Hibernation is used as a catch-all term for the inactivity of animals over winter, but there are different types of dormancy – torpor is quicker to wake from. Hibernating animals do still wake up during winter, to feed, drink, defecate and even move location.
ID GUIDE
1 EUROPEAN HEDGEHOG
Erinaceus europaeus
One of the few UK species to enter true hibernation, a hedgehog builds a ‘hibernacula’ nest from leaves, sticks, straw, bracken and reeds for winter.
Once settled, its body temperature can drop to below 10ºC and its heart rate to 20 beats a minute.
2 BATS
Chiroptera
Bats – such as this lesser horseshoe bat – hibernate in sites with stable, cool temperatures, such as caves and tunnels. Remarkably, no one knows where common pipistrelles spend winter.
3 HAZEL DORMOUSE
Muscardinus avellanarius
From tree tops, dormice move to ground level to hibernate in a nest woven from grass and leaves. During hibernation, a dormouse will lose 30% of its body weight; scientists estimate that it needs to weigh at least 15–18g to survive the winter.
4 EUROPEAN EDIBLE DORMOUSE
Glis glis
Introduced to the UK in 1902 from mainland Europe, this species also hibernates over winter. In autumn preparation, it feeds on fruits and nuts – particularly beech mast – doubling its body weight.
5 EUROPEAN BADGER
Meles meles
Badgers undergo torpor instead of hibernation, spending days or weeks in deep sleep. In autumn, they build fat reserves and collect dry grass, bracken or dead leaves for bedding in a snug sett.
6 RED SQUIRREL
Scirus vulgaris
Squirrels don’t hibernate but do sleep more in their dreys – nests made from twigs and moss – sometimes sharing with others. In autumn, a red squirrel caches nuts and fungi as a winter supply, and is able to find its nuts buried beneath snow.
7 WATER VOLE
Arvicola amphibus
In autumn, a water vole puts on body weight and stores food before undergoing torpor. Water vole populations can drop by around 70% in winter as older adults and underweight
