U.S. Department of the Interior. 

U.S. Geological Survey. 

Prepared in Cooperation with the U.S. Fish and Wildlife Service. 

Status Assessment and Conservation Plan 

for the Yellow-billed Loon (Gavia adamsii). 

Scientific Investigations Report 2004-5258. 
Status Assessment and Conservation Plan 

for the Yellow-billed Loon (Gavia adamsii)

U.S. Department of the Interior

U.S. Geological Survey

By Susan L. Earnst

U.S. Geological Survey.

Prepared in Cooperation with the U.S. Fish and Wildlife Service 

Scientific Investigations Report 2004–5258
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

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Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Suggested citation:

Earnst, S.L. 2004, Status Assessment and Conservation Plan for the Yellow-billed Loon (Gavia adamsii). 

U.S. Geological Survey, Scientific Investigations Report 2004-5258, 42 p.

Key words:

1. Yelllow-billed Loon. 2. Gavia adamsii. 3. Arctic. 4. Population size. 5. Population trend. 6. Distribution. 7. Alaska. 

8. National Petroleum Reserve-Alaska. 
Acknowledgments iii

Acknowledgments.

Funding to prepare this report was provided by the Nongame Bird Office, Division of Migratory Birds, Region 7, U.S. Fish and Wildlife Service. Kent Wohl, Brad Andres, Russ Oates, and 

Robert Leedy have been instrumental in supporting research and monitoring of Yellow-billed 

Loons and other loon species throughout Alaska. Discussions during annual Alaska Loon and 

Grebe Working Group meetings provided the framework for the Conservation Plan. I am grateful 

to the many individuals who shared unpublished materials and their expertise: Julian Fischer, 

Rodney King, Kathy Kuletz, William Larned, Ed Mallek, Philip Martin, Robert Platte, Robert 

Stehn, Ted Swem, Cynthia Wentworth, Debbie Wong (U.S. Fish and Wildlife Service); Amy Van 

Atten, Brian Fadely, and Kim Rivera (National Marine Fisheries Service); Suzanne Georgette 

and Sverre Pedersen (Alaska Department of Fish and Game); Jon Bart and Joel Schmutz (U.S. 

Geological Survey); Jeremy Kerr and Richard Fernandes (Canada Centre for Remote Sensing); 

Rick Johnson (ABR Inc.); David Evers (BioDiversity Research Institute); Kate Taylor (Loon Preservation Committee, Audubon Society of New Hampshire); Jeff Fair (Fairwinds Wildlife Services); 

and Tracey Gotthardt (Alaska Natural Heritage Program). The manuscript benefited from careful 

reviews by David Evers, Jeff Fair, Philip Martin, Judith McIntyre, Tamara Mills, Michael North, 

Robert Platte, Joel Schmutz, Kent Wohl, and 3 anonymous reviewers. Thanks to Ed Starkey and 

Ruth Jacobs (U.S. Geological Survey) for facilitating publication, to Erik Ackerson (Earth Design, 

Ink) for patiently and professionally preparing the layout and design, and to Ariel Pearlson for 

technical editing. Thanks to our many field assistants who made the Colville loon study possible 

and enjoyable.

Photographs on back cover by Paul Anderson (airplane over North Slope lakes), Charles 

Eldermire (loon landing on the Colville River Delta), and NASA (infrared imagery of the Colville 

River Delta purchased from AirMap U.S., Inc, Anchorage, Alaska). Other photographs taken by 

the author on the Colville River Delta. Thanks to Jeff Stephens for the illustration of the adult 

and chicks on page 36.
iv Status Assessment and Conservation Plan for the Yellow-billed Loon
Contents v

Contents. 

Abstract. ......................................................................................................................................................... 1. 

Status Assessment. ...................................................................................................................................... 2. 

1. Taxonomy. ......................................................................................................................................... 2. 

2. Legal Status. .................................................................................................................................... 2. 

3. Description. ...................................................................................................................................... 2. 

4. Range. ............................................................................................................................................... 3. 

5. Life-history Summary. .................................................................................................................... 4. 

A. Habitat Requirements. .......................................................................................................... 4. 

B. Reproductive Ecology. .......................................................................................................... 7. 

C. Demography. ........................................................................................................................... 9. 

D. Feeding Ecology. .................................................................................................................... 9. 

E. Movements and Migration. ................................................................................................ 10. 

F. Breeding Philopatry and Juvenile Dispersal. .................................................................. 10. 

G. Mortality. ............................................................................................................................... 11. 

6. Population Distribution, Size, and Trends. ................................................................................ 11. 

A. Relative Abundance and Distribution in Alaska. ............................................................ 11. 

B. Relative Abundance and Distribution in Canada. .......................................................... 13. 

C. Relative Abundance and Distribution in Russia. ............................................................ 13. 

D. Relative Abundance and Distribution on Wintering Sites. ........................................... 13. 

E. Population Size. ................................................................................................................... 14. 

F. Population Trends. ............................................................................................................... 15. 

7. Potential Threats to the Population. .......................................................................................... 17. 

A. Habitat Loss on the Breeding Grounds. ........................................................................... 17. 

B. Habitat Conservation on the Breeding Grounds . .......................................................... 20 

C. Habitat Loss and Mortality on the Wintering Grounds. ................................................. 21. 

D. Human Utilization: Subsistence Harvest and Fisheries Bycatch. ............................... 21. 

E. Disease or Predation. ......................................................................................................... 22. 

F. Other Anthropogenic and Natural Factors—Contaminants. ....................................... 23. 

8. Current Protection of Populations and Habitats. ..................................................................... 24. 

A. Current Protective Status of Yellow-billed Loons. ......................................................... 24. 

B. Land Ownership and Existing Habitat Protection. ......................................................... 24 

9. Current Conservation, Monitoring, and Research Actions. ................................................... 24 

A. Conservation and Education. ............................................................................................. 24. 

B. Monitoring Abundance on the Breeding Grounds. ........................................................ 25. 

C. Other Monitoring . ............................................................................................................... 27. 

D. Research. .............................................................................................................................. 30. 

Conservation Plan . ..................................................................................................................................... 33. 

Conservation Goal. ............................................................................................................................ 33. 

Research and Monitoring Goal. ...................................................................................................... 33. 

Research and Monitoring Objectives and Strategies. ............................................................... 33. 

Literature Cited. ........................................................................................................................................... 37. 
vi Status Assessment and Conservation Plan for the Yellow-billed Loon

List of Figures.

1. World-wide Yellow-billed Loon breeding and wintering range. .................................................... 3.

2. Yellow-billed Loon breeding and wintering range in Alaska. ......................................................... 4.

3. Relative abundance of Yellow-billed Loons on the North Slope of Alaska 

 during 1992–2003.. ........................................................................................................................... 8.

4. Yellow-billed Loon sightings and areas surveyed on the Seward Peninsula in 1992–1993 

 and from the Selawik National Wildlife Refuge to Point Hope. ............................................. 12.

5. Annual population indicies for Yellow-billed Loons in the Arctic Costal Plain

 and North Slope Eider surveys. .................................................................................................. 15.

List of Tables.

1. Species as rare as the Yellow-billed Loon. ..................................................................................... 16.

2. Average annual subsistence harvest of loons in villages from northwestern 

 to southwestern Alaska. .............................................................................................................. 23.

3. Conservation status of the Yellow-billed Loon as assigned by various conservation

 and governmental organizations. ............................................................................................... 25.
Abstract.

Because of its restricted range, small population size, specific habitat requirements, and perceived threats to its breeding 

habitat, the Yellow-billed Loon (Gavia adamsii) is a species 

of conservation concern to the U.S. Fish and Wildlife Service 

and the subject of a petition for listing under the Endangered 

Species Act. This Status Assessment synthesizes current 

information on population size, trends, and potential threats 

to Yellow-billed Loons, and the Conservation Plan identifies 

research and monitoring activities that would contribute to the 

conservation of this species. The preparation of this report was 

requested and funded by the U.S. Fish and Wildlife Service, 

Nongame Bird Office, Region 7.

The Status Assessment and Conservation Plan for the 

Yellow-billed Loon can be summarized as follows:

• Northern Alaska breeding grounds support an average 

of 3,369 individuals, including <1,000 nesting pairs in 

most years. The Yellow-billed Loon ranks as one of the 

10 rarest birds that breeds regularly within the mainland U.S. and one of only 20 with a North American 

population <16,000 individuals (Section 6-E).

• There is no evidence of a long-term trend in the Yellow-billed Loon population index since 1986 (-0.9% 

annual change), but interpretation of surveys is complicated by changes in observers and high annual variation, and the 95% confidence interval is large (-3.6% to 

+1.8% annual change). The low reproductive potential 

of Yellow-billed Loons suggests that recovery from a 

substantial decline would not occur rapidly. There are 

no systematic surveys of Canadian and Russian breeding populations (Section 6-F).

• The expansion of the oil industry into prime Yellowbilled Loon breeding habitat is a recent occurrence and 

we lack the necessary information to accurately predict 

its effect on the population. Most of northern Alaskaʼs 

Yellow-billed Loons (91%) occur on the National 

Petroleum Reserve–Alaska, virtually all of which is 

open or proposed to be opened to development and 

where there is no permanent or legal protection of Yellow-billed Loon habitat (Section 7-A).

• Other potential factors affecting the population are also 

addressed, such as contaminants, subsistence hunting, bycatch in subsistence and commercial fisheries 

on the breeding and wintering grounds, and health of 

the marine ecosystem off the coast of East Asia where 

Alaskaʼs Yelllow-billed Loons winter, but data are 

lacking to reach strong conclusions on most issues.

• The conservation goal adopted by the Alaska Loon and 

Grebe Working Group for the Yellow-billed Loon is to 

maintain a stable breeding population, of current size 

and distribution, across the extent of the loonʼs breeding range in Alaska. The Conservation Plan, designed 

to provide information necessary to meet this goal, 

puts forth seven objectives: 1) Conduct annual population surveys having negligible bias and 80% statistical 

power to detect a 3.4% annual decline, a decline that 

would result in a 50% loss of the population within 20 

years; 2) Obtain an unbiased and reliable estimate of 

the size of Alaskaʼs breeding population; 3) Identify 

geographic regions and habitats of importance during 

breeding, staging, and wintering periods; 4) Use demographic models to evaluate risks to the population; 

5) Identify potential effects of oil development on the 

breeding grounds and measures necessary to minimize 

the effects; 6) Evaluate the magnitude of subsistence 

harvest and bycatch and their potential effects on the 

population; 7) Develop a continent-wide and rangewide context for Alaskaʼs population and habitat 

objectives.

Status Assessment and Conservation Plan 

for the Yellow-billed Loon (Gavia adamsii).

By Susan L. Earnst 1.

1 U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, 

Snake River Field Station, 970 Lusk Street, Boise, ID 83706.
Status Assessment.

Northern Alaska breeding grounds support an average of 

3,369 Yellow-billed Loons (Gavia adamsii), and about 780 

more occur in western Alaska, making this species one of the 

least common regularly breeding birds in the mainland United 

States (Section 6–E). Because of its restricted range, small 

population size, specific habitat requirements, and the potential for oil development throughout its U.S. breeding range, 

the Yellow-billed Loon has been a Species of Management 

Concern, or Bird of Conservation Concern, to the U.S. Fish 

and Wildlife Service since 1995 (USFWS 1995, 2002a) and 

is the subject of a recent petition for listing under the Endangered Species Act (Center for Biological Diversity 2004).

The first part of this publication, the Status Assessment, 

provides a comprehensive and critical review of the published 

and unpublished data on Yellow-billed Loon population size, 

population trend, and potential threats to the population and 

its breeding and wintering habitat. The literature review relies 

heavily on that presented in North (1994), Barr (1997), and 

Fair (2002). The Status Assessment identifies gaps in our 

knowledge and in current monitoring programs. The last 

section of the publication, the Conservation Plan, details 7 

objectives and 29 specific strategies to fill gaps identified in 

the Assessment. 

The format of the Status Assessment follows that suggested by the U.S. Fish and Wildlife Service (USFWS 2000). 

The preparation of this document was requested and funded 

by the Nongame Bird Office, Division of Migratory Birds, 

Region 7, U.S. Fish and Wildlife Service. This document is 

a compilation of biological data and a description of past, 

present, and potential future threats to the Yellow-billed Loon. 

It does not represent a decision by the U.S. Fish and Wildlife 

Service, nor a policy statement by the U.S. Geological Survey 

or its scientists, on whether this taxon should be designated 

as a candidate species for listing as threatened or endangered 

under the Federal Endangered Species Act. That decision will 

be made by the Service after reviewing this document, other 

relevant biological and threat data not included herein, and 

all relevant laws, regulations, and policies. Regardless of the 

decision concerning candidate status, the species should benefit from the conservation recommendations that are contained 

in this document.

1. Taxonomy.

The Yellow-billed Loon and Common Loon (Gavia 

immer) are considered by the American Ornithologistsʼ Union 

(1998) to constitute a superspecies. It is likely that the Yellowbilled Loon and Common Loon shared a common ancestor as 

late as the Pleistocene, one million years ago (Storer 1978). 

No subspecies are recognized. 

The Yellow-billed Loon is known as the White-billed 

Diver in Eurasia (Cramp and Simmons 1977) and the Inupiat 

refer to it as tuutlik or King Loon (Georgette 2000).

2. Legal Status.

The Yellow-billed Loon is protected in the United States 

under the Migratory Bird Treaty Act, and in Canada under 

the Migratory Birds Convention Act; thus, like all nongame 

migratory birds, it technically is protected from take and 

undue harassment within these countries and their coastal 

waters. Although various government agencies and conservation groups have listed the Yellow-billed Loon as in need of 

special attention (see Section 8–A), these labels do not impart 

legal protection. 

3. Description.

The Yellow-billed Loon is distinguished from the worldʼs 

other four loon species by the color of its bill, which is yellow 

in breeding plumage and a pale yellow to ivory in wintering 

plumage. In breeding plumage, worn from late April to October or later, upperparts are black with striking white spots, the 

neck and head are black with purple and green gloss, and the 

chest and abdomen are white. Breeding plumage is similar 

to that of the Common Loon, except that the Yellow-billed 

Loon has a yellow rather than black bill, fewer and broader 

white lines in the necklace and upper foreneck, and fewer but 

larger white spots on upperparts. In their gray-brown winter 

plumage, the pale bill of the adult Yellow-billed Loon can be 

distinguished from the gray bill of the Common Loon, and the 

two species differ in various aspects of bill and head shape 

and the distinctness of the white auricle patch (Palmer 1962, 

and reviewed in North 1994). Male and female plumages are 

similar.

Chicks are completely downy and initially dark brown 

with some white on lower breast and abdomen, becoming 

lighter brown with more pronounced white underparts as they 

mature, particularly by about their third week. Juvenile plumage, acquired by about 10 weeks, is gray-brown and resembles 

adult winter plumage. Immature plumage differs among age 

classes, and from that of the Common Loon, but can probably 

only be distinguished by experienced observers at close range. 

Immatures are thought to acquire adult-like winter plumage 

(Basic) and then summer plumage (Definitive Alternate) at 

approximately age 3 (Palmer 1962, and reviewed in North 

1994).

The Yellow-billed Loon is larger than the sympatric Redthroated Loon (Gavia stellata) and Pacific Loon (Gavia pacifica). The body masses reported for male and female Yellowbilled Loons fall within a similar range (about 4.0–6.4 kg), but 

males are longer (838–920 mm vs. 774–831 mm) (reviewed in 

North 1994). Presumably average male body mass and size is 

greater than that of females within a given breeding site, but 

information on variation within and among sites has not been 

published. Yellow-billed Loon body mass also falls within 

the range reported for Common Loons, with the average adult 

mass of the latter varying widely with geographic location 

(4.4–6.0 kg for males, 3.3–4.7 kg for females) and migratory 

distance (reviewed in Evers 2004).

2 Status Assessment and Conservation Plan for the Yellow-billed Loon
Yellow-billed Loons, like other loons, have a highly modified leg and pelvic structure that is well adapted for swimming but allows only the most rudimentary form of standing 

and almost no ability to walk. Thus, loons must place nests at 

the waterʼs edge and must land and take flight from water.

4. Range.

Breeding.

The Yellow-billed Loon breeds patchily throughout the 

subarctic and arctic tundra of northern Alaska, Canada, and 

Eurasia (Fig. 1). In Alaska, the range extends from the Canning River westward to Point Lay; it also includes St. Lawrence Island and the coastal areas of the Seward Peninsula 

(Fig. 2). However, most of the breeding population lies in the 

central portion of this area, between the Colville River and 

Meade River, and breeding elsewhere is sparse. The breeding range in Canada and Russia has not been as well defined 

as in Alaska, where large-scale aerial surveys are used. Thus, 

although the Canadian and Russian ranges appear large, they 

may include large areas with few or no birds (Fig. 1). In Canada, the breeding range extends from just east of the MacKenzie River Delta to Hudson Bay, including the northern islands. 

It is most common on Banks Island and Victoria Island, and 

the lake district from Great Slave Lake northeast to northern 

Hudson Bay, and breeding elsewhere is sparse. In Russia, the 

Yellow-billed Loon breeds in the relatively narrow strip of 

coastal tundra from the Chukchi Peninsula in the east to the 

Taymyr Peninsula and the areas of the Novaya Zemlya River 

and Pechora River in the west. Its status from the Pechora 

River west to Finland is unclear. In Europe, small numbers 

have been reported breeding in northern Finland and Norway. 

This summary was based on North (1994), Barr (1997), and 

Fair (2002). Also see Sections 6–A to 6–C.

Figure 1. World-wide Yellow-billed Loon breeding (black) and wintering (hatched) range. From McIntyre (1991), North (1993), and Barr 

(1997) except for the following modifications: Alaska breeding range reduced based on data in Earnst et al. (in review) and Fig. 3 and 

southern extent of wetlands; Russian breeding range reduced based on the southern extent of tundra wetlands; and Asian wintering 

range extended based on Schmutz (written commun. 2003)

Status Assessment 3
Migration.

The Yellow-billed Loon is a regular migrant along the 

coastlines of northern Canada (MacKenzie River Delta, Banks 

Island, Amundsen Gulf), northern Alaska (Icy Cape, Barrow, 

and Oliktok Point just east of the Colville River Delta), and 

northwestern Alaska (St. Lawrence Island and off the western 

tip of Seward Peninsula), and is a rare migrant along the western Alaska coastline (Yukon-Kuskokwim Delta, Bristol Bay, 

Aleutian Islands, Alaska Peninsula) (reviewed in North 1993 

and 1994). Also see Section 5–E.

Winter.

Yellow-billed Loons winter regularly but sparsely in 

nearshore marine waters from Kodiak Island through Prince 

William Sound, and throughout southeast Alaska and British Columbia (Fig. 2). Irregular wintering occurs southwest 

of Kodiak Island along the Aleutian Islands and along the 

coast of Washington to Baja California. Also, several reliable 

sightings of migrating and wintering loons have been recorded 

in inland areas (reviewed in North 1994). Immatures and possibly some nonbreeding adults remain on wintering grounds 

throughout the year. In Eurasia, Yellow-billed Loons winter 

off the coast of Norway, the Kamchatka Peninsula of Russia, 

northern Japan, North Korea, and China (Fig. 1; reviewed in 

Barr 1997). Recent evidence suggests that Alaskan breeders 

winter off the coast of North Korea, Japan, and China (see 

Section 6–D).

5. Life-history Summary.

A. Habitat Requirements.

The nesting and brood-rearing lake.

Yellow-billed Loons require nesting and brood-rearing 

lakes that a) are large enough to allow easy take-off from 

open water; b) form an ice-free moat around shore in early 

spring that is large enough to protect nests from wind-blown 

ice and to allow adults to take flight; c) have clear water with 

a substantial population of small fish which can be eaten by 

adults and fed to chicks; d) have segments of gently sloping 

shoreline on which nesting and brooding can occur; and e) 

have sheltered areas, often vegetated, where young chicks can 

Figure 2. Yellow-billed Loon breeding (dark gray) and wintering (hatched) range in Alaska in relation to areas mentioned 

in the text.

4 Status Assessment and Conservation Plan for the Yellow-billed Loon
rest and take refuge during disturbances. Yellow-billed Loons 

are larger and heavier than the other tundra-breeding loons and 

so require a larger area of open water to ensure safe take-off 

and landing. More importantly, young are fed entirely from 

the brood-rearing waterbody; thus, successful reproduction 

apparently is restricted to lakes deep and large enough to support overwintering fish. The smallest brood-rearing waterbody 

recorded on the Colville River Delta is 13.4 ha (North and 

Ryan 1989); however, in a few cases, nests are placed on a 

waterbody as small as <1 ha from which very young chicks 

(<3 days of age) are moved overland to a nearby larger waterbody for the duration of brood-rearing (occurred in some years 

on 3 of 26 monitored territories on the Colville River Delta; 

Earnst unpubl. data). 

Lake size, depth, connectivity to streams, shoreline complexity, and proportion of shoreline in moist to aquatic cover 

types were each significant predictors of Yellow-billed Loon 

presence during intensive aerial surveys providing complete 

coverage of 757 lakes between the Colville and Meade rivers 

(Earnst et al. in press; also see Influence of habitat preferences on breeding distribution). Presence of low-lying cover 

types along the shore may be an indication of a gradually 

sloping shoreline and convoluted shorelines provide nesting 

and brood-rearing sites. Lake depth and connectivity are interpreted as measures of fish availability. Although connectivity 

is generally favorable for loons, lakes on the Colville River 

Delta that have large connections to a major river channel are 

susceptible to fluctuating water levels (and often have high 

turbidity) and are avoided for nesting (North and Ryan 1989); 

however, lakes with smaller connections that have flowing 

water only during high water events are not avoided on the 

Colville River Delta or elsewhere. Similarly, Common Loon 

presence has been correlated with connectivity at more southerly latitudes (Ruggles 1994).

Nests are placed at the waterʼs edge, typically in a lowlying, gently sloping area. Of the 11–18 nest sites investigated 

each year on the Colville River Delta, on average, 55% were 

on islands, 27% on peninsulas, 14% on lake shores other than 

peninsulas, and 4% on rafts or underwater hummocks formed 

from peat and emergent vegetation (Earnst unpubl. data). 

Similarly, among 20 nests in a previous study, 35% were on 

islands, 45% on lake shores including peninsulas, and 20% 

on hummocks surrounded by shallow water (North and Ryan 

1989). It is likely that islands are preferred relative to their 

availability. Although it is difficult to estimate island availability per se, an analysis based on waterbody types indicates that 

waterbodies with “deep open water with islands” are preferred 

for nesting over other waterbodies relative to their availability 

(Johnson et al. 2000). Nests sometimes are crushed by windblown ice and flooded by wind-induced waves, and presumably as a mechanism to minimize this threat, most nests are 

placed on the leeward lake or island shore (North and Ryan 

1989).

 Chicks often remain in sheltered, vegetated areas of 

large lakes when young (<1 week) but by 2–3 weeks of age 

are spending much time in the deep, open water of large lakes 

while parents make extensive dives throughout the lake and 

return with fish. When disturbed by the approach of humans, 

young chicks either hide in emergent vegetation (typically 

Carex aquatilis or Arctophila fulva) or follow their parents 

to the deep, open water of the lakeʼs center. Chicks continue 

to use sheltered bays for resting through at least the end of 

August (approx. 6 weeks of age). Young chicks are brooded on 

gently sloping shorelines and sometimes on the nest.

Territory composition and defense.

Most breeding territories consist of one waterbody, usually 17 ha to >100 ha, that is used for nesting and brood-rearing (e.g., North and Ryan 1989). A few territories consist of a 

section of 1 or more waterbodies. On the Colville River Delta, 

a few extremely large lakes with multiple bays and inlets, 

which provide visual isolation and multiple brood-rearing 

sites, may support more than one Yellow-billed Loon territory 

or a combination of Yellow-billed Loon and Pacific Loon territories (North 1994, Earnst pers. obs.). 

Yellow-billed Loons attempt to expel all other loons from 

territories, but on larger waterbodies, Red-throated Loons and 

Pacific Loons are sometimes able to forage for several hours 

before being discovered and expelled. In some cases, territory 

ownership has shifted between species (Earnst unpubl. data). 

For example, a nest bowl and breeding territory occupied by 

a Pacific Loon in 1996, 1998, and 2000 was occupied by a 

Yellow-billed Loon in 1997. In a second case, a lake used for 

brood-rearing by a pair of Pacific Loons in 1996, 1998, and 

2000, was used by a breeding pair of Yellow-billed Loons in 

1999. In both cases, the Yellow-billed Loon nest failed, and 

the pair was not observed on the territory in subsequent years, 

suggesting that it may have been a young pair attempting to 

establish a breeding territory and/or may have been a territory 

of marginal quality for Yellow-billed Loons.

Territory holders engage in intense fights, involving 

chases on the waterʼs surface and prolonged dives, with 

conspecifics and Pacific Loons (Earnst pers. obs.). It is well 

documented that loons kill and injure other loons and waterfowl by piercing them from beneath the waterʼs surface, or 

from above, by forcing the opponents neck and head underwater (e.g., McIntyre and Barr 1997). In fact, necropsies of 200 

Common Loons indicated that >50% had healed sternal punctures (McIntyre and Barr 1997). Yellow-billed Loons have 

been observed to kill waterfowl on the Colville River Delta (J. 

Helmericks pers. comm.), and a recently killed Pacific Loon 

with a fresh sternal puncture was found on the nesting lake of 

a Yellow-billed Loon (Earnst pers. obs.).

Influence of habitat preferences on breeding distribution

Some sections of the Arctic Coastal Plain do not contain 

lakes of sufficient size and depth to be suitable for Yellowbilled Loons, and this habitat distribution explains, in part, the 

distribution of the species in Alaska. It is less clear how well 

the attributes of lakes explain Yellow-billed Loon abundance 

at smaller geographic scales. In an attempt to model YellowStatus Assessment 5
billed Loon distribution and relative abundance in relation to 

habitat characteristics, intensive aerial surveys were conducted 

between the Colville and Meade rivers in 1998–2000 (Earnst 

et al. in press). Complete coverage of 21 plots, totaling 2,300 

km2, provided locations of 211 Yellow-billed Loons across the 

757 surveyed lakes. Lake attributes available on Geographic 

Information System (GIS) were used to identify Yellow-billed 

Loon habitats. Satellite imagery was used to classify lake 

depth as shallow (freezing entirely to the bottom) or deep (not 

freezing entirely) (Mellor 1987, Jeffries et al. 1996). Logistic 

regression analyses indicated that Yellow-billed Loons were 

more likely to be present on larger and deeper lakes, those 

within 100 m of a stream (a measure of connectivity), those 

with more complex shorelines, and those with a higher proportion of shoreline in aquatic or flooded vegetation (Earnst et al. 

in press). Yellow-billed Loon presence was negatively related 

to Pacific Loon presence, which could be due to the two species having different habitat associations or some degree of 

competitive exclusion. Not surprisingly, these variables did 

not predict Yellow-billed Loon presence perfectly. It is likely 

that attributes available from GIS data are imperfect correlates 

of factors important to loons, such as fish abundance, and that 

lakes judged to be ʻsuitableʼ based on GIS attributes alone are 

sometimes not suitable. It is also possible that Yellow-billed 

Loons tend to establish territories near conspecifics, and perhaps exhibit limited adult and juvenile dispersal (as do Common Loons; Evers 2004), thus creating a distribution more 

clumped than would be predicted based on resource availability, although this has not been quantified explicitly.

Although it would be useful to know whether breeding 

habitat availability is a factor limiting population size in Yellow-billed Loons, such a determination is problematic even 

in well-studied populations, and not possible with our current 

knowledge of Yellow-billed Loons. 

Use of marine waters during winter months.

Yellow-billed Loons spend roughly eight months exclusively in marine environments, and the health of this ecosystem is likely to have substantial (and largely unstudied) effects 

on population health. Population declines in other marine 

birds, such as Red-throated Loons (Groves et al. 1996) and sea 

ducks, are calling attention to the potential link between health 

of the marine ecosystem and avian population dynamics. 

Although habitat preferences or requirements on the wintering 

grounds have not been studied, it is clear that Yellow-billed 

Loons tend to occur near shore (rather than off the continental 

shelf), in waters protected by bays or archipelagos, and from 

50 to 61 degrees N latitude (North 1994). They winter primarily in the Gulf of Alaska, down the coastline of southeast 

Alaska to northern Washington, and off the Pacific Coast of 

Russia and East Asia (see below). 

Use of marine waters during staging and migration.

Most observations of migration are made from shore, and 

thus, probably underestimate the importance of offshore iceleads. Yellow-billed Loons appear to prefer open-water leads 

for resting and refueling rather than extensive open water 

(Searing et al. 1975), and large numbers of loons, eiders, and 

other marine birds have died in years when leads did not form 

(Barry 1976). Major ice-leads are known to form in the Chukchi Sea west of Barrow, Alaska, to Banks Island, Canada. In 

northern Canadian waters, three important spring staging areas 

in open-water leads have been identified (reviewed in Barr 

1997): 1) offshore from the eastern edge of the MacKenzie 

River Delta eastward about 200 km to the Bathurst Peninsula; 

2) off the west coast of Banks Island; and 3) the Lambert 

Channel polynya, which is at the southeast end of Amundsen 

Gulf. Alexander et al. (1997) conducted aerial surveys over 

the open-water leads described above and those elsewhere in 

the Amundsen Gulf during June 1986, 1987, 1992, and 1993. 

Yellow-billed Loons were abundant in the Lambert Channel 

polynya in both years it was surveyed (peak numbers of 259 

in 1992 and 332 in 1993), but were abundant in other leads 

during only one of four survey-years (1992), a year of little 

open water in the region. In addition, concentrations of staging 

Yellow-billed Loons have been observed off the mouths of 

the Anderson, Mason, and Horton rivers in Canada in years of 

late spring thaws (unpublished reports reviewed in Barr 1997). 

Individuals marked with satellite transmitters on Alaskaʼs 

North Slope staged for several days just north of St. Lawrence 

Island before continuing their migration down the Kamchatka 

Peninsula to wintering grounds off of East Asia (J. Schmutz 

pers. comm., see Section 5–E).

Use of marine waters during summer months by 

immatures, nonbreeders, and breeders.

If Yellow-billed Loons have a demography similar to that 

of Common Loons (see Section 5–C and 6–E), then nearly 

20% of the population may be in 1–2 year-old age classes 

(Earnst et al. in review). In Yellow-billed Loons, 1–2 year-olds 

are thought to remain in immature plumage and to summer 

on traditional marine wintering grounds (Palmer 1962, North 

1994) as do Common Loons (Evers 2004). On traditional 

wintering grounds in Alaskan waters, Yellow-billed Loons are 

regularly recorded at low densities during surveys of southeast 

Alaska, Lower Cook Inlet, and Prince William Sound during 

June and July (Agler et al. 1995a,b and Lance et al. 1999; see 

Section 6–A). It is not clear whether these observations were 

of individuals in immature plumage (presumably <3 years of 

age) or whether nonbreeders in adult plumage also were seen.

In far northern marine waters, concentrations of nonbreeding Yellow-billed Loons also have been reported during 

summer months, for example, in ice-free leads off the coasts 

of Canadaʼs arctic islands (Parmelee et al. 1967, Searing et al. 

1975, McLaren and Alliston 1981, and unpublished reports 

reviewed in Barr 1997). 

In addition, offshore of breeding grounds, aerial surveys 

have documented the regular occurrence of adult-plumaged 

Yellow-billed Loons. These sightings probably represent a mix 

of a) individuals that hold territories within a few kilometers 

6 Status Assessment and Conservation Plan for the Yellow-billed Loon
of the coast and make brief foraging trips to marine waters 

(Earnst pers. obs.), and b) young nonbreeding, nonterritorial 

birds (presumably 3–5 year olds) that sometimes summer on 

lakes near established breeding territories (e.g., North 1986), 

as do young nonterritorial Common Loons (Evers 2004), but 

may also spend parts of some summers offshore (Earnst et al. 

in review). Fischer et al. (2002) conducted offshore surveys up 

to 60 km from the shore between Harrison Bay and Brownlow 

Point (west edge of Arctic National Wildlife Refuge) in June–

August of 1999–2000, and they conducted nearshore surveys 

in barrier island lagoons between Oliktok Point (east edge of 

Colville River Delta) and Brownlow Point in July–August of 

1999–2000 (see place names in Figs. 2 and 3; also see Section 

6–A). During nearshore surveys, 67 Yellow-billed Loons were 

recorded and were more common near barrier islands (within 

400 m of island on mainland side) than along the mainland 

coastline (within 400 m of coastline), in mid-lagoon (between 

the barrier island and mainland strata), or in the marine strata 

(from barrier islands to 1.5 km seaward). During offshore 

surveys, 27 Yellow-billed Loons were recorded and were 

more common in the Harrison Bay Shallow Stratum, which 

borders high-density mainland sites (see Fig. 3), than elsewhere (18 loons in 693 km2

 surveyed vs. 9 loons in 4,747 km2

surveyed, respectively). Taken together, these results suggest 

that Yellow-billed Loons in marine waters are more common 

in shallow nearshore waters (<10 m, corresponding to roughly 

0–20 km offshore) than in deeper water; near barrier islands 

(when present) than in other nearshore habitats; and adjacent 

to mainland concentration areas than elsewhere. 

Yellow-billed Loons were fairly uncommon compared to 

other species recorded during nearshore and offshore surveys 

(comprising 0.06% and 0.14% of observations, respectively). 

However, a relatively small fraction of the study area bordered 

areas where Yellow-billed Loons are common breeders (Fig. 

3), and the total North Slope population size of Yellow-billed 

Loons is much smaller than that of the other focal species. The 

potential importance of marine habitat to Yellow-billed Loons 

in some areas is illustrated by the fact that density in the Harrison Bay Shallow Stratum (0.026 loons/km2

) was comparable 

to that recorded during mainland aerial surveys in the same 

years (0.033 loons/km2 in the Arctic Coastal Plain study area 

and 0.027 loons/km2 in the North Slope Eider study area, 

1999–2000; based on data in Earnst et al. in review). 

The importance of marine habitat to Yellow-billed Loons 

relative to other species may be more meaningfully interpreted 

relative to the speciesʼ relative abundance on the breeding 

grounds. For example, in nearshore and offshore surveys 

combined, 997 Pacific Loons, 230 Red-throated Loons, and 

94 Yellow-billed Loons were recorded. When considered as a 

proportion of the six-year population index (1997–2002) for 

these species (based on data in Mallek et al. 2004), the proportion is 0.04 for Pacific Loons, 0.06 for Red-throated Loons, 

and 0.04 for Yellow-billed Loons, suggesting a similar importance of the marine environment during the summer. Although 

this illustrates the value of considering overall population size, 

a more extensive marine survey would be needed to rigorously 

quantify the relative importance of marine habitat to these 

three species. 

B. Reproductive Ecology.

Pairs apparently form or re-form upon arrival on the 

breeding territory or while staging on adjacent rivers. Most 

males and females are thought to return to breeding territories 

used in past years (see Section 5–F) and established territory-holders occupy territories each year whether or not they 

attempt to breed (North and Ryan 1988). Individuals may 

arrive on the breeding grounds before an ice-free moat forms 

on their breeding lake, stage on open river channels, and make 

forays with vocalizations over breeding lakes (North and Ryan 

1988). Breeding lakes appear to be occupied as soon as open 

water is available to allow safe take-off, and eggs are laid a 

few to several days thereafter. Annual dates of hatch are variable. On the Colville River Delta, in the early spring of 1983 

and the late spring of 1984, Yellow-billed Loons first arrived 

at the end of May, breeding pairs first occupied territories 4 

to 11 June, and began incubation 15 to 23 June (N = 2 pairs; 

North and Ryan 1988). Similarly, in 1995–1999, average onset 

of incubation was 14 to 23 June (back-dated 28 days from 

average hatch dates of 11 to 20 July, N = 7 to 10 pairs) and 

reflected, in part, the timing of spring ice melt (Earnst unpubl. 

data). In 2000, after a late spring and a 100-year flood event 

which temporarily flooded many nest bowls, a small fraction 

of territorial pairs nested, and average hatch date was 6 days 

later than previously recorded averages (Earnst unpubl. data). 

Copulation occurs on land and may be followed by 

stylized nest-building movements. Nest bowls are typically 

bulkier than those of the sympatric Red-throated Loon and 

Pacific Loon (outer diameter 63 cm; bowl depth 3.8 cm) and 

constructed of peat, pendant grass (Arctophila fulva), and 

sedge species (usually Carex spp.) (North and Ryan 1989). 

Vegetation may be added during incubation. Nest sites from 

previous years often are reused.

Clutch size is almost always two eggs, and although 

two young typically hatch, most successful pairs rear only 

one chick (North and Ryan 1988, Earnst unpubl. data). Eggs 

are medium brown or olive brown with dark brown to black 

spots. Eggs are larger than those of sympatric breeding Pacific 

Loons (Earnst unpubl. data). Egg membranes and large shell 

pieces from successfully hatched eggs almost never are found 

in the nest but sometimes are found in deep water several 

meters from the nest, presumably placed there by parents, as 

occurs in Common Loons (McIntyre and Barr 1997). Both 

sexes incubate, nest attendance is very high (eggs covered 

95.3% of the time, based on 12 pairs over 216 hours; North 

unpubl. data, cited in North 1994), and the incubation period 

is 27–28 days (N = 3; North and Ryan 1988). Chicks are dry 

and active within hours of hatch and are capable of following 

parents onto water but will remain in the nest for many hours 

if undisturbed. On the few territories where chicks are moved 

from a small nesting waterbody to a large brood-rearing waterbody, chicks are moved when very young (1–3 days of age). 

Status Assessment 7
Although behavior during the move itself has not been directly 

observed in Yellow-billed Loons, Pacific Loon parents in similar habitats move chicks by actively leading them across land 

to the destination waterbody (Bergman and Derksen 1977, 

Earnst pers. obs.). The adult or chick uses its feet to thrust 

itself breast-first across the vegetation. 

Brooding occurs in the nest and on other gently sloping, easily accessible shorelines throughout the first 10 days 

of age (Sjölander and Ågren 1976, North 1994). In poor 

weather, older chicks sometimes are brooded, and chicks may 

be brooded on land by one parent while being simultaneously 

brought fish by the second parent (Earnst pers. obs.). Chicks 

of one pair reportedly were brooded while riding on a parentʼs 

back at a more southerly site (Sjölander and Ågren 1976), but 

back-riding was observed only once in a two-year study on the 

Colville River Delta (North 1994) and was not observed in a 

six-year study at the same site (Earnst unpubl. data). Chicks 

up to 45 days old rarely feed themselves (Sjölander and Ågren 

1976, North 1994, Earnst unpubl. data, but see Sage 1971). In 

one study, parents fed chicks from 0.30 to 1.43 food items/

chick/minute (North unpubl. data, cited in North 1994). Often 

both parents feed chicks during feeding bouts and both are 

often present on the waterbody, especially parents of twochick broods. For example, on the Colville River, both parents 

were present during 82% of brood checks and 70% of timebudget observations on two-chick broods and during 47% of 

brood checks and 51% of observations on one-chick broods 

(based on 132 visits to 23 broods, and 230 hours of observation on 10 broods; Earnst unpubl. data). Feeding rates, and a 

measure of fish availability from fyke-net sampling, will also 

be available from the latter study. 

Clutch replacement after predation has been reported 

in one possible case on southeast Victoria Island (Parmelee 

et al. 1967), and once near Alaktak, Alaska (Sjölander and 

Ågren 1976), but not on the Sagavinertok River (one year, 

Sage 1971) or the Colville River Delta (two years, North and 

Ryan 1988; and six years, Earnst unpubl. data). Replacement 

clutches, if they occur, are probably not successful unless laid 

very early in the season. For example, replacement clutches of 

Red-throated Loons, although common, rarely fledge young 

on the Colville River Delta (Earnst unpubl. data). 

8 Status Assessment and Conservation Plan for the Yellow-billed Loon

Figure 3. Relative density of Yellow-billed Loons on the North Slope of Alaska during 1992–2003. Based on the North Slope Eider and 

Arctic Coastal Plain aerial surveys. Relative density is not corrected for visibility bias. Modified from Earnst et al. (in review).
C. Demography.

Yellow-billed Loons reach maturity at age 3 but probably 

do not obtain a territory and nest until age 4–7 (North 1994). 

The proportion of nonterritorial adults and the survival rates 

of immatures and adults are unknown. A comparison to the 

closely related Common Loon may provide some insights into 

those demographic parameters that are poorly studied in Yellow-billed Loons. In Common Loons, the average age at first 

breeding is 6 (range 4–11 years), 19% of 3+ year-olds are nonterritorial on average, and annual survival is 70%, 80% and 

92% for ages 1, 2–3, and >3 years of age, respectively (Evers 

2004, M. Mittro, D. Evers, and M. Meyers, unpubl. data). 

In a two-year study (1983–1984) of Yellow-billed Loons 

on the Colville River Delta, 76%–79% of territorial pairs 

nested (North 1986), average clutch size was 1.88 and 1.89, 

and nesting pairs raised 1.29 and 0.94 chicks to age 2 weeks 

(North 1986, North and Ryan 1988). At the same site in 1989 

and 1990, 42% and 67–71% of territorial pairs nested, respectively (Field et al. 1993, North 1993).

In a six-year study (1995–2000) of Yellow-billed Loons 

on the Colville River Delta, 39%–89% of territorial pairs 

nested, and annual average clutch size was 1.63–2.0. Based on 

Mayfield survival rates, 4%–60% of individuals survived from 

laying to age 6 weeks each year, corresponding to an average 

of 0.08 to 1.20 chicks per nesting pair raised to age 6 weeks 

each year (Earnst unpubl. data). These productivity estimates 

are not directly comparable to Northʼs because he reports 

apparent nesting success rather than Mayfield-adjusted success. Combining the 10 years of data available for the Colville 

River Delta (all studies described above), the proportion of 

territorial pairs nesting ranged from 39% to 89% and averaged 

59%.

Much of the variation in reproductive success in the 

six-year study was due to years of late ice melt or extreme 

flooding, during which Yellow-billed Loon pairs hatched 

eggs up to two weeks later than in other years and had poorer 

brood-rearing success. High annual variation in productivity 

also has been noted in the other arctic-breeding loons—Pacific 

Loons and Red-throated Loons (e.g., Petersen 1989, Eberl and 

Picman 1993, and Earnst unpubl. data). In the more temperatebreeding Common Loon, annual variability within one wellstudied site (0.30–0.73 fledged young per territorial pair) and 

variability among sites (0.28–0.96 fledged young per pair) is 

also pronounced (reviewed in Evers 2004). In a 25-year study 

of Common Loons in New Hampshire, an average of 68% 

of territorial pairs attempted to nest, and they produced 0.52 

fledged young per territorial pair (Taylor and Vogel 2000).

In order to evaluate the potential demographic risks 

associated with the small population size in Alaska and 

world-wide, long-term studies of color-marked individuals 

are needed to ascertain immature and adult survival rates, age 

at first breeding, and patterns of breeding philopatry (return 

of a breeder to the same breeding site) and juvenile dispersal 

(distance from natal lake to site of first breeding). Telemetry 

studies would be useful in documenting the degree to which 

individuals from disparate breeding sites winter together and 

the size and location of the nonterritorial, nonbreeding component of the population. Genetic studies are needed to quantify 

the discreteness of various breeding concentrations across 

Alaska, Canada, and Russia. Long-term studies of nesting and 

brood-rearing success at multiple sites are needed to identify 

the causes of variation and to set the stage for investigations 

into the effects of oil-related development and global climate 

change. 

D. Feeding Ecology.

Adults on breeding territories typically forage in deep, 

open water where they make repeated, lengthy dives (average 

duration = 47.1 seconds, maximum 108 seconds; North 1994). 

Yellow-billed Loons are probably opportunistic foragers, taking prey in relation to their availability and ease of capture, 

and consuming most prey underwater (Barr 1997). When foraging in shallow water, as adults with young chicks often do, 

adults submerge bill and eyes beneath the surface, and move 

the neck and body forward in jerking motions as they probe 

the substrate, vegetation, and water column; a similar behavior 

has been described in Common Loons (Barr 1996, McIntyre 

and Barr 1997). 

Yellow-billed Loon chicks are fed small, minnow-sized 

fish throughout July and August (age approximately 6–7 

weeks). Ninespine sticklebacks (Pungitius pungitius) and least 

cisco (Coregonus sardinella) are thought to be the primary 

foods of chicks on the Colville River Delta based on time-budget observations of adults feeding chicks and subsequent sampling of fish availability at sites where loons forage (Earnst 

unpubl. data). Alaska blackfish (Dallia pectoralis), fourhorn 

sculpin (Myoxocephalus quadricornis), isopods, and amphipods also are available and probably utilized to some extent 

on breeding territories. In 230 hours of time-budget observations, Yellow-billed Loon parents only once brought a fish 

back from areas off the brood-rearing waterbody, and chicks 

rarely attempted to feed themselves (Earnst in prep). This is 

similar to the parental feeding strategy of Pacific Loons on 

the Colville River Delta, but in contrast to that of the smaller 

Red-throated Loon, which brings fish back from the ocean or 

river channel, and provides large fish at the upper bounds of 

the chickʼs ability to swallow, perhaps as a means to optimize 

energy delivered relative to distance flown. Yellow-billed 

Loon adults on the Colville River Delta often feed themselves 

from the brood-rearing waterbody, probably mostly on ninespine sticklebacks and least cisco since that is what is most 

available (see above), but parents also sometimes forage in 

nearby river channels or Harrison Bay where a larger variety 

of fish species are available (Earnst pers. obs.). 

There is little direct data on diet from stomach contents. 

In three specimens from marine waters, stomach contents 

included the following: Pacific staghorn sculpin (Leptocottus armatus), sculpin species (Myoxocephalus sp.), Pacific 

tomcod (Microgadus proximus), amphipods (Orchomonella

sp., Anonyx nirgax), isopods (Idothea sp.), shrimp (Pandalus 

Status Assessment 9
danae, Spirontocaris ochotensis), hermit crabs (Pagarus sp.), 

and marine worms (Nereis sp.) (reviewed in North 1994). 

Yellow-billed Loon adults and chicks regularly climb 

onto shore and face the water before defecating. Defecation 

by one family member is often followed by the same behavior 

in other members, and can be initiated by either a parent or 

chick (Earnst pers. obs.). A few locations on the brood-rearing 

waterbody tend to be used repeatedly, perhaps because they 

are low and easy to access. This behavior has been observed in 

other species that feed chicks from the brood-rearing waterbody—Common Loons (McIntyre and Barr 1997) and Pacific 

Loons (Earnst pers. obs.)—but not Red-throated Loons, which 

feed chicks from elsewhere. Some have speculated that this 

might be an adaptation to mark territories (e.g., North 1994, 

McIntyre and Barr 1997), since the white streaks are visible 

from the air, or a means of avoiding fouling of the water, 

perhaps as a disruption to the life cycle of a yet unidentified 

parasite (North 1994). It is unknown how often defecation 

occurs in the water.

E. Movements and Migration.

Pair members are thought to migrate separately from 

one another and to establish or re-establish pair bonds soon 

after arrival on the breeding grounds. North (1993) provides a 

thorough review of spring arrival and spring and fall migration dates across Alaska and Canada. First arrival in northern 

Alaska is usually the last third of May, and peak arrival is 

somewhat later. First arrival is later in Canada (1–15 June). 

Individuals and small groups may occupy open river channels before breeding lakes are sufficiently free of ice. Larger 

flocks may stage in marine bays. For example, a flock of 

60 was reported staging in spring at Shishmaref Inlet on the 

Seward Peninsula (Kessel 1989). During June, large numbers 

also stage in open-water leads off the northern coast of Canada 

along the mainland east of the MacKenzie River Delta, off 

western Banks Island, and in Lambert Channel at the southeast 

corner of Amundsen Gulf (Alexander et al. 1997). Also see 

Section 5–A.

Adults usually leave territories in northern Alaska during 

late August to mid-September but appear to remain on sites in 

Canada longer (North 1993). Breeders are reported to leave 

territories soon after fledging, sometimes moving to open rivers until forced out by ice (Sage 1971). Adults are thought to 

migrate separately from their offspring. Fall staging of 30–300 

individuals in late August to mid-September has been reported 

in Wainwright Inlet in Alaska, on Banks Island, in Yellowknife 

Bay on Great Slave Lake, and the area southwest of the breeding grounds around the Thelon Game Sanctuary in Canada 

(reviewed in North 1994). 

Migratory routes are poorly known. During spring 

migration, Yellow-billed Loons are known to follow leads in 

pack ice far from shore in the Chukchi Sea and Beaufort Sea 

(Richardson et al. 1975, Divoky 1984). Because most observations have been from shore, it is likely that we underestimate 

the importance of migration along ice-free leads away from 

shore. North (1994) cites the Yellow-billed Loon as a regular 

migrant along the northern Canada coastline, the northern 

Alaska coastlines of the Beaufort and Chukchi Seas (Icy Cape, 

Barrow, Oliktok Point), and along the northwestern Alaska 

coastline of the Bering Strait (St. Lawrence Island and western 

tip of Seward Peninsula). It is a rare migrant along the western 

Alaska coastline (Yukon-Kuskokwim Delta, Bristol Bay, Aleutian Islands, and Alaska Peninsula). Inland migration also has 

been reported in Alaska and elsewhere. 

North (1993) suspected that most Yellow-billed Loons 

that breed in northern Alaska and the Canadian arctic islands 

migrate across the Bering Sea to winter along the coast of 

Siberia or Japan, whereas birds from eastern mainland Canada 

migrate across an inland route, perhaps via Great Slave Lake, 

to winter in southeastern Alaska or British Columbia. His 

suspicion was based on the scarcity of observations of Yellow-billed Loons migrating along the coast of western and 

southwestern Alaska (i.e., Norton Sound to Alaska Peninsula), 

the correlation between the timing of arrival and departure 

from Canadian mainland breeding grounds with the timing 

of migratory sightings across inland Canada, and the shorter 

distance between breeding and wintering sites over an inland 

route. In July 2002, 5 Yellow-billed Loons were fitted with 

satellite transmitters while nesting near Inigok, approximately 

75 km inland from the Colville River Delta (J. Schmutz pers. 

comm.). They moved westward to the Chukchi Sea off the 

coast of Alaskaʼs Icy Cape between 20 and 30 September, 

moved slowly southward through the Bering Strait, and staged 

for several days just north of St. Lawrence Island. Most then 

migrated along the Kamchatka Peninsula, and once reaching the end, cut through the Kuril Islands towards Hokkaido 

Island (Japan), Sakhalin Island (Russia), and eventually the 

Sea of Japan and the Yellow Sea. Loons seemed to become 

stationary for the winter by the end of November, or perhaps 

December. As of mid-March 2003, the four individuals whose 

transmitters were still emitting a signal were wintering off the 

coast of Hokkaido, Japan (two), North Korea (one), and in the 

Yellow Sea between North Korea and China (one). The fifth 

loon was off the coast of North Korea when its transmitter 

failed in November. An additional six loons were fitted with 

transmitters in 2003 and showed similar patterns of movement 

and wintering sites (J. Schmutz pers. comm.). 

F. Breeding Philopatry and Juvenile Dispersal.

There have been no studies of color-banded individuals, thus nothing is known of breeding philopatry or juvenile 

dispersal. Researchers suspect that breeding philopatry is high, 

based on observations of repeated use of nests and territories 

(e.g., North 1994); however, the identity of individuals using 

those sites has not been confirmed. 

Given the scarcity of data on Yellow-billed Loons, 

some insights may be gained from philopatry in Common 

Loons. However, the degree of philopatry is likely affected 

by the degree of saturation of suitable breeding habitats, 

which is thought to be high in Common Loons (Evers 2001) 

10 Status Assessment and Conservation Plan for the Yellow-billed Loon
and is unknown in Yellow-billed Loons. In Common Loons, 

between-year territory fidelity was 80% for males and 82% 

for females. Of the loons that moved, 68% established new 

territories and moved 3.0 km on average; 32% became nonbreeders and moved 4.5 km on average (Evers 2001). Most 

between-year movement was thought to result from usurpation 

of the breeding territory by a competitor (see also Piper et al. 

2000). Average juvenile dispersal was 13 km (N = 45) (Evers 

unpubl. data). 

G. Mortality.

Estimates of adult and subadult annual mortality rates are 

not available due to the lack of studies on individually marked 

Yellow-billed Loons. Known sources of adult mortality 

include oil-spill related mortality (see Section 7–A), subsistence harvest for food and skins (see Section 7–B), bycatch in 

commercial and subsistence fisheries (see Section 7–B), dieoffs during spring migration in years when open-water leads 

are not available (Barry 1976), and aspergillosis (Remsen and 

Binford 1975), but the relative importance of these sources 

cannot be estimated with existing data. Predation on nests 

and young chicks is fairly common, but predation on adults 

is thought to be uncommon. See Section 7–C for a review of 

predation.

6. Population Distribution, Size, and Trends.

A. Relative Abundance and Distribution in 

Alaska.

Most Yellow-billed Loons on Alaska breeding grounds 

occur between the Colville River and Meade River but are 

distributed patchily therein. Yellow-billed Loons also breed 

sparsely east of the Colville River to the Canning River, and 

sparsely west of the Meade River to Point Hope, near the coast 

of Kotzebue Sound and the northern Seward Peninsula, and on 

St. Lawrence Island. 

In the following paragraphs, the mean ± standard error is 

given except where use of the mean ± 95% confidence interval 

(CI) half-width is noted.

Breeding grounds – Arctic Coastal Plain of Alaska.

The relative density of Yellow-billed Loons in northern 

Alaska has been well documented by ongoing U.S. Fish and 

Wildlife Service aerial waterfowl surveys—the Arctic Coastal 

Plain Breeding Pair Survey and the North Slope Eider Survey 

(described in Section 9–B), which were used to produce the 

relative density polygons illustrated in Fig. 3. The following 

description of this speciesʼ patchy distribution is taken from 

Earnst et al. (in review). Most of the population (53% of sightings recorded during the Arctic Coastal Plain Breeding Pair 

Surveys, 1992–2003) occurs within “concentration areas” (i.e., 

>11 individuals/100 km2, Fig. 3) that encompass only 12% of 

the study area. The largest is the contiguous concentration area 

between the Meade and Ikpikpuk rivers, which encompasses 

38% of Yellow-billed Loon sightings in 8% of the study area. 

The highest density subset therein (i.e., >21 individuals/100 

km2) encompasses 10% of sightings in only 2% of the study 

area (outlined in black in Fig. 3). The corrected population 

size estimate for North Slope breeding grounds is 2,221 (± 

460) Yellow-billed Loons in early June and 3,369 (± 663) in 

late June (Earnst et al. in review; Section 6–E).

Breeding grounds – northwestern Alaska.

The wetlands of Seward Peninsula and Selawik National 

Wildlife Refuge (Fig. 4) are not included in the annual surveys 

of the Arctic Coastal Plain (above), but were surveyed during early to mid-June in 1992–1993 and 1996–1997 using 

standard waterfowl breeding pair survey methods. Surveys of 

the two areas combined, which encompassed all likely Yellow-billed Loon breeding habitat on the Seward Peninsula and 

from Selawik National Wildlife Refuge to Point Hope yielded 

a population index of 730 ± 126 Yellow-billed Loons. When 

combined with an estimate of 50 loons on St. Lawrence Island 

(Fair 2002), the total population index for Yellow-billed Loons 

in western Alaska is 780 individuals. The two surveys are 

described in more detail below.

Selawik National Wildlife Refuge contains numerous large thaw lakes, estuaries, and brackish lakes along 

the Selawik and Kobuk river deltas. In early to mid-June in 

1992–1993 and again in 1996–1997, about 200 km2 and 800 

km2, respectively, of the 15,000 km2 of the refuge and adjacent wetlands along the Noatak River to the northwest were 

surveyed for waterbirds using typical breeding pair survey 

methods. Only 4 Yellow-billed Loons were seen (Fig. 4), 

resulting in a population index of 47 ± 25 individuals (Platte 

1999, USFWS unpubl. data). 

Seward Peninsula coastal wetlands, from the north edge 

of the Yukon Delta to the Baldwin Peninsula in Kotzebue 

Sound, were surveyed during 1992–1993. Approximately 

1,320 km2 were sampled across the 25,700 km2 study area, and 

61 Yellow-billed Loons were observed (Fig. 4) for a total population index of 683 ± 124 individuals in the study area (based 

on stratified sampling; USFWS unpubl. data). These sightings, 

which occurred along both the northern and southern coasts 

of the Seward Peninsula, constitute the southern-most sightings on Alaskan breeding grounds except for the few on St. 

Lawrence Island.

Marine habitat during summer – southern Alaska.

Immatures (1–2 year-olds) are thought to remain on the 

wintering grounds during the summer, as do Common Loons 

(Evers 2004). Of the known wintering areas off the shore 

of Alaska, marine boat-based surveys have been conducted 

in southeast Alaska, Lower Cook Inlet, and Prince William 

Sound. The combined population estimate for these areas was 

only 339 Yellow-billed Loons, but many loons were not identified to species. The large confidence intervals associated with 

Status Assessment 11
these estimates indicate that the true number of Yellow-billed 

Loons summering in southern Alaska, and any temporal or 

spatial patterns in abundance, are poorly known. The surveys 

are described below.

Southeast Alaska. Boat-based surveys conducted off 

the coast of the southeast Alaska archipelago (approximately 

Haines to Ketchikan) indicate a total abundance of 267 ± 422 

(CI) Yellow-billed Loons in this area in June–July 1994 (Agler 

et al. 1995a). The surveyed area extended to 5.6 km offshore, 

and was divided into a shoreline stratum <200 m from land 

(4,690 km2 with 3.2% of the area surveyed) and an offshore 

stratum >200 m from land (30,778 km2 with 0.5% of the area 

surveyed). Loons (all species combined) tended to occur at 

higher density in the shoreline stratum, but were seen throughout the area in low densities, usually in flocks of less than 6 

individuals. Population indices (individuals ± CI) for other 

species included Red-throated Loons 212 ± 195, Pacific Loons 

1,329 ± 990, Common Loons 1,639 ± 1,123, and unidentified 

loons 1,420 ± 1,527. 

Aerial surveys were conducted over coastal marine 

areas of southeast Alaska during late July to early August in 

1998–2002. Although loons were not identified to species, the 

surveys will indicate general patterns of loon habitat use when 

analyses are completed (J. Hodges pers. comm.).

Lower Cook Inlet. During boat surveys during the summer of 1993 in the Lower Cook Inlet of southern Alaska, 63 ± 

124 (CI) individual Yellow-billed Loons were estimated to be 

present in the 13,800 km2 study area (Agler et al. 1995b). Only 

about half of all loons observed were identified to species. 

Prince William Sound. During eight years of July boat 

surveys of Prince William Sound during the period 1972–

1998, the average population index for Yellow-billed Loons 

was only 9 individuals (range 0–51) (summarized in Lance et 

al. 1999). The study area included all of the Sound, with the 

shoreline stratum sampled at 25%, the coastal pelagic stratum 

at 22%, and the pelagic stratum at 29%.

Figure 4. Yellow-billed Loon sightings and areas surveyed on the Seward Peninsula in 1992–1993 and from the Selawik National 

Wildlife Refuge (NWR) to Point Hope in 1996–1997. Light gray areas were surveyed in two years; dark gray areas in one year. National 

Wildlife Refuges and National Parks (NP) are indicated. Based on Platte 1999.

12 Status Assessment and Conservation Plan for the Yellow-billed Loon
Marine habitat during summer – northern Alaska.

In addition, to the boat-based surveys in southern Alaska, 

aerial surveys have been conducted over Harrison Bay, offshore from the breeding grounds, where sightings presumably 

consisted of individuals holding territories nearby and probably some nonbreeders (described below).

Harrison Bay. Adult Yellow-billed Loons holding territories near the coast often commute to marine waters, where 

they are known to forage. Nonbreeders, particularly 3–5 

year-olds that are not yet holding territories, may also frequent 

marine waters off the breeding grounds. Lysne et al. (2004), 

in an early August aerial survey of all nearshore habitat from 

Kasegaluk Lagoon to the Canadian border, recorded 86 and 

210 Yellow-billed Loons in 2002 and 2003, respectively. 

Likewise, Fischer et al. (2002) gives the relative abundance 

of Yellow-billed Loons during June–August 1999–2000 from 

Harrison Bay to Brownlow Point. The survey is described in 

detail in Section 5–A. Yellow-billed Loons were more common in shallow nearshore water (<10 m, corresponding to 

roughly 0–20 km offshore) than deeper offshore water; near 

barrier islands (when present) than in other nearshore habitats; 

and adjacent to mainland concentration areas. For example, 

Yellow-billed Loons were several times more common in the 

Harrison Bay Shallow Stratum than elsewhere. In fact, density 

in the Harrison Bay Shallow Stratum (i.e., shallow water 

offshore of the Colville River Delta and area immediately 

west) was comparable to that on adjacent mainland breeding 

grounds (see Section 5–A).

B. Relative Abundance and Distribution in 

Canada.

In Canada, the Yellow-billed Loon breeds from the 

Alaska border to Hudson Bay and is most common on Banks 

Island and Victoria Island, and the lake district from Great 

Slave Lake northeast to northern Hudson Bay (Fig. 1). It 

breeds uncommonly on the Melville Peninsula and Adelaide 

Peninsula, in the vicinity of Queen Maud Gulf and Amundsen Gulf, and on Prince of Wales Island, Somerset Island, 

and King William Island. It breeds casually on Baffin Island, 

Devon Island, and south to Churchill, Manitoba. Five areas 

of breeding concentration have been identified (reviewed in 

North 1993, Barr 1997): 1) Banks Island; 2) western Victoria Island; 3) mainland south of the Kent Peninsula, east of 

Bathhurst Inlet, and to west of Ellice River; 4) west side of the 

Boothia Peninsula; 5) the lake district between Great Slave 

Lake and Baker Lake, including Thelon Game Sanctuary. 

Breeding is thought to be sparse outside these areas.

Fair (2002) provides a reasonable rationale for applying density estimates from various density strata on Victoria 

Island, the only large area that has been surveyed systematically (Cornish and Dickson 1996), to the other known concentration areas in Canada and arrives at a total Canadian population estimate of 8,000.

A better estimate of the size of the Canadian breeding 

population possibly could be derived by comparing GIS-based 

waterbody availability in areas with well-quantified estimates 

of loon density, such as those on Victoria Island, with areas of 

unknown density throughout the loonʼs range in Canada. However, any estimate will continue to be coarse until systematic 

surveys are flown throughout the range of the Yellow-billed 

Loon. 

C. Relative Abundance and Distribution in 

Russia..

The primary concentration areas in Russia (Fig. 1) 

appear to be on the Chukchi Peninsula, where Kondratiev 

(1989) estimated 2,000 individuals, and the Taymyr Peninsula (Rogacheva 1992). Fair (2002) argues convincingly that 

extrapolating densities from concentration areas to the entire 

Russian range would lead to unreasonably high total population size estimates. Based on 2,000 individuals on the Chukchi 

Peninsula, 2,000 on the Taymyr Peninsula, and 1,000 throughout the remainder of the range in Russia, Fair (2002) arrives 

at a more reasonable estimate of 5,000 Yellow-billed Loons in 

Russia.

The only systematic aerial surveys of Russian breeding 

grounds were conducted by Hodges and Eldridge (2001), who 

surveyed during 1993–1995 from Kolyunchin Bay on the 

Chukchi Peninsula in the east to the Lena River Delta in the 

west, a distance of 2,340 km (see place names in Fig. 1). The 

total study area size was 157,611 km2, or about 2.5 times the 

size of the Arctic Coastal Plain Survey study area in Alaska, 

and 2.1% of the area was sampled. The area included 4 major 

river deltas (Kolyma, Indigirka, Yana, and Lena) and much of 

the intervening coastline (extending up to 200 km inland). Yellow-billed Loons were observed sporadically from the Kolyunchin Bay to the Indigirka River Delta, but not further west. 

The estimated population size for the entire study area was 

674 individuals, which corresponds to an observed density of 

0.0043 loons/km2, compared to an average overall observed 

density of 0.047 loons/km2 on Alaskaʼs Arctic Coastal Plain 

Survey (1992–2003; Earnst et al., in review). If this density is 

extrapolated to the approximate breeding range in Russia (Fig. 

1), which appears to be 18–19 times the size of the range in 

northern Alaska, then one arrives at a very rough estimate of 

4,800–5,000 loons in Russia. Thus, until further information 

is available from systematic surveys or from lake availability, 

Fairʼs (2002) estimate of 5,000 seems reasonable. 

D. Relative Abundance and Distribution on 

Wintering Sites.

The relative abundance of Yellow-billed Loons on wintering sites is poorly known. It winters regularly, but sparsely, in 

nearshore marine waters from Kodiak Island through Prince 

William Sound, and throughout southeast Alaska and British 

Columbia (Figs. 1 and 2). It winters irregularly southwest of 

Status Assessment 13
Kodiak Island along the Aleutian chain and along the coast 

of Washington to Baja California. Of the 11 birds marked 

with satellite transmitters on Alaskan breeding grounds, all 

wintered off the coast of North Korea, Japan, or China (J. 

Schmutz pers. comm.). Yellow-billed Loon relative abundance 

on wintering sites has been quantified only in Alaskaʼs Lower 

Cook Inlet and Prince William Sound, and a combined estimate for Yellow-billed Loons and Common Loons is available 

for the bays of Kodiak Island (described below). The large 

confidence intervals associated with these estimates indicate 

that the true number of Yellow-billed Loons wintering near 

Alaskaʼs shores is poorly known. The surveys are described 

below.

Lower Cook Inlet. During boat surveys during the winter of 1994 in the Lower Cook Inlet of southern Alaska, 38 ± 

74 (CI) Yellow-billed Loons were estimated in the 3,700 km2

study area (Agler et al. 1995b). 

Prince William Sound. During 8 years of March boat 

surveys of Prince William Sound between 1972 and 1998, 

estimated abundance of Yellow-billed Loons was 20–50 

individuals in 3 years, 51–150 in 4 years, and 426 in 1 year 

(summarized in Lance et al. 1999). The high annual variation 

in number recorded is probably more due to sampling error 

and variation in percent of Yellow-billed Loons classified as 

unidentified loons rather than variation in number actually 

present. The average annual percentage of loons unidentified 

was 51% (range 5%–83%). The study area included all of the 

Sound with 13% of the shoreline stratum sampled, 14% of the 

coastal pelagic stratum, and 29% of the pelagic stratum.

Kodiak Island. During 1979–1984, marine birds in 

selected bays of Kodiak Island were surveyed in the fall 

(November) and in the winter (February) using strip transect 

surveys from a boat (Zwiefelhofer and Forsell 1989). Common Loons and Yellow-billed Loons were not identified 

separately, but together made up more than 95% of the loons 

identified. Presumably the vast majority were Common Loons. 

Average loon density during winter was 1.23 loons per km of 

shoreline sampled. Density was twice as high in the shallow 

Sitkalidak Strait area as compared to the deep Uyak Bay and 

Uganik Bay. Comparison of November and February estimates 

indicated that loons were still moving into the bays of Kodiak 

Island during November. The surveys have continued since 

1984 and will provide further information on relative abundance around Kodiak Island (Zwiefelhofer pers. comm.).

Southeast Alaska. Aerial surveys were conducted over 

coastal marine areas of southeast Alaska during late February 

to early March in 1998–2002. Analyses are in progress and 

should indicate general patterns of loon habitat use, although 

loons were not identified to species (J. Hodges pers. comm.).

E. Population Size.

The small population size and patchy distribution of the 

Yellow-billed Loon has caused concern about this speciesʼ vulnerability to changes in its environment (Center for Biological 

Diversity 2004). It is one of the rarest species breeding regularly in the mainland U.S. (Table 1). The Yellow-billed Loon 

corrected population size on northern Alaska breeding grounds 

during the early June North Slope Eider Survey is estimated at 

2,221 (± 460) individuals, with a 95% confidence interval of 

1,209 to 3,233 individuals (Earnst et al. in review). Some fraction of nonbreeding loons may arrive by the late June Arctic 

Coastal Plain Survey, when the corrected population estimate 

of 3,369 (± 663) individuals (95% CI: 1,910–4,828) is somewhat, but not significantly, higher than in early June (Earnst et 

al. in review). These estimates incorporate a correction factor 

to reduce bias. The correction factor, based on the ratio of 

loons observed during intensive lake-circling aerial surveys to 

the number observed during the North Slope Eider and Arctic 

Coastal Plain surveys, indicates that intensive surveys detect 

only 16% more individuals than the traditional waterfowl surveys (Earnst et al. in review). Further work is needed to obtain 

a correction factor based on a larger sample of years and aerial 

transects, and one that incorporates the ratio between the 

number of loons observed on an intensive aerial survey and 

ground surveys. The early June estimate corresponds well with 

a preliminary estimate of 2,129 (± 342) individuals from the 

first year of the two-year Yellow-billed Loon Survey (USFWS, 

unpubl. data; see Section 9–B for survey description). 

The North Slope is estimated to support <1,000 nesting 

pairs in most years (range 437 to 1,214 pairs; Earnst et al. in 

review), based on 81% of the 3,369 present in late June being 

territorial (as in Common Loons, Evers 2004) and 39%–89% 

of territorial Yellow-billed Loons attempting to breed per year 

(Section 5–C). Even if all of the 3,369 Yellow-billed Loons 

were territorial, the expected range would be only 593 to 1,499 

nesting pairs. Most nesting pairs have probably arrived by the 

time of the early June survey since nesting pairs arrive in late 

May or as soon as the first melt water appears on rivers (North 

and Ryan 1988, Earnst pers. obs.), and later arriving individuals are probably nonbreeders or younger, nonterritiorial birds 

as they are in Common Loons (Evers 2004). This estimate 

of <1,000 nesting pairs should be of particular interest in the 

conservation of Yellow-billed Loons.

A reasonable estimate for all Yellow-billed Loons on 

Alaskan breeding grounds is 4,149 individuals (3,369 on the 

Arctic Coastal Plain in late June, this section, plus 780 in 

western Alaska, Section 6–A). Another population of interest includes any birds that remain at sea and thus are not 

counted during breeding ground surveys. All 1–2 year-olds are 

assumed to remain at sea, as is true in Common Loons (Evers 

2004), since no immature-plumaged individuals have been 

observed on the breeding grounds. Earnst et al. (in review) use 

Common Loon demographic rates (reviewed in Section 5–C) 

and a simple stable-age population matrix, to estimate that 

approximately 19.8% of the June population (or 969 individuals) is 1–2 years of age. Also, the number of adult-plumaged 

birds present on breeding grounds in late June varies with 

spring temperatures such that approximately 14.1% of adultplumaged birds present during the warmest springs are predicted to be absent during an average spring (Earnst in review, 

and see Section 6–F). Thus, the total number of Yellow-billed 

14 Status Assessment and Conservation Plan for the Yellow-billed Loon
Loons on Alaska breeding grounds plus cohorts at sea is estimated to be 6,024 individuals (Earnst et al. in review).

The Yellow-billed Loon is one of the rarest birds that 

breeds regularly in the mainland U.S. (Table 1). A reasonable 

range-wide estimate for North American breeding grounds 

plus cohorts at sea is 16,000 individuals (Earnst et al. in 

review). This includes 6,024 individuals associated with 

Alaska (i.e., breeding grounds and at sea) and 9,975 individuals associated with Canada (i.e., 8,000 on breeding grounds 

[Fair 2002] plus 19.8% at sea). Among landbird, shorebird, 

waterfowl, and other waterbird species having >10% of their 

global population within the mainland U.S. (i.e., excluding 

Hawaiian and other island species), the Yellow-billed Loon 

is estimated to be among the 10 rarest in the U.S. and one of 

only 20 with a North American population estimate ≤ 16,000 

(Table 1).

F. Population Trends.

There is no evidence of a long-term trend in Yellowbilled Loons over the 18-year Arctic Coastal Plain Survey or 

the 12-year North Slope Eider Survey (Fig. 5). Earnst et al. (in 

review) estimated the trend using multivariate, mixed effects 

regression models that included data from both surveys and 

found no evidence of a statistically significant population 

trend since 1986 (annual change = -0.9% ± 1.2%). However, 

the 95% CI was large (-3.6% to +1.8%), indicating that the 

estimated trend is not statistically distinguishable from a total 

18-year population change of either -48% or +38%. The multivariate approach incorporated variables that were potential 

sources of bias in the trend, such as observer experience and 

spring weather, and variables that might reduce the variance in 

the trend, such as survey identity and observer type (pilot vs. 

passenger). It was particularly important to include observer 

experience, because observers saw more loons as they became 

more experienced, and average observer experience has 

increased since 1986. Spring weather was also important 

because more loons were recorded during warm springs (as 

measured by thaw-degree days) than cold springs on the Arctic 

Coastal Plain Survey. Springs tended to become warmer from 

1986 to 1996 but were variable thereafter, so thaw-degree days 

were a source of noise in the 18-year trend, rather than bias.

It is important to ask how likely existing surveys are to 

detect a substantial long-term decline if it were occurring. 

Both the 18-year Arctic Coastal Plain Survey and the 12-year 

North Slope Eider Survey had low power to detect a 3.4% 

decline, which would result in a 50% decline in 20 years 

(power = 62% and 26%, respectively, using simple log-linear 

regression; Earnst et al. in review). When multivariate models 

were used to combine the two surveys and incorporate covariates, power to detect a 3.4% decline was 81% (Earnst et al. in 

review). However, given the likelihood of additional sources 

of bias and the imperfect nature of our multivariate model of 

bias, actual power to detect a trend is probably lower (Bart et 

al. 2004). In addition, any declines more gradual than 3.4% 

would be more difficult to detect as statistically significant; 

0

1000

2000

3000

4000

5000

1985 1987 1989 1991 1993 1995 1997 1999 2001 2003

Year

ACP

NSE

Yellow-billed Loon population index

Status Assessment 15

Figure 5. Annual population indices for Yellow-billed Loons in the Arctic Coastal Plain (ACP) and North Slope Eider (NSE) surveys. 

Indices are not corrected by a visibility correction factor. The NSE covers a smaller area and thus has smaller annual indices. The 

population trend for 1986–2003 is near zero (-0.9% ± 1.2% annual change) with a 95% CI of 3.6% to 1.8% when multivariate models are 

used to combine the surveys and incorporate potential sources of bias and noise. Modified from Earnst et al. (in review).
Table 1. Species as rare as the Yellow-billed Loon (i.e, having population estimates ≤16,000 individuals). List derived 

from all full species recognized by the American Ornithologists’ Union having >10% of their global population within the 

mainland U.S. (i.e., excluding Hawaiian and other island species)a. 

Speciesb Population Size Estimatec

Status United States North America

 1. California Condor (Gymnogyps californianus)d 150 150 Endangered

 2. Whooping Crane (Grus americana)e 312 312 Endangered

 3. Gunnison Sage-Grouse (Centrocercus minimus)f 2,000 2,000 Candidate

 4. Kirtlandʼs Warbler (Dendroica kirtlandii)f 2,100 2,100 Endangered

 5. Piping Plover (Charadrius melodus)g 3,800 5,900 Endangered

 6. Black-capped Vireo (Vireo atricapillus)f 4,800 4,800 Endangered

 7. Wandering Tattler (Heteroscelus incanus)g 5,000 10,000

 8. Wilsonʼs Plover (Charadrius wilsonia)g 6,000 6,000

 9. Yellow-billed Loon (Gavia adamsii)h 6,000 16,000 Petition Pending

10. Gull-billed Tern (Sterna nilotica)i 7,000 7,000

11. Black Oystercatcher (Haematopus bachmani)j 8,700 10,800

12. American Oystercatcher (Haematopus palliatus)g 8,800 8,800

13. Rufous-winged Sparrow (Aimophila carpalis)f 9,600 9,600

14. Bristle-thighed Curlew (Numenius tahitiensis)g 10,000 10,000

15. Florida Scrub-Jay (Aphelocoma coerulescens)f 10,000 10,000 Threatened

16. Spotted Owl (Strix occidentalis)f 10,500 10,500 Threatenedk

17. White-tailed Kite (Elanus leucurus)f 10,900 10,900

18. Mountain Plover (Charadrius montanus)l 11,000 11,000 --l

19. Reddish Egret (Egretta rufescens)i 12,000 12,000

20. Pacific Golden-Plover (Pluvialis fulva)g 16,000 16,000

a

Rare island-breeding species not in this table include Dovekie (Alle alle), Xantusʼs Murrelet (Synthliboramphus hypoleucus), Ashy StormPetrel (Oceanodroma homochroa), McKayʼs Bunting (Plectrophenax hyperboreus), Island Scrub-Jay (Aphelocoma insularis), and several 

Hawaiian-breeding seabirds. Rare species not included in this table because <10% of the global population breeds in the U.S. include, among 

others, Stellerʼs Eider (Polysticta stelleri), Buff-breasted Sandpiper (Tryngites subruficollis), Sharp-tailed Sandpiper (Calidris acuminata), 

Snowy Plover (Charadrius alexandrinus), California Gnatcatcher (Polioptila californica), Aplomado Falcon (Falco femoralis), and Montezuma 

Quail (Cyrtonyx montezumae). Kittlitzʼs Murrelet (Brachyramphus brevirostris), a recent addition to the Candidate species list, has population 

estimate of 9,505–26,767 with a mid-point of 18,136 (USFWS 2004), just over the 16,000 cut-off. This table does not include species thought 

to be extinct in the wild, such as Ivory-billed Woodpecker (Campephilus principalis) and Eskimo Curlew (Numenius borealis). In addition, 

15 avian subspecies or races listed as Threatened or Endangered have North American populations ≤ 16,000 (http:/ecos.fws.gov/tess_public, 

accessed 15 September 2004).

b

 Population estimates for species not meeting the criteria for this list (i.e., those with >16,000 individuals in North America) taken from the 

sources listed in footnotes c-f below plus the North American Waterfowl Management Plan Committee (1998), Wetlands International (2002), 

and numerous species accounts in The Birds of North America series (A. Poole and F. Gill, editors). 

c

 Mean estimate if available, otherwise the midpoint of range used.

d

 Snyder and Schmitt 2002. Includes birds in captivity.

e

 Stehn 2004.

f

 Rich et al. 2003.

g

 Morrison et al. 2001.

h

 Earnst et al. in review.

i

 Kushlan et al. 2002.

j

 Andres and Falxa 1995.

k

 Threatened status applies to the Northern Spotted Owl (Strix occidentalis caurina) and the Mexican Spotted Owl (Strix occidentalis lucida).

l

 USFWS 2002b. Proposed for listing in 1999; withdrawn in September 2003 due to new information.

16 Status Assessment and Conservation Plan for the Yellow-billed Loon
for example, power to detect a 2.5% annual decline was only 

55%.

The population trend described above is based only on 

the breeding component of the population—ongoing breeding 

ground surveys do not monitor trends in immature or nonbreeding Yellow-billed Loons that remain in marine waters. 

Thus, to the extent that individuals from this nonbreeding pool 

replace individual territory holders as they die, this unmonitored pool masks, or delays the detection of, any trend on the 

breeding grounds.

There are no data on historical or recent population trends 

in Canada or Russia, but the literature provides no evidence 

for a large change in the breeding population in Canada (Barr 

1997).

7. Potential Threats to the Population.

There are good reasons to be concerned about any 

potential threat to Alaskaʼs breeding population of Yellowbilled Loons. Northern Alaskaʼs breeding population is small, 

with probably fewer than 1,000 pairs attempting to breed in 

an average year, and the low reproductive potential of Yellow-billed Loons means that the population will not recover 

from perturbations rapidly. It seems valuable, then, to consider 

carefully and research thoroughly each potential threat, and to 

monitor likely effects on survival and reproduction. At present, we lack the information necessary to predict the effect 

of potential habitat loss and other potential threats to local or 

range-wide populations.

In Yellow-billed Loons, as in other long-lived organisms, 

the growth rate of the population is most sensitive to factors 

that affect adult survival rather than those affecting rates of 

reproduction or chick survival (e.g., Caswell 1978, Brault and 

Caswell 1993). In other words, a proportionate change in adult 

survival will have a larger effect than the same proportionate 

change in reproduction or chick survival (see Caswell 1989). 

Thus, we would be most likely to see population declines that 

result from adult deaths, for example, due to oil spills, contaminants, subsistence harvest, fisheries bycatch, or disease. 

However, population declines due to a decline in reproduction 

or chick survival are also possible, especially if the declines in 

reproduction are large or persist over several years, as might 

occur if breeding habitat were lost or nest predators increased 

steadily over the course of oil development in previously 

undisturbed sections of the breeding range. 

Sections 7–A, C, D, E, and F represent categories of 

potential threats typically addressed in Status Assessments 

(USFWS 2000). Although these categories correspond to the 

five listing criteria considered under the Endangered Species 

Act, this document does not make or imply a recommendation 

concerning listing, instead, these criteria are used as a framework to describe existing knowledge and identify research 

needs.

A. Habitat Loss on the Breeding Grounds.

A potential source of Yellow-billed Loon breeding habitat 

loss is the continued expansion of the oil industry across the 

North Slope of Alaska and Canada, particularly within the 

National Petroleum Reserve-Alaska (NPR-A), which is home 

to approximately 91% of the Yellow-billed Loons on Alaskaʼs 

North Slope (Earnst et al. in review, and Fig. 3). Virtually all 

Yellow-billed Loon breeding areas are open or proposed to 

be opened to development (BLM 1998a,b, 2003, 2004a,b,c) 

and no permanent protection of Yellow-billed Loon habitat 

is proposed. About 23% of Yellow-billed Loons within the 

NPR-A are in the area of High Oil Potential which is likely to 

be developed first (Fig. III-A–29 in BLM 1998a, and Map 105 

in BLM 2003, Earnst et al. in review). Large-scale development may proceed rapidly in previously pristine environments 

and produce cumulative effects that are difficult to predict or 

reverse (National Research Council 2003). In addition to any 

habitat lost directly to gravel pads, habitat loss may arise from 

oil spills, roads, environmental contaminants, noise, changes 

in hydrology, increases in predator populations, and increased 

human activity in previously remote areas (BLM 1998a and 

2003, National Research Council 2003). It is difficult to 

predict the potential impact to Yellow-billed Loons within 

the NPR-A because very few individuals breed in the previously industrialized Kuparak and Prudhoe Bay Oilfields, and 

data on their response to disturbance is lacking. Likewise, it is 

difficult to predict the proportion of the population that might 

be affected because the proposed footprint of development 

changes (e.g., BLM 2004b,c), and cumulative effects of development are not always predictable or well quantified (National 

Research Council 2003).

This section (7–A) considers potential sources of direct 

and indirect habitat loss associated with oil-field development. 

I emphasize that there are no data on the nature nor magnitude 

of effects of development or disturbance on Yellow-billed 

Loons, and there are few relevant data from other species. This 

section simply uses knowledge of Yellow-billed Loon ecology 

to identify topics on which data are needed. None of the statements below provide evidence that effects on loons will occur. 

Overview of planned or existing development.

Northeast NPR-A. The original Record of Decision 

opened 87% of the 4.6 million acres of the Northeast NPR-A 

to oil and gas leasing (BLM 1998b). Of those areas where 

permanent surface structures were not to be allowed, the 

following are of particular relevance to Yellow-billed Loons: 

near Fish and Judy creeks, near Ikpikpuk and Miguakiak 

rivers, and within 0.25 mile of fish-bearing lakes within the 

Deep-Water Lake Zone. However, the Draft Amended EIS for 

the Northeast NPR-A would open 97% of the area (Preferred 

Alternative, BLM 2004b). In particular, the Preferred Alternative would allow drilling within all parts of the Teshekpuk 

Lake Surface Protection Area of any importance to Yellowbilled Loons (the Surface Protection Area encompasses 6% 

of Yellow-billed Loons recorded during Arctic Coastal Plain 

surveys, 1992–2003).

Status Assessment 17
Northwest NPR-A. The Record of Decision opened all 

8.8 million acres of the Northwest Planning Area to oil and 

gas leasing (BLM 2004a).

Alpine and Alpine Satellite Developments. The Colville 

River Delta and Fish Creek area contain a multitude of 

fish-bearing, deep lakes that are used regularly by breeding 

Yellow-billed Loons. Most of the land is managed by BLM 

under the guidance of the Record of Decision for the Northeast 

Planning Unit (described above). Between 1998 and 2001, the 

beginning of development on the Delta resulted in two production pads, a 2- to 3-mile gravel road, a 1-mile airstrip, processing facilities, a drilling mud plant, a maintenance complex, 

warehouse buildings, disposal wells, a large camp facility with 

waste and wastewater utilities, and a 34-mile long pipeline that 

connects to the Kuparuk Oilfield (BLM 2004c). 

In addition, the Preferred Alternative in a recent EIS 

accepts the key elements of ConocoPhillipsʼ proposed action 

for further development, including five new satellite drilling 

pads on the Colville River Delta and adjacent Fish Creek area, 

a bridge across the main channel of the Colville, a road system 

that connects to that outside the NPR-A, a drilling pad within 

the 3-mile setback that was designed to protect Fish Creek, 

and oil infrastructure within 500 feet of certain waterbodies 

(BLM 2004c). The latter three activities are requested exemptions to existing stipulations. The EIS also describes a scenario 

of Full Field Development for the next 20 years involving 22 

new production pads, up to 190 miles of new roads, 2 new 

processing facilities, multiple airstrips, and further exceptions 

to stipulations. 

Relevance of specific activities to Yellow-billed Loon 

habitat.

Roads and gravel pads. Roads and gravel pads, and 

the associated increase in dust dispersion, have profound 

direct and indirect effects on hydrology, snow-melt patterns, 

and thermokarst action of the tundra (Walker 1987, National 

Research Council 2003, also see review in BLM 1998a). Thermokarst erosion and water impoundment is estimated to affect 

twice the area directly covered by the footprint of the gravel. 

For example, the chosen alternative for the Northwest Planning Area (BLM 2004a), is expected to result in the long-term 

loss of 2,500 acres of tundra: 400 acres due directly to gravel 

placement on pads and roads, 800 acres due to thermokarst 

erosion and water impoundment, 400 acres due to docking 

or staging areas, 400 acres due to gravel mining from borrow 

pits, and 500 acres due to oil pipeline construction (p. V-23, 

BLM 2003). Roads also increase noise and provide access 

to previously remote sites, thus increasing the frequency of 

human disturbances in surrounding areas.

Oil spills near breeding territories. BLM (1998a) 

estimates that 20%–35% of crude-oil spills occur on or reach 

the tundra surrounding gravel pads, and it acknowledges that 

the spills most likely to damage large areas are those that enter 

a river or waterbody. Thus, the areas preferred by breeding 

loons—areas with high interconnectivity among waterbodies 

and river channels (as indicated by habitat preferences within 

the NPR-A, see Section 5–A)—are the areas where an oil 

spill is most likely to spread widely and rapidly. For example, 

within the Northeast Planning Area, BLM (1998a) considers 

the possible contamination of the Colville River and its tributaries to be one of the greatest concerns. 

Oil spills in the coastal Beaufort Sea. Yellow-billed 

Loons are regularly documented in the coastal Beaufort Sea 

during the breeding season (Fischer et al. 2002, Lysne et al. 

2004). The species is sometimes described as at low risk from 

a marine oil spill, relative to other species, because there are 

few individuals concentrated in one location at one time (BLM 

1998a, Stehn and Platte 2000). However, individuals holding territories near the coast commute from marine foraging 

sites to territories; thus, many loons are likely to cycle through 

the marine habitat daily and this provides the opportunity for 

a spill off the coast of an important breeding concentration 

area to affect a substantial proportion of the local population. 

Similarly, when the number of Yellow-billed Loons present in coastal waters is considered in relation to this speciesʼ

small breeding population size, the impact of coastal oil spills 

appears greater (see also Section 5–A). 

Yellow-billed Loons may also be vulnerable to nearshore oil spills during spring staging when they appear to use 

open-water leads off the northern coast of Alaska and Canada. 

Although spring staging is not well studied, and presumably 

the extent of open water and degree of congregation of loons 

varies annually, large numbers of Yellow-billed Loons have 

been reported in open-water leads in some years (Alexander et 

al. 1997). 

Ice roads. Ice roads, which are used by heavy machinery 

during the winter, are constructed by spraying water (pumped 

from nearby deep lakes or river channels) onto frozen tundra and wetlands to form multiple layers of ice into a thick 

roadbed. Ice roads that pass over lakes compact lake ice, and 

increase lake-ice depth, and thus delay melt (BLM 1998a). 

Because the timing of Yellow-billed Loon nest initiation is 

closely tied to ice melt on their breeding lake (North and Ryan 

1988), and productivity appears to be reduced in years with 

delayed nest initiation (Section 5–B), ice roads passing over 

breeding lakes may affect nest success if ice melt is delayed, 

although no studies have addressed this question. In addition, 

the increase in lake-ice depth and concomitant decrease in 

open water under the ice may affect overwintering fish populations (BLM 2003). 

Ice roads built over land may persist for as much as a 

month into the snow-melt period (BLM 2003) and cause melt 

water to persist even later into the spring (BLM 1998a). This 

is likely to affect only nest bowls and shorelines that lie within 

a few meters of the ice-road bed (ice-road location will be offset each year). The presence of melt water in a traditional nest 

bowl during the egg-laying period may reduce the territorial 

pairʼs probability of breeding in the year in question, although 

no studies have addressed this specific question. 

Pumping water from lakes and rivers. During oil-field 

development and operation, a considerable amount of water is 

18 Status Assessment and Conservation Plan for the Yellow-billed Loon
pumped from freshwater lakes and rivers to construct ice roads 

and for use by facilities. For example, water requirements are 

1.0 to 1.5 million gallons per mile of ice road, 2 million gallons per ice pad, and 1.6 million for drilling and camp use per 

site. In total, 295 million gallons of water, acquired from 90 

lakes, could be required each winter during exploration of the 

Northwest Planning Area (p. V-20, BLM 2003). 

Yellow-billed Loons could be affected by pumping 

water from freshwater lakes in two ways. First, reducing the 

free-water volume of lakes during the winter decreases the 

amount of water and oxygen available to overwintering fish 

populations on which Yellow-billed Loons depend during 

the breeding season. Second, loon species, including Yellowbilled Loons, appear sensitive to changes in water levels on 

nesting lakes. Typical nest placement in loon species is such 

that individuals can swim directly to, or very near, the nest 

bowl. The effect of water withdrawal may depend on whether 

it occurs during or prior to incubation. If water withdrawal 

causes a nest to become stranded away from the water during

incubation, it appears more likely to be abandoned or predated 

than other nests. For example, in a study of Pacific Loons in 

the Prudhoe Bay Oilfield, only 15% (2/13) of nests were successful on impoundments with large water-level drawdowns 

during the breeding season compared to 41% on natural ponds 

(Kertell 1996). Similarly, in a study of Common Loons on two 

lakes in New Hampshire, water-level fluctuations during incubation caused failure of all nine active nests in one year (seven 

were abandoned and two were predated) (Fair 1979, see also 

Barr 1986, McIntyre 1994). If water withdrawal causes a traditional nest bowl to be stranded prior to incubation, a potential 

(but currently uninvestigated) effect may be to decrease the 

pairʼs probability of nesting in the year in question. Although 

a pair is certainly capable of building a new nest bowl close to 

water, the stranding of the traditional bowl may serve as a cue 

that breeding conditions are undependable and result in deferment of reproduction to future years. Whether it occurs prior 

to or during incubation, the effect on nesting loons of withdrawing a given percentage of a lakeʼs free water volume will 

depend on the bathometry of the lake bottom and the slope 

of the shoreline near the nest. In the New Hampshire study, 

failed nests were stranded 0.61 m–30 m (2 feet–100 feet) from 

water horizontally and 0.33 m–0.91 m (16 inches–36 inches) 

vertically (Fair 1979); in the Prudhoe Bay study, the eight 

impoundments with low nest success had incurred surface area 

reductions of 25% to 69% (Kertell 1996).

In Yellow-billed Loons, water-level fluctuations are cited 

as one reason that individuals do not nest on those lakes with 

water levels that fluctuate with the river level (North and 

Ryan 1989). One might expect Yellow-billed Loons to be even 

less adapted to fluctuating water levels than Common Loons, 

because Yellow-billed Loons have not evolved with rainfall 

patterns and topography that produce naturally fluctuating 

water levels and do not have the same opportunity to re-nest or 

delay nest initiation as do more temperate-breeding Common 

Loons.

Increase in predator abundance. An increase in nest 

predators is a likely and potentially serious side-effect of 

development that needs further study (BLM 2003, National 

Research Council 2003). Potential nest predators such as 

Glaucous Gull (Larus hyperboreus), Common Raven (Corvus 

corax), arctic fox (Alopex lagopus), red fox (Vulpes vulpes), 

and grizzly bear (Ursus horribilis) are known to be attracted to 

human facilities, in part due to uncontained refuse. The breeding distribution of Common Raven in the arctic appears to be 

expanding parallel to that of human-made structures, which 

provide nesting sites (Day 1998). Arctic fox also benefit from 

food, shelter, and den sites associated with oil-field facilities 

and pipelines (Eberhardt et al. 1982), resulting in higher fox 

density and pup production in the Prudhoe Bay oil field than 

in surrounding areas (Burgess et al. 1993).

An increase in nest predators could have an important 

effect on Yellow-billed Loon productivity. Predation is probably the primary cause of egg loss and is responsible for some 

fraction of chick mortality. Any increase in predator abundance may be exacerbated by an increase in human activities 

near loon territories (see next paragraph). 

Noise and visual disturbance from aircraft, ground 

vehicles, and human presence. The potential negative 

impacts on wildlife due to human presence and persistent 

noise from aircraft, ground vehicle traffic, housing facilities, 

or oil production facilities is well recognized (e.g, Bowles 

1995, BLM 1998a, National Research Council 2003), but 

there are no relevant data on Yellow-billed Loons. Undisturbed 

loons have high nest attendance (North 1994) and are able to 

protect chicks from aerial predators (Earnst pers. obs.), but 

loons disturbed by human presence may leave nests and chicks 

exposed to predators. Increased predation of eggs and chicks 

due directly to human disturbance is well known in other 

northern-breeding waterbirds (e.g., Aahlund and Goetmark 

1989, Keller 1991) and human use of lakes has been associated with poorer productivity in Common Loons in some 

studies (e.g., Titus and VanDruff 1981). Additional behavioral 

responses to disturbance that have been documented in other 

species, and are worthy of investigation in Yellow-billed 

Loons, include nest abandonment (White and Thurow 1985), 

decreased prey delivery to young (Fernández and Azkona 

1993, Delaney et al. 1999), avoidance of otherwise favorable 

nesting or foraging habitat (Thorson et al. 2002), increased 

energy expenditure due to escape, wariness, or inefficient 

foraging (Knight et al. 1991), a change in territorial intrusions 

and defense (Fort and Otter 2004), and various physiological 

responses to stress (Washburn et al. 2003). 

Data are needed on both short-term behavioral responses 

and long-term effects of disturbance. At the behavioral level, 

some individuals, probably over the course of multiple 

breeding seasons, may habituate to nearby human activity 

and become less likely to exhibit a behavioral response (see 

Section 9–D). At the population level, because loons are 

long-lived and may be slow to abandon established territories 

even if breeding conditions become unfavorable, documenting 

any population-level effects of chronic disturbance on loon 

Status Assessment 19
abundance will require many years of detailed data. The Common Loon literature includes both examples of habituation at 

the behavioral level and of reduced productivity attributed to 

disturbance (reviewed in Evers 2004), but as a whole, it exemplifies the necessity of carefully designed studies to rigorously 

quantify disturbance and its effect on loons.

B. Habitat Conservation on the Breeding 

Grounds.

No laws or agency regulations specifically protect Yellow-billed Loons from potential breeding habitat loss arising 

from oil development. Although EISs include stipulations 

designed to reduce the environmental impacts of oil exploration and development (BLM 1998a,b, 2003, 2004a,b,c), stipulations are not considered to provide guaranteed, permanent, 

or legal protection for Yellow-billed Loon habitat. Stipulations 

are often worded vaguely and are “not intended as a prohibition of petroleum and related activities” (p. B-2, BLM 2004a), 

exceptions can be granted for a variety of reasons, including 

economic or logistic feasibility (p. 29, BLM 1998b; p. B-2, 

BLM 2004a), and stipulations and Protected Area designations 

can be revoked in subsequent documents, as evidenced by the 

Draft Amended EIS for the Northeast Planning Area (BLM 

2004b). Although typically written to protect other resources 

(e.g., fish), some stipulations, if followed, could provide 

incidental benefits to Yellow-billed Loon habitat and those 

stipulations are described below. 

Potential habitat conservation at the territory scale.

Most stipulations would provide protection at the territory rather than landscape scale (i.e., protection of individual 

lakes rather than large areas). 

Buffers relevant to oil spills. In recognition of the risk 

that any deterioration in water quality poses to fish, the EIS for 

the Northeast Planning Unit stipulated no permanent facilities 

within 0.25 miles of a fish-bearing waterbody within a geographic area called the Deep Water Lake Zone nor within 500 

feet from the high water mark of other lakes (BLM 1998b). 

In more recent EISs, the 0.25-mile set-back is applied to all 

lakes >4 m (BLM 2004a, and Preferred Alternative in BLM 

2004b). The definition of “deep lake” in this context as one >4 

m deep, rather than >2.1 m deep as is used in the context of 

water withdrawal (see below), affords less protection to Yellow-billed Loon habitat, because lakes between 2.1 m and 4 m 

deep typically do not freeze solid in the winter, may support 

overwintering fish (e.g., ninespine sticklebacks), and are used 

for nesting and brood-rearing by Yellow-billed Loons. For 

example, in a recent study, Yellow-billed Loons in the NPRA preferred both lakes 2–4 m and those >4 m over shallower 

lakes, but because lakes >4 m are quite rare on the North 

Slope, 64% of Yellow-billed Loon sightings were on lakes 2–4 

m and only 27% were on lakes >4 m (Earnst et al. in press). 

Some protection from oil spills also would be afforded 

by stipulations prohibiting permanent facilities within 0.5 to 

1 mile of selected creeks and rivers (and within 3 miles of a 

small section of Fish Creek) in the Northeast and Northwest 

NPR-A (BLM 1998a, 2004a,b). Adult Yellow-billed Loons 

sometimes make forays from breeding territories to nearby 

rivers for foraging, thus these stipulations may reduce the 

likelihood of oil contamination and other disturbance for these 

foraging loons. Because the proposed corridors are narrow, 

they will encompass few nesting and brood-rearing lakes, but 

the tendency for loon habitat to have hydrological connectivity to streams (e.g., Earnst et al. in press) suggests that any 

protection to streams within breeding concentration areas is 

beneficial. 

Buffers relevant to overwintering fish. Protection to 

overwintering fish populations and thus Yellow-billed Loon 

breeding and foraging sites could be afforded by those stipulations that a) restrict ice-road placement on deep lakes and 

deep-water pools in rivers (BLM 1998b), and b) limit water 

withdrawal to 15% of the estimated free-water volume from 

lakes 2.1 m or deeper and prohibit withdrawal from rivers, 

streams, shallow lakes, or any lake connected to a fish-bearing stream (BLM 1998b). More recent EISs include similar 

stipulations, but also allow withdrawal of up to 30% from 

lakes 1.5 to 2.1 m if they contain only ninespine stickleback 

or Alaska blackfish (BLM 2004a, and Preferred Alternative in 

BLM 2004b). 

Buffers specific to Yellow-billed Loons. The EIS for the 

Northwest Planning Area and the Preferred Alternative in the 

Amended Draft EIS for the Northeast Planning Area includes 

a stipulation that encourages the industry to conduct aerial 

surveys for 3 years before construction of facilities within 

1 mile of a lake >25 acres (10.1 ha) in size and to consider 

a 1-mile buffer around recorded nest sites and a minimum 

500-meter buffer around the remainder of the lake shoreline 

(BLM 2004a, and Preferred Alternative in BLM 2004b). The 

extent to which the stipulation recommends a reduction in 

development within this buffer is not clear. On the Colville 

River Delta (Alpine), a large housing facility and airstrip were 

placed within 1 mile of previously known Yellow-billed Loon 

nests (see maps in Burgess et al. 2000), but the development 

occurred before these recent stipulations were released.

Since there are no published data on distances at which 

human activity causes Yellow-billed Loons to depart from 

nests or exhibit other responses, a well-designed experiment 

would aid the industry and U.S. Fish and Wildlife Service in 

quantifying appropriate buffer widths (e.g., Blumstein et al. 

2003). It is logical that different buffer widths are appropriate for different types of disturbance, and this is reflected in 

the variety of buffers that have been proposed. For example, 

a relatively small buffer may minimize the probability that 

an oil spill will reach a traditionally occupied lake (e.g., the 

0.25-mile buffer around fish-bearing lakes; BLM 1998b), but a 

buffer of 1 mile or more may be necessary to minimize effects 

of human presence on nests and young broods (e.g., the 1-mile 

buffer around recorded nest sites; BLM 2004a), and permanent, large geographic preserves of no development may be 

necessary to avoid landscape-scale effects such as an increase 

20 Status Assessment and Conservation Plan for the Yellow-billed Loon
in predators (e.g., the Teshekpuk Lake Special Area and Atqasuk Wetlands; Schoen and Senner 2002). 

Potential habitat conservation at the landscape scale.

Audubonʼs Alternative Plan for the Western Arctic is the 

only plan that proposes permanent protection or protection at 

the landscape scale (Schoen and Senner 2002). The plan calls 

for long-term, coordinated conservation in the western arctic 

and proposes substantial habitat protection in two large areas 

of the NPR-A that together encompass 27% of Yellow-billed 

Loons recorded during the Arctic Coastal Plain aerial survey during 1992–2003. These areas are described more fully 

below.

In Audubon Alaskaʼs alternative plan, abundance data 

for key fish, mammal, and bird species were synthesized into 

“biological hotspots” and special protection was proposed 

within five Special Areas (Schoen and Senner 2002). Protection within two of these areas would be of importance to 

breeding Yellow-billed Loons. Audubonʼs alternative plan 

proposes that all known high-density Yellow-billed Loon 

nesting areas within the Teshekpuk Lake Special Area receive 

permanent habitat protection and that all nesting areas within 

the Atqasuk Wetlands be protected from effects of oil development. The Teshekpuk Lake Special Area, designated by the 

Secretary of Interior in 1977, encompasses 1.7 million acres 

(one-third of which is water) centered around Teshekpuk 

Lake (see Fig. I–8 in Schoen and Senner 2002). The Teshekpuk Lake Special Area contains 14% of the Yellow-billed 

Loons recorded during the Arctic Coastal Plain Survey during 

1992–2003.

Audubon also proposes that all Yellow-billed Loon nesting areas within the 2.1 million acre Atqasuk Weltands area 

be protected from effects of oil development (habitat alteration, pollution, predator increases, and disturbance during the 

nesting season). The Atqasuk Wetlands lie south of the Barrow peninsula and between Teshekpuk Lake on the east and 

Wainwright and Peard Bay on the west (see Fig. I–8 in Schoen 

and Senner 2002). The Atqasuk Wetlands area contains 

numerous deep lakes and encompasses 13% of Yellow-billed 

Loons recorded during the Arctic Coastal Plain Survey during 

1992–2003.

C. Habitat Loss and Mortality on the Wintering 

Grounds..

The vulnerability of marine wintering habitat to oil spills 

was illustrated in late March 1989 when the Exxon Valdez

spilled 11 million gallons of oil into Prince William Sound. 

Loons and other diving species are among those that may be 

particularly susceptible to oil-spill mortality because they 

often rest on the water and are likely to resurface in oil when 

they dive for food and to escape disturbance, including oil 

(King and Sanger 1979). Over 30,000 oiled bird carcasses 

were recovered, and total mortality was estimated at 250,000 

birds (Piatt and Ford 1996). Originally, 87 Yellow-billed Loon 

carcasses were reported (Piatt et al. 1990, McIntyre 1991), but 

most were later discovered to be Common Loons. The corrected number of Yellow-billed Loon carcasses was thought 

to be about 5 (J. Barr pers. comm., cited in Fair 2002), which 

would result in a total mortality estimate of 17–50 individuals 

if a 10%–30% carcass recovery rate is assumed (Piatt et al. 

1990). In a comparison of pre- and post-spill avian densities in 

oiled and unoiled areas of Prince William Sound, Irons et al. 

(2000) concluded that loons (all species combined) exhibited 

a weak negative effect from the oil spill in the year of the 

oil spill (1989) and in 1993. In another analysis by the same 

authors (Lance et al. 1999), a taxon was considered recovering 

from effects of the oil spill if densities in the oiled areas were 

increasing at a significantly greater rate than densities in the 

unoiled areas. Based on winter but not summer surveys, loons 

showed trends consistent with a recovery. Presumably the statistical power to detect a trend was substantially lower during 

the summer when relatively few loons remained in the area. 

There is also reason for concern about potential oilrelated effects on wintering grounds off the coasts of Russia, 

Japan, North Korea, and China (Center for Biological Diversity 2004), where Alaskaʼs breeding Yellow-billed Loons 

appear to winter (Section 5–E) and where pollution and other 

effects may be less regulated than in the United States.

D. Human Utilization: Subsistence Harvest and 

Fisheries Bycatch.

Subsistence harvest..

Approximately 1,331 adult loons were harvested annually 

in the four regions from northwestern to southwestern Alaska 

surveyed from 1987 to 2000 (Table 2). Of those harvested, 

207 per year were reported as Yellow-billed Loons; however, 

this estimate is not reliable due to problems with species 

identification (e.g., Fair 2002). For example, Yellow-billed 

Loons were reported harvested from the Yukon-Kuskokwim 

Delta (110 individuals and several eggs per year) and Togiak 

National Wildlife Refuge (52), but Yellow-billed Loons do not 

breed in these areas and are thought to be relatively uncommon migrants (see Section 4). Yellow-billed Loons were also 

taken from St. Lawrence and Diomede islands (37) and the 

Bering Strait mainland (2) where they are uncommon breeders but common migrants. Across all sites, most take occurred 

during spring and fall when this species was likely passing 

through on migration. 

Compared to other areas of Alaska, the opportunity for 

subsistence harvest of Yellow-billed Loons is greatest on the 

North Slope of Alaska where they are more common during 

summer months, but there is little data from North Slope villages. In northern Canada, this species is hunted throughout its 

breeding range by Native hunters and may be a regular source 

of food in a few regions (reviewed in Barr 1997). 

In conclusion, because of the uncertainty of species 

identification and especially the scarcity of harvest surveys on 

the breeding grounds, the magnitude and potential impact of 

Status Assessment 21
subsistence harvest on Alaskaʼs population of Yellow-billed 

Loons is uncertain. Improving the identification guide used 

during interviews and distributed to subsistence hunters, and 

tailoring some questions specifically to address loon take 

and identification, would be an inexpensive means of providing valuable data on the harvest of Yellow-billed Loons and 

other loon species. See Section 9–C and Conservation Plan, 

Strategy 6.1.

Bycatch in commerical fisheries.

Loons are known to be susceptible to bycatch (entanglement and accidental drowning) in near-shore gillnets. For 

example, Red-throated Loons and Common Loons accounted 

for 68% (1,633 birds) and 21% (503 birds), respectively, of all 

birds drowned in gillnets off the mid-Atlantic coast from New 

Jersey to North Carolina during the winter of 1998 (Forsell 

1999). However, Yellow-billed Loons in Alaska waters are 

probably less susceptible to commercial fisheries because the 

salmon gillnet fishery occurs in southern Alaska during the 

summer (April–September), especially in June and July, when 

most Yellow-billed Loons are on northern breeding grounds 

in Alaska and Canada. In over 9,000 active and drift gillnet 

sets observed during the summers of 1990 and 1991 in Prince 

William Sound and the Unimak Island area, only seven loons 

were killed: two Common Loons, four Red-throated Loons, 

and one unidentified loon (Wynne et al. 1991, 1992). Similarly, in over 4,200 active and drift gillnet sets observed during 

the summers of 1999 and 2000 in Cook Inlet, loons (species 

combined) were observed within 10 m of only 17 sets, and 

only two loons became entangled, one in Kachemak Bay and 

one on the Kenai Peninsula (Fadely 2002).

Alaskan longline, pot, and trawl fisheries are conducted 

during the winter (September–April) on the wintering grounds 

of the Yellow-billed Loon, but because they are conducted offshore of the Continental Shelf, they do not often take Yellowbilled Loons. The longline fishery is unlikely to attract loons 

(unlike surface-feeding seabirds), and this is confirmed by the 

low average annual take of “other” species (i.e., loons, grebes, 

cormorants, waterfowl, storm-petrels, shorebirds, jaegers, and 

kittiwakes) during 1993–1999, which was estimated as 1.9 

individuals per year in the Gulf of Alaska fishery and 29.1 per 

year individuals in the Bering Sea/Aleutian Island longline 

fishery. Pot and trawl fisheries sometimes take diving birds, 

but no loons were captured during the 1993–1999 observed 

pot fisheries in either region, and trawl fisheries took an 

estimated total of anywhere from 2 to 860 “other” individuals 

during 1997–1999. This summary is based on data from the 

National Marine Fisheries Service (NMFS 2001).

In conclusion, bycatch in commercial fisheries in 

southern Alaskan waters does not appear to be a threat to Yellow-billed Loons, because gillnet fisheries occur during the 

summer when Yellow-billed Loons are rare. However, more 

information is needed on the extent of winter gillnet fisheries, 

and thus the potential for bycatch, in East Asian waters. 

Bycatch in subsistence fisheries

Unlike bycatch in commercial fisheries, bycatch of 

Yellow-billed Loons in subsistence gillnet fisheries on the 

breeding grounds may be substantial. For example, Parmelee 

et al. (1967) suggest that many may die in fish nets each year 

on Victoria Island, where seven dead adults were found in the 

few nets checked by the research party. In Alaska, bycatch is 

particularly likely near large rivers such as the Meade River 

(J. King pers. comm.) and Colville River, where Yellow-billed 

Loons frequently fish in river channels and subsistence fishing 

is common. Bycatch in subsistence fisheries is not currently 

monitored by U. S. Fish and Wildlife Service or Alaska 

Department of Fish and Game programs; however, it seems 

that loon bycatch could be monitored easily and efficiently 

using the same monitoring program as that used for the fishery 

itself. 

In conclusion, bycatch of Yellow-billed Loons (and Redthroated Loons) in summer subsistence fisheries in northern 

Alaska warrants monitoring by agency programs, at least until 

its magnitude has been estimated (see Section 9–C, and Conservation Plan, Strategy 6.4). 

E. Disease or Predation.

Predation is probably the primary cause of egg loss, 

which is as high as 77% some years, and the cause of some 

fraction of chick mortality, although starvation also plays an 

important role in reduction of two-chick to one-chick broods 

during early brood-rearing (Earnst in prep). In northern 

Alaska, nest predators known to prey on Yellow-billed Loon 

nests include Glaucous Gull, Parasitic Jaeger (Stercorarius 

parasitica), and arctic fox (North and Ryan 1988, Earnst pers. 

obs.). Other predators that coexist with Yellow-billed Loons 

include Snowy Owl (Nyctea scandiaca), Pomarine Jaeger 

(Stercorarius pomarinus), Common Raven, red fox, and grizzly bear. Although parents use repeated jabs from their sharp 

bills to defend chicks from predators, young chicks (primarily those <2 weeks of age) sometimes are taken by Glaucous 

Gulls and Parasitic Jaegers (Earnst pers. obs). Chicks may be 

left exposed when parents are disturbed by human activities, 

in foraging dives elsewhere on the brood-rearing waterbody, 

or engaged in territorial interactions with other loons (Earnst 

pers. obs.). Increased predation of nests and chicks due to an 

increase in predator abundance is a likely and potentially serious risk associated with encroaching human activities including oil development (see Section 7–A).

Predation on adult Yellow-billed Loons is thought to 

be uncommon. The potential threat of disease to adults and 

young is unknown. Die-offs on the breeding or wintering 

grounds have not been reported, but given the remoteness of 

marine wintering areas and most breeding areas, it is unlikely 

any such die-offs would be noted. For example, in Common Loons, die-offs due to botulism and aspergillosis are not 

uncommon; exposure to mercury and subsequent microphallid 

trematode infestation has been implicated in the mortality of 

22 Status Assessment and Conservation Plan for the Yellow-billed Loon
large numbers of loons; and infestations of cryptocotyle flukes 

were found in 30,000 emaciated loons (reviewed in McIntyre 

and Barr 1997). 

F. Other Anthropogenic and Natural Factors—

Contaminants.

Although loons are susceptible to contaminants because 

of their top position in the food chain, contaminants are not 

known to be a problem in loons breeding in northern Alaska. 

Bioaccumulation of mercury has been documented in Common Loons in the eastern U.S. and Canada (reviewed in 

McIntyre and Barr 1997, Evers 2004), where air pollution and 

acid rain have led to mercury accumulation in fish and their 

predators, such as loons. Similarly, lead poisoning, from ingestion of lead sinkers attached to fish jigs, is a leading cause 

of adult mortality in some places (McIntyre and Barr 1997, 

Scheuhammer et al. 2003, Evers 2004). 

Mercury contamination in Common Loons breeding in 

Alaska is less elevated than elsewhere in North America, as 

indicated in blood and feathers (Evers et al. 1998) and eggs 

(Evers et al. 2003). None of the individuals sampled in Alaska, 

which were primarily from the Kenai National Wildlife 

Table 2. Average annual subsistence harvest of loons in villages from northwestern to southwestern Alaskaa. Yellow-billed Loon status 

is designated as breeding (B) or migrating (M). For locations of sites, see Fig. 2.

Site and years Status

Yellow-billed 

Loons

Common 

Loons

Pacific or 

Arctic Loons

Red-throated 

Loons

Unidentified 

Loons Total Loons

Bering Strait Mainlandb, 1995 B, M 2 20 4 0 4 30

St. Lawrence Islandc, 1995–96 B, M 37 195 66 0 8 306

Northwest Arcticd, 1996–97 B, M 0 71 2 6 1 80

Yukon-Kuskokwim Deltae, 1987–97 M 110 567 59 96 0 832

AK Pen./Becharof NWRf, 1995–99 M 0 0 0 0 0 0

Aleutian Islandsg, 1996–97 M 0 0 0 0 0 0

Togiak NWRh, 1995–99 M 52 26 0 3 0 81

Dillingham areah, 1995, 1997, 1999 M 0 2 0 0 0 2

a Loons were not addressed in survey questionnaires in the Galena-Ruby area (Webb 1999) or Allakaket-Bettles area (Wong et al. 2000), but Yellow-billed 

Loons are not expected to be common in either area. 

b Paige et al. 1996.

c Paige et al. 1996; Kawerak, Inc and Alaska Department of Fish and Game 1997. Diomede Island also included in 1996.

d Georgette 2000. The Northwest Arctic includes the Selawik National Wildlife Refuge, Kobuk National Park, and Cape Krusenstern National Park areas.

e Wentworth 1998.

f USFWS, unpubl. data.

Refuge and the Matanuska-Susitna Valley, had mercury levels 

likely to cause adverse effects. Similarly, preliminary data 

from egg and blood samples of Red-throated Loons from 

the Copper River Delta, Yukon-Kuskokwim Delta, Cape 

Espenberg, and the Colville River Delta indicate no obvious 

elevation of mercury or lead. Selenium levels were similar to 

other marine birds in the region, and it is unclear whether such 

levels might have negative effects (Schmutz 2002). Polychlorinated biphenyl (PCB) levels were low in the 40 eggs analyzed except for three individual Red-throated Loons from the 

Copper River and Yukon-Kuskokwim Delta that had high PCB 

concentrations. Similarly, necropsies on >300 loons (Common Loons and Yellow-billed Loons) dying during the Exxon 

Valdez oil spill revealed no ingested lead (McIntyre and Barr 

1997). Nonetheless, it would be worthwhile to obtain data on 

heavy metal loads in Yellow-billed Loons breeding at several 

locations throughout northern Alaska to assess current risks 

and provide a baseline for comparison to future years. 

Status Assessment 23
8. Current Protection of Populations and 

Habitats.

A. Current Protective Status of Yellow-billed 

Loons.

Other than being protected under the Migratory Bird 

Treaty Act, as are all migratory birds, the Yellow-billed Loon 

and its habitat receive no special legal protection. The U.S. 

Fish and Wildlife Service was petitioned to consider the Yellow-billed Loon for listing under the Endangered Species Act 

in April 2004 (Center for Biological Diversity 2004). The U.S. 

Fish and Wildlife Service has considered the Yellow-billed 

Loon a Species of Management Concern since 1995 (USFWS 

1995) and now includes it on the similar list of Birds of Conservation Concern (USFWS 2002a) (Table 3). This designation implies that research and monitoring of this species is 

given priority over that of species not on the Birds of Conservation Concern list. Similarly, an internal nomination has been 

drafted within the State of Alaska Department of Fish and 

Game to consider listing the Yellow-billed Loon as a Species 

of Special Concern under which the agency would review the 

loonʼs population status and would consider giving Yellowbilled Loons special consideration during monitoring, management, and land use planning processes (T. Rothe pers. comm.). 

Based on the Yellow-billed Loonʼs current population status 

and concern about oil and gas exploration and development in 

the National Petroleum Reserve-Alaska, the National Audubon 

Society included it in the highest category of concern in its 

national “Audubon Watchlist 2002” (www.audubon.org/bird/

watchlist) and in the “Alaska WatchList” (Audubon Alaska 

2002). The WatchList highlights species believed to be vulnerable or declining and helps to identify priorities for research, 

monitoring, and conservation. The Natural Heritage Program 

lists the Yellow-billed Loon as “Vulnerable” in the United 

States and “Apparently Secure” in Canada (NatureServe 

2001). The Committee on the Status of Endangered Wildlife 

in Canada lists the Yellow-billed Loon as a species “Not at 

Risk,” although the status report submitted to the Committee 

recommended that it be listed as “Vulnerable” (Barr 1997). 

In Russia, the Yellow-billed Loon is listed in the Red Book of 

the Russian Soviet Federation of the Socialist Republics and 

the Yakutian Republic, the official government list of rare and 

endangered species (reviewed in Fair 2002). 

B. Land Ownership and Existing Habitat 

Protection.

Throughout its range in Alaska, Canada, and Russia, the 

Yellow-billed Loon breeds almost exclusively on lands without special protection. In Alaska, most of the breeding range 

is under federal ownership, although some is owned by the 

State of Alaska and Native Corporations. Although a few pairs 

are known to breed on Selawik National Wildlife Refuge and 

the Bering Land Bridge National Monument (Fig. 4 and Platte 

1999) in western Alaska, the number of Alaskaʼs Yellow-billed 

Loons breeding on protected lands is negligible. None are 

known to breed on the Arctic National Wildlife Refuge. In 

northern Alaska, 91% of individuals on the breeding grounds 

occur within the National Petroleum Reserve of Alaska (NPRA)(Earnst et al. in review), which is managed by the Bureau of 

Land Management and on which oil development is planned 

(e.g., BLM 1998b, 2004a,b). No legal or permanent provisions 

for Yellow-billed Loon habitat protection have been made in 

any part of the speciesʼ range on the North Slope (but see Section 7–D).

In Canada and Russia, the amount of Yellow-billed Loon 

habitat under government protection is thought to be insignificant, although in Canada some is likely protected on Migratory Game Sanctuaries and other protected areas on Banks 

Island, and Queen Maud Gulf Lowlands (Barr 1997).

Similarly, the marine wintering grounds of Yellow-billed 

Loons, which are heavily used by commercial and subsistence 

fisheries and as oil transportation corridors, receive no special 

habitat protection, and the Migratory Bird Treaty Act extends 

only to loons within 3 miles (4.8 km) of the coast. The health 

of the marine ecosystem in U.S. waters is monitored by various National Oceanic and Atmospheric Administration and 

National Marine Fisheries Service programs. Little is known 

of marine environmental conditions and potential threats off 

the coast of Russia, Japan, China, and the Korean Peninsula 

(but see Center for Biological Diversity 2004) where Alaskaʼs 

breeding Yellow-billed Loons likely winter (see Section 5–E).

9. Current Conservation, Monitoring, and 

Research Actions.

A. Conservation and Education.

Several conservation and education programs have 

highlighted Alaskaʼs five species of breeding loons, including 

Yellow-billed Loons.

Alaska Loon and Grebe Working Group.

The Alaska Loon and Grebe Working Group is a collection of biologists, managers, and enthusiasts interested in 

working together to elevate the status of loons in Alaska. The 

goals of the Working Group are to 1) facilitate exchange of 

information among biologists, managers, and the public; 2) 

identify conservation and management issues faced by Alaskaʼs loons; 3) review and identify gaps in knowledge of loon 

distribution, status, and ecology; and 4) facilitate collaborative 

projects among agencies and others. The Working Group was 

first convened in December 1997 and has met annually.

24 Status Assessment and Conservation Plan for the Yellow-billed Loon
North American Loon Fund.

Although most efforts of the North American Loon Fund 

concentrated on Common Loons in the northeastern United 

States, it also provided resources relevant to educators and 

biologists in Alaska, and helped fund some loon research in 

Alaska, including the Alaska Loon Watch Survey (see next 

paragraph).

Alaska Department of Fish and Game, Division of Wildlife; 

and the Audubon Society, Alaska Chapter.

Together these organizations produced the Alaska Loon 

Festival, a one-day event designed to educate the public about 

loon conservation, celebrate the arrival of loons in Anchorage, 

raise funds for loon conservation, and recruit volunteers for 

the Loon Watch Program (a survey of Common Loons, Pacific 

Loons, and Red-throated Loons nesting in the MatanuskaSusitna Valley, Anchorage area, and Kenai Peninsula). The 

Alaska Loon Festival was held annually in most years during 

1989–2002 and grew substantially in attendance during that 

period. 

The Alaska Center for the Environment, Valley Chapter.

The Alaska Center for the Environment also has been 

active in loon education and provided support for the Alaska 

Loon Festival and the Alaska Loon Watch Program in past 

years. 

The Nongame Migratory Bird Program of the U.S. Fish 

and Wildlife Service, Region 7.

The Nongame Migratory Bird Program office has 

coordinated the Alaska Loon Watch Program since 2000 and 

continues to produce and fund loon-specific educational materials while working closely with the Alaska Loon and Grebe 

Working Group. 

B. Monitoring Abundance on the Breeding 

Grounds.

Yellow-billed Loons are monitored in Alaska during two 

annual aerial waterfowl surveys conducted by U. S. Fish and 

Wildlife Service—the Arctic Coastal Plain and North Slope 

Eider surveys. In addition, a two-year lake-circling survey, 

designed specifically for Yellow-billed Loons, was conducted 

during June 2003–2004. Yellow-billed Loons are not recorded 

during aerial waterfowl surveys in Canada or Russia.

Arctic Coastal Plain and North Slope Eider aerial 

waterfowl surveys.

The two ongoing, annual aerial waterfowl surveys conducted in northern Alaska, described in detail below, differ 

primarily in area covered, timing, and survey intensity. 

Description of surveys. The Arctic Coastal Plain Breeding Pair Survey has been flown annually since 1986 and 

encompasses the 61,645 km2 of contiguous wetland habitat 

north of the Brooks Range and from Point Lay in the west to 

Kaktovik in the east (Fig. 3). Average initiation and completion dates were 26 June and 3 July, respectively, during 1986–

2003, with timing adjusted annually to account for snow-melt 

phenology. The survey, which was designed to monitor all 

waterfowl, closely follows the design and protocol of the 

North American Waterfowl Breeding Pair Survey (Smith 

1995). Transects are 0.4 km wide, 18.5 km apart, and flown 

in an amphibious Cessna aircraft at 30–45 m above ground 

level and 145–170 km/hr. Beginning in 1998, survey lines 

have been offset from the previous yearʼs lines, such that a set 

Table 3. Conservation status of the Yellow-billed Loon as assigned by various conservation and governmental organizations. The 

categories reported here do not carry legal protection.

Organization State/Country Status Reference

U.S. Fish & Wildlife Service U.S.A. Species of Management Concern, 1995

Bird of Conservation Concern, 2002

Petition pending for listing under E.S.A.

USFWS 1995.

USFWS 2002a.

Center for Biological Diversity 2004.

State of Alaska Alaska yet to be determined ---

National Audubon Society Alaska Watchlist species Audubon Alaska 2002

Natural Heritage Program U.S.A.

Canada

Vulnerable

Apparently Secure

NatureServe 2001

Committee on the Status of Endangered 

Wildlife in Canada

Canada Not at Risk NatureServe 2001

Yakutian Republic and Russian Soviet 

Federation of the Socialist Republics

Russia Red Book listing Reviewed in Fair 2002

Status Assessment 25
of lines is repeated every fifth year. In all, 10 different sets of 

survey lines were used during 1986–2003. For more details, 

see King and Brackney (1997) and Mallek et al. (2004).

The North Slope Eider Survey has been flown annually since 1992 and encompasses the 30,755 km2

 of wetland 

habitat on the North Slope from approximately Icy Cape in the 

west to the Canning River in the east (Fig. 3). Average initiation and completion dates were 10 June and 18 June, respectively, during 1992–2003. The survey was designed to monitor 

male Spectacled Eiders (Somateria fischeri) which remain on 

the breeding grounds only during a narrow two- to three-week 

window between the onset of melt and the end of egg-laying. Survey timing is adjusted annually relative to ice melt on 

shallow wetlands and the arrival of eiders. Transects are 0.4 

km wide with center lines 9.6 km apart; in 1998 and 1999, 

transects in a study area around Teshekpuk Lake were placed 

4.8 km apart. Flight altitude, speed, and data recording is similar to that described above for the Arctic Coastal Plain Survey. 

Beginning in 1998, survey lines were offset 2.4 km from the 

previous yearʼs lines, such that a set of lines is repeated every 

fifth year. In all, eight different sets of survey lines were used 

during 1992–2003. For more details see Larned et al. (2003).

Power to detect a trend. Power can be thought of as 

the probability of detecting a given true decline of interest as 

statistically significant with the current dataset. For the purpose of the Yellow-billed Loon Status Assessment, a decline 

of interest is considered to be 3.4%, which would result in an 

overall decline of 50% in 20 years; and the desirable degree 

of power, or probability of detecting the decline as statistically significant (at P = 0.05), is considered to be 80% (Bart 

et al. 2004). The 3.4% annual decline is used as a compromise 

between smaller annual declines that would be of interest, 

but difficult to detect with reasonable expenditure of effort 

and money, and higher annual declines that would be easier 

to detect logistically but would result in a population size 

from which it may be difficult for a long-lived bird with low 

annual productivity to recover. Both the 18-year Arctic Coastal 

Plain Survey and the 12-year North Slope Eider Survey had 

low power to detect a 3.4% decline (power = 62% and 26%, 

respectively; Earnst et al. in review), and survey intensity 

was such that few Yellow-billed Loons were observed each 

year ( x = 45.7 and 57.5 individuals, respectively). When 

multivariate, mixed effects models were used to combine the 

two surveys and incorporate thaw-degree days and observer 

experience as covariates, power to detect a 3.4% decline was 

81% (Earnst et al. in review). However, if other potential 

sources of bias, or the imperfect nature of this model of bias, 

are acknowledged, the actual power to detect a trend is probably lower (Bart et al. 2004). More gradual annual declines 

would be more difficult to detect as statistically significant; 

for example, power to detect a 2.5% annual decline (40% total 

decline in 20 years) was only 55%.

Assessing potential bias in the population trend. Bias 

in a trend estimate is caused by a trend in the detection ratio 

(i.e., the ratio between number observed and number actually 

present). The presence of bias reduces power to detect a trend 

and makes interpretation of the trend problematic (Bart et al. 

2004). In analysis of Arctic Coastal Plain and North Slope 

Eider survey data it was important to account for observer 

experience because 12 different passenger-observers have 

participated in the two surveys, and evidence suggests that 

average observer experience increased over the survey period 

(1986–2003) and that observers detected more loons as they 

became experienced (Earnst et al. in review). As a result, 

observer experience produced a positive bias in the population 

trend. This bias was further evidenced by a change in population trend from positive to negative when observer experience 

was added to multivariate models. Spring weather was also 

a potential source of bias, because more birds were observed 

during warm springs than cold springs on the Arctic Coastal 

Plain survey. However, there was not a consistent trend in 

early spring temperature from 1986 to 2003, instead springs 

tended to become warmer from 1986 to 1996 but were variable thereafter, so spring temperatures were a source of noise 

in the 18-year trend, rather than bias (Earnst et al. in review).

Lake-circling aerial surveys for Yellow-billed Loons.

In 2003 and 2004, U. S. Fish and Wildlife Service conducted lake-circling surveys to quantify Yellow-billed Loon 

habitat preferences and population size. The study area, which 

was equivalent to that of the Arctic Coastal Plain Survey 

and the Yellow-billed Loonʼs range on the North Slope, was 

divided into one high- and one low-density stratum based on 

observed density during Arctic Coastal Plain and North Slope 

Eider surveys. Plots were placed randomly within the strata, 

and each lake >7 ha and having its centroid inside the plot 

was surveyed by circling the lakeʼs perimeter and also flying 

down the center of larger lakes. Lakes were re-circled if necessary to confirm species identification or presence of nests. A 

pilot- and passenger-observer recorded each loonʼs location 

on a topographic map and in a GIS-based computer system. A 

total of 141 plots were surveyed during the two-year survey 

(2003 and 2004). In addition, the study design called for rivers 

and lakes of all sizes to be surveyed on 6 plots to confirm that 

the vast majority of loons were sighted on lakes >7 ha, and 8 

plots were surveyed by the two aerial crews in rapid succession to confirm that the crews were detecting similar numbers 

of loons. 

Although originally designed primarily to quantify 

habitat preferences and population size, it would be useful to 

repeat the survey periodically to estimate population trend.

Survey design considerations.

For the purpose of obtaining a more precise and less 

biased estimate of population trend, a lake-circling survey has 

several advantages over a multi-species transect survey. First, 

because detection rates are high in lake-circling surveys, there 

is less potential for large differences between observers or 

other factors affecting visibility, and thus less potential for a 

trend in the detection ratio and a bias in the population trend 

estimate. This approach of directly reducing bias is likely to 

26 Status Assessment and Conservation Plan for the Yellow-billed Loon
be more stable than using multivariate models to tease apart 

sources of bias and noise from the real trend as described 

above. Second, the lake-circling survey samples a higher 

proportion of loon habitat (i.e., lakes) and records many times 

more loons than transect surveys, thus providing more precise 

annual estimates of abundance that contribute to more precise 

trends across time. Third, the lake-circling method as used in 

Earnst et al. (in press) was cost-effective (9.4 sightings/survey-hour compared to 5.6 sightings/survey-hour on traditional 

flight lines within intensive plots), and provided presence/

absence on a lake-by-lake basis which was useful for other 

objectives, such as understanding habitat preferences.

If ongoing transect surveys are to be used rather than 

lake-circling surveys, modifications to existing surveys could 

be used to decrease bias and increase precision in the trend 

estimate. To increase precision, one possibility is to increase 

number of transects flown annually, particularly if proportionately more lines are flown in high-density loon strata. 

Simulations based on existing data could be used to predict 

the gain in precision resulting from adding a given number of 

transects. To reduce bias in the transect surveys, it would be 

worthwhile to incorporate a measure of the detection rate into 

the survey design (Anderson 2001, Thompson 2002, Bart et 

al. 2004). One possibility is the use of formal double sampling 

in which intensive lake-circling is conducted along a subset 

of extensive survey lines each year (Cochran 1977, Bart and 

Earnst 2002). However, the current low sampling intensity 

on the North Slope Eider and Arctic Coastal Plain surveys 

(only 46–58 Yellow-billed Loons observed each year) would 

necessitate double sampling over most of the transects to 

provide a suitable sample. If more survey lines were added to 

increase precision, as discussed above, then the use of double 

sampling with lake-circling surveys over a subset of transects 

might become a statistically feasible means of reducing bias, 

but simulations would be needed to determine whether this 

approach would be any more cost-effective than simply implementing the lake-circling survey across the full study area. 

Other means of reducing bias, such as distance sampling 

(Quang and Lanctot 1991, Lanctot and Quang 1992, Buckland 

et al. 2001), could be investigated. Recommended sample 

sizes for distance sampling would only be met if enough 

transects were added to approximately double the number of 

loons observed per year. If distance sampling is considered, it 

is critical to first conduct a well-designed study to determine 

whether assumptions of the method are met. In particular, it 

is unlikely that all loons at 0 distance from the transect line 

are detected, because failing to detect individuals beneath 

the plane is a well-known problem. In addition, accurately 

estimating distance and angle of detections from the plane is 

difficult and time-consuming and competes with the need to 

record all individuals of all species on fast-moving, multi-species surveys, such as the North Slope Eider and Arctic Coastal 

Plain surveys (Caughley 1974). 

The timing of surveys is another important consideration. 

Yellow-billed Loons arrive on breeding grounds as soon as 

melt water is available on rivers (often late May), and begin 

occupying territories a few to several days later or as soon 

as lakes within their territory attain a suitable moat of open 

water (North and Ryan 1988). Because the annual timing of 

ice melt on lakes is highly variable in the arctic and directly 

affects Yellow-billed Loon nesting phenology (see Section 

5–B), the optimal window for survey initiation will also vary. 

On the Colville River Delta in 1995–1999, average onset of 

incubation was 14 to 23 June (Section 5–B; Earnst in prep). If 

breeding pairs were on territories 7–9 days prior to incubation 

and on the breeding grounds several days prior to that (as in 

North and Ryan 1988), both the North Slope Eider and Arctic 

Coastal Plain survey probably were timed appropriately to 

monitor breeding pairs in most years (average survey initiation 

8 and 27 June, respectively, during 1995–1999). Because some 

nonbreeders apparently arrive during the interval between the 

two surveys, and additional nonbreeders (presumably non-territorial 3–5 year-olds that have not yet established territories) 

come to the breeding grounds in some years but not others 

(Earnst et al. in review), the Arctic Coastal Plain Survey 

results in a higher estimate of population size and a population 

trend that is more variable and difficult to interpret. To investigate effect of survey timing, surveys could include a formal 

sampling of snow or lake-ice cover across geographic strata 

to provide a quantitative measure of relative timing between 

regions and years. Measures of snow and lake-ice cover could 

be estimated from satellite imagery or aerial photographs 

taken concurrently with the avian survey. Similarly, a subset 

of plots could be surveyed at regular intervals throughout the 

breeding season to document the regularity with which breeders, nonbreeders, and failed breeders are present on traditional 

lakes throughout the season. Further ground studies, especially 

of marked birds, also would be helpful in relating breeding 

status to lake occupancy. 

C. Other Monitoring.

Monitoring abundance in marine waters during summer 

months.

Southern Alaska. Summer boat surveys for seabirds 

were conducted in southeast Alaska in 1994 (Agler et al. 

1995a), in Lower Cook Inlet in 1993 (Agler et al. 1995b), and 

throughout Prince Williams Sound for eight years during July 

1972–1998 (Lance et al. 1999). The surveys were designed 

to assess seabird populations, and only about half of all loons 

were identified to species because their diving behavior made 

identification difficult. Yellow-billed Loon population indices 

were low, and confidence intervals were large. For example, 

in southeast Alaska, the Yellow-billed Loon population index 

was 267 ± 422 (95% CI) individuals, but 1,420 loons were 

unidentified (Agler et al. 1995b), making the population index 

too imprecise to be useful. Since similar surveys probably will 

be repeated periodically (K. Wohl pers. comm.), investigations 

are needed into the feasibility of survey methods that would 

improve loon species identification during boat-based seabird surveys. If surveys were substantially improved, annual 

Status Assessment 27
estimates of the number of juveniles and adults remaining in 

southern wintering areas during the breeding season might be 

useful in understanding annual variation in number of adults 

present on breeding grounds and their productivity. 

Northern Alaska. Fischer et al. (2002) conducted aerial 

surveys for waterbirds during the summers of 1999 and 

2000 off the coast of northern Alaska from Harrison Bay to 

Brownlow Point (also see Section 5–A). A total of 27 and 

67 Yellow-billed Loons were recorded during offshore and 

nearshore surveys, respectively. In addition, aerial surveys for 

molting sea ducks have provided partial (1999 and 2001) or 

complete (2002 and 2003) coverage of nearshore habitat off 

the Arctic Coastal Plain, from the Canadian border in the east 

to Kasegaluk Lagoon, south of Point Lay, in the west (Lysne 

et al. 2004). A total of 210 and 86 Yellow-billed Loons were 

observed in 2002 and 2003, respectively. Both sets of surveys 

(Fischer et al. 2002, Lysne et al. 2004) seem useful in identifying the relative importance of various nearshore areas, and 

this information is particularly pertinent given that some will 

be affected by oil development. However, the use of marine 

surveys to identify spatial patterns in relative abundance and 

monitor trends through time is limited unless they use standardized survey lines and an effort per unit area that is consistent across areas and years. High annual variation in number 

using marine waters is expected (e.g., see Earnst et al. in 

review) and will hamper detection of any change in abundance 

across years.

Monitoring abundance in marine waters during winter 

months.

Winter boat surveys for seabirds were conducted during 1972–1998 throughout Prince William Sound (Lance et 

al. 1999), during 1979–2002 in the bays of Kodiak Island 

(Zwiefelhofer and Forsell 1989, D. Zwiefelhoffer pers. 

comm.) and during 1993 in the Lower Cook Inlet (Agler et al. 

1995b). Winter surveys are plagued by the low percentage of 

individual loons identified to species. In the Prince William 

Sound surveys, the percentage of unidentified loons varied 

substantially between years (5%–83%), indicating that observers probably varied in identification skills. If these surveys 

are to be repeated on an intermittent basis, it would be useful 

to investigate methods that might allow more accurate loon 

identification. More accurate loon identification, and thus a 

better estimate of Yellow-billed Loon abundance, would aid 

in evaluating the proportion of the North American population 

that winters in Alaskan waters. 

The abundance and distribution of Yellow-billed Loons 

has not been investigated off the coast of East Asia where 

much of Alaskaʼs breeding population may winter (see Section 

5–E).

Monitoring productivity.

In long-lived species with delayed reproduction, a decline 

in productivity may not be detectable in indices of adult abundance until after a several year delay. Monitoring productivity 

may thus provide an early warning of potential population 

declines, but only if the sampling design and protocol have 

high power to detect a trend despite the high annual variability in productivity exhibited by this species. Also, monitoring productivity in addition to adult abundance provides an 

opportunity to identify which demographic parameters, if 

any, are changing and thus producing the overall population 

trend. Currently, there are no ongoing efforts for long-term 

monitoring of productivity; however, eight years of detailed 

productivity data are available for the Colville River Delta 

(for 1983–1984, in North and Ryan 1988, and for 1995–2000 

in Earnst unpubl. data), with less detailed data available for 

several intervening years (McIntyre 1991, Field et al. 1993, 

Smith et al. 1993, 1994).

Two objectives for collecting long-term productivity data 

can be distinguished: 1) to identify changes (i.e., trends) in 

productivity across time; and 2) to identify factors affecting 

productivity, including differences across geographic areas and 

years, and thus better understand factors affecting population 

dynamics and the locations of demographic sources and sinks. 

The first is a form of monitoring and the second is a research 

objective, but both are discussed here because they are closely 

linked conceptually and logistically. For the first objective, the 

minimum information needed is the number of chicks present 

in an area at a time near fledging. For the second objective, it 

is valuable to consider the individual components of productivity (proportion of pairs nesting, clutch size, nesting success, 

and brood-rearing success).

If we are interested primarily in detecting trends in 

productivity (first objective, above), annual monitoring of a 

large sample of pairs likely will be required in order to detect 

a trend amidst the high annual variability typical of Yellowbilled Loons and other loon species (Section 5–C). Monitoring should be conducted across a large geographic area or at 

several individual sites, because it is likely that some regions 

or habitats are acting as demographic sinks and others as 

sources. Monitoring on an annual basis, rather than every five 

years or so, would provide more ability to distinguish annual 

variability from a long-term trend in productivity. A powerful 

monitoring scheme would be intensive ground monitoring of 

20–30 territorial pairs at each of five sites, or more, each year. 

This approach would provide considerable power to detect a 

trend in productivity and would provide the detailed information necessary to address the second objective (see above) of 

understanding the cause of changes in productivity. The disadvantage of this approach, of course, is that it requires substantial funding on a continuous basis. Two alternate approaches 

are considered here. 

Annual aerial surveys. The advantage of annual aerial 

surveys is that a large geographic area can be covered each 

year, but the disadvantages are that a) the trend in the indices 

will be difficult to interpret due to low detection ratios and b) 

the indices will provide little information relevant to factors 

affecting productivity (the second objective). First, experience 

during intensive, lake-specific surveys for Yellow-billed Loons 

indicates that broods are difficult to detect (Earnst pers. obs.). 

28 Status Assessment and Conservation Plan for the Yellow-billed Loon
The location of the more visible parent is not a reliable indicator of the broodʼs location because parents sometimes swim 

away from chicks when the plane approaches, chicks often 

dive or hide in vegetation while the parent remains visible, and 

even if undisturbed, chicks are sometimes left alone on open 

water while the parent is diving for food. As a result, detection ratios are likely to be low, and there will be significant 

opportunity for bias in a trend estimate caused by such things 

as a) changes in average observer skill or within-observer 

improvement, or b) changes in survey timing relative to chick 

size and thus visibility. Although helicopter surveys may provide a higher detection ratio, they also are more expensive and 

cause more disturbance to loons. Given the detection rate issue 

and the problem of high annual variability in productivity, any 

trend will be difficult to detect and a power analysis should be 

conducted for any proposed survey design before implementation is considered.

The best timing for brood-rearing surveys is late in 

brood-rearing when chicks are larger and thus more visible. 

Late surveys also provide the most ecologically meaningful index to final productivity (i.e., number fledging). However, late-brood rearing may not be a good time to obtain an 

estimate of adult abundance if adult occupancy of territorial 

lakes becomes less reliable as brood-rearing progresses or if 

the number of nonbreeders present varies among years (e.g., 

Earnst et al. in review). Thus, in addition to any productivity 

survey, a lake-circling survey or intensive transect survey during early nesting is needed to adequately monitor adult abundance (see Survey design considerations). If only one survey 

is affordable, the relative importance and likelihood of success 

of quantifying trend in abundance versus trend in productivity 

should be carefully weighed.

If aerial surveys are used, the parameter being estimated 

should be the number of broods (or chicks) per lake or per 

km2. Estimates of other parameters, such as the proportion 

of adults having chicks or the proportion of nests producing 

chicks, have more potential for bias because detection ratios 

of the numerator and denominator are unlikely to be the same 

and unlikely to vary together. Also, annual variation in both 

the numerator and denominator will contribute to noise in the 

trend, decreasing statistical power to detect a trend. Thus, to 

estimate broods/km2, an appropriate sampling design and protocol would be lake-circling of lakes chosen systematically or 

randomly, perhaps including more intensive sampling in highdensity strata, rather than a sample restricted to lakes known to 

have had loons or nests during earlier aerial surveys.

Repeated ground-based monitoring. A second alternative is to conduct intensive ground work at several sites for 

several years (say, five sites for five years), and to repeat the 

work at the same sites every 4–5 years. The advantage of 

this approach is that it provides dependable estimates of each 

component of productivity and a firm foundation with which 

to investigate factors affecting productivity. Intensive ground 

work also would lend itself well to studies of foraging ecology, habitat use, and the survival and site-fidelity of banded 

individuals (see Section 9–C). The disadvantages are that the 

sampling is less frequent and covers less area. Ground-based 

monitoring may result in monitoring fewer pairs than would 

intensive aerial surveys (but more than transect-based surveys which detect <60 individuals per year, Section 9–B), but 

would be less subject to visibility biases and observer differences. More detailed work on statistical power and potential 

biases in trend estimates may help resolve the issue of which 

approach is best for monitoring only (first objective), but any 

interest in understanding causes of variation in productivity 

(second objective) will tip the scales towards ground-based 

monitoring. A combination of aerial and ground-based productivity monitoring may prove most desirable.

Monitoring subsistence harvest.

Alaska Department of Fish and Game and U. S. Fish and 

Wildlife Service monitor subsistence harvest by conducting 

personal interviews or providing survey forms to families 

within native villages. Within each village, the survey goal is a 

complete census in small villages or a randomly drawn sample 

of 25%–50% of households in larger villages. The interviewer, 

who is typically a local resident, asks the primary hunter in 

the sample household to identify species taken on the basis of 

an identification card (a color photocopy of the relevant page 

from the National Geographic Guide to Birds) and a list of 

Native names for those species that occur in the area. There 

appear to be significant problems in identification of loons (S. 

Georgette pers. comm., Fair 2002), perhaps especially between 

Yellow-billed Loons and Common Loons, as suggested by the 

extraordinarily large take of Yellow-billed Loons (1,100 over 

10 years on the Yukon-Kuskokwim Delta), including eggs, 

in a region where Yellow-billed Loons do not breed and only 

rarely occur during migration. The problem is compounded by 

the lack of a known Yupʼik name for the Yellow-billed Loon. 

To alleviate this and other identification problems, U. S. Fish 

and Wildlife Service recently has begun to use a color identification card (rather than the previous black-and-white version) 

during interviews. Other potential means of improving data 

quality include a) providing seminars to educate interviewers 

about species identification, and b) asking specific questions 

about loon species identification during the interview. See 

Conservation Plan, Strategy 6.l.

Monitoring bycatch.

Waterbird bycatch in Alaskaʼs salmon gillnet fishery is 

monitored by the National Marine Fisheries Serviceʼs observer 

program with assistance from U. S. Fish and Wildlife Service. 

The program consists of a series of two-year projects that are 

rotated among geographic areas. Trained observers are placed 

on a sample of fishing vessels where they monitor the number (per set-hour) of seabirds entangled, released alive, and 

drowned in both drift and active gillnet sets. In a subsample of 

nets, observers also record number of seabirds in the vicinity 

of nets. Loons are recorded to species. Sites completed to date 

include Prince William Sound and South Unimak (1990–1991; 

Wynne et al. 1991, 1992), and Cook Inlet (1999–2000; Fadely 

Status Assessment 29
2002), and those underway or planned include Kodiak Island 

(2002–2003) and southeast Alaska (2004–2005). Bycatch 

is not monitored in gillnet fisheries on East Asian wintering 

grounds where much of Alaskaʼs breeding population may 

winter (see Section 5–E and Conservation Plan, Strategy 6.2

and 6.3).

Seabird bycatch also is monitored in Alaskaʼs groundfish 

fisheries which include trawl, longline, and pot fisheries in 

the Gulf of Alaska and Bering Sea/Aleutian Island regions. 

Groundfish fisheries are conducted offshore of the Continental 

Shelf, making interactions with loons less likely. Loons are 

categorized as “other birds” (along with grebes, cormorants, 

waterfowl, storm-petrels, shorebirds, jaegers, and kittiwakes) 

in printed reports, but the electronic database can be searched 

for numbers of Gaviidae (all species combined) captured. 

The number of observed captures is extrapolated to the entire 

annual fishery on the basis of set-hours or number of baited 

hooks.

Bycatch in subsistence gillnet fisheries on Yellow-billed 

Loon breeding grounds is not currently monitored, but is of 

particular importance because the timing of fishing coincides 

with peak loon abundance (unlike fisheries on the wintering 

grounds). In most areas on Alaskaʼs breeding grounds, the 

subsistence harvest of fish is monitored annually, and it seems 

that loon bycatch could be monitored concurrently with little 

additional effort or expense. This would be particularly useful 

if careful attention were paid to species identification. See 

Conservation Plan, Strategy 6.4.

D. Research.

Yellow-billed Loons are the least studied of the worldʼs 

five species. This section identifies important gaps in our 

knowledge of Yellow-billed Loon ecology and demography; 

results of past research are reviewed throughout the Status 

Assessment. Two types of studies are needed to address 

the gaps identified below: 1) long-term research on banded 

individuals conducted concurrently at several sites to estimate 

demographic parameters (e.g., survival of adults and immatures, age of first-breeding) and to investigate causes of spatial 

and temporal variation in productivity; and 2) studies on 

marine wintering grounds to investigate foraging ecology, diet, 

energetics, and exposure to contaminants.

Breeding ecology and demography.

More is known about factors affecting productivity and 

habitat requirements during the breeding season than about 

other aspects of Yellow-billed Loon ecology, but key pieces 

to the puzzle remain missing. For example, the eight years of 

productivity data from the Colville River Delta suggest high 

annual variability, depending in part on the timing of spring, 

and this is consistent with studies of other loon species. This 

variability, however, makes problematic something as simple 

as obtaining a baseline annual average of chicks fledged per 

pair, for a pre- versus post-development comparison. Furthermore, it is possible that processes influencing productivity 

operate differently in other North Slope breeding areas, and 

multi-year data sets from other areas are lacking. Similarly, 

data are available to investigate whether some lake or habitat 

types are associated with consistently high annual productivity 

on the Colville study site, but not elsewhere.

On a larger scale, it is also useful to identify habitat 

characteristics correlated with Yellow-billed Loon distribution 

across the North Slope. An initial model, based on variables 

available from GIS, has been developed (see Section 5–A; 

Earnst et al. in press) and a more powerful modeling effort is 

underway by the same collaborators (USFWS, unpubl. data), 

but ground-based habitat work at key sites is an important, 

missing link at present. A combination of intensive aerial 

surveys, GIS analyses, and ground-based surveys and habitat 

work at several sites could address the following questions. 

How well do lake characteristics discernable from GIS data 

correlate with fish presence? How much does fish abundance 

vary (as opposed to mere presence), and does it correlate 

with Yellow-billed Loon presence or productivity? What lake 

characteristics are important other than presence of fish, stable 

water levels, the availability of gently sloping shoreline for 

nesting, and the availability of protected, vegetated bays for 

brood-rearing? Is the clumped nature of Yellow-billed Loon 

distribution due to the distribution of available habitat, or is 

a social phenomenon at play, such as a tendency to hold territories within hearing/vocalization distance of other Yellowbilled Loons? Why are unoccupied lakes that appear to have 

appropriate characteristics (based on GIS data) unoccupied? 

Possible answers to the latter question include the possibility 

that Yellow-billed Loons are not abundant enough to saturate 

the habitat, relevant habitat features have not been identified 

or adequately measured, or some sort of competition with 

Pacific Loons is preventing the typically dominant Yellowbilled Loon from becoming established in a high-density 

Pacific Loon area.

Spatially explicit demographic models can be used to 

evaluate a populationʼs response to perturbation in specific 

demographic parameters (e.g., survival or productivity) across 

varying temporal and geographic scales. For example, one 

could ask whether a 50% reduction in productivity of loons 

within the High Oil Potential zone (Fig III–A–29 in BLM 

1998b; Map 105 in BLM 2003) is likely to have an important 

impact on population stability. Such models can be misleading or little more than guesswork unless based on a large and 

rigorously collected dataset (e.g., Beissinger and Westphal 

1998). Studies of banded individuals are needed to estimate 

the demographic parameters that comprise the model: annual 

survival rates of adults and immatures, age of first breeding, and age-specific productivity. Information is needed on 

productivity from different regions of the breeding grounds 

and across many years to evaluate the extent to which some 

regions serve as demographic sources or sinks. Such information also would serve as baseline data for evaluating effects on 

productivity of changes in habitat or environmental stressors 

such as noise and pollution. 

30 Status Assessment and Conservation Plan for the Yellow-billed Loon
One approach for meeting these multi-year, multi-location objectives is to do intensive work during five years at 

each of five sites and to repeat the study at regular intervals 

(say, every 4–5 years). The approach of a five-year, five-site 

study is attractive because it could meet several objectives 

simultaneously: a) obtain ground-based detection ratios of 

adults and broods; b) quantify the consistency of territory 

occupancy from the early stages of spring ice melt through 

late brood-rearing; c) monitor productivity; d) estimate demographic variables and establish a color-marked population that 

can be revisited periodically to assess adult survival, philopatry, and age-specific productivity; e) assess spatial and temporal variation in productivity; and f) assess spatial variation 

in habitat preferences and the habitat-productivity relationship. The five-year, five-site study would need to be repeated 

periodically to meet several of its purported objectives (i.e., 

monitoring productivity, estimating detection ratios as part of 

double sampling, and resighting banded individuals), but even 

one set of five years at five sites would substantially increase 

understanding of Yellow-billed Loon breeding ecology. 

Effects of anthropogenic disturbance.

There are no data on how Yellow-billed Loons will 

respond to disturbance at the local population level or at the 

individual behavioral or physiological level. Research is 

needed on both short- and long-term effects of disturbance. 

To address effects at the local population level, a high priority 

should be placed on monitoring lake occupancy and productivity in designated areas for several years before and after development. Because only a few loons will be available at a given 

site, it will be necessary to design a large study that allows 

combining of data across sites. Although aerial surveys are 

useful in establishing patterns, ground studies are also needed 

to identify processes by which development affects productivity. For example, is the change in productivity associated with 

changes in rate of nest predation, nest abandonment, chick 

predation, chick starvation, prey delivery, or percent of time 

parents spend incubating or on the lake?

Addressing effects of disturbance at the individual level 

may reveal effects that are masked at the local population 

level. Relevant parameters to quantify include time and energy 

expended fleeing or alert, foraging efficiency, possible avoidance of otherwise favorable nesting or foraging habitat, prey 

delivery to young, incubation constancy, and physiological 

indicators of stress (Knight et al. 1991, Delaney et al. 1999, 

Thorson et al. 2002, Washburn et al. 2003, see Section 7–A). 

A typical approach is to measure an individualʼs response to a 

well-quantified disturbance event (e.g., a 70 decibel noise at 

500 m lasting for 5 minutes) using either “naturally” occurring 

or experimentally introduced disturbance events. Disturbance 

studies must overcome several design issues. For example, 

few Yellow-billed Loons are likely to be available at a given 

site, especially for “natural” episodes of disturbance, thus 

arguing in favor of combining data across sites. More importantly, an individualʼs response to disturbance is expected to 

vary dynamically with the perceived cost of remaining relative 

to leaving (Ydenberg and Dill 1986) and thus to be highly 

variable among individuals and situations. For example, 

flushing distance is known to vary with angle of approach 

and starting distance of the observer, stage of incubation, time 

of day, distance to refuge, type of disturbance, and extent to 

which individuals have been previously exposed to similar 

disturbance (reviewed in Blumstein 2003 and Blumstein et al. 

2003). Similarly, loons might react differently to a noise or 

other disturbance emanating from across a large expanse of 

open water than to the same disturbance at the same distance, 

but across land. Likewise, loons on smaller lakes may perceive 

a given event as a greater danger than those on larger lakes.

The conditions under which individuals habituate to a 

specific type of disturbance is also highly variable and will 

affect the results and interpretation of studies designed to measure response to disturbance. Habituation is the tendency, over 

the course of multiple weeks or multiple breeding seasons, 

for an individual to become less likely to respond to a given 

disturbance. Habituation is more likely with predictable, lowlevel disturbances and is typically specific to a disturbance 

type (e.g., Anthony et al. 1995). Thus an individual habituated 

to mechanical noise might continue to respond strongly to 

human presence. Individuals engaged in different behaviors, 

or at different stages of the nesting cycle, might exhibit different tendencies to habituate. During habituation or apparent 

habituation, individuals may become less likely to flee (Keller 

1989) but continue to exhibit more subtle signs of behavioral 

and physiological stress (Fowler 1999).

There are no published data on distances at which 

human activity causes Yellow-billed Loons to depart from 

nests or interrupt normal chick-rearing behavior. Incidental 

observations suggest that parents may leave the nest when 

an approaching human is as much as 1 mile away or as close 

as a few meters, depending on the size of the waterbody, 

topography, stage of incubation, and a multitude of other 

factors (Earnst pers. obs.). A well-designed study, using the 

approaches discussed above, is needed to determine a buffer 

width that will reduce various types of impacts on nests and 

young broods.

At the population level, quantifying the extent to which 

a given development scenario will affect Yellow-billed Loons 

is even more problematic. Our understanding of the effect at 

the population level is only as valid as our knowledge about 

how loons react to disturbance at the individual level, at what 

distance they react, and how their reaction translates into 

decreased productivity or survival (e.g., Pereira et al. 2004). 

The validity also depends on how well the development footprint used in the model corresponds with actual changes to the 

landscape. For example, the final predicted footprint changes 

as the expanding oilfield infrastructure and the market-price 

of oil make previously remote areas logistically and economically accessible (see BLM 2004b,c). 

Status Assessment 31
Wintering ecology..

Evidence of widespread declines in sea duck populations, 

and of large-scale changes in the marine ecosystem, highlight 

the importance of wintering ecology to population dynamics. 

Information is needed on Yellow-billed Loon diet during the 

winter, factors that affect winter survival and body condition, 

and how winter body condition affects the probability of successful reproduction the following spring. There is growing 

evidence that climate can effect a rapid shift in the organization of marine ecosystems, and that annual and decadal 

patterns in marine fish abundance correspond to climate 

phenomena, such as the Pacific Decadal Oscillation (reviewed 

in Francis et al. 1998). However, we have no information 

on whether Yellow-billed Loon overwinter survival, or their 

abundance and productivity in the following spring, is related 

to winter forage fish availability.

In order to relate wintering ecology to breeding population dynamics, we need to identify the wintering sites of 

known breeding populations. Based on distributions and 

observations during migration, North (1994) surmised that 

Yellow-billed Loons breeding in northern Alaska may winter 

in eastern Asia while Canadian breeders may winter off the 

Pacific coast from southern Alaska to California. An ongoing 

study using satellite transmitters is providing the first substantiated evidence that individuals nesting on the North Slope of 

Alaska spend the winter off the coast of East Asia (J. Schmutz 

pers. comm., see Section 5–E).

32 Status Assessment and Conservation Plan for the Yellow-billed Loon
Conservation Plan.

The conservation goal of maintaining a stable breeding 

population of current size and distribution was established by 

the Alaska Loon and Grebe Working Group during its 2000 

Annual Meeting. The Conservation Plan identifies the information necessary to achieve, and evaluate progress towards 

achieving, the conservation goal. Recommendations are based 

on published literature, unpublished reports, unpublished data 

and personal observations, the opinion of loon biologists, 

discussions by the Alaska Loon and Grebe Working Group at 

annual meetings in 1997–2002 (especially 2000), and from 

that groupʼs first status assessment, Status of Loons in Alaska 

(McCaffery 1998). 

Three-fourths of the strategies have been designated high 

priority. In most cases, the lack of a high-priority designation 

stems from the difficulty of gathering and interpreting relevant 

data (e.g., strategies pertaining to effects of disturbance and 

monitoring of wintering populations). Note that many of the 

high-priority strategies could be addressed within the framework of a multi-year, multi-location study (see Section 9–D).

Conservation Goal.

Maintain a stable breeding population, of current size and 

distribution across the loonʼs breeding range in Alaska 

(Alaska Loon and Grebe Working Group, 2000 annual 

meeting).

Research and Monitoring Goal.

Obtain the information necessary to achieve, and evaluate 

progress towards achieving, the Conservation Goal.

Research and Monitoring Objectives and 

Strategies.

OBJECTIVE 1. Conduct annual population surveys having 

negligible bias and 80% statistical power to detect a 3.4% 

annual decline, a decline that would result in a 50% loss 

of the population within 20 years. (Rationale in Sections 

6–D, 6–F, 9–B, 9–C, and Earnst et al. in review.)

Strategy 1.1. Consider implementing an annual aerial survey 

with appropriate timing, survey methods (e.g., lake circling), 

sampling intensity, and stratification designed specifically 

for monitoring the population trend of Yellow-billed Loons. 

High Priority.

Strategy 1.2 Continue to use the North Slope Eider Survey and 

the Arctic Coastal Plain Breeding Pair Survey to estimate 

temporal trends and distribution on the breeding grounds. 

Consider improvements to the surveys that would provide 

more precise and less biased temporal trends. High Priority.

a. Consider increasing the number of transects in both 

surveys, particularly in strata of high loon concentration. 

b. To reduce potential sources of bias, consider means 

of reducing observer turnover, increasing observer skill, 

and decreasing variability among observers.

c. Consider incorporating visibility correction factors or 

a form of double sampling to estimate biases.

d. Consider quantifying annual snow-melt phenology 

and conducting repeated surveys over a subset of the 

area to document loon arrival in conjunction with 

ongoing surveys.

Strategy 1.3. Use existing data to compare the statistical 

power and feasibility of ground-based and intensive aerial 

surveys, and combinations thereof, to detect temporal 

trends in productivity. Incorporate a study design that would 

identify environmental factors affecting temporal and spatial 

variation in productivity. (See also Strategy 3.3 and 4.3.) 

High Priority.

OBJECTIVE 2. Obtain an unbiased and reliable estimate 

of the size of Alaskaʼs breeding population. (Rationale in 

Sections 5–A, 6–A, 6–E, and 9–B.)

Strategy 2.1. Consider conducting a one-time, intensive 

aerial survey that incorporates a visibility correction factor, 

is designed specifically for Yellow-billed Loons, and is 

conducted across the breeding range in Alaska, to estimate 

population size on Alaskan breeding grounds. High Priority. 

a. Continue to analyze data from the 2003–2004 lakecircling surveys to evaluate whether this objective has 

been met or whether additional data for a more robust 

visibility correction factor are needed.

Strategy 2.2. As more demographic data and therefore more 

sophisticated population models become available, continue 

to use models to estimate size of the 1–2 year-old age class 

which presumably remains at sea.

Strategy 2.3. Use long-term banding and telemetry studies 

across multiple sites to estimate the fraction of young, 

nonterritorial adults (presumably 3–5 year-olds) and any 

older, nonnesting, territorial adults that remain at sea. Also 

estimate the proportion of time that territory holders, both 

those nesting and not nesting in the year in question, are 

temporarily absent from their traditional breeding lake at 

different stages of the breeding season. High Priority.

OBJECTIVE 3. Identify geographic regions and habitats 

of importance during breeding, staging, and wintering 

periods. (Rationale in Sections 5–A, 5–B, 5–E, 6–A, 9–B, 

and 9–C.)

Strategy 3.1. Continue to use the North Slope Eider and the 

Arctic Coastal Plain Breeding Pair surveys to quantify 

regions of high breeding density. In addition, consider using 

a periodic intensive survey to identify more precisely areas 

of concentration. High Priority.

Conservation Plan 33
Strategy 3.2. Quantify habitat preferences and continue to 

develop a habitat-based model of distribution using available 

GIS layers and results of intensive aerial surveys for Yellowbilled Loons. The model could estimate the probability of 

Yellow-billed Loon presence based on lake characteristics 

and other features of the landscape. High Priority.

Strategy 3.3. Determine differences in productivity among 

habitats and among geographic locations. High Priority.

Strategy 3.4. Continue to identify staging and wintering sites 

and migratory pathways of known breeding populations. 

High Priority.

Strategy 3.5 Design and implement a survey, or modify 

existing surveys, to estimate relative abundance and thereby 

identify key wintering sites in southern Alaska waters. 

Likewise, consider innovative collaborations to estimate 

relative abundance among wintering sites in the Yellow 

Sea and Sea of Japan, where Alaskaʼs breeding population 

appears to winter. (See also Strategy 7.3.)

OBJECTIVE 4. Use demographic models to evaluate risks to 

the population. (Rationale in Sections 5–B, 5–C, 5–F, and 

9–D.)

Strategy 4.1. Develop spatially-explicit demographic models 

to estimate the populationʼs response to varying degrees of 

perturbation to adult survival and productivity across varying 

geographic scales. High Priority.

Strategy 4.2. Quantify age-specific productivity and survival 

and other demographic parameters necessary for the model. 

Investigate patterns in and factors causing spatial and 

temporal variation in productivity and other demographic 

parameters. High Priority.

Strategy 4.3. Determine whether areas of breeding 

concentration, and particular habitats within those areas, 

function as population sources and evaluate whether they 

warrant special protection to maintain population stability. 

High Priority.

Strategy 4.4. Develop genetic markers that can be used to 

evaluate the degree of genetic overlap among breeding 

concentrations, and thus the extent to which such 

concentrations should be considered discrete population 

segments in demographic models and conservation efforts. 

Strategy 4.5. Estimate overwinter survival, its annual 

variation, and the effects of ice conditions and forage 

fish availability. Design programs to monitor relevant 

components of the wintering ecosystem once factors that 

affect overwinter survival have been identified. High 

Priority.

OBJECTIVE 5. Identify potential effects of oil development 

on the breeding grounds and measures necessary to 

minimize the effects. (Rationale in Sections 7–A, 7–B, and 

9–D.)

Strategy 5.1. Obtain baseline data that can be used to evaluate 

the impact of oil development. High Priority.

a. Gather pre- and post-development data on 

productivity, factors affecting productivity, and lake 

occupancy in the vicinity of proposed industrial 

development. (See also Strategy 5.4.)

b. Obtain baseline data on the abundance of nest and 

chick predators.

c. Obtain baseline data on the contaminant loads of 

adults and eggs on key breeding areas.

d. Obtain baseline data on water quality in large lakes 

near proposed industrial development.

Strategy 5.2. Evaluate the potential effects of various types of 

disturbance on territorial loons.

a. Quantify effects of noise from vehicles, aircraft, 

and humans on breeders during incubation and broodrearing.

b. Quantify effects of proximity to housing facilities, 

runways, roads, and pipelines on breeders during 

incubation and brood-rearing. 

c. Quantify the effects mentioned above on various 

components of loon productivity and behavior—lake 

occupancy, probability of initiating a nest, clutch 

size, number of young fledged, time-budgets, energy 

expenditure, and stress-induced hormonal changes.

Strategy 5.3. Evaluate whether a 1-mile (1.6–km) nodisturbance buffer around traditional nest sites sufficiently 

minimizes disturbance to breeding pairs (BLM 2004a,b), 

whether a similar buffer around breeding lakes is also 

needed, and whether buffers of different size are needed for 

different types of disturbance.

Strategy 5.4. Develop site-specific maps detailing traditional 

nesting, foraging, and wintering sites near existing and 

proposed oil developments and pipelines. The maps should 

be useful to government agencies in issuing permits and to 

the industry in identifying priorities in spill prevention and 

response plans. (See also Strategy 5.1a.) 

a. Conduct intensive, species-specific aerial surveys 

during at least three years to map traditional nesting 

lakes, foraging sites (including river channels and 

off-shore waters), and wintering sites in locations 

specifically targeted for development. Use a welldesigned sampling plan that allows estimation of 

number of individuals and nests, changes through time, 

and a comparison to other sites.

b. Continue the surveys during and after development to 

assess potential impacts of development.

Strategy 5.5. Determine the effect of reduced water levels 

in traditional Yellow-billed Loon breeding lakes resulting 

from ice-road and ice-pad construction. Quantify effects on 

subsequent lake occupancy, probability of nest initiation, 

productivity, and forage fish populations. High Priority.

34 Status Assessment and Conservation Plan for the Yellow-billed Loon
Strategy 5.6. Identify high-density breeding areas in which 

protective measures deemed useful for Yellow-billed Loons 

(see above) could benefit a large fraction of the breeding 

population. (See also Strategy 3.1.) High Priority.

OBJECTIVE 6. Evaluate the magnitude of subsistence 

harvest and bycatch and their potential effects on the 

population. (Rationale in Sections 7–D and 9–C.)

Strategy 6.1. Improve the reliability of estimates from the 

Subsistence Harvest Survey by providing educational and 

outreach programs that emphasize species identification to 

hunters and those conducting the survey.

Strategy 6.2. Continue to evaluate bycatch of Yellow-billed 

Loons in commercial gillnets on the wintering grounds in 

Alaska. 

Strategy 6.3. Work with experts in other countries to evaluate 

the magnitude of bycatch in commercial gillnets on non-U.S. 

wintering grounds. (See also Strategy 7.3.) 

Strategy 6.4. Initiate a program to monitor bycatch of Yellowbilled Loons in subsistence gillnets on northern Alaska 

breeding grounds. Bycatch on the breeding grounds is likely 

Conservation Plan 35

to be more important than that on wintering grounds, 

because the fishery occurs during peak loon abundance. 

High Priority.

OBJECTIVE 7. Develop a continent-wide and range-wide 

context for Alaskaʼs population and habitat objectives.

Strategy 7.1 Work with experts in Canada and Russia to 

evaluate threats to breeding populations and to encourage 

future monitoring of temporal trends. High Priority.

Strategy 7.2. Work with experts in Canada and Russia to use 

digitized topographic maps, aerial photographs, satellite 

imagery, and habitat models (the latter derived from 

Alaskan surveys) to estimate breeding population size and 

distribution in Canada and Russia. The resulting map of 

predicted relative abundance could aid in identifying strata 

for systematic surveys and could be updated when results of 

such surveys become available. High Priority.

Strategy 7.3. Work with experts in Canada, Russia, Japan, 

China, and North and South Korea to evaluate wintering 

distribution, connections between breeding and wintering 

areas, and threats to wintering populations. High Priority.
36 Status Assessment and Conservation Plan for the Yellow-billed Loon

Illustration by Jeff Stephens
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