The reindeer or caribou (Rangifer tarandus) 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. More recent studies suggest the splitting of reindeer and caribou into six distinct species over their range.
Reindeer occur in both migratory and sedentary populations, and their herd sizes vary greatly in different regions. The tundra subspecies are adapted for extreme cold, and some are adapted for long-distance migration.
Reindeer vary greatly in size and color from the smallest, the Svalbard reindeer (R. (t.) platyrhynchus), to the largest, Osborn's caribou (R. t. osborni). Although reindeer are quite numerous, some species and subspecies are