Reindeer (Rangifer tarandus): Caribou Facts and Habitat

Reindeer or caribou?

Reindeer and caribou are one species. In Europe and Asia, “reindeer” is used for both wild and herded animals. In North America, wild animals are called caribou and the semi-domesticated animals herded in Alaska and Canada are called reindeer. The English word reindeer comes from Old Norse hreinn, while caribou comes through French from the Mi’kmaq word qalipu, usually translated as “snow shoveler,” a reference to the way the animals dig through snow for food.

Biologists divide the species into several subspecies and ecotypes (populations adapted to a particular habitat and lifestyle): migratory barren-ground caribou of the tundra, mostly sedentary woodland caribou of the boreal forest, mountain caribou, the small Peary caribou of the Canadian high Arctic and the short-legged Svalbard reindeer. Recent genetic studies have suggested splitting Rangifer into several species, but that proposal is debated and the IUCN still treats it as one. Read more in are reindeer and caribou the same?

Appearance

Reindeer are sturdy, medium-sized deer with a deep chest, a broad muzzle covered in hair and large, rounded hooves. Coat color varies with subspecies, sex and season, from dark chocolate brown in woodland caribou to nearly white in Peary caribou and some Greenland animals. In fall, many have a pale neck and mane, a white rump and white “socks” above the hooves. Domestic reindeer are often lighter, heavier and shorter-legged than wild ones and can be white or patchy.

The coat is a two-layer system: a dense, woolly underfur and long guard hairs that are hollow and filled with air. This traps heat close to the body and also makes reindeer float high in the water when they swim. Their noses contain folded bones with a large surface area that warm incoming air before it reaches the lungs and recover moisture from each breath out.

Antlers are the reindeer’s best-known feature. Bulls carry large, sweeping racks with a flattened brow tine that projects over the face; in the biggest animals the antlers can be about 1 m (39 in) wide. Relative to body size, reindeer have the largest antlers of any living deer. Cows grow smaller, simpler antlers. See do female reindeer have antlers? for how the two sexes’ antler cycles differ.

How big are reindeer?

Size varies a great deal across the range. Southern and forest-dwelling caribou are the largest, while high Arctic island forms such as the Svalbard reindeer are the smallest, with a shoulder height as low as about 80 cm (31 in).

Weight changes sharply through the year. Bulls build up thick layers of fat in late summer, sometimes more than 7 cm (3 in) deep on the back and rump, and then barely eat during the fall rut. They can lose a large share of their body weight, often quoted at up to 40 percent, by the time it is over.

Habitat and range

Reindeer have a circumpolar distribution. Wild herds live in Alaska, northern Canada, Greenland, Norway, Finland and across northern Russia, and semi-domesticated herds range across northern Scandinavia, the Russian North and northern Mongolia. Reindeer were introduced to Iceland in the 18th century and still live wild in its east, and a small free-ranging herd has grazed the Cairngorms in Scotland since the 1950s.

They use three main kinds of habitat. Tundra (treeless Arctic plains) provides summer grazing and calving grounds. Taiga, the northern conifer forest, offers shelter and lichen-rich winter range. Mountains and high plateaus such as Norway’s Hardangervidda hold some of the last wild reindeer in Europe. Reindeer once ranged much farther south, into Germany, Britain, Poland and the northern United States, but hunting and habitat change pushed them north. Caribou are now considered gone from the contiguous United States.

Diet and feeding

Reindeer are herbivores and ruminants, with a four-chambered stomach that ferments plant food with the help of microbes. Their signature winter food is lichen, especially reindeer lichen (Cladonia rangiferina), often wrongly called reindeer moss. Few large mammals can live on lichen, which is rich in carbohydrates but poor in protein. Reindeer have specialized gut microbes that break down lichen compounds most animals cannot digest.

In winter, reindeer locate food under the snow by smell and dig feeding holes, or craters, with their front hooves. In summer they switch to green food: the leaves of willows and birches, sedges, cotton grass, flowering plants and mushrooms. They occasionally chew shed antlers for minerals, and there are records of them eating lemmings and bird eggs. More detail is in what do reindeer eat?

Behavior and migration

Reindeer are social animals. Groups are small in winter but join into huge aggregations in spring and summer, sometimes tens of thousands strong. Large groups help them watch for predators and escape the clouds of mosquitoes, black flies and warble flies that plague them in the Arctic summer.

Many tundra herds are migratory. They spend winter in the forest edge and walk to traditional calving grounds on the tundra each spring, then back again in fall. A 2019 study comparing tracked land mammals worldwide found that caribou make the longest terrestrial migrations on the planet, with round trips of more than 1,000 km (620 mi). Woodland caribou and most European reindeer migrate much shorter distances or stay in one area. See how far do caribou migrate? and the longest animal migrations.

Reindeer communicate with grunts and snorts, and cows and calves call to keep in contact. Their knees, or more precisely tendons in their feet, produce a clicking sound with each step. They also see ultraviolet light, and their eyes undergo a remarkable seasonal color change, from gold in summer to blue in winter, that helps them see in the long Arctic night.

Reproduction, life cycle and lifespan

The rut, or mating season, runs from late September to early November depending on the region. Bulls shed the velvet from their antlers in late summer, their necks swell, and they spar and sometimes fight seriously for access to cows. Dominant bulls may mate with a group of roughly 5 to 20 cows, and they stop feeding for much of the rut.

Pregnancy lasts about 7.5 months (around 228–234 days). A single calf, rarely twins, is born in May or June. Newborn calves weigh about 6 kg (13 lb) on average, can stand within minutes and follow their mother within an hour or so, and can outrun a person after just one day. They begin grazing within a few weeks, but continue to suckle into the fall. Cows in good condition may breed at about 16 months, but most first give birth at 2 or 3 years of age.

Wild cows commonly live 10–15 years and some reach about 17. Bulls usually live shorter lives, often under 10 years, because the rut leaves them exhausted and injured just as winter begins. In captivity reindeer can live about 20 years. Calves face high mortality in their first weeks of life.

Predators and threats

The gray wolf is the most important natural predator of adult reindeer, and some wolf packs follow caribou herds year-round. Brown bears, black bears and wolverines also take reindeer, mainly calves and weak animals, and golden eagles hunt newborn calves on the calving grounds. On Svalbard, polar bears have been filmed hunting reindeer. The gray wolf profile describes how wolves hunt large prey.

Climate change is a growing problem. Warmer, wetter winters bring more rain-on-snow events, which leave a crust of ice over the lichens that reindeer cannot break through. In winter 2013–14, tens of thousands of reindeer starved on Russia’s Yamal Peninsula after such an event. Other threats include roads, mining, logging and oil and gas development, which fragment ranges, plus predation boosted by the open habitats that humans create.

Conservation status

The IUCN lists Rangifer tarandus as Vulnerable, based on a global decline of about 40 percent over roughly three generations (about 25 years) and a decreasing population trend. Some herds have collapsed: Canada’s George River herd fell from roughly 800,000 caribou in the early 1990s to fewer than 9,000 by 2018. Other herds, such as the Porcupine herd of Alaska and Yukon, have remained relatively stable or grown.

Three subspecies have become extinct in historical times, including Dawson’s caribou of Haida Gwaii in Canada. In Canada, the boreal woodland caribou is listed as Threatened, and several mountain populations are Endangered. In Europe, wild mountain reindeer survive mainly in southern Norway, and the Finnish forest reindeer has recovered from near extinction to a few thousand animals.

Relationship with people

Reindeer have fed and clothed Arctic peoples for thousands of years. The species is the only deer herded on a large scale. Sámi herders in Norway, Sweden and Finland, and Nenets, Evenk, Chukchi and other peoples in Russia, herd more than two million semi-domesticated reindeer for meat, hides and antlers. In North America, Indigenous peoples such as the Gwich’in and Inuit depend on wild caribou, and the animals are central to their cultures.

Reindeer were introduced to Alaska from Siberia in the 1890s to start a herding industry. Today they are also famous worldwide as Santa Claus’s sleigh team, a tradition popularized by the 1823 poem “A Visit from St. Nicholas.”

Myths and facts

• Myth: reindeer and caribou are different animals. They are the same species; the names reflect region and whether the animals are herded.
• Myth: only male reindeer have antlers. Most cows grow antlers too, and in December the antlered animals are more likely to be females, since adult bulls usually shed theirs after the rut.
• Myth: reindeer moss is a moss. It is a lichen, a partnership between a fungus and algae.
• Fact: reindeer adjust their daily rhythm. In the constant light of the Arctic summer and the darkness of winter, they do not follow a strict 24-hour body clock and instead rest and feed in short cycles through the day.