Townsend's big-eared bat (Corynorhinus townsendii) is a North American bat that hibernates in caves and mines. These underground habitats also are important roost sites during fall swarming, a period during which bats undergo preparation for hibernation. During swarming bats are very active at night, rousing frequently several times a night to fly within and between roosts. During hibernation nighttime activity is suppressed so that bats rouse and move infrequently. Daytime activity is suppressed during both periods by daily torpor. Both hibernacula and swarming roosts have particular thermal requirements associated with energetic optimization. Swarming roosts tend to have a higher minimum temperature than hibernacula, facilitating efficient arousal from torpor. Both roost types have low maximum temperatures, facilitating conservation of stored body fat resources. We explored and tested preferences of C. townsendii for microclimates in these habitats. Our results confirm that C. townsendii prefers habitats that are thermally constrained such that temperatures and related microclimate variables are optimum for swarming or hibernation activities.