Basic Facts About Sonoran Pronghorns
Known as "prairie ghosts" because they are so elusive, the Sonoran pronghorn (Antilocapra americana sonoriensis) is the fastest land mammal in North America. Smaller and lighter in color than other pronghorn subspecies, it is uniquely adapted for survival in harsh arid conditions.
Sonoran pronghorns are reddish brown on their backs and sides and have lighter colored undersides. They have bright white markings on their heads and necks; males have black faces and black patches on the sides of their necks.
Male Sonoran pronghorns sport large black pronged horns, while females have short black horns.
Sonoran pronghorns eat herbs, cacti, and desert grasses.
Approximately 100 Sonoran pronghorn remain in the wild in the United States. There is also a small population held in a captive breeding program on the Cabeza Prieta National Wildlife Refuge in southwest Arizona. There are approximately 650 pronghorn in Mexico.
Historically, Sonoran pronghorn traveled across vast expanses of the Sonoran Desert in Arizona, California, and Sonora, Mexico. Currently it is confined to fragments of its former range, with only three small populations remaining – one in southwest Arizona, and two separate populations in Mexico.
Sonoran pronghorn have evolved in unique ways to adapt to the harsh desert environment. For example, it can erect its stiff bristle-like body hair in patches to release body heat in extremely hot weather. The pronghorn’s exceptional speed and excellent vision help it to avoid predators and take advantage of scarce desert forage.
Mating Season: September and October
Gestation: 250 days.
Offspring: 1 fawn; twins when there is abundant food.
Does are ready to mate at 16 months and bucks are ready by one year of age.
Competition for food plants by cattle grazing in the Sonoran region was the primary factor in the steep decline of the pronghorn. This practice has now been halted in the areas where pronghorn remain. The species is also sensitive to human disturbance, including military aviation activities in the Goldwater Range, and both the illegal activity in the border region and the law enforcement response. Roads, fences, railroad tracks and human development have reduced and fragmented the wide spaces they need in which to forage successfully.
In addition to these historic and ongoing threats, climate changes already underway in the southwest are threatening to push the pronghorn over the edge of extinction. Survival of fawns is determined mainly by the amount of precipitation falling in the winter and by the length of the drought interval until the monsoon rains start in the summer. Winter precipitation governs the amount of forage available to nursing females, and summer precipitation determines the food available to the young, newly weaned fawns. Adult survival is also influenced by precipitation, probably because in dry conditions, animals are forced to forage in valleys where the vegetation is denser and predators are less visible.
The U.S. population very nearly died out in 2002, when a 13-month drought wiped out all but 21 animals. The U.S. Fish and Wildlife Service intervened to prevent extinction by providing water and forage and initiating a captive breeding program, and is planning to establish a second population at nearby Kofa National Wildlife Refuge. These actions have helped the numbers to creep back up, however the species’ chances of surviving climate change without continued intervention may be slim. As climate change increases the length and intensity of droughts in the Sonoran desert, the pronghorn is likely to face extreme difficulty reproducing successfully.