Rent a room in the Alps: winter den site preferences of native and reintroduced brown bears

The management and conservation of large carnivores is a challenging task because of their great spatial requirements and the hostility encountered in certain socio-political contexts. Particular fundamental requirements concern those species, such as brown bears ( Ursus arctos ), that need to hibernate in order to optimise the balance between energy acquisition and energy expenditure during winter. Thus, a thorough knowledge of bears’ winter behaviour is critical to ensure a proper management and protection of this species. The aim of the present study was to assess the location and features of the hibernation sites of a bear population reintroduced in the Central-Eastern Alps (Italy). Sixty-five bear dens and 85 unused caves were located and described. Bears were found to select natural rock caves ( N = 64) located in medium-high slope at an altitude between 520 and 1950 m a.s.l.. Caves usually were in poorly accessible areas with low human disturbance. In particular, the comparison between used and unused caves showed that three main factors drove the selection of hibernation sites by brown bear: (i) small entrance and suitable length of the cave, (ii) their location in wooded areas and (iii) high level of solar radiation and favourable internal micro-climatic conditions. Caves selected by bears showed significantly higher monthly temperatures from October to March (especially in October and November, when bears typically search for a suitable hibernation site) than caves that were not used despite their similar structural characteristics. No differences in cave selection were found between native and reintroduced bears, suggesting that cave selection was driven by objective cave characteristics, rather than by population-specific traditions. Lastly, among different age and sex classes, pregnant females were found to select caves with a greater total length, located in more hidden areas and with more solar radiation around the entrance. Brown bear cave selection seems therefore to be driven mainly by measures, exterior habitat features and inner temperature.