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Grizzly Bears

North American grizzly bears (Ursus arctos) are a genetic variety of brown bears, which were first detected in the fossil record relatively recently (about 500,000 years ago). Although grizzly bears belong to the order of carnivores (flesh-eating mammals), they exhibit many traits that allow them to subsist on a highly varied non-meat diet that can, at times, consist almost entirely of fibrous vegetation.

Grizzly Bears in North America

Grizzly Bear Foraging Behavior

Coefficients of Productivity for Yellowstone's Grizzly Bear Habitat

Grizzly Bear and cubs, photo
Grizzly Bear with cubs (Ursus arctos)
Courtesy Tom Smith (tom_smith@usgs.gov)

Grizzy bear adults are large for a carnivore and, depending on the quality of habitat, weigh between 200 and 1000 pounds. This large size allows them to subsist on a lower quality diet by reducing the amount of energy that they need per pound of body weight. Large size also facilitates the long-range movements and very large ranges that allow grizzly bears access to a wide variety of foods. In the arctic, ranges of males and females can average as large as 2,600 square miles and 810 square miles per year, respectively. Compared to North American black bears (Ursus americanus) occupying the same habitat, grizzly bears are roughly two times larger in size and have ranges between 2 and 16 times more extensive.

Grizzly Bear Fishing, photo
Grizzly bear fishing © 2002 Corel

Besides their large size, grizzly bears can be distinguished from other bears by their long claws and the large mass of muscles over their shoulders that constitute their distinctive "hump." These features have typically been interpreted as adaptations to digging, and, indeed, grizzly bear diets are distinguished from the diets of all other northern bears by the amounts of roots that they consume. Grizzly bear diets are also distinguished from the diets of black bears by greater amounts of meat obtained from fish and large herbivores such as moose and elk. Where grizzly bears have access to meat, especially where they fish for spawning salmon in coastal waterways of the North Pacific, they grow much larger and exist at much higher densities. Along the Alaska coast there can be as many as 140 bears per 100 square miles.

Grizzly Bear Standing Tall, photo
Courtesy Tom Smith (tom_smith@usgs.gov)

Whitebark Pine Cones and Seeds, photo
Courtesy Kate Kendall
(katherine_kendall@usgs.gov) At their peak, grizzly bears probably subsisted on bison in the Great Plains, acorns in California and the Southwest, salmon in northern coastal areas, elk and whitebark pine seeds in the Rocky Mountains, and berries everywhere. Unfortunately, many of the important grizzly bear foods are threatened. For example, whitebark pine, which is the source of heavily used whitebark pine seeds (see picture at left), is being eliminated by white pine blister rust (a virulent non-native fungal pathogen).

SBSC Grizzly Bear Contact:
David Mattson, Flagstaff, AZ, (928) 523-9080, david_mattson@usgs.gov

More Information about Grizzly Bears and Related Topics:

USGS Interagency Grizzly Bear Study Team (IGBST):
http://nrmsc.usgs.gov/research/igbst-home.htm

USGS Status and Trends of the Nation's Biological Resources - Rocky Mountains (includes Grizzly Bear Information):
http://biology.usgs.gov/s+t/SNT/noframe/wm146.htm

Greater Glacial Area Bear DNA Project - Monitoring Grizzly Bear Populations using DNA:
http://nrmsc.usgs.gov/research/beardna.htm

USGS Alaska Science Center Brown Bear Projects:
http://www.absc.usgs.gov/research/brownbears/brownbears.htm

USGS Status and Trends of the Nation's Biological Resources - Whitebark Pine:
http://biology.usgs.gov/s+t/SNT/noframe/wm147.htm