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Some Animals Don’t Actually Sleep for the Winter, and Other Surprises About Hibernation

Some Animals Don’t Actually Sleep for the Winter, and Other Surprises About Hibernation

It isn’t just groundhogs—find out which animals hibernate and why.

Grades

3 - 12

Subjects

Biology, Ecology, Storytelling

Image

Arctic Ground Squirrel Upright

Hibernating animals slow their metabolisms, cooling their bodies by 5° to 10°C (9° to 18°F). Arctic ground squirrels (Spermophilus parryii) can take this much further, cooling their bodies to subfreezing temperatures.

Photograph by Thomas and Pat Leeson
Hibernating animals slow their metabolisms, cooling their bodies by 5° to 10°C (9° to 18°F). Arctic ground squirrels (Spermophilus parryii) can take this much further, cooling their bodies to subfreezing temperatures.
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Some people are not fans of winter. To them, the idea of hibernating may sound pretty good. Hibernation is just like taking a long nap until spring, right? Not quite. Hibernation is very different from what happens when you sleep.

What Is Hibernation?

Metabolism is a process that keeps us alive. It is how the food we eat turns into energy. This energy keeps our bodies working. During hibernation, metabolism slows down. Animals that are hibernating do not eat. They use very little energy.

Marina Blanco is a scientist. She studies the dwarf lemurs (Cheirogaleus spp.) of Madagascar. This is an island country in Africa. Their heart normally beats up to 300 times in one minute, Blanco said. During hibernation, their heart rates slow down. Their heart can beat less than six times in one minute. Their breathing slows down too.

This is very different from sleep. During sleep, animals still breathe normally. Hibernation is a deeper kind of rest. In fact, animals have to sometimes "wake up" from their hibernation to get some sleep.

Why Do Animals Hibernate?

Kelly Drew is a scientist. She said that hibernation is a way for animals to save energy.

Hibernation is often seen as winter behavior. It makes sense to want to save heat energy when it is cold. Some animals hibernate when it is warm, though. It helps them stay cool.

Thomas Ruf is an animal expert. He said animals may hibernate to stay safe from predators. They don't smell or move much when they hibernate. This makes it harder to find them.

What Actually Happens when Animals Hibernate?

When animals hibernate, they slow their metabolism. They do this by cooling their bodies. Usually, they reduce their temperature by 5 to 10 degrees Celsius (9 to 18 degrees Fahrenheit). Animals do not stay frozen the whole time though. Sometimes they wake and warm up.

What Kinds of Animals Hibernate?

Many animals that hibernate are mammals. These are animals that have fur or hair. They have a backbone and breathe air. Bears are probably the most famous example. However, scientists are not all sure that bears are really hibernators. Most animals that hibernate wake up now and then during hibernation. Bears can go 100 days or so without waking.

Most mammals that hibernate are small. Many weigh less than 2.2 kilograms (one pound), Ruf said. Little bodies cannot store very much heat. They need to save energy more than larger animals do.

What Animal Hibernates the Longest?

It is not clear which animal hibernates the longest. It might be the edible dormouse (Glis glis). This tiny animal can hibernate for more than 11 months.

In one science experiment, a brown bat hibernated in a refrigerator. It did not wake up for 344 days. That is even longer than 11 months. However, this bat did not choose to hibernate. It also did not survive its long hibernation.

Media Credits

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Director
Tyson Brown, National Geographic Society
Author
Heather Brady
Production Managers
Gina Borgia, National Geographic Society
Jeanna Sullivan, National Geographic Society
Program Specialists
Sarah Appleton, National Geographic Society, National Geographic Society
Margot Willis, National Geographic Society
Producer
Clint Parks
other
Last Updated

February 26, 2024

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