Creature Feature Fridays: Meet the Mighty Grizzly Bear

Welcome to Creature Feature Fridays! Each week, in partnership with the incredible wildlife photography of Julia Cook, we’ll take you into the heart of the Greater Yellowstone Ecosystem- introducing you to the fascinating creatures that roam our backyard. From bears to bison, moose to marmots, and every wild track in between, our goal is to bring you closer to the wild creatures that make Yellowstone’s wildlife so unforgettable.

This week’s spotlight is on one of Yellowstone’s most iconic and awe-inspiring animals: the grizzly bear. A symbol of strength, wilderness, and the enduring spirit of the West, grizzlies are powerful, intelligent, and full of surprises. Let’s dig into some of the most amazing things about them.

#1 They’re Big—and Surprisingly Fast!

Grizzly bears are among the largest land mammals in North America. Males in the Greater Yellowstone Ecosystem (GYE) typically weigh between 300–700 pounds, with females ranging from 200–400 pounds. Some individuals tip the scales even more—the heaviest recorded in Yellowstone weighed 715 pounds, with a close runner-up named “Grizzly 566” weighing 712 pounds.

Despite their size, grizzlies are surprisingly agile. They can run up to 40 miles per hour, though not for long distances. Still, their ability to sprint and maintain speed in bursts makes them highly effective predators, especially when pursuing prey like elk calves or small mammals.

Grizzlies also stand about 3.5 feet tall at the shoulder when on all fours and can live 15 to 30 years in the wild. Their sheer presence in the landscape is nothing short of majestic.

#2 That Big Shoulder Hump? It’s All Business.

One of the easiest ways to distinguish a grizzly from a black bear is the prominent hump over its shoulders. That hump is made entirely of muscle and gives grizzlies the strength to dig dens, uproot plants, flip rocks, and even move logs and boulders in search of food.

Grizzlies also have longer, more curved claws than black bears—adapted for digging rather than climbing (though they can climb trees when young or lightweight). Their build is perfectly suited for life in Yellowstone’s forests and meadows.

#3 Grizzlies Love a Good Buffet! They Eat Just About Everything.

Grizzly bears are opportunistic omnivores with an impressively varied diet. In the Greater Yellowstone Ecosystem, they’re known to consume at least 266 species across four animal kingdoms. Their diet includes plants (67%), invertebrates (15%), mammals (11%), along with fish and fungi.

They forage for roots, berries, grasses, pine nuts, army cutworm moths (found in high alpine areas), cutthroat trout, rodents, and carrion from bison, elk, moose, and deer. They'll also seek out garbage or human food if it's accessible—hence the importance of bear-aware practices in the park.

Grizzlies are not picky eaters—whatever helps them pack on the pounds for hibernation, they’ll find it. Yellowstone offers a rich and diverse food supply, which has helped sustain and recover the local population.

#4 Hibernation: Nature’s Superpower.

Grizzlies are considered super hibernators, and for good reason. They enter dens from late fall through early spring, remaining inside for up to 7 months without eating, drinking, urinating, or defecating. Yet, their body temperature only drops by about 12°F, allowing them to react quickly if disturbed.

Inside the den, respiration slows to 1 breath every 45 seconds, and the heart rate drops from 40–50 to just 8–19 beats per minute. To survive, they metabolize fat stores, but in a remarkable twist, their bodies recycle nitrogen from urea into protein, helping them maintain muscle and organ mass.

Dens are typically dug on north-facing slopes at 6,500 to 10,000 feet in elevation, often under large trees or in deeply vegetated areas where snowfall helps insulate against frigid temps. Bears may move up to one ton of earth in 3–7 days to create a den chamber just large enough to curl up inside—then line it with bedding like spruce boughs to retain heat.

#5 Fierce, Devoted, and Full of Wisdom—Mama Bears are Amazing!

Grizzly bears are known for their intense devotion to their cubs. After mating in the spring, a female grizzly will delay the implantation of her fertilized egg until fall—an adaptation that ensures she only carries her pregnancy to term if she has built up enough fat reserves. She’ll then give birth in her winter den, typically to one to three cubs. Cubs are tiny at birth, weighing less than a pound, and rely on their mother’s warmth and milk to survive the harsh winter months.

While most litters consist of one to three cubs, a four-cub litter is extremely rare, documented only 11 times since grizzly bear monitoring began more than 50 years ago. Even more rare is a litter of five cubs, spotted in 2024—the only known occurrence in Yellowstone’s recorded history from 1959 to present. Scientists believe this unusual event may have been the result of cub adoption—a behavior that has been documented through genetic analysis. In this case, two mother bears with cubs were seen in close proximity, and the mixing of young may have resulted in one female “adopting” cubs from the other. Regardless, this is impressive and speaks to the social complexity of grizzly behavior.

Despite their strong maternal instincts, only about 49% of grizzly cubs survive their first year. Predators, harsh weather, food scarcity, and other bears (including males) pose constant threats. That makes every surviving cub a testament to a mother’s tireless effort to teach, defend, and feed her young.

A legacy on Four Paws: Grizzly Bear #399

One of the most famous and beloved bears in the Greater Yellowstone Ecosystem was Grizzly Bear #399, a true matriarch whose life left a lasting legacy. Born in 1996, #399 lived to be 28 years old, making her one of only 12 grizzly bears documented in the region to reach that age or older—just 0.6% of all bears studied by the Interagency Grizzly Bear Study Team since 1973.

#399 wasn’t just known for her longevity. She was the oldest documented grizzly in the GYE to reproduce, giving birth to a cub in 2023 when she was 27 years old. Over her lifetime, she produced an incredible 18 offspring, including a litter of four cubs in 2020—a rare occurrence that made her one of just 14 grizzlies to have quadruplets since records began in 1959.

Her presence just outside Grand Teton National Park drew photographers, wildlife watchers, and conservationists from around the world. She became a symbol of hope and resilience, showing that with the right protection, grizzlies and humans could coexist. Tragically, Grizzly #399’s remarkable journey came to an end on October 22, 2024, when she was killed in an accidental vehicle collision about 40 miles south of Grand Teton. Her legacy lives on in her offspring—and in the many lives she touched.

#6 Yellowstone is One of Their Last Wild Strongholds.

Grizzly bears once ranged across most of the western United States, but due to habitat loss, human conflict, and unregulated killing, their numbers declined sharply. In 1975, they were listed as a Threatened Species under the Endangered Species Act.

Today, the Greater Yellowstone Ecosystem and northwest Montana are the only places south of Canada where large grizzly populations remain. Thanks to conservation efforts, Yellowstone’s grizzly population has rebounded—from about 136 in the 1970s to an estimated 965 as of 2022. Roughly 150–200 grizzlies have home ranges that include Yellowstone National Park.

Still, grizzly bears require vast home ranges—800–2,000 square miles for males, 300–550 square miles for females—and the overlap between bear habitat and human activity presents ongoing challenges. That’s why efforts to reduce food attractants and educate the public are critical to ensuring humans and bears can coexist peacefully.

Whether you see them in the wild or admire them from afar, grizzly bears are a living symbol of Yellowstone’s untamed spirit. Their resilience, adaptability, and strength continue to inspire wonder—and remind us just how wild this corner of the world still is.

Thanks for joining us for the very first Creature Feature Friday! Stay tuned next week as we introduce another incredible Yellowstone local—paired with more breathtaking photos from Julia Cook Photography.

Visit Julia Cook's Website to view her other amazing work!