Prey choice and nestling hunger: an experiment with pied flycatchers,Ficedula hypoleuca

Prey choice variation was studied in a multiple-prey loader, the pied flycatcher, Ficedula hypoleuca, by manipulating the body condition of the adults and the hunger level of the nestlings. Parents with high and low body weight brought back similar prey when they were feeding an experimental brood of five hungry nestlings, but parents with high body weight fed the brood at a higher frequency than those with low body weight. Parents with high body weight took more small prey when they were feeding five hungry nestlings than when they were feeding two well-fed nestlings. The latter result is consistent with a recent model of central place foraging, which takes into account the costs of staying away from the nest. Alternatively, the parents may have changed the currency for energy maximization, and hence the criteria for prey choice; e.g. a shift from net to gross energy maximization would imply a less selective prey choice.