By Tanya Dewey
Other Geographic Terms:
Brown bears occupy a variety of habitats, from desert edges to high mountain forests and ice fields. In North America they seem to prefer open areas such as tundra, alpine meadows, and coastlines. Historically, they were common on the Great Plains prior to the arrival of European settlers. In Siberia, (Wilson and Ruff, 1999)occurs primarily in forests, while European populations are restricted mainly to mountain woodlands. The main habitat requirement for is some area with dense cover in which it can shelter by day.
(176 to 1320 lbs)
(3.28 to 9.18 ft)
One of the largest of living carnivores, grizzly bears are 1 to 2.8 meters in length from head to rump and their tails are 65 to 210 mm long. They are 90 to 150 cm tall at the shoulder and can tower at an intimidating height of 8 feet when standing upright on their hind legs. They range in weight from 80 to more than 600 kg. On average, adult males are 8 to 10% larger than females. (Wilson and Ruff, 1999)is largest along the the coast of southern Alaska and on nearby islands where males average 389 kg and females average 207 kg, though some males have been weighed at as much as 780 kg. Size rapidly declines to the north and east, with individuals in southwestern Yukon weighing only 140 kg on average. Fur is usually dark brown, but varies from cream to almost black. Individuals in the Rocky Mountains have long hairs along the shoulders and back which are frosted with white, giving a grizzled appearance, hence the common name grizzly bear in that region. Brown bears are extremely strong and have good endurance; they can kill a cow with one blow, outrun a horse, outswim an Olympian, and drag a dead elk uphill.
Sexual dimorphism: male larger.
Brown bear females typically breed every 2 to 4 years.
Breeding occurs from May to July.
Female brown bears copulate with multiple males during estrus, which lasts 10 to 30 days. Males may fight over females and guard them for 1 to 3 weeks. Female receptivity is probably communicated by scent marking throughout her territory.
polygynandrous (promiscuous) .
Mating of brown bears takes place from May to July. Fertilized eggs develop to the blastocyt stage, after which implantation in the uterus is delayed. The blastocyt becomes implanted approximately 5 months after mating, usually in November when the female has entered her winter sleep. A 6 to 8 week gestation follows, with births occuring from January to March (usually while the female is still in hibernation). Total gestation time, including pre-implantation, ranges from 180 to 266 days. Females remain in estrus throughout the breeding season until mating occurs and do not ovulate again for at least 2 (usually 3 or 4) years after giving birth. Two to three offspring are generally born per litter.
Brown bears mature sexually between 4-6 years of age, but continue growing until 10-11 years old. Bears have been known to live and reproduce in Yellowstone Park at 25 years of age, and potential lifespan in captivity is as great as 50 years. (Wilson and Ruff, 1999)
Young are born blind, helpless, and naked, weighing only 340 to 680 grams. By 3 months old cubs weigh about 15 kg, by 6 months weight averages 25 kg. Lactation continues for 18 to 30 months, although the cubs are eating a wide variety of foods by about 5 months of age. Cubs remain with the mother until at least their second spring of life (usually until the third or fourth). Male brown bears do not contribute parental care. (Wilson and Ruff, 1999)
no parental involvement; altricial ; pre-fertilization (protecting: female); pre-hatching/birth (provisioning: female, protecting: female); pre-weaning/fledging (provisioning: female, protecting: female); pre-independence (provisioning: female, protecting: female); extended period of juvenile learning.
Brown bears in the wild can live for 20 to 30 years, although most brown bears die in their first few years of life. In captivity, brown bears have been known to live up to 50 years. (Wilson and Ruff, 1999)
individuals may be active at any time of the day, but generally forage in the morning and evening and rest in dense cover by day. Brown bears may excavate shallow depressions in which to lie. Seasonal movements of have been observed, with individuals sometimes traveling hundreds of kilometers during the autumn to reach areas of favorable food supplies, such as salmon streams and areas of high berry production.
Home ranges overlap extensively and there is no evidence of territorial defense, although bears are generally solitary. Occasionally, bears may gather in large numbers at major food sources and form family foraging groups with more than one age class of young. Under these conditions, dominance hierarchies are usually formed and maintained with aggression. Highest-ranking individuals are large adult males, although the most aggressive bears are females with young. Least aggressive and lowest-ranking are adolescents. The only social bonds formed are between females and young.
begins hibernation in October to December, and resumes activity in March to May, with the exact period dependent on the location, weather, and condition of the individual. In certain southern locales, hibernation is very brief or may not occur at all. Most often, brown bears dig their own dens and make a bed out of dry vegetation. Burrows are usually located on a sheltered slope, either under a large stone or among the roots of a mature tree. Dens are sometimes used repeatedly year after year.
Home ranges can be as large as 2,600 sq km, but are on average between 73 and 414 sq km, with male ranges nearly 7 times greater than female ranges. Home ranges overlap extensively.
Communication and Perception
Brown bears communicate primarily through smells and sounds. Brown bears can be heard making moaning noises sometimes while they are foraging. They scratch and rub on trees and other landmarks to communicate territorial boundaries and reproductive status.
Brown bears have an excellent sense of smell (able to follow the scent of a rotting carcass for more than two miles), human-level hearing, but relatively poor eyesight.
Brown bears are omnivorous, eating almost anything nutritious. Their diet changes with seasonal availability of different food sources. They eat a wide variety of plant foods, including grasses, sedges, roots, moss, and bulbs. Fruits, nuts, berries, bulbs, and tubers are taken extensively during summer and early autumn. They consume insects, fungi, and roots at all times of the year and also dig mice, ground squirrels, marmots, and other fossorial animals out of their burrows. Moth larvae have been demonstrated to be especially important sources of protein and fat when brown bears are putting on fat in the fall. In the Canadian Rockies and other areas, grizzly bears (the subspecies of brown bear in that area) are quite carnivorous, hunting moose, elk, mountain sheep, and mountain goats. Occasionally black bears are preyed upon. In Alaska, brown bears have been observed to eat carrion and occasionally capture young calves of caribou and moose. Brown bears have also been observed to feed on vulnerable populations of breeding salmon in the summer in these areas. (Wilson and Ruff, 1999)
mammals; fish; carrion ; insects.
leaves; roots and tubers; seeds, grains, and nuts; fruit; bryophytes.
Because of their size and aggressiveness towards threats, brown bears are not often preyed upon. Humans have persecuted them throughout recent history and some cubs may be attacked by other bears or by mountain lions or wolves, although this is very rare.
Brown bears are important predators and seed dispersers in the ecosystems in which they live.
Economic Importance for Humans: Negative
Brown bears have been long considered the most dangerous animal in North America, although real danger of attack from this animal is often exagerated. In general, brown bears attempt to avoid human contact and will not attack unless startled at close quarters with young or engrossed in a search for food. They are unpredictable in temperament, however, and often exhibit impulsive and petulant behavior.
Brown bears have been persecuted extensively as predators of domestic livestock, especially cattle and sheep, although their actual impact on the livestock industry is probably negligible.
Ways that these animals might be a problem for humans:
Economic Importance for Humans: Positive
Brown bears have been widely sought as big game trophies and are currently subject to regulated sport hunting throughout much of their range. Once brown bears were used for their meat and hides but these products are not currently in high commercial demand. Some bear body parts (such as gall bladders) bring high prices on the traditional Asian medicine market, although no true medicinal benefit of these parts has ever been documented.
Currently, brown bears help to fuel an ecotourism industry, especially in areas such as Yellowstone National Park, Wyoming and parts of Alaska.
Ways that people benefit from these animals:
body parts are source of valuable material; ecotourism .
Their conservation status depends on the population. Some populations are clearly endangered, others are not. Brown bear numbers have dropped dramatically since the turn of the century, when settlers and livestock flooded the West, driving these bears out of much of their former range. Brown bears now cling to a mere 2 per cent of their former range. Logging, mining, road construction, resorts, subdivisions, golf courses, etc. have all encroached on suitable bear habitat, resulting in a decrease in bear numbers. Brown bear numbers were estimated at 100,000 in the conterminous United States in the early 1900's, but there are now fewer than 1,000. Brown bears are still fairly common in the mountainous regions of western Canada and Alaska, perhaps numbering about 30,000 individuals. In Eurasia there are an estimated 100,000 brown bears, with about 70,000 of those living in the Soviet Union. However, habitat destruction and persecution threaten brown bears throughout their range. A growing market in bear products for the Asian market, despite a complete lack of evidence that products made from bear parts have any medical value, threatens bear species throughout Eurasia and western North America.
Tanya Dewey (author), Animal Diversity Web, University of Michigan Museum of Zoology.
Liz Ballenger (author), University of Michigan.