In hibernation, the posture of the bat appears to buffer it from environmental extremes. These postures are sensitive to climate change and disturbance. The ears are either erect or coiled. If there is just one bat, its wings are wrapped around its body. If there is a group of bats, the wings of each bat are folded and the ears may or may not be coiled.
Bats lose weight in the winter because their fat reserves are being depleted.
The more frequently they are aroused, the more weight they lose. During the winter months, Plecotus townsendii hibernate either individually or in groups composed of several hundred bats, and they hibernate in mines or caves. In the summer, these bats roost in a wide variety of locations, including limestone caves, lava tubes, and human-made structures. This species has declined due to direct killing by people and because of abandonment of roosts caused by disturbance due to explorers and vandals. These bats are skillful echo-locaters.