Caribou (Rangifer tarandus, a member of the deer family Cervidae) are found throughout the Arctic and are known as reindeer in Eurasia. Caribou apparently originated in alpine habitats in the New World during the late Pliocene (4.2-2.5 million years ago). As climates cooled during the Pleistocene (about 2 million years ago), caribou adapted to cold dry climates followed by the spread of tundra habitats across the north and into Eurasia via the Bering land bridge. Together, the caribou of North America and Greenland and the reindeer of Eurasia now have the most extensive circumpolar distribution of any living hoofed mammal.

The name "caribou" likely derives from the Micmac word xalibu — "the one who paws," an apt name for this animal of cold and snowy regions. Caribou are well furred, even on their muzzles, with hollow guard hairs that trap air for added insulation as well as buoyancy when swimming. Their large, concave hooves splay out for traction on snow and boggy ground and double as efficient digging scoops to reach ground lichens through snow. Unique among deer, both males and females possess antlers. Females retain their smaller antlers until just after calving and use them during winter to defend feeding craters in the snow from other females as well as males, which drop their antlers earlier (November for older, breeding males, and by April for younger males). Adult caribou travel with ease and can easily outrun their primary predators, wolves. While lichens are their primary winter food, they also feed on low shrubs, moss, grasses, and cottongrass, and leaves of dwarf birch and willow in spring and summer.

Although caribou have been divided into a number of subspecies, there is no consensus on their validity. However, distinctions based on habitat can be made among three ecotypes: woodland, barren ground, and Arctic caribou.

Barren ground caribou crossing the tundra, Northwest Territories, Canada.

Copyright Paul Nicklen/National Geographic Image Collection

Barren ground caribou crossing the tundra, Northwest Territories, Canada.

Copyright Paul Nicklen/National Geographic Image Collection

Woodland caribou occur in relatively small populations (hundreds to thousands of individuals) in boreal forest across North America, including the mountainous areas of the west. Prior to deforestation following European settlement of North America, woodland caribou ranged much farther south. Today, many populations are threatened by human activities. Woodland caribou are large; males weigh up to 250 kg and females up to about 125 kg. Although considered sedentary, woodland caribou do move among a variety of habitats, using lowland forested habitats during spring/summer and alpine or coastal tundra areas in winter, particularly if snow is deep.

Barren ground caribou represent the classic migratory ecotype, traveling thousands of kilometers annually between calving areas on tundra and wintering areas within the boreal zone. They occur in relatively discrete populations (herds) across the north, each named for its calving area (such as the Porcupine caribou herd). Their populations may number in the tens to the hundreds of thousands; they also go through decades-long cycles of abundance driven by factors like weather, forage abundance, and predation. Barren ground caribou are intermediate in size, with males weighing up to 150 kg and females up to about 90 kg.

Arctic (or Peary's) caribou are the smallest of the ecotypes: males weigh 65 kg and females 52 kg. This dwarfing is a consequence of the short growing season, low plant productivity, and long and cold winters that they face in the High Arctic (up to 80° N). Arctic caribou may be particularly vulnerable to extreme weather events.

Caribou breed during a relatively brief fall rut. In woodland populations, males attempt to defend small groups of females, whereas barren ground males follow a single estrus female until she is ready to mate. Consequently, woodland caribou males have antlers more suitable for combat with other males while barren ground males have antlers more useful for display to attract females. Once copulation occurs, the male abandons the female and seeks additional mates. Only the larger males typically breed.

Gestation is approximately 228 days. Pregnant barren ground caribou cows migrate to a traditional calving ground in April or May; the timing of the migration may vary depending on snow conditions and, if spring is late, females may drop their calves before reaching the calving grounds. Once on the calving grounds, the females disperse and calve over a brief (i.e., 10-day) period. Poor weather may kill many calves, but predators are not common. Wolves den below treeline and pup in May; thus, most do not follow the cows to the calving ground. Nevertheless, some wolves as well as bears, wolverines, foxes, and golden eagles take their toll.

Woodland cows do not aggregate for calving. After spending the winter in groups, females disperse into forested areas and calve near lakes, ponds, and wetlands in late May or June. Woodland females attempt to hide their calves from predators, which they cannot escape through migration. Still, the major cause of mortality of the young, especially those under a month of age, is wolf or bear predation.

To further reduce predation risk, caribou calves are among the most precocial of deer neonates, capable of moving around on their own soon after birth, and are fed one of the richest milks (25-38% milk solids). This may speed up development, but represents a heavy investment on the mother, limits her to a single calf, and may result in her failure to calve every year during periods of nutritional stress.

After calving, barren ground females form postcalving aggregations, which may number in the tens of thousands or more, and begin to utilize the spring greenup of vascular plants occurring on the tundra. Soon after, hordes of mosquitoes, black flies, and the larger nose bot and warble flies emerge and force caribou to seek habitats such as windy ridges, coastlines, or snow banks where insect activity is lower. These measures, however, limit the ability of caribou to feed. Once insect activity declines in late summer, the aggregations disperse and caribou focus on eating before fall frosts end the season's productivity.

Bulls do not follow females to the tundra calving grounds but remain on richer vegetation, in order to maximize growth during the short summers. By fall, a male may have acquired a reserve of fat representing 15% of his body weight, including a large supply of back fat up to 8 cm thick, to see him through the rut. Antlers grown during this same period may represent 5% of a male's lean weight.

The indigenous peoples of the north have relied on caribou for thousands of years, hunting them at river crossings or driving them into ambushes. Every language group had one or more names for caribou. The

Inuit called them tuktu. One group of Dene from western Canada were known as Etthen-eldeli-dene or "caribou eaters" and followed a nomadic lifestyle centered on the caribou. For all the peoples of the north, caribou meant food, hides for clothing, boots, boats and shelter, bones and antlers for tools, sinew for thread, and fat for fuel.

Most indigenous cultures created stories and customs centered upon the caribou. One Dene legend, for example, spoke of caribou coming to Earth from the Milky Way; in another, caribou came down to Earth from the aurora borealis. The dependence of humans on caribou is also reflected in a variety of customs concerning respect. Caribou migrations may suddenly change after years or decades of regularity, leaving hunters with the prospect of starvation. For the Dene, these sudden departures from tradition might follow disrespectful treatment of caribou.

Fred Harrington

See also Caribou Hunting; Reindeer; Reindeer Pas-toralism

Further Reading

Banfield, Alexander W.F., The Mammals of Canada, Toronto:

University of Toronto Press, 1974 Burham, Dorothy K., To Please the Caribou: Painted Caribou-Skin Coats Worn by the Naskapi, Montagnais, and Cree Hunters of the Québec-Labrador Peninsula, Toronto: Royal Ontario Museum, 1992 Calef, George, Caribou and the Barren-Lands, Toronto: Firefly Books, 1981

Hall, Ed, People and Caribou in the Northwest Territories, Yellowknife, Northwest Territories: Department of Renewable Resources, Government of the Northwest Territories, 1989 Jackson, Lawrence J. & Paul T. Thacker, Caribou and Reindeer Hunters of the Northern Hemisphere, Aldershot, Hampshire: Ashgate, 1997 Kelsall, John P., The Migratory Barren-Ground Caribou of

Canada, Ottawa: Canadian Wildlife Service, 1968 Morrison, David A., Caribou Hunters in the Western Arctic: Zooarchaeology of the Rita-Claire and Bison Skull Sites, Ottawa: Canadian Museum of Civilization, 1998 Russell, H. John, Nature of Caribou: Spirit of the North,

Vancouver: Douglas and McIntyre, 1998 Thorpe, Natasha, Naikak Hakongak, Sandra Eyegetok & Kitikmeot Elders, Thunder on the Tundra: Inuit Qaujimajatuqangit of the Bathurst Caribou, Victoria, British Columbia: Tuktu and Nogak Project, 2002 Walker, Tom, Caribou: Wanderer of the Tundra, Portland, Oregon: Graphic Arts Center Publishing Company, 2000

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