Feeding and Nesting Ecology of Sympatric South Polar and Brown Skuas

Abstract

Abstract In the 1979-1980 and 1980-1981 austral summers, I examined nesting and feeding ecology of South Polar (Catharacta maccormicki) and Brown (C. lonnbergi) skuas near Palmer Station, Antarctica. As earlier studies had suggested, South Polar Skuas fed mostly at sea on fish, and Brown Skuas fed mostly on penguin eggs and chicks. These dietary differences correlated with differences in the skuas' time budgets, activity patterns, territory types, breeding chronologies, nest densities, clutch sizes, and fledging success. With combined data from this and other studies at Palmer, I calculated average productivity for both species over 7 breeding seasons. Brown Skuas fledged higher and more consistent numbers of young per pair, probably because of their more accessible and reliable food source.