Communal breeding in green woodhoopoes as a case for reciprocity

Abstract

RECIPROCITY¹, or reciprocal altruism², and kin selection³ are concepts basic to sociobiology. Although both theories have been widely accepted⁴, little critical evidence exists for either^5,6. Communal, or cooperatively breeding, birds are important organisms for testing these theories because nonbreeding helpers regularly provide aid to nestlings, such as food and protection. Helpers are often related to the nestlings they aid, frequently being older siblings^7,8, leading some authors to conclude that kin selection is the evolutionary basis for the apparent altruism seen in cooperative breeders^8,9. However, the possible influence of other, individual strategies has not been completely separated from kin selection for any communal bird; this would require elimination of kinship ties as a variable⁵. Aid by a helper to an unrelated young bird must either be considered an ‘accident’ or it suggests that factors other than, or in addition to, kin selection might be the evolutionary bases for helping behaviour, at least in that particular species. Here we report information on a tropical, communal bird, the green wood-hoopoe (Phoeniculus purpureus), that suggests helping is a strategy for personal gain¹⁰.