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Cabeza Prieta Natural History Association
Sonoran Desert Mammals

Ajo Peak at Night

 

Pronghorn
(Antilocapra americana sonoriensis)

Diet: herbivorous
Color: tan or reddish-tan, with white on sides, rump, belly, chest, inner legs, cheeks, and lower jaw
Active Period: active all times
Abundance: endangered

One of a Kind

Unique on the planet, the Pronghorn's scientific name-- Antilocapra americana-- means "American antelope goat", but it is neither antelope nor goat, despite it's close resemblance to African antilopes. The pronghorn is the only surviving member of an ancient family dating back 20 million years. The Sonoran Pronghorn (A. a. sonorensis) is one of five subspecies in western North America, and is perhaps America's most endangered mammal.

The Pronghorn is the only animal in the world with branched horns (not antlers) and the only animal in the world to shed its horns, as antlers are shed, annually. However, what the Pronghorn is most famous for is being the fastest animal in the western hemisphere, capable of running at 60 miles an hour while making 20-foot bounds, and capable for running at up to 40 miles per hour for long periods.

Where Pronghorn Live

Pronghorn occupy grasslands, brushlands, and open plains and deserts from Saskachewan, Canada to Sonora, Mexico, and live in all the deserts of the American southwest. The Sonoran Pronghorn is found only in one area in southwestern Arizona near Ajo, Arizona, and in two populations in northern Sonora.

The Sonoran Pronghorn in southern Arizona probably numbered in the tens of thousands at the start of the nineteenth century, but unregulated hunting, livestock grazing, drought and habitat fragmentation by fencing, railroads, highways, and water diversion projects caused the population to decline. Currently the United States population is about thirty. The two Mexican populations contain about 15-20 and 300-400 animals.

What do Pronghorn Look Like?

An adult Pronghorn has a deer-like body and weighs between 90 and 125 pounds. Standing about 3 to 3½ feet tall at the shoulder, they have large, protruding eyes which provide excellent vision up to four miles and a field of vision of 320 degrees. When startled, the Pronghorn often shows its white tail and rump patch before fleeing.

The upper body and outside of the legs are tan to brown. The cheeks, lower jaw, chest, belly, inner legs and rump are usually white. The male has a broad, black band down the snout to a black nose, a black cheek patch, and black horns.

Pronghorn Behavior

Sonoran Pronghorn are extremely sensitive animals that can be active both day and night, alternating sleep with vigilant feeding. Opportunistic foragers, Pronghorn feed on a wide variety of grasses, herbs, forbs, shrubs, and sometimes cacti and domestic crops. Like cows, they have a four-part stomach, and this enables them to digest rough forage while extracting available moisture.

Because Pronghorns evolved in open terrain, they rely on their keen eyesight and blazing speed as defensive mechanisms. They never learned to jump over even low barriers, and are averse to crossing railroad tracks, fences, roadways or other obstacles, and consequently Pronghorn were eliminated from vast areas when they were prevented from traveling across ancestral areas.

Female Pronghorn usually give birth annually after they reach two years of age, and separate from the herd to give birth to one or two fawns from March to May. The young weigh four to twelve pounds at birth and are about 15" tall. Within a day or two the young can sprint at speeds up to 25 miles per hour. Mortality is high, with about 40% dying by mid-July due to stress and predation. Pronghorn are estimated to live nine or ten years on average, and to twelve years in captivity.

The Pronghorn's Future

The Sonoran Pronghorn has been federally listed as "endangered" since March 11, 1967. Endangered status means that a plant or animal is "…in danger of extinction throughout all or a part of its range." The Fish and Wildlife Service is the federal agency responsible for administration of the Endangered Species Act, and is committed to the recovery of this endangered species.

Working with other agencies and organizations, the refuge has developed and begun to implement a recovery plan for the Sonoran Pronghorn that provides a framework and process designed to increase the population so that the animal can be removed from the endangered list. Currently (2004) a captive breeding and transplant strategy has been initiated, modeled after a successful captive breeding program developed for the endangered Peninsular (Baja) pronghorn subspecies. Three animals from Sonora, Mexico and southern Arizona are the initial brood stock, and plans are underway to expand the breeding population. If successful, within a few years animals can be released back into suitable Arizona and Sonora habitats.

News Release: March 5, 2005
Endangered Pronghorn Births Signal Success

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