Top of Your Head...
Why Do You Suppose Caribou Have Antlers?
and Writing Connections >>
balancing heavy bones on your head and carrying them everywhere you
go! Any idea why caribou have such amazing antlers?
Antler development is a unique phenomenon of nature. In some species such as
moose and deer only males grow antlers whereas in caribou both males and females
grow antlers each year. In all cases it is an annual process that separates
antlered animals from horned animals that usually grow a set of horns over
a lifetime. The bulls can develop spectacular antlers at times exceeding 125
cm in length, 112 cm across and as much as 15 to 20 pounds. While all mature
caribou bulls develop antlers, fewer than 5% of females fail to develop antlers.
Gov't. of the Northwest Territories, Division of Natural Resources.
year, the antlers are grown and shed, then re-grown and shed again. The
entire process of antler development begins each spring and starts from
two permanent stumps of bone called pedicles on the head of each caribou.
As the antlers grow they are covered in a hairy skin called velvet. Beneath
this outer layer of furry skin are thousand of blood vessels and nerves
that carry calcium and other minerals to the developing, soft cartilage-like
tissue. During this phase they remain soft and fragile but as a measure
of compensation they also grow at an astounding rate, as much as 2.5 cm
in a day. This makes them the fastest growing tissue in the animal world.
This growth uses hard-earned energy--one can't help but wonder why.
This growth process occurs throughout the entire summer months. At times the
growth is so rapid that the dietary intake of food cannot supply enough minerals
and the bull’s body actually uses calcium from its entire skeletal system.
The bull’s body then replaces the lost calcium when antlers growth ceases
and while prime forage is still abundant.
in nature there is a season--and there's also a reason! Here caribou
biologist Doug Urquart describes the seasonal differences between the
antlers of males and females:
development is 3-6 months out of phase between the sexes. For example,
the male's antlers begin developing in March, grow rapidly from May
to July, and are completely hardend and out of velvet by mid-September.
Following the rut, antlers are shed in early November by older males,
but may be kept until April by some of the younger ones. Female antlers
develop from June to September and are out of velvet by late September.
The females' antlers are retained throughout the winter. Pregnant
females drop their antlers within days of calving. Barren cows shed
their antlers before the spring." (Provided courtesy of the
Government of the Northwest Territories, Division of Natural Resources.)
The developing antlers also offer a unique and built in cooling system. As
the warm blood rushes to the antlers ensuring rapid growth it is quickly cooled
by the outside air, which then allows the bull’s entire body to cool.
Mother Nature’s built in air conditioner.
what reasons might female caribou keep their antlers during the winter,
while males drop theirs in the fall?"
are the male caribou antlers generally much larger than the female's?"
might the females antlers begin to develop after calving?"
some reasons why both male and female caribou have antlers, but in
other kinds of deer only the male animals have antlers?"
WHEN something happens often helps explain WHY it happens, so try to
think of what kinds of energy that goes into growing antlers and the
different ways antlers can be used. Then guess the reasons for the
the differences Urquart describes.
a life-sized pair of caribou antlers and put them on display. Find
something that weighs the same as caribou antlers do, and try to
balance them on your head.
to your own weight, calculate how heavy your antlers would be. (Average
body weights for Porcupine caribou are: male 130 kg/285 lbs, and
female 90 kg/198 lbs.)
a chart showing when caribou have their antlers. Use headings like
developing/velvet, hardened/out of velvet, no antlers. Compare male
and female, with extra headings for pregnant and barren females and
young animals. Use the chart to create a list of generalizations
about caribou and their antlers.