Barn owl (Tyto alba) siblings vocally negotiate resources

Current theory proposes that nestlings beg to signal hunger level to parent s honestly, or that siblings compete by escalating begging to attract the a ttention of parents. Although begging is assumed to be directed at parents, barn owl (Tyto alba) nestlings vocalize in the presence but also in the ab sence of the parents. Applying the theory of asymmetrical contests we exper imentally tested three predictions of the novel hypothesis that in the abse nce of the parents siblings vocally settle contests over prey items to be d elivered next by a parent. This 'sibling negotiation hypothesis' proposes t hat offspring use each others begging vocalization as a source of informati on about their relative willingness to contest the next prey item delivered . In line with the hypothesis we found that (i) a nestling barn owl refrain s from vocalization when a rival is more hungry, but (ii) escalates once th e rival has been fed by a parent, and (iii) nestlings refrain from and esca late vocalization in experimentally enlarged and reduced broods, respective ly. Thus, when parents are not at the nest a nestling vocally refrains when the value of the next delivered prey item will be higher for its nest-mate s. These findings are the exact opposite of what current models predict for begging calls produced in the presence of the parents.