Unrelated helpers neither signal contributions nor suffer retribution in chestnut-crowed babblers

Alloparental care by distant/nonkin that accrue few kin-selected benefits requires direct fitness benefits to evolve. The pay-to-stay hypothesis, under which helpers contribute to alloparental care to avoid being expelled from the group by dominant individuals, offers one such explanation. Here, we investigated 2 key predictions derived from the pay-to-stay hypothesis using the chestnut-crowed babbler, Pomatostomus ruficeps, a cooperatively breeding bird where helping by distant/nonkin is common (18% of nonbreeding helpers). First, we found no indication that distant or nonkin male helpers advertised their contributions toward the primary male breeder. Helpers unrelated to both breeders were unresponsive to provisioning rates of the dominant male, whereas helpers that were related to either the breeding male or to both members of the pair were responsive. In addition, unrelated male helpers did not advertise their contributions to provisioning by disproportionately synchronizing their provisioning events with those of the primary male breeder or by provisioning nestlings immediately after him. Second, no helper, irrespective of its relatedness to the dominant breeders, received aggression when released back into the group following temporary removal for 1-2 days. We therefore find no compelling support for the hypothesis that pay-to-stay mechanisms account for the cooperative behavior of unrelated males in chestnut-crowned babblers.