Dietary niche partitioning in brown skuas (Stercorarius lonnbergi) during the chick-rearing period at Nar？bski Point on King George Island, Antarctica

Abstract

Brown Skuas (Stercorarius lonnbergi) are known to feed on other birds or eggs during the breeding season. In some cases, however, a few pairs monopolize a penguin colony, and the other skuas mainly forage in the sea. We installed automatic camera traps to monitor two groups of breeding Brown Skua pairs on King George Island: the nests of Group A were located near a Gentoo Penguin (Pygoscelis papua) colony, while those of Group B were relatively far away. From the resulting photographs, we were able to distinguish the food items that parents brought to the nest and could confirm the egg hatching date. Overall, 97.1% of the food items that group A brought to the nest were from the penguin colonies, while 94.1% of the prey items of group B were fish. Group A had a hatching date at least 8 days earlier than Group B. Our results show that a few Brown Skua pairs that bred near the penguin colony fed primarily on penguin nest contents such as eggs or chicks within their feeding territory and had earlier hatching dates. The Brown Skuas that nested close to penguin nests may have had advantages in foraging and breeding performance.