Exploitation of inland-breeding Antarctic petrels by south polar skuas

During the austral summer of 1996/1997 we studied south polar skuas at Svar thamaren, Dronning Maud Land, Antarctica,:where the world's largest known c olony of Antarctic petrels is found. Our censuses suggested approximately 2 50 full-grown skuas and 140,000 breeding pairs of petrels were present. Dur ing their breeding season, skuas did not visit the open sea at least 200 km from the site; they relied entirely on prey caught and scavenged from the petrel colony. Because the site is so isolated, we asked whether the prey ( petrels) had swamped the predators (skuas), or whether there was evidence t hat predator numbers were limited by the size of the prey population. Parti cularly at the end of the petrel incubation period, we found a close corres pondence between the energy required by adult skuas and their chicks, ascer tained from time budget studies, and the rate at which petrel eggs disappea red from the colony. This suggests that, in this closed system, the predato r population was limited by the prey population, and that predator swamping was not an advantage that petrels gained by nesting in this remote locatio n.