Tree- and Stand-Scale Roost Selection and Partitioning by Bats Barbastella barbastellus Schreber, 1774 and Pipistrellus pygmaeus Leach, 1825 in a European Lowland Forest

Our research focused on the roost preferences of two bat species in a forest environment. Throughout the Anthropocene, people have heavily altered the landscape. Forested habitation has declined, with remaining forests becoming fragmented and often deprived of old trees that provide shelter opportunities for bats. TReMs (tree-related microhabitats) are essential for forest-dwelling bat species as they provide an opportunity to roost and shelter. Following an infestation of Ips typographus L., the Białowieża Forest is saturated with dead spruce trees. We investigated roost selection in two forest-dwelling species, Barbastella barbastellus and Pipistrellus pygmaeus. To examine similarities or differences in roost selection between species, we radio-tracked 24 barbastelles and 13 soprano pipistrelles over three breeding seasons. We located a total of 48 barbastelle roosts and 15 pipistrelle roosts, together with the characteristics of the surroundings. We found that barbastelles select roosts almost exclusively in dead spruce trees (43/48), while pipistrelles selected roosts predominantly in live (n = 8) and dead (n = 5) broadleaved trees. Our results show that both bat species have clear differences in roost tree preference. In our study area, with an abundance of exfoliating bark, barbastelles showed a preference for roosting under flaking bark despite the availability of crevices within broadleaved trees. Our findings provide useful insight into forestry practices, highlighting the importance of standing dead trees.