Loons Without Lakes: Draining Tundra Lakes in Bering Land Bridge National Preserve

A Yellow-billed Loon sits low on its nest. NPS/Stacia Backensto.

Flying their loon surveys over Bering Land Bridge National Preserve in western Alaska in 2018, biologists witnessed widespread drying of coastal lakes, likely a consequence of a warming climate. Six large lakes used by Yellow-billed, Pacific and Red-throated Loons had drained quickly. What was left were bare mudflats without loons, and without the fish, invertebrates and plants that shelter and feed the birds while they nest and raise chicks.

The preserve is one of only a handful of places around the Arctic with lakes suitable for Yellow-billed Loons. The scientists were struck by how many lakes had drained, how big they were and how close together, and wondered whether this was a one-off and whether it would affect the loons.

A large lake where Yellow-billed Loons nest, June 2009. NPS/Melanie Flamme.

The same lake in September 2018, drained sometime between late June and early September. NPS/Sarah Swanson.

A demanding bird

The Yellow-billed Loon is the rarest loon in North America. It was considered for listing under the Endangered Species Act in 2009 because of its small world population, its narrow habitat needs and its slow breeding. It was not listed, but more recent work on its genetics, its exposure to contaminants, its migrations and its use of habitat suggests it may be vulnerable.

As the heaviest of the loons, it may need up to a quarter of a mile of water to take off, and it relies on large, deep lakes to catch fish, to dive away from predators and to raise its young. It competes with other loons for the best nesting sites, and it is strongly faithful to them, returning to defend the same lake year after year.

Lakes in decline

More than a decade of loon surveys, combined with satellite images of the preserve's lakes going back to the mid-1980s, show that the loons' nesting lakes are changing fast. In parts of the survey area, lake area has held steady since the mid-1980s. But the low coastal plain along the Bering Sea, rich in lakes and the best loon habitat, has been losing water at about 3 square miles per decade since 2000, when its lakes covered about 60 square miles. In 2018 the loss jumped: 3 square miles of lake drained in a single summer.

Northeastern Bering Land Bridge National Preserve. Lakes that drained in 2018 are marked with triangles and labelled with the share of their area lost and the water lost in hectares (a hectare is about 2.5 acres). NPS/David Swanson.

Why the lakes drain

The preserve lies in the zone of continuous permafrost, where the ground stays frozen year-round and holds large amounts of ice. Lakes draining from time to time is a natural part of this landscape, and much of the coast is marked by the basins of old lakes. What happened in 2018 was something else. At Kotzebue, the period from the winter of 2017–18 through the summer of 2018 was the warmest since records began in the 1940s, capping a run of record warm years from 2014.

The many drainages were probably the result of that long warm spell, helped by unusually deep snow in the winter of 2017–18, which let the lakes overflow and cut new outlets. Photographs show that most drained when the ice-rich ground beside them thawed and sank, deepening the outlet until the lake emptied all at once.

A channel carved into the tundra when a Yellow-billed Loon nesting lake drained in June 2018. NPS/Jared Hughey.

Watching the sentinels

As top predators in their lakes, Yellow-billed Loons are sentinels, among the first to show changes that Alaska's wildlife is likely to face as the climate keeps warming. So far the preserve's population appears fairly stable. Whether that holds, and how the loons will cope with so many lakes draining, is what the Park Service's continued monitoring of lakes and loons is meant to find out.

Sources

• National Park Service, "Loons without lakes," Arctic Network Inventory and Monitoring; rewritten in hubnx's own words. Photographs and map: NPS.