CONFIRMATION OF COOPERATIVE POLYANDRY IN THE GALAPAGOS HAWK (BUTEO-GALAPAGOENSIS)

Without genetic tests of parentage, descriptions of mating systems must be considered hypothetical. Here we confirm the existence of cooperative polyandry in the Galapagos hawk (Buteo galapagoensis) using multilocus minisatellite DNA fingerprinting. In this species, breeding groups consist of one adult female and from one to eight males (the modal number of males is two). In polyandrous groups, all males copulate with the female and participate in the provisioning of the young. DNA samples from 66 individual hawks from ten breeding groups on the island of Santiago revealed mixed paternity in most groups. Multiple paternity was detected in five of six groups that produced two chicks in one breeding attempt (year). In addition, different males sired young in consecutive years in five of six groups in which male group membership was constant. Patterns of paternity suggest that reproductive success was randomly distributed among males within groups, with males apparently having equivalent probabilities of siring each young. Analysis of genetic similarity indicates that males within groups were typically not close relatives. These results demonstrate that the mating system of the Galapagos hawk is polyandrous, with relatively egalitarian relations among unrelated males belonging to the same breeding group.