Helping others to obtain benefits, even at a cost to oneself, poses an evolutionary puzzle [1]. While kin selection explains such "selfless" acts among relatives, only reciprocity (paying back received favors) entails fitness benefits for unrelated individuals [2]. 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 [3]. 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.

中文翻译：

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鹦鹉自愿互相帮助获得食物奖励。

帮助他人即使从中付出代价也要获得利益，这是一个进化难题[1]。虽然亲属选择可以解释亲属之间的这种“无私”行为，但只有互惠（偿还所收到的恩惠）才能为无亲属的个人提供健身福利[2]。迄今为止，在少数哺乳动物但没有禽类的动物中报道了亲社会帮助（为实现基于行动的目标提供自愿援助）和互惠性的实验证据[3]。为了深入了解这些行为的进化起源，需要研究非哺乳动物物种的社会亲和力和互惠能力。我们在涉及“令牌转移”的工具帮助范式中测试了两种鹦鹉物种。在这里，演员可以向他们的邻居提供令牌，可以与实验人员交换食物。为了验证鹦鹉是否理解任务的偶然性，我们系统地改变了伙伴的存在和交换的可能性。我们发现，非洲灰鹦鹉会自动并自发地将令牌转移给特定的合作伙伴，而在控制条件下发生的转移则少得多。迁移受双联隶属关系强度的影响，部分受接听者注意力吸引行为的影响。此外，一旦角色互换，小鸟就会获得帮助。相比之下，蓝头金刚鹦鹉几乎没有转移任何令牌。社会容忍度方面的物种差异可能解释了这种差异。这些发现表明，基于亲社会态度的工具性帮助，