Habitat use of Bechstein’s Bat (Myotis bechsteinii) and woodpeckers reveals the importance of old-growth features in European beech forests

Abstract

Old-growth forests provide valuable habitats for bat and woodpecker species worldwide. However, the abundance of old-growth related habitat features is frequently reduced in managed forests. Bechstein’s Bat (Myotis bechsteinii, Kuhl 1817) is globally restricted to old-growth deciduous forests in Europe and therefore a species of high European conservation priority. Since the species prefers woodpecker cavities for roosting, woodpeckers are keystone species for Bechstein’s Bat. We surveyed woodpecker activity and forest structural features within 16 roost sites of Bechsteińs Bat and a random sample from the surrounding managed forest within the centre of the global distribution of Bechsteińs Bat. We found above-average quantity of old-growth related habitat features in the roost sites of Bechstein’s Bat. Five of six occurring woodpecker species revealed significantly higher densities in the roost sites of Bechstein’s Bat, demonstrating a distinct preference of the woodpeckers and the bat in managed forests for old, deciduous stands with high basal areas of large living trees (DBH > 50 cm), bearing deadwood structures and highest available tree cavity densities. Furthermore, when comparing the direct surroundings of roost trees to their wider surroundings (16 ha), cavity density and other old-growth features reached their maxima in the direct surroundings of roost trees (mean = 19.3 cavities ha−1), demonstrating a distinct habitat selection of Bechsteińs Bat for patches with maximum available cavity density on large and fine spatial scale. We found a close relation between the basal area of trees with limb break offs (>20 cm base diameter) and tree cavity density, which leads us to the conclusion that specifically injured but still vital, large trees play a major role for the development and long-term persistence of tree cavities. Finally, our analyses revealed a threshold of 20 (DBH > 50 cm) or 10 (DBH > 70 cm) large deciduous trees bearing deadwood structures per ha to fulfil the minimum habitat requirements of the woodpeckers and Bechstein’s Bat. Obviously, Bechsteińs Bat and the associated woodpeckers explicitly selected forest patches, which most closely resembled primeval forest benchmarks, emphasising the importance of maintaining and developing forest patches, providing the mentioned habitat features within managed forests.