An understanding of the spatial organization of endangered species is particularly important in the light of habitat degradation and fragmentation. In bats, little is known about whether and how space is organized between individuals of the same species. We investigated space use in four maternity colonies of Bechstein's bats. We were able to show for the first time that spatial organization reflects the social organization in Bechstein's bats. We found a strong segregation of foraging ranges within colonies, and an even stronger segregation between different colonies. Our results suggest that the spatial organization of females is determined by foraging efficiency. It is crucial to determine the essential characteristics of both feeding and roosting core areas. We provide a precise prediction of effective population size and space requirements. Thereby, implications for the protection of Bechstein's bats and assumedly also for other bat species with a similar social and spatial organization can be deduced.