Information on the roost requirements of small, temperate-zone hibernating bats, which can spend up to 8 months in hibernation, is crucial to their conservation. We studied male big brown bats (Eptesicus fuscus) in southeastern Alberta, Canada, to investigate the physical and microclimate characteristics of hibernacula used by this species in a prairie river valley (Dinosaur Provincial Park, DPP). We monitored roosting behavior and movement, and also compared microclimate conditions (temperature and humidity) within these crevice hibernacula to those of random crevices within the study area, and to conditions inside 4 known cave hibernacula in central and northern Canada. Our results show that male E. fuscus in DPP use rock-crevice hibernacula with less variable temperatures than ambient and random crevice temperatures, with evidence of winter roost fidelity within and between years. Bats used only 3 hibernacula and, although mid-winter flight is common in our study area, there was little movement by bats between hibernacula. Rock-crevice hibernacula were warmer and more thermally stable than other available crevices in DPP, and drier but not necessarily colder than known cave hibernacula elsewhere. Our study is the first to examine crevice roost selection by bats during winter, and suggests that specific hibernacula are important for individual bats, despite the fact that numerous crevices are available.