Context-dependent honest begging in Cory?s shearwaters (Calonectris diomedea): influence of food availability

Abstract

A key question in parent-offspring conflict is if provisioning is controlled primarily by parents or by their offspring, and how this interaction is mediated behaviourally. We recorded the vocalisations of chicks of Cory’s shearwater (Calonectris diomedea) during feeding sessions in a season with abundant food. Cory’s shearwater chicks conveyed information about their body condition through begging, and parents were responsive to the level of solicitation. In order to test experimentally for the effects of saturation on begging, we supplemented chicks’ food. Observational and experimental data both indicated that satiated chicks did not beg, and consequently no feeding occurred. Adults decreased their attendance following the decreased demand of supplemented chicks. We compare the results with data from a poor breeding season. The data suggest that only during the good season was variation in begging large enough to be detected and to serve as a reliable signal to the parents. Our results are in line with the predictions of a recent model indicating that begging signals were most informative to the parents in a context when there was a class of satiated individuals which stand to gain no benefit from the resource (and hence will refrain from signalling).