A comparison of the hibernation patterns of seven bat species in Estonia
We investigated whether bat species with a more northerly border of distribution would hibernate in colder conditions and use fewer crevices and clusters for hibernation than species with a more southerly northern border of distribution. To this end, we measured the temperature and water vapour pressure (as an absolute measure of humidity) of hibernation locations, crevice occupation and clustering among seven sedentary bat species in Estonia. The pond bat (Myotis dasycneme), Daubenton’s bat (Myotis daubentonii) and Brandt’s bat/whiskered bat (Myotis brandtii/mystacinus) hibernated at higher temperatures and humidity whereas the northern bat (Eptesicus nilssonii), the brown long-eared bat (Plecotus auritus) and Natterer’s bat (Myotis nattereri) hibernated at lower temperatures and humidity. The majority of northern bats, Daubenton’s bats, brown long-eared bats and Natterer’s bats hibernated solitarily whereas Brandt’s bats/whiskered bats and pond bats tended to hibernate in clusters. All Natterer’s bats hibernated in crevices whereas the six other species hibernated both in crevices and hanging freely on the wall/ceiling. Northern bats inhabiting regions further north than the other six species typically hibernated alone on the wall/ceiling, whereas pond bats, whose distribution border lies further south than those of the other six species, hibernated in warmer and more humid conditions, and often in clusters. However, Natterer’s bats inhabiting regions further north than those of pond bats, but whose northern border of distribution lies further south than those of the remaining five species preferred lower temperatures and humidity than the other five species. The results suggest that during the hibernation season in the north of Europe, pond bats focus on saving energy during arousals and subsequent periods of euthermy, whereas Natterer’s bats focus on saving energy during hibernation.