Benefits of begging for yellow-headed blackbird nestlings.

For begging to benefit chicks, parents must respond to increased begging by bringing more food. To investigate whether parents change their provisioning in response to begging levels, I enhanced the begging levels of broods of yellow-headed blackbirds, Xanthocephalus xanthocephalus, using recorded vocalizations. In a short-term experiment, females and males doubled their visits to broods without reducing their load sizes during 2 h of playback. Nestlings gained more mass during the playback period than during a 2-h control period. In a long-term experiment, nestlings gained more mass in nests from which begging calls were broadcast over a 5-day period than nestlings in nests without playback. Copyright 1998 The Association for the Study of Animal Behaviour.