Cooperation in non-family groups as a strategy for reproducing in variable climates

Christina Hansen Wheat, Emily O'Connor, Philip Ashley Downing , Ashleigh S Griffin, Charlie Kinahan Cornwallis 

Cooperative breeding is more common in extreme, variable environments, suggesting it may improve climate resilience. However, whether specific features of these systems evolved in response to particular environmental challenges remains unclear. Using phylogenetic analyses across birds, we test two predictions. First, cooperative breeding with unrelated individuals (‘nonfamily’) is an adaptation to environmental variability because groups form faster than multigenerational family groups. Second, species with larger groups can breed in more extreme environments. We found that nonfamily cooperation is more frequent, and groups are larger, in hot environments with variable precipitation, whereas family cooperation is more frequent in hot but stable environments, with group size varying independently of climate. Compared with closely related pair-breeders, both nonfamily and family cooperative breeders occupy broader, drier climatic niches. These results show that ecological associations with cooperative breeding depend on how groups form, and that nonfamily cooperation may help birds reproduce in areas with unpredictable precipitation.