The reindeer (Rangifer tarandus), also known as the caribou in North America, is a deer from the Arctic and Subarctic, including both resident and migratory populations. While overall widespread and numerous, some of its subspecies are rare and one (or two, depending on taxonomy) have already gone extinct.
The reindeer varies considerably in colour and size, and both genders grow antlers, though these are larger in the males and there are a few populations where females lack them completely.
Hunting of wild reindeer and herding of semi-domesticated reindeer (for meat, hides, antlers, milk and transportation) are important to several Arctic and Subarctic people. Even far outside its range, the reindeer is well known due to the myth in which Santa Claus's sleigh is pulled by flying reindeer, a popular secular element of the Christian holiday of Christmas.
The reindeer is a widespread and numerous species in the northern Holarctic, being present in both tundra and taiga (boreal forest). 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 Canada, Alaska (USA), and the northern conterminous USA 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 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 Fennoscandia and Russia, with a herd of approximately 150-170 reindeer living around the Cairngorms region in Scotland. The last remaining wild tundra reindeer in Europe are found in portions of southern Norway.
A few reindeer from Norway were introduced to the South Atlantic island of South Georgia in the beginning of the 20th century. Today, there are two distinct herds still thriving there, permanently separated by glaciers. Their total numbers are no more than a few thousand. The flag and the coat of arms of the territory contain an image of a reindeer. Around 4000 reindeer have been introduced into the French sub-Antarctic archipelago of Kerguelen Islands. East Iceland has a small herd of about 4000-5000 animals.
Caribou and reindeer numbers have fluctuated historically, but many herds are in decline across their range. This global decline is linked to climate change for northern, migratory caribou and reindeer herds and industrial disturbance of caribou habitat for sedentary, non-migratory herds.
In the Santa Claus myth, Santa Claus's sleigh is pulled by flying reindeer. These were first named in the 1823 poem "A Visit from St. Nicholas", where they are called Dasher, Dancer, Prancer, Vixen, Comet, Cupid, Dunder, and Blixem. Dunder was later changed to Donder andóin other worksóDonner (in German, "thunder"), and Blixem was later changed to Bliksem, then Blitzen (German for "lightning"). Some consider Rudolph as part of the group as well, though he was not part of the original named work referenced previously. Rudolph was added by Robert L. May in 1939 as "Rudolph the Red-Nosed Reindeer".
According to the British comedy panel game QI, Rudolph the Red-Nosed Reindeer and all of Santa's other reindeer must be either female or castrated, because male reindeer lose their antlers during winter.