Biogeography of the Brown Bear (Ursus arctos)
Department of Geography, San Francisco State University, California
Source: U.S. Fish & Wildlife Service
The brown bear is a variable species, occupying much of the northern hemisphere. Its life history is broad, requiring a wide range of elevations covering an expansive range. The brown bear is one of 8
extant species of Ursidae; its closest living relative is the polar bear (Ledje & Arnason 1996, Nowak 1991, Storer & Tevis 1955, Talbot & Shields 1996b).
In many areas, the brown bear has been driven to extinction (Novikov 1965, Storer & Tevis 1955). In other areas, it is decreasing in numbers due to human activities (Domico 1988, U.S. Fish & Wildlife Service 1995). In this paper, I will give an overview of the natural history and biogeography of the brown bear. In addition, I will discuss the conservation efforts currently taking place to restore populations of the brown bear to sustainable levels in the United States.
The brown bear (Ursus arctos) is a very widespread species, originally native to much of the Northern Hemisphere (Nowak 1991, Storer &Tevis 1955). The brown bear once occupied most of Western North America, from the Great Plains to California and from Mexico to Alaska (U.S. Fish & Wildlife Service 1995). In Eurasia, brown bears originally occurred from northern Africa, Spain, and Italy northward into Scandinavia and eastward through Asia to Japan (Middle East Technical University 1995, Storer & Tevis 1955)(Appendix 2). Although brown bears can be found in a variety of habitats, pristine mountain forests, open meadows, and large river valleys make up their preferred habitats (Domico 1988).
Today, the brown bear's distribution is greatly reduced (Appendix 3). Many of the populations that were once continuous are now disjunct (Waits, Talbot, Ward, & Shields 1998). Human activities, such as habitat destruction and hunting, have resulted in extirpations of some populations. Brown bears were eliminated from most of western Europe, though a few scattered populations still persist in Poland, the former Czechoslovakia, Austria, Italy, southern France, northern Spain, and southern Norway. (Domico 1988, Novikov 1965, Nowak 1991, Waits et al. 1998).
In the United States, tens of thousands of brown bears were killed by humans during the nineteenth century, not only for their commercial value, but due to the threat they posed to livestock as well as to humans. Brown bears were eliminated from California by 1922, from Oregon by 1933, and from the southwest by 1935 (Domico 1988, Storer and Tevis 1955). In the conterminous United States, their present range is approximately 2 percent of their historical range (U.S. Fish & Wildlife Service 1995). Brown bears still occupy parts of northwestern Montana, northern Idaho, northeastern Washington, and the Greater Yellowstone Ecosystem (Nowak 1991).
The brown bear population of Canada's Great Plains have been eliminated, except for a small population in west-central Alberta. In Africa, the brown bear was extirpated during the mid-nineteenth century (Nowak 1991).
Many of the remaining brown bear populations
are restricted to northern and mountainous regions. In Alaska and western
Canada (except southern British Columbia), brown bear populations remain
relatively unaffected by anthropogenic activities (Paetkau et al. 1998,
Waits et al. 1998). There is also a large population in the former Soviet
Union (Nowak 1991).
The size of brown bears vary greatly with geography, with overall length ranging from 5.5 to 9.2 feet (170-280 cm)(Domico 1988, Nowak 1991, Rausch 1963). In general, male brown bears are larger than females, although their sizes overlap. In the contiguous United States, a male can be as long as 7 feet (213 cm) in length, and can weigh from 300 to 600 pounds (136 to 272 kg). Females generally weigh between 200 and 400 pounds (91 to 181 kg)(U. S. Fish & Wildlife Service 1995).
The brown bears found along the coast of southern Alaska are the largest of all bears (although some argue that polar bears are larger). Brown bears that weighed as much as 1720 pounds (780 kg) have been recorded in this region. To the north and east of this area, the brown bear's size declines rapidly (Nowak 1991, Sacco 1997).
Despite its name, the brown bear's
fur is highly variable, ranging from cream to black in color. In the Rocky
Mountains, the brown bear's fur is often tipped with silver, giving it
a "grizzled" appearance. Because of this characteristic, the brown bear
is referred to as the grizzly bear in the contiguous United States. The
"grizzled" fur also occurs in brown bears of the Himalayas (Domico 1988,
Middle East Technical University 1995, Nowak 1991, U.S. Fish & Wildlife
The area an animal uses in pursuit of its biological requirements is referred to as a home range (Craighead, Sumner, & Mitchell 1995, Middle East Technical University 1995). Generally, the brown bear has a relatively large home range, although it varies by the amount of resources available. The home range of a brown bear in the Rocky Mountains is approximately 347 square miles (900km2). In the Brooks Range of Alaska, an average brown bear's home range is 521 square miles (1350 km2). In a salmon-rich coastal area of Alaska, a brown bear's home range is only about 10.5 square miles (27 km2). Males occupy a home range that is 4 to 6 times greater than that of a female. The home range of a male will likely overlap the home ranges of 2 to 3 females (Mase & Waller 1997, Middle East Technical University 1995, Noss, Quigley, Hornocker, Merril, & Paquet 1996).
As one of the largest carnivorous land mammals, the brown bear is at the top of the food chain-adult brown bears do not have any natural predators. This is not to suggest that they are strictly carnivorous. Rather, they are largely omnivorous; plants account for approximately 80 to 90 percent of the brown bear's diet in the form of vegetation, fruits, nuts, bulbs, and roots. Additionally, brown bears tear apart logs and turn over rocks in search of insects. The brown bear's primary source of meat comes from big game carcasses that did not survive the winter (Nowak 1991, U. S. Fish & Wildlife Service 1995). Occasionally, brown bears will prey on deer, elk, moose calves, or small burrowing mammals. During summer and autumn, spawning salmon is an important food source along the Pacific coasts of Canada, Alaska, and northeastern Siberia (Nowak 1991, U.S. Fish & Wildlife Service 1995). Recently, a brown bear has been documented preying on a denning adult black bear in interior Alaska. However, this type of feeding behavior is not well documented (Smith & Follman 1993).
With a few exceptions, brown bears are for the most part, solitary animals. The only lasting social bond is between a female and her young, which lasts approximately 2-3 years (Nowak 1991, U.S. Fish & Wildlife Service 1995). During salmon spawning runs in Alaska, brown bears were observed feeding in family groups consisting of more than one age class of young (Nowak 1991). Additionally, males and females form temporary bonds lasting 1-3 weeks during the mating season, which occurs between May and July (Novikov 1962, Nowak 1991). Throughout the breeding season, female brown bears are in estrus until they mate. Females only enter estrus once every 2-4 years (Nowak 1991).
During the autumn months, brown bears search for a place to dig a den. In doing so, they sometimes travel many miles before they find a suitable area. The dens are usually located on a high elevation slope, where deep snow will accumulate. Often, the dens will be located under tree roots (U.S. Fish & Wildlife Service 1995).
Brown bears enter their dens in October or November, where they sleep through the winter season. During this period, brown bears do not eat or drink (Nowak 1991, U. S. Fish & Wildlife Service 1995). Their body temperature drops, which reduces enzyme activity and slows down their metabolism (Harris 1996). Their caloric needs are fulfilled by fat reserves which were accumulated during the summer and autumn seasons (Middle East Technical University 1995, U. S. Fish & Wildlife Service 1995).
Although mating occurs between May and July, the embryos do not begin to develop until the female enters her den, up to 6 months later. If the female has not accumulated enough fat to sustain herself and her developing cubs, the embryos will not develop (U. S. Fish & Wildlife Service 1995).
Brown bear cubs are usually born in January. Blind and weighing less than 1 pound (454g) at birth, cubs grow quickly and often weigh over 20 pounds (9 kg) when they emerge from the den in spring. An average litter is 2 cubs, but can range from 1 to 4. (Nowak 1991, U.S. Fish & Wildlife Service).
Brown bears come out from their dens between March and May. When a brown bear comes out of its den, its first food will sometimes be carrion that did not survive the winter. Brown bears usually travel to lower elevations in order to reach vegetated areas (U.S. Fish & Wildlife Service 1995).
The mother supplies her cubs with milk for almost a year, and stays with them for 2 to 3 years. The cubs reach puberty at approximately 4 to 6 years, and in some instances, may not breed until they are 8 years old (Nowak 1991, U.S. Fish & Wildlife Service 1995). A brown bear's life span in the wild is approximately 15 to 20 years, and in some cases, they will live to be 30 years old (U.S. Fish & Wildlife Service 1995).
Evolution and Systematics
Some 30 to 40 million years ago, there existed a family of small carnivorous mammals. Based on the fossil record, we classify these extinct animals as miacids (Miacidae). Miacids are the only known prehistoric representatives to Order Carnivora, the predatory placental mammals of today (Middle East Technical University 1995). There are seven families in Carnivora: Canidae (dog), Procyonidae (raccoon), Mustelidae (weasel), Viverridae (mongoose), Hyaenidae (hyena), Felidae (cat), and Ursidae (bear)(Ewer 1973).
The origins of Family Ursidae can be traced back to Cephalogale, a small, dog-like animal which lived in Europe during the early to mid-Tertiary. Cephalogale was the ancestor to Ursavus elmensis, the first bear-like carnivore. From this origin came the Ursidae family (Sacco 1997).
Members of Ursidae dispersed throughout the world. Ursidae first appeared in North America during the late Miocene. In Europe and Asia, Ursidae appeared during the late Eocene. Ursidae arrived in South Africa during the Pliocene, and finally, in North Africa during the Pleistocene (Nowak 1991).
The Ursidae family consists of eight living species in three genera: Tremarctos, Ailuropoda, and Ursus (Nowak 1991). The genus Tremarctinae consists of the spectacled bear (T. ornatus), Ailuropoda consists of the giant panda (A. melanoleuca), and the most represented genus, Ursus, includes the Asiatic black bear (U. thibetanus), the American black bear (U. americanus), the polar bear (U. maritimus), the Malaysian sun bear (U. malayanus), the sloth bear (U. ursinus), and the grizzly or brown bear (U. arctos)(Nowak 1991, Talbot & Shields 1996b).
The spectacled bear diverged from other members of Ursidae approximately 12-13 million years ago, which is close to the time of divergence of the ancestral giant panda. The sloth bear lineage diverged later, approximately 7 million years ago.
Between 6-7 million years ago, there
was a rapid radiation of the remaining members of the genus Ursus. Approximately
6 million years ago during the late Pliocene, the lineage containing the
Asiatic black bear and the American black bear diverged. Within approximately
1 million years of this event, the Asiatic and American black bears diverged
from each other. The sun bear diverged from the lineage approximately 5
million years ago from the lineage leading to the polar bear and the brown
bear, which diverged approximately 300,000-400,000 years ago (Sacco 1997,
Talbot & Shields 1996b)(Fig. 1).
It is generally agreed upon that the evolutionary origin of the brown bear is in Eurasia. However, there is not enough evidence to determine whether if it originated in Europe or Asia (Masuda, Aiurzaniin, Yoshida 1998).
There are many subspecies of brown bears (U. arctos sspp.) worldwide. However, the exact number and classification of subspecies is not widely agreed upon (Nowak 1991). Some early taxonomists have suggested that there are as many as 90 subspecies in North America and 271 subspecies of brown bears in Eurasia. However, many consider this to be a case of excessive over-splitting (Talbot & Shields 1996a). More recent findings indicate that there are two to nine subspecies of brown bears in Eurasia, and seven Eurasian subspecies (Nowak 1991, Rausch 1963, Waits et al. 1998).
Conservation in the United States
Brown (grizzly) bears have a reputation of being brutal killers of livestock and people, though many of the stories that are the basis for their reputation are probably gross exaggerations. As settlers and livestock filled the West during the nineteenth century, the grizzlies were eradicated in most of their range. The development of roads have intensified this process, giving access to hunters, poachers, developers, and the extractive industries (Chadwick 1999, Nowak 1991).
In the conterminous western United States, there may have been as many as 100,000 grizzly bears during the early 1800s. Today, there are probably fewer than 1,000 grizzly bears, classifying them as a federally listed threatened species by the U.S. Fish & Wildlife Service. These remaining grizzlies are scattered throughout Montana, Wyoming, Idaho, and Washington in geographically and ecologically isolated subpopulations (Domico 1988, Nowak 1991, Primm 1996, U. S. Fish & Wildlife Service 1995). These small, isolated populations are subject to stochastic events which may lead to extirpation (Bader 1991). In the Northern Rockies, more than 38,600 square miles (100,000 km2) may be required for long term sustainability of the grizzly bear (Noss et. al 1996). Their large home range requirements, coupled with low reproductive rates, have made it difficult for them to make a comeback.
Currently, there is an effort by conservationists to restore the grizzly bear populations in the Northern Rockies. Connecting existing populations of grizzly bears with biological corridors will allow grizzlies to migrate from one area to another, which will reduce the inhibiting effects of a small population. Protecting an area that is large enough to sustain the grizzly bear will also protect its prey, as well as smaller carnivores, and the majority of native plants and animals. This is known as the umbrella species concept, because everything under the grizzly bear's "umbrella" is protected (Bader 1991, Noss et al. 1996).
Many ranchers and developers, as well as the extractive industry, are opposed to such conservation efforts. In their eyes, the grizzly bear is a pest and a barrier to economic development. Some argue, however, that a healthy grizzly bear population is more economically beneficial in the long-term than ranching, developing, and extracting resources (Bader 1991).
Some of the efforts to restore grizzly bear populations have succeeded. The grizzly bear population in the Greater Yellowstone Ecosystem has met the U. S. Fish and Wildlife Service's recovery target, and is currently growing at an annual rate of about 5 percent. In the North Continental Divide Ecosystem in and around Glacier National Park, the grizzly bear population has nearly reached the recovery goals set by the U. S. Fish & Wildlife Service (U.S. Fish & Wildlife Service 1995, Wilkinson 1998).
The brown bear historically occupied much of the northern hemisphere. Due to human activities, its present range is reduced to mountainous regions and northern latitudes. The distribution of the brown bear was once considerably continuous worldwide. Today, its distribution is fragmented in many areas, most notably those in or around developed areas. In Canada, Alaska, and northern Eurasia, brown bear populations are still flourishing.
Although taxonomically a carnivore, the brown bear, like other members of Family Ursidae, is quite omnivorous. Meat accounts for a relatively small portion of their diet. Due to their vast requirements, brown bears have a relatively large home range. However, the size of the home range varies with geography.
Female brown bears become sexually mature between the ages of 4 to 6 years old, and only mate every 2 to 4 years. Birth occurs in winter while the mother is in her den. A brown bear's litter ranges in size from 1 to 4 cubs. The mother raises her cubs alone. After 2 to 3 years, the mother leaves the cubs to tend for themselves.
Conservation efforts have been implemented in the management of the brown bear. Due to its requirements for a wide home range, a viable population of brown bears requires more continuous habitat than is available in the conterminous United States. By connecting existing brown bear habitats via corridors, enough habitat can be connected to support sustainable brown bear populations.
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Source: U.S. Fish & Wildlife Service
Appendix 1. Taxonomic classification of the
brown bear (Ursus arctos ).
Species: Ursus arctos
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