Arctic Brown Bears Push Their Bodies to the Max

A new study reveals a delicate hibernation balancing act.

By the editorial staff of Park Science magazine

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About this article

This article was originally published in the "Research Roundup" section of Park Science magazine, Volume 39, Number 2, Summer 2025 (August 29, 2025).

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Brown bear wandering the tundra looking for food before it dens for the winter.

Image credit: NPS / Erika Jostad

As apex predators, brown bears occupy a key role in Arctic ecosystems: their fate can tell us how these systems are doing overall. Hibernation is a vital part of every bear’s life cycle, and their health depends on it. But some bears live near or above the Arctic Circle, where winters are particularly long and fierce.

A team of scientists did a study to find out how Arctic brown bears decide when to begin hibernating and when to emerge. They published their results in the journal, Wildlife Biology, in February 2025. Their findings show that some individuals hibernate almost as long as theoretically possible.

The bears in the study hibernated for 206 days on average. But incredibly, one bear hibernated for 233 days—a full 64 percent of the year. When there was lots of food in the fall, bears delayed entering their dens. Females with cubs stayed in their dens longer in the spring, with late snowmelt also delaying den exits. Pregnant females chose dens at higher elevations where snow would remain until later in the season. The authors suggest this could be because the bears anticipated they would need to hibernate longer.

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Deacy and others. 2025. Denning chronology in an Arctic brown bear population. Wildlife Biology.