Food, friends or family: What drives delayed dispersal in group-living animals?

In Focus: Nelson-Flower, M. A., Wiley, E. M., Flower, T. P., & Ridley, A. R. (2018). Individual dispersal delays in a cooperative breeder: Ecological constraints, the benefits of philopatry and the social queue for dominance. Journal of Animal Ecology, 87, 1227-1238. Explaining why sexually mature individuals in social species delay dispersal and independent breeding is a major unresolved evolutionary puzzle. In this issue, Nelson-Flower, Wiley, Flower, and Ridley () use a comprehensive dataset to study delayed dispersal in cooperatively breeding southern pied babblers. They test traditional hypotheses relating to ecological constraints inhibiting individuals to reproduce independently and benefits of philopatry motivating individuals to stay. Importantly, they also test the recently developed dual-benefits hypothesis, which explicitly takes into account that groups (even those containing unrelated individuals) may form because of opportunities for collective actions that increase the fitness of the whole group. While they show that male dispersal decisions are mainly determined by ecological constraints and the presence of related individuals, female dispersal cannot be explained this way. Instead, females from smaller groups were more likely to disperse than females from larger groups. In combination with evidence that smaller groups are more likely to accept (unrelated) subordinates and clear (collective-action) benefits of living in a larger group in this species, the study provides empirical evidence that considering social context and collective-action benefits as part of a comprehensive predictive framework is important to explain the evolutionary stability of delayed dispersal, group formation and, ultimately, cooperative breeding