Caribou Photos
(Rangifer tarandus)
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Approximately 1 million wild caribou inhabit Alaska. © Patrick J. Endres
Caribou 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.
In Europe, caribou are called reindeer, but in Alaska and
Canada only the domestic forms are called reindeer. There 7 subspecies and Alaska has only the barren-ground subspecies.
General description
 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. © Patrick J. Endres
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). Caribou in northern and southwestern Alaska are generally
smaller than caribou in the Interior and in southern parts of
the state.
Life history
 Most adult cows are pregnant every year and give birth
to one calf — twins are very rare.. © Patrick J. Endres
Calving occurs in mid-late May in Interior Alaska and in early
June in northern and southwestern Alaska. If females are in
very good condition they can breed when they are 16 months old,
but in most herds they do not breed until they are 28 months
old. Wolves, grizzly bears,
and golden eagles kill large numbers of newborn calves.
 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. © Patrick J. Endres
After
calving, caribou collect in large “postcalving aggregations”
to avoid predators and escape mosquitoes and warble flies. These
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.
 Most fights between bulls are brief bouts, but violent fights
occur, and many bulls are seriously injured or killed during
the rut. © Patrick J. Endres
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.
 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. © Patrick J. Endres
Most fights between bulls are brief bouts, but violent fights
occur, and many bulls are seriously injured or killed during
the rut. Many injured or exhausted bulls are killed by wolves
and bears after the rut. 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.
Food habits
 Large herds often migrate long distances (up
to 400 miles/640 km) between summer and winter ranges.. © Patrick J. Endres
Like most herd animals, the caribou must keep moving to find
adequate food. Large herds often migrate long distances (up
to 400 miles/640 km) between summer and winter ranges. Smaller
herds may not migrate at all. In summer (May-September), caribou
eat the leaves of willows, sedges, flowering tundra plants,
and mushrooms. They switch to lichens (reindeer moss), dried
sedges (grasslike plants), and small shrubs (like blueberry)
in September.
Movements
 Caribou movements are probably triggered by changing weather
conditions, such as the onset of cold weather or snowstorms.
Once they decide to migrate, caribou can | 
