The grizzly bear (Ursus arctos horribilis) , also known as the silvertip bear , is a subspecies of brown bear (Ursus arctos) that generally lives in the uplands of western North America. This subspecies is thought to descend from Ussuri Brown Bears which crossed to Alaska 100,000 years ago, though they did not move south until 13,000 years ago.
Grizzlies are normally solitary active animals, but in coastal areas the grizzly congregates alongside streams, lakes, rivers, and ponds during the salmon spawn. Every other year, females ( sows ) produce one to four young (commonly two) which are small and weigh only about 500 grams (one pound). A sow is protective of her offspring and will attack if she thinks she or her cubs are threatened.
Description
Grizzly size and weight varies greatly according to geographic location. Inland bears, particularly those of the Yukon region, may weigh as little as 300 lbs (136 kg) for adult males. The largest populations are found in coastal areas where weights are typically 500-750 lbs (225–420 kg). Populations found in Katmai National Park and the Alaskan Peninsula may approach or just exceed 1000 lbs (450 kg), indeed some specimens rival the Kodiak bear in size and weight. The females are on average 38% smaller, at about 250–450 pounds (114–160 kg), an example of sexual dimorphism. On average, grizzly bears stand about 1 meter (3.3 ft) at the shoulder when on all fours and 2 meters (6.6 ft) on their hind legs, but males often stand 2.44 meters (8 ft) or more on their hind legs. On average, grizzly bears from the Yukon River area are about 20% smaller than typical grizzlies. Formerly, taxonomists listed brown and grizzly bears as separate species. The Grizzly is classified as a Brown Bear subspecies, Ursus Arctos Horribilis. The term “brown bear” is commonly used to refer to the members of this subspecies found in coastal areas where salmon is the primary food source, but in fact, these are just coastal grizzlies in contemporary taxonomic classification. Inland bears and those found in northern habitats are more often called “grizzlies.” Brown bears on Kodiak Island are classified as a distinct subspecies from those on the mainland because they are genetically and physically isolated. The shape of their skulls also differs slightly.
The grizzly's coloring ranges widely depending on geographic areas, from blond to deep brown, red or even grey. The grizzly has a large hump over the shoulders, which is a muscle mass used to power the forelimbs in digging. The hind legs are more powerful, however. The muscles in the lower legs provide enough strength for the bear to stand up and even walk short distances on its hind legs, giving it a better view of its surroundings. 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 56 kilometres per hour (35 miles per hour). However, they are slower running downhill rather than uphill because of the large hump of muscle over the shoulders. They have very thick fur to keep them warm in brutal, windy, and snowy winters.
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. Compared to other North American brown bear subspecies, a grizzly has a silver tipped pelt and is smaller in size. This size difference is due to the lesser availability of food in the grizzlies' landlocked habitats. They are similar in size, colour and behaviour to the Siberian Brown Bear (Ursus arctos collaris) .
Name
The word "grizzly" in its name refers to "grizzled" or grey hairs in its fur, but when naturalist George Ord formally named the bear in 1815 he misunderstood the word as "grisly", to produce its biological Latin specific or subspecific name " horribilis ".
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. There may still be a small population in Colorado in the southern San Juan Mountains. In September 2007 a hunter produced evidence of grizzly rehabilitation in the Selway-Bitterroot ecosystem by killing a male grizzly. 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 Mexico, European countries, some areas of Canada and in the United States. However, it is expected that its re-population 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.
Diet
Although grizzlies are of the order Carnivora and have the digestive system of a carnivore, they 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, elk, bison, caribou and even black bears. Grizzly bears 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 readily scavenge food, behaviour that can lead them into conflict with other species, such as wolves and humans. A few have been known to eat humans.
The grizzly bears that reside in the American Rocky Mountains are not as large as Canadian or Alaskan grizzlies. This is due, in part, to the richness of their diet which in Yellowstone consists of whitebark pine 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 moves in a zig-zag pattern, nose to the ground, hoping to find unsuspecting animals to feed on.
In preparation for winter, bears gain hundreds of kilograms of fat, during a period of hyperphagia, before going into a state of false hibernation. The bear often waits for a substantial snowstorm before it enters its den, such behaviour lessening 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.
Interspecific competition
Most notable in Yellowstone have been the interactions between gray wolves and grizzly bears. Since the reintroduction of gray wolves to Yellowstone, many visitors have witnessed a once common struggle between a keystone species, the grizzly bear, and its historic rival, the grey 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 uses its keen sense of smell to locate the kill. 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 quick nips at its hind legs. Thus, the bear will sit down and use 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.
Black bears generally stay out of grizzly territory but grizzlies may occasionally enter their terrain to obtain food sources both bears enjoy, such as pine nuts, acorns, mushrooms, and berries. When a black bear sees a grizzly coming it either turns tail and runs or climbs a tree. Black bears are not strong competition for prey because they have a more herbivorous diet. Confrontations are rare because of the difference in size, habitat, and diet of the bear species. When this happens it is usually with the grizzly
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