Childrens Illustrated Encyclopedia

254

Hibernation

Senses such as hearing

and sight are inactive

during hibernation.

Dormouse

one of the best-known hibernators is

the dormouse. In the fall it feeds

eagerly to build up stores of body fat,

then settles into a winter nest among

tree roots or in dense undergrowth. Its

heart slows to only one beat every few

minutes, and its breathing slows down.

Its body temperature also drops to a

few degrees above the surroundings.

Black Bear

The winter sleep of bears, skunks,

and chipmunks is not as deep as

the true hibernation of bats and

mice. The american black

bear’s heartbeat slows but

the body temperature

drops by only a few

degrees. This means that

the bear can stir itself

from its winter sleep

quite rapidly during a

spell of slightly warmer

weather. although it

wakes up, the bear does

not eat and continues to

live off its body fat until

the spring. some female

bears give birth during the

winter months.

maNY Warm-BlooDeD aNImals need extra energy in order

to stay warm in the cold winter months, but the source of that

energy—food—is scarce in the winter. some animals survive

winter by migrating to a warmer place; others, such as

bats and hedgehogs, hibernate in a safe and

unexposed place such as a nest, burrow, or cave. In

true hibernation, the body processes slow down

almost to a standstill—the heartbeat occurs only

every now and then, and the animal takes only a few

breaths per minute. The body temperature falls to

only a few degrees above the outside temperature—

as low as 32°F (0°c) in a hamster. If the outside

temperature drops below zero,

chemical reactions in the animal’s

body switch on to keep it from

freezing to death. a hibernating

animal feasts on extra food in the

fall so it can build up reserves of

fat in its body and survive the

winter months without food.

Up to half of body

weight is lost

during hibernation.

Torpor

To save energy,

some small,

warm-blooded

animals such

as bats and

hummingbirds

allow their bodies

to cool and their

heartbeat and breathing

to slow down for part of the day or

night. This is called torpor. large animals such as bears do

not become torpid because they would need too much energy

to warm up again afterward. Bats often huddle together as

they hang upside down to prevent too much heat loss. When

the cold season comes, bats fly to a special cave or tree called

a hibernaculum, where they begin true hibernation.

aesTIvaTIoN

many desert animals sleep during the hot, dry

season to survive the intense heat. This is called

aestivation—the opposite of hibernation.

Desert creatures that aestivate include lizards,

frogs, insects, and snails. Before aestivation

begins, snails seal their shell openings with a

film of mucus that hardens in the heat.

Snails cluster on

grass stems to

aestivate, away

from predators

on the ground.

Find out more

animals

Bats

Bears and pandas

migration, animal

snails and slugs

Dormouse curls up

into a ball shape to

reduce heat loss

from its body.

Dormouse builds

nest on or near

ground, using stems,

moss, and leaves.

Furry tail wraps around

face for protection

and insulation.

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