In an environment subjected to rapid anthropogenic alterations, the distribution and abundance of mammalian species often reflect their flexibility in habitat use. The northern bat (Eptesicus nilssonii) is patchily distributed in Germany, where it is classified as a critically endangered species, but is abundant in Scandinavia. To assess its flexibility in habitat use, we radiotracked 10 females and 3 males captured at a maternity roost in Lower Saxony, Germany, during the summers 2002–2003. These bats had access to a variety of habitats including pristine areas (unimproved grassland and forest) and anthropogenically altered habitats (pastures, euthrophic lakes, urban area). The widely overlapping home ranges had a median area of 524 ha. They extended asymmetrically around the maternity roost and reflected a preference for elevations around and below roost level, that is, 365 m elevation. Males traveled up to 70 km per night during exploring flights. E. nilssonii used forest habitats opportunistically before birth of the young and avoided them thereafter, whereas most bats preferred urban habitats and especially streetlamps after births. Intraspecific encounters were more frequent after births, particularly around streetlamps, suggesting an increased intraspecific competition at these sites. Interestingly, females spent 27% but males only 3% of their foraging time hunting with conspecifics. Thus, the species is a habitat generalist for which urban areas provide a supplementary seasonal habitat. However, because such habitats may not always remain profitable, natural habitats of forest and grassland will remain essential to the survival of this bat species in Germany.
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