Ecological, demographic and social factors shape helping decisions at different spatial scales in a facultative cooperative breeder

Jennifer Morinay, Ben J Hatchwell

The fitness consequences of cooperative breeding are increasingly well understood, but the ecological and demographic factors driving helping remain contentious. Comparative and single-species studies have identified factors that promote the evolution of helping, but analyses typically test single hypotheses so the relative importance of different factors, and the spatial scale of their influence, remain unknown. Our aim was to investigate multiple social and demographic drivers of helping decisions using 27 years of data from a facultative cooperative breeder, the long-tailed tit Aegithalos caudatus. We analysed the decisions to help or not by 1,338 failed breeders to investigate the influence of metrics related to predation pressure, population density, availability of relatives and timing of breeding. We also examined the scale at which these features acted (100-1000m from a failed nest). We found that the availability of nests at a broad spatial scale of 400-500m from the failed nest was higher around those failed breeders that decided to help than those that did not. Specifically, helpers of either sex were surrounded by lower predation pressure, while male helpers were surrounded by more breeding attempts, more active nests, and later nests. However, the most important factor driving helping, and from a very fine spatial scale (100+m), was kinship: future helpers were surrounded by more social first order kin than non-helpers. This effect held for males, but not females, when considering the genetic pedigree. Our findings highlight the interplay of multiple ecological, demographic and social factors, acting at different spatial scales, offering new insights into the drivers of sociality.