The price of associating with breeders in the cooperatively breeding chestnut-crowned babbler: foraging constraints, survival and sociality

Understanding the costs of living with breeders might offer new insights into the factors that counter evolutionary transitions from selfish individuals to cooperative societies. While selection on early dispersal is well-understood, it is less clear whether costs are also associated with remaining with family members during subsequent breeding; a pre-requisite to the evolution of kin-based cooperation. We propose and test the hypothesis that living in groups containing breeders is costly and that such costs are exacerbated by increasing group size. For example, in group-living central-place foragers, group members might suffer from resource depletion when foraging in a restricted area during breeding and significant costs of repeatedly travelling between foraging patches and the site of offspring. Using the cooperatively breeding chestnut-crowned babbler (Pomatostomus ruficeps), for which grouping during breeding is obligatory, we show that reproduction is associated with substantially...