Color: Varies from pure black to brown, cinnamon, or
blonde; in the Rocky Mountains, approximately
50% are black with a light brown muzzle.
Height: About 3 ft (0.9 m) at the shoulder.
Weight: Male: 210-315 lbs (95-143 kg); Female:
135-160 lbs (61-73 kg) (Barnes and Bray 1967).
Home Range Size: Males: 6-124 mi2 (16-321 km2);
Females: 2-45 mi2 (5-117 km2) (Mack 1988).
Life Expectancy: 15 - 20 years in the wild;
30+ years in captivity.
Grizzly Bear (Ursus arctos horribilis)
Color: 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.
Height: About 3-1/2 ft (1.0 m) at the shoulder.
Weight: Male: 216-717 lbs (98-325 kg); Female:
200-428 lbs (91-194 kg) (Blanchard 1987).
Home Range Size: Males: 813-2075 mi2 (2106-5374 km2);
Females: 309-537 mi2 (801-1391 km2)
(Blanchard and Knight 1991).
Life Expectancy: 15 - 20 years in the wild;
30+ years in captivity.
Physical and Behavioral Characteristics
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.
Bears are omnivores that have relatively unspecialized
digestive systems similar to those of carnivores. The
primary difference is that bears have an
elongated digestive tract, an adaptation that allows
bears more efficient digestion of vegetation
than other carnivores (Herrero 1985). Unlike ruminants,
bears do not have a cecum and can only poorly digest
the structural components of plants (Mealey 1975).
To compensate for inefficient digestion of cellulose,
bears maximize the quality of vegetal food items
ingested, typically foraging for plants in
phenological stages of highest nutrient
availability and digestibility (Herrero 1985).
The food habits of grizzly bears in Yellowstone
National Park have been described in detail by Knight
et al. (1984). Overall, whitebark pine nuts,
graminoids, and ungulates are the most
important foods in the grizzly bear's diet. Grizzly
bear food habits are influenced by
seasonal variation in available foods.
Spring
From March through May, ungulates, mostly elk and
bison, comprise a substantial portion of a grizzly
bear's diet. Grizzly bears feed on ungulates primarily
as winter-killed carrion but also through
predation on elk calves. Other items consumed
during spring include grasses and sedges, dandelion,
clover, spring-beauty, horsetail, and ants.
Grizzly bears also feed extensively on whitebark
pine nuts stored in red squirrel caches, especially
during springs when an abundance of pine
nuts have been left over from the previous
fall (Mattson and Jonkel 1990).
Summer
From June through August, grizzly bears continue to
consume grasses and sedges, dandelion, clover,
spring-beauty, whitebark pine nuts, horsetail, and ants.
In addition, thistle, biscuitroot, fireweed,
and moths are eaten. Predation on elk calves
continues until late-June/early-July when grizzly
bears are no longer able to catch calves
(Gunther and Renkin 1990). In areas surrounding Yellowstone
Lake, bears feed extensively on spawning
cutthroat trout (Reinhart 1990). Starting around midsummer,
grizzly bears begin feeding on strawberry,
globe huckleberry, grouse whortleberry, and buffaloberry.
By late summer, bistort and yampa
are included in the diet, and grasses, sedges,
and dandelion become less prominent.
Fall
From September through October, whitebark pine nuts
are the most important bear food. Other items
consumed during fall include: grasses and sedges,
bistort, yampa, strawberry, globe huckleberry, grouse
whortleberry, buffaloberry, clover, horsetail,
dandelion, ungulates, ants, and moths.
Black Bears
The food habits of black bears in the Yellowstone
ecosystem are similar to those of grizzly bears.
The primary difference is the absence of roots in the
diet of black bears (Knight et al. 1988). Black bears
have short, curved claws better suited for climbing
than digging. In contrast, grizzly bears have longer,
straighter claws and a larger shoulder muscle mass
which makes them more efficient at digging
for food items in the soil such as roots, bulbs,
corms, and tubers, as well as rodents and their caches (Herrero 1978).
Information on this page is from the Yellowstone National Park Site.
For more information on the bears please be sure to visit
Yellowstone National Park Web Site
Click on "Nature" then click on "YellowStone Wildlife pages" then "Bears"
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