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We analysed the distribution and relative abundance of Myotis daubentonii in the lowlands and uplands around the Lahn river near the city of Giessen (Hessen, Central Germany). We assumed a positive correlation between distribution and relative abundance of the trawling M. daubentonii with the amount of water surface in our study area. We further expected an unequal distribution of male and female M. daubentonii especially during the energy demanding pregnancy and lactation period of females. Daubenton's bats were found at 75% of the 64 ponds and lakes we surveyed by standardized nightly spotlight counts. The number of Daubenton's bats correlated positively with the area of the water surface and negatively with the distance to the nursery colonies. Nursery colonies were located with radio-tracking and existed predominantly in the lowlands close to the Lahn river. Mean flight distance between nursery colonies and foraging areas was 2.3 km (mean ± 1.4 km, range: 0.6–6.3 km). Sex ratio was determined at three sites studied in detail from 1992–2003 by mist-netting along regular used flight paths (n = 1,847 caught individuals). The number of female per male M. daubentonii was unequal and differed significantly between the three sites. In the lowland we found one site clearly dominated by females (median = 4.3 females per male, percentages of females 79.3%, n = 169 individuals) and a second site with an almost balanced sex ratio (median = 1.1 females per male, percentages of females 50.3%, n = 939 individuals). At the third site in the uplands males outnumbered females (median = 0.2 females per male, percentages of females 13.5%, n = 739 individuals). The percentages of females remained largely constant from spring to mid summer and changed at the beginning of September. The study revealed that a detailed knowledge of the spatial distribution of gender specific roost sites and key foraging habitats is necessary for the establishment of meaningful monitoring and conservation measures for bats.
Worldwide species density of bats is highest in forests ecosystems. European primeval forests are now reduced to a few small and isolated patches because almost all forests are subject to management. Therefore, knowledge about bats in ancient and near-natural forests in Europe is scarce. In the well-preserved forest stands of the Belovezhskaya Pushcha National Park in Belarus we studied the bat community (1), the presence of maternity colonies and their preference in tree roost selection (2) and parameters of roosts used by forest dwelling bats (3). By mist-netting surveys, we identified 13 bat species and acoustic data suggested the presence of another three species. We detected 15 maternity colonies of seven bat species by radio-tracking reproductive females and 40 tree roosts within the forest. Roosts of Barbastella barbastellus, Pipistrellus pygmaeus and Plecotus auritus were almost exclusively behind the loose tree bark of decaying trees, or within narrow crevices. Myotis nattereri and Nyctalus leisleri showed a preference towards hollows (e.g., woodpecker-made cavities) within oak trees (Quercus robur). Our study shows that all tree-dwelling bat species are highly dependent on natural processes within forests that allow the formation of roost sites. Therefore, we strongly support that the natural aging process of trees, as well as the consequences of natural disturbance (e.g. through weather), should be permitted. This should extend beyond the protected zones of National Parks. In contrast, sanitary cuttings decrease the habitat's suitability for forest-dwelling bats. Finally, our results indicate that the forest complex of Belovezhskaya Pushcha and Białowieża is one of the most important bat areas in Europe.
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