What Is Hibernation? How Animals Shut Down for Winter

White mouse held in a gloved hand

What is hibernation? Calling it “winter sleep” is the most common mistake. Sleep is a brief, easily reversible state. Hibernation is a planned, deep suppression of metabolism — body temperature crashes, heart rate collapses, and the animal cannot simply be woken up. A hibernating ground squirrel is closer to a switched-off machine than to a … Read more