Climate change may disrupt how the grizzlies of Fat Bear Week sleep


Fat Bear Week 2022 celebrates grizzlies preparing for hibernation, but climate change may alter their sleep

It’s Fat Bear Week — an annual, very online, celebration where you can vote for your favorite “chonky bears” in Katmai National Park and Preserve starting Wednesday, while watching the animals stuff themselves silly before they hibernate.

But enjoy Fat Bear Week while it lasts, because climate change may be altering grizzly bear habits — including when and how long they hibernate, what they eat and where they roam.

Bear sitting in some green brush at the edge of a wooded area

Warmer temperatures mean a shorter nap time

Grizzly bears, technically a subspecies of brown bears, may face shorter hibernation periods because of climate change, according to a 2016 study published in Behavioral Ecology and Sociobiology.

The researchers found that bears’ cue to leave their dens is tied to temperature. When spring average monthly maximum temperatures increased by four degrees Celsius (7.2 degrees Fahrenheit), bears emerged 10 days earlier, but delayed leaving their den by a week with a 1.25-meter (4 foot and 1.25 inch) increase in snowfall.


Another factor: food availability. When berries are ready to eat (and when they’re not) generally drives when bears go into their dens for the winter, the study found. When more berries are available during the fall because of milder weather and extended growing seasons, bears will delay hibernation.

… And more bear/human contact

In North America, human-brown bear conflicts are increasing in areas where bears are expanding into private lands bordering national parks, posing a threat to livestock and people, according to the authors of a 2014 study on global bear-human conflicts in the journal Conservation Letters.

This growing range and shorter hibernation periods could mean bears and humans are interacting in the same areas for longer amounts of time, the authors of the 2016 study wrote. And while this may sound more dangerous for the people than the bears, humans are actually the primary driver of grizzly deaths worldwide.

And what bears eat (and don’t eat) affects the whole food cycle

Most of us have seen pictures of grizzly bears up to their thighs in rivers, catching and eating salmon. But it turns out, bears, if given the choice, actually prefer berries.

In Alaska’s Kodiak Island, just southwest of Katmai National Park and Preserve, dozens of Kodiak brown bears typically feast on salmon (which are plentiful). But during a particularly warm summer in 2014, the bears were nowhere to be found, Inside Climate News reported. During the peak salmon run, the bears were instead found munching on red elderberries.


A 2017 study published by the Proceedings of the National Academy of Sciences suggested that climate change is altering the timing of seasonal events, which means that different species interact at different times of year than they did before.

Typically, brown bears eat salmon earlier in the season before switching to berries. In this case, when the brown bear suddenly had berries and salmon available at the same time, it opted for the berries, which require less energy to breakdown and allow the bears to grow more quickly. This phenomenon also likely happened two years later, after the study concluded.

A bear in whitewater currents trying to catch a flapping fish in its mouth

What’s the result? A disrupted food web. Fewer salmon, for instance, were killed off by the bears, who typically decimate up to 75 percent of the population, Inside Climate News reported. “The reduction in salmon deaths would likely benefit the salmon population but could imperil other parts of the island’s ecosystem that derive nutrients from the salmon carcasses that are dragged onto shore by the bears,” Phil McKenna, the article’s author, wrote.

What does this mean for future Fat Bear Weeks?

It’s tough to say.

“We have not specifically seen impacts of climate change on the bears yet,” Amber Kraft, an interpretation and education program manager at Katmai National Park and Preserve, wrote in an email. Currently, the park isn’t monitoring when bears enter and exit their dens, so it’s possible they may not immediately notice changes.

“We do know that salmon are especially vulnerable to increased temperatures and reduced precipitation and whatever affects the salmon, will affect the bears of Brooks River,” Kraft wrote. “With increased temperatures, salmon are less likely to leave the coolness of the lakes to venture upstream to the bears and to spawn. Acidification of the oceans continues to affect all of its fishes, including salmon. Streams may dry up and the salmon will be unable to reach their native streams to spawn.”

Three bears standing in whitewater currents in a river

A declining bear population will likely follow a declining salmon population, she wrote. Loss of the salmon population could also pose a concern for human-bear contact. “Coastal brown bears are much more tolerant of people, largely due to abundant natural foods,” Kraft wrote. “If those foods disappear, they are much more likely to have negative interactions with people.”

“While Bristol Bay still boasts one of the healthiest runs in the world, climate change affects the ocean, rivers, and lakes the salmon depend on,” Kraft added. “There is a delicate balance in the Brooks River ecosystem and the competition for resources, which could have adverse effects on not only the bears, but the other fish and animals.”

But for now, the bears of the Brooks River in Katmai National Park and Preserve have been feasting on salmon in their final preparation for winter, and thousands of voters are ready to celebrate their success. In this single-elimination style tournament, only one bear will be crowned reigning champion on Fat Bear Tuesday, which, this year, falls on Oct. 11.

Since the inaugural event, 480 Otis — an angler known for unmatched ability to conserve energy by letting the salmon come to him, once catching 42 fish in a single go that way — has claimed the title four times, more than any other bear. He won most recently last year, when roughly 800,000 people cast their vote, which doesn’t even include the number of votes cast in the Fat Bear Junior competition for fattest cubs, Kraft said.


As of Wednesday, voting is open. Happy Fat Bear Week to all those who celebrate!

Thanks to Lillian Barkley for copy editing this article.

  • Anna Deen
    Anna Deen

    Data Visualization Reporter

    Anna Deen is a data visualization reporter at Grid.