About Grizzly Bear

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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.

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". Most female grizzlies weigh 150 - 350 kilograms (330 - 770 pounds), while males weigh on average 230 - 450 kg (500 - 1000 lb). New born bears may weigh less than 500 grams.

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 wiped out in Canada. 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. In March 2007, the U.S. Fish and Wildlife Service "de-listed" the population, effectively removing Endangered Species Act protections for grizzlies in the Yellowstone National Park area. On September 22, 2009, a federal judge reinstated protection for the bears.

Reproduction

Grizzly bears have one of the lowest reproductive rates of all terrestrial mammals in North America. This is due to numerous ecological factors. Grizzly bears do not reach sexual maturity until they are at least five years old. 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. 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. Once the young leave or are killed, females may not produce another litter for three or more years depending on environmental conditions. Male grizzly bears have large territories, up to 4,000 square kilometers (1,500 sq mi), making finding a female scent difficult in such low population densities.

Grizzlies are subject to fragmentation, a form of population segregation. Fragmentation causes inbreeding depression, which leads to a decrease in genetic variability in the grizzly bear species. This decreases the fitness of the population for several reasons. First, inbreeding forces competition with relatives, which decreases the evolutionary fitness of the species? Secondly, the decrease in genetic variability causes an increased possibility that a lethal homozygous recessive trait may be expressed; this decreases the average litter size reproduced, indirectly decreasing the population.