Brown bear (Ursus arctos)
|Also known as:||Grizzly bear, Mexican grizzly bear|
|Size||Head-body length: 1.5 - 2.8 m (2)|
Shoulder height: 0.9 -1.5 m (2)
Male weight: 135 - 545 kg (2)
Female weight: 80 - 250 kg (2)
- The largest form of brown bear is the Kodiak bear, weighing up to an astounding 780 kilograms.
- The home range of a brown bear is extremely large, reaching up to 2,000 square kilometres in males.
- Brown bears can survive for over half a year without eating, drinking, urinating or defecating whilst in hibernation.
- Brown bears are opportunistic and seasonal feeders, moving in response to food aggregations such as spawning salmon.
- During hibernation, female brown bears are able to give birth and nurse cubs, incurring huge energetic costs and a 40 percent loss in body weight.
The brown bear is classified as Least Concern (LC) on the IUCN Red List (1) and listed on Appendix II of CITES. Brown bear populations in Bhutan, China and Mongolia are listed on Appendix I of CITES (3).
One of the largest carnivores on Earth (4), the brown bear (Ursus arctos) is perhaps the most archetypal of all bear species; indeed the genus and species name both mean “bear” in Latin and Greek respectively (2). The brown bear shows incredible geographical diversity, and the single species recognised today was at one point in history divided into 232 living and 39 fossil species and subspecies (2). Some of the more well-known subspecies of brown bear include the grizzly bear, named for its silver tipped fur, and the Kodiak bear, the largest form of brown bear, which can reach up to 780 kilograms, and is found on islands off southern Alaska (2) (4).
All forms of brown bear are powerfully built, with a prominent shoulder hump, a large head, and long, robust claws, which are better suited for digging rather than tree-climbing (5). The coat varies in colour, locally between individuals and geographically, appearing brown, blonde, brown with silver-tips, and near black (2). Where their ranges overlap, the brown bear and the American black bear (Ursus americanus) may be confused due to the potential similarities in coat colour. However, the brown bear is usually larger, with a snout that rises more abruptly to the forehead (4).
Not only does the brown bear have the largest range of any bear species, it is also one of the world's most widely distributed terrestrial mammals (1). While today the strongholds for this species are found in northern regions, mostly within Russia, Canada and Alaska, up until the mid-1880s the brown bear occurred as far south as North Africa and, until the 1960s, was also found in Mexico. In addition, during the Middle Ages, populations were found in mainland Europe, including the British Isles (2). Fragmented populations of the brown bear do still occur in some parts of southern and eastern Europe, as well as in the Middle East, and central and eastern Asia as far as Japan (1) (2).
In accordance with its expansive range, the brown bear inhabits a wide variety of habitats (1). While forest and woodland are commonly occupied by this species, it is less dependent on the presence of trees than some other bear species, and can be found above the tree-line at elevations of up to 5,000 metres. Large populations can also be found along coastlines, in tundra, and in desert and semi-desert regions (2).
An opportunistic feeder, the brown bear has a varied omnivorous diet which consists predominantly of berries and nuts, but also includes grasses, roots, insects, salmon, small mammals and large ungulates (2) (4). Larger animal prey may be either taken as carrion or actively hunted, particularly by grizzly bears. Probably the most carnivorous subspecies, these formidable predators can bring down moose, elk and even black bears. While the brown bear may be encountered throughout the day, it is mostly active during the early morning and evening. Seasonal movements are made in response to food aggregations, such as spawning salmon, during which time large numbers of bears may gather in relatively small areas (4). Brown bears have extremely large home ranges, varying from 200 to 2,000 square kilometres in males, and 100 to 1,000 square kilometres in females (2). While typically solitary, brown bears tolerate the presence of conspecifics and do not appear to be territorial, although adult males may fight for dominance (4).
During the mating season, from May to July, the males compete for females (4), and dominant males may attempt to guard a chosen mate from rival males while the female is in oestrus (5). Both males and females may mate with several different partners, and may also form short-lived pair bonds lasting from several weeks to a few hours (5). After mating, the fertilised eggs undergo delayed development and do not implant in the female’s womb until around November (2). Thereafter, the eggs continue development with the young born between January and March, resulting a total gestation period of 6.5 to 8.5 months (2) (4). The reason for this delayed development is that it causes the cubs to be born during the winter hibernation, allowing maximum time until the following winter for the cubs to grow large enough to survive hibernation without the mother (2). A litter of between one and four cubs is produced, which are weaned at five months and reach reproductive maturity at four to six years old (4). The first litter is usually produced between the ages of five and ten, and there is usually a period of two to five years between successful litters (2).
Like all northern bears, brown bears hibernate throughout winter, preserving energy by reducing heart rate and body temperature by a few degrees. Hibernation takes place in a den, often dug into a sheltered slope, in which the bear may survive for over half a year without eating, drinking, urinating or defecating (2) (4). This remarkable feat is achieved by utilising stored fat for energy and by recycling waste products normally excreted as urine to conserve fluids and produce amino acids. Incredibly, the female brown bear is also able to give birth and nurse a litter of cubs during hibernation, although the energetic cost is high and can incur a 40 percent loss of body weight (2).
As a result of its wide distribution, the brown bear has an apparently large, healthy global population, which believed to exceed 200,000 individuals, and is not currently considered to be threatened. Nevertheless, while some populations are stable and even expanding, many local populations, such as those in Europe, are small, fragmented, and in danger of extirpation (1). As a result of livestock predation and in response to the fact that this species may attack humans, it has, historically, been heavily persecuted (2). Today, the brown bear is most commonly hunted for sport, or poached for the commercial trade in bear paws and gall bladders (1) (4). Hunting legislation varies between countries, but where permitted, it is controlled through the use of permits and maximum annual quotas. However, due to difficulties with the development of monitoring plans, the sustainability of quotas in some regions is questionable, and there are also significant ongoing problems, such as in the Russian Far East, with illegal hunting (1).
In addition to losses through hunting, many brown bear populations are at risk from habitat loss and fragmentation. As human activities such as agriculture, highways and settlements expand, they reduce available habitat for this species and also result in the fragmentation of populations. The reduced size of the isolated populations can then lead to detrimental genetic effects (1).
There are several national and international measures in place to protect and conserve the brown bear (1). International trade in this species is regulated in accordance with the Convention on International Trade in Endangered Species (CITES), with most populations listed on Appendix II, which permits a limited amount of trade up to a specific annual quota. Populations from parts of central Asia are, however, listed on Appendix I, making all international trade illegal (1) (3).
In some regions this species is also protected by national laws—although enforcement levels vary—and by virtue of its presence in protected areas. Many countries also have conservation management plans in place to mitigate threats and promote the recovery of some of the smaller, more vulnerable populations. Many of these are proving successful; for example, in some parts of the United States outside Alaska, small populations of grizzly bears, which are protected by the Endangered Species Act, have shown a significant population increase. This has been further enhanced by augmenting the populations with bears from other regions, and by carrying out reintroductions (1).
To learn more about bear conservation visit:
The International Association for Bear Research and Management:
Smithsonian National Zoological Park:
Ursus International Conservation Institute:
For further information on the brown bear see:
BBC Wildlife Finder:
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- Amino acids: molecules which form the building blocks of proteins.
- Carrion: the flesh of a dead animal.
- Conspecifics: individuals belonging to the same species.
- Gestation: the state of being pregnant; the period from conception to birth.
- Oestrus: the time of ovulation (release of an egg from the ovary) in female mammals, when the female becomes receptive to males, also known as ‘heat’.
- Omnivorous: feeding on both plants and animals.
- Subspecies: a population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
- Territorial: an animal, a pair of animals or a colony that occupies and defends an area.
- Tundra: treeless, grassy plains characteristic of arctic and sub-arctic regions. They are very cold and have little rainfall.
- Ungulate: a hoofed, grazing mammal.
IUCN Red List (May, 2009)
- Macdonald, D.W. (2006) The Encyclopedia of Mammals. Oxford University Press, Oxford.
CITES (May, 2009)
- Nowak, R.M. (1991) Walker's Mammals of the World. The Johns Hopkins University Press, Baltimore and London.
- Feldhamer, G.A., Thompson, B.C. and Chapman, J.A. (2003) Wild mammals of North America: biology, management, and conservation. 2nd Edition. The Johns Hopkins University Press, Baltimore, Maryland.