A combination of clear, readable text and appealing, detailed pencil drawings--in a fascinating look at the physical and chemical changes in animals during hibernation, estivation, and sleep. Included are animals like ground squirrels, whose body temperatures drop to near freezing during the winter due to a blood substance called HIT (Hibernation Inducement Trigger); the grizzly bear, who spends five months without eating, drinking, urinating, or defecation, nourished by a special layer of brown fat; snakes and amphibians, who hibernate during the winter and aestivate during hot dry periods; and daily dormants like bats, hummingbirds, and shrews, who save energy by going dormant for part of each day. Sleep, a kind of limited hibernation, is discussed with speculation on whether animals dream. A satisfying, informative science title in handsome format. Index.