Indiana bats typically spend the winter in caves or mines. However, a few bats have been found hibernating on a dam in northern Michigan. They need very specific conditions to survive the winter hibernation period, which lasts about 6 months. As the microclimate in a hibernaculum fluctuates throughout the winter, Indiana bats sometimes fly to different areas within the hibernaculum to find optimal conditions, but this does not appear necessary for every hibernaculum. Indiana bats may even switch between nearby hibernacula in search of the most appropriate hibernating conditions. Indiana bats are generally loyal to specific hibernacula or to the general area near hibernacula that they have occupied previously. Critical winter habitats of Indiana bats have been designated by the U.S. Fish and Wildlife Service and include 13 hibernacula distributed across Illinois, Indiana, Kentucky, Missouri, Tennessee, and West Virginia.