations during summer staging activities will be localized to discrete flight paths, designed to 

avoid cormorant colonies, and ground personnel will also avoid close approach to avoid 

disturbance. Aerial bait application operations will not begin until after breeding seasons are 

over. 

Bait stations will be installed on the islet off Ayugadak Point during the breeding season of the 

birds that likely breed on this islet, and it is possible that these activities will cause perceptible 

disturbance to individual burrow-nesting breeding birds. However, field personnel will be trained 

to avoid burrows and in techniques for burrow repair in the rare case where a burrow is damaged. 

Impacts from this disturbance are not likely to be perceptible within these birds’ local 

populations. 

Overall, there is no reason to believe that localized disturbances over the temporal scale 

described in the Proposed Action will result in measurable effects to any of the marine bird 

species on Rat Island. 

Indirect effects – Rats are known predators of marine birds in the Aleutians. A successful rat 

eradication will release these species from the risk of rat predation and may lead to an increase in 

marine bird abundance and diversity on Rat Island. 

Cumulative effects – When foxes were present on Rat Island, there were likely few or no 

breeding marine birds on the island. Since fox eradication, some species of marine birds on Rat 

Island have likely increased. However, continued rat predation may be keeping populations of 

many of these species smaller than they would be if Rat Island were rat-free. 

In general, marine birds have large ranges, and it is possible that individual birds present on Rat 

Island are presently experiencing harm elsewhere in their ranges. In particular, occasional 

interactions with fisheries may cause disturbances to seabirds, especially near human-populated 

areas. However, there are no impacts anticipated as a result of the Proposed Action that could be 

considered additive to any external impacts that marine birds may be facing. 

In the foreseeable future, there is the possibility for rat eradication efforts on additional Aleutian 

Islands. These eradications are unlikely to occur soon enough after the Rat Island project to 

contribute to cumulative effects on marine birds that were affected by the eradication on Rat 

Island. In the long term, a successful archipelago-wide rat eradication program may lead to 

noticeable improvements in the population health of Aleutian seabirds. 

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Chapter 4: Environmental Consequences 

In conclusion, there is no reasonable risk for measurable cumulative effects on marine birds that 

can be linked to the Proposed Action. 

Significance of effects to marine birds on and around Rat Island – Marine bird species present on 

Rat Island are also present on the surrounding islands and there is likely gene flow between these 

islands. There is no reason to believe that any impacts to individual birds will lead to noticeable 

changes in the marine bird community on Rat Island over the long term. There is likewise no 

reason to believe that impacts to individual birds on Rat Island will result in measurable 

population-level changes for the species elsewhere. Therefore, this analysis concludes that 

implementation of the Proposed Action will not result in significant effects to any of the marine 

bird populations analyzed here. 

4.5.4.5. Scavenging and predatory seabirds 

The following two species of marine birds are analyzed separately because they have different 

foraging strategies which make them more vulnerable to exposure to brodifacoum than the other 

marine birds (Section 4.5.4.4). Gulls are opportunistic scavengers and predators and jaegers are 

kleptoparasites and predators on other birds. 

• Glaucous-winged gull 

• Parasitic jaeger 

Brodifacoum toxicity risk – There are studies that have established an average LD50 for a 

seabird (the southern black-backed gull) at <0.75 mg/kg (Godfrey 1985, as cited in Erickson and 

Urban 2002). However, for the sake of consistency and caution, the lower value of 0.26 mg/kg 

will be used as with the other birds analyzed in this document. The average mass range for adults 

of these species is between around 500 g (1.1 lb) for jaegers (Wiley and Lee 1999) and 1000 g 

(2.2 lb) for gulls (Verbeek 1993). This places these birds between the 100 g and 1000 g (.2 and 

2.2 lb) size classes on Table 4.1. Consequently, this table 4.1 estimates the portion of daily food 

intake that must be bait for these species to be at a 50% risk of mortality as between 10% and 

20%. Because gulls and jaegers may be at risk of both primary and secondary exposure (see 

further analysis below), an actual bait pellet intake of a lower proportion of their diet may still 

contribute to some birds reaching a 50% risk of mortality, if they also consume animals (such as 

rats or invertebrates) that were previously exposed to brodifacoum. 

Brodifacoum exposure risk – Any gulls or jaegers that are present on Rat Island during bait 

application activities will likely encounter bait pellets on the ground in both upland (0.33 

pellets/m2

 or 0.28 pellets/sq yd) and coastal (0.7 pellets/m2 or 0.6 pellets/sq yd) areas. Most of 

the bait on land will be consumed, primarily by rats, within 10 days of the final bait application, 

but a scattered few pellets may remain present for up to a few months after the application. Gulls 

and jaegers, if they are present, are likely to consume bait pellets. Through predation and/or 

scavenging, both species are also both likely to consume rats that have been exposed to 

brodifacoum, as well as invertebrates (Verbeek 1993; Wiley and Lee 1999). In a trial eradication 

in the Aleutians, most (88% of) rat carcasses were found underground, out of reach of avian 

scavengers (Buckelew et al. 2007a). Any exposed rat carcasses may be available for 

consumption by scavengers for up to 30 days. Some invertebrates on the island may continue to 

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Chapter 4: Environmental Consequences 

register measurable levels of brodifacoum for as long as bait pellets are available in the 

environment (Howald et al. 2005). The actual likelihood of gulls or jaegers experiencing 

secondary exposure through the consumption of rats and invertebrates will decline from high 

(immediately after bait application) to very low (within 30 days of bait application). 

Jaegers breed in the Aleutians, but leave for wintering grounds far to the south by midSeptember (Wiley and Lee 1999; Gibson and Byrd 2007). Jaegers are therefore unlikely to be 

present during or after the bait application. Gulls are generally resident and some are likely to be 

present on Rat Island year-round. Overall, gulls are very likely to be exposed to brodifacoum. 

Jaegers are unlikely to be exposed to brodifacoum. 

Overall risks from brodifacoum use – While precise figures are unavailable, a conservative 

analysis must assume that the toxicity of brodifacoum to both gulls and jaegers is high. Gulls are 

likely to be exposed to the toxin, but exposure is unlikely for jaegers. Overall, therefore, as a 

result of brodifacoum use as described in the Proposed Action: 

• Some gulls are likely to die from brodifacoum exposure; and 

• Due to their migratory patterns, jaegers are unlikely to die or be exposed sub-lethally. 

Risks from the operation – Birds have been reported to flush in response to noise from lowflying helicopters (US Air Force and US Fish and Wildlife Service 1988). Altered breeding 

success has also been reported in gulls as an indirect effect of noise disturbance (US Air Force 

and US Fish and Wildlife Service 1988). Helicopter operations during summer staging activities 

will be localized to discrete flight paths, making disturbance to nesting gulls unlikely but 

possible. However, aerial bait application operations will not begin until after breeding seasons 

are over for gulls on Rat Island. 

Bait stations will be installed on the islet off Ayugadak Point during the breeding season of the 

gulls that likely breed on this islet, and it is possible that these activities will cause perceptible 

disturbances to some nesting gulls. However, impacts from this disturbance are not likely to be 

perceptible within these birds’ local populations. 

There is no reason to believe that localized disturbances over the temporal scale described in the 

Proposed Action will result in measurable effects to gulls or jaegers. 

Indirect effects – Rats are known predators of seabirds in the Aleutians. A successful rat 

eradication will release seabirds from the risk of rat predation and may lead to an increase in the 

abundance of seabirds on Rat Island, including gulls and jaegers. Because gulls and jaegers both 

prey on seabirds, and parasitic jaegers in the Aleutians often rely on seabird kleptoparasitism 

(stealing food from other birds) (Wiley and Lee 1999), an increase in local seabird populations 

will provide more food resources for both of these birds. 

Persistent rat predation on shorebirds in the Aleutians has also contributed to inflated populations 

of some intertidal invertebrates that would normally be heavily predated by shorebirds. A 

possible increase in the abundance of shorebirds after rat removal may facilitate the 

transformation in the intertidal ecosystem from invertebrate-dominated to algae-dominated, as 

are many of the intertidal ecosystems on rat-free Aleutian islands (Kurle et al. in review). 

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Chapter 4: Environmental Consequences 

However, it is unlikely that intertidal community shifts after rat eradication will measurably 

affect the feeding success of gulls or jaegers. 

Cumulative effects – When foxes were present on Rat Island, there were likely few or no 

breeding marine birds on the island. Since fox eradication marine bird population on Rat Island 

has likely increased. However, continued rat predation may be keeping populations of many 

seabirds from becoming reestablished on Rat Island and remnant populations are likely smaller 

than they would be in a rat-free state. This current persistent downward population pressure is 

likely more substantial than any short-term negative impacts that may occur as a result of the 

Proposed Action. 

Gulls and jaegers have large ranges, and it is possible that individual birds present on Rat Island 

are presently experiencing harm elsewhere in their ranges. In particular, occasional interactions 

with fisheries may cause disturbances to seabirds, especially near human-populated areas. 

However, there are no impacts anticipated as a result of the Proposed Action that could be 

considered additive to any external impacts that these birds may be facing. 

In the foreseeable future, there is the possibility for rat eradication efforts on additional Aleutian 

Islands. These eradications are unlikely to occur soon enough after the Rat Island project to 

contribute to cumulative effects on scavenging seabirds that were affected by the eradication on 

Rat Island. In the long term, a successful archipelago-wide rat eradication program may lead to 

noticeable improvements in the population health of Aleutian seabirds. 

In conclusion, there is no reasonable risk for measurable cumulative effects on either gulls or 

jaegers that can be linked to the Proposed Action. 

Significance of effects to scavenging seabirds on and around Rat Island – Glaucous-winged gulls 

and parasitic jaegers are present on the surrounding islands and there is likely gene flow between 

these islands. There is no reason to believe that any impacts to individual birds will lead to 

noticeable long-term changes in gull or jaeger populations on and around Rat Island. There is 

likewise no reason to believe that impacts to individual birds on Rat Island will result in 

measurable population-level changes elsewhere in their range. Therefore this analysis concludes 

that implementation of the Proposed Action will not result in significant effects to either 

glaucous-winged gull or parasitic jaeger populations. 

4.5.4.6. Common raven 

Brodifacoum toxicity risk – The conservative LD50 value of 0.26 mg/kg will be used to estimate 

brodifacoum toxicity to ravens, as with the other birds analyzed in this document. The average 

mass for ravens in Alaska is between 1100 and 1200 g (2.4 and 2.7 lb) (sexes combined) 

(Boarman and Heinrich 1999). This places ravens in the 1000 g (2.4 lb) size class on Table 4.1. 

According to the Table, the estimated portion of daily food intake that must be bait for a raven to 

be at a 50% risk of mortality is about 20%. Because ravens are at risk of both primary and 

secondary exposure (see further analysis below), an actual bait intake of less than 20% of their 

diet may still contribute to some ravens reaching a 50% risk of mortality, if they also consume 

prey or scavenged animals that were previously exposed to brodifacoum. 

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Chapter 4: Environmental Consequences 

Brodifacoum exposure risk – Any ravens that are present on Rat Island during bait application 

activities are likely to encounter bait pellets on the ground in both upland (0.33 pellets/m2 or 0.28 

pellets/sq yd) and coastal (0.7 pellets/m2

 or 0.6 pellets/sq yd) areas. Bait will be consumed and 

cached by rats within days after application, but some pellets may remain for a few months. 

In a trial eradication in the Aleutians, most rat carcasses were found underground (88%), out of 

reach of scavenging ravens (Buckelew et al. 2007a). Any exposed rat carcasses may be available 

for consumption by ravens for up to 30 days. Howald et al (1999) documented ravens using rat 

carcasses on Langara Island. Thirteen ravens were found poisoned by brodifacoum after baiting, 

both from feeding directly on the bait and feeding on poisoned rats. Ravens may also consume 

invertebrates exposed to brodifacoum. Some invertebrates on the island may continue to register 

measurable levels of brodifacoum for as long as bait pellets are available in the environment 

(Howald et al. 2005). The actual likelihood of ravens experiencing secondary exposure through 

the consumption of rats and invertebrates will decline from high (immediately after bait 

application) to negligible (within 30 days of bait application). Overall, ravens are very likely to 

be exposed to brodifacoum. 

Overall risks from brodifacoum use – While precise figures are unavailable, a conservative 

analysis must assume that the toxicity of brodifacoum to ravens is high. Furthermore, their food 

habits make them very likely to be exposed to the toxin. Overall, therefore, if they are present on 

Rat Island during or soon after bait application operations, some ravens are likely to die or 

experience sub-lethal effects from brodifacoum exposure. 

Risks from the operation – There is little information on the disturbance effects of helicopter 

flyovers on ravens. Birds are generally considered to be sensitive to disturbance during breeding 

activities, but ravens have not been noted to be particularly vulnerable to breeding-season 

disturbances. There is no reason to believe that disturbance over the temporal scale described in 

the Proposed Action will result in measurable effects to ravens. 

Indirect effects – Ravens likely prey on rats as part of their diet on Rat Island. Rat eradication 

may force ravens to change their food habits. Ravens are adept at adjusting to changes in food 

availability (Boarman and Heinrich 1999), so the disappearance of rats is unlikely to result in any 

noticeable effects. Ravens in the Aleutians also readily prey on seabirds and their eggs. The 

negative impacts that rats have on seabird colonies may be indirectly reducing food availability 

to ravens on Rat Island. The Proposed Action may result in an overall increase in food 

abundance (seabirds) for ravens on Rat Island. 

Cumulative effects – Ravens in Alaska have never been considered at risk or threatened. There 

are no known past impacts to ravens in Alaska that would add to effects caused by the Proposed 

Action. 

Ravens can have large ranges, and it is possible that individual ravens present on Rat Island are 

presently experiencing harm elsewhere in their ranges. However, there are no impacts anticipated 

as a result of the Proposed Action that could be considered additive to any external impacts that 

ravens may be facing. 

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Chapter 4: Environmental Consequences 

In the foreseeable future, there is the possibility for rat eradication efforts on additional Aleutian 

Islands. These eradications are unlikely to occur soon enough after the Rat Island project or close 

enough to Rat Island to contribute to cumulative effects on ravens that were affected by the 

Proposed Action. 

Thus, there is no reasonable risk for measurable cumulative effects on ravens that can be linked 

to the rat eradication on Rat Island. 

Significance of effects to ravens on and around Rat Island – Ravens are present on the islands 

surrounding Rat Island (see Table 3.2) and there is likely gene flow between ravens on Rat 

Island and ravens on surrounding islands. Furthermore, the raven population on Rat Island is 

thought to be very small (Buckelew et al. 2007b). There is no reason to believe that the impacts 

to individual birds that are predicted above as a result of brodifacoum use will lead to noticeable 

changes in Rat Island’s raven community over the long term. There is likewise no reason to 

believe that impacts to individual birds on Rat Island will be measurable elsewhere in the region, 

such as through changes in regional populations. Therefore this analysis concludes that 

implementation of the Proposed Action will not result in significant effects to ravens. 

4.5.4.7. Small and medium-sized passerines (other than ravens) 

Effects of the Proposed Action on the following species of passerine birds (also called songbirds) 

will be analyzed: 

• Winter wren 

• Song sparrow 

• Lapland longspur 

• Snow bunting 

• Gray-crowned rosy finch 

Brodifacoum toxicity risk – There are studies that have established an average LD50 for a 

passerine (the song sparrow) at “<6” mg/kg (Godfrey 1985, as cited in Erickson and Urban 

2002). However, for the sake of consistency and caution, the lower value of 0.26 mg/kg will be 

used as with the other birds analyzed in this document. The average mass range for a small adult 

of these species is between less than 9 g (0.3 oz) (for winter wrens) (Hejl et al. 2002) and more 

than 40 g (1.4 oz) (for gray-crowned rosy finches) (MacDougall-Shackleton et al. 2000). This 

places the passerines analyzed here in the 25 g (0.9 oz) size class on Table 4.1. According to the 

estimates in this table, the estimated portion of daily food intake that must be bait for these birds 

to be at a 50% risk of mortality is very low, about 4% (a fraction of a pellet). Because these 

passerines may be at risk of both primary and secondary exposure (see further analysis below), 

an actual bait pellet intake of even less than 4% of their diet may still contribute to some birds 

reaching a 50% risk of mortality, if they also consume invertebrates that were previously 

exposed to brodifacoum. 

Brodifacoum exposure risk – Any passerine birds that are present on Rat Island during bait 

application activities will be likely to encounter bait pellets on the ground in both upland (0.33 

pellets/m2

 or 0.28 pellets/sq yd) and coastal (0.7 pellets/m2 or 0.6 pellets/sq yd) areas. Most of 

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Chapter 4: Environmental Consequences 

the bait on land will be consumed, primarily by rats, within 10 days of the final bait application, 

but a scattered few pellets may remain present for up to a few months after the application. Some 

invertebrates on the island may continue to register measurable levels of brodifacoum for as long 

as bait pellets are available in the environment (Howald et al. 2005), but the actual risk of birds 

experiencing secondary exposure through the consumption of invertebrates will decline from low 

(immediately after bait application) to negligible (within 30 days of bait application). 

Animals on Rat Island are only at risk of exposure to brodifacoum if they are likely to consume 

bait pellets and/or if they are likely to prey or scavenge on animals that have consumed the bait 

pellets. While the makeup of each bird’s diet varies considerably, all of the birds analyzed in this 

section can be characterized as omnivorous (feed at least occasionally on invertebrates) to an 

extent (Hejl et al. 2002; Hussell and Montgomerie 2002; MacDougall-Shackleton et al. 2000; 

Lyon and Montgomerie 1995; Arcese et al. 2002). All of the passerine birds analyzed in this 

section are therefore likely to experience both primary and secondary exposure to brodifacoum if 

they are present during or after bait application. Of the birds analyzed here, three are considered 

likely to be present during fall bait application operations: 1) winter wrens, 2) gray-crowned rosy 

finches, and 3) snow buntings. Because most, if not all, Lapland longspurs leave for their 

southern wintering grounds by the end of September and do not arrive again in the Aleutians 

until April, they are unlikely to be present during bait application (Gibson and Byrd 2007; 

Hussell and Montgomerie 2002). No song sparrows were detected during bird surveys in summer 

2007 (Buckelew 2007b), but a few birds have been seen on the island in past surveys (Table 3.2), 

so a few song sparrows could possibly be on Rat Island during bait application. 

Song sparrows were present in August 2007 on the islet off Ayugadak Point (Buckelew et al. 

2007b). If bait stations can be used exclusively on this islet, according to the criteria described in 

the Proposed Action (Section 2.2), the islet’s song sparrows are unlikely to be exposed to 

brodifacoum, but not completely protected from exposure. If bait needs to be broadcast on the 

islet, these sparrows are likely to be exposed. 

During a trial using baits containing brodifacoum on islets in the Bay of Islands (off Adak 

Island), four (26%) song sparrows with radio transmitters and presumed alive at the beginning of 

the bait trial survived at least 21 days after baiting. Five (33%) of the tagged sparrows were 

recovered dead, five (33%) were missing, and one sparrow (7%) had an active transmitter but its 

fate was unknown. Additionally, fifteen untagged song sparrows were found dead in carcass 

searches following baiting (Buckelew 2007a). 

Overall, based on the availability of brodifacoum in the environment over time, and the food 

habits and distribution and migratory patterns of the passerine birds known from Rat Island: 

• Winter wrens, gray-crowned rosy finches, and snow buntings are likely to be exposed to 

brodifacoum; 

• Although unlikely, Lapland longspurs may be exposed to brodifacoum; 

• If song sparrows are present they are likely to be exposed to brodifacoum; and 

• Song sparrows on the islet off Ayugadak Point are likely to be exposed to brodifacoum if 

it is necessary to broadcast bait on the islet, and less likely to be exposed if bait stations 

can be used exclusively. 

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Chapter 4: Environmental Consequences 

Overall risks from brodifacoum use – While precise figures are unavailable, a conservative 

analysis must assume that the toxicity of brodifacoum to the passerine birds on Rat Island is 

more or less uniformly high. Based on each bird’s likelihood of exposure, therefore: 

• Some winter wrens are likely to die or experience sub-lethal effects as a result of the 

Proposed Action; 

• Some gray-crowned rosy finches are likely to die or experience sub-lethal effects as a 

result of the Proposed Action; 

• Some snow buntings are likely to die or experience sub-lethal effects as a result of the 

Proposed Action; 

• It is somewhat unlikely that any Lapland longspurs will die or experience sub-lethal 

effects as a result of the Proposed Action; and 

• If bait must be broadcast on the islet off Ayugadak Point, some song sparrows are likely 

to die or experience sub-lethal effects as a result of the Proposed Action; but 

• If bait stations can be used exclusively on this islet, song sparrows are somewhat unlikely 

to die or experience sub-lethal effects. 

Risks from the operation – There is little information on the disturbance effects of helicopter 

flyovers on passerines. Birds are generally considered to be sensitive to disturbance during 

breeding activities, and altered breeding behaviors have been noted as a result of aircraft 

disturbance (US Air Force and US Fish and Wildlife Service 1988). Helicopter operations during 

summer staging activities will be localized to discrete flight paths, making disturbance to nesting 

passerines unlikely but possible. Aerial bait application operations will not begin until well after 

the breeding season is over for these species. 

Bait stations will be installed on the islet off Ayugadak Point during song sparrow breeding 

season, but it is unlikely that these activities will cause perceptible disturbance to breeding birds. 

There is no reason to believe that disturbance over the temporal scale described in the Proposed 

Action will result in measurable effects to any of the passerines analyzed. 

Indirect effects – Rats are known predators of all life stages of landbirds elsewhere (Atkinson 

1985) and in the Aleutians (H. Jones, pers. comm.). Rats may have caused a major decline in 

winter wren and song sparrow populations on Amchitka Island (White et al. 1977). A successful 

rat eradication will release passerine birds from rat predation pressure and may lead to an 

increase in passerine numbers on Rat Island. 

Cumulative effects – When foxes were present on Rat Island, they likely preyed on passerines at 

least occasionally. Fox eradication from Rat Island released passerines from that predation 

source, but rats remained. Today, rat predation may be keeping passerine populations on Rat 

Island much smaller than they would be in a rat-free state. This current persistent downward 

population pressure is likely more substantial than any short-term negative impacts that may 

occur as a result of the Proposed Action. 

In the foreseeable future, there is the possibility for rat eradication efforts on additional Aleutian 

Islands. These eradications are unlikely to occur soon enough after the Rat Island project or close 

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Chapter 4: Environmental Consequences 

enough to Rat Island to contribute to cumulative effects on passerines that were affected by the 

Proposed Action. 

Significance of effects to small and medium-sized passerines on and around Rat Island – The 

passerine birds analyzed here are present on the islands surrounding Rat Island and there is likely 

gene flow between these islands. There is no reason to believe that the impacts to individual 

birds that are predicted above as a result of brodifacoum use will lead to noticeable changes in 

the passerine community on Rat Island over the long term. Results from a 2006 trial eradication 

elsewhere in the Aleutians support this conclusion; although some passerines (song sparrows) 

did experience mortality from brodifacoum, this species remained extant after bait application on 

all treated test islands (Buckelew et al. 2007a). There is likewise no reason to believe that 

impacts to individual birds on Rat Island will result in measurable population-level changes in 

these passerines elsewhere in their range. This analysis concludes that implementation of the 

Proposed Action will not result in significant effects to the passerine bird species analyzed. 

4.5.5. Impacts to Bald Eagles 

Brodifacoum toxicity risk – There are studies that have established an average LD50 for the 

Australasian harrier at 10 mg/kg (Godfrey 1985, as cited in Erickson and Urban 2002). 

However, for the sake of consistency and caution, the lower value of 0.26 mg/kg will be used, as 

with the other birds analyzed in this document. The average mass range for bald eagles in Alaska 

is between about 4000 and 6000 g (8.8 and 13.2 lb) (sexes combined) (Buehler 2000). The 

estimates of bait intake needed to reach an LD50 threshold illustrated in Table 4.1 are not 

informative for animals such as the bald eagle that are exclusively carnivorous (Buehler 2000). 

However, given the average sized eagle and a very conservative LD50 assumption of 0.26 

mg/kg, one eagle will need to eat enough primarily-exposed prey animals to ingest the equivalent 

of at least 17 bait pellets to reach a 50% risk of mortality from the brodifacoum. As a note of 

comparison, if the LD50 figure of 10 mg/kg is used instead, the LD50 threshold for an average 

bald eagle is not reached until a bird has eaten enough primarily-exposed prey animals to ingest 

the equivalent of between 600 and 1000 pellets. This discrepancy between figures indicates that 

the potential toxicity risk to eagles is still poorly understood, but the risk may be much lower 

than this analysis assumes. 

Brodifacoum exposure risk – Bald eagles are exclusively carnivorous and have a very low 

likelihood of primary exposure to brodifacoum. They are opportunistic predators, but generally 

demonstrate a preference for fish whenever they are available (Howald et al. 1999; Anthony et 

al. 1999). In the absence of available fish, eagles in the Aleutians will prey on seabirds and 

mammals. Because eagles are known to feed on rats, as well as birds, they will have a high 

likelihood of exposure to brodifacoum for a period of time immediately following bait 

application. While rats are still alive on the island, eagles are likely to prey on them as well as 

birds that may have been exposed to brodifacoum, and they are also likely to scavenge on the 

carcasses of rats and birds as well. In a trial eradication in the Aleutians, most (88% of) rat 

carcasses were found underground, out of reach of avian scavengers (Buckelew et al. 2007a). 

Any exposed rat or bird carcasses may be available for consumption by scavengers such as 

eagles for up to 30 days. The actual likelihood of eagles experiencing secondary exposure 

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Chapter 4: Environmental Consequences 

through the consumption of rats or birds is probably dependent on the seasonal availability of 

fish in the nearshore waters of Rat Island. By a conservative estimate, assuming that eagles will 

be feeding at least occasionally on rats during bait application operations, their likelihood of 

brodifacoum exposure will decline from high (immediately after bait application) to negligible 

(within 30 days of bait application). 

Overall risks from brodifacoum use – The toxicity of brodifacoum to bald eagles is high, but 

lower than other birds analyzed in this document due to eagles’ much larger size. The risk that 

eagles will be exposed to measurable levels of brodifacoum is also thought to be high initially 

after bait application, but the local availability of fish (especially spawning salmonids) at the 

time of the bait application may correspondingly reduce eagles’ brodifacoum exposure risk if 

birds move off Rat Island to see salmon on nearby Amchitka where many spawning streams 

occur (Simenstad et al 1977). For comparison, no eagles were found dead or sick or suspected of 

brodifacoum exposure in 2006 during a trial removal of rats near Adak Island (Buckelew et al. 

2007a). Furthermore, evidence from Langara Island (Howald et al. 1999) indicates that the 

likelihood of bald eagles ingesting a lethal dose of brodifacoum through consumption of 

brodifacoum-exposed rats and birds may be low. According to the most conservative analysis, 

some bald eagles may be exposed to brodifacoum residues, but are unlikely to die as a result of 

bait application on Rat Island. 

Risks from the operation – Eagles have been reported to flush in response to noise from lowflying helicopters (US Air Force and US Fish and Wildlife Service 1988). Eagles are also likely 

to flush when approached by personnel. Eagles are generally considered to be more sensitive to 

disturbance during breeding activities, although there is little evidence to suggest that sound 

disturbances over a short temporal scale cause alterations in breeding success. 

During early summer staging operations, when bald eagles will be nesting or raising chicks, 

project managers will plan helicopter flight lines that remain more than 305 m (1000 ft.) away 

from all known eagle nests on the island based on nest surveys conducted before flight lines are 

finalized. Aerial bait application operations will not begin until after the breeding season is over 

for eagles on Rat Island (Gibson and Byrd 2007; Buehler 2000). There is no reason to believe 

that disturbance over the temporal scale described in the Proposed Action will result in 

measurable effects to bald eagles. 

Indirect effects – Bald eagles likely rely on rats as a food source on Rat Island (Murie 1940; 

Anthony et al. 1999). However, the best scientific evidence indicates that current bald eagle 

predation on rats in the Aleutians is relatively low (~13% of their total diet; Anthony et al. 1999). 

Rat removal from Rat Island may therefore force eagles to change their food habits, but only by a 

small amount. It is unlikely that rat eradication will result in reduced feeding success for bald 

eagles, as bald eagles have the ability to switch prey depending on food availability (Anthony et 

al. 1999). 

The negative impacts that rats have on seabird colonies may be indirectly reducing food 

availability to bald eagles on Rat Island. If the Proposed Action successfully facilitates growth in 

seabird colonies on Rat Island, it may in fact result in an overall increase in food abundance for 

eagles, which appear to catch seabirds with less difficulty than catching rats. 

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Chapter 4: Environmental Consequences 

Cumulative effects – Like most raptors, bald eagles are sensitive to persistent organic pollutants 

in the environment. Some examples of these pollutants that occur in the Aleutian environment 

include polychorinated biphenlys (PCBs) and organochlorine pesticides such as DDT. Military 

actions, both from World War II and in the last 50 years, are said to be responsible for 

polychlorinated biphenyl (PCB) contamination in bald eagles in the Aleutians (Anthony et al. 

1999). These high concentrations can be linked to reduced breeding success in some cases 

(Anthony et al. 1999) and may affect bald eagle populations on Rat Island. In the lower 48 states, 

bald eagles were nearly driven extinct as a result of DDT pesticide use in the early-to-mid 

1900’s; however, due to its remoteness, DDT did not affect Alaskan bald eagle populations 

(Buehler 2000). Since the abandonment of DDT use, populations in the lower 48 have rebounded 

enough to warrant the recent delisting of the bald eagle from the Endangered Species list. 

There is evidence, however, that Aleutian bald eagles still contain organochlorine pesticides and 

mercury in their systems and that those contaminants can reduce bald eagle breeding success 

(Anthony et al. 1999). Organochlorine pesticides are mostly used as insecticides and typically 

associated with agricultural use. Although sources of those pesticides are far from the Aleutians, 

bald eagles are exposed to them secondarily, mostly through the seabirds in their diet (Anthony 

et al. 1999). Despite ongoing evidence of contamination, bald eagles in Alaska remain at or near 

their carrying capacity (Buehler 2000). 

In the foreseeable future, there is the possibility for rat eradication efforts on additional Aleutian 

Islands. These eradications are unlikely to occur soon enough after the Rat Island project to 

contribute to cumulative effects on bald eagles that were affected by the eradication on Rat 

Island. 

Thus, there is no reasonable risk for measurable cumulative effects on bald eagles that can be 

linked to the Proposed Action. 

Significance of effects to bald eagles on Rat Island – Eagles are present on the islands 

surrounding Rat Island and there is likely gene flow between eagles on Rat Island and eagles on 

surrounding islands. There is no reason to believe that the potential impacts to individual birds as 

a result of brodifacoum use will lead to noticeable changes in eagle population numbers on or 

around Rat Island over the long term. There is likewise no reason to believe that impacts to 

individual birds on Rat Island will result in measurable population-level changes elsewhere in 

their range. Therefore this analysis concludes that implementation of the Proposed Action will 

not result in significant effects to bald eagle populations. 

Compliance with the Bald Eagle Management Guidelines – The management guidelines for bald 

eagles circulated by FWS recommend measures to minimize impacts of actions, both by the 

government and by private entities, on bald eagles. The recommended measures relevant to the 

Proposed Action include 1) avoiding operating aircraft within 305 m (1000 ft.) of the nest during 

breeding season, and 2) using pesticides only in accordance with federal and state laws. The 

Proposed Action will adhere to these guidelines. 

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Chapter 4: Environmental Consequences 

4.5.6. Impacts to Other Species On and Around Rat Island 

4.5.6.1. Rock ptarmigan 

Brodifacoum toxicity risk – There are studies that have established an average LD50 for another 

medium-sized galliform bird, the ring-necked pheasant Phasianus colchicus, at 10 mg/kg 

(Godfrey 1985, as cited in Erickson and Urban 2002). However, for the sake of consistency and 

caution, the lower value of 0.26 mg/kg will be used, as with the other birds analyzed in this 

document. The average mass for ptarmigan is about 500 g (1.1 lb) (Holder and Montgomerie 

1993). This places ptarmigan between the 100 g and 1000 g (.2 and 2.2 lb) size classes on Table 

4.1. According to this table, the estimated portion of daily food intake that must be bait for a 

ptarmigan to be at a 50% risk of mortality is between 10% and 20%. 

Brodifacoum exposure risk – Ptarmigan that are present on Rat Island during bait application 

activities will likely encounter bait pellets in both upland (0.33 pellets/m2

 or 0.28 pellets/sq yd) 

and coastal (0.7 pellets/m2

 or 0.6 pellets/sq yd) areas. Most of the bait will be consumed, 

primarily by rats, within 10 days of the final bait application, but a scattered few pellets may 

remain present for up to a few months after the application. Because ptarmigan are almost 

exclusively herbivorous (Holder and Montgomerie 1993), they are very unlikely to experience 

secondary exposure. Overall, ptarmigan on Rat Island are likely to be exposed to brodifacoum. 

Overall risks from brodifacoum use – While precise figures are unavailable, a conservative 

analysis must assume that the toxicity of brodifacoum to ptarmigan is high. Furthermore, they 

are likely to be exposed to the toxin. Overall, therefore, some ptarmigan are likely to die or 

experience sub-lethal effects as a result of the implementation of the Proposed Action. 

Risks from the operation – Ptarmigan responses to low-flying aircraft have not been reported. 

However, experiments subjecting nesting upland game birds to simulated sonic booms found that 

no birds flushed as a result, and there were no changes in hatching success (US Air Force and US 

Fish and Wildlife Service 1988). Ptarmigan in remote areas delay their flush responses, often 

allowing humans to approach to within less than 10 m (33 ft.). There is no reason to believe that 

disturbance over the temporal scale described in the Proposed Action will result in measurable 

effects to ptarmigan. 

Indirect effects – Rats are known predators of ground-nesting birds in the Aleutians and may be 

preying on ptarmigan, including eating their eggs. A successful rat eradication may lead to an 

increase in ptarmigan numbers on Rat Island. 

Cumulative effects – When foxes were present on Rat Island, there were likely few breeding 

ptarmigan on the island. Since fox eradication the ptarmigan population on Rat Island has 

certainly increased. However, continued rat predation may be keeping ptarmigan populations on 

Rat Island smaller than they would be in a rat-free state. This likely downward population 

pressure may be more substantial than any short-term negative impacts that may occur as a result 

of the Proposed Action, and removal of rats may increase the population of ptarmigan. 

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Chapter 4: Environmental Consequences 

In the foreseeable future, there is the possibility for rat eradication efforts on additional Aleutian 

Islands. These eradications are unlikely to occur soon enough after the Rat Island project or close 

enough to Rat Island to contribute to cumulative effects on ptarmigan that were affected by the 

Proposed Action. 

Thus, there is no reasonable risk for measurable cumulative effects on ptarmigan populations in 

the Aleutians that can be linked to the rat eradication on Rat Island. 

Significance of effects to ptarmigan on and around Rat Island – Townsend’s Rock ptarmigan 

occurs on other islands in the Rat Islands group, including the large islands of Amchitka and 

Kiska (Gibson and Byrd 2007), so loss of some birds at Rat Island will not affect the subspecies 

at the population level. It is unlikely that impacts to individual birds on Rat Island will result in 

measurable population-level changes elsewhere in the region. Therefore this analysis concludes 

that implementation of the Proposed Action will not result in significant effects to ptarmigan 

populations. 

4.5.6.2. Freshwater fish 

Effects of the Proposed Action on the following freshwater fish will be analyzed: 

• Dolly varden 

• Stickleback 

• Pink salmon 

Brodifacoum toxicity risk – There are no brodifacoum LD50 data available for fish, so 

brodifacoum toxicity in fish through oral ingestion of brodifacoum is unknown. Researchers 

have collected data on the lethal concentration of brodifacoum necessary to kill 50% of rainbow 

trout (Oncorhynchus mykiss) in a laboratory study – a value referred to as “LC50” that is 

measured in mg of active ingredient/liter of solution (also see Section 4.2.2.1.2). Researchers 

obtained the figure for trout, 0.04 mg/L, by suspending brodifacoum in water pumped through 

aquarium tanks and exposing fish to the brodifacoum suspension for 96 continuous hours. 

Because of the very low water solubility of brodifacoum, such an extreme exposure scenario will 

not occur for any fish species present on Rat Island. For context, however, if we assume that 

brodifacoum was 100% soluble in water and is broadcast into streams on Rat Island at a rate of 

17 kg/ha, the application rate for coastal areas, the maximum brodifacoum concentration in an 

average-sized stream (based on geographic data collected in summer 2007; Buckelew et al. 

2007b) would be less than 0.0004 mg/L, or more than 100 times lower than the concentration 

needed for 50% mortality in trout. Upland areas would experience a lower application rate of 8 

kg/ha. 

Brodifacoum exposure risk – During and immediately following bait application operations, 

stream-dwelling fish may encounter bait pellets at an average density of 0.7 pellets/m2

 (0.6 

pellets/sq yd), but these pellets will disintegrate in the water and become unavailable within 

hours. Tests conducted by researchers on a wide variety of fish species have shown that marine 

fish are largely uninterested in bait pellets as food items (Buckelew et al. 2007a; Howald et al. 

2005; USFWS 2005; Empson and Miskelly 1999; A. Wegmann, pers. obs.). It is similarly 

unlikely that fish present in freshwater habitat on Rat Island will demonstrate an affinity for 

99
Chapter 4: Environmental Consequences 

pellets. The fish analyzed here are primarily carnivorous, feeding on invertebrates. Some aquatic 

invertebrates may consume bait immediately after it enters the water, but it will only be available 

in pellet form for a matter of hours. The risk for freshwater fish of secondary exposure is very 

low. Finally, most of the streams on Rat Island are tiny and discontinuous, making viable fish 

habitat on the island extremely limited. During observational stream surveys conducted in 

summer 2007, fish were recorded in very few streams. No pink salmon were reported during this 

survey, and salmon habitat in particular is extremely limited on the island. 

Overall, none of the fish species analyzed here are likely to be exposed to toxic amounts of 

brodifacoum as a result of the Proposed Action. 

Overall risks from brodifacoum use – While precise toxicity figures for fish are not available, the 

exposure risk for freshwater fish on Rat Island is very low, and the overall risk for mortality or 

sub-lethal brodifacoum exposure in fish is negligible. 

Risks from the operation – Personnel may enter streams incidental to traveling by foot around 

the island. Additionally, the installation of temporary field camp facilities may have highly 

localized impacts on potential fish habitat. None of these activities will result in perceptible 

impacts to the fish species analyzed here. To further mitigate for potential impacts to fish, 

personnel will conduct formal surveys in any streams that may be affected by camp installation 

activities and will take all reasonable measures necessary to avoid disturbing streams that are 

identified as high-quality fish habitat. 

Indirect effects – No indirect effects can be reasonably expected on these three fish species as a 

result of the Proposed Action. 

Cumulative effects – There is no reasonable possibility that the Proposed Action will contribute 

to cumulative impacts on the fish species analyzed here. 

Significance of effects to freshwater fish on Rat Island – There is no reason to believe that the 

Proposed Action will contribute to perceptible changes in the freshwater fish community on Rat 

Island or the freshwater fish community anywhere else in the region. Therefore this analysis 

concludes that implementation of the Proposed Action will not result in significant effects to 

freshwater fish populations. 

4.5.6.3. Terrestrial Vegetation 

As described above in Section 4.2.2, this document will analyze the impact of the Proposed 

Action on the vegetative communities found on Rat Island. The analysis will give special 

consideration to a rare species, the Aleutian wormwood, which is endemic to the Rat Islands 

group. 

Risks from the operation – During staging operations in early summer, the project crew will 

cause moderate but localized and temporary disturbances to the plant community in five discrete 

locations: three bait storage areas (where bait will be kept in sealed containers), one fuel storage 

facility (where fuel will be stored and contained according to all applicable safety standards), and 

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Chapter 4: Environmental Consequences 

a camp area (see Figure 6). Bait station installation activities on the islet off Ayugadak Point will 

result in minor and highly localized vegetation disturbance, as will crews traveling by foot on 

Rat Island as well as the islet off Ayugadak Point. During the fall bait application operations, 

helicopters landing at each staging location and personnel traveling by foot will both cause 

minor-to-moderate but localized and temporary damage to vegetation. 

At the outset of early summer staging operations, personnel will conduct formal surveys for 

Aleutian wormwood at all sites where staging, storage or camp structures may be installed. All 

reasonable measures will be taken to avoid conducting any of these higher-impact activities in 

areas where the likelihood of damaging Aleutian wormwood is high. Additionally, field crew 

will be trained to identify Aleutian wormwood in the field and crew members will visibly mark, 

record, and avoid large stands of wormwood when encountered during operations. 

Indirect effects – Rats are known to feed on vegetation on the Aleutian Islands (Dunlevy and 

Scharf 2006; S. Ebbert, pers. comm.), sometimes with noticeable or major local effects. Rat 

removal may in fact benefit local or even island-wide vegetation communities, potentially 

returning species composition, abundance & biomass more similar to rat-free islands in the 

Aleutians. 

Cumulative effects – There is no reasonable possibility that the Proposed Action will contribute 

to negative cumulative impacts on Rat Island’s plant community. 

Significance of effects to plants on Rat Island – It is possible that the removal of rats will result 

in perceptible changes to the vegetative communities on Rat Island, ultimately returning to a 

composition reflecting its previously undisturbed state. However, it is likely that the vegetation 

response to rat removal will be imperceptible or localized rather than island-wide. Therefore this 

analysis concludes that implementation of the Proposed Action is not likely to result in 

significant negative effects to the vegetation on Rat Island, but will likely produce at least 

moderate beneficial effects in returning Rat Island vegetation to a more natural condition. 

4.5.7. Impacts to Water Resources 

Some bait pellets are likely to inadvertently enter bodies of fresh water on Rat Island and 

potentially drift into nearshore marine waters during bait application operations. However, the 

bait application techniques described will include mitigation measures to limit bait entry into 

water bodies to a level well under the target bait application rate. 

Even if bait enters water bodies on or around Rat Island at the full application rate, it is very 

unlikely to contribute to detectable levels of brodifacoum in the water column. The low water 

solubility and strong chemical affinity of brodifacoum to the grain matrix of the bait pellets 

largely prevents the rodenticide from entering aquatic environments via run-off. Furthermore, the 

concentration of brodifacoum in bait pellets is so low that even if we assume the compound was 

highly water soluble, and was broadcast into the water at an application rate of 17 kg/ha, the 

maximum brodifacoum concentration in an average-sized stream would be less than 0.0004 

mg/L, or more than 100 times lower than the concentration needed for 50% mortality in trout 

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Chapter 4: Environmental Consequences 

(stream size based on geographic data collected in summer 2007; Buckelew et al. 2007b). 

Similar hypothetical brodifacoum concentrations in lakes and the nearshore marine environment 

would be even lower. 

Marine water samples from the intertidal zone of Anacapa Island taken 24 and 48 hours after 

aerial brodifacoum bait application did not detect any brodifacoum (Howald et al. 2005). In a 

more extreme example, a truck transporting brodifacoum bait pellets in New Zealand went off a 

coastal road and spilled more than 20 tons into the nearshore environment. Just 36 hours after 

this catastrophic spill, researchers could no longer detect any brodifacoum in the water column at 

the center of the spill site. Furthermore, within nine days of the spill, even the marine sediment at 

the spill site no longer registered a detectable amount of brodifacoum. 

There is no reasonable likelihood that water bodies on or surrounding Rat Island will register 

biologically harmful, or even detectable, levels of brodifacoum as a result of bait application to 

the island. Samples will be collected before and after baiting and tested for brodifacoum. 

4.5.8. Impacts to Designated Wilderness 

The aircraft, equipment, tools, personnel and installations required to conduct a successful nonnative invasive rat eradication will produce short term negative impacts on the wilderness 

character of Rat Island. The eradication effort will require manipulation of the existing 

ecological processes in an effort to restore natural systems that have been disrupted through the 

introduction of an invasive species. The personnel and equipment necessary for the operation 

have the potential to decrease a visitor’s opportunity to experience solitude and unconfined 

recreation. However, due to the extremely remote the location of Rat Island it is unlikely visitors 

would be present during the eradication effort. The long term benefits of an enduring wilderness 

with restored ecological systems gained through a successful rat eradication are greater than the 

short term negative impacts the effort may have to the wilderness character of Rat Island. 

4.5.9. Impacts to Historical and Cultural Resources 

None of the temporary infrastructure that will be installed as part of the Proposed Action will be 

placed within the four historical sites selected by The Aleut Corporation. Personnel presence 

within these sites will be limited, and no activities that require disturbing the soil (such as 

infrastructure installation) will be conducted within them. Furthermore, personnel will be briefed 

on how to identify possible artifacts. Any artifacts or suspected historical sites that are found 

during project operations, both within and outside The Aleut Corporation-selected sites, will be 

mapped, clearly marked and avoided. As a result of these measures, there is no reasonable 

likelihood that personnel foot traffic will have impacts to archaeological or cultural resources 

within these sites and our knowledge of, and thus ability to protect, historical and cultural sites 

on Rat Island may actually be enhanced. 

The FWS is required by ANCSA to consult with The Aleut Corporation before conducting 

management actions that will affect the historical sites selected on Rat Island. Additionally, the 

102
Chapter 4: Environmental Consequences 

FWS will consult with the Region 7 FWS Regional Historical Preservation Officer before 

implementing the Proposed Action, as required under the National Historic Preservation Act. 

4.5.10. Impacts to Social and Economic Values 

4.5.10.1. Refuge visitors 

There are no records of recreational visits to Rat Island since the FWS began managing it in 

1913 as part of the original Aleutian Islands Refuge. However, up to four tour boats may pass 

within view of the island during a typical summer season. There is no reasonable risk that the 

Proposed Action will impact the health or safety of any Refuge visitors. However, interim scenic 

alteration of the island will be evident from the temporary field camps and small equipment 

storage structures, which will be partially visible from nearby waters for the duration of the 

project (from early summer through late fall). This visual alteration will degrade the pristine 

character of Rat Island, but this degradation will be temporary. By the summer season following 

eradication operations, visitors to Rat Island will no longer have their experience compromised 

in any way. In fact, in the intermediate to long term, an increase in nesting seabirds on the island 

after rats are removed will likely enhance the visitor experience of Rat Island as a wildlife 

refuge. 

4.5.10.2. Fishery resources 

The likelihood of marine fish being exposed to brodifacoum is negligible, and the likelihood of 

rat eradication activities having an impact on marine fish that is noticeable in a commercial 

fishery (either in the form of brodifacoum residues or catch amounts or compositions) is 

essentially nil. In advance of helicopter operations for bait application, any vessels in the vicinity 

of Rat Island will be notified of these planned activities and asked to avoid the island during this 

period of time. This request is not expected to noticeably impact the area’s fisheries. 

4.5.10.3. Subsistence resources 

There are no records of current or recent use of Rat Island by rural Alaskans, either for 

subsistence or cultural purposes. Due to its extreme isolation, there is no reasonable likelihood 

that the Proposed Action will affect the use of Rat Island for subsistence or recreational hunting 

or gathering by rural Alaskans or other island users. 

Some of the migratory bird species that use Rat Island may be harvested elsewhere on their 

migratory routes, particularly the Aleutian cackling geese that migrate eastward in fall along the 

Aleutian chain. However, observational studies have shown that geese are unlikely to consume 

bait pellets. There is therefore no reasonable likelihood that geese harvested elsewhere will carry 

any brodifacoum residue. In the extremely unlikely scenario that a goose or other bird that 

ingested brodifacoum on Rat Island was harvested elsewhere and consumed, there is no 

reasonable likelihood that a harmful quantity of brodifacoum will be ingested. Using the 

conservative LD50 value applied elsewhere in this analysis – 0.04 mg/kg – the average human 

103
Chapter 4: Environmental Consequences 

104

male would need to ingest the equivalent of between 400 and 600 bait pellets to reach a 50% risk 

of mortality. 

Regardless, the FWS will inform the hunting and subsistence use communities in the Aleutians 

of the minute theoretical risk of cackling geese being exposed to brodifacoum on Rat Island and 

then continuing their eastward migration. Because the goose migration season will likely begin 

before bait is applied to Rat Island, the FWS will encourage concerned hunters to harvest geese 

earlier in the season. There is no reasonable risk that migratory birds on Rat Island will be 

carrying brodifacoum residue by the subsequent fall migration. 

Figure 16. Field camp in Gunner’s Cove on Rat Island, 2007. 
Chapter 4: Environmental Consequences 

Table 4.3. Summary: Impacts of the Proposed Action, by issue Issue Sub-issue Likelihood and nature 

of impacts from rodenticide use 

Likelihood and nature of impacts from the operation 

Likelihood impacts 

Restoration efficacy 

NA NA Proposed ac

effectively erestore habit

Native biological resources 

Marine mammals (including listed species) 

Very unlikely Likely - disturbance (minor and 

temporary) 

Birds (including listed species) 

Taxon-dependent; mortality likely in some species 

Somewhat likely - localized nesting disturbances during early summer staging period 

Rat eradicatincreases in Rat Island 

Freshwater fish Very unlikely Very unlikely Plants None Likely - localized, temporary and 

mostly minor damage to native vegetation 

Rat eradicatchanges in tcommunities Island, towa

Water resources Very unlikely None Wilderness character 

None Likely - temporary structures and 

motorized equipment operation (no permanent effects) 

Rat eradicatwilderness c

Historical/cultural resources 

NA Unlikely 

Social/economic values 

Very unlikely Unlikely - temporary scenic 

alteration, visitation by public during operations is unlikely 
5. Consultation and Coordination 

5.1. PREPARERS

Laurie Daniel, Alaska Maritime National Wildlife Refuge 

Vernon Byrd, Alaska Maritime National Wildlife Refuge 

Steve Ebbert, Alaska Maritime National Wildlife Refuge 

Kent Sundseth, Alaska Maritime National Wildlife Refuge 

5.2. CONTRIBUTORS

Jacob Sheppard, Island Conservation 

Gregg Howald, Island Conservation 

Stacey Buckelew, Island Conservation 

Holly Jones, Island Conservation 

5.3. AGENCIES, ORGANIZATIONS, AND PERSONS CONSULTED 

FWS Alaska Regional Office: 

Tom Melius, Regional Director 

Todd Logan, Refuges Division Chief 

Mike Boylan, Refuges Supervisor 

Lenny Corin, Fisheries and Ecological Services Division Supervisor 

Phil Johnson, Environmental Contaminants Division Supervisory Biologist 

Ann Rappoport, Anchorage Field Office Supervior 

Greg Balogh, Endangered Species Division Chief 

Ellen Lance, Endangered Species Biologist 

Doug Burn, Marine Mammals Division Supervisory Biologist: Sea otter 

Angie Doroff, Marine Mammals Biologist: Sea otter 

Denny Lassuy, Invasive Species Coordinator 

Helen Clough, Conservation Planning and Policy Division Chief 

Danielle Jerry, Realty and Natural Resources Division Chief 

Debbie Corbett, Regional Archaeologist, Cultural Resource Management Program 

Department of the Interior (DOI): 

Hans Neidig, Special Assistant to the Secretary of the Interior for Alaska 

NMFS: 

Mike Williams, NMFS Protected Resources Division, Anchorage 

 
Chapter 5: Consultation and Coordination

Lowell Fritz, NMFS National Marine Mammal Laboratory, Seattle 

Department of Agriculture (USDA)/APHIS: 

Corey Rossi, Wildlife Services Alaska District Supervisor 

John Eisemann, National Wildlife Research Center, Registration Manager 

State of Alaska: 

Rosemarie Lombardi, ADEC Pesticide Program 

Tammy Davis, ADF&G Statewide Invasive Species Coordinator 

Forrest Bowers, ADF&G Bering Sea-Aleutian Islands Area Mgt Biologist, Dutch Harbor 

Christine Schmale, ADF&G Wildlife Conservation, harbor seal research program 

Ellen Fritts, ADF&G Wildlife Conservation Statewide Invasive Rodent Mgt Plan 

Karol Kolehmainen, ACMP, Aleutians West CRSA Coordinator 

Judy Bittner, State Historic Preservation Officer 

Congressional Delegation staff: 

Jim Egan, for Senator Stevens 

Bob Walsh, for Senator Murkowski 

Greg Kaplan, for Congressman Young 

Alaska Native Organizations: 

The Aleut Corporation – Thomas Mack, President and Troy Johnson, CEO 

Aleutian/Pribilof Islands Assoc. (APIA) – Karen Pletnikoff, Environmental Program Mgr. 

NGOs: 

The Nature Conservancy – Steve MacLean, Bering Sea Program Manager 

Alaska Community Action on Toxics (ACAT) – Pam Miller, Executive Director 

Wilderness Society – Nicole Whittington-Evans, Associate Regional Director 

107
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Cory’s shearwater Calonectris diomedea in Corsica. Marine Ornithology 23(1): 1-10. 

Tobin, M.E. and M.W. Fall. 2005. Pest control: Rodents. In: Agricultural Sciences, Encyclopedia 

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Tomich, P.Q. 1986. Mammals in Hawai`i. 2nd edition. Bishop Museum Press, Honolulu, HI. 

Tomkins, R.J. 1985. Breeding success and mortality of dark-rumped petrels in the Galápagos, 

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US Fish and Wildlife Service. 1993. Environmental Assessment – Proposed Emergency Use of 

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US Fish and Wildlife Service. 1997. Threatened fish and wildlife; change in listing status of 

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US Fish and Wildlife Service. 1999. Endangered and threatened wildlife and plants; proposal to 

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Veltre, D.W. and M.J. Veltre. 1983. Resource utilization in Atka, Aleutian Islands, Alaska. 

Alaska Department of Fish and Game, Division of Subsistence. Technical Paper Number 88. 

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Washington, D.C., and The American Ornithologists’ Union, Philadelphia, PA. 

Williams, J. and G. Howald. 2007. Wildlife observations at Rat Island, September 4-6, 2002. US 

Fish and Wildlife Service Report: AMNWR 07/03. Homer, AK. 

Withrow, D.E., G.C. Bouchet and L.L. Jones. 1985. Response of Dall’s porpoise (Phocenoides 

dalli) to survey vessels in both offshore and nearshore waters: Results of 1984 research. Int. N. 

Pacific Fish. Comm. Doc. U.S. Natl. Mar Mammal. Lab., Seattle, WA 

Witmer, G. 2005. Field efficacy trial of 0.005% diphacinone broadcast bait to control introduced 

Norway rats on Kiska Island, Alaska. Unpublished Final Report, QA-1229. USADA/APHIS/WS 

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Juneau, AK. 

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resources. Chapman and Hall, London 
Appendix 1: The status of birds that are likely to be present at Rat Island in 

Common name Scientific name Status at Rat I. Special 

protection 

Likely Status in SeptemberOctober 

Emperor goose Chen canagica Winter 

resident 

Most not present until November 

Aleutian cackling goose Branta canadensis

leucopareia

Rare breeder and migrant 

State Species of Special Concern 

Passing flocks primarily in Sept. 

Aleutian green-winged teal Anas crecca nimia Probably 

resident 

Present in low numbers 

Pacific common eider Somateria mollissima 

v-nigrum

Resident Present in 

nearshore marine waters 

Harlequin duck Histrionicus histrionicus Resident, nonbreeders in 

summer 

Wintering birds arriving in October 

Rock ptarmigan Lagopus muta townsendi Resident present in small 

flocks 

Fork-tailed storm-petrel Oceanodroma furcata Present on islet 

off Ayugadak Pt. 

Not likely present on the main island 

Leach’s storm-petrel Oceanodroma leucorhoa Present on islet 

off Ayugadak Pt. 

Not likely present on the main island 

Red-faced cormorant Phalacrocorax pelagicus Possibly resident Low numbers in 

nearshore marine waters 

Pelagic cormorant Phalacrocorax urile Resident Low numbers in 

nearshore marine waters 

Bald eagle Haliaeetus 

leucocephalus

Probably resident 

Protected under BGEPA 

Present on cliffs and bluffs 

Peregrine falcon Falco peregrinus pealei Resident Present on cliffs Pacific golden plover Pluvialis fulva Seasonal 

migrant 

Passing birds possibly present 
Appendix 1: Status of birds likely to be present at Rat Island in the fall 

Common name Scientific name Status at Rat I. Special 

protection 

Likely Status in SeptemberOctober 

Black oystercatcher Haematopus bachmani Resident Present in 

intertidal 

Wandering tattler Heteroscelus incanus Seasonal 

migrant 

Present in small numbers in intertidal 

Ruddy turnstone Arenaria interpres Seasonal 

migrant 

Present in small numbers in intertidal 

Pectoral sandpiper Calidris melanotos Seasonal 

migrant 

Present in small numbers in upland 

Sharp-tailed sandpiper Calidris acuminata Seasonal 

migrant 

Present in small numbers in upland 

Rock sandpiper Calidris ptilocnemis Resident Present in 

intertidal zone 

Glaucous-winged gull Larus glaucescens Resident Present in 

intertidal zone 

Parasitic jaeger Stercorarius parasiticus Possibly 

breeding 

Present in upland 

Pigeon guillemot Cepphus columba Resident Present in 

nearshore marine waters 

Whiskered auklet Aethia pygmaea Possibly nesting 

on islet off Ayugadak Pt. 

A few present in nearshore waters 

Horned puffin Fratercula corniculata Likely breeding 

in cliff crevices 

A few present in nearshore marine waters 

Tufted puffin Fratercula cirrhata Breed on islet off 

Ayugadak Pt. 

Present in 

nearshore marine waters 

Short-eared owl Asio flammeus Seasonal 

migrant 

One or two possibly present in uplands 

Common raven Corvus corax Very rare visitor 

apparently 

One or two birds possibly present 
Appendix 1: Status of birds likely to be present at Rat Island in the fall 

Common name Scientific name Status at Rat I. Special 

protection 

Likely Status in SeptemberOctober 

Winter wren Troglodytes troglodytes Resident Present near 

beaches 

Song sparrow Melospiza melodia Rare on Rat I., 

common resident on islet off Ayugadak Pt. 

Possibly one or two present on Rat I. near beaches 

Lapland longspur Calcarius lapponicus Breeding Pre-migratory 

flocks in September 

Snow bunting Plectrophenax nivalis Possibly resident Present in uplands Gray-crowned rosy-finch Leucosticte tephrocotus

griseonucha

Possibly resident Present in coastal 

areas 

Data from: Gibson and Byrd 2007; Buckelew et al. 2007b, and from historic observations documented in Appendix 2.
Appendix 2: Historical observations of Wildlife at Rat Island (1937 – 2

Species 1937 Notes 1969 Notes 1982 Notes 1984 Notes 1989 Notes 2002 Notes BIRDS Mallard P 

No broods observed 

N. Pintail P 

No broods observed 1 

N. Shoveler P 

No broods observed 

Green-winged Teal 2 pair P 

No broods observed 15 

one w/brood 6 

Greater Scaup P 

No broods observed 

Common Eider 30 50 P 

No broods observed 72 

Harlequin Duck + a few seen 52 P 22 106 Rock Ptarmigan + 

several seen P

1 nest, <6 birds 15 50+ plus broods 

Yellow-billed Loon 1 skull found Fork-tailed Storm-Petrel P

Seen from ship offshore 

Unid Cormorant 157 P 50 

>50 both species 

Pelagic Cormorant + a few noted 6 1 Red-faced Cormorant 3 7 Bald Eagle 8 4 pairs 4 nests 14 P 11 9 ad., 2 im 12 Peregrine Falcon 6 P 1 <11 

count includes duplicates 

Osprey ?

Reported but doubtful 

Black Oytercatcher 4 2 pairs 2 P 

None nesting 8 1 

Whimbrel 1 Ruddy Turnstone PRinged/Semipal. Plover 1 Species 1937 Notes 1969 Notes 1982 Notes 1984 Notes 1989 Notes 2002 Notes Rock Sandpiper + several P 4 20 Parasitic Jaeger 4 2 pairs 1 P 

2 seen all summer 8 
Appendix 2: Historical observations of wildlife at Rat Island, 1937-2004 

Species 1937 Notes 1969 Notes 1982 Notes 1984 Notes 1989 Notes 2002 Notes Oriental Cuckoo 1 specimen Glaucouswinged Gull + common P 100 500+ Common Murre 12 Thick-billed Murre Pigeon Guillemot + a few 56 + 

scattered adults, 1 fledgling 

Marbled Murrelet Ancient Murrelet 12 dozen + 125 P Parakeet Auklet 2 Crested Auklet 4 P Whiskered Auklet P

seen from ship offshore 

Least Auklet 1 Horned Puffin + only a few 56 Tufted Puffin + a few 210 Common Raven 4 P Winter Wren P C 

common near beaches 6 

Gray-crowned Rosy-Finch + several P 1 5 Snow Bunting + common P 4 Song Sparrow P 1 Lapland Longspur + common P C 

common in interior 300+ 

MARINE MAMMALS Harbor Seal 22 

on beach 1 mi e. Krysi Pt. 25 

Sea Otter + abundant Steller Sea Lion 

a few near Ayugadak Pt. 

SOURCE Murie 1937 

Berns 1969 

Dragoo & Deines 1983 

Hanson et. al. 1984 Byrd 1989 

Williams and Howald 2007 

DATES OF SURVEY 

29-Jun1937 1-Jul- 2007 25 May-29 July 84 12-Aug-1989 4-6 Sept. 2002 
Appendix 3: Minimum Requirements Decision Guide 

ARTHUR CARHART NATIONAL WILDERNESS TRAINING CENTER 

MINIMUM REQUIREMENTS 

 DECISION GUIDE 

WORKSHEETS 

“. . . except as necessary to meet minimum requirements for the administration of the 

area for the purpose of this Act...” 

– the Wilderness Act, 1964 

Please refer to the accompanying MRDG Instructions for filling out this guide. 

The spaces in the worksheets will expand as necessary as you enter your response.

Step 1: Determine if any administrative action is necessary. 

Description: Briefly describe the situation that may prompt action. 

After their introduction more than 200 years ago, rats dramatically changed the natural 

ecological processes of Rat Island in the western Aleutian Island archipelago. Prior to this 

introduction, the island supported significant populations of breeding seabirds and other ground 

nesting birds which evolved in the absence of mammalian predators. Rats have also had 

detrimental impacts on the vegetation and inter-tidal life of the island. Eradicating rats from this 

island would restore wilderness character and allow for the recovery of extirpated wildlife 

populations on this wilderness island. 

 
Appendix 3: Minimum Requirements Decision Guide 

To determine if administrative action is necessary, answer the questions listed in A - F 

on the following pages.

A. Describe Options Outside of Wilderness 

Is action necessary within wilderness?

 Yes: No: 

 

 

Explain: 

More than ten islands in the Aleutian archipelago have had rats introduced to them. However, 

not all of these islands are suitable for a successful rat eradication project. For a rat eradication 

effort to be feasible with existing technology, an island must be less than 10,000 acres and must 

not be within 2 km of an island which also supports a population of rats. These requirements 

narrow the list to a small number of islands which have some, if not all of their acres as 

wilderness. Conducting a successful rat eradication to restore natural diversity in the Aleutian 

Islands isn’t possible outside of wilderness. 

B. Describe Valid Existing Rights or Special Provisions of Wilderness Legislation 

Is action necessary to satisfy valid existing rights or a special provision in wilderness legislation (the 

Wilderness Act of 1964 or subsequent wilderness laws) that allows consideration of the Section 4(c) 

prohibited uses? Cite law and section.

 Yes: No: Not Applicable: 

Explain: 

There are no special provisions that apply in the Wilderness Act (1964). 

C. Describe Requirements of Other Legislation 

Is action necessary to meet the requirements of other laws?

 Yes: No: Not Applicable: 

Explain: 

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Appendix 3: Minimum Requirements Decision Guide 

One of the establishing purposes of Alaska Maritime NWR set forth in PL 96-487; ANILCA 

Section 303(1)(B)(i) is “to conserve fish and wildlife populations in their natural diversity...”. 

D. Describe Other Guidance 

Is action necessary to conform to direction contained in agency policy, unit and wilderness management 

plans, species recovery plans, tribal government agreements, state and local government and 

interagency agreements? 

Yes: No: Not Applicable: 

Explain:

The Alaska Maritime NWR Comprehensive Conservation Plan recognizes the detrimental 

impacts of introduced predators to refuge resources and that their removal would provide the 

most tangible benefits possible for the restoration of bird populations and species diversity. 

Wilderness management guidance found in U.S. Fish and Wildlife Service Policy 6 RM 8.8 

states “Motorized equipment may be used in special circumstances if it is the minimum tool 

necessary to accomplish a task safely and without long term impairment of the area’s wilderness 

character.” National Wildlife Refuge System Policy on Biointegrity 601 FW3 directs refuges 

to “control populations of invasive species, and provide for restoration of native species and 

habitat conditions in invaded ecosystems.” Presidential Executive Order 13112 on Invasive 

Species directs Federal agencies whose actions may affect the status of invasive species to 

“detect and respond rapidly to and control populations of such species in a cost-effective and 

environmentally sound manner”.

E. Wilderness Character 

Is action necessary to preserve the qualities of wilderness character including: untrammeled, 

undeveloped, natural, outstanding opportunities for solitude or a primitive and unconfined type of 

recreation, or unique components that reflect the character of this wilderness area? 

Untrammeled: Yes: No: Not Applicable: No Change:

Explain: 

The untrammeled character of this wilderness has already been affected through human influence 

since rats were introduced by shipwreck over 200 years ago. However, an effort to eradicate this 

invasive species might also be construed as a manipulation of natural processes that negatively 

affects the untrammeled character of this wilderness. 

Undeveloped: Yes: No: Not Applicable: No Change: 

Explain:

131
Appendix 3: Minimum Requirements Decision Guide 

The proposed action would require the use of temporary platforms and mechanized equipment 

over a short period of time. However, this would not result in any permanent improvements of 

the island and it would retain its undeveloped character. 

Natural: Yes: No: Not Applicable: No Change: 

Explain: 

Over time, rats have disrupted the natural ecological systems of the island. Rat Island lost its 

primeval character and differs from neighboring wilderness islands which have not been altered 

through human influence. Successfully eradicating rats from the island would restore the 

wilderness character of this area. 

Outstanding opportunities for solitude or a primitive and unconfined type of recreation:

 Yes: No: Not Applicable: No Change: 

Explain: 

The personnel and equipment necessary for this operation have the potential to decrease a 

visitor’s opportunity to experience solitude and unconfined recreation. However, Rat Island is so 

remote it is unlikely visitors would be present during the proposed eradication. 

Other unique components that reflect the character of this wilderness 

Yes: No: Not Applicable: No Change: 

Explain:

F. Describe Effects to the Public Purposes of Wilderness 

Is action necessary to support the public purposes for wilderness (as stated in Section 4(b) of the 

Wilderness Act) of recreation, scenic, scientific, education, conservation, and historical use?

Recreation: Yes: No: Not Applicable: 

Explain:

Scenic: Yes: No: Not Applicable: 

Explain:

Rats feed extensively on vegetation and their activity alters habitats affects the distribution of 

certain plants species over time. Rats have caused the extirpation of seabird colonies which 

previously provided scenic value to this wilderness. 

Scientific: Yes: No: Not Applicable: 

Explain:

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Appendix 3: Minimum Requirements Decision Guide 

A successful rat eradication would provide valuable information about how natural systems 

recover from the elimination of an invasive species. This information would be available for 

public education. 

Education: Yes: No: Not Applicable: 

Explain:

Conservation: Yes: No: Not Applicable: 

Explain:

The removal of rats from the island would allow species that had been extirpated from the island 

to re-colonize. This would allow the public to experience an area that has regained its primeval 

character.

Historical use: Yes: No: Not Applicable: 

Explain: 

Step 1 Decision: Is any administrative action necessary in wilderness? 

Yes: No: More information needed: 

Explain:

The presence of rats has changed the natural wilderness character of Rat Island. The proposed 

invasive rat eradication would restore natural ecological processes that have been disrupted for 

more than 200 years. The Wilderness Act provides agencies with a responsibility to preserve the 

wilderness character of the areas they administer. This project would allow the agency to meet 

it’s responsibilities to preserve the wilderness character of Rat Island, provide for public 

purposes associated with wilderness, restore native wildlife populations and secure an enduring 

resource of wilderness for the nation. 

If action is necessary, proceed to Step 2 to determine the minimum activity. 

133
Appendix 3: Minimum Requirements Decision Guide 

Step 2: Determine the minimum activity.

Please refer to the accompanying MRDG Instructions for an explanation of the effects 

criteria displayed below. 

Description of Alternatives 

For each alternative, describe what methods and techniques will be used, when the activity 

will take place, where the activity will take place, what mitigation measures are necessary, 

and the general effects to the wilderness resource and character. 

Alternative #1, No Action 

Description: 

An eradication of invasive rats on Rat Island would not be conducted.

Effects: 

 Wilderness Character

 “Untrammeled” 

The existing components or processes of ecological systems of Rat Island would 

not be manipulated if the eradication is not conducted. The current conditions are 

influenced by the presence of an invasive species. 

 “Undeveloped” 

It would not be necessary to construct temporary structures. The imprint of human 

activity would be unnoticed. 

 “Natural” 

Natural conditions and ecological systems on the island would continue to be 

disrupted by the presence of invasive rats. Restoration of conditions on the island 

to support the natural biological diversity of the region would not be possible. 

 “Outstanding opportunities for solitude or a primitive and unconfined type of 

recreation” 

Opportunities for visitors to experience solitude and unconfined recreation would 

be maintained. However, visitors will not experience the diversity of wildlife 

species present on nearby wilderness islands due to the presence of rats. 

 Heritage and Cultural Resources 

Cultural resource sites could not be disturbed by human activity associated with 

eradication operations if no action is taken. The burrowing and chewing activities of rats 

have the potential to damage or disturb cultural artifacts found in ancient house pits and 

midden sites. 

134
Appendix 3: Minimum Requirements Decision Guide 

 Maintaining Traditional Skills 

Traditional skills and travel methods will not be used if the proposed eradication does not 

occur. 

 Special Provisions 

No special provisions or rights identified in the Wilderness Act or other legislation will 

apply if the proposed action is not taken. 

 Safety of Visitors, Personnel, and Contractors 

 The safety of personnel will not be a factor if no action is taken. 

 Economic and Time Constraints 

No funding will be required and time constraints will not be applicable if no action is 

taken. 

 Additional Wilderness-specific Comparison Criteria 

None identified. 

Alternative # 2 

Invasive Rat Eradication using Equipment, Rodenticide and Temporary 

Structures 

Description: 

An invasive rat eradication would be conducted on Rat Island using equipment, and helicopters 

to broadcast rodenticide on Rat Island. It would require the use of power tools to construct tent 

platforms and landing platforms for the helicopters. Large concrete blocks will be used to 

anchor the helicopters when not in use. Generators would be used at times to supply electricity 

for electronic equipment essential to the success and safety of the operation. 

Effects: 

 Wilderness Character

 “Untrammeled” 

The existing ecological process influenced by the long term presence of an 

invasive species will be significantly manipulated by the rat eradication. The 

manipulation is intended to restore the ecological components present prior to the 

introduction of rats. 

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Appendix 3: Minimum Requirements Decision Guide 

 “Undeveloped” 

The structures necessary for the successful completion of the proposed eradication 

will result in increased visibility of man’s work. 

 “Natural” 

Successful completion of the proposed eradication would eliminate an invasive 

species that has been present on the island for over 200 years. The action would 

allow the natural biological diversity to recover and restore the natural conditions 

of the island prior to the introduction of an invasive species. 

 “Outstanding opportunities for solitude or a primitive and unconfined type of 

 recreation” 

During the six week duration of the proposed eradication effort, the opportunity for 

visitors to experience solitude will be adversely affected. Over time, the 

eradication would restore natural conditions that would enhance the wilderness 

experience of visitors. 

 Heritage and Cultural Resources 

The eradication effort would not adversely affect the cultural resources known to exist on 

Rat Island. Eradication of the rats may provide some protection to artifacts at risk from 

the burrowing and chewing activities of rats. 

 Maintaining Traditional Skills 

The eradication effort will not involve the use of traditional skills. 

 Special Provisions

 No special provisions apply to the proposed eradication effort. 

 Safety of Visitors, Personnel, and Contractors 

There is a risk to agency personnel and contractors when traveling over rough terrain and 

through the use of tools and equipment. In particular, the use of helicopters brings an 

additional level of risk. All required certifications, training and protective equipment 

requirements will be met during the proposed operation. The weather in the Aleutian 

Islands poses risks that are uncontrollable, but can be minimized through proper planning 

and preparedness. 

 Economic and Time Constraints 

The estimated cost for this project is $2.4 million and the eradication work on the island is 

expected to take six weeks. The large size and rugged terrain of Rat Island coupled with 

the limited time frame available to broadcast the rodenticide makes this alternative the 

only method with a reasonable expectation of success. 

 Additional Wilderness-specific Comparison Criteria

None identified.

136
Appendix 3: Minimum Requirements Decision Guide 

Step 2 Decision: What is the Minimum Activity? 

Please refer to the accompanying MRDG Instructions before describing the selected 

alternative and describing the rationale for selection. 

Selected alternative: Alternative #2 

An eradication of non-native rats will be implemented in the fall of 2008 on Rat Island. The 

rats will be eradicated using cereal grain pellets containing the rodenticide brodifacoum 

broadcast over the island surface from hoppers slung beneath two helicopters. Total 

helicopter flight time for the bait distribution will take approximately 70 hours. The operation 

will occur over a six week period and require a crew of approximately 20 people. No 

overland mechanized transport will be used. 

Field camp and support facilities for the operation will require the installation of 15 – 20 tent 

platforms and three bait loading platforms that will be pre-fabricated prior to arrival at Rat 

Island. Some limited use of motorized drills may be necessary to install the platforms. 

Helicopters would also be used to transport bait and fuel to three staging areas. Two small 

generators would be used to supply power for equipment critical to the success and safety of 

the operation. Helicopters would be used to transport any unused fuel, bait, or other material 

associated with the staging areas off the island. 

Rationale for selecting this alternative: 

This alternative is the only method with a reasonable chance of successfully eradicating nonnative invasive rats from Rat Island. Rats occupy a variety of habitats across the entire island 

and multiply quickly. A successful eradication requires that a lethal dose of rodenticide is 

delivered to every rat on the island quickly enough for the bait to be consumed before it 

deteriorates. Broadcasting the bait across the island with helicopters is the only method that 

can distribute the bait evenly across the rugged terrain of the entire island in the time needed 

to be effective. Although the use of helicopters, platforms and some equipment will cause 

adverse impacts to wilderness character over the short term, a successful eradication will 

restore wilderness character that has been lost due to the presence of an invasive species. 

Monitoring and reporting requirements: 

Following the completion of the project, the removal of all material, equipment, structures 

and installations will be documented and filed at the headquarters of Alaska Maritime NWR. 

Check any Wilderness Act Section 4(c) uses approved in this alternative: 

 mechanical transport landing of aircraft

 motorized equipment temporary road

137
Appendix 3: Minimum Requirements Decision Guide 

 motor vehicles structure or installation

 motorboats 

Record and report any authorizations of Wilderness Act Section 4(c) uses according to agency 

procedures.

 

Approvals Signature Name Position Date 

Prepared by: 

Recommended: 

Recommended: 

Approved: 

138
Appendix 4: ANILCA 810 Evaluation 

Alaska Maritime National Wildlife Refuge 

Evaluation of the Effects on Subsistence Uses and Needs 

(ANILCA Section 810 Evaluation) 

The U.S. Fish and Wildlife Service, acting for the Secretary, is required by Section 810 of the 

Alaska National Interest Lands Conservation Act (ANILCA) to evaluate the effects on 

subsistence uses and needs in determining whether to withdraw, reserve, lease, or otherwise 

permit the use, occupancy, or disposition of public lands on national wildlife refuges in Alaska. 

The evaluation of effects of this Proposed Action or use on subsistence uses and needs is 

documented below. If this evaluation concludes a finding that the Proposed Action would result 

in significant restriction to subsistence uses, and we wish to proceed, we must initiate further 

procedural requirements of Section 810. 

Proposed Action/Use: 

Rat Island is a remote, uninhabited island located in the central Aleutian Islands, Alaska. 

Norway rats (Rattus norvegicus) were introduced to Rat Island by shipwreck in the 1780’s. 

Since that time, rats have caused adverse impacts to natural species on the island and extirpated 

nesting seabirds. The purpose of the Proposed Action is to eradicate introduced, non-native rats 

from Rat Island and maintain it’s rodent free status, which will facilitate the restoration of the 

natural island ecosystem and improve habitat quality for many of the native species. 

To accomplish the Proposed Action, Alaska Maritime NWR has partnered with The Nature 

Conservancy and Island Conservation to eradicate non-native Norway rats from Rat Island. 

A successful eradication will require rodenticide to be delivered into every potential rat territory 

on the island and timing the eradication to maximize the probability that 100% of the rat 

population will be exposed to the rodenticide. A re-introduction of rats to the island must also be 

prevented. This method of eradication involves an aerial application of a grain pellet, containing 

rodenticide, using specialized spreader buckets suspended beneath helicopters. The eradication 

is scheduled to be initiated in fall of the year, which coincides with the completion of the rat 

breeding cycle and a natural rat food resource decline on the island. The combination of food 

scarcity with bait availability to all rat territories on the island maximizes the potential for 

successful eradication. A more thorough description of the project including maps of the project 

area can be found in the Environmental Assessment, Restoring Wildlife Habitat on Rat Island 

(USFWS 2007). 

Evaluation: 

1. Subsistence Resources, Uses and Needs in the Affected Area: 

 
Appendix 4: ANILCA 810 evaluation 

In the Aleutians, residents have traditionally made use of the following types of resources: 

marine resources, including fish, (salmon, halibut, cod, etc.); marine mammals (Stellar sea lions, 

sea otters and harbor seals); intertidal resources such as sea urchins, razor clams, butter clams, 

cockles, mussels, and chitons, crab and shrimp. Plants harvested include berries (blueberries, 

salmonberries, mossberries, strawberries, and lingonberries), wild celery (Angelica lucida), wild 

rice (Fritillaria camschatcensis) giant kelp, and fiddlehead ferns. Birds are harvested, including 

ducks, geese, or ptarmigan. Eggs are collected primarily from gull colonies, although mallard, 

merganser, puffin, and murre eggs are also collected, depending on the location. 

2. Effect of Proposed Action or Use on Subsistence Uses and Needs. 

The propsed action should have no effect on subsistence uses or needs. Rat Island is uninhabited 

and is located more than 322 km (200 mi) from the nearest rural community of Adak, Alaska. 

The subsistence resources used by rural residents in the Aleutian Islands are harvested near the 

islands where the communities are located. Rat Island is not known to have been used for 

subsistence purposes since the 1800’s. 

3. Availability of other lands for the purpose sought to be achieved. 

The goal of the proposed project is to restore the natural diversity of species and habitats to Rat 

Island. Therefore, no other lands can be used to achieve the purpose. 

4. Alternatives which would reduce or eliminate the Proposed Action from lands needed 

for subsistence purposes. 

There is no way to accommodate the Proposed Action other than to conduct a rat eradication on 

Rat Island. If successful, the project has the potential to restore traditional subsistence resources. 

Finding: 

Based on review and evaluation of information indicated above and in the supporting references 

indicated below, I have determined that the Proposed Action will not result in a significant 

restriction of subsistence uses. The Proposed Action will occur hundreds of miles from the 

nearest rural community and the island intended for restoration has not been used for subsistence 

purposes in over a century. If successful, the Proposed Action has the potential to restore 

populations of traditional subsistence resources. 

Agency Decision: 

A finding of no significant restriction in subsistence uses completes the Section 810 

requirements. The Proposed Action or use may be authorized. 

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Appendix 4: ANILCA 810 evaluation 

Supporting References: 

Alaska Policy Manual, U.S. Fish and Wildlife Service 

Alaska Maritime National Wildlife Refuge, Final Comprehensive Conservation Plan, 

Environmental Impact Statement, Wilderness Review. Record of Decision signed August 26, 

1988. 

Alaska National Interest Lands Conservation Act (ANILCA), 1980. 

Service Manual - Region 7, U.S. Fish and Wildlife Service 

Subsistence Management for Federal Public Lands in Alaska, Final., 1992 

Fall, James A. Amy Paige, Vicki Vanek, and Louis Brown. 1998. Subsistence harvests and uses 

of birds and eggs in fours communities of the Aleutian Islands area; Akutan, False Pass, Nelson 

Lagoon, and Nikolski. Alaska Department of Fish and Game, Division of Subsistence, Technical 

Paper No. 243. Juneau. 

Veltre, Douglas W. and Mary J. Veltre. 1981. Resource Utilization in Unalaska, Aleutian 

Islands, Alaska. Alaska Department of Fish and Game, Division of Subsistence. Technical Paper 

Number 58. Contract 82-0790. 

Veltre, Douglas W. and Mary J. Veltre. 1983. Resource utilization in Atka, Aleutian Islands, 

Alaska. Alaska Department of Fish and Game, Division of Subsistence. Technical Paper Number 

88. Contract 83-0496. 

Wolfe, Robert J. and Amy W. Paige, Cheryl l. Scott. 1990. The subsistence harvest of migratory 

birds in Alaska. Alaska Department of Fish and Game, Division of Subsistence Technical Paper 

No. 197. Juneau. 

 Signature: 

 

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