When it's the females' time to migrate, they can give birth to two babies in one year because they're in a warmer climate. Some tropical bats don't have to worry about migrating or hibernating because they live in a warmer climate. When bats hibernate they are totally inactive. Their breathing slows down and their body temperatures drop. If they are disturbed while they are hibernating, they will use up all of their energy and then die.
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.