Rangifer tarandus
caribou
(Also: reindeer)

Caribou have a nearly circumpolar distribution. The woodland subspecies of caribou (Rangifer tarandus caribou) can be found as far south as 46o north latitude, while other subspecies (Peary caribou [R. t. pearyi] and Svalbard reindeer [R. t. platyrhynchus]) can be found as far north as 80o north latitude. Once found as far south as Germany, Great Britain, Poland, and Maine (USA), over-hunting and habitat destruction have diminished the historic range of caribou.

Caribou inhabit arctic tundra and subarctic (boreal) forest regions.

The various subspecies of caribou display a wide range of size. Generally speaking, the subspecies inhabiting the more southerly latitudes are larger than their northern cousins. Caribou can have shoulder heights of up to 120 cm and total length ranges from 150 to 230 cm. They have short tails. There is marked sexual dimorphism, with males of some subspecies being twice as large as females. The coat of the caribou is an excellent, lightweight insulation against the extreme cold temperatures they face. The hairs are hollow and taper sharply which helps trap heat close to the body and also makes them more buoyant. Color varies by subspecies, region, sex, and season from the very dark browns of woodland caribou bulls in summer to nearly white in Greenland (R. t. groenlandicus) and high Arctic caribou. White areas are often present on the belly, neck, and above the hooves. The hooves are large and concave, which support them in snow and soft tundra, conditions that they often face. The broad hooves are also useful when swimming. Caribou make an audible clicking noise while walking, which is produced from tendons rubbing across a bone in the foot. Rangifer tarandus is the only species of deer in which both sexes have antlers. Mature bulls can carry enormous and complex antlers, whereas cows and young animals generally have smaller and simpler ones. Mature bulls usually shed their antlers shortly after the rut whereas cows can keep theirs until spring.

Females generally have longer life spans than males, some over 15 years. Bulls are highly susceptible to predation after the rut, which can leave them injured and/or exhausted. Bulls typically live less than 10 years in the wild. Average life expectancy is 4.5 years.

Caribou are known to travel distances greater than any other terrestrial mammal. The can traverse more than 5,000 kilometers in a year, with extensive migrations in spring and fall. They can reach speeds of 80 km/hr. Spring migration leads the caribou off the winter range back to calving grounds. Use of traditional calving grounds is the basis by which caribou herds are defined. Caribou are gregarious and the largest groups, which can number in the tens of thousands, are found during the summer months. This behavior is thought to bring about some measure of relief from harassing mosquitoes, warble flies, and nose bot flies. As cooler weather arrives, groups become smaller but caribou may aggregate again during the rut and fall migration. Bulls spar with competitors to keep them from breeding with females in their area. Most encounters are brief, but serious battles do occur which can result in injury or death. Most caribou winter in forested areas, where snow conditions are more favorable. Caribou are able to locate forage under snow, apparently by their ability to smell it. To reach the forage they use their front paws to dig craters. Dominant caribou frequently usurp craters dug by subordinate animals.

Caribou communicate among themselves through vocal, visual, chemical, and tactile cues. They have a keen sense of smell, which allows them to find food buried deep under snow.

Caribou are primarily grazing herbivores. Their diet is most variable during the summer, when they consume the leaves of willows and birches, mushrooms, cotton grass, sedges and numerous other ground dwelling species of vegetation. Lichens are an important component of the diet, especially in winter, but are not eaten exclusively.

Calves are highly vulnerable to predation by bears, wolves, and other predators during their first week of life. Healthy adult caribou are less susceptible to predation until old age and illness weakens them. By traveling in herds, caribou increase the number of individuals that can watch for predators.

Through their foraging activities, caribou have a dramatic impact on communities of vegetation throughout their range. They are also important prey species for large predators, such as bears and wolves, especially during the calving season.

There are no negative impacts of caribou.

Caribou have been used extensively for their meat, fur and antlers. Reindeer, the domesticated subspecies of caribou, have been herded throughout their range for thousands of years.

Although Alaska, with its more than 30 herds, has nearly double the number of caribou (1,000,000) than people, caribou in the contiguous US are considered endangered. Caribou in Alaska are of the barren-ground subspecies, whereas extant (WA, ID) and extinct (ME) herds are of the woodland subspecies. The Selkirk Herd, inhabiting WA, ID, and southern British Columbia numbers only around 30 members. They are listed as Endangered under the Endangered Species Act in these regions. Loss of habitat, overhunting, and other factors has contributed to the precarious position the woodland caribou now exists in the US. Worldwide, the caribou population is estimated to be around 5 million. The largest herds now occur in Alaska, Canada, and Russia. Humans have heavily hunted this species. They have been extinct in most parts of Europe since at least the 1600s. Exploration for oil and minerals in Canada may threaten woodland caribou habitat. High Arctic caribou populations are also thought to be vulnerable.

Despite their status in the wild, domestic herds of reindeer flourish in the Old World, in Canada, in Alaska, and in the lower 48 states including Michigan.

Caribou, and their domestic counterparts - reindeer, have been very important in the cultures of native peoples througout the arctic. Several Siberian, Scandinavian, and American native cultures are built around herding caribou.