Patterns of recruitment, relatedness and cooperative breeding in two populations of long-tailed tits

Cooperative breeding has evolved primarily in species in which individuals are organized into family groups, and kin selection is considered to be a major force in the evolution of helping behaviour. Family groups are generally thought to form through delayed or limited dispersal, but dispersal patterns vary considerably both between species and in different populations of the same species, and the relationship between dispersal, kinship and cooperation is poorly understood. In this study, we combined long-term observational and genetic data to compare the patterns of demography, kinship and helping in two populations of long-tailed tits, Aegithalos caudatus, a species that exhibits kin-biased helping by failed breeders but not delayed dispersal. Both populations had the same annual breeding success, but philopatric recruitment rates were significantly higher in one population, especially for females. This led to a correspondingly higher proportion of individuals having at least one close relative in that population. Surprisingly, however, there was no difference in the pattern of helping behaviour between the two populations in terms of helper prevalence, helper sex or the relatedness between helpers and the breeders they assisted. We discuss possible explanations and highlight the limitations of population-level analyses for understanding the relationship between demography and cooperation.