The degree of reproductive synchrony between neighboring females was examined within a natural population of meadow voles, Microtus pennsylvanicus. Females of this species are territorial, with oscillations in home range size dependent on lactational state. Home range oscillations were observed for 57 females who were radiotracked during the successful rearing of offspring. These oscillations were more prevalent at high population densities. Females with overlapping home ranges exhibited oscillations which were asynchronous to each other. Asynchronous reproduction between adjacent territorial females would increase saturation density of the population and interruption of this reproductive timing would disrupt population social structure.