Résumé
In cooperative species, helpers often assist close relatives and kin selection is thought to be a major selective force underlying the evolution and maintenance of helping. However, in some cases helpers may be unrelated individuals, which require other types of explanation. Here, we used genetic analyses and observations of feeding behaviour to investigate the relationships between helping at the nest and relatedness in a species where helpers vary in their relatedness to the breeders, the sociable weaver, Philetairus socius. We also investigated the effect of age and breeding group size on feeding behaviour. We found no overall increase of feeding rate with relatedness. Instead, the relationship between helpers' feeding rate and relatedness changed with age. Yearling helpers, which were typically the offspring of one or both parents, did not feed significantly more often when more related to the nestlings or the breeding male or female but did bring larger prey when more related to the nestlings or breeding female. For adult helpers, contrary to the expectations of the kin selection hypothesis, the feeding rate and the size of the prey brought was negatively linked to their relatedness to the nestlings and the breeding female. These results suggest that the reasons for helping in this population change with age. Indirect benefits seem important for yearling helpers while direct benefits may influence the evolution and maintenance of helping behaviour in adult helpers.