WINTER SLEEP G205

 WINTER SLEEP

Some birds will fly away to the south when the weather turns cold. Other birds and all animals stay with you, but you will not see all the animals all through the winter. In the cold weather some of them hibernate.

They go to sleep in all kinds of places. Red squirrels disappear inside trees, bears use caves, frogs go deep under the mud, and many other animals dig tunnels in the earth. A good many animals sleep under the snow. There is a lot of air in loose snow, and this helps to keep the cold out.

Some warm-blooded animals, like the cat, the dog or the wolf, do not need to hibernate; they lead an active life which keeps up their normal body temperature even in very cold winter weather. But for a cold-blooded creature such as a frog or a snake it is a different matter. When the air temperature is below freezing, the creature's body temperature drops too. It cannot move about in its usual way. Then it has no choice but to lie down and sleep. To do that, it must find a place where it can keep fairly warm; and it must be a place where its enemies cannot find it.

Hibernation is more than sleep. It is a very deep sleep. The animal's temperature drops to just over zero centigrade, and its heart beats very slowly. People who find hibernating animals asleep often think that they are dead: the body feels very cold, and the creature may breathe only once every five minutes. A hibernating animal cannot feel any pain. You can touch it, or even pull its tail, without causing it to move or wake up. In its hibernating state it can even live in a poisonous atmosphere for a long time without any ill effect.

Hibernating in that way, the animal can sleep all through the winter. You might wonder how it manages to live without eating for so many months. The answer lies in two facts. The first is that it has stored supplies of fat in its body during the summer and autumn. The second is connected with the main use the body makes of food—to supply the energy for movement. We have seen that the hibernating animal reduces movement to far below the ordinary level. Even the movements of the heart and lungs are greatly reduced. The animal hardly makes any movement, hardly uses any energy, and hardly needs any food.

Some animals, including some bears, only half-hibernate. That is to say, they sleep during the winter but their sleep is not such a deep one, and their body temperature does not drop. In the autumn the bear eats and eats and becomes very fat indeed. His hair grows longer. Soon he has a thick covering of fat and fur. In November he finds a place in a cave or under a tree and just lies down and goes to sleep. On warm winter days he may think that spring has arrived; he gets up and walks around. When he sees that the snow is still thick on the ground, he quickly goes to sleep again.

The squirrel is an animal which makes secret food stores for the winter. It hides large quantities of nuts inside trees. In the old stories which taught moral lessons to children, the squirrel was a 'good' animal: it saved something for the future.