Lesser Scaup diets during migration and winter in the Mississippi flyway

We examined diets of Lesser Scaup (Aythya affinis) during midwinter (N = 41) in southwestern Louisiana (1986), and during spring (N = 57) and fall (N = 48) in northwestern Minnesota (1984–1988). Diets of males and females generally were similar during migration and winter. Diets of adults and immatures differed during fall migration but were similar during winter. In fall, immature scaup fed heavily on amphipods and did not consume certain foods, such as fish and fingernail clams, that were important in adult diets. Aggregate percent dry weight of animal foods was higher during fall (adults 91%, immatures 93%) and spring (92%) than during midwinter (61%). Important foods during all periods were crustaceans, insects, and mollusks.