The pronghorn antelope (Antilocapra americana) is a species of ruminant that is the sole living representative of its family, the Antilocapridae. This family was much more diverse during the Pliocene and early to mid-Pleistocene periods. The Antilocapridae is an exclusively North American family, and pronghorns are not closely related to the true antelopes, which are members of the Bovidae, a family that also includes cows, water buffalo, sheep, and goats. Pronghorns occur in the prairies and semideserts of southwestern Canada, the western United States, and northern Mexico.
Pronghorns are similar in size to the smaller deer of the Americas, such as the white-tailed deer (Odocoileus virginianus). Pronghorns stand about 3 ft (1 m) tall at the shoulders, and mature animals typically weigh between 88 and 132 lb (40 and 60 kg). Males (bucks) are somewhat larger than females (does). Pronghorns have and a relatively long head, with large eyes and long ears.
Pronghorns are ruminants, having a stomach divided into four chambers, each of which is concerned with a particular aspect of the digestion of the fibrous plant biomass that these herbivores feed upon. Rumination includes the rechewing of regurgitated food that has already spent some time fermenting in one of the fore pouches of the stomach. Pronghorns eat grasses and other herbaceous plants, as well as the tissues of woody plants.
Pronghorns have relatively small, unbranched, divergent horns, which are persistent and not shed annually as are the antlers of deer. These antlers are outgrowths of the frontal bones of the skull, and they develop in both sexes, although those of females are smaller, and are sometimes missing. Although pronghorns retain their horns throughout their life, they are the only ungulate that renews the outer sheath of the horns each year. The sheath is shed at the end of each breeding season, after the new sheath has grown upward from the skull under the old sheath. Anatomically, the horn sheath is derived from fused hairs.
Pronghorns have a polygamous breeding system. Male pronghorns fight among themselves during the summer breeding season, and they use a musky scent to mark their territory while attempting to round up as many females as possible into a harem. Most females give birth to twin young, known as kids. Although the kids are precocious and capable of standing and walking within a short time of their birth, their mother keeps them hidden from predators in vegetation during the day.
Pronghorns are the fastest land animals in the Americas, and are capable of running at a speed of 50 mi/h (80 km/h) over a distance of 1 mi (1.5 km), or at a cruising speed of about 30 mi/h (50 km/h) for longer distances. When a pronghorn senses danger, it dashes off at high speed, while alerting other animals to the threat by raising a ruff of bright white hair on the rump, which can be seen glinting in the sun over a great distance. However, pronghorns are very curious animals, and they can be easily attracted by a person lying on the ground and waving a red flag, or waving their arms and legs about. Unfortunately, this curiosity makes pronghorns an easy mark for hunters, because it is not difficult to lure these animals within the killing range of rifles. Interestingly, these tricks did not work well for the aboriginal plains Indians, because the pronghorns could rarely be lured close enough to be killed with a bow and arrow.
Pronghorns are migratory animals, moving extensively between their winter and summer ranges, especially in the northern parts of their range. Unfortunately, pronghorns are easily constrained by mesh or woven fences, because they will not jump vertically over a barrier. Pronghorns will, however, pass through the strands of barbed wire, as long as there is sufficient space between the strands, or between the lowest strand and the ground. If attention is given to this rather simple yet critical requirement of pronghorns, these animals can be rather easily sustained on fenced landscapes.
Prior to the settlement of the Great Plains by European farmers and ranchers, the pronghorn was an enormously abundant animal. It may have maintained a population of 40 million animals. At that time, only the American buffalo (Bison bison) was a more populous large animal in North America, with an estimated abundance of 60 million individuals. The ecological changes that accompanied the agricultural conversions of the prairies, coupled with rapacious market hunting during the late nineteenth century, caused a great diminishment in the abundance of pronghorns. By the early nineteenth century this species was diminished to only about 20,000 individuals in its range north of Mexico. Fortunately, thanks to strong conservation efforts the pronghorn now numbers more than 500,000 animals, and this species now supports a sport hunt over most of its range.
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Wilson, D.E., and D. Reeder. Mammal Species of the World. 2nd ed. Washington, DC: Smithsonian Institution Press, 1993.