Yellow-Billed Loon Population Size on the North Slope of Alaska

The Yellow-billed Loon breeds on large, deep, fish-bearing lakes on the tundra of northern Alaska, Canada, and Russia. Due to its specific habitat requirements, restricted range, small population size, and perceived threats to its breeding and wintering habitat, the Yellow-billed Loon is a species of concern to USFWS. The species was the subject of a petition for listing under the Endangered Species Act at the time of this study. Within the United States, the Yellow-billed Loon breeds primarily within the National Petroleum Reserve-Alaska, 95% of which has been opened or is proposed to be opened, for oil and gas development. Despite this concern, rigorous estimates of population size and trend were lacking in the peer-reviewed literature at the time of our study.

To estimate population size and trend, we used two annual aerial waterfowl surveys flown by the USFWS, encompassing 1986-2003 and 1992-2003, and we used mixed-effects regression models to reduce bias and sampling error associated with improvement in observer skill and annual effects of spring phenology. There was no long-term trend in abundance for the 1986-2003 period. The average population size was <3,500 individuals, and we estimate that <1,000 nesting pairs inhabit northern Alaska in most years. The highest concentration of Yellow-billed Loons occurred between the Meade and Ikpikpuk Rivers; across all of northern Alaska, 53% of sightings occurred within 12% of the area. See Earnst et al. 2005.

Funding Sources

USFWS Region 7 Migratory Bird Program

Yellow-Billed Loon Habitat Preferences on the North Slope of Alaska

Yellow-billed Loons nest on large waterbodies and rely almost entirely on the nesting lake for the food that they feed their young. As a result, Yellow-billed Loons are expected to nest primarily on lakes that support fish. We conducted intensive aerial surveys and used landscape-scale habitat descriptors to model habitat preferences across the majority of the species' breeding range on the North Slope, a 23,500 km² area between the Colville River and Meade River. Of the 757 lakes censused, Yellow-billed Loons occupied 15%, and Pacific Loons occupied 42%. Yellow-billed Loon presence was 13 times more likely on deep lakes and 4.7 times more likely on medium depth lakes than on shallow lakes that freeze to the bottom during the winter and are therefore devoid of self-sustaining fish populations. On shallow lakes, hydrological connectivity to streams was also an important predictor of Yellow-billed Loon presence, presumably because connectivity increased the likelihood of fish presence on small lakes. Yellow-billed Loons were also more likely to be present on lakes with aquatic vegetation and complex shorelines, both of which provide loon nesting and brood-rearing sites and fish habitat. Pacific Loon absence was a positive predictor of Yellow-billed Loon presence when added to habitat models – Yellow-billed Loons were 4 times more likely to be present on lakes without Pacific Loons. See Earnst et al. 2006.

Funding Sources

USFWS Region 7 Migratory Bird Program

Breeding Habitat Partitioning and Reproductive Success of Yellow-Billed, Pacific, and Red-Throated Loons on the Colville River Delta, Northern Alaska

This study investigates niche overlap among three loon species and attempts to understand the processes that affect loon productivity and habitat use across years and habitat types. All components of annual productivity (proportion of pairs nesting, clutch size, survival during incubation, survival during brood-rearing) were monitored during each of 6 years (1995-2000) by searching known breeding territories during early incubation. Nests and brood-rearing lakes were revisited every 7-10 days through the end of August. There was substantial between-year variation in productivity, particularly in Yellow-billed Loons, and preliminary results suggest that the variation is related to the timing of spring ice melt. Fish and invertebrate abundance were sampled in brood-rearing waterbodies and time-budget data were collected during brood-rearing. Food availability and other wetland characteristics will be related to parental feeding rate, brood success (particularly ability to raise 2 rather than 1 young), and between-year consistency in territory occupancy and breeding status. Movements among brood-rearing waterbodies are fairly common in Pacific Loons and Red-throated Loons; causes and consequences of brood movement are being investigated. In a given year, I monitored approximately 16 Yellow-billed Loon, 50 Pacific Loon, and 50 Red-throated Loon nests and broods. Because nest and brood surveys were conducted in a thorough and systematic fashion across the Delta in each year, data will be useful in elucidating changes in population size across years, as well as habitat preferences at the landscape and within-territory scale.

Funding Sources

USFWS Region 7 Migratory Bird Program