Finally, triggered by the onset of deep hibernation in the fall and able now to take advantage of the seasons fat reserves, the blastocysts attach themselves to the uterine wall and growth begins anew. Most of this can be attributed to their salmon rich fall diet. In spite of their size, grizzlies can cover ground at incredible speeds. A U.S. National Park Service researcher once clocked a sub adult grizzly galloping at 36 miles per hour. Not only do grizzlies make great sprinters, they also have the endurance of ultra marathoners, being capable of traveling extremely long distances without having to stop for rest.
Grizzly bears have an imposing physical presence.
Their leg bones and shoulders are almost grotesquely massive. They have skulls like river rocks. The hump on the grizzly's back that distinguishes it from a black bear is a thick wad of muscle which enables the bear's powerful digging ability. It is not uncommon to find portions of estuaries in the Great Bear Rainforest looking like they've been freshly roto-tilled after grizzlies have been digging in them for high protein foods such as rice root. Grizzly claws, which can be four to six inches long, are slightly curved and adapted more for digging, as opposed to the hooked claws of black bears which are adapted for tree climbing.