Forest islands in farmland provide vital roost trees year-round for giant and common noctule bats: Management implications

Forest islands in agricultural landscapes may be vital for biodiversity conservation, providing habitats for a variety of species, including bats. Our study focused on a forest island in NE Italy, where we observed mixed-species groups of giant (Nyctalus lasiopterus) and common (Nyctalus noctula) noctules roosting at the site. The giant noctule is highly endangered across Europe, and our findings shed light on its roosting preferences, providing key information to inform sustainable forestry practices that take this species into account. Using photographic methods and direct observation, we established that both common and giant noctules occur year-round in the forest island, with giant noctules giving birth, hibernating, and probably mating there. The bats preferred aspen trees and trees rich in cavities with high canopy closure and reduced sun exposure found in the forest interior, while they avoided forest edges. Rot cavities were frequently used, but we found no selection for cavity type, entrance height, or aspect. Despite the common belief that forestry activities in winter have negligible impact on bats, the felling of roost trees during this time can result in significant bat mortality since both common and giant noctules use these trees for hibernation. The number of cavities in a tree is a reliable predictor of a noctule roost, so it is advisable, year-round, to protect trees with cavities. Sustainable forestry practices should incorporate measures to provide roosting opportunities for bats, especially noctules. Our study only pertains to a single forest fragment. While our findings are novel and informative and highlight the conservation value of the forest island we studied, at this stage, they should not be generalized to all forest islands. We, therefore, encourage further large-scale studies to determine whether other forest islands are used similarly and to assess the broad-scale conservation implications of our work, particularly for threatened species such as the giant noctule.