When Do Bats Hibernate?

Bats seek a suitable hibernaculum (place to hibernate) in response to changes in the weather. In the UK this is usually from October or November. With such tiny bodies energy conservation is crucial. The reduced supply of insects in winter months means it is not possible to balance this increased energy need in the colder months with the food supply. Even in hibernation bats might cluster together to reduce energy loss. They are not asleep throughout the whole hibernation period. Period of wakefulness might be filled with drinking, some foraging for food, urination, defecation and occasionally in some species mating. However bats are in a deep sleep for periods as long as two months. Hibernation ends in Spring around March or April. Bats choose their hibernaculum for its constant temperature and humidity and so it is thought their awakening is governed by some sort of internal mechanism more than changes in external temperatures.