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What is hibernation?

Hibernation is a term that ecologists use quite a lot, certainly when discussing animals such as dormice and bats. However, what does it mean and do our animals really hibernate?

Let’s imagine a scenario

An animal lives in a place which is warm and has lots of food available from spring to autumn, but in winter it is very cold and there is no food to eat. To survive winter, it could employ a few strategies e.g. eat a lot before winter and huddle with others to keep warm (e.g. some penguins and bees); store food for winter (e.g. squirrels and some corvids); move away to warmer areas (migratory birds); have thick layers of fur or feathers (bears, seabirds); have anti-freeze type chemicals in their blood (some fish and insects); or slow its metabolism down and sleep through the winter (some bees, hedgehogs and some bats).

The last one is hibernation

This is the process where the rate of energy output is reduced, with a fall in breathing rate, heart rate and body temperature. Consequently, the animal’s fat and energy stores can then be eked out over the winter until there is enough food available to forage on in the spring.

Some animals can conserve energy loss by going into torpor – this can be done at any time of year, allowing the animal to go out and feed when they can. This is seen in bats regularly leading up to winter, so that they can react to a food supply being available, without having to spend a lot of energy maintaining higher body temperatures than is necessary.

Waking up from hibernation and torpor costs a lot in terms of energy too – the animal must bring its body temperature and metabolism back up to normal levels, so that it can go and forage and in the case of bats, fly. This means that some of the reserves that the animal has built up before going into torpor or hibernation gets spent during the waking up period. If the animal gets woken up too frequently over the winter period, it is unlikely to have the reserves it needs to survive into the next year.

Safe locations to hibernate

Most animals tuck themselves into locations where they are safe from predation and disturbance, though animals such as bats and dormice can hibernate in unlikely places too. Read about bat roosts. Bats are regularly found in unlikely places such as under wooden barge boards and on wall tops (some species of bats), and dormice can make their hibernation nests on the ground next to roads or on the open woodland floor.

Impact of climate change

With a changing UK climate meaning that our winters are getting warmer and wetter, there are more chances of animals such as bats waking up more often during this time to forage, without much food being around to support them. We can help by making sure that development is resilient by ensuring landscaping provides food for wildlife year-round with lots of nectar-rich native species including early and late flowering species, plus ivy and hedges, scrub and trees. Read more from The Bat Conservation Trust on encouraging bats.