Reproductive Strategies of South Polar Skuas: The role of food in chick survival and sibling aggression

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Until the development of the ideas of inclusive fitness and parent- offspring conflict among avian populations, infanticide has been viewed inimical to the theory of natural selection. Several hypotheses about the circumstances by which siblicide, cannibalism, and adoption of foreign chicks should occur have been suggested recently and studies on the reproductive strategies of birds commonly consider the trade-offs facing parents that are trying to raise chicks. The purpose of the proposed research will be to test hypotheses concerning the role of food availability and parental feeding as a cause of sibling aggression leading to siblicide and nestling starvation in the South Polar Skua, Catharacta maccormicki, on Ross Island, Antarctica. The South Polar Skua represents one of the few examples where sibling aggression is mediated by hunger. The Food Amount Hypothesis predicts less aggression between chicks in provisioned nest (food supplement), resulting in fewer cases of siblicide, higher growth rates, and increased reproductive success. The causes and timing of egg and chick mortality will also be determined and how skuas adjust their reproductive strategies from one year to the next. The proposed research will be devoted to developing a quantitative description (mechanism) of siblicide or the importance of siblicide to the reproductive success of the South Polar Skua.