Duration of Hibernation: From September to April
Type of Hibernation: True hibernation
The only flying mammals, bats when left alone are the longest true hibernators. Species like the Big Brown bat are known to hibernate for long durations between sixty seven to eighty days. During this time, they live off the fat that is stored in their bodies, and their heartbeat drops from 400 beats per minute to 25 beats per minute. By February and March, some bats leave their hibernacula (places where bats hibernate) to find food and water. By the time spring approaches and the hibernation ends, most bats will have lost around half their body weight.