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Caribou
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Caribou

Animals - Mammals - Deer

Caribou in Denali National Park

The range of the Denali Caribou Herd is almost exclusively within the boundaries of Denali National Park and Preserve. The Denali Herd inhabits most of the park east of the Foraker River and north of the Alaska Range throughout most of the year. Some animals of the Denali Herd will occasionally travel south of the Alaska Range toward the vicinity of Cantwell during the calving season. Biologists place great value on the research conducted on the Denali Herd because it is the only barren-ground caribou herd in North America of such a large size class that is currently not hunted. It also shares its range with a natural complement of large predators and both predator and prey populations within Denali are naturally regulated.

During the summer the body of the caribou is generally covered by brown fur. Coloration is variable, ranging from pure white through tan to dark brownish gray, with lighter rump and undersides. In the winter the coat turns grayish to almost white in color and gets thicker and longer than the summer coat. The coat is made of two layers: a guard coat made of straight, tubular hairs and a wooly undercoat. Calves are brown and unspotted. Mature caribou stand approximately four feet tall at the shoulder, eight feet in length and weigh from 130 to over 350 pounds. Caribou hoofs are very large and form a nearly circular print - acting like snowshoes to keep the animal from sinking in the snow. Both males (bulls) and females (cows) grow antlers standing as high as three feet or more.

The Caribou breeding season occurs during late September though October. Cows begin breeding when they are around 2.5 years old. After breeding the gestation period lasts 225-235 days with the calves usually born mid-May to early June. Like the other members of the deer family bulls spar with each other during the rut for breeding access to the females. During these fights the bulls will charge each other with their heads cocked downward. They run into each other antlers first, rear up, and on their hind legs and paw at each other with the front hooves. Injuries are rare, however, the bulls will occasionally get their antlers locked together, which can result in death for both animals.

In the spring the females will migrate towards areas known as calving grounds to give birth in safety. According to studies, the number of predators on the calving grounds is less than the caribou encounter on their winter range. Instincts to reach these areas are so strong with the caribou that they are able to travel through adverse conditions like deep snow, steep mountains and icy rivers. The young are born shortly after the females arrive on the grounds.

The size of the Denali Caribou Herd has fluctuated greatly over the last 80 years. It once numbered over 20,000 caribou during the 1920's and 1930's. During the 1940's through the 1960's, the herd declined to 10,000 animals but remained somewhat stable. Further declines occurred during the 1970's when numbers reached a low of approximately 1,000 animals. The herd was subject to harvest until the mid 1970's but all harvest was discontinued as a result of the precipitous population decline. Studies from the late 1970's indicated that early calf survival was very poor even though adult cows were in good condition and had adequate food resources. Predation on young calves was thought to be a major factor in the population decline. The Denali Caribou Herd has experienced some periods of growth during the last 20 years. It increased by approximately 10% per year between 1977 and 1990. By 1990, the herd numbered 3,700 animals. However, the winter of 1990-91 was very severe and set new snowfall records. The herd declined as much as 30% between 1990 and 1991, likely due to weather induced stresses and increased vulnerability to predation. Currently, there are approximately 1,760 caribou in Denali National Park and Preserve.

Reproduction Comments:

Breeds mostly in October. Gestation lasts about 227-230 days. Cows bear usually 1, sometimes 2, young in May and June (early June in northern British Columbia). Calves precocious. Adult females sometimes skip reproduction for a year, in response to nutritional stress (Cameron, 1994, J. Mamm. 75:10-13). In northeastern Alaska and adjacent Canada, 80% of adult females (age 3 years or older) gave birth each year (Fancy et al. 1994).

Ecology Comments:

Gregarious; in tundra, usually in bands of 10-50 or loose herds of about 1,000. Sexes may segregate seasonally. May form herds after fawning (not in southeastern Manitoba). Tundra caribou may travel extensively in summer in attempt to avoid bothersome insects (Fancy et al. 1989).

Often incurs high calf loss, mostly due to predation (Bergerud et al. 1984). In south-central Alaska, Bergerud and Ballard (1988) concluded that wolf predation limited caribou recruitment, though winter starvation was proposed as the important population control by another researcher.

In northeastern Alaska and adjacent Canada, first-year survival of calves was 51%; mean annual survival rate was 84% for adult females and 83% for adult males; hunting mortality for the herd averaged 2-3% annually (Fancy et al. 1994).

In Quebec, home range size of adult females averaged 148 sq km and did not vary seasonally or annually (Ouellet et al. 1996).

White-tailed deer carry and disperse into the environment meningeal worms that usually are fatal to moose and caribou but are clinically benign in deer; hence, white-tailed deer, through worm-mediated impacts, commonly are believed to exclude moose and caribou from areas where deer occur (see Schmitz and Nudds 1994).

Non-Migrant: N

Locally Migrant: Y

LongDistance Migrant: Y

Mobility and Migration Comments:

In areas where still ranges freely, may form herds and migrate seasonally. Tundra populations may migrate 800 miles between summer and winter ranges; other popualtions make seasonal elevational migrations. In northern Alaska, winters in northern foothills of Brooks Range, females reach calving areas along coastal plain by mid-May; population highly aggregated near arctic coast and river deltas in July (Carruthers et al. 1987); begin return migration to winter range in September-October; cows annually may travel over 5000 km (Fancy et al. 1989). Heard and Williams (1992) described the migration in the Northwest Territories, Yukon, and Alaska as follows: cows begin migration to tundra in March-April, reach calving grounds in time for early June parturition; adult males migrate later but most reach tundra by June; return to tree line by early September, may not enter forest until October. Did not migrate in southeastern Manitoba (Darby and Pruitt 1984).

Habitat Comments:

Artic tundra (including tussock tundra and sedge meadow), subartic taiga, mature coniferous forest, semi-open and open bogs, rocky ridges with jack pine, and riparian zone. Migratory herds in Alaska, Yukon, and Northwest Territories winter in boreal forest, summer in tundra.

In northern British Columbia, seeks high south slopes in mountains as calving site (Bergerud et al. 1984). Porcupine Herd of northeastern Alaska and northwestern Yukon: females give birth on patches of bare ground within snowfields (Eastland et al. 1989); cows select areas north of the foothills (snow conditions permitting), thereby reducing exposure of calves to predators.

In winter in northeastern Alberta, woodland caribou selected forested fen peatland complexes; feeding activity was concentrated in forested raised bog islands, which may have been related to increased lichen biomass in these habitats (Bradshaw et al. 1995). "Mountain" caribou of southeastern British Columbia depend upon the arboreal lichens of older coniferous forests with high canopy closure, especially in late winter (Apps et al. 2001).

Food Comments:

Eats various plants: leaves, buds and bark of trees and shrubs; grasses; sedges; forbs; mushrooms; terrestrial and arboreal lichens. In summer moves to new areas to find new plant growth.

Phenology Comments:

Primarily diurnal, feeding crepuscularly.

Length: 210 centimeters

Weight: 270000 grams

References:

NatureServe. 2010. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. Available http://www.natureserve.org/explorer. (Accessed: February 3, 2011 ).

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