Some animals hibernate over the winter, going into a very deep sleep.

Hibernating animals usually retreat to a den, a burrow, or a hollow log for protection and shelter.

During "true hibernation", the animal's body temperature drops, and its rate of breathing slows down.

Dormouse

Most animals will eat lots of food before hibernating, adding body fat that will feed them and keep them warm during the winter.

When most hibernating animals wake up in the spring, they are very hungry.

The word dormouse probably comes from the French verb 'dormir' which means to sleep.

Common dormice hibernate from October to April in nests on or near the ground.

They make their nests under hedges and at the base of tree trunks.

They build up stores of body fat in the autumn and sleep curled up in a ball.

When they are awake their body temperature is about 34-38 degrees centigrade, but during hibernation it drops to less than 10 degrees.

Hedgehogs

Not all animals spend the whole winter asleep.

Some hibernating animals wake up if the weather is mild and may leave their nest to get food.

Hedgehogs hibernate for five or six months during the winter.

It needs to be at least 500 grammes in weight in order to survive hibernation, because its energy supply comes from fat reserves stored under its skin.

By November most hedgehogs have begun to hibernate.

They build nests from leaves and grass under hedgerows, in old rabbit burrows and underneath compost heaps.

They carry nesting materials in their mouth to their hideaway and burrow inside and turn round and round to make a cozy den.

They finally wake up in March or April when the weather is warmer and food is easier to find.

Hibernating pets

Your pet tortoise will need to hibernate.

The exact beginning and end of hibernation varies from year to year but usually is between October/November and March/April.

As the weather gets colder the tortoise will begin to slow down and will stop eating, this is when you should prepare the hibernation box - a cardboard box large enough to comfortably house it.

While hibernating the tortoise should be left alone apart from an occasional check to see that it has not woken up.

When it does wake up in spring you may have to unglue its eyes by gently bathing them with wet cotton wool.

Make sure it has enough fresh water to drink and try giving it different foods (it may not eat at first).

It can be put outside on warm and sunny days but must not get cold or wet.

Pond life

Frogs and newts also hibernate.

The adult male frogs will hibernate at the bottom of the pond. Female frogs and newts will bury themselves under rocks and stones.

If you have a pond in your garden, it is important to make sure it doesn't get iced-over in very cold weather as hibernating frogs may suffocate.

If your pond does get a covering of ice, make a hole in it by pouring on warm water rather than bashing the ice with a heavy object as this may disturb the hibernating frogs.