North American waterfowl winter throughout a large geographic area, and the choice of wintering site has a direct impact on survival and fitness. Climatic and food variables are the most commonly cited factors influencing abundance and distribution of wintering migratory birds, including waterfowl. We conducted stratified aerial surveys at a northern latitude wintering site, Great Salt Lake (GSL), Utah, to describe the importance of this wintering area and to examine the influence of weather and food on the abundance of total ducks, Northern Shovelers (Anas clypeata), and goldeneye species (Bucephala spp.). Surveys indicated that up to 270,000 ducks use the GSL during winter, making it an important wintering area in the Pacific Flyway. Peak abundance of total ducks was positively correlated with overwinter temperatures. Northern Shoveler abundance was positively correlated with elevation of the GSL; higher lake elevation indicated more open water and hence more overwintering habitat. Goldeneye abundance was correlated with the continental population of the species and food abundance. All models had moderate fit (r2 > 0.40). The GSL is unique in the United States as it is a large body of water where consistent ice cover does not occur and foraging habitat is available to ducks throughout winter. Our results suggest that ambient temperature and habitat availability are primary factors in the abundance of total wintering waterfowl, though food abundance seemed to influence wintering population size of individual duck species. We hypothesize that ducks endure the cold, hypersaline conditions on the GSL to exploit the abundant food supply and remain close to primary breeding regions.
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Vol. 76 • No. 1