Sharp-tailed Grouse square off in intense battles for territory and breeding rights. Male grouse form mating arenas, or leks, where they congregate to compete for small territories and perform mating displays for visiting females. This crowded arrangement leads to continual fighting as the males strive to outdo each other. In most populations, only a few top males are chosen as suitable mates by the receptive females. In this mating system, called lek polygyny, females leave the lek after mating and rear their young without male assistance. In environments where females and resources are difficult to simultaneously defend, and where a male’s parental care does not contribute to the welfare of offspring, lek polygyny is an effective mating system.