Why Alaska’s Bears are Waking Up Mid-Hibernation

One of the great marvels of nature is how bears, the largest carnivore in North America, are able to hibernate all winter, living off stores of fat they have built up through the rest of the year. Alaska has well over 130,000 bears, so winter is a welcome respite to their prey. But in recent years, more and more bears have been groggily waking up from hibernation early, staggering across the landscape and sometimes into towns looking for food. And often, they just stay up and go full-blown springtime mode as early as January. Explore with us why the bears are suddenly craving midnight snacks during the long, dark Alaskan winters and how it affects their place in the environment.

Alaska’s Three Bears

Alaska has three distinct bear species, each adapted to thrive in the extreme terrain and climate of the far north. Bears can be found in the northern rainforests along Alaska’s panhandle, the interior forests and mountains, and the treeless Arctic. They are second only to humans as apex predators in the region, and play a crucial ecological role in keeping down species of prey animals, fertilizing the forest floor with carcasses and fish scraps, and distributing seeds through their scat.

Black bear (Ursus americanus)

The black bear (Ursus americanus) is the most widely distributed bear species and is found across North America. According to the Alaska Department of Fish and Game, there are about 100,000 black bears in the state. They can weigh anywhere from 90-600 pounds and stand about 3 feet high at the shoulder. They eat berries, grasses, roots, insects, fish, carrion, bird eggs, and small mammals. They’re also attracted to towns where they can find garbage and pet food around houses. They usually hibernate as early as October and as late as May. Females give birth during hibernation. Black bears don’t hibernate as deeply as smaller mammals, such as ground squirrels, so they can easily wake up if disturbed during the winter by changing temperatures or noises outside their dens, like other animals scrounging around or loud storms.

Brown bear (Ursus arctos)

Anywhere from 30-35,000 brown bears (Ursus arctos) inhabit Alaska. This includes grizzly bears, a subspecies of the brown bear. Brown bears grow larger in coastal areas of Alaska than inland, they can reach 300-1,500 pounds, and they are generally 3.5-5 feet tall at the shoulder. Their habitat includes Alaska, western Canada, and the northwestern United States as well as Europe and Asia. In Alaska they hibernate from as early as October and remain in their dens as late as May. Like black bears, they give birth while hibernating and can be easily awakened due to the higher body temperature they maintain than other hibernating mammals, keeping their hibernation light.

Polar bear (Ursus maritimus)

Polar bear (Ursus maritimus) are the largest carnivores on the planet, weighing 900-1,600 pounds and measuring 4-5.3 feet at the shoulder. They are found all around the Arctic coastlands, including Alaska, Canada, Greenland, and Russia. About 4,000-7,000 live in Alaska. This species doesn’t hibernate in the winter, as this is prime hunting season for them to catch seals out on the sea ice pack. The only exceptions are pregnant females who go into semi-hibernation to give birth. Climate change is causing Arctic sea ice to melt earlier and freeze later, so polar bears are spending more time on land. In Alaska and Russia, observers have seen polar bears stalking and killing reindeer, which are not their usual prey.

Grumbly in the Tumbly

Wildlife officials in Alaska have noted an increase in reports of bear sightings earlier in the year than normal. Grouchy bears have been leaving their dens in the dead of winter searching for food, and fighting with each other just like it was spring. This unexpected behavior is especially dangerous for hunters, rangers, and homeowners in wilderness areas who may be taken by surprise more easily by bears who should be sleeping.

Not Just Alaska

Early-rising bears are not a problem unique to Alaska. Half a continent away in Ontario, Canada, the staff of Bear Creek Exotic Wildlife Sanctuary have had a chance to study the behavior of three black bears for years and have seen firsthand what happens when hibernation ends early. Raised in captivity before their rescue, these bears are not suitable for release in the wild but have a safe home at Bear Creek, a donor-funded organization.

Mary Barros, Executive Director and Director of Animal Welfare at the Sanctuary attributes briefer hibernation to mild weather. “Typically the two females never woke up through hibernation unless it was a really sunny warm day,” she says. “The male would come out sometimes to drink water and go back in his den. Last year, the temperature rose above 44 degrees F in January, and they all woke up and refused to go back down. So we had to start feeding them and spring started really early for them. Fortunately, this winter we got a lot of snow so it has been a more normal hibernation this year.”

Rising Temperatures

Mary’s observation reflects a scientific consensus. Field observations indicate that above-average temperatures disrupt the bears’ natural hibernation cycles. Researchers found that black bears in Colorado left hibernation on average 3.5 days earlier for every 34 degrees F increase in the average minimum temperature in spring.

Milder winters and early-warming springs can make dens feel uncomfortably warm. Moreover, melting snow and ice and spring thunderstorms can cause dens to flood and rudely awaken bears from dormancy. The noise of storms and the activity of birds and other animals in the area on unseasonably warm days also trigger bears to wake up. The altitude of the den has a lot to do with it, as dens higher in the mountains may stay more reliably cold through the whole season.

Physiological Issues

One brown bear study found that bears tend to start hibernation based on their environment but end it based on their internal physiology. Temperature and the timing of the first snowfall influence when bears retreat into their dens. In hibernation, their bodies adjust to the ambient temperature and reach normal levels when the temperature reaches freezing — around 32 degrees F. Thus, warm days can easily rouse them to early foraging and fighting.

Food Availability

If food is available to them when they get up, it incentivizes bears to stay awake. Hibernation is nature’s way of keeping bears alive through the winters when food is scarce. That’s especially important because so much of these omnivores’ diet comes from berries and greenery. That kind of food just isn’t available in winter.

However, sustained warmer temperatures can change things. Less snow cover means bears can dig for roots more easily. It also lets plants start producing tender shoots and berries earlier in the spring. Insects are a big part of their diet, too. If warmer temperatures cause insects to hatch early, bears are all about it.

Bears also raid towns and farms for garbage or livestock for a more reliable food source. Human-sourced bear food is a year-round problem. It can keep some bears awake—even if a warm spell is followed by weeks of typical winter cold.

The Impact of Early Rising

Early rising awakens bears at a time when food sources are still tenuous. The temperatures can still be reversed by more seasonable weather. Thus, they may deplete their fat reserves too quickly and become malnourished. This makes them vulnerable to disease and incentivizes them to come dangerously close to human settlements in search of food. In places where food is more reliable, bears can become obese. Eating a lot without using up their winter fat first can pack on the pounds. And like people, bears can get diabetes and other obesity-related problems.

The presence of major predators also affects the habits of prey species and the natural environment in unexpected ways. For example, when wolves were re-introduced into Yellowstone National Park, deer, and elk became more cautious about grazing in open meadows near the river, sticking to more deeply wooded areas instead for cover. This allowed trees to start returning to the meadows, stabilizing the river banks and helping with flood control. Similarly, prey animals of bears adjust their behavior depending on when and where they might be in most danger of becoming lunch.

No Easy Fixes

This is a problem that really doesn’t have a solution at the local level. It’s a part of climate change. And it’s not likely to be reversed, even if all countries aggressively controlled carbon emissions. Bears, their prey, and people will have to adapt to a new, warmer world.