Begging tactics of nestling yellow-headed blackbirds, Xanthocephalus xanthocephalus, in relation to need

Theoretical models suggest that begging may signal nestling need. 'Need' for food can be either short term (hunger) or long term (amount of food required to hedge, which may be influenced by body condition, sex or rank in the brood). Studies have shown that begging carries information about short-term need, but have not provided evidence that begging can carry information about long-term need. Signals of long-term need may be unstable if larger chicks out-compete their needler siblings. This study investigated whether nestling yellow-headed blackbirds beg according to long-term need in field and laboratory experiments. In yellow-headed blackbirds, smaller nestlings, males and chicks in poor condition should value food more highly. When hunger level was controlled, males and chicks in poor condition begged more than females and chicks in good condition, respectively, and chicks begged more when paired with larger rather than smaller nestmates. In yellow-headed blackbirds, even when nestmates have unequal competitive abilities, begging can carry information about nestling long-term need for food. (C) 1996 The Association for the Study of Animal Behaviour