ARTICLE

leveled

ARTICLE

leveled

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.
Selected text level

For people who aren't fans of winter, animals that hibernate seem to have the right idea. After all, hibernation is like taking a long nap until spring comes, right? Not quite. Hibernation is very different from what happens when you sleep.

What Is Hibernation?

Hibernation is a state that lasts a very long time. During this state, metabolism slows down. Metabolism is the process that takes place in plants and animals to keep them alive. It is how the food we eat turns into energy that keeps our bodies working.

Marina Blanco is a scientist. She studies the dwarf lemurs (Cheirogaleus spp.) of Madagascar, an island country in Africa. Dwarf lemurs are the only primates that hibernate on a regular schedule. Blanco said metabolism is "slowed down or completely halted" during hibernation.

When dwarf lemurs hibernate, they reduce their heart rates. An active lemur's heart beats up to 300 times a minute, Blanco said. During hibernation, it can beat less than six times a minute. Breathing slows down too. Hibernating lemurs can go up to 10 minutes without taking a breath.

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

Why Do Animals Hibernate?

Kelly Drew is a scientist who studies a kind of squirrel that hibernates. She said that hibernation is a way for animals to save energy.

Hibernation is often seen as winter behavior. However, animals that live in cold areas aren't the only ones that hibernate. Some animals hibernate to beat the heat.

For some animals, hibernation does not have to do with temperature. Some animals hibernate when there's no food, Drew said. For example, spiny creatures called echidnas will hibernate after fires. They wait until food grows back before they go back to normal activities.

Scientists found that some animals hibernate to stay safe. Thomas Ruf is one of the scientists who believe this. He said animals don't smell or move much when they hibernate. This makes it hard for predators to find them.

What Actually Happens when Animals Hibernate?

To slow their metabolism, animals cool their bodies. They usually lower their temperature by 5 to 10 degrees Celsius (9 to 18 degrees Fahrenheit). Animals don't stay in their frozen state the whole time, though. Sometimes they wake and warm up.

Why they do this is a big mystery, Ruf said. Some scientists think the animals need to wake up to fight disease. Others think they stop hibernating so they can sleep.

What Kinds of Animals Hibernate?

There are many mammals that hibernate. Bears are probably the first that come to mind. However, there have been questions about whether bears are really hibernators. Most animals that hibernate wake up now and then during hibernation. Bears can go 100 days or so without needing to wake.

Most mammals that hibernate are small. The average hibernator weighs less than 91 kilograms (one-fifth of a pound), Ruf said. Little animals tend to lose heat more quickly. They need to save energy more than larger animals do.

What Animal Hibernates the Longest?

It's hard to say which animal hibernates the longest. A good choice would be edible dormice (Glis glis). They can hibernate for more than 11 months at a time.

In one experiment, a brown bat (Eptesicus fuscus) hibernated in a refrigerator for 344 days. That shows that bats may deserve the prize. However, the bat in this experiment didn't choose to hibernate. It also didn't survive its long hibernation.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

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

For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.

Media

If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text

Text on this page is printable and can be used according to our Terms of Service.

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

Related Resources