Caribou (Rangifer tarandus) live in the arctic tundra, mountain tundra, and northern forests of North America, Russia, and Scandinavia. The world population is about 5 million. Caribou in Alaska are distributed in 32 herds (or populations). A herd uses a calving area that is separate from the calving areas of other herds, but different herds may mix together on winter ranges.

All caribou and reindeer throughout the world are considered to be the same species, but there are 7 subspecies: barren ground (Rangifer tarandus granti), Svalbard (R.t platyrhynchus), European (R.t. tarandus), Finnish forest reindeer (R.t. fennicus), Greenland (R.t. groenlandicus), woodland (R.t. caribou) and Peary (R.t. pearyi). Alaska has only the barren-ground subspecies, but in Canada the barren-ground, woodland, and Peary subspecies are found.

Caribou have large, concave hoofs that spread widely to support the animal in snow and soft tundra. The feet also function as paddles when caribou swim. Caribou are the only member of the deer family (Cervidae) in which both sexes grow antlers. Antlers of adult bulls are large and massive; those of adult cows are much shorter and are usually more slender and irregular. In late fall, caribou are clove-brown with a white neck, rump, and feet and often have a white flank stripe. The hair of newborn calves is generally reddish-brown. Newborn calves weigh an average of 13 pounds (6 kg) and grow very quickly. They may double their weight in 10-15 days. Weights of adult bulls average 350-400 pounds (159-182 kg). However, weights of 700 pounds (318 kg) have been recorded. Mature females average 175-225 pounds (80-120 kg).

Large groups of caribou stay together in the high mountains and along seacoasts where wind and cool temperatures protect them from summer heat and insects. After insect numbers decline in August, caribou scatter out and feed heavily on willow leaves and mushrooms to regain body weight.

The shedding of velvet (the fur covering on antlers) in late August and early September by large bulls marks the approach of the rutting (breeding) season and the start of fall migration. Mature bulls frequently have more than three inches of fat on the back and rump, which is used to provide energy needed during the rut. The necks of adult bull caribou swell enormously in September due to the natural production of steroid hormones like testosterone. Fighting begins in early September and becomes more frequent as the rut approaches at the end of the month. Most fights between bulls are brief bouts, but violent fights occur, and many bulls are seriously injured or killed during the rut. Wolves and bears kill many injured or exhausted bulls after the rut. Unlike many other members of the deer family, bull caribou do not control a harem of cows. Instead, they control a space around themselves, and prevent other bulls from breeding females within their space. The largest bulls shed their antlers in late October, but small bulls and non-pregnant cows do not shed their antlers until April. Pregnant females usually retain their antlers until calves are born in late May or early June.

By Tom Dade

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