Reproductive self-regulation among large free-roaming mammals is a well-documented but poorly understood phenomenon. Our limited knowledge of the physiological mechanisms which determine reproductive self-regulation in mammalian species is currently derived from studies of rodents and primates. The goal of this study is the identification of primary factors involved with female reproductive self-regulation among large wild ungulates. It is important to recognize that the focus of this work is primarily directed toward the understanding of the differences in reproductive performances among two contrasting herds ofthe North American bison of Yellowstone National Park.
