The Big Sleep

When the nights are long and temperatures low, we sometimes wish we could just snuggle up under the blankets and sleep through winter until the spring sun wakes us up again. For some animals, however, this is not a matter of comfort but key for survival...

Winter is a quiet time for wildlife. It often feels like Mother Nature has gone to sleep. Trees have shed their leaves, no flies and wasps bother us and few birds can be spotted out and about. Everything seems to take a rest and gather strength before the hustle and bustle start again in the spring.

In those long, dark winter months food sources are scarce. Different species have developed different coping mechanisms to survive the cold season. Some avoid the adverse conditions by migrating to warmer climates, like many bird species. Others, such as badgers and foxes, reduce their activity and spend more time in their setts and dens. Some animals go further and spend the winter in hibernation.

Fox in winter — Red fox in the snow © Danny Green/2020VISION

Close to death

Hibernation is often compared to sleeping, but it is a state of inactivity closer to death: the whole body activity is brought down to a bare minimum; body temperature falls so low that it nearly matches outside temperatures. The heart rate is reduced to several beats per minute and respiration stops altogether save for a few breaths every couple of minutes.

Hibernation is frequently used interchangeably with other states of dormancy: Many species go into diapause, a state of suspended development to cope with adverse conditions. It is mainly seen in insects but can apply to other species such as fish or birds, too. Amphibians enter a state of torpor, which can best be described as semi-hibernation because it takes place for shorter periods of time. Hibernation is also, by definition, restricted to winter.

Some animals are falsely considered hibernators, when in reality, they enter a light torpor with many interruptions. In the UK, only three mammals are true hibernators: hedgehogs, bats and dormice.

Hedgehog in autumn leaves — Hedgehog © Tom Marshall

Hedgehogs spend the winter months in piles of dead leaves, stacks of logs, compost heaps or under garden sheds. They usually go into hibernation between October and April, but this can vary depending on the weather. They need to put on significant weight for hibernation, so in the summer months, they munch on beetles, caterpillars and earthworms.

Dormouse — Hazel dormouse © Terry Whittaker/2020VISION

Dormice hibernate in their underground burrows between October and April or May. This rather long period of hibernation not only protects them from the cold weather, but increases their survival chances. The main cause of death for small rodents is predators, so it’s much safer for them to stay hidden from view. In the time before hibernation, they will gain weight to become up to twice their normal size and lose half of their body weight again during hibernation.

Specialists in energy conservation, bats can drop their heartbeat to 20 beats per minute and take as little as five breaths per minute in winter. They leave their roosting sites around November and move to their hibernation site, or hibernaculum, which can be a hollow tree, under a roof, a cave or a bat box. Bats will emerge from their hibernation around April. During hibernation, bats wake up now and then for short periods of time to excrete and stock up on food.

Help your local hibernators

The best way to support our furry friends throughout the winter months is to provide shelter and food. If you have hedgehogs visiting your garden, supplementary feeding such as specialist hedgehog food or even cat food can prove vital to them. You can also provide a safe shelter for them to rest: Pile up fallen leaves or, if you're feeling crafty, build a hedgehog house, a bat box or an insect hotel and put it up in a quiet corner. If you accidentally disturb a hibernating animal, please don’t move it. Cover it back over and leave it alone. When the first sunrays of spring warm the earth, hibernators are ready for the warmer weather – just like us!