Tree Cavities used as Bat Roosts in a European Temperate Lowland Sub-Atlantic Forest

The availability of suitable roosts may be the major limiting factor for maternity colonies of bats in forests. Most studies on the use of tree cavities by bats have focused on analysing occupancy by a single species, and not by the entire bat community. To provide guidelines for forest management conducive to sustaining bats in a temperate lowland European forest, we studied the occupancy of tree cavities by bats of all species. In six different habitat types of 4 to 10 ha, all tree cavities were recorded and described according to 47 qualitative and quantitative descriptive variables. Logistic regression analyses were computed to predict the occupancy of cavities by bats, and to identify the most relevant variables for use as bat roosts. With or without potential competitors in the analyses, bats mainly used cavities in healthy main branches, with a large entrance located high above the ground. They did not use peeling bark or cavities on secondary branches, nor cavities covered by spider webs. Despite a large number of potential roosts in the area, bats tend to be selective and the types of roosts were less diverse than described in the literature. Not surprisingly guidelines for forest management aimed at bat conservation include keeping healthy old trees, which provide various types of cavities.