The number of strong social bonds is linked to survival in a cooperative bird

Gabriel Munar-Delgado, Matthieu Paquet, Babette Fourie, Franck Theron, André Ferreira, Claire Doutrelant, Rita Covas

Recent evidence from large mammals, including humans, shows that the quality of social associations beyond general group size can positively influence health and survival. However, whether individuals in other taxa consistently differ in sociality in ways that affect fitness and thus provide a basis for selection remains largely unexplored. In this study, we examined how individual sociality relates to survival probabilities in a population of sociable weavers (Philetairus socius), a highly cooperative bird. We combined social network analysis with multi-state capture–recapture models to quantify the number of strong social bonds each individual had and to estimate survival probabilities. We found that sociality was positively associated with survival: individuals with medium and high sociality showed higher survival probabilities than those with low sociality. Additionally, individuals were more likely to remain in the same sociality category across years than to shift to another, and when transitions occurred, they followed a gradual pattern, with adjacent shifts more common than abrupt changes, supporting the idea of stable individual differences in sociality. These findings support a link between sociality and individual fitness, and suggest that stable social traits may provide a basis for evolutionary change.