Fat Bear Week: How Brown Bears Get Ready for Winter
Get the inside scoop on how Alaska’s giant brown bears pack on hundreds of pounds to survive winter hibernation, and meet the heavyweight contenders of Brooks Falls!
Cast Your Ballot for Fattest Bear!
Who packed on the most impressive winter pounds at Brooks Falls? Tap to vote!
Bear 747
"The Jumbo Jet"Est. 1,400+ lbsBear 480 (Otis)
"Zen Master of Brooks Falls"Est. 1,150 lbsBear 128 (Grazer)
"Fierce Salmon Matriarch"Est. 1,000 lbsBear 151 (Walker)
"The Waterfall Acrobat"Est. 1,100 lbsA thousand-pound brown bear named Walker stands patiently on a rocky ledge at the top of Brooks Falls in Alaska’s Katmai National Park and Preserve. Around him, a dozen other massive bears wait with wide-open jaws as silver sockeye salmon leap up and over the six-foot-tall waterfall. SNAP! With lightning speed, Walker catches a wriggling fish mid-air. Welcome to the biggest wildlife eating spectacle on Earth!
On-Camera Snacking at Brooks Falls
The bears don’t know it, but throughout July, August, and September, they are being watched, studied, and cheered on by millions of people across the globe via live wildlife cameras. It looks like an all-day pie-eating contest, but for brown bears, packing on the pounds is serious survival business.
To survive the freezing sub-zero Alaskan winter, brown bears must build up enough thick body fat to sustain them for up to seven months without eating, drinking, or even leaving their dens. When the annual feeding frenzy kicks off in July, adult male bears weigh between 600 and 900 pounds. By the time Fat Bear Week arrives in October, the chunkiest contenders tip the scales at over 1,400 pounds!
🍔 The Wild Cheeseburger Math
A single fresh sockeye salmon swimming upstream contains approximately 4,500 calories. That is equivalent to eating nine fast-food cheeseburgers in one fish!
A hungry adult brown bear can catch and devour 30 to 40 salmon every single day. That means during peak feeding season, a Katmai bear consumes nearly 180,000 calories per day—the same energy as eating 360 cheeseburgers daily!
Hyperphagia: The Brain’s Eating Superpower
How does a bear eat 40 salmon in an afternoon without feeling completely stuffed? In late summer, bears enter a remarkable physiological state called hyperphagia (pronounced hi-PER-fay-zhuh).
During hyperphagia, biochemical signals in the bear’s brain temporarily turn off the sensation of fullness. Their metabolism shifts into overdrive to convert nearly every bite of protein and healthy omega-3 fatty acids directly into energy-dense blubber. Bears will forage and fish for up to 16 hours a day!
Spring Weight
600 – 800 lbs
Autumn Fat Bear
1,200 – 1,400+ lbs
Winter Slumber
5 to 7 Months
Light Hibernation: Sleep With One Eye Open
You might think hibernation means being frozen solid until spring, but brown bears actually experience torpor (light hibernation). While smaller mammals like marmots and chipmunks go into deep hibernations where their body temperature drops almost to freezing, a brown bear stays warm and ready for action.
- Heart Rate Drops: From a normal 70 beats per minute down to just 8 to 12 beats per minute.
- Breathing Slows: A resting bear may take just one or two breaths every minute.
- Body Temp: Drops only about 10°F, remaining warm enough that mother bears can nurse and care for newborn cubs born inside the den in January!
- Zero Waste: Bears do not eat, drink, urinate, or defecate for months. Their bodies recycle urea into amino acids to maintain strong bones and muscle tissue without exercise!
Meet the Contenders of Katmai
Every October, Katmai park rangers choose 12 famous brown bears for a single-elimination tournament bracket where fans vote online for the most impressive transformation. Meet some of the legendary heavyweights:
Bear 747 — "The Jumbo Jet"
True to his airliner nickname, 747 is one of the largest brown bears ever documented on Earth. Weighing over 1,400 pounds, his stomach hangs so low it practically skims the riverbed! He dominates the prime fishing spot called "The Jacuzzi" at the base of the falls.
2x Fat Bear Week ChampionBear 480 — "Otis the Zen Master"
Now an elderly elder bear in his late 20s, Otis has missing teeth and moves slowly, but he is a master of patience. Instead of chasing salmon, he sits calmly in his favorite shallow eddy and scoops fish up as they swim past him.
4x Fat Bear Week ChampionBear 128 — "Grazer the Fierce"
One of the most formidable female bears on the river. Grazer is a devoted mother bear who will fearlessly charge bears twice her size to protect her cubs and secure the best salmon pools.
Fan Favorite ContenderWhy Fatness Means Ecological Victory
While Fat Bear Week is hilarious and fun to watch, it represents one of the healthiest wild ecosystems left in North America. Katmai National Park has over 2,200 brown bears—more bears than people on the entire Alaskan Peninsula!
Because Bristol Bay’s rivers are completely undammed and protected from industrial pollution, millions of wild salmon return each summer. Without clean water and healthy salmon runs, these magnificent bears couldn’t survive. So when you cast your vote for your favorite fat bear, you are also celebrating clean rivers and protected wilderness!
