Reindeer

The reindeer, called caribou in North America, is a deer with a circumpolar distribution across Arctic, subarctic, tundra, boreal and mountainous regions of Northern Europe, Siberia and North America. It is the only member of the genus Rangifer. Populations may be migratory or sedentary, tundra subspecies are adapted for extreme cold, and some travel long distances. Reindeer are unique among deer in that females may grow antlers, though how common this is varies between populations. They are the only deer successfully semi-domesticated on a large scale, and wild and domestic animals have long supplied Arctic peoples with food, clothing and shelter.

About the reindeer

The reindeer, called caribou in North America, is a deer native to the Arctic, subarctic, tundra, boreal and mountain regions of Northern Europe, Siberia and North America. It is the only representative of the genus Rangifer, and it is the only deer successfully semi-domesticated on a large scale, long herded and hunted by Arctic peoples for food, clothing and shelter.

Reindeer and caribou are traditionally treated as one species, Rangifer tarandus, with several subspecies, though recent studies suggest splitting them. Size and color vary a lot. The Svalbard reindeer of the Svalbard Archipelago is the smallest form, while Osborn's caribou is the largest. Northern populations tend to be smaller and whiter, and southern ones larger and darker.

Antlers set the reindeer apart. It is the only deer in which females normally grow antlers too, though how many females do so varies by population. A big bull's antlers are, on average, the second largest of any living deer after the moose, and the largest relative to body size. In the largest subspecies they can reach 100 cm (39 in) across and 135 cm (53 in) along the main beam. Bulls drop their antlers in late autumn or early winter after the rut, while cows keep theirs until they give birth in spring. Once the bulls have shed theirs, antlered cows take the top ranks in the feeding hierarchy and gain access to the best forage.

The coat has a dense, woolly undercoat under long, hollow, air-filled guard hairs that trap heat and make reindeer float high in the water. Large, crescent-shaped hooves support the animal in snow and soft tundra and serve as shovels when digging for food. In summer the foot pads are soft and spongy for grip on wet tundra; in winter they shrink and harden, so the animal walks on the sharp rim of the hoof, which bites into ice and crusted snow.

Reindeer can see ultraviolet light, down to wavelengths of about 320 nm, well below the human limit of 400 nm. Many things that blend into the landscape to human eyes, such as urine and fur, stand out sharply in ultraviolet, and the ability may help reindeer pick out lichens against bright snow. The reflective layer at the back of the eye also changes from gold in summer to blue in winter.

Behavior and diet

Reindeer are ruminants with a four-chambered stomach. In winter they live largely on lichens, especially reindeer lichen (Cladonia rangiferina), and they are the only large mammal able to digest lichen. A gut bacterium unique to reindeer breaks down usnic acid, a toxic compound many lichens produce. They dig "craters" through snow to reach it, finding food by smell. In warmer months they eat willow and birch leaves, sedges, grasses and mushrooms.

They also gnaw and partly eat shed antlers as a dietary supplement. When food is scarce in spring, there is some evidence they occasionally eat lemmings, fish such as Arctic char, and bird eggs.

Some North American caribou herds make the longest migrations of any land mammal, traveling up to 5,000 km (3,000 mi) a year. Migrating herds usually cover 19–55 km (12–34 mi) a day and can run at 60–80 km/h (37–50 mph). In spring, small groups merge into herds of 50,000 to 500,000 animals. Reindeer are strong swimmers, normally moving at about 6.5 km/h (4 mph) and up to 10 km/h (6.2 mph), and migrating herds readily cross wide rivers and lakes.

Many reindeer make a clicking sound as they walk, caused by tendons slipping over small bones in the feet. The click can be heard several hundred meters away, and louder clicks signal a bigger animal, helping set rank in the herd.

Mating happens from late September to early November. Bulls lock antlers and shove, and a dominant bull may gather 15–20 cows. He stops eating during the rut, and bulls can lose as much as 40% of their pre-rut weight. A single calf weighing about 6 kg (13 lb) is born in May or June. Calves can graze after about 45 days, and a calf only a day old can already outrun an Olympic sprinter.

Range and habitat

Reindeer live in a ring around the top of the world, in tundra and boreal forest from Svalbard, Norway, Finland and Russia to Alaska, Canada, the Arctic islands and Greenland. Large wild populations remain in Norway, Finland, Siberia, Greenland, Alaska and Canada. The Taimyr herd in Russia is the largest wild herd in the world, swinging between 400,000 and 1,000,000 animals.

Historically the range reached farther south. In North America, caribou once lived in the northern contiguous United States from Maine to Washington. The last southern mountain caribou herd in the lower 48 states dwindled to a handful of animals, and caribou are now considered extirpated from the contiguous United States.

Reindeer have also been introduced to and gone feral on islands such as Iceland, South Georgia and the Pribilof Islands, and a free-ranging semi-domesticated herd lives in Scotland. In Sweden, about 250,000 reindeer live in herds managed by Sámi villages.

Reindeer vs caribou

"Reindeer" and "caribou" are two names for the same species. Reindeer is the usual European name, while North Americans call wild animals caribou. In everyday use, "reindeer" often means the semi-domesticated form herded in Eurasia.

Conservation status

The reindeer is listed as Vulnerable on the IUCN Red List, assessed in 2016 after an observed population decline of 40% over about 25 years. The species as a whole remains numerous and widespread, but many herds are shrinking.

Climate change is a major driver for migratory herds, and industrial disturbance of habitat for herds that stay put. Longer autumns bring freezing rain that seals lichen under ice; in 2016, more than 81,000 reindeer in Russia were reported to have died after this happened. Canada's George River herd fell from 800,000–900,000 in the 1990s to fewer than 9,000 by 2018.

Three subspecies are already extinct, and in Canada the boreal woodland caribou is designated Threatened and the Peary caribou Endangered. Wolves, bears and wolverines prey on reindeer, golden eagles take calves, and the gray wolf is the most effective natural predator of adults. White-tailed deer commonly carry a brainworm that causes fatal neurological symptoms in reindeer.