Awake in Winter: How Climate Change is Disrupting Black Bear Hibernation

Imagine stepping outside on a crisp winter morning and spotting a black bear rummaging through your trash can. Snow blankets the ground, and the air is chilly—conditions we associate with bears being fast asleep in their dens. But increasingly, that’s not the case. Across North America, black bears are staying awake longer into winter or skipping hibernation altogether. So what’s going on?

It turns out that warming winters, driven by climate change, are reshaping the natural behaviors of many species, including black bears. These changes are having profound impacts on ecosystems and leading to more frequent encounters between bears and humans.

Why Would Bears Be Awake in Winter?

Hibernation is one of nature’s most fascinating survival strategies. For bears, it’s not quite the deep sleep we imagine. Unlike “true hibernators” such as bats or ground squirrels, whose body temperatures drop dramatically during hibernation, black bears maintain near-normal body temperatures while slowing their metabolism and reducing their heart and breathing rates. This state allows them to conserve energy during the cold months when food is scarce.

To prepare for hibernation, bears enter a period of hyperphagia in late summer and fall, consuming up to 20,000 calories per day to pack on the fat reserves that sustain them through the winter. Once in their dens, they rely on those reserves, burning up to 4,000 calories daily while their heart rates drop to around eight beats per minute. Typically, black bears hibernate from around September to April, depending on their location.

Warming winters are throwing this delicate balance off course. Hibernation behavior, which for bears is intricately tied to cold temperatures and the seasonal availability of food, is being upended. As winter minimum temperatures rise, black bears are spending fewer days hibernating. Research shows that with every 1°C (1.8°F) increase in regional winter temperatures, they stay awake an additional six days on average. By mid-century, it’s expected that black bears could remain active for 15 to 39 more days each year—a dramatic shift with significant implications.

By 2050, black bears could be awake for an extra month every year on average.

What a Warming Winter Means for Black Bears

If bears stay awake too long, wake too early, or skip hibernation entirely, they face a significant problem: food scarcity. In winter, natural fall food sources like berries and nuts are unavailable, and spring vegetation hasn’t yet emerged. Bears that expend energy without replenishing it may burn through their fat reserves too quickly, leading to malnutrition or starvation.

These challenges are compounded by other climate-related changes. Reduced snowpack, another symptom of warming winters, leads to earlier stream drying and lower summer water levels. This reduces the availability of the plants and other resources bears rely on to build fat stores in the first place. In short, warm winters not only disrupt hibernation but also affect bears’ ability to prepare for it.

Sharing Winter with Black Bears

As bears face greater challenges in finding natural food, they’re increasingly turning to human settlements for easy meals. Garbage cans, bird feeders, and even cars with leftover fast-food wrappers can all attract hungry bears. These encounters often lead to conflict, which rarely ends well for the bear. Bears that become too accustomed to human food sources are more likely to be euthanized or relocated—a solution that’s both costly and stressful for the animal.

In places like Colorado, these conflicts are already becoming more frequent. Mild winters and growing urbanization are bringing bears closer to human activity year-round, leading to more calls about bears raiding trash bins or wandering into backyards, even in the cold season. Addressing these conflicts is essential not only for human safety but also for the well-being of bear populations.

Keeping Hungry Bears at Bay

If you live in bear country, you might not usually expect to worry about them in the winter. But as warming winters begin to keep bears awake, it’s more important than ever to take steps to discourage bears from approaching your home or campsite even during these colder months. Here are a few tips:

• Secure Your Trash: Keep garbage inside until collection day or use bear-proof containers.
• Take Down Bird Feeders: While birds need food in winter, feeders can be irresistible to bears.
• Keep Cars Clean: Don’t leave food or scented items like gum or wrappers in your vehicle. Keep doors locked.
• Practice Safe Camping: Store all food, toiletries, and scented items in bear-proof containers, and never keep them in your tent.
• Be Prepared Outdoors: Carry bear spray when hiking and use bear bells to alert wildlife to your presence.
• Control Pets: Keep dogs leashed and under control to avoid startling a bear.

Remember, most black bear encounters are non-aggressive. Bears typically avoid humans, but hunger can make them more determined. By following these steps, you can help reduce conflicts and keep both bears and people safe throughout the year.

Turning Conflict into Coexistence

Warming winters are reshaping the natural rhythms of wildlife, and black bears are just one example of how climate change is creating new challenges for animals and humans alike. But with awareness, preparation, and respect, we can learn to share our changing world with bears.

It’s important to remember that these conflicts are ultimately a symptom of larger environmental issues. By addressing climate change and supporting conservation efforts, we can help restore the balance of ecosystems and give bears the resources they need to thrive in the wild. We can work together to turn conflict into coexistence—a win for us, for bears, and for the planet.

This article by Braelei Hardt was first published by The NWF Blog on 24 January 2025. Lead Image: Credit: Gabe Ginsberg/GettyImages.

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