One of the most striking things about grizzlies is their diversity. Differences in basic physical characteristics such as size and coat color are reflected in the variety of local names given the animals: silvertip, yellow bear, Toklat grizzly (golden coat with chocolate paws), and brownie, to name a few. Groups and individuals also vary strongly in their feeding habits, home range sizes, social interactions, personalities, and traditions passed along from mothers to young.
Though it can be immense as an adult, the mighty grizzly comes into the world naked, helpless and weighing a mere one to one-and-a-half pounds. These animals are quick learners with good memories, and they continue to add information throughout their lives, which may last 30 years or more in the wild. They are slow to mature, requiring four or five years to reach breeding age. Mating takes place in May or June. However, in a pattern known as delayed implantation, the fertilized egg doesn't attach to the uterus wall immediately. Instead it doesn't begin to develop until late autumn, when the mother retires into a den for the winter.
Some use natural caves as den sites, but most dig their own holes in the ground and line the bedchamber with grasses or conifer boughs. Although females may give birth to as many as four cubs in a litter, twins are most common, and the usual interval between births is three to four years. This gives grizzlies one of the lowest reproduction rates of any mammal, a crucial consideration when it comes to protecting the species and trying to restore its numbers.
The denning period is variable, depending upon location, weather and condition of the animal. Whereas black bears enter a period of true dormancy with marked lowering of the heartbeat and respiration rate, grizzlies experience only a minor drop in their metabolism and body temperature during the cold months. They may be easily aroused and occasionally venture out of their den during mild winters.
As omnivores, grizzlies feed on a variety of vegetation including roots, sprouts and fungi. They also dine on a smorgasbord of insects, fish, and warm-blooded animals. Apart from the two- to three-year-long association of cubs with their mother, the bears are generally solitary. Yet they may congregate in fairly large numbers on slopes with rich berry patches, around carcasses or insect masses, and along salmon spawning channels. Many are found in ancient forests and other types of dense cover, but the species is equally at home in open areas such as tundra, prairie foothills, alpine meadows, and coastlines.
The grizzly is a symbol of the American wilderness. It remains one of the most dramatic, imposing life forms anywhere on Earth. Not all that long ago, the Great Bear shared dominion over the western half of the continent with Native Americans. But as U.S. settlement expanded, grizzly numbers plummeted, first due tounchecked hunting, trapping and poisoning, then as a result of habitat loss.
By 1975, with just one percent of its original population left on barely two percent of its original range, the species was officially listed as threatened with extinction in the lower 48 states.