Acoustic evidence of bats using rock crevices in winter: A call for more research on winter roosts in North America

The Northern Long-eared Myotis (Myotis septentrionalis) is known to hibernate in mines and caves, often using cracks within these hibernacula as roost sites. We hypothesized that M. septentrionalis might use deep cracks in rock outcrops for hibernation as well. To test this hypothesis, we placed acoustical bat detectors near rock outcrops away from any known mines or caves during winter in Nebraska. We documented calls of M. septentrionalis as well as Perimyotis subflavus and Eptesicus fuscus in December near rock outcrops, which suggests that individuals of all three species were hibernating in rock crevices in winter. Of the 34 sites we monitored, we identified the calls of M. septentrionalis at two sites (about 250 km apart). The dominant rocks at both sites were limestone and shale with large, deep cracks. Given the recent listing of this species as threatened by the US Fish and Wildlife Service, it is important to understand the possible role of cracks in rock outcrops as alternative hibernacula.