Pronghorn

About the pronghorn

The pronghorn is a hoofed mammal native to the interior of western and central North America. Despite being known colloquially as the American antelope or prairie antelope, it is not actually an antelope at all — it only resembles one because of parallel evolution, filling a similar ecological role to the antelopes of the Old World. It is the sole surviving member of the family Antilocapridae; during the Pleistocene, roughly 11 other antilocaprid species lived in North America, some with long or dramatically twisted horns, but only the pronghorn remains today. Its closest living relatives, somewhat surprisingly, are the giraffe and the okapi.

Adult males measure 4.3 to 4.9 feet (1.3–1.5 m) from nose to tail and stand 2.7 to 3.4 feet (82–104 cm) at the shoulder, weighing 88 to 143 pounds (40–65 kg). Females stand the same height but weigh less, 75 to 106 pounds (34–48 kg). Both sexes carry horns made of a bony core covered in a keratinous sheath that is shed and regrown every year. Male horn sheaths average about 9.8 inches (25 cm) and end in a forward-pointing prong, the feature that gives the species its name; female horns, when present, are smaller, averaging 4.7 inches (12 cm), straight, and only rarely pronged. Distinct white fur marks the rump, sides, belly, breast, and throat, and males can be told apart by a small patch of black hair at the jaw.

The pronghorn's most famous trait is speed. It is the fastest land mammal in the Western Hemisphere, capable of sustained bursts up to 55 mph (88.5 km/h) over 800 meters (0.5 mi), and it can hold 35 mph (56 km/h) for 4 miles (6.5 km) — a pace it can keep up far longer than a cheetah could manage. That endurance is backed by an oversized windpipe, heart, blood volume, and lungs relative to its body size, plus a light bone structure and hollow hair. Researchers believe this speed evolved to outrun predators that no longer exist, chiefly the American cheetah, since no living North American predator comes close to matching a pronghorn's pace.

Behavior and diet

Pronghorns form mixed-sex herds through the winter. Come early spring, those herds split apart: young males form bachelor groups, females organize into bands, and adult males either hold a territory or defend a harem of females, a strategy that can shift depending on rainfall, resources, and the local population. Where conditions support it, territorial males mark and defend their ground with scent, vocalizing, and by challenging rivals; if posturing fails to settle a dispute, males lock horns and fight. Females have their own courtship strategies, ranging from "sampling" several males before choosing, to "quiet" females that pair with one male for the whole breeding period.

Diet is broad and mostly plant-based. Studies found forbs making up 20 to 62 percent of intake depending on the population, with shrubs, grasses, and — in some areas — cacti filling out the rest; pronghorns are ruminants and chew cud like cattle or sheep. Many of the plants they eat are unpalatable or even toxic to domestic livestock, though pronghorns still compete with ranch animals for forage in shared range. Healthy populations generally stay within 3 to 4 miles (5–6.5 km) of water, and one tracked migration in Idaho covered more than 160 miles (260 km) between the Pioneer Mountains and the Continental Divide.

Breeding takes place in mid-September, after which the gestation period runs 7 to 8 months — notably longer than most North American hoofed mammals, roughly six weeks longer than a white-tailed deer's. Twin fawns are common, and newborns weigh 4 to 9 pounds (2–4 kg), most often around 7 pounds (3 kg). For their first three to four weeks, fawns spend most of the day hiding in vegetation, meeting their mother for brief nursing sessions rather than staying at her side. Males are weaned two to three weeks before females, and both sexes reach sexual maturity at 15 to 16 months, though males typically do not breed until age three.

Range and habitat

Before European settlement, the pronghorn ranged in huge numbers across the region west of the Mississippi River, an area sometimes called the "American Serengeti" for the scale of its bison, elk, and pronghorn herds. Its present range still sits west of the Mississippi, stretching from southern Saskatchewan and Alberta in Canada south through much of the western United States — including Arizona, Colorado, Idaho, Kansas, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, Oregon, South Dakota, Texas, Utah, Washington, and Wyoming — and on into Mexico. The species has been extirpated from Iowa and Minnesota in the U.S. and from Manitoba in Canada.

Pronghorns favor open terrain at elevations of 3,000 to 5,900 feet (910–1,800 m), with the densest populations found where annual rainfall runs 10 to 16 inches (254–406 mm). Because they are built for running in the open rather than jumping, low fences on ranch land can trap or injure them; conservation groups such as the Arizona Antelope Foundation have worked to remove the bottom strand of barbed wire from range fences so pronghorns can pass beneath safely.

Conservation status

The pronghorn is classified as Least Concern (LC). At the turn of the 20th century, members of the wildlife conservation group Boone and Crockett Club believed the species was headed for extinction, a stark contrast to its current stable status and the vast herds recorded in the centuries before European settlement. Its recovery reflects sustained conservation attention across its western range, though the specific programs behind that turnaround are not detailed here. Predation today comes from cougars, wolves, coyotes, grizzly bears, bobcats, and golden eagles, which take fawns and occasionally adults; the species may have evolved its remarkable speed to escape predators, like the American cheetah, that are now extinct.