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 broods that were closer to their own failed nesting attempts and that were already being cared for by other helpers. Both effects likely reflect the limited choice available to helpers: although individuals breed close to relatives within kin neighbourhoods, a high rate of nest predation constrains helpers’ choice of broods. In other species where cooperatively-breeding groups form after natal dispersal, a greater range of options may be available and here more detailed analysis of group formation will be helpful for determining the decision rules that underpin partner choice and permit stable cooperation in the face of alternative options.

These data are a subset of a larger dataset collected over the course of a long-term (27-year) study of the ecology and behaviour of long-tailed tits (Aegithalos caudatus).