Food habits of breeding white-winged scoters

Twenty-four adult and 10 duckling white-winged scoters were collected on four lakes in central Saskatchewan during the summers of 1977–1980. Hyalella azteca was the most important scoter food and made up 97% (aggregate percent dry weight) of the diet for 13 breeding females, 84% for 11 breeding males, and 100% for 10 ducklings. Hyalella azteca was consistently the most abundant food organism present in Eckman dredge samples taken at scoter feeding sites. Adults consumed H. azteca that were significantly larger than those consumed by ducklings. Both adults and ducklings fed primarily by diving at sites 1–3 m deep, but adults fed at deeper sites than ducklings. Timing of reproduction in white-winged scoters seems to be closely timed with increases in the biomass and abundance of Hyalella and possibly other invertebrate foods.