Parental care in nesting hawks: breeding experience and food availability influence the outcome

Parental food provisioning and sibling rivalry have inspired abundant investigations of evolutionary conflicts within families. Nevertheless, their joint effects have seldom been assessed in relation to parental and environmental state. We investigated state dependency of feeding behaviors through the complete nesting phase in a species whose young both partly beg for food and partly self-feed, the northern goshawk Accipiter gentilis. After hatching, when young relied on being fed beak-to-beak, siblings achieved equal amounts of food irrespective of hatching rank, body condition, and sex. However, mothers new to a territory fed their offspring less than experienced ones independently of food availability. This pattern persisted also after nestlings grew and initiated to self-feed and aggressively monopolize prey. Mothers never interfered with aggressions but stayed with their even feeding strategy paying little attention to begging activity. Although mothers' even feeding strategy is likely to equalize siblings' survival probabilities when food is abundant, the fact that nestlings in good condition monopolize prey in self-feeding situations will boost brood asymmetries when food decreases. Because new mothers feed their offspring less than experienced ones, aggressive sibling rivalry will be particularly crucial among mothers lacking previous local breeding experience. Albeit hitherto overlooked, feeding behaviors constitute important mechanisms explaining experience-related differences in reproductive performance of wild animals. Copyright 2011, Oxford University Press.