PREDATOR - The Grizzly Bear

Grizzly bears (Ursus arctos horribilis) have concave faces, a distinctive hump on their shoulders, and long claws about two to four inches long. Both the hump and the claws are traits associated with a grizzly bear’s exceptional digging ability. Grizzlies are often dark brown, but can vary from very light cream to black. The long guard hairs on their backs and shoulders frequently have white tips and give the bears a "grizzled" appearance, hence the name "grizzly." The correct scientific name for the species is “brown bear,” but only coastal bears in Alaska and Canada are referred to as such, while inland bears and those found in the lower 48 states are called grizzly bears.







Behavior
Grizzly bears are normally solitary animals. However, they are not very territorial and they may be seen feeding together where food is abundant, such as at salmon streams and whitebark pine sites. Females will rear their cubs for 2-3 years. When a female grizzly bear leaves her mother, they often set up their home range quite close to their mother’s home range. Males will typically range further, but may also remain close by.

Grizzly bears need to eat a lot in the summer and fall in order to build up sufficient fat reserves to survive the winter denning period. This is particularly true for pregnant females, who must have sufficient fat reserves to give birth to approximately one-pound cubs in January or February and then nurse them to about 20 pounds before emerging from the den in April or May.


Physical characteristics
Grizzly bears are large and range in color from very light tan (almost white) to dark brown. They have a dished face, short, rounded ears, and a large shoulder hump. The hump is where a mass of muscles attach to the bear’s backbone and give the bear additional strength for digging. They have very long claws on their front feet that also give them extra ability to dig after food and to dig their dens.

Most adult female grizzlies weigh 130–180 kg (290–400 lb), while adult males weigh on average 180–360 kg (400–790 lb). Average total length in this subspecies is 198 cm (6.50 ft), with an average shoulder height of 102 cm (3.35 ft).  One study found that the average weight for an inland male grizzly was around 272 kilograms (600 lb) and the average weight for a coastal male was around 408 kilograms (900 lb). For a female, these average weights would be 136 kilograms (300 lb) inland and 227 kilograms (500 lb) coastal, respectively. On the other hand, an occasional huge male grizzly has been recorded which greatly exceeds ordinary size, with weights reported up to 680 kg (1,500 lb). A large coastal male of this size may stand up to 3 meters (9.8 ft) tall on its hind legs and be up to 1.5 metres (4.9 ft) at the shoulder.

Hunting and diet
Although grizzlies are of the order Carnivora and have the digestive system of carnivores, they are normally omnivores: their diets consist of both plants and animals. They have been known to prey on large mammals, when available, such as moose, elk, caribou, white-tailed deer, mule deer, bighorn sheep, bison, and even black bears; though they are more likely to take calves and injured individuals rather than healthy adults. 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 inland individuals. Grizzly bears also readily scavenge food or carrion left behind by other animals. Grizzly bears will also eat birds and their eggs, and gather in large numbers at fishing sites to feed on spawning salmon. They frequently prey on baby deer left in the grass, and occasionally they raid the nests of raptors such as bald eagles.

Canadian or Alaskan grizzlies are larger than those that reside in the American Rocky Mountains. This is due, in part, to the richness of their diets. In Yellowstone National Park in the United States, the grizzly bear's diet 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. With the high fat content of salmon, it is not uncommon to encounter grizzlies in Alaska weighing 540 kg (1,200 lb).

Although the diets of grizzly bears vary extensively based on seasonal and regional changes, plants make up a large portion of them, with some estimates as high as 80–90%. Various berries constitute an important food source when they are available. These can include blueberries, blackberries, salmon berries, cranberries, buffalo berries, soapberries, and huckleberries, depending on the environment. Insects such as ladybugs, ants, and bees are eaten if they are available in large quantities. In Yellowstone National Park, grizzly bears may obtain half of their yearly caloric needs by feeding on miller moths that congregate on mountain slopes. When food is abundant, grizzly bears will feed in groups. For example, many grizzly bears will visit meadows right after an avalanche or glacier slide. This is due to an influx of legumes, which the grizzlies consume in massive amounts. When food sources become scarcer, however, they separate once again.


Social structure and home range
Except for females with cubs, grizzlies are normally solitary, active animals, but in coastal areas, grizzlies gather around streams, lakes, rivers, and ponds during the salmon spawn. Male grizzly bears have large territories, up to 4,000 km2 (1,500 sq mi), making finding a female scent difficult in such low population densities. Population fragmentation of grizzlies may destabilize the population from inbreeding depression.


Reproduction and life cycle
Every other year, females (sows) produce one to four young (usually two) that are small and weigh only about 450 grams (1 lb) at birth. A sow is protective of her offspring and will attack if she thinks she or her cubs are threatened.

Grizzly bears are one of the slowest reproducing land mammals. Females do not typically reproduce until they are four or five years old. Grizzly bears mate between May and July, but the female’s body delays implantation of their eggs in the uterus until October or November. If the female has not gained enough fat over the summer to survive and raise cubs, implantation may not occur. A grizzly’s ability to garner enough quality calories through the summer is not just crucial for her survival, but also for her reproductive ability. On average, females produce two cubs in a litter and the mother cares for the cubs for up to two years, during which the mother will not mate. Males do not help raise the cubs. In fact, males can be a danger to the cubs, so females often avoid male grizzly bears while rearing their cubs.

Once the young leave or are killed, females may not produce another litter for three or more years, depending on environmental conditions.

Litter size is between one and four cubs, averaging twins or triplets. Cubs are always born in the mother's winter den while she is in hibernation. Female grizzlies are fiercely protective of their cubs, being able to fend off predators as large as male bears bigger than they are in defense of the cubs. Cubs feed entirely on their mother's milk until summer comes, after which they still drink milk but begin to eat solid foods. Cubs gain weight rapidly during their time with the mother — their weight will have ballooned from 4.5 to 45 kg (10 to 99 lb) in the two years spent with the mother. Mothers may see their cubs in later years but both avoid each other.

The average lifespan for a male is estimated at 22 years, with that of a female being slightly longer at 26.

Distribution and habitat
Grizzly bears are found many different habitats, from dense forests to subalpine meadows, open plains and arctic tundra. In North America, grizzly bears are found in western Canada, Alaska, Wyoming, Montana, Idaho and a potentially a small population in Washington. Historically, they could be found from Alaska to Mexico and from California to Ohio.


Wolf vs Black Bear
With 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 gray wolf. The interactions of grizzly bears 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. The grizzly bear uses its keen sense of smell to locate the kill. As the wolves and grizzly compete for the kill, 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). While wolves usually dominate grizzly bears during interactions at wolf dens, both grizzly and black bears have been reported killing wolves and their cubs at wolf dens even when the latter was in defense mode.

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.

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