Reindeer (Rangifer tarandus)

The reindeer (Rangifer tarandus), also known as the caribou in North America, is a species of deer with circumpolar distribution, native to Arctic, subarctic, tundra, boreal, and mountainous regions of northern Europe, Siberia, and North America. This includes both sedentary and migratory populations. It is the only representative of the genus Rangifer. Herd size varies greatly in different geographic regions.

R. tarandus varies in size and colour from the smallest subspecies, the Svalbard reindeer, to the largest, the boreal woodland caribou. The North American range of caribou extends from Alaska through the Yukon, the Northwest Territories and Nunavut into the boreal forest and south through the Canadian Rockies. The barren-ground caribou, Porcupine caribou, and Peary caribou live in the tundra, while the shy boreal woodland caribou prefer the boreal forest. The Porcupine caribou and the barren-ground caribou form large herds and undertake lengthy seasonal migrations from birthing grounds to summer and winter feeding grounds in the tundra and taiga. The migrations of Porcupine caribou herds are among the longest of any mammal. Barren-ground caribou are also found in Kitaa in Greenland, but the larger herds are in Alaska, the Northwest Territories, and Nunavut.

The Taimyr herd of migrating Siberian tundra reindeer (R. t. sibiricus) in Russia is the largest wild reindeer herd in the world, varying between 400,000 and 1,000,000. What was once the second largest herd is the migratory boreal woodland caribou (R. t. caribou) George River herd in Canada, with former variations between 28,000 and 385,000. As of January 2018, there are fewer than 9,000 animals estimated to be left in the George River herd, as reported by the Canadian Broadcasting Corporation. The New York Times reported in April 2018 of the disappearance of the only herd of southern mountain woodland caribou in the contiguous United States with an expert calling it "functionally extinct" after the herd's size dwindled to a mere three animals. After the last individual, a female, was translocated to a wildlife rehabilitation centre in Canada, the woodland caribou was considered extirpated from the Lower 48.

Some subspecies are rare and two have already become extinct: the Queen Charlotte Islands caribou of Canada and the East Greenland caribou from East Greenland. Historically, the range of the sedentary boreal woodland caribou covered more than half of Canada and into the northern states of the contiguous United States woodland caribou have disappeared from most of their original southern range and were designated as threatened in 2002 by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Environment Canada reported in 2011 that there were approximately 34,000 boreal woodland caribou in 51 ranges remaining in Canada (Environment Canada, 2011b). Siberian tundra reindeer herds are also in decline, and Rangifer tarandus is considered to be vulnerable by the IUCN.

Arctic peoples have depended on caribou for food, clothing, and shelter, such as the Caribou Inuit, the inland-dwelling Inuit of the Kivalliq Region in northern Canada, the Caribou Clan in the Yukon, the Iñupiat, the Inuvialuit, the Hän, the Northern Tutchone, and the Gwichʼin (who followed the Porcupine caribou for millennia). Hunting wild reindeer and herding of semi-domesticated reindeer are important to several Arctic and subarctic peoples such as the Duhalar for meat, hides, antlers, milk, and transportation. The Sámi people (Sápmi) have also depended on reindeer herding and fishing for centuries.  In Sápmi, reindeer are used to pull a pulk, a Nordic sled.

Male ("bulls") and female ("cows") reindeer can grow antlers annually, although the proportion of females that grow antlers varies greatly between population and season. Antlers are typically larger on males. In traditional United States Christmas legend, Santa Claus's reindeer pull a sleigh through the night sky to help Santa Claus deliver gifts to good children on Christmas Eve.