Hibernation

All British bats hibernate. They build up fat during the autumn and find a cool, humid, sheltered place such as a crevice in a cave. All their body systems slow down in order to save energy and their heart rate drops to around 20 beats per minute when hibernating - compared with 1,000 beats per minute in flight. During mild spells in winter, bats may wake up and fly to feed or move to a different site.