The diving times, diving distances, foraging rates, intraspecific and interspecific interactions between canvasbacks (Aythya valisineria), ring-necked ducks (A. co-Uaris) , lesser scaup (A. affinis) and redheads (A. americana) were studied on coastal winter habitats in South Carolina. Diving times, distances and foraging rates varied between habitats of different water depths and between species, but with few exceptions not between sexes. Canvasbacks were the dominant birds and actively defended foraging sites against other birds, particularly ringnecks. During late winter when food resources were presumed limited, male canvasbacks excluded females from preferred foraging sites. Temporal and/or spatial segregation of habitats between sexes of the other species was not demonstrated. Exclusion of individuals from optimal winter foraging areas may have significant implications affecting population dynamics of waterfowl.