Elder barn owl nestlings flexibly redistribute parental food according to siblings’ need or in return for allopreening

Kin selection and reciprocation of biological services are distinct theories invoked to explain the origin and evolutionary maintenance of altruistic and cooperative behaviours. Although these behaviours are considered as non-mutually exclusive, the cost-to-benefit balance to behave altruistically or to reciprocally cooperate, and the conditions promoting a switch between such different strategies have rarely been tested. Here we examined the association between allofeeding, allopreening and vocal solicitations in wild barn owl (Tyto alba) broods under different food abundance conditions: natural food provisioning, and after an experimental food supplementation. Allofeeding was mainly performed by elder nestlings (hatching is asynchronous) in prime condition, especially when the cost of forgoing a prey was small (when parents allocated more prey to the food donor and after food supplementation). Nestlings preferentially shared food with siblings that emitted very intense calls, thus pot...