Foraging site fidelity shapes the spatial organisation of a population of female western barbastelle bats

Information about the spatial distribution of individual foraging habitats, which determines the space required by a population to be viable, is vitally important for the conservation of bats. Detailed knowledge of this kind is crucial for the design of nature reserves and management plans. Recent field studies that examined habitat use and home range distribution of bats largely ignored factors like traditional range use vs. intra- and interspecific competition, which may be responsible for the spatial organisation of a population home range. We investigated the home range sizes and distribution of a maternity colony of the western barbastelle bat via radio telemetry in four consecutive tracking sessions (2004-2007). Based on 19 data sets with a total of 2737 fixes obtained from 12 females, we examined (i) how colony members partition the population home range (home range overlap analysis), and (ii) if individuals tracked over several years exhibit site fidelity. Home range sizes ranged from 125 to 2551 ha (median: 403 ha), with a median number of 2 core areas (range: 1-5 core areas per individual per year). The core area sizes ranged from 5 to 285 ha (median: 67 ha). A home range and core area overlap analysis showed that site fidelity across years seems to be more important for home range distribution than competition among colony members. This allows researchers to combine information from several years to get a deeper insight into the population's spatial requirements.