The grizzly bear population within the Yellowstone ecosystem is estimated to be approximately 280-610 bears. The park does not have a current estimate of the black bear population; black bears are considered to be common in the park.
: Varies from pure black to brown, cinnamon, or blonde; in the Rocky Mountains, approximately 50% are black with a light brown muzzle.
About 3 ft (0.9 m) at the shoulder.
: Male: 210-315 lbs (95-143 kg); Female: 135-160 lbs (61-73 kg) (Barnes and Bray 1967).
: Males: 6-124 mi 2 (16-321 km 2 ); Females: 2-45 mi 2 (5-117 km 2 ) (Mack 1988).
15 - 20 years in the wild; 30+ years in captivity.
: Varies from black to blonde; frequently with white-tipped fur giving a grizzled, silver-tipped appearance. In the Yellowstone ecosystem, many grizzly bears have a light brown girth band.
: About 3-1/2 ft (1.0 m) at the shoulder.
Male: 216-717 lbs (98-325 kg); Female: 200-428 lbs (91-194 kg) (Blanchard 1987).
: Males: 813-2075 mi 2 (2106-5374 km 2 ); Females: 309-537 mi 2 (801-1391 km 2 )
Life Expectancy: 15 - 20 years in the wild; 30+ years in captivity.
The physical and behavioral differences between black bears and grizzly bears have been described in detail by Herrero (1978). Black bears are primarily adapted to use forested areas and their edges and clearings. Although grizzly bears make substantial use of forested areas, they also make much more use of large, non-forested meadows and valleys than do black bears. Black bears have short, curved claws better suited to climbing trees than digging. This enables black bears to forage for certain foods, such as mast, by climbing trees. In contrast, grizzly bears have longer, less curved claws and a larger shoulder muscle mass better suited to digging than climbing. This enables grizzly bears to efficiently forage for foods which must be dug from the soil such as roots, bulbs, corms, and tubers, as well as rodents and their caches. The primary difference between the food habits of black bears and grizzly bears in the Yellowstone ecosystem is the absence of roots in the diet of black bears (Knight et al. 1988).
Behaviorally, black bears are generally much less aggressive than grizzly bears and rely on their ability to climb trees to allow themselves and their cubs to escape predators such as wolves, grizzly bears, or other black bears. Grizzly bears are generally one and one-half to two times larger than black bears of the same sex and age class within the same geographic region. Grizzly bears are also more aggressive than black bears and more likely to rely on their size and aggressiveness to protect themselves and their cubs from predators or other perceived threats.
Another behavioral difference between black bears and grizzly bears is the length of time cubs are under their mother's care. Black bear cubs are born in the winter den, spend the summer following birth with their mother, den with her again in the fall, then separate from her early the next summer as yearlings. Grizzly bear cubs spend two and one-half and sometimes three and one-half years under their mother's care before separation.