Some bears hibernate in hollowed-out tree trunks. Some take a months-long rest beneath thick brambles and brush. Others dig into the hills to forge snug dens. And still others discover caves to hide away from the biting winter chill. But wherever a bear chooses to hibernate, the objective is the same. It's a keen adaptation to avoid the long, ruthless winter famine. Hibernating animals — including ground squirrels, groundhogs, and bats — slow their breaths, reduce their heartbeats, and substantially wind down, or depress, their metabolisms. Such dramatic changes can be taxing on their bodies, but the alternative, amid a starving winter, is almost certain death. So, come fall, the animals go into a controlled, coma-like state.
