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

I investigated the short-term regulation of parental provisioning rate in b lue tits by videotaping the parents at the nest. An additional feeding expe riment allowed a comparison between the behaviour of parents rearing their brood under normal and supplemented feeding conditions. Videotaping reveale d 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 par ents solicited them with a particular call to make them open their beaks. P arents spent significantly longer away from the nest immediately after utte ring these feeding calls. Provisioning rate returned to the usual levels as soon as the chicks started begging again, but supplemented parents took le ss time to do so than controls (i.e. parents not provided with additional f ood). 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 cont rols, took larger larvae when they stayed away from the nest for longer. Th is suggests that parents in the supplemented group could use more time to r each good feeding sites or, more probably, increase their prey selectivity. Blue tits continually monitored the begging behaviour of their offspring a nd responded accordingly by adjusting their feeding rate, with immediate co nsequences for prey choice. (C) 2001 The Association for the Study of Anima l Behaviour.