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Barren-ground
Caribou
Description
 Barren-ground
caribou adult males stand about 110 cm high at the shoulder. They weigh
about 140 kg in the fall when they are in their prime, but only about 100
kg in November after a month of mating activity.
Caribou have long legs that end in
large, broad, sharp-edged hooves. This adaptation enables caribou to dig
craters through ice and snow to feed themselves during the winter months.
As well, their hooves provide good support and traction when traveling
over snow, ice or muskeg, allowing caribou to move quickly and escape
being eaten by predators. In winter, the fleshy pads between their hooves
shrink and the hair between their toes forms tufts that cover the pads.
Caribou walk on the horny rims of their hooves and the hair
protects the pads from contacting the frozen ground.
Lichens
are common in the Arctic and caribou are one of the few mammals adapted to
feed on them. Caribou have a rumen (large
stomach) that can digest lichens. They
can also recycle urea, which is one of the products of protein digestion. The ability to breakdown urea reduces the amount of water
caribou need to eliminate toxins from their body.
This is an advantage during the winter months when water is scarce.
The
caribou's coat varies in colour seasonally. Each year, caribou lose their coat during the summer moult. Adult
males are the first to begin moulting in late June.
Nursing cows have the greatest nutritional needs and complete their
moult last. During the
moult, hair falls out in large patches revealing a new coat.
When the shedding is complete, caribou are dark brown with a
distinctive white belly and white mane.
Adult males also sport a white flank stripe and white socks above
their hooves. Throughout the
summer months, white-tipped guard hairs grow out turning the caribou a
more uniform light brown colour by fall.
The guard hairs are hollow and during the summer months give the
caribou buoyancy, which is helpful as they swim across rivers and lakes.
In the winter, the air cells in the guard hairs act as an
insulating layer to conserve body heat, resulting in a coat that is
exceptionally warm. Over the
winter, the caribou’s coat fades to light beige.
 Caribou
are the only species in which both males and females grow antlers.
Females probably have antlers so they can defend their
winter-feeding craters from other caribou.
Barren-ground caribou have the largest antlers relative to body
size. Bulls have large antlers to advertise their strength to other bulls
and to the cows. The design of the antler branches makes the bulls look
large from the side view, and they are prominently displayed during the
rut. When threat displays
escalate into a fight, bulls lower their heads and charge with their
antlers. The antler branches
grapple together as the bulls shove and push each other. Caribou calves
have short spike antlers that increase in size and complexity each year
until the animals are quite old. Older
caribou have smaller antlers with fewer branches.
Antler
growth is directly related to how well caribou are feeding.
If food is restricted or low in nutrition, caribou grow smaller
antlers. Antlers are shed and
regrown each year. As the bone core of the antlers grows, it is covered
with velvet. The velvet is skin richly supplied with nerves and blood
vessels and densely covered by short hairs.
As the antlers reach their full size in September, the velvet dries
and falls off in strips aided by the caribou thrashing their antlers
against bushes. Adult males may shed their antlers as early as November,
just after the rut. Younger males and barren cows may retain their antlers
until April, while pregnant females lose their antlers a few days after
calving in June.
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