Characteristics of winter roosts of bat species in southern Finland

We determined the characteristics of hibernation locations of the northern bat Eptesicus nilssonii, Brandt's bat Myotis brandtii/whiskered bat Myotis mystacinus, Daubenton's bat Myotis daubentonii and brown long-eared bat Plecotus auritus in southern Finland during the winters 2002–2003 to 2005–2006. All of the species had species-specific hibernation conditions. E. nilssonii hibernated in colder (2.0±0.1°C) and drier (78.0±0.6%) locations than the other species. A total of 20% of E. nilssonii hibernated in temperatures that were below 0°C. M. daubentonii selected warmer (4.4±0.1°C) and more humid (88.2±0.5%) locations than the other species. M. brandtii/mystacinus usually hibernated clustered up to 13 individuals, while the other three species preferred to hibernate solitary. Most of M. brandtii/mystacinus, E. nilssonii and P. auritus hibernated in crevices, while most of M. daubentonii preferred to hibernate on the wall/ceiling. The number of bats found in each hibernaculum was relatively small. The largest number of bats counted was 121, of which 109 were M. daubentonii. M. brandtii/mystacinus tended to gather in larger numbers (up to 83) than E. nilssonii and P. auritus, which were represented by few individuals (up to 16 and 7, respectively) at each hibernaculum. Knowledge of the bat hibernation requirements is needed, e.g., when manipulating conditions to be more suitable for bat hibernation in subterranean sites.