How does hibernation work?
by Sheena Lee Faherty
In the fall of the year most forms of animal life prepare for the coming winter. Many of the birds fly south; the squirrels gather nuts and hide them in the ground, and the bees store up honey. Those who have played throughout the summer and autumn with never a thought for the winter, often die from the cold and lack of food. Most of the lazy grasshoppers, so happy in the warm seasons, die in the winter. Only their eggs, buried in the ground, survive and hatch in the spring.
Several animals spend the winter sleeping. This winter sleep is known as “hibernation.” The grizzly bear, for instance, eats plentifully through the summer and fall up to within a month before hibernating. By that time he is “almost solid fat.” Then he digs a hole in some hillside or goes into a crevice where the snow falls the deepest, curls up, and sleeps until March.
During this winter sleep all body activities slow down. The heart beats more slowly, breathing almost stops, and the body becomes almost cold. In this sleep of several months, buried in the ground below the frost, without food or water, and with but little air, the bear is unconscious of the severe cold above him.
When the grizzly bear comes out of his den in the spring he is still rather plump. He does not eat for the first week or so but he does drink plenty of water. Gradually he adds grasses and herbs until finally his normal appetite returns.
The polar bear mother “dens up” in an ice cave where the little ones are born during the winter. There she remains quiet, but does not sleep all the time.
Among the animals that sleep soundly for several months, take no food, and seem almost dead, is the woodchuck. It is often called a “seven sleeper” because it usually sleeps seven months (from the first of October to the end of April).
Some animals store up food in their burrows and awaken occasionally to feed, and then go back to sleep again. The European dormouse does this and just before hibernation acts peculiarly; he is either slow and stupid or extremely lively. He then curls himself up into a round ball with fore paws on his cheeks, nose pointing toward his stomach, and tail wrapped around his body and head. In the sleep that follows, he becomes so cold and rigid that his body may be rolled like a ball.
The chipmunk prepares for winter by storing seeds and nuts in hidden chambers connected with his underground den. When storing this food he may attempt to carry four white oak acorns in each cheek pocket. Once in a while his pouches are so full that his head is too wide to go into the burrow entrance unless he turns it sidewise.
Like the dormouse, the chipmunk does not sleep soundly all winter, but awakens at intervals, feeds on the stored food, and then curls up in his cozy den for another nap. When warm weather brings him to life again he announces his return to the world by mounting a log and singing a series of bird-like “chock-chocks.” Other chipmunks, just coming from their winter quarters, join in this happy song.
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| Bats hibernating in a silver mine. |
Not only birds and mammals prepare for winter, but reptiles and amphibians. In the early fall the garter snakes congregate on warm, sunny hills where they find crevices or burrows deep enough in the ground to prevent the frost reaching them. As long as the days are sunshiny, they come up to bask for brief intervals before the long sleep sets in.
Turtles and newts bury themselves in the mud and water as the frogs and salamanders often do. Toads, however, crawl into holes and cover themselves with soil and grass.
Certain insects pass the winter in sleep. The common house fly hides in some dark corner of the house and remains in deep sleep. When disturbed, it drops to the. floor like a dead fly or acts stupidly.
A few fishes, like the carp, eel and minnows lie dormant in the mud beneath the ice during the severe parts of the winter.
With the coming of spring, all awaken from their winter sleep or “hibernation” and start their busy lives again. Wood.
