The reindeer, known as caribou when wild in North America, is an Arctic and Subarctic-dwelling deer.
About 1 million live in Alaska, and a comparable number live in northern Canada.
There are an estimated 5 million reindeer in Eurasia, mainly semi-domesticated.
The last remaining European herds of the genetic wild reindeer are found in central Norway.
In the wild, most caribou migrate in large herds between their birthing habitat and their winter habitat.
Their wide hooves help the animals move through snow and tundra; they also help propel the animal when it swims.
Reindeer are ruminants, having a four-chambered stomach.
They mainly eat lichens in winter, especially reindeer moss.
However, they also eat the leaves of willows and birches, as well as sedges and grasses.
There is some evidence to suggest that on occasion they will also feed on lemmings, arctic char and bird eggs.