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The study was carried out in central and north-eastern Poland in order to assess bat occurrence in small winter roosts located in house-cellars, in relation to the share of the surrounding landscape taken by forest cover and the distance separating the different sites from forests of at least 1 km². Data from single checks in 2243 cellars in 1990–2007 revealed a positive relationship (R² = 0.33, P <0.001) between the percentage of cellars occupied by bats and the forest cover (range: 2–58%) in sections of surrounding landscape covering between 30 and 220 km². Forest cover in the landscape within 1 km of the cellar appeared to have a slight influence on the number of species and species diversity (Simpson’s index; respectively R² = 0.14, P = 0.006 and R² = 0.13, P = 0.011). Both number of species and species diversity were progressively lower with increasing distance from the nearest forest covering an area of 1 km² or more (for both R² = 0.15, P = 0.005). Myotis nattereri (Kuhl, 1817) and Barbastella barbastellus (Schreber, 1774) were significantly more likely to colonise the cellars surrounded by landscape with a higher level of forest cover (P = 0.001 and 0.031), while M. nattereri was also more likely to be found in those at shorter distances from forests (P = 0.005). No such relationships were reported for either Plecotus auritus (Linnaeus, 1758) or Myotis daubentonii (Kuhl, 1817).
Numbers of wintering Natterer’s bats Myotis nattereri (Kuhl, 1817) and Daubenton’s bats M. daubentonii (Kuhl, 1817) were monitored at seven study sites (three single large hibernacula and four groups of roosts) in central Poland. The longest monitoring period was 1987–2009, the shortest – 1999–2009. The aim of the study was to find out if the numbers of the two species are stable, or if any trends could be detected. For most of the study period, bats were counted twice during each hibernation season: in autumn (November/December) and in winter (January/February). The numbers of Natterer’s bats show a strong increase all over the study area – a trend similar to that reported earlier from other parts of the country. Daubenton’s bats, on the other hand, declined in the hibernacula located in the north-eastern part of the study area, while in those located in the south-western part their numbers were stable or even slightly increased. A decrease in the numbers of Daubenton’s bats is in contrast with reports from other hibernacula in Poland and elsewhere in Europe, where the species increases in numbers. The changes in the numbers of both studied species could be explained by neither changes in the hibernacula nor weather conditions during the study period, so our results probably reflect changes in the numbers of local populations.
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