1 Clutton-Brock T. Cooperation between non-kin in animal societies.

2 Taborsky M.

Frommen J.G.

Riehl C. Correlated pay-offs are key to cooperation.

3 Massen J.J.M.

Lambert M.

Schiestl M.

Bugnyar T. Subadult ravens generally don’t transfer valuable tokens to conspecifics when there is nothing to gain for themselves.

Helping others to obtain benefits, even at a cost to oneself, poses an evolutionary puzzle []. While kin selection explains such “selfless” acts among relatives, only reciprocity (paying back received favors) entails fitness benefits for unrelated individuals []. So far, experimental evidence for both prosocial helping (providing voluntary assistance for achieving an action-based goal) and reciprocity has been reported in a few mammals but no avian species []. In order to gain insights into the evolutionary origins of these behaviors, the capacity of non-mammalian species for prosociality and for reciprocity needs to be investigated. We tested two parrot species in an instrumental-helping paradigm involving “token transfer.” Here, actors could provide tokens to their neighbor, who could exchange them with an experimenter for food. To verify whether the parrots understood the task’s contingencies, we systematically varied the presence of a partner and the possibility for exchange. We found that African grey parrots voluntarily and spontaneously transferred tokens to conspecific partners, whereas significantly fewer transfers occurred in the control conditions. Transfers were affected by the strength of the dyads’ affiliation and partially by the receivers’ attention-getting behaviors. Furthermore, the birds reciprocated the help once the roles were reversed. Blue-headed macaws, in contrast, transferred hardly any tokens. Species differences in social tolerance might explain this discrepancy. These findings show that instrumental helping based on a prosocial attitude, accompanied but potentially not sustained by reciprocity, is present in parrots, suggesting that this capacity evolved convergently in this avian group and mammals.