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

Jennifer Morinay, Ben J Hatchwell

Species-specific and comparative studies have identified multiple ecological and demographic factors promoting the evolution of helping in cooperative breeding systems. However, analyses typically employ univariate analyses, the relative importance of different factors remaining unknown. Moreover, the potential for factors to operate at different spatial scales is virtually unexplored. We aimed to investigate multiple ecological and demographic drivers of sex-specific helping decisions in the long-tailed tit Aegithalos caudatus, a cooperatively breeding species in which failed breeders may redirect their care to raise another pair’s brood. We investigated the influence of breeding density, availability of relatives, predation pressure on nests and timing of breeding on 1,580 helping decisions by males and females collected over 26 years, examining the spatial scale at which each driver operated. In univariate analyses, decisions to help were positively associated with local breeding density (males), presence of relatives (both sexes) and time of breeding (males), but negatively associated with predation pressure (both sexes). Thus, the decisions made by males and females were driven by different combinations of drivers. Moreover, the spatial scale at which each driver was influential varied from local (100m) to global (750m and beyond) in population terms. In a multivariate analysis, the relative contribution of each driver to helping decisions was approximately equal. In conclusion, our results highlight the importance of considering the interplay of multiple ecological and demographic factors in driving cooperative decisions, and demonstrate that the influence of each driver may differ according to sex and the spatial scale investigated.