The pronghorn is the fastest land animal in the Americas and the last of an evolutionary line that belongs to no one else. Everything else in its family, the Antilocapridae, went extinct thousands of years ago. That leaves Antilocapra americana the sole survivor of a branch of hoofed mammals that evolved entirely in North America. It looks like an antelope and gets called one across the West, but it is not an antelope at all. Its nearest living relatives are the giraffe and the okapi. A tan, white-bellied animal the size of a small deer, running flat out across sagebrush country, is a genuinely singular thing to watch.
Built to outrun a ghost
It isn’t a true antelope, despite the familiar western nickname.
Speed defines the pronghorn. It can sprint at better than 55 miles an hour and hold close to 35 to 40 for miles at a stretch. No living predator on the continent keeps up. Coyotes, mountain lions, bobcats, and gray wolves all take pronghorn, but almost always the young, the sick, or animals caught against a fence, rarely a healthy adult in the open. The usual explanation is that the pronghorn is fast for a predator that no longer exists. It shared the Pleistocene plains with an American cheetah, Miracinonyx, and the speed that once outran that cat now outruns nothing, a piece of deep time still carried in the animal’s body.
That body is built for the effort. Relative to size, a pronghorn’s heart, lungs, windpipe, and blood volume all run about three times larger than those of a comparable mammal. That hardware feeds oxygen to the muscles fast enough to sustain a gallop rather than a short burst. The legs are long and light, cushioned on two toes with no dewclaws, and the stride can stretch beyond twenty feet at full extension. This is endurance running, not the startle-and-stop bounce of a deer.
The marks that give it away
A pronghorn stands about waist high at the shoulder and weighs roughly 75 to 145 pounds, with bucks a little heavier than does. The coat is rich tan to rufous over the back and flanks, cut sharply against a white belly, a broad white rump, and two clean white bands across the throat. Bucks add black to the picture: a dark mask down the muzzle, black patches on the sides of the neck, and a short black mane.
The horns are the real signature, and unlike anything else on the continent. They grow over a permanent bony core, the way a cow’s or a sheep’s do. But the outer black sheath is shed and regrown every year like an antler, a combination found in no other living animal. A buck’s horns rise about ten inches and throw a short forward-pointing prong partway up, the fork that gives the species its name. Does usually carry short, straight spikes, often no longer than their ears. Set high and wide in the skull, the eyes take in more than 300 degrees and pick up movement miles away, which is why a pronghorn so often sees you long before you see it.
Alarm travels through the herd without a sound. A startled animal erects the long white hairs of its rump patch into a flared disc that flashes across open ground and, at the same moment, releases a musk from the rump glands strong enough for a person to catch downwind. The nearest lookalike from a distance is a deer. Up close there is little confusion. At range across grassland, a mule deer or the pale rump of an elk can briefly read as a pronghorn until the horns, ears, and gait sort it out.
Where they run, and where they used to
Pronghorn are a creature of the open interior West. Today they range from the prairie provinces of Canada south through the Great Plains and Intermountain basins to northern Mexico, concentrated in a broad band of sagebrush steppe and short-grass prairie. Wyoming holds the densest herds by far, with Montana, Colorado, the Dakotas, and the high deserts of the Great Basin close behind. The animal thrives wherever the ground stays open and the sightlines stay long, from near sea level up to alpine basins, though most sightings fall in the sagebrush belt between about 4,000 and 6,000 feet.
The range used to be much larger. Before European settlement, pronghorn grazed east across the tallgrass prairie nearly to the Mississippi, part of a plains fauna so vast that some writers call it the American Serengeti. As farmland and fences replaced the open grassland, the eastern edge collapsed, and the species disappeared from states like Minnesota and Iowa where it once occurred. What remains is a western animal, tied to the country that stayed wild and open.
Habitat comes down to one requirement above all: open ground you can see across and run through. Pronghorn read the horizon for danger and trust their legs to answer it, so grassland, sagebrush flats, and semidesert basins suit them and dense timber does not. In dry country they stay within a few miles of reliable water through summer. In the harshest deserts of the Southwest, a small and endangered population hangs on among creosote, cactus, and gravel flats far from the lush prairies of the north.
Fences and the long walk
For an animal shaped by open distance, the modern West is a maze. Pronghorn are strong runners but poor jumpers, and rather than clear a fence they duck under the bottom wire. A tight woven-wire or low barbed-wire fence with no gap can stop a herd cold, even with good grass and water in plain sight on the other side. Fragmentation of this kind is now one of the central problems in pronghorn conservation.
It matters most where the animals still move long distances. In the northern Rockies, some herds make seasonal journeys of well over a hundred miles between summer and winter range, among the longest overland mammal migrations left in the Lower 48. One celebrated route funnels animals through a corridor that pinches, in places, to only a few hundred yards wide. A single stretch of bad fence or a new subdivision there could sever a migration that has run for thousands of years. Keeping those corridors open, with wildlife-friendly fencing and highway crossings, is where much of the practical conservation work now happens.
Feeding the sagebrush sea
Pronghorn are selective browsers more than grazers. Forbs, the broad-leaved wildflowers and weeds of the prairie, make up the bulk of the diet through the growing season, supplemented by shrubs and, in the driest ranges, a surprising amount of cactus. Sagebrush, rabbitbrush, and winterfat carry them through winter, when green forbs vanish and woody plants become the only reliable food. They take small, careful bites and often seek out plants that cattle and sheep avoid, including some laced with defensive chemistry other grazers cannot handle. Pound for pound they eat little; a single cow eats as much forage as dozens of pronghorn.
Social life shifts with the seasons. Winter draws animals into large mixed herds, sometimes hundreds strong on the open plains, for the safety of many eyes. As spring arrives the herds break apart. Bucks stake out territories or gather harems of does from roughly late March into fall, and the loose winter aggregations give way to smaller, defended groups.
The pronghorn year
Breeding peaks in mid-September across the north and runs later in southern populations. What follows is one of the longest pregnancies of any hoofed animal its size, close to 250 days, so that fawns arrive the following May. Does usually carry twins, the outcome of a strange internal contest: several embryos begin to develop, but only the strongest one or two implant fully while the rest are reabsorbed.
Newborns weigh only a few pounds and are dangerously small, but precocial. Within minutes a fawn can stand and nurse. For its first three weeks it lies pressed flat and nearly scentless in the grass while its mother grazes at a distance and returns only to feed it. She eats the afterbirth and the fawn’s waste to keep predators from scenting it out. Within a couple of weeks those spindly legs can already outpace most predators, and the fawn joins the wider herd. Pronghorn reach breeding age at around sixteen months, though young bucks rarely hold territory before their third year. Wild animals live perhaps seven to ten years, with a few does reaching sixteen.
Back from the brink
The pronghorn’s recent history is one of collapse and recovery. Tens of millions once covered the western grasslands, rivaling the bison. Market hunting and the plowing of the plains drove the total below twenty thousand by the 1920s, a crash nearly as steep as the bison’s. Hunting regulation, refuges, and translocation reversed it, and the continental population now sits somewhere between half a million and a million. The IUCN lists the species as Least Concern, and across most of the West it is secure and often abundant.
The exception lies at the southern edge. The Sonoran pronghorn of the Arizona and Mexican deserts has been listed as endangered in the United States since 1967, its numbers propped up by captive breeding, managed water, and habitat work. The peninsular pronghorn of Baja California is rarer still. For these desert races, drought, roads, and severed movement corridors remain constant threats. For the species as a whole the long-term question is less about survival than about space: whether enough open, connected country remains for an animal built, above all else, to run.
