Grizzly bear

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Grizzly bear
Image:Grizzly Denali edit.jpg Ursus arctos horribilis
Conservation status
Image:Status iucn3.1 EN.svg Endangered
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Carnivora Family: Ursidae Genus: Ursus Species: U. arctos Subspecies: U. a. horribilis
Trinomial name
Ursus arctos horribilis (Ord, 1815)
Image:Leefgebied grizzlybeer.JPG Range map

The grizzly bear Ursus arctos horribilis, also known as the silvertip bear, is a subspecies of brown bear (Ursus arctos) that lives in the uplands of western North America.

Normally a solitary active animal, in coastal areas the grizzly congregates alongside streams and rivers during the salmon spawn. Every other year females (sows) produce one to four young (most commonly two) which are small and weigh only about 500 grams (one pound). Sows are very protective of their offspring.

Contents 1 Description 2 Range 3 Diet 4 Interspecies competition 5 Attacks on humans 5.1 Precautionary measures 6 Legal status 7 Protection 8 Reintroduction in North America 8.1 Historic range 8.2 Human threat of extinction 8.3 Rewilding 8.4 Ecological effects 8.5 Social effects 8.6 Steps involved 8.7 Minimum viable populations 9 See also 10 References 11 External links

[edit] Description

Grizzly bears reach weights of 180–680 kilograms (400–1,500 pounds) and stand 2.44 m (8 ft) tall on its hind legs.; the male is on average 1.8 times as heavy as the female, an example of sexual dimorphism. This dimorphism suggests that size is an important factor in the male's ability to successfully compete for and attract breeding opportunities. Their coloring ranges widely across geographic areas, from blond to deep brown or black. These differences, once attributed to subspeciation, are now thought to be primarily due to the different environments these bears inhabit, particularly with regard to diet and temperature.

The grizzly has a large hump over the shoulders, which is a muscle mass used to power the forelimbs in digging. The head is large and round with a concave facial profile. In spite of their massive size, these bears can run at speeds of up to fifty-five kilometers per hour (thirty-five miles per hour).

Grizzlies can be distinguished from most other brown bear subspecies by their proportionately longer claws and cranial profile which resembles that of the polar bear.^[1] Compared to other North American brown bear subspecies, a grizzly's pelt is silver tipped and is smaller in size. This size difference is due to the lesser availability of food in the grizzlies landlocked habitats.^[2] They are similair in size, colour and behaviour to the Siberian Brown Bear (Ursus arctos collaris).^[3]

[edit] Range

The current range of the grizzly bear extends from Alaska, south through much of Western Canada, and into portions of the Northwestern United States including Idaho, Montana, Washington and Wyoming, extending as far south as Yellowstone and Grand Teton National Parks, but is most commonly found in Canada. It is argued by some that there still remains a small population in Southern Colorado in the Southern San Juan Mountains. In September of 2007 a hunter produced evidence of Grizzly reinhabitation in the Selway-Bitterroot ecosystem by killing a male grizzly.^[4] Its original range also included much of the Great Plains and the Southwestern states, but it has been extirpated in most of those areas. The grizzly currently enjoys legal protection in the United States. However, it is expected that its repopulation of its former range will be a slow process, due equally to the ramifications of reintroducing such a large animal to areas which are prized for agriculture and livestock and also to the bear's slow reproductive habits (bears invest a good deal of time in raising young). There are currently about 60,000 wild grizzly bears located throughout North America. Brown bears (of which the grizzly bear is a subspecies) can live up to thirty years in the wild, though twenty to twenty-five is normal.[1]

[edit] Diet

Bears, although of the order Carnivora are actually omnivores since their diet consists of both plants and animals. They have been known to prey on large mammals such as moose, deer, sheep, caribou and even black bears. Grizzly bears will feed on fish such as salmon, trout, and bass, and those with access to a more protein-enriched diet in coastal areas potentially grow larger than interior individuals. Grizzly bears will readily scavenge food, behavior that can lead them into conflict with other species, such as wolves and humans.

The grizzly bears that reside in the American northwest are not as large as Canadian or Alaskan sub-species. This is due, in part, to the richness of their diet which in Yellowstone consists of whitebark pine nuts, roots, tubers, grasses, various rodents, army cutworm moths and scavenged carcasses, none of which match the fat content of the salmon available in Alaska and British Columbia. During early spring, as the bears emerge from their dens, elk and bison calves are actively sought. The bear will move in a zig-zag pattern, nose to the ground, hoping to find unsuspecting animals to feed on.

In preparation for winter, bears will gain hundreds of kilograms of fat, during a period of hyperphagia, before going into a state of false hibernation. The bear will often wait for a substantial snowstorm before it enters its den. Presumably, this behavior lessens the chances that predators will be able to locate the den. The dens themselves are typically located at elevations above 6,000 feet on northern-facing slopes. There is some debate amongst professionals as to whether grizzly bears technically hibernate. Much of the debate revolves around body temperature and the ability of the bears to move around during hibernation on occasion. Grizzly bears have the ability to "partially" recycle their body wastes during this period. In some areas where food is plentiful year round, grizzly bears skip hibernation altogether.

[edit] Interspecies competition

Most notable in Yellowstone have been the interactions between gray wolves and grizzly bears. Since the reintroduction of gray wolves to Yellowstone, many lucky visitors have witnessed a once common struggle between a keystone species, the grizzly bear, and its historic rival, the gray wolf. The interactions of U. arctos horribilis with the wolves of Yellowstone have been under considerable study. Typically, the conflict will be over a carcass, which is commonly an elk killed by wolves. The grizzly bear will use its strong sense of smell to locate the kill first. Then the wolves and grizzly will play a game of cat and mouse. One wolf may try to distract the bear while the others feed. The bear then may retaliate by chasing the wolves. If the wolves become aggressive with the bear it is normally in the form of careful nips at its hind legs. Thus, the bear will sit down and ease its ability to protect itself in a full circle. Rarely do interactions such as these end in death or serious injury to either animal. One carcass simply isn't usually worth the risk to the wolves if the bear has the upper hand (due to strength and size) or to the bear (if the wolves are too numerous or persistent). Over time, it seems the grizzly bears have benefited from the presence of the gray wolf because of increased food availability.

[edit] Attacks on humans

Grizzlies are considered by some experts to be the most aggressive bears, even by the standards of brown bears.^[5] It is thought that this greater aggression evolved as a response against predation. Unlike the smaller black bears, adult grizzlies are too large to escape danger by climbing trees, so they respond to danger by standing their ground and ward off their attackers. Increased aggressiveness also assists female grizzlies in better ensuring the survival of their young to reproductive age.^[6] Mothers defending cubs are the most prone to attacking, being responsible for 70% of grizzly caused human fatalities.^[7]

[edit] Precautionary measures

It is imperative for all campers in areas inhabited by grizzly to maintain a clean campsite. Reports have indicated that something as innocuous as a tube of chapstick will enticed a bear to come near a campsite in search of food. Any bear that is conditioned to finding food around campsites, will almost always return and expect the same reward. The bear is then a threat to campers and itself, and park rangers will be forced to kill it. For backcountry campers, hanging food between trees at a height unreachable to bears is a common procedure, although some grizzlies can climb and reach hanging food in other ways. An alternative to hanging food is to use a bear canister.

When travelling in grizzly territory, it is imperative that the hikers are aware of their surroundings at all times, recognizing the signs of bear presence in the area. A grizzly track is unlike that of a black bear in that one can trace a single line from the innermost point on the left toe to the innermost point on the right toe without intersecting the pad of the foot. Other signs include: talus slopes that appear raked, fallen logs which have been torn up, and high claw marks on trees. Surprising a bear typically precedes the most violent attacks. It is reccomended that a lot of noise be made when travelling in grizzly inhabited areas, so as to avoid surprising the animal, though this approach is ineffective should the bear be feeding on a carcass. In this case, the hiker must listen for ravens or other scavengers which may also be frequenting the kill site. If a bear is encountered at close quarters, the hiker should slowly back away, speaking softly. If the bear has refrained from charging, it probably does not feel threatened. In the unfortunate event that the bear does charge, and the hiker is not equipped with a sidearm or bear spray, the hiker must promptly drop to the ground stomach-first, leaving his/her backpack on as a barrier between the bear and him/her, and cover his/her head and ears with his/her arms. In this situation fighting back will almost certainly intensify and prolong the attack.

[edit] Legal status

The grizzly bear is listed as threatened in the contiguous United States, and endangered in parts of Canada. In May 2002, the Canadian Species at Risk Act listed the Prairie population (Alberta, Saskatchewan and Manitoba range) of grizzly bears as being extirpated in Canada^[8]. In Alaska and parts of Canada however, the grizzly is still legally shot for sport by hunters. On January 9, 2006, the US Fish and Wildlife service proposed to remove Yellowstone grizzlies from the list of threatened and protected species.

On September 3, 2007, a rare grizzly bear (400–500 pounds, 6–8 years old) was killed by a hunter (from Tennessee) near Kelly Creek 3 miles from Montana border (while on a guided trip, hunting black bear with bait). In April, the U.S. Fish and Wildlife Service lifted Endangered Species Act protections for grizzlies in Yellowstone National Park. The bear was in the Selway-Bitterroot ecosystem that includes part of north-central Idaho and western Montana. Federal and state wildlife officials investigated the killing.^[9]

Some biologists have argued that the word horribilis should be removed from the bear's taxonomic name, as its negative connotations may hinder conservation efforts. This change would not be permitted by the International Code of Zoological Nomenclature.

[edit] Protection

Many national parks, such as Yellowstone and Grand Teton, and Theodore Roosevelt National Park have laws and regulations in place to protect the bears.

On March 22, 2007, The US Federal Government stated that Grizzly bears in and around Yellowstone National Park (Greater Yellowstone Ecosystem) no longer need Endangered Species Act protection. Several environmental organizations including the NRDC have since brought legal suit against the federal government to relist the grizzly bear.

Environment Canada consider the Grizzly bear to a "special concern" species, as it is particularly sensitive to human activities and natural threats. In Alberta and British Columbia, the species is considered to be at risk^[10]

[edit] Reintroduction in North America

[edit] Historic range

The present range of grizzly bears in the United States has significantly decreased within the past 200 years. In the mid 1800s, populations were distributed throughout the western United States including all of Montana, Wyoming, and Colorado, and most of Idaho, Washington, Oregon, California, Arizona, Alaska, New Mexico, Utah, North Dakota and South Dakota, and parts of Nebraska, Kansas, Nevada, Oklahoma, and Texas. The following is a table of reported Grizzly Bear populations in Canadian jurisdictions from 1991 to 2001/2002:

Population estimates by jurisdiction^{[citation needed]}

	1991	2001-2002
Alberta	575 to 660	750 to 841
BC	1300 to 1340	1375 to 1400
Yukon	6300 to 6300	6300 to 6350
NWT	5050 to 5065	5080 to 5100
Nunavut	900	950 to 1000
Alb.nat.	205 to 215	185 to 193
Totals	14330 to 14480	14640 to 14884

[edit] Human threat of extinction

The primary explanation for the range and population decreases of grizzly bears in North America has been anthropogenic. With the gold rush beginning in the late 1840s, people began to establish settlements throughout the indigenous ranges of the grizzly bear. People killed the bears for their meat, fur, and because they were seen as a threat to humans. Additional contact between bears and settlers increased with western expansion, which led to a rapid decline in grizzly bear populations. By 1870, grizzly bears were scarce, even in the state of California where they were once plentiful.

[edit] Rewilding

The ideas of rewilding and reintroducing species to their natural environment are concepts based in conservation biology with the purpose of recovering lost biodiversity. Grizzly bears are just one of many species that have been diminished by the activities of humans, and reintroducing them to wilderness areas inside their historic ranges is a significant step in improving the natural biodiversity within the United States.

[edit] Ecological effects

The reintroduction of grizzly bears in habitats where they have naturally lived in the past has many positive effects on the surrounding ecosystem. As terrestrial predators, grizzly bears indirectly influence their ecological community from the top-down, causing a cascade effect which impacts the trophic levels within the community structure, and other organisms within the area. In the absence of grizzly bears, ungulate populations can increase beyond natural levels, dramatically altering vegetation structure and decreasing avian species richness, which both vary inversely with ungulate abundance. Grizzly bears also directly influence plant communities through digging habits. As they dig and forage for selective vegetation, grizzly bears disturb the nutrient structure in the soil which increases the available ammonium and nitrate levels for other plant species. In these ways, grizzly bears can increase the natural diversity of their habitat and help bring the ecosystem dynamics closer to a stable equilibrium.

[edit] Social effects

Communities of farmers and people who live adjacent to designated grizzly bear reintroduction reserves will be more susceptible to bear attacks and property damage. This is one of the main problems with reintroduction practices. People can feel threatened by animals such as the grizzly bear appearing in their neighborhoods. This may lead to protests against the implementation of the reintroduction project. Therefore, the chosen wilderness area must be as remote as possible in order to limit grizzly bear encounters with human populations and prevent the occurrence of any negative social impacts.

[edit] Steps involved

When an adequate wilderness area of historical grizzly bear range is selected for the reintroduction, grizzly bears must be transported from one of the remaining populations within North America. Existing historical samples of preserved skin from grizzly bears who previously lived in the chosen area can be analyzed for their DNA properties. DNA samples from the remaining grizzly bear populations in North America can then be compared to the historical samples in order to determine the best possible match. The DNA analysis will provide the most precise method for selecting grizzly bears from populations that will have the highest probability of survival in the selected area of reintroduction.

[edit] Minimum viable populations

After a site is chosen for reintroduction, the number of grizzly bears released into the area must be large enough for the population to survive in the long run. A minimum number of 200-250 grizzly bears on a reserve ranging from 8,556 to 17,843 square kilometers (3,303 to 6,889 mi²) is required for a low probability of species decline and an average extinction time greater than 20 years. A smaller group of individuals will result in a certain population decline or extinction and reintroduction efforts will result in failure.

[edit] See also

• List of fatal bear attacks in North America by decade
• Grizzly-polar bear hybrid

[edit] References

• Ursus arctos horribilis (TSN 202385). Integrated Taxonomic Information System. Accessed on 18 March 2006.

• Banfield, A.W.F. The Mammals of Canada. National Museum of Natural Sciences, National Museums of Canada, University of Toronto Press, 1987. ISBN 0-8020-92298.
• CBC News article on possible "grolar bear" (Polar Bear/Grizzly Bear hybrid)
• Committee On The Status of Endangered Wildlife in Canada (COSEWIC) Assessment and Update Status Report on the Grizzly Bear (Ursus arctos) in Canada, 2002 2.1 MB PDF file.
• Cronin, M.A., Amstrup, S.C., Garner, G.W., and Vyse, E.R., 1991. Interspecific and specific mitochondrial DNA variation in North American bears (Ursus). Canadian Journal of Zoology 69: 2985-2992.
• Herrero, Stephen, Bear Attacks. Piscataway N.J: New Centuries Publishers, 1985. ISBN 0-8329-0377-9.
• Waits, L.P., Talbot, S.L., Ward, R.H., and Shields, G.F., 1998. Mitochondrial DNA phylogeography of the North American brown bear and implications for conservation. Conservation Biology 12: 408-417.
• Snyder, Susan. The California Grizzly Bear in Mind. The Bancroft Library, University of California, Berkeley, 2003.
• Berger, J., B. Stacey, L. Bellis, and M. P. Johnson. 2001. A Mammalian Predator-Prey Imbalance: Grizzly Bear and Wolf Extinction Affect Avian Neotropical Migrants. Ecological Applications 11(4): 947-960
• Mattson, J. and Troy Merrill 2001. Extirpations of Grizzly Bears in the Contiguous United States, 1850-2000. Conservation Biology 16(4): 1123-1136.
• Wielgus, R. B. 2002. Minimum viable population and reserve sizes for naturally regulated grizzly bears in British Columbia. Biological Conservation 106: 381-388.
• Tardiff, S. E. and J. Stanford 1998. Grizzly Bear Digging: Effects on Subalpine Meadow Plants in Relation to Mineral Nitrogen Availability. Ecology 70(7): 2219-2228.
• Groom, M. J., G. K. Meffe, and C. R. Carroll. Principles of Conservation Biology. Third Edition. Sunderland, Massachusetts: Sinauer Associates, 2006.

[edit] External links

• Smithsonian National Museum of Natural History species account-Grizzly Bear
• UN Works
• Grizzly bears - the ultimate carnivore
• Grizzly Bear Outreach Project Information on the history, biology, and conservation of North American Grizzly Bearsan:Onso gris

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