Pronghorn

Name and taxonomy

The name describes the horn: a sheath that forks, with a short tine pointing forward. No member of the ox family has a branched horn. Spanish explorers saw the animal in the 16th century, but Lewis and Clark made the first careful record in 1804 near the Niobrara River. Clark called it a buck goat of this country and compared it to the antelopes and gazelles of Africa. The ornithologist George Ord gave it its scientific name in 1815.

Antilocapra probably means antelope-goat, and americana marks its home. It is the only species in the family Antilocapridae, within the order Artiodactyla. Five subspecies are named, among them the Sonoran pronghorn of Arizona and Sonora and the Baja California pronghorn. Other English names are American antelope, prong buck and prairie antelope, and in Mexico it is the berrendo.

Evolution and relatives

The pronghorn is the survivor of a family that once filled North America. About 11 other antilocaprids lived during the Pleistocene, many with long or twisted horns. Three other genera, Capromeryx, Stockoceros and Tetrameryx, were still alive when people first entered the continent. All of them are gone.

The family belongs to the infraorder Pecora, so its cousins are the deer, the bovids and the musk deer. Its closest living relatives are the giraffe and the okapi. Like a giraffe, it grows a bony horn core covered in skin. In the pronghorn that skin turns into a horn sheath, and the sheath is shed. Its likeness to the antelopes of the Old World is a case of parallel evolution for the same open-country life. Bone studies from Natural Trap Cave show that American cheetahs, American lions and wolves all ate pronghorns in the ice age.

Appearance

An adult buck measures 130 to 150 centimetres from nose to tail and stands 82 to 104 cm at the shoulder. Bucks weigh 40 to 65 kilograms and does 34 to 48 kg, though the sexes stand the same height. The tail is short, up to 10.5 cm. The body is barrel-shaped on long slender legs, and each foot has two hooves and no dewclaws. The coat is reddish tan above and white on the belly, chest, rump and two bands across the throat.

The hair is coarse and hollow, and it traps air for insulation in the winter wind. A buck wears a black cheek patch, a short black mane and a black band across the forehead. Buck horns run 12 to 43 cm, about 25 cm on average, with the prong. Doe horns are 1 to 6 cm, straight, and often hard to see at all. The eyes are huge and set high on the skull, with a field of view of about 320 degrees.

Habitat and range

Pronghorns live on grassland, sagebrush steppe and desert from sea level to about 3,500 metres. They keep to open ground with long sight lines and avoid anything closed in. The densest herds live between 910 and 1,800 metres where 254 to 406 millimetres of rain falls a year. Most animals stay within 8 kilometres of water, though juicy forbs can replace drinking for weeks.

The range runs west of the Mississippi from southern Alberta and Saskatchewan through 16 western states into Mexico. The Sonoran subspecies reaches Baja California Sur and San Luis Potosi in shrinking numbers. Iowa, Minnesota and Manitoba have lost the species. An introduction to Lanai in Hawaii in 1959 dwindled to about 12 animals by 1983. GBIF holds records from 7 countries, nearly all of them the United States, Canada and Mexico.

Many populations migrate to snow-free winter range. A herd in Idaho walks more than 260 kilometres from the Pioneer Mountains across Craters of the Moon to the Continental Divide. At one point that route narrows to a gap only 200 yards wide. Wyoming herds travel about 300 miles round trip between the Upper Green River and Grand Teton. No land migration in the lower 48 states is longer.

Diet and feeding

The pronghorn is a picky browser that nibbles small amounts of many plants. Forbs, the soft broad-leaved plants of the prairie, are the favourite food in summer. In one study forbs made up 62% of the diet, shrubs 23% and grasses 15%. Another study found 40% cacti, 22% grass, 20% forbs and 18% shrubs. Grass is eaten mainly as fresh spring growth.

In winter, northern herds depend on sagebrush, and herds on bare grassland can starve while sagebrush herds nearby do well. Pronghorns eat plants that poison cattle and sheep, helped by a large liver. They dig through snow with their hooves and follow wind-blown ridges where the ground is bare. Like cattle, they chew the cud in a four-chambered stomach. In dry country an animal may drink up to 3 litres a day, and one cow is said to eat as much as 38 pronghorns.

Behaviour and social life

Pronghorns are almost never alone. In winter both sexes gather in large herds, which break up in early spring. Summer groups hold up to about 12 animals: does with fawns, or young bucks in bachelor bands. Adult bucks live alone on territories they hold from March to the end of the rut in October. Does keep a rank order, and a dominant doe shoves lower does away from good feeding spots.

A buck marks his ground with scent from glands below the ears, and with scrapes where he sniffs, paws, urinates and defecates. Rivals stare, snort-wheeze, thrash their heads, grind their teeth and walk side by side with heads low. If neither backs down they lock horns and push, and a fight of about 2 minutes can leave a serious wound. Where rain is plentiful bucks hold territories, and where it is scarce they follow and guard a harem instead.

The animals feed and rest in cycles around the clock and seldom seem to sleep. An undisturbed herd walks about 6 kilometres a day. Pronghorns are curious and will walk towards something strange until they can tell what it is. They cannot jump, so they crawl under fences, sometimes at speed, and a fence with a low bottom wire can stop a whole migration.

Communication and senses

Sight comes first. The big eyes sit high and far back, and a pronghorn can pick out an object about two miles away. When one sees danger, the white hair on its rump stands up and shows from a great distance. At the same time two rump glands release a scent that people compare to buttered popcorn. Humans have smelt it 65 to 100 feet downwind of an alarmed herd.

Scent runs through pronghorn life. Glands sit on the cheeks, between the hooves, on the rump and, in bucks, on the back. A courting buck approaches a doe from behind, waves his head to show his cheek patches and spread his scent, and calls softly. A territorial buck gives a falling snort-wheeze with his mane, rump and cheek patches raised. A doe knows her fawn by sight, sound and smell together.

Reproduction and life cycle

The rut falls in mid September to October in the north and from July to October in the south. A doe in season samples several bucks, or provokes fights between them and mates with the winner. Her choice matters: a small set of bucks sires about 60% of each year's fawns. She sheds 4 to 7 eggs, and as many as 7 embryos may start, but the crowding kills all but one or two. Pregnancy lasts about 252 days, or 235 by another count, which is long for a North American hoofed animal.

Fawns arrive in late May and June, and all the does in a herd drop their fawns in the same few days. A first-time mother usually has one fawn, and after that twins are the rule. A newborn weighs 2 to 4 kilograms, most often 3, and stands within minutes. For its first 21 to 26 days it lies hidden while its mother feeds within about two miles. She eats the afterbirth and the fawn's droppings so that no scent gives it away.

Within days a fawn can outrun a person, and by 3 weeks it is nibbling plants. Does breed at about 16 months, and bucks, though fertile in their first year, seldom mate before their third. A wild pronghorn lives about 10 years and rarely 15. One captive animal reached 17.

Predators and threats

Coyotes, cougars, wolves, bobcats and grizzly bears hunt pronghorns, and golden eagles take fawns and even adults. Jaguars probably take some in the far south-west. Most kills are fawns or weak animals, because a healthy adult simply runs. It can hold 56 kilometres an hour for 6.5 km, 68 km/h for 1.5 km, and 88.5 km/h for 800 metres. Cornered, it strikes with its hooves and horns.

Hard winters, deep snow and drought kill more pronghorns than predators do in many years. Bluetongue, a virus carried by midges from sheep, has wiped out local herds. Fences, highways and railways cut migration routes and can leave herds to starve on one side. Sheep strip the forbs and sagebrush that pronghorns need, and cattle bring worms and heavier parasite loads. Cars kill many where roads cross the range.

Population and conservation

Before European settlement perhaps 35 million pronghorns roamed the plains, alongside the bison herds of the so-called American Serengeti. Market and sport hunting cut that to about 13,000 by the 1920s. The Boone and Crockett Club thought the species doomed and began restocking refuges in 1910. In 1927 the club and the Audubon Society bought land in northern Nevada for the Sheldon Antelope Refuge. President Roosevelt enlarged it to 222,000 hectares in 1936, the true start of the recovery.

Today the IUCN lists the pronghorn as Least Concern, with 500,000 to a million animals. About half live in Wyoming, where for a time they outnumbered people. Only one game species in North America outnumbers it, and it is hunted under permit in every western state. Yellowstone counted 500 to 600 in 2024, back from a sharp fall in the early 1990s.

Two subspecies are in deep trouble. Fewer than 300 Sonoran pronghorns survive in the United States and 200 to 500 in Mexico, and their US count once fell to 21. About 200 Baja California pronghorns live in and around breeding pens. Both are on the US endangered list, and Mexican animals sit on CITES Appendix I. Groups such as the Arizona Antelope Foundation now remove the bottom wire from fences so herds can pass.

Relationship with humans

Plains peoples hunted the pronghorn as a staple food. Lewis and Clark wrote that tribes near the Rockies ran them down on horseback and shot them with arrows. The Mandan built a strong pen with brush wings and drove whole herds gently into it. Its curiosity probably made it easy to lure with a waving cloth, a trick that hunters still describe.

Today it is a prized game animal, and hunters on open range succeed up to 90% of the time. Ranchers gain too, because pronghorns eat noxious weeds and thrive on land that cattle have overgrazed. In deep snow a herd may move into wheat or alfalfa and cut the yield. The pronghorn is the emblem of the American Society of Mammalogists.

In culture and myth

The pronghorn holds a large place in Native American story and ceremony, usually under the name antelope. In Plains tradition the antelope is a messenger, and one that walked into camp carried word from the spirit world. In Blackfoot tradition, the creator Napi made the bighorn and the antelope, and a second tale explains the difference between deer and antelope. A Yokut story tells why antelopes live on the plains, and an Apache tale follows a woman who married an antelope.

In Pueblo tradition, antelope clans, called Kurts or Kuts-hano in the Keres languages, exist in several villages of New Mexico. Some Pueblos dance an Antelope Dance. In Hopi tradition the Antelope Society is one of the few religious orders that admits women as well as men. Chop is the Hopi antelope kachina. American writers and hunters made the pronghorn a symbol of the open West, and it appears on state wildlife emblems and hunting art.