A clean nest is important for successful breeding in most bird species, because parasites and bacterial infestations can reduce nestling survival. In cooperatively breeding species, caregivers may either share nest and chick sanitation activities or specialize in different tasks related to chick care, such as food provisioning, nest sanitation, and territory and nest defense. We used video-recorded observations at nests of cooperatively breeding Carrion Crows (Corvus corone corone) to describe sanitation behaviors and analyze the factors that influenced individuals' contributions to each particular task. We then combined data on sanitation and chick provisioning to investigate whether labor was divided within the group and whether individuals specialized in any particular task. Finally, we asked whether nest sanitation was flexible and responded to current conditions—in particular, food availability in the territory. In a controlled experiment, we supplemented 11 territories with food during the breeding season, reducing the costs of caring for the young. We found that in the cooperative groups, breeding females carried out the vast majority of sanitation tasks (i.e. nest and chick cleaning and fluffing of the nest's inner layer), whereas other group members contributed relatively little to these activities, with the exception of fecal-sac removal, which was done by any adult present at the nest during excretion. We suggest that the greater contribution of females occured because a clean nest is beneficial not only for the brood, but also for breeding females, which perform all incubation and brooding and are therefore more exposed to nest parasites. Nest sanitation also proved to be condition dependent and decreased in experimentally food-supplemented territories, where birds may have been in healthier condition and therefore less likely to transmit parasites to the brood. We suggest that extending the study of division of labor to different tasks other than chick provisioning is important to widen our understanding of the evolution and maintenance of cooperative breeding.
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Vol. 132 • No. 3