Reciprocal Altruism in Birds: A Critical Review

Many proposed examples of reciprocal altruism are either misidentified or involve questionable assumptions concerning the costs and benefits accruing to the interactors. Waltz’s (Am. Nat. 118: 58%592,198l) definition of reciprocal altruism as an interaction in which “one individual aids another in anticipation that the recipient will return the favor benefiting the actor in the future” is not sufftciently restrictive: there must also be a direct fitness cost to the individual performing the original beneficent act that is less than the fitness benefit received when the act is reciprocated (again at a cost) by the second individual. Several recurring problems in identifying potential examples of reciprocal altruism are discussed, including the assumption that restraint is an act of altruism and the misclassification of “generational mutualisms,” in which individuals helping to raise young are “repaid” one generation later by the offspring they assisted in raising. No definite case of reciprocal altruism is currently known in birds, but examples in which this phenomenon may be involved include helping behavior in a few cooperative breeders and communal feeding in several taxa including gulls, jays, and juncos.