This document may be used, with this header included, for noncommercial purposes within a subscribed institution . No copies of this work may be distributed electronically outside of the subscribed institution, in whole or in part, without written permission from the JHU Press . As protection against the rigorous climate in which it lives, the caribou has a heavy coat of woolly underfur and straight, stiff, tubular guard hairs. Coloration varies widely, but most individuals are predominantly brownish or grayish above and have white or pale underparts, inner legs, and buttocks. The winter pelage is somewhat paler.
Some animals are dark brown or almost black, and some are quite pale.
The subspecies R. t. pearyi, of northern Greenland, Ellesmere Island, and nearby islands, is almost pure white. Rangifer is the only genus of the deer family in which both sexes are antlered. Although there is great diversity in the shape of the antlers, they are usually long, sweeping beams with forwardly projecting brow tines. The broad, flat, and deeply cleft hooves aid in walking on soft ground and snow. When the caribou walks, a clicking noise is produced by a tendon slipping over a bone in the foot.