As the leaves start to change and temperatures drop, everyone is preparing to settle in for the winter — including bears.
Though we may like to imagine bears entering their caves for a long winter’s nap, is this really what happens in hibernation?
Learn about hibernation and how bears — and humans — can prepare for it from bear expert and Mutual of Omaha’s Wild Kingdom Co-Host Dr. Rae Wynn-Grant.
Why do animals hibernate in the winter?
Hibernation is a biological process where an animal’s body temperature drops very low and its metabolism slows way down. Though it’s commonly associated with bears, other animals such as frogs, bats, lemurs and hedgehogs also hibernate.
“For a lot of mammals that hibernate, there are certain seasons where whatever they eat isn’t available,” Dr. Rae said. “So, over an evolutionary timeline, their bodies have adapted to not being out and about the world during these times. Hibernation allows them to survive these extreme conditions.”
Hibernation is almost always related to cold weather when many plants go dormant and other animals burrow in their dens. The animals that depend on these food sources need to hibernate to conserve energy and survive.
Bears prepare for hibernation
Bear hibernation varies throughout the world, and not all bears hibernate in the winter. In warmer climates, such as southern California, bears may not hibernate because food sources are still available.
But for those that do, they must prepare for the winter with a process called hyperphagia. This is when bears attempt to build as much body fat as possible, usually in early fall, so that they can have plenty of fat to sustain them in hibernation.
One iconic example of hyperphagia is Fat Bear Week in Alaska’s Katmai National Park and Preserve. This internet phenomenon is a tournament-style bracket where fans can vote for their favorite “fat” bear — bears in the national park who enjoy the wild salmon as they build fat to survive the cold Alaskan winters. Because Alaska’s winters come early, Fat Bear Week happens in October, giving fans time to watch the bears on trail cams and cast their votes before the bears go into hibernation.
In other parts of the U.S., bear hibernation season may not begin until November or December. If you’re visiting an area where bears may be present, it’s important to be cautious as bears prepare for hibernation.
Bear dens: mama bear, baby bear
Bears are solitary creatures who will hibernate on their own, except for a mama bear. A female bear only gives birth during hibernation. All black bears have similar birthdays, with most cubs being born in January.
During the next hibernation season when the cubs are a year old, they’ll once again hibernate with their mother. But after they exit the den, all the bears will go off on their own.
Taking precautions during hibernation season
In bear country, it’s especially important before hibernation season to make sure your backyard or campsite is bear proofed. One way to keep bears away is to properly dispose of your trash and keep your food in bear-safe containers.
“These are peak times when we’ll find bears in people’s backyards because their literal biological instincts are saying, ‘you will die in a couple of months if you don’t eat everything in sight,’” Dr. Rae said.
Get more tips to camp among wildlife.
Another important tip is to stay on the trail because bears don’t hibernate in caves.
“For some reason, someone created this narrative that bears hibernate in caves, but caves aren’t a common thing,” Dr. Rae said. “They create their own hibernation dens under people’s decks, along riverbanks, under highways, in fallen logs. Sometimes they honestly lay down and let snow fall over them.”
Dr. Rae saw this while filming an upcoming Protecting the Wild episode, where she found a mama bear hibernating under a tree.
“This wasn’t some massive tree. I could put my arms around it if I wanted to!” Dr. Rae said. “It was a fallen tree, a giant bear and three cubs under it. It was a half mile from someone’s house in the remote area of a forest.”
If you plan to enjoy winter recreation, be mindful and stay on the trail because a path commonly traversed by humans likely won’t be a spot where bears choose to hibernate. And if you’re participating in other winter activities, such as snowmobiling and cross-country skiing, you’ll want to be cautious as well. You could be walking on top of a bear den!
“Because bears aren’t completely asleep as they’re always worried about their own safety, they could wake up if they’re disturbed and will abandon their den … which could be very problematic,” Dr. Rae said.
How do bears stop hibernating?
Scientists are still learning what exactly happens during hibernation and how bears emerge from it.
“There’s an inconsistency on how they come out or how they know to,” Dr. Rae said. “Some bears live in areas where there’s a lot of snow and it begins to melt and starts to flood the den. They get woken up by cold wet water. Other bears, their bodies just kind of get the signal.”
A signal could be changing temperatures in their environment or other biological factors. Plus, with their fat stockpile depleting, bears simply need to eat!
“It takes several days or a week for their metabolism to get back to where it once was,” Dr. Rae said.
And just as bears are starting to return, so are other animals and plants. At first, bears will only have a little bit of food available, allowing them to slowly increase their metabolism.
Oh, and those fat bears? They’re not so chunky when winter is over.
“Ideally, they have burned through all their body fat,” Dr. Rae said. “They should have a little excess because when they emerge in the spring, it might still be a bit snowy and there might not be a lot to eat.”
If you’re planning on visiting an area with native bears this fall or winter, be sure to check with the area’s wildlife department to make sure you’re prepared.
For more bear facts, check out this story with Dr. Rae about why winter is the best time to research bears. And learn about one bear species that never hibernates — the sloth bear.
Plus, watch the Mutual of Omaha’s Wild Kingdom Protecting the Wild episode, “Rescue, Rehab and Release,” to see the heartwarming story of two black bear cubs that return to the wild.
