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Bears can be really hungry when they wake up from hibernation! (J.-L. Klein & M.-L. Hubert/Biosphoto)

Wake-Up Time in the Wild

Scientists are studying bears as they emerge, hungry but healthy, from their winter naps

By Cody Crane | March 20 , 2011
<p>For up to seven months, bears barely move at all during their winter slumber. (Paul Souders/Getty Images)</p>

For up to seven months, bears barely move at all during their winter slumber. (Paul Souders/Getty Images)

This Sunday, March 20, is the first official day of spring in North America, and the weather is getting warmer. That means animals that slept throughout the cold winter all across the U.S. are starting to stir. This winter slumber is called hibernation, and scientists are studying just how animals like bears can sleep for months and stay healthy.


Bears are particularly good at hibernating. During the winter, a bear’s body changes dramatically. For up to seven months, bears do not have to eat, drink, or take a bathroom break.

Animals hibernate as a way to use less energy. During hibernation, a bear’s heart beats at one fourth its normal rate, and its body temperature drops by 10 degrees Fahrenheit. It survives by burning fat it put on during the fall—which makes it very hungry when it wakes up.

Bears hibernate much differently than smaller animals, like woodchucks and squirrels. For one, bears are light sleepers and will react if disturbed. Tiny hibernators sleep so deeply it’s hard to wake them up at all.

Small animals’ heart rates become very slow, and their temperatures drop close to the freezing point. They also must periodically wake up to eat from their stockpile of food and eliminate bodily wastes before heading back to sleep.


In the spring, a bear emerges from its den as healthy as ever despite being as hungry as, well, a bear. The same cannot be said for humans who stay in bed for long periods of time due to illness. They become weak from not using their muscles and bones. The same thing happens to astronauts, who don’t have to use much energy to move in the weightlessness of space.

Researchers find that the science behind bear hibernation has much to teach humans. “A bear scarcely moves for months, yet comes out of its den, gives a yawn, and is on its way,” says Dave Garshelis, a research biologist from the Minnesota Department of Natural Resources. Garshelis studies these sleepy creatures because he thinks the way bears hibernate could help humans.

Bears maintain their muscle strength during hibernation with the help of bacteria in their guts. The bacteria recycle muscle that has been broken down into protein—a natural substance found in food that helps grow new muscles.

Seth Donahue, a biomedical engineer at Michigan Technological University, also studies bear hibernation. He discovered that bears create a bone-building chemical that keeps their bones strong during hibernation. Donahue hopes to develop a new medicine based on the bears’ hormone to treat humans with bone diseases.

Scientists believe bears still have much to teach us. Other studies are being done to see if bear vomit can help keep human kidneys healthy, and if bear blood can help give surgeons more time to operate.

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