Bats are very unusual mammals. They are very plentiful and have lived on earth for 50,000,000 years which is longer than many mammals. Bats are one of nature's wonders, and helpful to mankind. Bats hibernate mostly in caves but are also found in mines, tunnels, old buildings, and attics. This is because the temperature in these places stays cool and moist.
Humidity is also a great factor.
When bats hibernate and don't eat or drink for four or five months, they can dry out. In the cave, the temperature ranges from 40 degrees Fahrenheit to 48 degrees Fahrenheit, but when the temperature in the cave drops, the bat's temperature also drops from around 104 degrees Fahrenheit to about 32 degrees Fahrenheit. When the bats are hibernating all their body functions slow down. For example, breathing drops from about 200 breaths per minute to as low as 23 breaths per minute. Bats that migrate go to a warm place in the winter and return home when it gets warm again.