W: Some animals in cold climates hibernate.
This means that they spend the winter months in
a very long and deep sleep. Many animals find
shelter underground. They dig out shelters to
sleep in. Animals that cannot dig find cracks or
holes at the base of trees and bushes. If they like
the place they find, they might use it for years
and years.
Animals that hibernate include cold-blooded
animals, such as lizards, frogs, and snakes. Many
warm-blooded animals also hibernate, such as
mice, bats, and squirrels. When these animals
are hibernating, they seem like they are not alive
at all. Warm-blooded animals seem colder to the
touch. However, their blood is still very warm.
Hibernating animals have a very slow heartbeat.
They almost stop breathing. Extra blood sugar
and fat in their bodies keep them alive. They eat
lots of food just before they hibernate.
Winters that do not stay cold are dangerous
for hibernating animals. They can sometimes
wake up in their shelters when it gets a little
warm. Then they use energy by moving around.
During winter, there is very little food. These
animals can get very thin and weak. If they move
around too much and do not eat, they can die.
Animals hibernate to escape the cold. There
are also animals in hot climates that escape the
heat. During very hot or dry weather, they sleep
underground. This is called aestivation.