Multiple benefits drive helping behavior in a cooperatively breeding bird: an integrated analysis

Several hypotheses exist to explain the seemingly altruistic helping behavior of cooperative breeders, although the general utility of these hypotheses remains unclear. While the potential importance of inclusive fitness benefits (kin selection) is traditionally widely appreciated, it is increasingly recognized that direct benefits may be more important than assumed. We use an integrative two-step framework to assess support for current hypotheses in purple-crowned fairy-wrens, a species where subordinates vary in relatedness to breeders and helping increases productivity. After establishing that assumptions of pay-to-stay and social prestige hypotheses (predicting that helping functions as 'paying rent' to stay on the territory or as a signal of individual quality, respectively) were not met, and that parentage by subordinates is extremely rare, we tested whether subordinates adjusted nestling feeding rates following the predictions of the kin selection and group augmentation hypothes...