The caribou or reindeer (Rangifer tarandus) is a northern species of deer occurring in the boreal and arctic regions of North America and Eurasia. At one time, caribou and reindeer were considered to be separate species, but these animals are fully interfertile and are now considered to be the same species. In North America they are called caribou, whereas in Eurasia they are known as reindeer. However, there are well-differentiated, geographically distinct populations of these animals, which are designated as subspecies. Northern caribou are relatively small, while southern caribou are larger, with the biggest males (bucks) weighing up to 660 lb (300 kg).
Caribou are even-toed, hoofed mammals in the order Artiodactyla and suborder Ruminanta. They are in the family Cervidae, along with other species of deer. Like other deer and cattle, caribou have a four-chambered stomach capable of digesting the tough, fibrous plant and lichen materials containing cellulose that comprise most of their diet. Caribou ruminate, which means they re-chew forage that has previously fermented in the fore-pouches of their stomach.
Like other deer (family Cervidae), caribou have deciduous antlers, which are long, branching, bony outgrowths of the frontal bones of the skull. During their growth, antlers are covered with a heavily vascularized tissue called velvet, which eventually dries and is peeled or rubbed off, leaving the bare bone exposed. Unlike other species of deer, both sexes of caribou can develop antlers. However, the antlers of mature male animals are much larger and more elaborate than those of females. The males use their antlers for jousting during the rutting season, when they attempt to assemble a harem of does. The antlers of adult bucks grow most rapidly from May to July, and are at their largest size in August. By October the antlers are hard and velvet free, and are used in ritualized combat with other males, although this can escalate into real fighting. Soon after the rut, the joint between the antler and the skull weakens, and the antler is shed, usually by early December. Antler growth in female caribou
starts later (June to September), and shedding is delayed until April or May when the calves are born.
The newborn calves of caribou are very precocious, and are able to stand within only one-half hour of birth. After a few days, calves are capable of running several kilometers an hour, and can keep up with the moving herd. This rapid development is, of course, an adaptation to reducing the predation rate of young calves, the stage with the highest risk of mortality.
In North America, the most northerly subspecies is the Peary caribou (Rangifer tarandus pearyi). This relatively small, whitish subspecies is a resident of the high-arctic islands of northern Canada. Peary caribou gain weight during the warmest two to three months of the year, foraging on grasses and forbs (broadleaf herbs) in relatively productive wet meadows and dwarf-shrub tundra. During most of the rest of the year, however, these animals must survive on the much sparser and less nutritious vegetation of upland, relatively snow-free ridges.
Farther to the south are woodland, or barren-ground caribou (these are mostly R. t. caribou in the east, and R. t. groenlandicus in the west). These relatively large, brown-colored caribou tend to undertake long-distance, seasonal migrations, which can exceed 600 mi (1,000 km) in their circuitous passage. The caribou often swim across large rivers during those journeys. During the growing season, these caribou move to open habitats such as tundra and muskeg (the latter is mostly peaty wetlands with tussock meadows and low woody vegetation), where they calve and feed on the lush growth of grasses, sedges, forbs, and young twigs of shrubs. At the end of the growing season, the barren-ground caribou migrate back to the boreal forest, where they feed largely on arboreal and ground lichens during the winter. More southerly caribou living in mountainous terrain undertake vertical migrations, to alpine tundra and meadows during the summer, and montane forest in winter.
In general, the winter diet of caribou consists of foods that are not very nutritious, such as lichens, twigs, and dried grasses and forbs. Caribou tend to slowly lose weight on this poor quality diet, during a time when there are great energy demands for thermoregulation in cold temperatures and windy conditions. During summer, a much wider range of more nutritious foods is available, and caribou put weight on at that time. Summer foods include grasses, sedges, forbs, new twigs and foliage of shrubs, mushrooms, and berries. Caribou will also opportunistically eat lemmings and birds eggs.
Caribou are rather social animals, tending to occur in groups of various size. These assemblies are loosely segregated by sex and age-class, and their size can vary seasonally. The density of animals in the groups also varies, being more compact when caribou are harassed by predators such as wolves or humans, or sometimes if the animals are being severely bothered by biting flies. During the autumn migrations and the rutting period, woodland caribou may occur in enormous herds of tens of thousands of animals, which disperse into much smaller herds at other times.
Caribou have an excellent sense of smell, but do less well visually. Sometimes, these animals can be closely approached from downwind. Caribou can be quite curious, and humans can occasionally approach these animals while walking directly towards them and holding their arms straight up, roughly simulating the silhouette of an oncoming caribou. When frightened, caribou usually run a short distance, circle around until they catch a confirming scent of the intruder, and then move to a safer distance.
Wolves are the most important natural predators of caribou, but grizzly bear, wolverine, and lynx also kill some animals. Caribou were also a staple food for aboriginal humans in North America, and they continue to be an important game species throughout their range. In some areas caribou have been overharvested, and they have been widely extirpated from most of the southern parts of their original North American range, for example in Maine, the Maritime Provinces, parts of the southern boreal forest, and parts of the Rocky Mountains. In one unusual case, about 10,000 caribou drowned in northern Quebec when a hydroelectric authority released huge quantities of water into a river that the animals had to traverse.
Reindeer (R. t. tarandus) have long been domesticated by northern peoples of Eurasia, such as the Lapps of northern Scandinavia. Reindeer have also been introduced to the western Arctic of North America, and to subarctic South Georgia Island in the Southern Hemisphere, in attempts to develop commercial enterprises. Domestic reindeer are husbanded for their meat, hide, and milk. In recent years, a large export market has developed in China and elsewhere in eastern Asia for reindeer or caribou horn in velvet, which is made into a powder used in traditional medicine. Domestic reindeer have also been used to pull small sleighs and wagons.
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