Although most commonly called antelope, the pronghorn (Antilocapra americana) 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 skin.
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.
©2020 ESER Program.