Pronghorn (Antilocarpa Americana) are the fastest land mammals in North America, with top speeds over 55 mph and sustained trots of 25 mph. Though often referred to as antelope, the pronghorn is not closely related. In fact, pronghorn are different enough from other hoofed animals that they've been placed in their own taxonomical family (Antelocapridae). One primary distinction is their horns, which curl backwards, are hollow and shed annually - the only animal with this combination (deer and elk antlers are solid, while goats and cows do not shed).
Size and Lifespan: Both sexes grow backward-curving horns that split into forward-pointing prongs for which the animal is named. Male horns can grow over a foot, while females average 2-6". Adult pronghorn stand 2.5 - 3.5' at the shoulder, averaging 105 - 120 lbs (female and male, respectively). Pronghorn average 9-11 years in the wild before age subjects them to predation, or the inability to keep pace with their herd into new feeding areas.
Range: Pronghorns range across the plains and grasslands of North America. Once numbering over 30 million in the early 1800s, hunting and habitat loss drove populations down to 15,000 by 1915. A moratorium on hunting through the 1940s helped stop this decline. Today there are nearly 1 million pronghorn in their natural range and introduced areas, which include five recognized subspecies: American / Common (Canada to Northern AZ), Oregon (SE OR), Peninsular (Baja Mexico), Mexican / Chihuahuan (NM, TX, AZ), and Sonoran (AZ, Mexico).
Pronghorn Habitat and Diet: Pronghorn live in dry, open grasslands that do not exceed 30" in height, an important criteria for avoiding predators. Pronghorn feed on grasses, sagebrush, and other locally available vegetation. They have a four-chamber stomach to process this fibrous material. Pronghorn are ruminates, which means they chew cud, or partially digested, regurgitated food. This secondary form of mechanical digestion assists the breakdown of stiff vegetation.
Pronghorn Mating and Breeding: Pronghorn amass herds in the winter that can number a few dozen to hundreds. Large herds and incomparable speed enable pronghorn to rest throughout the day. The herd moves as one, a technique aimed at deflecting and confusing predators. Herds disassemble in the spring as bucks break off into bachelor groups or strike out on their own in an attempt to establish a small territory. Males battle energetically for mating rights, but serious injuries are uncommon. Males amass harems of 2-20 females and breed in late summer, after which they drop the hollow sheath from their horns. Females give birth to one or two young the following spring. They leave newborns hidden in the grass, nursing at 30 second intervals every 4-5 hours. Newborns can outrun a human after just a few days. Up to 50% of newborns will not live to their second year; females that do generally remain with the herd. Adolescent males will face aggression from older males, and eventually leave to live alone or among other bachelors. Both sexes reach sexual maturity after 16 months, through males seldom breed before 3 years due to competition.
Predation: Pronghorn face varying degrees of predation depending on their location. Few natural predators remain in the American Midwest, though coyotes may find success with young / sick animals, and human hunting keeps populations in check. In less developed areas like Wyoming, mountain lion, wolves and grizzly bear pose only a moderate threat. With so few successful predators, why all the speed? It's thought pronghorn developed this trait to outrun now-extinct hunters like the North American Cheetah. Surprisingly, pronghorn are very poor jumpers, and their ability to find new food sources is heavily impacted by fences - perhaps their greatest threat today. When startled pronghorn will raise the hair on their rumps to display a white warning patch that can be seen for miles across open plains.