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Hibernating animals hover between life and death

Posted in Animals, Biology, Fish, Nature, Wildlife on Friday, 22 February 2013

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This edited article about hibernation originally appeared in Look and Learn issue number 152 published on 12 December 1964.

Hibernating animals, picture, image, illustration

A cutaway landscape showing hibernating animals by David Nockels

During the cold winter months you will sometimes find butterflies and moths hidden away behind curtains and pictures or in corners of rooms that are little used. They look quite dead, but if you move them carefully to some place that is warm you will see them gradually fluttering back into life.

In the same way, you may find a hedgehog buried in the leaves at the bottom of a ditch or rolled up in a ball under a garden shed. If you have a pet tortoise it will disappear in winter – unless you come across it in some sheltered spot drawn into its shell and to all appearance lifeless.

These are only a few of the many creatures who escape the cold of winter and manage without food by going into the deep sleep called hibernation.

The term “hibernation” comes from the Latin word hibernatus, meaning “winter quarters.” And that is exactly what hibernating creatures do: they go into winter quarters and sleep soundly until spring brings warmth again.

In countries of northern and western Europe and North America many animals find their supply of food cut off in winter and would starve. So they go into a long deep slumber, and keep themselves alive on the fat that has accumulated in their bodies when they were able to feed in the summer and autumn.

Unlike the birds, which can fly for thousands of miles to warmer lands where food is plentiful, most animals cannot travel long distances to places in search of food.

Practically all animals that hibernate are those that are unable to get their accustomed food in winter. They have not learned like the squirrels, for example, to gather in a supply of nuts and seeds to last them through the cold months of the year.

Bats hibernate in caves and old buildings, huddled together in huge clusters to keep each other reasonably warm. Dormice and voles sleep the winter through in deep burrows in the ground, while frogs bury themselves in the mud of ponds or in loose soil and rotting stumps.

Hibernation is simply a form of sleep, but a very deep sleep. At the same time, the hibernating animal’s body temperature falls until it is almost as low as that of cold-blooded creatures like snakes and other reptiles.

So deep is the animal’s sleep that it appears to lose all its normal feelings and reactions. If you touch a hibernating hedgehog it does not automatically raise its spines as it would do in summer.

The animal’s normal body functions come to an almost complete standstill. You can hardly see it breathe, and it does not move, hovering between life and death for months on end.

Indeed, a hibernating animal is so close to death that if you suddenly disturb it, it may die. When it wakes with the coming of spring it does so very gradually.

Because it does not move about and is just alive and no more, it uses up very little energy. That is why it can do without food. Food is the “fuel” that gives an animal its energy.

But it is not only warm-blooded, fur-covered creatures that hibernate.

Earthworms burrow deep in the ground below the reach of frost, and snakes curl up in crevices in rocks or holes in the ground. Snails hibernate by closing the “front door” of their shells with a gum-like material and go to sleep until the spring sun warms them and brings them out again.

There are even fish that sleep the winter through. Those normally living in brooks and shallow streams retire to deeper water, and some species actually bury themselves in the mud until the water gets warm again.

Sharks which live on minute sea creatures called plankton go to sleep in the winter when their food supply runs out. They sink deep into the ocean where they sleepily float about.

Young swifts caught in sudden cold spells before their normal time for migrating, become sleepy and huddle in their nests in a partial hibernation called the torpid state.

In the Arctic the female polar bear does not actually hibernate, but digs herself a shelter deep in the snow where she passes the long, cold months half-awake. It is during this period that she gives birth to her cubs.

There are some creatures that wake up from hibernation for short periods. On mild winter evenings bats leave their dormitories for short hunting expeditions; so occasionally do tortoises and hedgehogs.

But woe betide those adventurers if there is a sudden drop in temperature. The cold may kill them before they can return to their winter quarters.

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