Helpers but not breeders adjust provisioning effort to year-round territory resource availability in carrion crows

Abstract

In most cooperatively breeding bird species, individuals live year round in all-purpose territories that may vary greatly in quality. Territory resource availability is likely to influence the investment in provisioning the brood, and different group members may respond in different ways, according to individual strategies of investment in self-maintenance or current reproduction. Although this may be important for understanding division of labour within the group, few studies have investigated how individuals respond to changing conditions ‘at home’. In cooperatively breeding carrion crows, Corvus corone, chick provisioning is costly and both breeders and helpers allocate additional resources to self-maintenance, rather than the current brood, when food availability is temporarily augmented during the breeding season. However, here we show that helpers, but not breeders, increased their chick-feeding rate when territory resources were experimentally enhanced throughout the year. These results indicate a role of year-round territory quality in shaping cooperation at the nest in this species. We suggest that the probabilities of reproducing in the following breeding season, which are higher for breeders than for helpers, modulate the effect of long-term resource abundance on individual provisioning decisions, leading to a higher investment in the current brood by helpers only.