Scientific Name: Ursus arctos
Grizzly bears are intelligent, adaptive omnivores, capable of utilizing diverse food sources. Historically, this amazing species has lived in much of the Earth’s northern temperate zone.
Where do They Live?
Across their range, grizzly/brown bears occupy boreal forests, arctic tundra, mountainous regions, and even some deserts. Their distribution is the widest of all bear species and among the greatest among terrestrial mammals, reflecting the species’ adaptability and omnivorous feeding habits.
Worldwide, U. arctos numbers approximately 200,000 individuals, with most of these living in Russia. Among the eight bear species of the world, grizzly/brown bears rank a distant second in numbers to the American black bear (U. americanus).
The members of this species that live in the interior of North America are usually called “grizzly bears,” because the light-colored tips of their hair give them a “grizzled” appearance; this feature also explains another nickname “silvertip.”
Contrary to Hollywood portrayals of grizzlies as marauding giants, most Rocky Mountain grizzlies are modest in size relative to brown bears elsewhere.
What do Grizzlies Eat?
Grizzlies feed on fish, ungulates, rodents, grasses, sedges, forbs, berries, mushrooms, insects, and mast crops like acorns and pine seeds. In some habitats, grizzlies are largely vegetarian, even though they are unable to fully digest plant fiber. They are able to utilize plant foods by selectively consuming plants at the phenologic stage that offers the most nutrition.
Compared to wolves and big cats, grizzlies are relatively inefficient predators. Very young elk and moose calves are vulnerable to grizzly predation, as are mature male ungulates weakened by breeding season. Grizzlies scavenge much of the meat they consume from carcasses of ungulates dead from other causes.
Grizzlies breed in May and June typically. The female grizzly then maintains the embryo(s) in a dormant stage until she dens in the fall; this strategy, called delayed implantation (http://en.wikipedia.org/wiki/Delayed_implantation), allows the cubs to be born in the safety of the winter den. Also, delayed implantation may keep the mother grizzly from sacrificing nutrition to embryonic cubs in times of scarcity; if there is not enough food to support the mother, cubs, and milk development, pregnancy ceases.
Grizzly cubs are born in the winter den in January or February, and weigh about one pound. The cubs emerge from the den with their mother in the spring, the beginning of a two to four year rearing process. During this period, the mother grizzly is notoriously protective of her offspring, and will often defend them with physical aggression.
D. J. Mattson, 1990, “Human impacts on bear habitat use,” International Conference on Bear Research and Management 8, 33-56
Craighead et al., The grizzly bears of Yellowstone; C. Servheen, 1989, “The management of the grizzly bear on private lands: Some problems and possible solutions,” pp. 195-200 in M. Bromley, ed., Bear-people conflicts: Proceedings of a symposium on management strategies, Northwest Territories Department of Renewable Resources, Yellowknife; Mattson, “Human impacts on bear habitat use;”. A. Gunther, 1994, “Bear management in Yellowstone National Park, 1960-93,” International Conference on Bear Research and Management 9, 549-560.
Craighead et al., The grizzly bears of Yellowstone; J. L. Weaver, P. C. Paquet, and L. F. Ruggiero, 1996, “Resilience and conservation of large carnivores in the Rocky Mountains,” Conservation Biology 10, 964-976.
Scientific name: Ursus americanus
Status: Least concern
Size: 5 to 6 ft (1.5 to 1.8 m) long
Weight: 200 to 600 lbs (90 to 270 kg)
Despite their name, black bears vary widely in color, ranging from nearly white (Kermode bears of the Canadian Pacific coast) to jet black, with a wide palette of reddish browns, blonde, dark brown, and bluish black in between.
Lifespan: 20 years
Black bears of North America are by far the most common of the world’s eight bear species. In fact, there are far more black bears (roughly 750,000 continent-wide) than the total number of the other seven bear species combined (roughly 250,000 total).
Where do They Live?
According to fossil records and genetic studies, black bears have apparently been evolving in North America for the past 3.5 million years. They evolved primarily in forested habitats, and tend to be excellent tree climbers. In addition to forests, black bears live in mountains, swamps, and some barren areas like the glaciated tidelands of southeastern Alaska, and arctic plains in Quebec and Labrador.
Black bears den in the winter, generally utilizing an existing cave, rock outcropping, or a hollow tree. Unlike grizzly bears, they typically do not excavate a den, although some black bears will dig extensive dens. Black bears are not as efficient at digging as grizzlies, since their short, curved claws are mostly adapted for tree climbing instead of digging.
How Do They Protect Themselves?
Black bears typically will flee from a perceived threat, either by escaping into forest cover or by climbing trees. This behavioral pattern differs greatly from grizzly bears, which will typically use aggression to neutralize a perceived threat. Black bears have therefore been far more successful at living near modern humans than grizzly bears have.
What Do They Eat?
Extremely omnivorous, black bears feed on fish, ungulates, rodents, grasses, sedges, forbs, berries, mushrooms, insects, and crops like acorns and pine seeds. Compared to wolves and big cats, bears are relatively inefficient predators. Very young elk and moose calves are vulnerable to black bears. Black bears scavenge much of the meat they consume from carcasses of ungulates dead from other causes.
Black bears are usually solitary, except for females with dependent cubs. Mating occurs in from May through July. The female black bear then maintains the embryo(s) in a dormant stage until she dens in the fall; delayed implantation (http://en.wikipedia.org/wiki/Delayed_implantation) allows the cubs to be born in the safety of the winter den. Cubs are born in the winter den in January or February, and weigh less than one pound. The cubs emerge from the den with their mother in the spring.
Map courtesy of British Columbia Grizzly Bear Conservation Strategy, Province of British Columbia, Ministry of Environment, Lands and Parks.