Loons without lakes

Amy Larsen, Melanie J. Flamme, David K. Swanson, Sarah C. Swanson

A Yellow-billed Loon sits low on its nest.

NPS/Stacia Backensto

While flying loon surveys in Bering Land Bridge National Preserve in 2018, biologists witnessed widespread drying of coastal lakes, the likely consequences of a warming climate. Six sizeable lakes used by Yellow-billed, Pacific and Red-throated Loons drained rapidly (Figures 1a and 1b). Left behind were barren mudflats bereft of loons; gone were the fish, invertebrates and vegetation that provide cover and nourishment to the birds while nesting and chick-rearing. Bering Land Bridge NP is one of a handful of regions throughout the Circumarctic that contain lakes suitable for Yellow-billed Loons. Scientists were surprised by the large number, size and close proximity of the drained lakes, and were left wondering if this was an unusual event, and whether it would impact loon populations in the area.

Left image
Figure 1a. A large lake where Yellow-billed Loons nest in Bering Land Bridge National Preserve in June 2009.
Credit: NPS/Melanie Flamme

Right image
Figure 1b. The same lake in September 2018 catastrophically drained sometime between late June and early September.
Credit: NPS/Sarah Swanson

Yellow-billed Loons are the rarest loon species in North America, and were considered for Endangered Species Act listing in 2009 due to low global population, specific habitat requirements, and low fecundity (Federal Register 2014). Though they were not listed, recent studies on population genetics, exposure to environmental contaminants, migration patterns and habitat use suggest the species may be vulnerable. As the heaviest loon species, they can require up to one-quarter mile to take off from water and depend on large, deep lakes to forage for fish, escape predators (by diving), and raise young (Earnst et al. 2006). They compete (Haynes et al. 2014; Schmidt et al. 2014) with other loons for ideal nesting sites and are highly philopatric (Schmutz et al. 2014), meaning they return to and defend the same nesting lakes each year.

More than a decade of loon population survey data, combined with satellite imagery of lakes in Bering Land Bridge NP dating back to the mid-1980s, indicate remarkable changes in the nesting lakes of loons are underway. Lake surface area in some portions of the loon survey area has remained stable since the mid-1980s, but the lake-rich low coastal plain bordering the Bering Sea–prime loon habitat–has been losing water at a rate of about 3 square miles per decade since 2000, when lakes covered about 60 square miles. Lake surface area dropped abruptly in 2018, when 3 square miles of lakes drained in a single summer.

Figure 2. Satellite image of northeastern Bering Land Bridge National Preserve. Lakes that drained in 2018 are marked with a triangle and labeled with the water area loss in percent of the original lake area and water loss in hectares (about 2.5 acres).

NPS/David Swanson

Figure 3. Aerial photograph of a channel carved into the tundra after rapid and catastrophic lake drainage of a Yellow-billed Loon nesting lake in June 2018, Bering Land Bridge National Preserve.

NPS/Jared Hughey

Bering Land Bridge NP lies in the continuous permafrost zone, meaning that ground in the region is continuously frozen. The ground here also contains large quantities of ice. Periodic lake drainage is a natural part of the ecology in this region and much of the coastal landscape is scarred with old drained lake basins. However, the rapid changes observed last year were a stark contrast from previous years. According to long-term climate monitoring at Kotzebue, Alaska, the period encompassing the winter of 2017-18 through the summer of 2018 was the warmest since records began in the 1940s, following a series of record warm years that began in 2014. The numerous lakes that drained this year were likely due to the extended warm conditions that have dominated the region since 2014, enhanced by exceptionally deep snow in the winter of 2017-18 that helped the lakes overflow and erode new outlets. Photographs of the lakes show that most drained when ice-rich ground adjacent to the lakes thawed allowing the ground to subside, deepening the lake outlet and causing the lakes to catastrophically drain (Figure 3).

As top predators in lake ecosystems, Yellow-billed Loons are sentinels, acting as early indicators of ecological changes that Alaskan wildlife are likely to see in the coming years as climate warming continues. So far, the Yellow-billed Loon population in Bering Land Bridge NP appears relatively stable (Schmidt et al. 2014). Will that trend hold in the future? How will loons cope with the widespread draining of lakes? We will continue monitoring lakes and loons to better understand these rapid changes occurring in the Arctic.



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References
Earnst, S. L., R. Platte and L. Bond. 2006. A landscape-scale model of Yellow-billed Loon (Gavia adamsii) habitat preferences in northern Alaska. Hydrobiologia 567: 227-236.

Federal Register. 2014. Endangered and Threatened Wildlife and Plants; 12-month Finding on a Petition to List the Yellow-billed Loon as Threatened or Endangered. 50 CFR Part 17, Federal Register Vol. 79, No. 190/59195-59204.

Haynes, T. B., J. A. Schmutz, M. S. Lindberg, K. G. Wright, B. D. Uher-Koch, and A. E. Rosenberger 2014b. Occupancy of Yellow-billed and Pacific Loons: Evidence for interspecific competition and habitat mediated co-occurrence. Journal of Avian Biology. doi:10.1111/jav.00394

Schmidt, J. H., M. J. Flamme, and J. Walker. 2014. Habitat use and population status of Yellow-billed and Pacific Loons in western Alaska, USA. The Condor, 116(3):483-492. http://www.bioone.org/doi/full/10.1650/CONDOR-14-28.1

Schmutz, J. A., K. G. Wright, C. R. DeSorbo, J. S. Fair, D. C. Evers, B. D. Uher-Koch, and D. M. Mulcahy. 2014. Size and retention of breeding territories of Yellow-billed Loons in Alaska and Canada. Waterbirds. doi:10.1675/063.037.sp108