Pronghorn Antelope of Greater Yellowstone

Pronghorn herd, South Fork Shoshone Valley, Absaroka Mountains, Cody Wyoming

When Yellowstone became a national park in 1872, the pronghorn population was reported to be in the thousands. However, the number of these animals declined as the Yellowstone area became settled. In addition, hunting continued in the park until 1883. By 1886, when the U.S. Cavalry arrived to administer the park, the pronghorn had been largely decimated. The Cavalry took measures to increase the number of these animals. Their tactics, controlling predators and providing supplemental feed, proved successful almost immediately.

The Pronghorn is a species of artiodactyl mammal native to interior western and central North America. Though not a true antelope, it is often known colloquially in North America as the Prong Buck, Pronghorn Antelope or simply Antelope, as it closely resembles the true antelopes of Africa and fills a similar ecological niche due to convergent evolution. The pronghorn is the ‘real' Great Plains large mammal. Although we often associate bison with rolling prairies, they are more adapted for living in woodland habitats than the American pronghorn. In fact, the pronghorn has never found subsistence outside the High Plains and sagebrush flats of the American West.

The most unique pronghorn attribute is their speed. Although running is their last defense, they are the world's fastest land animals. They can sprint up to 60 mph and sustain 30 mph for miles. In fact, although a cheetah could outrun them in a hundred-yard dash, the pronghorn would prevail in anything longer. The pronghorn's speed is its main defense against predators. The newborns, for the first few days of their lives, are vulnerable to coyotes. Pronghorn does guard fawns closely, and they often remain perfectly still, their dappled gray coat blending in with the grasses and shrubs, so that predators cannot detect them. By the end of their first week, they are running about, and soon are young speedsters themselves. As adults, their coats turn brown with distinctive white patches on their stomach and rump. A pronghorn doe gestates for over eight months, mating in September and giving birth in May. A fawn is typically five to seven pounds when born, and twins are common. At four days old, a fawn can already outrun a human; at one week, it can outrun a dog. Since an adult pronghorn can outrun its predators, predation on the young is the most common natural threat. The pronghorn’s predators include wolves, coyotes, bobcats, cougars, and even golden eagles. Pronghorns reach sexual maturity within 16 months, although males usually do not breed until three years of age.

Pronghorn antelope, Yellowstone National Park

The Pronghorn is the only surviving member of the family Antilocapridae. Bands of Pronghorns live in open grasslands, forming small single-sex groups in spring and summer, and gathering into large mixed herds, sometimes up to 1,000 strong, in the fall and winter.

Pronghorns were brought to scientific notice by the Lewis and Clark Expedition, which found them in what is now South Dakota, USA. The range extends from southern Saskatchewan and Alberta in Canada south through the United States (southwestern Minnesota and central Texas west to northeastern California), to Sonora and San Luis Potosí in northern Mexico. Up to 40 million of these graceful animals used to roam North America, By 1908, hunting pressure had reduced the Pronghorn population to about 20,000. Protection of habitat and hunting restrictions has allowed their numbers to recover to an estimated population of between 500,000 and 1,000,000. There are about 5000 present in the Yellowstone area today. The Yellowstone population expresses much of the genetic variation that was formerly widespread in the species, but is no longer present elsewhere.

Pronghorn graze below the Grand Tetons in Grand Teton National Park

While pronghorn are not endangered, the population that summers in Grand Teton National Park, part of the Greater Yellowstone Ecosystem, had been reduced to less than 200 animals in recent years. Since wolves were reintroduced in 1995, the pronghorn population in Grand Teton has increased by approximately 50 percent. Since 1991, the Yellowstone pronghorn population has declined by approximately 50 percent and now hovers between 204 and 235 animals. Research is underway to determine possible causes. This decline is a concern because current research indicates that such a small, isolated population is susceptible to extinction from fairly commonplace natural events such as a severe winter or disease outbreak.

These pronghorn have the longest migration— more than 200 miles round-trip of any land mammal in the lower 48 states. Considering their speed-specific defense system, it is no surprise pronghorn don't like to go places where they can't see far and run fast. Unfortunately, human development has created bottlenecks along their migration routes that vary from 328 to 2000 feet wide. In other places the routes are blocked. Since Pronghorn aren’t built for jumping, even poorly designed fences can close a migration route, and the animals don't seek an alternate route, they just stop migrating.

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