The mating system of the acorn woodpecker (Melanerpes formicivorus) is among the most complex of any vertebrate: groups consist of up to seven breeding males, as many as three reproductive females and a variable number helpers (offspring of previous years that remain on the natal territory and do not breed). Males compete to mate and females lay their eggs communally in the same nest. Breeders of the same sex are almost always close relatives, either siblings or parents and offspring. Previous work showed that joint-nesting groups of females, unlike males, share parentage equally. This project will determine the factors that influence reproductive sharing in acorn woodpecker societies by combining fieldwork on color-marked birds with modern molecular techniques to identify individuals that successfully produce young within social groups and to quantify their behavior. A primary goal of the project is to understand the fitness consequences of cooperative breeding and to integrate findings into the larger questions of the evolution and ecology of group living in highly social species, including humans.
