Why do bears eat 20,000 calories a day before hibernation

It's the fall feeding frenzy that packs on the pounds before hibernation, building toward Fat Bear Week at Katmai.

4 days ago

Updated: September 20, 2026, 12:06 pm EDTPublished: September 20, 2026, 11:24 am EDT

A coastal brown bear rolling in a field of orange and red fireweed near the coast in Katmai National Park, Alaska. — A coastal brown bear rolls through a field of fall-colored fireweed along Kinak Bay in Katmai National Park, Alaska, part of the same hyperphagia drive fueling this year's Fat Bear Week contestants.
(Paul Souders/Getty Images)

Right now, a black bear near you could be trying to eat 20,000 calories a day. Neither the number nor the urgency behind it is an exaggeration. This is what fall asks of every bear headed into winter.

What's actually happening

The behavior is called hyperphagia, a pre-hibernation feeding frenzy that kicks in as daylight shortens and temperatures drop. Bears eat and drink nearly nonstop for weeks, some packing away 15,000 to 20,000 calories in a single day. Processing that much food takes water, too: bears in hyperphagia can drink up to to 2 gallons a day just to keep up.

(MORE: Humans don bear suits in adorable wildlife rehab effort)

Why the math works this way

Bears don't eat, drink or go to the bathroom during hibernation, so every calorie they'll burn over the winter has to be stored as fat before they den up. Hyperphagia is that stockpiling window, compressed into a few frantic weeks of near-constant foraging. It's also why bears lose some of their normal caution around people this time of year: the National Park Service warns that a bear that gets access to human food during hyperphagia can lose its natural food preferences altogether, making it bolder and more dangerous around people going forward.

A black bear walking along a street in a suburban neighborhood, with houses and a sidewalk in the background. — A black bear moves through a suburban neighborhood, the kind of encounter that becomes more common each fall as bears in hyperphagia search farther from their usual range for calories.
(Sean Davis/Getty Images)

Why bears are turning up closer to people right now

That's the same hunger showing up on your street. Throughout the country, bears in hyperphagia have been overturning trash cans, leaving scat on lawns, and setting dogs barking at night as they search neighborhoods for anything calorie-dense. It's not aggression. It's a bear working through the same 20,000-calorie problem it would be solving in the wild, just with easier targets.

(MORE: Man doesn't notice the bear behind him)

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The Fat Bear Week connection

Katmai National Park in Alaska turns that same feeding frenzy into a public event every fall. Its brown bears fatten up on salmon instead of trash cans, and Fat Bear Week lets the public vote, bracket-style, on which bear "did the best job packing on the pounds for winter." Last year's contest pulled in more than 1.7 million votes from over 100 countries, and 2025's champion was Bear 32, nicknamed "Chunk." This year's bracket dropped Thursday, with voting running Sept. 22-29.

A brown bear standing in a river, catching a salmon mid-leap. — A brown bear catches a salmon in Alaska, the calorie-dense catch that helps Katmai's bears pack on the pounds ahead of Fat Bear Week.
(Mantaphoto/Getty Images)

Weather.com Content Development Manager Joy Kigin chases stories where weather, science and culture meet everyday life, the kind that spark conversations and, now and then, a smile.

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