Bears

Eight species, and why their winter sleep is not true hibernation.

There are eight living bear species: brown, American black, Asian black, polar, giant panda, sloth, sun and spectacled. They range from the almost entirely herbivorous panda to the almost entirely carnivorous polar bear.

Winter dormancy

Bears enter a winter dormancy that differs from the deep hibernation of small mammals. Body temperature drops only a few degrees rather than to near ambient, and a bear can wake and move if disturbed. Heart rate and metabolism fall sharply, and the animal does not eat, drink or excrete for months, living on fat and recycling urea into protein. Females give birth during it.

Diet

Most species are omnivores whose diet tracks the season: shoots in spring, berries and insects in summer, nuts and salmon in autumn. Polar bears are the exception, depending on seals hunted from sea ice, which ties them directly to ice extent.