The pronghorn's closest living relatives are thegiraffe andokapi.[14] The antilocaprids are part of the infraorderPecora, making them distant relatives ofdeer,bovids, andmoschids.
The pronghorn is the fastest land mammal in the Americas, with running speeds of up to 55 mph (88.5 km/h). It is the symbol of theAmerican Society of Mammalogists.[15]
Pronghorn were first seen and described by Spanish explorers in the 16th century, but the species was not formally recorded or scrutinized until theexpedition in 1804–06 by CaptainMeriwether Lewis and Second LieutenantWilliam Clark.[17] Following the discovery of a fewsubspecies of thesharp-tailed grouse, Lewis and Clark came across the pronghorn near themouth of theNiobrara River, in present-dayNebraska. Clark was among the first Euro-Americans to publish the experience of killing a pronghorn, and described his experience as follows:[18]
I walked on shore to find an old Vulcanoe [theIonia Volcano?] ... in my walk I killed a Buck Goat of this Countrey, about the height of the Grown Deer, its body Shorter the horns which is not very hard and forks2⁄3 up one prong Short the other round & Sharp arched, and is immediately above its Eyes the Color is a light gray with black behind its ears down the neck, and its face white round its neck, its Sides and its rump round its tail which is Short & white; Verry actively made, has only a pair of hoofs to each foot, his brains on the back of his head, his Nostrals large, his eyes like a Sheep he is more like the Antilope or Gazelle of Africa than any other Species of Goat.
Pronghorns have distinct white fur on theirrumps, sides, breasts, bellies, and across their throats. Adult males are 4.3–4.9 ft (1.3–1.5 m) long from nose to tail, stand 2.7–3.4 ft (82–104 cm) high at the shoulder, and weigh 88–143 lb (40–65 kg). The females are the same height as males, but weigh 75–106 lb (34–48 kg). The feet have twohooves, with nodewclaws. Their body temperature is 100 °F (38 °C).[8][20][16][21]
Each horn of the pronghorn is composed of a slender, laterally flattened blade of bone, which is thought to grow from the frontal bones of the skull, or from the subcutaneous tissues of the scalp, forming a permanent core.[23] As in theGiraffidae, skin covers the bony cores, but in the pronghorn, it develops into akeratinous sheath which isshed and regrown annually. Males have a horn sheath about4.9–17 in (12+1⁄2–43+1⁄4 cm) (average 9.8 in or 25 cm) long with a prong. Females have smaller horns that range from 0.4–2.4 in (1–6 cm) (average 4.7 in or 12 cm) and sometimes barely visible; they are straight and very rarely pronged.[16]
Males are further differentiated from females in having a small patch of black hair at the angle of themandible. Pronghorns have a distinct,musky odor. Malesmark territory with apreorbital scent gland on the sides of the head.[8]
The preorbital gland's secretion contains the highly odoriferous compound, 2-ethyl-3-methylpyrazine, which also the major volatile component found on the animal's back in the male's medial gland.[24]
Male and female animals have glands that are exposed when the white hair on the rump stands up. 2-Pyrrolidinone, the major compound in the rump gland, has an odor reminiscent of buttered popcorn to humans. The flared rump hair and odor alert adjacent animals of a possible danger.[25]
Pronghorns have well developed glands on each hoof. Like many ungulates, these interdigital (hoof) glands contain chemical compounds that are known to have antimicrobial activity against soil and mammalian pathogens.[26]
The pronghorn is the fastest land mammal in the Western Hemisphere, being built for maximumpredator evasion through running. Their top speed is dependent upon the length of time over which it is measured. It can run 35 mph (56 km/h) for 4 mi (6.5 km), 42 mph (68 km/h) for 1 mi (1.5 km), and 55 mph (88.5 km/h) for 800 metres (0.5 mi).[20][27] Although it is slower than the Africancheetah,[28] it can sustain top speeds much longer than cheetahs.[7] The pronghorn may haveevolved its running ability to escape from now-extinct predators such as theAmerican cheetah, since its speed greatly exceeds that of allextant North American predators.[7][29]: 318 Carbon and nitrogenisotope comparisons between pronghorn, horses,bighorn sheep,bison,American cheetahs,American lions, and wolves of theNatural Trap Cave found that while American cheetahs seemed to subsist on pronghorns, they did not do so exclusively. In fact, pronghorns were also important prey of American lions and wolves.[30] Compared to its body size, the pronghorn has a largewindpipe, heart, blood volume,erythrocites, and lungs to allow it to take in large amounts of air when running.[31] Additionally, pronghornhooves have two long, cushioned, pointed toes, which help absorb shock when running at high speeds.[32] They also have an extremely light bone structure and hollowhair.
Male pronghorns tend to have a higher level of physical activity than females, and apparently also have a greater blood volume relative to body size.[31]
Pronghorns are built for speed, not for jumping. Since their ranges are sometimes affected by sheep ranchers' fences, they can be seen going under fences, sometimes at high speed. For this reason, the Arizona Antelope Foundation and others are in the process of removing the bottombarbed wire from the fences, and/or installing a barbless bottom wire.[33]
The pronghorn has been observed to have at least 13 distinctgaits, including one reaching nearly 24 ft (7.3 m) per stride.[7]
When a pronghorn sees something that alarms it, the white hair on the rump flares open and exposes two highly odoriferous glands that releases a compound described as having an odour "reminiscent of buttered popcorn." This sends a message to other pronghorns by both sight and smell about a present danger. This scent has been observed by humans 65 to 100 feet downwind from alarmed animals. The major odour compound identified from this gland is 2-pyrrolidinone.[34]
Prior to the arrival of Europeans, the pronghorn was particularly abundant in the regions west of theMississippi River which is still its primary range today. The amount of wildlife was considered to be so vast at one time that the prehistoric American Prairie—and as recently as 200 to 300 years ago—has been dubbed the "American Serengeti", due to the once-millions-strong herds ofbison,elk, and pronghorn, as well as many other now-extinctmegafauna.
Pronghorns prefer open terrain at elevations between 3,000 and 5,900 ft (910 and 1,800 m), with the densest populations in areas receiving around10–16 in (254–406+1⁄2 mm) of rainfall per year. They eat a wide variety of plant foods, often including plants unpalatable or toxic to domesticlivestock, though they also compete with them for food.[20] In one study,forbs comprised 62% of their diet,shrubs 23%, andgrasses 15%.[20] Another study similarly found forbs comprised 20%,cacti 40%, shrubs 18%, and grass 22%.[16] Pronghorns chewcud (ruminate).
Historical range of pronghorn subspecies
Healthy pronghorn populations tend to stay within 3–4 mi (5.0–6.5 km) of a water source. The majority are found within 5 mi (8 km) of a water source.[39]
Cougars (Puma concolor),wolves (Canis lupus),coyotes (Canis latrans),grizzly bears (Ursus arctos horribilis) andbobcats (Lynx rufus) are major predators of pronghorns.[42]Golden eagles (Aquila chrysaetos) have been reported to prey on fawns and adults.[42][43]Jaguars (Panthera onca) also likely prey on pronghorns in their native range in the southwestern United States and in northern Mexico. In thePleistocene, jaguars would likely be dangerous to pronghorns as a short-range ambush predator.[44]
Pronghorns form mixed-sex herds in the winter. In early spring, the herds break up, with young males forming bachelor groups, females formingharems, and adult males living solitarily.[29] Some female bands share the same summer range, and bachelor male bands form between spring and fall. Females form dominance hierarchies with few circular relationships.[45] Dominant females aggressively displace other females from feeding sites.
Adult males either defend a fixed territory that females may enter, or defend a harem of females. A pronghorn may change mating strategies depending on environmental or demographic conditions.[29]: 228 Where precipitation is high, adult males tend to be territorial and maintain their territories withscent marking,vocalizing, and challenging intruders.[46] In these systems, territorial males have access to better resources than bachelor males.[46] Females also employ different mating strategies. "Sampling" females visit several males and remain with each for a short time before switching to the next male at an increasing rate asestrous approaches. "Inciting" females behave as samplers until estrous, and then incite conflicts between males, watching and then mating with the winners.[47] Before fighting, males try to intimidate each other. If intimidation fails, they lock horns and try to injure each other.[16] "Quiet" females remain with a single male in an isolated area throughout estrous.[47] Females continue this mating behavior for two to three weeks.[16]
When courting an estrous female, a male pronghorn approaches her while softly vocalizing[48][29] and waving his head side to side, displaying his cheek patches.[49] Thescent glands on the pronghorn are on either side of the jaw, between the hooves, and on the rump.[16] A receptive female remains motionless, sniffs his scent gland, and then allows the male to mount her.[29]
Pronghorns have agestation period of 7–8 months, which is longer than is typical for North American ungulates. They breed in mid-September, and the doe carries her fawn until late May. The gestation period is around six weeks longer than that of thewhite-tailed deer. Females usually bear within a few days of each other.[20] Twin fawns are common.[32] Newborn pronghorns weigh 4–9 lb (2–4 kg), most commonly 7 lb (3 kg). In their first 21–26 days, fawns spend time hiding in vegetation.[46] Fawns interact with their mothers for 20–25 minutes a day; this continues even when the fawn joins anursery.[46] The females nurse, groom, and lead their young to food and water, as well as keep predators away from them.[46] Females usually nurse the young about three times a day.[20] Males areweaned 2–3 weeks earlier than females.[46]Sexual maturity is reached at 15 to 16 months, though males rarely breed until three years old. Theirlifespan is typically up to 10 years, rarely 15 years.[20][16][21]
Merriwether Lewis and William Clark made several other observations on the behavior of the pronghorn and how the local tribes hunted them. They described the animal, which they referred to as the "Antelope" or the "Goat", as follows:[19]
Of all the animals we have seen the Antelope seems to possess the most wonderful fleetness. Shy and timorous they generally repose only on the ridges, which command a view of all the approaches of an enemy ... When they first see the hunters they run with great velocity ... The Indians near the Rocky Mountains hunt these animals on horseback, and shoot them with arrows. TheMandans' mode of hunting them is to form a large, strong pen or fold, from which a fence made of bushes gradually widens on each side. The animals are surrounded by the hunters, and gently driven towards this pen, in which they imperceptibly find themselves enclosed, and are then at the mercy of the hunters.
At the turn of the 20th century, members of the wildlife conservation groupBoone and Crockett Club had determined that the extinction of the pronghorn was likely. In a letter fromGeorge Bird Grinnell, Boone and Crockett Club chairman of the game preservation committee, toWalter L. Fisher,Secretary of the Interior, Grinnell stated, "The Club is much concerned about the fate of the pronghorn which appears to be everywhere rapidly diminishing." By the 1920s,hunting pressure had reduced the pronghorn population to about 13,000.[7] Boone and Crockett Club memberCharles Alexander Sheldon, in a letter to fellow member Grinnell, wrote, "Personally, I think that the antelope are doomed, yet every attempt should be made to save them." Although the club had begun their efforts to save the pronghorn in 1910 by funding and restocking theWichita Game Refuge inOklahoma, theNational Bison Range inMontana, and theWind Cave National Park, inSouth Dakota, most of the efforts were doomed since experience demonstrated that after initial increases the pronghorns would die off because of the fenced enclosures.
In 1927, Grinnell spearheaded efforts along with the help ofT. Gilbert Pearson of Grinnell'sNational Audubon Society to create theCharles Alexander SheldonAntelope Refuge in northernNevada. About 2900 acres of land were jointly purchased by the two organizations and subsequently turned over to the Biological Survey as a pronghorn refuge. This donation was contingent upon the government's adding 30,000 acres of surrounding public lands. On June 20, 1929, United StatesPresident Herbert Hoover included the required public lands upon request of theDepartment of Agriculture and theDepartment of the Interior after learning that the Boone and Crockett Club and the National Audubon Society were underwriting the private land buyout. On January 26, 1931, Hoover signed the executive order for the refuge. On December 31, 1936, President Franklin Roosevelt signed an executive order creating a 222,000-hectare (549,000-acre) tract; this was the true beginning for pronghorn recovery in North America.[52]
The protection of habitat and hunting restrictions have allowed pronghorn numbers to recover to an estimated population between 500,000 and 1,000,000 since the 1930s.[2] Some recent decline has occurred in a few localized populations,[20] due tobluetongue disease which is spread from sheep, but the overall trend has been positive.
Pronghornmigration corridors are threatened byhabitat fragmentation and the blocking of traditional routes. In a migration study conducted by Lava Lake Institute for Science and Conservation and theWildlife Conservation Society, at one point, the migration corridor bottlenecks to an area only 200 yards wide.[53]
Pronghorns are now quite numerous, and outnumbered people inWyoming and parts of northernColorado until just recently. They are legally hunted in western states for purposes of population control and food. No major range-wide threats exist, although localized declines are taking place, particularly to theSonoran pronghorn, mainly as a result of livestock grazing, the construction of roads, fences, and other barriers that prevent access to historical habitat, illegal hunting, insufficient forage and water, and lack ofrecruitment.[2]
Three subspecies are considered endangered in all (A. a. sonoriensis,A. a. peninsularis), or part of their ranges (A. a. mexicana). The Sonoran pronghorn has an estimated population of fewer than 300 in the United States and 200–500 in Mexico, while there are approximately 200 Peninsula pronghorn in Baja California.[2] Populations of the Sonoran pronghorn in Arizona and Mexico are protected under theEndangered Species Act (since 1967), and a recovery plan for this subspecies has been prepared by U.S. Fish and Wildlife Service.[2] Mexican animals are listed onCITES Appendix I. Pronghorns have game-animal status in all of the western states of the United States, and permits are required totrap or hunt pronghorns.[2]
^Wood, William F. (2011). "2-Ethyl-3-methylpyrazine in the subauricular and median glands of pronghorn, Antilocapra americana".Biochemical Systematics and Ecology.39 (2):159–169.Bibcode:2011BioSE..39..159W.doi:10.1016/j.bse.2011.01.015.
^Wood, William F. (2002). "2-Pyrrolidinone, a putative alerting pheromone from rump glands of pronghorn, Antilocapra Americana".Biochemical Systematics and Ecology.30 (4):361–363.Bibcode:2002BioSE..30..361W.doi:10.1016/S0305-1978(01)00097-7.
^J. Cancino; R. Rodríguez-Estrella; A. Ortega (1995). "First Aerial Survey of Historical Range for Peninsular Pronghorn of Baja California, Mexico".Journal of the Arizona-Nevada Academy of Science.28 (1):46–50.JSTOR40024301.
^Brunton BB: Kootenai. In: Handbook of North American Indians, Volume 12: Plateau. edn. Edited by Walker DE, Jr. Washington, DC: Smithsonian Institution; 1998: 223–228.ISBN0-16-049514-8
^Bruchac, Joseph (1992).Native American Animal Stories. Fulcrum Publishing.ISBN978-1-55591-127-0.
^Sheldon, Charles (1955).A History of the Boone and Crockett Club. Boone and Crockett Club.
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