A home for the many? Beaver lodges as hotspots for bird and mammal diversity.

Diversity loss is a growing global concern. Keystone species and ecosystem engineers play a crucial role in maintaining and enhancing diversity. The Eurasian beaver (Castor fiber) is one such species, impacting the landscape through activities such as felling trees, digging tunnels, building dams, and constructing lodges. Numerous studies have shown that beavers increase diversity especially related to their dams. However, the relationship between beaver lodges and diversity is rarely studied. Therefore, we have mapped the diversity of birds and mammals at active beaver lodges in south-eastern Norway. The study was carried out in three large rivers without beaver dams. We installed wildlife cameras at 18 active beaver lodges in the autumn and 17 in the spring, matched with an equal number of paired control sites across the river. Beaver lodges had higher abundance, species richness and Shannon Diversity Index of animals (birds and mammals) than control sites in autumn, but the differences were less pronounced in spring. We found that six species were especially attracted to the beaver lodges. Our results support the concept of beaver lodges as local diversity hotspots for animals particularly in autumn, most likely due to the availability of resources such as food, shelter and warm microclimates on the lodge. Our findings also illustrate the role of beavers as ecosystem engineers beyond the impacts of dam construction. This knowledge may help to increase the diversity of both birds and mammals in habitats across the northern hemisphere.