most commonly called antelope, the pronghorn (Antilocapra
is not related to true antelope from Africa. In fact, the pronghorn
has no relatives at all -- it is the only member of its family.
As the fastest North American hoofed animal, a pronghorn can run in bursts
of 60 to 70 miles per hour and can maintain speeds of 20 to 30 miles
per hour for up to an hour. This is especially impressive for such a
small animal -- the average adult stands less than three feet tall
at the shoulder and weighs less than 150 pounds.
Since pronghorn live in open areas, they have features that appear
to be special adaptations to to their grassland habitat. During cold
Idaho winters, the pronghorns' long, coarse coat keeps the animal
warm even in severe weather. Hollow outer hairs, which flatten
against the body, provide insulation. During the warmer months, the
pronghorns' winter coat is shed and a thinner coat allows for more
ventilation as the hairs are able to ruffle up and let air reach the
When pronghorn are
alarmed, they raise the hairs on their white rump to form a highly
reflective white patch. This signals alarm to other pronghorn, like
a beaver slapping its tail. To help see others' alarm signals and to
watch for predators, pronghorn have excellent eyesight, estimated to
be six times better then human eyesight. Their long eyelashes shade
their eyes from the bright sun.
The pronghorn is the only animal in the
world with branched horns (not antlers) and the only animal in the
world to shed its horn sheathes, as if they were antlers. The
horn sheath of the pronghorn is different from either the antlers of
deer or the true horns of cattle or bison. Antlers are shed annually
and are made of bone. True horns are never shed and are made of
compressed hair and keratin growing on a bony core. The horn sheath
of a pronghorn is a little of both. It is made of keratin growing on
a bony core and it is shed annually.
Pronghorn are one of the most abundant big game animals in the
western United States and the most abundant on the INL. The ESER
Program counts pronghorn on the site each summer and winter. From
the actual count of observed pronghorn, estimates of total INL
population are made using Transect II software. Yearly
estimates show that an average of 500 of these animals
live on the INL during the summer and anywhere from 600-6,500 pronghorn winter here.
In severe winter seasons, pronghorns from throughout the state and
as far away as Montana migrate to the INL to escape the harsher weather conditions of
their summer ranges. The number of wintering pronghorn on the INL
is extremely variable, depending on the severity and timing of the
winter. During early, harsh winters the numbers can be low because
many animals migrate through the area and winter farther south. The
numbers are also low during mild winters because the pronghorn stay
farther up the mountain valleys bordering the site.