Grizzly Bear Information
(Ursus arctos horribilis)
Order: Carinicora (flesh eating animals)
Family: Ursidae (bears)
Body: The grizzly bear is the largest of all carnivorous land mammals. The terms "brown bear" and "grizzly bear" are often used interchangeably, but actually the two animals are slightly different. A third term, "silvertip", is occasionally used for this bear. The term brown bear is used for bears that are found in coastal areas, where salmon are the primary food source. The term grizzly bear is used for bears that live in the interior and northern areas. The grizzlies tend to be 2/3 the size of the brownies, and are often more aggressive. The term grizzly will be used for all the bears in this species focus section.
Grizzly bear coloration ranges from light blond to dark brown, with males usually being darker than the females. Many bears have a lighter body with darker legs. Grizzlies have a shallow face, small ears, and long, slightly curved claws. The distinctive hump on their neck is a muscular and bony adaptation to allow for quick bursts of speed and for forceful digging. The male (boar) averages 7 feet tall, standing on his hind feet, and weighs form 400 to 900 pounds. Occassionally, boars have been known to weigh up to 1400 pounds and stand 9 feet tall, with skulls measuring 18 inches long by 12 inches wide. Female grizzlies (sows) are smaller and often weigh around half as much as boars of the same age who live within the same range. After storing fat for their hibernation, the bears will weigh aout 25% more than when they emerge in the spring.
Diet: Grizzlies are omnivorous and eat a large variety of foods. They are often able to find carcasses of winter-kill animals after they emerge from their dens, but they mainly eat grasses and early herbaceous plants. During the summer, their diet includes fruits, berries, and shrubs. Another major food source, is the insects they find in old logs or under rocks. About 85% of a grizzlies food comes from plant sources. In addition to carrion, the meat in a bears diet comes from salmon, elk or moose calfs, or smaller mammals such as marmots and squirrels. Grizzlies have a well developed sense of smell and can smell food from up to a mile away.
Range: The grizzly bear only occupies 2% of its historic range in the contiguous states. They once roamed the land from northern Alaska and Canada, southward to central Mexico, and from California eastward to the mid-plains states. Grizzly habitat includes a variety of forests and moist grasslands or meadows located near the mountains. They need extensive amounts of land for their home ranges, with boars roaming from 200 to 500 square miles, and sows ranging from 50 to 300 sqare miles. Bears will seek higher, isolated grounds in the winter for hibernation. They travel between summer and winter ranges using riparian areas and valley floors. In Alaska, grizzlies can be found everywhere except parts of the Aleutian Islands past Unimak Island, and on the island south of Frederick Sound in the Southeast.
Challenges: The grizzly bear was eliminated from nuch of the western US by the late 1800s. Their population numbers had decreased from around 50,000 in 1800 to less than 1000 bears in 1975. Human land development into areas previously part of the grizzly's range, led to many conflicts. Through habitat destruction, unregulated hunting, trapping, and killing due to fears that the bears were a threat to livestock and man himself, the bears numbers continued a downward spiral. In 1975, the grizzly was finally listed as a Threatened species and given protection.
Efforts at reintroduction have met with some success, but many people would rather not see the bears in the wild again, as they still consider them a threat. Today grizzlies can be found in Wyoming, Montana, Washington, and Idaho, as well as Alaska and parts of western Canada. There are an estimated 30,000 grizzlies in Alaska, and another 22,000 in Canada. The main threats to the bears now are habituation and continued habitat degredation. Habituation occures when the grizzlies begin to associate people with food. If they are allowed to feed on trash, bird feeders, pet food, livestock carcasses, and food improperly stored by campers, then they begin to make the connection that people mean food. They can become aggressive around people, and in the worst case scenarios, are killed either by a government agency or by citizens in self-defense.
Life History: Grizzly bears have the second slowest reproduction rate of any North American land mammal, with only the musk oxen being slower. Their breeding season peaks in early June, but runs from May to July. Bears do not choose life long mates, and a dominant boar may mate with several sows a year. Sows in different ranges reach sexual maturity at different ages, but generally between the ages of 4 to 9 years old, they are ready to mate. Once they reach breeding age, they only mate every 3 years or so. The grizzly sow exibits delayed implantation of the embryo into the uterus. Impregnation occurres in the spring, but the embryo lies dormant during the summer and fall as the sow gains weight for her winter hibernation. If she does not gain enough weight, then the embryo will not develop.
As winter approaches, the grizzly heads for higher ground to build a den for hibernation. They prefer high, remote mountain slopes, where deep snow will remain until spring. These dens are often dug under the roots of large trees. Pregnant sows are usually the first ones to den, in October or November, and the last ones to leave. During hibernation, the grizzly's metabolism, heart rate, and body temperature are decreased and its need for food and water are basically eliminated. They survive by burning the fat that they stored during the summer feeding frenzy. In areas with warmer climates, it is not uncommon for the grizzlies to stay active all winter and not to hibernate.
Around the end of January, the sow will usually give birth to her young in the winter den. The cubs are hairless and weigh less than one pound. Litter sizes range from 1 to 4, with 2 cubs being the most common. The number of cubs depends somewhat on the quality of the bears summer range. The mother and cubs will stay in the den nursing until early spring. The cubs gain weight rapidly and by the time that they leave the den, they average 22 pounds. They often have a white collar of hair around their neck for the first year. Cubs remain dependent on their mother's milk for the first year of their lives and the family unit of sow and cubs will stay together for up to 3 years. When the family breaks up, the sow is ready to breed again. Females have been well documented to adopt orphaned cubs and raise them as their own. Less than half the cubs born will survive to reach breeding age. Predators such as man, mountain lions, wolves, and aggressive boars can all kill cubs. The boar may kill the cubs in order for the sow to be ready to mate sooner. Male grizzlies have been known to live for 22 years, with females living to 26 years of age.
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