The behavioral ecology of the American Wigeon (Anas americana) over its annual cycle
Wishart, Richard A.
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The behavioral ecology of the American Wigeon (Anas americana) was studied over its annual cycle in western Canada between 1974 and 1978. The objective of this work was to examine the cross-seasonal interactions of the biology and behavior of the wigeon as they underlie the evolution of its mating system. The wigeon was more herbivorous than any other dabbling duck studied so far and spent a considerable amount of time feeding in upland habitats. Vegetation was important in the diet year round but particularly from late summer through the winter. Plant seeds were a rich source of protein and carbohydrate early in the spring. During breeding stages animal foods were selected by wigeons, particularly females. Wigeons usually did not feed on small crustaceans and gastropods but selected larger aquatic insect foods. Relative to other Anas soecies, the wigeon has a goose-like bill whose structure facilitates feeding on upland and aquatic vegetation. With the evolution of this specialization, efficient surface-straining of small foods has been sacrificed. To increase food digestibility, wigeons altered gizzard grit composition and organ sizes. Through these mechanisms I have demonstrated how wigeons have been able to increase the efficiency of digestion.