Partners save the Sonoran pronghorn.

The endangered Sonoran pronghorn (Antilocapra americana sonoriensis) of Arizona and Mexico is among one of the Department of Defense's most eye-catching tenants. This graceful holder of the North American land speed record can run at speeds up to 60 miles (95 kilometers) per hour, and its large eyes can detect movement 4 miles (6.5 kilometers) away. Once widespread in the southwestern desert, the Sonoran pronghorn is now restricted to three isolated herds, two in Mexico and one in America. With a total population of fewer than 500 animals, it is highly endangered.

The Barry M. Goldwater Range, one-half managed by the Air Force and the other by the Marine Corps, contains most of the Sonoran pronghorn's remaining habitat in the United States. At more than 1.7 million acres (688,000 hectares), the Goldwater Range looms large on the Arizona landscape as a prized military training area. Significantly, the 860,000-acre (348,000-ha) Cabeza Prieta National Wildlife Refuge adjoins the training range, as does Organ Pipe Cactus National Monument. All three areas come together at the Mexican border.

Rallying to a Species in Need

A devastating drought in 2002 reduced the animal's numbers to an all-time low. At one point, the U.S. population fell to an estimated 21 animals. In a textbook example of a conservation partnership, the Arizona Game and Fish Department (AGFD) and the U.S. Fish and Wildlife Service responded to the threat by assembling a wide array of stakeholders to prevent the extinction of Sonoran pronghorns north of the border. The Air Force, Marine Corps, Mexican government, two Arizona hunting clubs, zoo veterinarians, and University of Arizona volunteers all played a part. By early 2004, three major recovery projects were underway with Air Force and Marine Corps help.

The first project was inspired by an interesting discovery about the drinking habits of Sonoran pronghorns. Some experts maintained the desert mammal would not drink water from artificial sources. In a last ditch effort to save the pronghorn from extinction, staff from the AGFD, the Service, and the Marine Corps carried water coolers up to 4 miles (6.5 kin) off road to test this assertion. They discovered the wary desert animals were willing to drink from artificial sources. With this knowledge, the agencies resolved to drill a series of wells to create "watering holes" for the pronghorn.

The second project addressed the need to ensure long-term sources of browsing forage. Irrigation plots created on the Goldwater Range and the refuge now support the growth of grasses, weeds, and shrubs for pronghorn subsistence.

Finally, the National Park Service, the Fish and Wildlife Service, the Air Force, and the Marine Corps spent significant funds to erect a breeding enclosure on the refuge in January 2004. The AGFD made swift arrangements with the Mexican government to integrate genetically diverse Sonoran pronghorns from one of two isolated populations south of the border. The stress of travel was fatal to four of seven Mexican animals, halting the Mexican project temporarily. In December of 2004, however, seven adults (some American and some Mexican) were captured and relocated into the breeding enclosure. The animals began feeding and forming social relationships.

In the spring of 2005, pronghorns in the captive breeding area gave birth to 10 fawns, including four sets of twins. Four died in a particularly hot, dry stretch in July, probably due to an absence of accessible forage in the pen's washes, where the pronghorns spend most of their time. In response, the partners from the recovery team beefed up irrigation in the captive breeding area, with help from 11 Marine and Navy volunteers. Civilian and Air Force volunteers assisted AGFD monitors by hanging 2.5 miles (4.0 km) of shade cloth in the pen.

Despite a wet autumn, vegetation dwindled again in December 2005, this time due to below-average temperatures. Monitors again stepped in and placed alfalfa around the pen. A volunteer group from the refuge constructed a feeder.

The AGFD monitors, with assistance from the Service and the Marines, have found occasional damage to the fence as a result of illegal human immigration from Mexico. So far, they have repaired the fence quickly and no coyotes have seized the resulting opportunity to enter the enclosure.

Back to Mexico

In January of 2006, the AGFD went back to Mexico to assess its population and to capture new pronghorns for the Cabeza Prieta breeding pen. The teams used improved tranquilizing and capture technology to minimize stress for healthy transport to Arizona. One buck and three apparently pregnant does are alive and well from the recent Mexican capture. As in 2005, the recovery team took measures to expedite the international transport process and reduce stress to the animals.

The Future

With assistance from the nearby Marine Corps Air Station Yuma and the Kofa National Wildlife Refuge, the pronghorn recovery team is assessing the possibility of establishing a herd at Kofa. This would bring the number of Mexican and American herds to four, with two in each country.

For now, the future of Sonoran pronghorn is looking brighter. A population that likely would have disappeared over the last five years has rebounded with the help of a few dedicated individuals from AGFD, DoD, Department of Interior, and hard-working volunteers. The Marine Corps is keeping an eye on this species, and is leaving infrastructure in place to help the Sonoran pronghorn again, as needed.

by Captain Aaron Otte, U.S.M.C.