Five Surprising Facts About Hibernation
A Wildlife Article from All-Creatures.org

FROM Jess Webb, League Against Cruel Sports
December 2021

Each individual species has its own incredible methods of coping with the UKs extreme weather, but hibernation is among the most remarkable.

League Against Cruel Sports

As the weather gets colder you might notice that much of our wondrous wildlife seems to disappear. Where have these incredible animals gone? Each individual species has its own incredible methods of coping with the UKs extreme weather, but hibernation is among the most remarkable. Here are five facts you might not know about this astonishing survival strategy.

1. Hibernation is not a deep sleep

On the contrary, some animals have been known to wake up from hibernation to get some sleep.

Hibernation is a state of extreme inactivity. When in hibernation, the animal slows their heart rate to survive the cold winter temperatures and lack of food. Unlike sleep, this involves quite extreme physiological changes, including lower body temperature and metabolism reduced to 5% of its normal rate.

2. Few mammals hibernate in the UK

Only three British mammals truly hibernate: dormice, hedgehogs and bats. They retreat to their dens, caves or nests around October/November and remain there until early spring of the following year. Bats wake from hibernation every so often to rehydrate themselves with a drink of water.

Foxes, badgers, birds and squirrels do not hibernate and instead sleep in their dens for shorter periods while the weather is at its coldest, venturing out whenever its warm enough to forage for food.

3. Reptiles, amphibians and some insects hibernate

Reptiles and amphibians could not survive the winter without hibernating; colder temperatures do not suit exothermic (or cold-blooded) creatures. Many reptiles will dig themselves into loose soil, hide in a compost heap or bury themselves under a pond liner to keep the harsh weather out.

If you own a pond, it is vital you keep it from freezing over during the winter. Otherwise, fish and any hibernating amphibians will be starved of oxygen. You can prevent your pond from freezing over by pouring warm water in the same place every day, to create an opening in the ice.

You should never smash the ice, or pour boiling water on the surface, as this could cause unnecessary trauma to the fish. It is not essential to heat the whole pond; all you need is a break in the ice to allow oxygen in.

In addition to reptiles and amphibians, some insects, such as ladybirds and bumblebees, also hibernate. For insects this process is known as diapause; their bodies enter a state of suspended animation and their appetite and development slow down dramatically. They will hide in homes, sheds, under rocks and inside trees.

4. Climate change is affecting hibernating animals

Evidence suggests rising temperatures in the UK are disrupting hibernating species. In some cases the animals are entering hibernation too late; in others, they are emerging too early.

These timing issues can be fatal to the animal. If the weather becomes drastically colder before they have the chance to prepare, or they use all their stored energy before they can replace it, the animal is left with few paths to survival.

All hibernating species are affected by climate change, including hedgehogs, frogs and insects. You can help any animals who are struggling over winter by planting trees or shrubs in your garden that can provide food. Holly, spindle, hawthorns, blackthorn, rowan berries, juniper and dog rose will all be gratefully received by any hedgehogs nearby.

5. Birds do not hibernate

Many birds use migration as their preferred survival strategy in winter. The main difficulties they face at this time of year are extreme weather conditions and a lack of food. Rather than hibernating, birds such as swallows will fly as far as 200 miles per day to reach warmer and more habitable climes. Swallows spend their winters in Africa where they can find their main food source of insects more easily.



Winter is a difficult time for all our wondrous wildlife. While the survival of some species relies on hibernation, other species do not have the luxury of being out of sight, and out of mind. Foxes, hares and deer are being targeted right now as hunting season is already in full swing; hunts will continue meeting, and tearing animals apart, until March or April at least.

All animals deserve a safe and comfortable winter.


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