Pronghorn

• 1. Introduction

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  The pronghorn can run 55 miles per hour over half a mile, faster than anything else on land in the Americas. It outpaces every predator that lives alongside it today, by a wide margin. Antilocapra americana is not an antelope, though people across North America call it the American antelope, prong buck, and prairie antelope. It only looks like the antelopes of the Old World because it evolved, separately, to fill the same kind of ecological niche. So why does a grass-eater on the western plains carry the speed to flee a cheetah? Whose horns curve forward and branch in a way no ox ever managed, then fall off and grow back every single year? And how did an animal whose herds once rivaled the great plains of Africa come within sight of vanishing for good?

• 2. The Last Of A Lost Family

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  About 11 other antilocaprid species roamed North America during the Pleistocene epoch, many sporting long or spectacularly twisted horns. Three of those genera, Capromeryx, Stockoceros, and Tetrameryx, were still alive when the first humans arrived on the continent. All three are now extinct. The pronghorn is the only surviving member of the family Antilocapridae, the last branch of a once-crowded tree. Its nearest living relatives are not the deer or cattle it grazes beside. They are the giraffe and the okapi. The antilocaprids belong to the infraorder Pecora, which makes the pronghorn a distant cousin of deer, bovids, and moschids. That kinship to the Giraffidae shows up in the animal's head, where skin covers a bony core, just as it does on a giraffe's skull.

• 3. A Name Earned By Its Horns

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  The horn sheaths give the pronghorn its name. Each sheath branches and carries a forward-pointing tine, unlike the horns of any animal in the ox family Bovidae. The structure underneath is strange in its own right. Each horn is a slender, laterally flattened blade of bone, thought to grow from the frontal bones of the skull or from the tissues beneath the scalp, forming a permanent core. Over that core grows a keratinous sheath, and here the pronghorn does something almost no other horned mammal does. It sheds the sheath and grows a new one every year. Males carry a horn sheath averaging 9.8 inches long, ranging from 4.9 to 17 inches, each tipped with a prong. Females have far smaller horns, averaging 4.7 inches and sometimes barely visible, usually straight and only very rarely pronged. A male also carries a small patch of black hair at the angle of his jaw, a marking no female has.

• 4. Chemistry Of A Scent

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  The pronghorn carries a distinct, musky odor that follows it across the plains. Much of that signaling runs on chemistry. The preorbital gland on the sides of a male's head secretes 2-ethyl-3-methylpyrazine, the same highly odoriferous compound found on the male's back in his medial gland. He uses the preorbital gland to mark territory. The rump tells a different story. Both males and females have glands hidden under the white rump hair, and when that hair stands up, the glands are exposed. The major compound there is 2-pyrrolidinone, and to a human nose its odor is reminiscent of buttered popcorn. People have smelled it 65 to 100 feet downwind from an alarmed animal. Even the feet are chemically armed. Well-developed glands sit between the hooves, and like the interdigital glands of many ungulates, they hold compounds with antimicrobial activity against soil and mammalian pathogens.

• 5. Built To Outrun Ghosts

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  Top speed for a pronghorn depends on how far you ask it to go. It can hold 35 miles per hour for 4 miles, 42 miles per hour for 1 mile, and 55 miles per hour over half a mile. The African cheetah is faster in a sprint, but cannot sustain its top speed anywhere near as long. The puzzle is that nothing alive in North America can catch a pronghorn, so its speed seems built for predators that no longer exist, such as the American cheetah. Evidence from Natural Trap Cave supports this. Carbon and nitrogen isotope comparisons among pronghorn, horses, bighorn sheep, bison, American cheetahs, American lions, and wolves showed the American cheetah fed on pronghorns, though not exclusively. American lions and wolves hunted them too. The body is engineered to match. Relative to its size the pronghorn has a large windpipe, heart, blood volume, erythrocytes, and lungs to gulp air at a run. Its hooves carry two long, cushioned, pointed toes that absorb shock, its bones are extremely light, and its hair is hollow. Naturalists have counted at least 13 distinct gaits, one of them stretching nearly 24 feet per stride. Yet the animal is built for speed, not jumping. Where sheep ranchers' fences cross its range it goes under rather than over, sometimes at full speed. That habit is why the Arizona Antelope Foundation and others remove the bottom barbed wire from fences or install a barbless bottom strand.

• 6. An American Serengeti

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  West of the Mississippi River, the pronghorn was once particularly abundant, and that region remains its primary range today. The prehistoric American Prairie has been called the American Serengeti, its herds of bison, elk, and pronghorn once millions strong as recently as 200 to 300 years ago. The animal favors open terrain between 3000 and 5900 feet, densest where 10 to 16 inches of rain fall each year, and it rarely strays far from water, with most found within 5 miles of a source. Its diet leans on plants that domestic livestock find unpalatable or toxic. One study put forbs at 62 percent, shrubs at 23 percent, and grasses at 15 percent; another found forbs at 20 percent, cacti at 40 percent, shrubs at 18 percent, and grass at 22 percent. Today the range runs from southern Saskatchewan and Alberta down through the western United States into Mexico, where the Sonoran pronghorn reaches from Baja California Sur into Sonora and San Luis Potosi. The animal has been wiped out from Iowa, Minnesota, and Manitoba. One migration is staggering. A study by the Lava Lake Institute for Science and Conservation and the Wildlife Conservation Society tracked a route of more than 160 miles, from the foothills of the Pioneer Mountains through Craters of the Moon National Monument to the Continental Divide. Dr. Scott Bergen of the Wildlife Conservation Society called the pronghorns the true marathoners of the American West, confirming that Idaho supports a major overland mammal migration, an increasingly rare phenomenon.

• 7. Harems And Hidden Fawns

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  In winter the pronghorn gathers into mixed-sex herds. By early spring those herds break apart, young males forming bachelor groups, females forming harems, and adult males living alone. Dominant females aggressively push others off the best feeding sites. Adult males either hold a fixed territory or guard a harem, and they may switch strategies as conditions change. Where rain is plentiful, males turn territorial, marking scent, vocalizing, and challenging intruders, with the territory holders claiming the better resources. Females play their own games. A sampling female visits several males in turn, switching faster as estrus nears. An inciting female samples until estrus, then provokes fights between males and mates with the winner. A quiet female stays with a single male in an isolated spot throughout estrus. Before a fight, males try to intimidate each other; if that fails they lock horns and try to injure one another. A courting male approaches softly vocalizing and waving his head side to side to show his cheek patches, and a receptive female stands still, sniffs his scent gland, and lets him mount. The gestation runs 7 to 8 months, unusually long for a North American ungulate and about six weeks longer than a white-tailed deer's. They breed in mid-September, and the doe carries until late May. Twin fawns are common, weighing 2 to 4 kilograms at birth, most often 3. For their first 21 to 26 days the fawns lie hidden in vegetation, meeting their mothers only 20 to 25 minutes a day. Sexual maturity comes at 15 to 16 months, though males rarely breed before three years, and a pronghorn typically lives up to 10 years, rarely 15.

• 8. From The Edge Of Extinction

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  Spanish explorers first saw and described pronghorns in the 16th century, but the species went unrecorded in detail until the 1804-06 expedition of Captain Meriwether Lewis and Second Lieutenant William Clark. They came across it near the mouth of the Niobrara River, in present-day Nebraska, and Clark was among the first Euro-Americans to publish an account of killing one, calling it a Buck Goat that reminded him more of the Antilope or Gazelle of Africa than any other goat. The American ornithologist George Ord gave the species its first formal description in 1815. Long before any of that, Plains Indians and peoples of the Northwest Plateau hunted the pronghorn as a principal food source, and the Mandans drove herds into a widening brush fence that funneled into a strong pen. Then the herds collapsed. At the turn of the 20th century the Boone and Crockett Club judged extinction likely, and George Bird Grinnell wrote that the pronghorn appeared everywhere rapidly diminishing. By the 1920s hunting had cut the population to about 13,000, and member Charles Alexander Sheldon wrote that he thought the antelope were doomed, yet every attempt should be made to save them. Early efforts faltered, since fenced enclosures killed the animals off after initial gains. The turning point came through land. In 1927 Grinnell, joined by T. Gilbert Pearson of the National Audubon Society, pushed to create a refuge in northern Nevada; about 2900 acres were bought and turned over to the Biological Survey, contingent on the government adding 30,000 acres of public land. President Herbert Hoover added those lands in 1929 and signed the executive order on the 26th of January 1931. On the 31st of December 1936, President Franklin Roosevelt signed an order creating a 549,000 acre tract, the true beginning of pronghorn recovery. Numbers have since climbed to an estimated 500,000 to 1,000,000. The fight is not over for every population: the Sonoran pronghorn numbers fewer than 300 in the United States and 200 to 500 in Mexico, protected under the Endangered Species Act since 1967, while only about 200 Peninsula pronghorn survive in Baja California.