The role of complex vegetation structures in determining hawking bat activity in temperate forests

Forests constitute one of the most important feeding and foraging habitats for bats. Because bat populations are declining, most likely due to habitat loss or fragmentation, it is imperative to understand the issues concerned with timber exploitation on bat conservation. We investigated the foraging activity of edge- and open-space foragers in relation to stand and vegetation structure, characteristics that are commonly affected by forestry. Acoustic surveys, culminating to 713 point count sites were undertaken covering 46 different forest massifs across mainland France over 6 years. We used generalized linear mixed models to analyse the activity of ten species: 6 edge-habitat and 4 open-habitat foragers. Pipistrellus pipistrellus was the most detected edge-habitat forager, while Nyctalus leisleri was the most recorded of the open-habitat foragers. Eptesicus serotinus and P. pipistrellus responded positively to heterogeneous vertical vegetation volume. In addition, P. kuhlii and P. nathusii responded negatively to tree basal area. Barbastella barbastellus, Hypsugo savii, and P. nathusii were associated with either ground deadwood and/or logging tracks and minor-traffic roads, confirming the importance of edge space. Finally, B. barbastellus, E. serotinus, and P. nathusii were positively linked to the presence of tree microhabitats. This study demonstrates that bat use in forests is complex and multifaceted. Maintaining ground deadwood and heterogeneity of vegetation, at the forest plot scale, should ensure the ecological functioning of exploited forest systems and the conservation of edge- and open-habitat foraging bats.