They are very closely related, so closely that they are now usually considered different races of the same species, Rangifer tarandus. Even the somewhat smaller domesticated reindeer are part of the same group.
Caribou coloration varies widely, from nearly black to brown to gray to almost white, and some populations migrate hundreds of miles, with some preferring the arctic tundra for summer and the edges of woodlands for winter.
Their coats may vary from mostly brown in summer to gray in winter.
Caribou or reindeer range from Scandinavia, European Russia, and Siberia to Greenland, Alaska, and Canada. They have even been introduced into the island of South Georgia in the South Atlantic.
There are nine races or subspecies of caribou or reindeer; many of the European races are domesticated.
Reindeer are the only deer in which both sexes have antlers, which they shed at different times of the year.
It has been suggested that the females’ antlers help them compete for food in the unusual herds that reindeers form, which are both large, with up to forty females per male, and coed, though adult males are often solitary until it comes time to gather a harem.