Northwest Alaska’s Yellow-billed Loons: A Population 2-2.5 Times Larger Than Thought

In April, rafts of Yellow-billed Loons float in the Yellow Sea of China, feasting on fish to fuel their migration to Alaska. The species is considered one of the ten rarest breeding birds of the mainland U.S., occurring only in Alaska, and is of international concern: the global population is estimated at between 16,650 and 21,000 birds. Approximately 20-25% occur seasonally in Alaska, where the summer breeding population is estimated at less than 5,000. Most nest on the Arctic Coastal Plain in the National Petroleum Reserve-Alaska, land earmarked for oil and gas development.

Two National Park Service units on the northwest coast show another picture. About 1,500 Yellow-billed Loons are estimated to nest in Bering Land Bridge National Preserve and Cape Krusenstern National Monument, coastal parklands that may give the birds and their nesting habitat more protection. Aerial surveys across both parks in 2011 and 2013 indicate that Alaska’s northwestern breeding population is about 2-2.5 times larger than previously thought.

Why the birds are worth watching

Loons of the Seward Peninsula often feed in marine habitats, unlike those of the Coastal Plain, which leaves them especially exposed to an oil spill as oil exploration and vessel traffic grow in the region. Because they use both fresh water and the sea, Yellow-billed Loons are indicators of water quality and give insight into the movement of marine-derived nutrients and into changes in ecological communities along rivers and coasts. They are large, long-lived top predators of fish in lake ecosystems, so contaminants can build up in them. Some winter in the highly contaminated Yellow Sea, and they and their eggs are potentially harvested by Alaska Natives. And because the birds return to the same breeding sites each year, they suit long-term monitoring of occupancy, density, distribution and contaminant loads.

What the surveys found

The park service has monitored the loons with the U.S. Fish and Wildlife Service since 2005 to document long-term trends. The surveys are designed to find Yellow-billed Loons but record every loon species seen. In the 2011 and 2013 surveys the birds nested at 205 lakes and used an additional 207 of 1,291 lakes in the study area. The likelihood that the same lakes would be used in later years was high (greater than 70%), which suggests strong loyalty to particular nest lakes.

The similar Pacific Loon often needs the same kind of lake and may compete with the Yellow-billed. Pacific Loons were more likely to use lakes in the study area, yet in some cases Yellow-billed Loons kept them out; the competition is greater on the Coastal Plain. Both species used a broader area of lake habitat for nesting and foraging than previously thought, and the article says more study is needed to understand why they pick particular lakes. Overall, the results suggest the two parks may support significant populations of both species, warranting additional consideration for conservation.

What is in the eggs

To judge the health of the birds and of their lakes, the park service tests eggs and small prey fish from nesting lakes. An egg carries a signature of the contaminants an adult met away from the breeding grounds; the fish show what is present locally. The tests cover metals such as mercury, persistent organic pollutants, organochlorine pesticides, perfluorinated hydrocarbons, PCB congeners and polybrominated diphenyl ethers. Preliminary results from eggs suggest mercury may be approaching levels that could impede reproduction in loons nesting in these parks, and eggs from the Coastal Plain gave similar results. When the article was written, the northwestern data were being compared with Coastal Plain data to see the contaminants across all Yellow-billed Loons in Alaska.

Lakes from above, and DNA

Little is known about which lake traits (type, connectivity, depth, flood regimes) Yellow-billed Loons prefer in northwestern Alaska. Data on fish in Arctic lakes, an important factor in where these fish-eating birds nest, are lacking too. With the U.S. Geological Survey and the University of Alaska Fairbanks, the park service is building a geospatial database of lake type, connectivity, depth and flood regimes from high-resolution satellite imagery, space-borne synthetic aperture radar (ifSAR) imagery, ice-growth models and weather-station data. Winter and spring radar images of hundreds of lakes in Bering Land Bridge let researchers estimate depth and spot areas that stay partly unfrozen all year, which may serve as overwintering areas for fish and so attract loons. The work was slated to finish by late 2017.

Genetics adds two tools. Water samples from nesting lakes are tested for environmental DNA (eDNA), trace fragments shed by organisms that can reveal which species live in a lake. And swabbing the surface of a loon egg picks up shed epithelial cells of the adults and maternal blood, so DNA from the pair can be collected without handling the birds, since both parents brood. From it the team developed over 20 polymorphic microsatellite markers that give each bird its own genotype, a DNA fingerprint, used to identify individuals, to confirm that pairs return to the same nest sites and to explore family relationships such as paternity.

Swabbing Yellow-billed Loon eggs for genetic samples. NPS Photo / Melanie Flamme.

The genetic analyses, done at the USGS Molecular Ecology Laboratory, also compare Yellow-billed Loons with Alaska’s other four loon species: Pacific, Red-throated, Arctic and Common. Preliminary results indicate that Yellow-billed Loons have lower genetic variation than the others, both in allelic variation and in heterozygosity. Early eDNA tests of their nesting lakes detected many fish species as well as Yellow-billed Loons, and both lines of research were ongoing.

Putting it together

Taken together, the aerial surveys, contaminant tests, lake database, eDNA and population genetics fill gaps named in the species’ Status Assessment and Conservation Plan, to inform careful, science-based management across Alaska.

The project has a youth strand as well. Since 2013 the park service has recruited five students from urban and rural Alaska to learn video storytelling at the Alaska Teen Media Institute. They travelled with scientists to see the loons in their habitat and made three videos, which are on the Alaska NPS YouTube channel.

Sources

• Melanie Flamme and Stacia Backensto, National Park Service, Collaborative Conservation of the Rare Alaskan Yellow-billed Loon, Alaska Park Science, volume 16 (Science in Alaska’s Arctic Parks); rewritten in hubnx's own words.