Every autumn, millions of people around the world gather online to celebrate a unique viral tradition: Fat Bear Week. Hosted by Alaska’s Katmai National Park and Preserve, this annual tradition is a single-elimination tournament that invites the public to cast votes for the brown bears of the preserve.
Fat Bear Week originally began as Fat Bear Tuesday in 2014, when former Katmai National Park ranger Mike Fitz noticed Facebook users posting side-by-side photos comparing brown bears’ midsummer bodies to their fall seasonal weight gains.
To highlight their transformations, Fitz created an online contest where users voted for their favorite bear by liking the photos. This competition was won by Bear 480, better known as Otis.
Driven by overwhelming public interest and engagement, organizers expanded the single-day event into the first week-long Fat Bear Week in 2015.
While the March Madness-Esque bracket is lighthearted and fun, the bears’ seasonal weight highlights a crucial biological process called hyperphagia. During hyperphagia, bears enter a period of extreme feasting. Usually, bears feast on salmon to store the life-saving energy required for harsh winters.
The bears typically enter this stage during mid-summer and will spend weeks foraging for up to 22 hours a day, according to Friends of the Bridger-Tenton.
Most bears hunt alongside Katmai’s Brook River. This river hosts one of the healthiest, most abundant salmons runs left on Earth. Thousands of salmon swim upstream, and the bears congregate at the Brooks River to feast on fatty salmon, eggs and skin, consuming tens of thousands of calories per day.
The National Library of Medicine states that during winter hibernation, bears spend four to six months without eating, drinking or exercising. For them, gaining extra weight is not a luxury, it’s a matter of life or death. To stay alive, their bodies burn stored fat for energy, causing them to lose up to one-third of their body weight by spring.
Toward the fall season, the bears gradually wind down their binge-eating and eventually stop. They continue drinking fluids and flushing out waste. Around this period, Fat Bear Week begins. This year’s competition ran from Tuesday, Sept. 22 to Tuesday, Sept. 29.
Voters compared photos of the bears from when they were slim in late summer to their current massive look.
In early summer, adult male bears typically weigh 600 to 900 pounds, depending on population numbers and food availability. By autumn, they are typically 1,000 pounds. The female bears, also known as sows, weigh around one-third less than males in mid-summer. In the fall, they weigh around 400 to 700 pounds.
The four semi-finalists for Fat Bear Week 2026 were: The 132 Family, Bear 910, Bear 89 (also known as “Backpack”) and Bear 164 (also known as “Bucky Dent” or “Bucky”). Although voters learn fun facts about the bears, their specific weights are not shared.
The 132 Family features a large adult female with grizzled dark brown fur, forward leaning ears and a wide belly. Her face is distinguished from other bears by the inverted “V” of dark fur on her forehead. She is a recent mother to her fourth litter of cubs, and although her weight isn’t specified, she is a top contender for Fat Bear Week.
Bear 910 is a female brown bear, first identified in 2019 at the Brooks River in Katmai National Park and Preserve. She is recognized for her large, blond, floppy ears. Bear 910 recently made wildlife history in 2023 by adopting her sister’s cub. Besides this, she gained an impressive amount of weight, making her another top contender for the competition.
Backpack is an adult male bear known for climbing onto his mother’s back when he was a cub as they waded through the Brook. Unlike most of the many dominant, aggressive bears in the tournament, Backpack is known for a remarkably docile and non-confrontational temperament.
The last bear to mention is Bucky, a large adult male who has grizzled brown fur and blond-tipped ears. Many find it easy to identify him by the line of darker fur near his eyes and upper muzzle.
Bucky was first identified as an independent 2.5-year-old in 2019 and has risen in dominance over the years. Productive fishing spots are often limited at the Brooks River, especially for young bears. Bucky challenges other bears for preferred fishing spots and dominance, even when no fishing spot is in dispute.
Male brown bears in Katmai usually reach their peak size and strength when they are about 12-20 years old. Bucky is estimated to be only 9 years old, so there’s a good chance he could grow even larger and more dominant.
Win or lose, every bear in the bracket has accomplished what matters most: packing on the life-saving fat needed to endure the harsh months ahead. As the voting closes and the bears head into hibernation, Katmai’s champions leave behind an eager online audience to watch their impressive transformations begin all over again next summer.