Social living without kin discrimination: experimental evidence from a communally breeding bird

In many cooperative animal societies, individuals can recognize their relatives and preferentially direct helping behaviors towards them. However, the ability to learn kin recognition cues may be constrained in societies with low relatedness, since group membership alone is not a reliable proxy for kinship. Here, we examine kin discrimination in the greater ani (Crotophaga major), a communally nesting bird in which several unrelated males and females reproduce in a single, shared nest and provide parental care to the mixed clutch of young. Each adult, therefore, is closely related to some nestlings in the clutch and unrelated to others. Food is limited and starvation is a significant cause of nestling mortality, suggesting that adults should increase their fitness by preferentially feeding their own offspring in the mixed clutch. To test this hypothesis, we cross-fostered broods of nestlings between pairs of nests, such that none of the nestlings in the manipulated nests were related to any of the adults feeding them. We found no evidence that adult greater anis discriminate between their own and unrelated nestlings: adults at cross-fostered groups fed nestlings at the same rates as adults at control (sham-manipulated) nests, and rates of nestling starvation were equal at cross-fostered and control nests. These results suggest that adult greater anis do not recognize their own nestlings, and they are consistent with the hypothesis that genetically encoded markers for kin recognition are rare in birds.