The reindeer (Rangifer tarandus), also known as 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.While overall widespread and numerous, some of its subspecies are rare and at least one has already gone extinct.Reindeer vary considerably in colour and size.