The use of insect-created microhabitats by hibernating bats

Cerambyx cerdo larval corridors are alternative shelters for bats wintering in Central Europe. We found that the number of bats hibernating in dead or dying oak trees correlated with thermal conditions during the week preceding each observation. Bats decide on their hibernation conditions by choosing trees with appropriate parameters and suitable hiding places within the tree. Bats were located in 46 % of monitored trees with circumferences of 240-600 cm. Up to 19 individuals were recorded in a single tree, mainly in corridors oriented to the warmer facing direction, located at heights of 0.6-15.5 m above ground level. Bats were significantly more often recorded in trees with a large number of available corridors. The depth of hiding in the corridor (0-29 cm from the entrance) was significantly greater during the deep hibernation phase, the coldest part of winter, suggesting a reaction to climatic conditions. Current practices in tree management and forestry, cutting down trees inhabited by Cerambyx cerdo which do not consider the presence of bats during winter, may pose a threat to the population of these mammals. Introducing legal regulations requiring such zoological supervision would be an appropriate form of active protection for bats during the observed increase in winter temperatures and the associated greater availability of tree shelters providing suitable hibernation conditions.