For protein and fat, it eats massive quantities of acorns and pine nuts. The female then holds her fertilized embryo in a kind of suspended animation until she eats enough. Unless she gets sufficient fat supplies stored in fall, she will reabsorb the embryo and not reproduce that year. In late fall, a black bear will find a place to dig a den. With broad, five-toed paws tipped with nonretractable claws, it scoops out a cozy bedroom under a rocky crevice or overhang.
Hibernation reduces the bear's energy consumption at a time when food is scarce.
But a bear's winter sleep is not true hibernation, like mice and ground squirrels undergo. Rodents go into a deep sleep, their metabolism nearly halts, and their body temperature plummets from 100 degrees to 40. Even so, each week hibernating rodents must wake up, move around and take a bathroom break. Bears don't do any of that. Sleeping lightly, they lie motionless for months and their body temp drops only 10 degrees.