SLOW LEARNING OF FORAGING SKILLS AND EXTENDED PARENTAL CARE IN COOPERATIVELY BREEDING WHITE-WINGED CHOUGHS

This is the first study to associate costs of extended juvenile development and the necessity of cooperative breeding. Juvenile choughs require unusually long periods to attain foraging independence. The transition is gradual, usually taking about 200 d after fledging. These results show a clear relationship between the amount of help a juvenile gets, the nature of its transition to foraging independence (TFI), and its prospects of surviving its first year. Despite high variance within broods, individuals with greater numbers of helpers in their group receive more food from begging and remain dependent for longer periods. Juveniles invariably lose weight over winter, but those that remain dependent on adults for food for longer periods both begin and emerge from winter with higher body weights. However, these individuals lack experience and are poorer foragers throughout winter. Three years of survival data show that juveniles with high numbers of adults to care for them have better prospects of surviving their first year. It is suggested that juveniles must optimize between acquiring sufficient food from begging and devoting sufficient time to learning to forage. Juveniles probably apply a learning rule to maximize fitness when faced with varying numbers of helpers and siblings. I show that a number of avian and mammalian cooperative breeders have unusual causes of delayed breeding. In these species, costs of parental care may constrain independent reproduction when the development of their young is exaggerated. Examples include unusually large litters or body size of young, or a difficult foraging niche causing extra burdens on developmental time budgets.