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.
Grizzly bears are North America’s second largest land carnivore, after the polar bear. Size and weight varies greatly according to geographic location. Inland bears, particularly those of the Yukon region, may weigh as little as 300 lbs (136 kg) for adult males. The largest populations are found in coastal areas where weights are typically 500-900 lbs (225–420 kg). Populations found in Katmai National Park and the Alaskan Peninsula may approach or just exceed 1000 lbs (450 kg); some specimens rival the Kodiak bear in size and weight. The females are on average 38% smaller, at about 250–450 pounds (114–160 kg), an example of sexual dimorphism. On average, grizzly bears stand about 1 meter (3.3 ft) at the shoulder when on all fours and 2 meters (6.6 ft) on their hind legs, but males often stand 2.44 meters (8 ft) or more on their hind legs. On average, grizzly bears from the Yukon River area are about 20% smaller than typical grizzlies. Formerly, taxonomists listed brown and grizzly bears as separate species. The Grizzly is classified as a Brown Bear subspecies, Ursus Arctos Horribilis. The term “brown bear” is commonly used to refer to the members of this subspecies found in coastal areas where salmon is the primary food source, but in fact, these are just coastal grizzlies in contemporary taxonomic classification. Inland bears and those found in northern habitats are more often called “grizzlies.” Brown bears on Kodiak Island are classified as a distinct subspecies from those on the mainland because they are genetically and physically isolated. The shape of their skulls also differs slightly.
The grizzly's coloring ranges widely depending on geographic areas, from white to almost black, and all shades in between.The grizzly also has a large hump over the shoulders, which is a muscle mass used to power the forelimbs in digging. This muscle is commonly used to dig for their various vegetative food sources. The hind legs are more powerful, however. The muscles in the lower legs provide enough strength for the bear to stand up and even walk short distances on its hind legs, giving it a better view of its surroundings. The head is large and round with a concave, disk-shaped, facial profile. In spite of their massive size, these bears can run at speeds of up to 56 kilometres per hour (35 miles per hour). However, they are slower running downhill rather than uphill because of the large hump of muscle over the shoulders. They have very thick fur to keep them warm in brutal, windy, and snowy winters.
Grizzlies can be distinguished from most other brown bear subspecies by their proportionately longer claws and cranial profile which resembles that of the polar bear. Compared to other North American brown bear subspecies, a grizzly has a silver tipped pelt and is smaller in size. This size difference is due to the lesser availability of food in the grizzlies' landlocked habitats. They are similar in size, color and behaviour to the Siberian Brown Bear (Ursus arctos collaris). Grizzly bears also characteristically have claws that are twice the length of their toes.