Grizzy Bear in a meadow.
Grizzy Bear in a meadow. Credit: NPS

As the weather cools and days shorten, bears are bulking up and preparing for a long winter hibernation. 

Each fall, American Black bears and grizzly bears enter a process called hyperphagia. During this time, they will consume 10 times the amount of calories they need to in the spring, gaining as much as four pounds a day. 

During hyperphagia, bears are more active and national park visitors may have a chance to see them in action. But it’s also important to remain extra vigilant, as bears can be more aggresive. 

Bears often need to travel long distances to find enough calories. They hyperfocus on finding food and seldom sleep more than three or four hours a day. This often makes bears protective of food sources they find and more aggressive toward people disturbing their search. 

National parks with large bear populations are urging visitors to #BeBearAware. This includes staying at least 100 feet away from bears and being especially careful with bear-safe food storage. 

National Park Service Bear Map (Lower 48).

“The reward of unsecured human food can quickly change a bear’s natural feeding behavior,” wrote Rocky Mountain National Park officials. “You can help save a bear’s life by preventing them from obtaining human food, scented items, and garbage.”

When the weather gets too cold and the food supply runs out, the bears will retreat to their dens for the winter. Bears can spend up to six months in hibernation without eating, drinking, or expelling waste.

Depending on the location, bears might start hibernating between November and December and won’t emerge until spring.

To see if bears have been spotted in the park you’re planning to visit, go to the National Park Service Bear Map.


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Heather Bergeson is a writer and editor based in Utah. Heather has written about travel, sports, business and the outdoors for Stowaway magazine, Utah Business magazine and Moab Sun News. She has a bachelor's...