Data on nest choices by long-tailed tit helpers

Cooperative breeding sometimes occurs when adult breeders form groups following natal dispersal and mating. In such cases, individuals typically face a choice of potential social partner with whom to cooperate. Selection of appropriate social partners is crucial to maximising the fitness payoffs from cooperation, but our understanding of the criteria guiding social partner choice is limited. Here, we analyse helping decisions by long-tailed tits (Aegithalos caudatus), which may redirect their care to assist breeders in raising offspring following the failure of their own breeding attempts. In this species, helpers show a preference for helping relatives at nearby nests, but it is unclear whether other criteria that may affect helper fitness are also important in helping decisions. Contrary to expectations, when controlling for kinship, we found that helping decisions were not sensitive to the size or age of broods available to be helped. Individuals were, however, more likely to help br...