Real hibernators can't be awakened by disturbance, but bears can, as researchers who've visited their winter lairs know. At times their pulses fall to eight beats per minute. One reason the seemingly invincible grizzly is in such danger from man is that it reproduces slowly. Females don't mate until they are at least 4 or 5 years old. Plus, cubs stay with their mothers for up to four years, and only females without cubs will mate.
Females typically produce one or two cubs at a time.
Wildlife managers fear that we're killing grizzlies as fast as they can reproduce, despite best efforts to the contrary. Despite the fact that Yellowstone grizzly numbers seem to be fairly stable, some experts say that such a small population in such an isolated wilderness pocket is too vulnerable to further habitat reduction, mismanagement or act of nature. These people predict extinction for the Yellowstone grizzlies within 100 years. And park officials help preserve their tiny island of isolation, closing trails and campsites near kills, and in certain high-use seasons closing whole areas to human traffic. Even if you're in their territory, a grizzly can scent your presence at several hundred yards and will generally retreat without your ever knowing he was near.