Age-related provisioning behaviour in the cooperatively breeding acorn woodpecker: testing the skills and the pay-to-stay hypotheses

Abstract

Helpers in cooperatively breeding acorn woodpeckers, Melanerpes formicivorus , gain indirect fitness benefits by provisioning related offspring, but may also gain direct fitness benefits by any of several mechanisms. We tested the ‘skills’ hypothesis, which proposes that provisioning behaviour provides helpers with experience that allows them to be more successful when they breed later in life, and the ‘pay-to-stay’ hypothesis, which proposes that provisioning behaviour by helpers is rewarded by dominant breeders, allowing helpers to remain in their natal group longer, thus reaping nepotistic benefits. We found that young helpers provisioned at relatively low rates, which in most cases increased with age, a necessary requirement of the skills hypothesis. Analyses of birds with known feeding histories, however, revealed that helper males that fed young at higher rates had no greater reproductive success later in life than less helpful helper males, contrary to the skills hypothesis. In accord with pay-to-stay, males that fed more as second-year helpers remained in their natal group as helpers significantly longer and were more likely to inherit than were male broodmates that fed less. An analysis controlling for the time that birds remained in their natal groups, however, failed to indicate that prior feeding history played a significant role in these differences, which are more likely to be a consequence of differences in dispersal behaviour. In acorn woodpeckers, as in other species of cooperative breeders in which helpers are close relatives, the primary benefits of provisioning behaviour are indirect via kin selection rather than direct via either the acquisition of skills or payment of rent.