Grizzly Bear

The grizzly bear (Ursus arctos horribilis), also known as the silvertip bear or just the grizzly or North American brown 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 from eastern Russia 100,000 years ago, though they did not move south until 13,000 years ago.[1]

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.

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".

Description
Most female grizzlies weigh 150 - 350 kilograms (330 - 770 pounds), while males weigh on average 230 – 450 kg (500 - 1000 lb). Newborn bears may weigh less than 500 grams. Although variable from blond to nearly black, grizzly bear fur is typically brown in color with white tips.[3] A pronounced muscular hump occurs on their shoulders which strengthens their front limbs for digging and running; they can attain speeds of 55 km/hr (35 mph). The hump is also a good way to determine a black bear from a brown bear, as black bears do not have this hump.

Range
Brown bears are found in Asia, Europe and North America giving them one of the widest ranges of bear species. The ancestors of the grizzly bear originated in Eurasia and traveled to North America approximately 50,000 years ago.[4] This is a very recent event in evolutionary time, causing the North American grizzly bear to be very similar to the brown bears inhabiting Europe and Asia.

In North America, grizzly bears previously ranged from Alaska to Mexico and as far east as the Hudson Bay area.[4] In North America, the species is now found only in 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.

In September 2007, a hunter produced evidence of grizzly bears returning to the Selway-Bitterroot Wilderness ecosystem, in Idaho and western Montana, by killing a male grizzly bear.[5]

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 bear appears on the Flag of California, though they are extinct in the state, the last one having been shot in 1922.[6]

In Canada, there are approximately 25,000 grizzly bears occupying British Columbia, Alberta, the Yukon, the Northwest Territories, Nunavut and the northern part of Manitoba.[4] Combining Canada and the United States, grizzly bears inhabit approximately half the area of their historical range.[4] In British Columbia, grizzly bears inhabit approximately 90% of their original territory. There were approximately 25,000 grizzly bears in British Columbia when the European settlers arrived.[4] However, population size significantly decreased due to hunting and habitat loss. In 2008, it was estimated there were 16,014 grizzly bears. Population estimates for British Columbia are based on hair-snagging, DNA-based inventories, mark-recapture and a refined multiple regression model.[7]

Other provinces and the United States may use a combination of methods for population estimates. Therefore, it is difficult to say precisely what methods were used to produce total population estimates for Canada and North America, as they were likely developed from a variety of studies. The grizzly bear currently has legal protection in Mexico, European countries, some areas of Canada and in the United States. However, it is expected that repopulating its former range will be a slow process, due to the effects of reintroducing such a large animal to areas prized for agriculture and livestock and to the bear's slow reproductive habits. There are currently about 55,000 wild grizzly bears located throughout North America.[4]

Brown bears (of which the grizzly bear is a subspecies) can live up to 30 years in the wild, though 20 to 25 is normal.

Reproduction
Grizzly bears have one of the lowest reproductive rates of all terrestrial mammals in North America.[9] This is due to numerous ecological factors. Grizzly bears do not reach sexual maturity until they are at least five years old.[4] [10] Once mated with a male in the summer, the female delays embryo implantation until hibernation, during which miscarriage can occur if the female does not receive the proper nutrients and caloric intake.[11] On average, females produce two cubs in a litter[10] and the mother cares for the cubs for up to two years, during which the mother will not mate.<sup class="reference" id="cite_ref-Blood_3-7">[4] Once the young leave or are killed, females may not produce another litter for three or more years, depending on environmental conditions.<sup class="reference" id="cite_ref-ReferenceA_11-0">[12] Male grizzly bears have large territories, up to 4,000 square kilometres (1,500 sq mi),<sup class="reference" id="cite_ref-PW_8-1">[9] making finding a female scent difficult in such low population densities.

Grizzlies are subject to population fragmentation, which tends to reduce the population by causing inbreeding depression.

Diet
Although grizzlies are of the order Carnivora and have the digestive system of carnivores, they are actually omnivores, since their diet consists of both plants and animals. They have been known to prey on large mammals, when available, 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 also readily scavenge food, on carrion left behind by other animals.<sup class="reference" id="cite_ref-12">[13]

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 mostly of whitebark pine nuts, tubers, grasses, various rodents, army cutworm moths and scavenged carcasses. None of these, however, match the fat content of the salmon available in Alaska and British Columbia.

Plants make up approximately 80%–90% of a grizzly bear's diet. Various berries make up a large portion of this. These can include blueberries (Vaccinium cyanococcus), blackberries (Rubus fruticosus), salmon berries (Rubus spectabilis), cranberries (Vaccinium oxycoccus), buffalo berries (Shepherdia argentea), and huckleberries (Vaccinium parvifolium), depending on the environment. Insects such as ladybugs, ants and bees are eaten, but only if they are available in large quantities. At low quantities, the energy gained is not worth the foraging energy output.<sup class="reference" id="cite_ref-hww.ca_13-0">[14] When food is abundant, grizzly bears will feed in groups. For example, many grizzly bears will visit meadows right after there has been an avalanche or glacier slide. This is due to an influx of legumes, such as Hedysarum, which the grizzlies consume in massive amounts.<sup class="reference" id="cite_ref-bear.org_14-0">[15] When food sources become scarcer, however, they separate once again.

In preparation for winter, bears can gain approximately 400 lb (180 kg), during a period of hyperphagia, before going into false hibernation. The bear often waits for a substantial snowstorm before it enters its den: such behaviour lessens the chances that predators will find the den. The dens are typically at elevations above 6,000 feet (1,800 m) on north-facing slopes. There is some debate amongst professionals as to whether grizzly bears technically hibernate: much of this debate revolves around body temperature and the ability of the bears to move around during hibernation on occasion. Grizzly bears can "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 in the defense of young or over a carcass, which is commonly an elk killed by wolves.<sup class="reference" id="cite_ref-15">[16] 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 is not 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).

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 being the aggressor. The black bear will only fight when it is a smaller grizzly such as a yearling or when the black bear has no other choice but to defend itself.

The segregation of black bear and grizzly bear populations is possibly due to competitive exclusion. In certain areas, grizzly bears outcompete black bears for the same resources.<sup class="reference" id="cite_ref-ApplsMcLellan_16-0">[17] For example, many Pacific coastal islands off of British Columbia and Alaska support either the black bear or the grizzly, but rarely both.<sup class="reference" id="cite_ref-17">[18] In regions where both species coexist, they are divided by landscape gradients such as age of forest, elevation and openness of land. Grizzly bears tend to favor old forests with high productivity, higher elevations and more open habitats compared with black bears.<sup class="reference" id="cite_ref-ApplsMcLellan_16-1">[17]

The relationship between grizzly bears and other predators is mostly one-sided; grizzly bears will approach feeding predators to steal their kill. In general, the other species will leave the carcasses for the bear to avoid competition or predation. Any parts of the carcass left uneaten are scavenged by smaller animals.<sup class="reference" id="cite_ref-ReferenceA_11-1">[12] Cougars, however, generally give the bears a wide berth. Grizzlies have less competition with cougars than with other predators, such as coyotes, wolves, and other bears. When a grizzly descends on a cougar feeding on its kill, the cougar usually gives way to the bear. When a cougar does stand its ground, the cougar will use its superior agility and its claws to harass the bear, yet stay out of its reach until one of them gives up.

Coyotes, foxes, and wolverines are generally regarded as pests to the grizzlies rather than competition, though coyotes and wolverines may compete for smaller prey, such as rabbits and deer. All three will try to scavenge whatever they can from the bears. Wolverines are aggressive enough to occasionally persist until the bear finishes eating, leaving more than normal scraps for the smaller animal.