High frequency of polyandry in a lek mating system

The adaptive significance of polyandry by female birds in the absence of direct benefits remains unclear. We determined the frequencies of polyandrous mating and multiple paternity in the ruff, a lekking shorebird with a genetic dimorphism in male mating behavior. More than half of female ruffs mate with, and have clutches fertilized by, more than one male. Individual females mate with males of both behavioral morphs more often than expected. Polyandrous mating was more likely following copulation interference, but interference was uncommon. The multiple paternity rate of ruffs is the highest known for avian lekking species and for shorebirds. The general hypothesis that pair-bond constraints are the major selective factor favoring multiple mating in birds does not predict our findings. Active genetic diversification, which has been widely dismissed as a functional explanation for polyandrous mating in birds, may apply with respect to the behavioral polymorphism in ruffs because of a Mendelian genetic basis for male behavioral morph determination and aspects of male–male cooperation and female choice. However, rates of multiple paternity in other species of lekking birds are higher than generally realized, and the potential benefits of diversification in general deserve further consideration.