Monthly censuses were carried out during the winter of 1975–76 at five Myotis sodalis hibernacula in eastern Missouri. The caves were of different types, but all exhibited mid-winter temperatures well below those of most other caves in the region. Early in the season when temperatures were uniform throughout the caves, bats roosted in high, deep cave sites. By mid-winter, temperatures were colder at sites near the cave entrances. Bats subsequently moved to these sites and formed larger clusters than they did at the warmer sites. The relationship between clustering behavior, rock temperature, and cave configuration is discussed.