Ornis Scandinavica 19: 249-256
Sea duck use of coastal habitats in southeastern Newfoundland varied by shoreline type and distance from shore. Harlequin Ducks exploited areas relatively close to shore and adjacent to sunkers (skerries) when foraging. Oldsquaws, Black Scoters, and Common Eiders foraged at similar distances from shore, on average, however eiders primarily used areas adjacent to bedrock slabs where water was deeper (>3m) than areas off bedrock ledges and cobble beaches where oldsquaws and scoters fed. Substrate studies adjacent to seven defined shoreline classes confirmed that there were regular differences in microhabitat features. We were unable to reject a hypothesis that the sea ducks species similar in morphology would demonstrate greater separation in habitat space than dissimilar species for Harlequin Ducks versus Oldsquaws, whereas, for Common Eiders versus Black Scoters, there was least separation in these species of similar morphology. Food use by eiders and Oldsquaws at Cape Race, where Harlequin Ducks and scoters were virtually absent, suggested that competitive niche shift may be occurring at Cape St. Mary's where all species are syntopic. Habitat use by wintering sea ducks at Cape St. Mary's is in partial agreement with current concepts of interspecific competition although our evidence did not constitute proof that competition was occurring.