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Caribou are usually clove-brown with a white neck, rump and feet, and often have a white flank stripe. They are the only members of the deer family in which both sexes grow antlers. Antlers of adult bulls are large while those of adult cows are much shorter and are usually more slender and irregular. They have large, concave hooves that spread widely to support the animal in snow and soft tundra. The coat of the caribou acts as 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 makes them more buoyant.
The Alaska Zoo has a reindeer herd to teach people about this species. Caribou and reindeer are the same species, with reindeer referring only to domesticated animals raised primarily for meat in Alaska and Canada. In Europe, all wild and domestics of this species are called reindeer.
The first 17 reindeer were brought to western Alaska from Siberia on U.S. ships in 1892. Marine mammals had been depleted by outside whaling ships, and caribou numbers were down. Reindeer were a good supplemental meat source for Alaska Natives. They grew in importance and were even used in a reindeer postal route in 1899 between St. Michael and Kotzebue. Alaska Natives still own and herd reindeer today, primarily on the Seward Peninsula. Captive herds are used in research projects to teach scientists more about caribou biology and management.
Like most migratory animals, caribou must keep moving to find adequate food. Large herds often migrate long distances (up to 400 miles) between summer and winter ranges. Smaller herds may not migrate at all. Caribou movements are probably triggered by changing weather conditions, such as the onset of cold weather. Once they decide to migrate, caribou can travel up to 50 miles per day.
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 their diet, especially in winter.
The shedding of velvet (the covering on the antlers) in late August and early September by large bulls marks the approach of the rutting (breeding) season and the start of fall migration. Unlike other members of the deer family, bull caribou do not control a harem of cows. Instead, they control a space around themselves to prevent other bulls from breeding with females in their space. The largest bulls shed their antlers in late October, with smaller bulls and non-pregnant cows shedding theirs in April. Pregnant females usually retain their antlers until calves are born in late May or early June. Most adult cows are pregnant every year and give birth to one calf. After calving, caribou collect in large “post-calving aggregations” to avoid predators, such a bears and wolves, and escape mosquitoes and other insects. These large groups of caribou stay together in high mountains and along seacoasts where wind and cool temperature protect them from predators, summer heat and insects.
There are approximately 900,000 wild caribou, distributed into 32 herds or populations, in Alaska. Caribou are somewhat cyclic in number, but the timing of declines and increases, and the size to which herds grow, is not very predictable. Although overhunting caused some herds to remain low in the past, today, varying weather patterns (climate), population density, predation by wolves and grizzly bears, and disease outbreaks determine whether most herds increase or decrease.
Alaska Science Forum, Reindeer and Caribou Populations
Caribou publication, USFWS
Frequently asked questions about caribou, USFWS, Arctic National Wildlife Refuge
Notebook series, ADFG
Shefferly, N. and K. Joly. 2000. "Rangifer tarandus" (On-line), Animal Diversity Web