Unexpected allies: reintroduced Eurasian beavers boost bat and hazel dormouse activity in Mediterranean riverine ecosystems

Abstract Ecosystem engineers such as beavers play a key role in shaping their habitats by modifying their physical environment and providing resources for other species. Beavers alter their surroundings by building dams, lodges, and canals, ultimately transforming rivers into dynamic networks of ponds and wetlands that may enhance biodiversity, by benefiting both terrestrial and aquatic wildlife. Rivers and the surrounding vegetation cover such as gallery and riparian forests are key habitats to several taxa, including bats and small mammals, two species-rich and conservation-relevant groups of vertebrates. Riverine ecosystems provide foraging, shelter, and commuting opportunities to these mammals. Recent evidence from northern Europe and North America suggests positive impacts on bat populations by beaver activities, due to the increased abundance of aquatic insects in beaver-modified environments, whereas the effects upon small mammals are less known. We aimed at assessing the effects of recently released beavers upon conservation relevant bats and small mammals in a Mediterranean context by following a bioacoustics monitoring approach. We compared bat and hazel dormouse diversity and activity at sites with and without beaver activity along three rivers in central Italy. Acoustic surveys confirmed higher bat and hazel dormouse activity levels at “beaver” sites with respect to control ones, particularly in areas surrounded by higher forest cover. Beaver sites exhibited a more pronounced positive response in bat activity levels as the surrounding forest cover increased. We also report that acoustically-detected hazel dormouse responded positively to beaver presence. We thus showed that both bats and dormice appeared to benefit from the presence of beavers at the sampled sites. Our study sheds light the ecological importance of beavers in enhancing habitat diversity and promoting biodiversity across aquatic and terrestrial ecosystems, highlighting positive effects upon conservation relevant taxa.