Short-term regulation of food-provisioning rate and effect on prey size in blue tits, Parus caeruleus

I investigated the short-term regulation of parental provisioning rate in blue tits by videotaping the parents at the nest. An additional feeding experiment allowed a comparison between the behaviour of parents rearing their brood under normal and supplemented feeding conditions. Videotaping revealed that parents changed their provisioning rate as an immediate response to the absence of begging by chicks. When chicks did not beg for food, the parents solicited them with a particular call to make them open their beaks. Parents spent significantly longer away from the nest immediately after uttering these feeding calls. Provisioning rate returned to the usual levels as soon as the chicks started begging again, but supplemented parents took less time to do so than controls (i.e. parents not provided with additional food). Changes in provisioning rate had effects on both the type and size of prey brought to the brood. Females often responded to low brood demand by returning to the nest without food. Food-supplemented parents, but not controls, took larger larvae when they stayed away from the nest for longer. This suggests that parents in the supplemented group could use more time to reach good feeding sites or, more probably, increase their prey selectivity. Blue tits continually monitored the begging behaviour of their offspring and responded accordingly by adjusting their feeding rate, with immediate consequences for prey choice. (C) 2001 The Association for the Study of Animal Behaviour.