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Ursus arctosbrown bear

By Tanya Dewey and Liz Ballenger

Geographic Range

Ursus arctos once ranged throughout northern and central Europe, Asia, the Atlas mountains of Morocco and Algeria, and western North America as far south as Mexico. They are now found in extremely small numbers from western Europe and Palestine to eastern Siberia and the Himalayan region, possibly the Atlas Mountains of northwest Africa, and Hokkaido. Northern North American populations in Alaska and western Canada remain fairly stable. Many populations in the United States have been extirpated, including those of the Sierra Nevada and southern Rockies. Northern Mexican populations were extirpated in the 1960's. (Wilson and Ruff, 1999)

Habitat

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, Ursus arctos occurs primarily in forests, while European populations are restricted mainly to mountain woodlands. The main habitat requirement for Ursus arctos is some area with dense cover in which it can shelter by day. (Wilson and Ruff, 1999)

Physical Description

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. Ursus arctos 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. Distance between the canines is from 6 to 8 cm. 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. (Wilson and Ruff, 1999)

  • Sexual Dimorphism
  • male larger
  • Range mass
    80 to 600 kg
    176.21 to 1321.59 lb
  • Range length
    1 to 2.8 m
    3.28 to 9.19 ft

Reproduction

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. (Wilson and Ruff, 1999)

Mating of brown bears takes place from May to July. Fertilized eggs develop to the blastocyst stage, after which implantation in the uterus is delayed. The blastocyst 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 occurring 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)

  • Breeding interval
    Brown bear females typically breed every 2 to 4 years.
  • Breeding season
    Breeding occurs from May to July.
  • Range number of offspring
    3 (high)
  • Average number of offspring
    2
  • Average number of offspring
    2
    AnAge
  • Range gestation period
    180 to 266 days
  • Range weaning age
    18 to 30 months
  • Range time to independence
    2 to 3 years
  • Range age at sexual or reproductive maturity (female)
    4 to 6 years
  • Range age at sexual or reproductive maturity (male)
    4 to 6 years

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)

  • Parental Investment
  • 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

Lifespan/Longevity

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)

Behavior

Ursus arctos 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 Ursus arctos 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.

Brown bears begin a period of inactivity in October to December, and resume activity in March to May, with the exact period dependent on the location, weather, and condition of the individual. In southern areas, this period of inactivity is very brief or may not occur at all. This period is marked by a deep sleep in which these bears allow their body temperature to drop by a few degrees. It is not true hibernation and bears can generally be aroused readily from their winter sleep.

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.

Ursus arctos moves with a slow, lumbering walk, although it is capable of moving very quickly and can easily catch a black bear. Brown bears are mainly terrestrial, although they can often be found swimming or preying upon fish in the water. Adults are unable to climb trees. (Wilson and Ruff, 1999)

Home Range

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. (Wilson and Ruff, 1999)

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. (Wilson and Ruff, 1999)

Food Habits

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)

  • Animal Foods
  • mammals
  • fish
  • carrion
  • insects
  • Plant Foods
  • leaves
  • roots and tubers
  • seeds, grains, and nuts
  • fruit
  • bryophytes
  • Other Foods
  • fungus

Predation

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. (Wilson and Ruff, 1999)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Brown bears are important predators and seed dispersers in the ecosystems in which they live.

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. (Wilson and Ruff, 1999)

  • Positive Impacts
  • body parts are source of valuable material
  • ecotourism

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 exaggerated. 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. (Wilson and Ruff, 1999)

  • Negative Impacts
  • injures humans
    • bites or stings

Conservation Status

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. (Wilson and Ruff, 1999)

Contributors

Tanya Dewey (author), Animal Diversity Web.

Liz Ballenger (author), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carrion

flesh of dead animals.

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

delayed implantation

in mammals, a condition in which a fertilized egg reaches the uterus but delays its implantation in the uterine lining, sometimes for several months.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

holarctic

a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

World Map

Found in northern North America and northern Europe or Asia.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nomadic

generally wanders from place to place, usually within a well-defined range.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

taiga

Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

tundra

A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Allen, T.B., ed. 1979. Wild Animals of North America. The National Geographic Society, Washington, D.C.

Nowak, R.M. and J.L Paradiso. 1983. Walker's Mammals of the World. 4th edition. John Hopkins University Press, Baltimore, MD.

Tubarek, G. 1993. Survivors in the Shadows: Threatened and Endangered Mammals of the American West. Northland Publishing Company, Flaggstaff, Arizona.

Wilson, D., S. Ruff. 1999. The Smithsonian Book of North American Mammals. Washington: Smithsonian Institution Press.

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