Hibernation.

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Hibernation.
On some mornings, you might not feel like getting up. On cold mornings, you might want to
stay snuggled warmly in bed. You might say, "I'm just going to hibernate today." You mean that
you are not going out. When animals hibernate, it means something very different.

HOW DO ANIMALS HIBERNATE?
An animal hibernates by becoming inactive. It enters a kind of sleep. Many changes take place in the
animal's body. Most of the animals that hibernate are mammals. Mammals hibernate in winter, when it's
cold.
Animals first must get ready to hibernate. They eat a lot of food. The food gets stored in their bodies as
fat. Then the animal goes into a cave, underground burrow, or some other shelter. It needs to be safe
from cold weather and enemies when it hibernates.
The hibernating animal's body makes less and less energy. It makes very little body heat. The animal's
body temperature drops.
The animal's heartbeat slows down. It breathes slowly. Animals without much energy go into a kind of
very deep sleep.

WHY DO ANIMALS HIBERNATE?
Animals usually hibernate in winter. It is cold outside during the winter. The animals could freeze to
death.
There is not much food around to eat in winter. The animals could starve to death. Animals need food to
make energy. A hibernating animal makes less energy, so it does not have to eat. A hibernating animal
can live off of fat stored in its body.
Some animals that live in deserts--including some squirrels and insects--go into a kind of deep sleep
during summer. This sleep is called estivation. They sleep underground during the blazing heat. Their
bodies slow down so that they do not need to drink water. There is not much water in a desert in the
summer.

WHAT ANIMALS HIBERNATE?
A number of warm-blooded animals hibernate. Warm-blooded animals make their own body heat from
food energy. Chipmunks, ground squirrels, hamsters, and hedgehogs are warm-blooded animals that
hibernate. The common poorwill is the only bird that hibernates all winter.
Some cold-blooded animals hibernate, too. Cold-blooded animals cannot make body heat. Their bodies
are the same temperature as the air or water around them. Frogs, toads, and other amphibians are coldblooded animals that hibernate. Lizards, snakes, turtles, and other reptiles also are cold-blooded and
hibernate.
Some animals spend part of their day in a deep sleep like hibernation. This deep sleep is called
dormancy. Bats and some kinds of birds go dormant each day.

DO BEARS HIBERNATE?
Bears spend several months during the winter sleeping in dens. They do not eat. Scientists do not know
whether bears really hibernate. Some scientists say that the body temperature of bears does not drop
low enough for true hibernation.

HOW DO HIBERNATING ANIMALS WAKE UP?
Animals hibernate for several months. Every once in a while, the animal wakes up. Chipmunks and
squirrels eat nuts and other food they have stored in their burrows. Then they go back to sleep again.
Hibernating animals wake up when their bodies get warm again. The bodies of cold-blooded animals do
not warm up until the outdoor temperature gets warm. Warm-blooded animals may start shivering. This
motion helps their bodies warm up. Small animals warm up and come out of hibernation much faster
than large animals.
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