Evolution of Polyandry in Birds

Abstract

Polyandry in which one female forms either simultaneous or sequential pair bonds with more than one male is a rare vertebrate mateship system. Prior to 1972 only two cases were known with certainty among birds. All other reports of polyandry were based on inadequate information. Recently, polyandry has been demonstrated in several additional species. Surprisingly, they all belong to the avian order Charadriiformes. Comparisons of the existing polyandrous systems suggest that they can be arranged in a sequence that leads through a series of relatively minor differences from monogamy to simultaneous polyandry. Polyandrous species differ from species with other mateship systems in the following ways: females large, females more aggressive, egg or clutch size reduced, production of multiple clutches. Except in some sequential systems, the small, subordinate males perform all incubation behavior and provide all parental care for the chicks. In the Charadriiformes, polyandry has evolved in conjunction with sex role reversal and with assumption of incubation and parental behavior by the male. It is not clear why role reversal and parental behavior are related. The simplest forms of polyandry are in high-latitude birds, but the best developed forms are found in tropical species.