Feeding Territories and Breeding Success of South Polar Skuas

ABSTR•CT.--Territorial and foraging behavior of the South Polar Skua (Catharacta maccormicki) were studied in 1971-72 at the Cape Hallett Adglie Penguin (Pygoscelis adeliae) rookery. The skua population was at maximum 98 pairs, and the Adglie Penguin population was some 43,000 pairs. The size of the skuas' territories varied between 0.5 and 1.8 ha (between 730 and 3,190 penguin pairs). Areas between adjacent territories overlapped. The behavior of three dyemarked pairs in their territories is described. A large enough feeding territory in the penguin rookery apparently enabled certain skua pairs to subsist exclusively on a penguin diet throughout the whole skua breeding season. Skuas breeding farther away from the penguin rookery usually defended only nest territories, which were much smaller than the above all-purpose territories. They hunted in the northwest part of the rookery in "preferred feeding areas" that were not defended against other skuas. Some pairs apparently foraged at sea. The number of skuas hunting per unit area is about sixfold in the parts of the rookery used by skuas as preferred feeding areas, but no resulting decline in penguin breeding success could be found. The breeding success of skua pairs with feeding territories was significantly higher than that of pairs with preferred feeding areas. The possible causes of this difference are discussed.---Max Planck-lnstitut fiir Verhaltensphysiologie, Ethologische Abteilung, 8131 Seewiesen, West Germany. Accepted 3 May 1976.