Family-living and cooperative breeding in birds are associated with the number of avian predators.

Cooperative breeding occurs when individuals contribute parental care to offspring that are not their own. Numerous intra- and inter-specific studies have aimed to explain the evolution of this behaviour. Recent comparative work suggests that family living (i.e., when offspring remain with their parents beyond independence) is a critical steppingstone in the evolution of cooperative breeding. Thus, it is key to understand the factors that facilitate the evolution of family living. Within-species studies suggest that protection from predators is a critical function of group living, through both passive benefits such as dilution effects, and active benefits such as prosocial antipredator behaviours in family groups. However, the association between predation risk and the formation and prevalence of family groups and cooperative breeding remains untested globally. Here we use phylogenetic comparative analyses including 2984 bird species to show that family living and cooperative breeding are associated with increased occurrence of avian predators. These cross-species findings lend support to previous suggestions based on intraspecific studies that social benefits of family living, such as protection against predation, could favour the evolution of delayed dispersal and cooperative breeding.