Hibernating Bears: Brian Barnes has been studying bears in a hibernaculum in Fairbanks, Alaska: "Bears don't eat, drink, urinate or defecate for six or seven months," he says. They make their own water, probably by metabolizing fat, and they get rid of wastes by breaking them down internally. "They're a closed system. All they need is air, and they can do just fine. They're a metabolic marvel."