Parrots Voluntarily Help Each Other to Obtain Food Rewards

Abstract

Helping others to obtain benefits, even at a cost to oneself (altruism), poses an evolutionary puzzle (Clutton-Brock 2009). While kin selection explains such ‘selfless’ acts amongst relatives, only reciprocity (paying back received favours) entails fitness benefits for unrelated individuals (Taborsky et al. 2016). So far, experimental evidence for both altruistic helping and reciprocal altruism has been reported in a few mammals but no avian species (Massen et al. 2015). In order to gain insights into the evolutionary origin of altruistic helping and reciprocity, the capacity for altruism of non-mammalian species needs to be investigated. We tested two parrot species in an instrumental helping paradigm involving ‘token transfer’. Here, actors could provide tokens to their neighbour, 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. Additionally, transfers were affected by the strength of the dyads’ affiliation and partially by the receivers’ attention-getting behaviours. 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 altruistic helping based on a prosocial attitude, accompanied but not necessarily sustained by reciprocity, is present in parrots, suggesting that this capacity evolved convergently in this avian group and mammals.

Keywords: altruism, altruistic helping, prosociality, parrots, reciprocity, social tolerance