The reindeer (Rangifer tarandus), also known as the caribou when wild in North America, is an Arctic and Subarctic-dwelling deer, widespread and numerous across the northern Holarctic.

Distribution and habitat

The reindeer is a widespread and numerous species in the northern Holarctic. Originally, the reindeer was found in Scandinavia, Eastern Europe, Russia, Mongolia, and northern China north of the 50th latitude. In North America, it was found in Alaska, Canada, and the northern US from Washington to Maine. In the 19th century, it was apparently still present in southern Idaho. It also occurred naturally on Sakhalin, Greenland, and probably even in historical times in Scotland and Ireland. During the late Pleistocene era, reindeer were found as far south as Nevada and Tennessee in North America and Spain in Europe. Today, wild reindeer have disappeared from many areas within this large historical range, especially from the southern parts, where it vanished almost everywhere. Large populations of wild reindeer are still found in Norway, Siberia, Greenland, Alaska, and Canada.

Domesticated reindeer are mostly found in northern Scandinavia, Russia, and Iceland (where they were introduced by humans in the 18th century). The last remaining wild reindeer in Europe are found in portions of southern Norway. The southern boundary of the species' natural range is approximately at 62° north latitude.

Anatomy

The female varies in weight between and measures long. The male (or "bull") is typically larger (although the extent to which varies in the different subspecies), weighing and measuring in head-and-body length. Shoulder height can measure from , and the tail adds . Both sexes grow antlers, which (in the Scandinavian variety) for old males fall off in December, for young males in the early spring, and for females in the summer. The antlers typically have two separate groups of points (see image), a lower and upper. Domesticated reindeer are shorter-legged and heavier than their wild counterparts. The bull reindeer's antlers are the second largest of any extant deer, after the moose, and can range up to in width and in beam length.

Reindeer have specialized noses featuring nasal turbinate bones that dramatically increase the surface area within the nostrils. Incoming cold air is warmed by the animal's body heat before entering the lungs, and water is condensed from the expired air and captured before the deer's breath is exhaled, used to moisten dry incoming air and possibly absorbed into the blood through the mucous membranes.

Reindeer hooves adapt to the season: in the summer, when the tundra is soft and wet, the footpads become sponge-like and provide extra traction. In the winter, the pads shrink and tighten, exposing the rim of the hoof, which cuts into the ice and crusted snow to keep it from slipping. This also enables them to dig down (an activity known as "cratering")"In the winter, the fleshy pads on these toes grow longer and form a tough, hornlike rim. Caribou use these large, sharp-edged hooves to dig through the snow and uncover the lichens that sustain them in winter months. Biologists call this activity "cratering" because of the crater-like cavity the caribou's hooves leave in the snow." All About Caribou - Project CaribouImage of reindeer cratering in snow. through the snow to their favorite food, a lichen known as reindeer moss. The knees of many species of reindeer are adapted to produce a clicking sound as they walk.