Brown (Grizzly) Bear

As of January 2009 . . .

  • Number in Yellowstone ±150 with home ranges wholly or partially in park; ±600 in Greater Yellowstone Ecosystem.
  • Where to see:  Dawn and dusk in the Hayden and Lamar valleys, on the north slopes of Mt. Washburn, and from Fishing Bridge to the East Entrance.

Behavior & Size

  • Males weigh 300–700 pounds, females weigh 200–400 pounds; adults stand about 31⁄2 feet at the shoulder.
  • May live 15–30 years.
  • Home range: male, 813–2,075 square miles, female, 309–537 square miles.
  • Agile; can run up to 35–40 mph.
  • Can climb trees but curved claws and weight make this difficult.
  • Adapted to life in forest and meadows.
  • Food includes rodents, insects, elk calves, cutthroat trout, roots, pine nuts, grasses, and large mammals.
  • Mates in spring; gives birth the following winter; 1–3 cubs.
  • Considered true hibernators.


  • Yellowstone is one of only two major areas south of Canada still inhabited by grizzly bears.
  • In 1975, the grizzly bear was listed as a threatened species under the Endangered Species Act.
  • In 2007, the grizzly bear population in the Yellowstone ecosystem was delisted from the federal threatened species list.

The grizzly bear (Ursus arctos horribilis) is a subspecies of brown bear that once roamed the mountains and prairies of the American West. Today, the grizzly bear remains in a few isolated locations in the lower 48 states, including Yellowstone.

The name “grizzly” comes from silvertipped or “grizzled” hairs on some animals’ coats. However, the coloration of black and grizzly bears is so variable that it is not a reliable means of telling the two species apart. Particularly when bears are not fully grown or when seen only briefly or at a long distance, it can be difficult to correctly identify one bear species from another.

It is commonly said that grizzly bears cannot climb trees. This is not true, especially when the bears are small. As grizzlies increase in size and as their claws grow longer, they have a harder time climbing. Stories that bears cannot swim or run downhill are also wrong.

Grizzlies can sprint up to 40 miles per hour.  Bears are generally solitary, although they may tolerate other bears when food is plentiful. Mating season occurs from mid-May to mid-July, and bears may mate with multiple partners during a single season.  Females do not breed until at least age 4 or 5. Bears experience “delayed  implantation,” meaning that the embryos do not begin to develop until late November or December. This appears to be a strategy allowing the mother bear to save up energy until entering her winter den, where the cubs are born in late January or February.

A litter of one to three cubs is common, litters of four cubs occur  occasionally. Male bears take no part in raising cubs and may pose a threat to younger bears. A mother grizzly will usually keep her cubs with her for two winters following their birth, after which time she (or a prospective suitor) chases the subadult bears away so she can mate again. Female cubs frequently establish their home range in the vicinity of their mother, but male cubs must disperse farther in search of a home.

They can be effective predators, especially on such vulnerable prey as elk calves and spawning cutthroat trout. They also scavenge meat when available, such as from winter-killed carcasses of elk and bison, from road-killed wildlife, and from wolves and cougars. They eat small mammals (such as pocket gophers) and insects (such as ants and army cutworm moths that summer on high-elevation talus slopes), both of which provide important, high-protein food. A grizzly’s long claws and strong shoulders enable it to efficiently dig for roots, bulbs, corms, and tubers, and rodents and their caches. They also eat a wide variety of plants, including whitebark pine nuts, berries, sedges, grasses, glacier lilies, dandelions, yampas and biscuitroots, horsetails and thistles. They will eat human food and garbage where they can get it. This is why managers emphasize that keeping human foods secure from bears increases the likelihood that humans and bears can peacefully co-exist in greater Yellowstone.

Grizzlies have a social hierarchy that determines which bears dominate the best habitats and food sources:

  1. Adult males
  2. Lone adult females, females with two year-old cubs; females with yearlings
  3. Females with cubs of the year
  4. Subadults of either sex

Subadult bears, who are just learning to live on their own away from mother’s protection, are most likely to be living in poor quality habitat or in areas nearer roads and developments. Thus, young adult bears are most vulnerable to danger from humans and other bears, and to being conditioned to human foods. Food-conditioned bears are removed from the wild population.

Like black bears, grizzlies spend most of their time feeding. This effort increases during “hyperphagia,” the predenning period in autumn. They locate or excavate
dens on densely vegetated, north-facing slopes between 6,562–10,000 feet. Grizzlies enter their winter dens between mid-October and early December. Although grizzlies are considered true hibernators (see black bear description for more on this), they do sometimes awaken and leave their dens during the winter.

During certain times of the year, portions of Yellowstone are closed or have use restricted for the purposes of ensuring the bears have unhindered access to habitat (and to protect humans).  You can see where these areas are and the times bear management protocols are in place HERE.

SourceYellowstone National Park: Resources and Issues, 2009

How to tell the difference between Black Bear and a Grizzly