Defenders Magazine

Looking for Help

Can government biologists keep the Sonoran pronghorn from slipping into oblivion?

By Peter Friederici

© U.S. Fish and Wildlife Service

John Hervert strolls along a deflated blue irrigation hose that winds among the dry rocks in the Cabeza Prieta National Wildlife Refuge just north of the Mexican border. “We’re planning to put the tomatoes in over here," he jokes, indicating where the hose ends in a desert wash lined with lush trees, shrubs and vines.

Hervert is a biologist with the Arizona Game and Fish Department, not a gardener, but this summer he has been raising a crop: a new generation of the endangered Sonoran pronghorn.

The Sonoran is one of the rarest of five subspecies of the American pronghorn, a fleet-footed animal that once roamed western North America by the millions. Now confined to the dry heart of the Sonoran Desert on both sides of the U.S.-Mexico border, the Sonoran pronghorn has declined precipitously in recent years. In 1994, an estimated 250 of these animals inhabited southern Arizona; in 2001, some 138 did; by the end of 2002, that number had dropped to only about 21. Several hundred still remain in Mexico, but one of the two populations there has also declined.

In an attempt to rescue the animals, Hervert and his government colleagues are trying out two strategies. One is Hervert’s gardening project (technically known as “forage enhancement"), which entails watering the desert so that the pronghorn will have more food to eat. The other involves capturing and breeding the creatures in safe, controlled conditions. If these emergency measures fail, the prognosis is grim. Says John Morgart, who coordinates the pronghorn recovery effort for the U.S. Fish and Wildlife Service, “this is a species truly on the brink."

Often called antelopes because of their superficial resemblance to denizens of Africa’s savannas, pronghorn are actually native to North America and unrelated to their Old World counterparts. But the tawny, goat-sized pronghorn of America do share one important characteristic with Africa’s antelope: blazing speed. They can race across the landscape as fast as 60 miles per hour, outrunning any predator. Before the arrival of European settlers, an estimated 40 million pronghorn made their homes on the American range—but decades of hunting and habitat destruction cut their numbers by perhaps 99 percent.

The Sonoran pronghorn were never as numerous as their relatives, and their numbers continued to decline even as their kin elsewhere in the West began to recover in the 20th century. The few Sonorans left in the United States today are confined almost exclusively to a dry patchwork of federal lands spanning about 5,000 square miles in southern Arizona.

For all its wild appearance, this habitat is hardly undisturbed, and the pronghorn on it have faced many challenges. The international border fence and a highway keep groups of the creatures separated from each other. Cattle ranching consumes scarce forage and dissects habitat with additional fences. Bombing and tank maneuvers take place on the Goldwater Air Force range. Drug smugglers and illegal immigrants cross the border, and federal agents pursue them in sport-utility vehicles. New roads are carved into the fragile desert soil, and invasive plant species spread along them. Recreational use disturbs vegetation and the animals themselves. The federal government is responsible for regulating these activities so they don’t harm pronghorn, but has failed to do so adequately, conservationists say.

Perhaps most troubling, pronghorn can no longer reach the few rivers that carve through the desert, which once served as green refuges during the driest months. Fences, highways and crops keep them from the Gila, Colorado and Sonoita rivers—which themselves have been altered, and in some places dried up, by modern civilization. As a result, Sonoran pronghorn are less buffered from the natural boom-and-bust cycles of the desert than they once were.

“In the desert, things swing back and forth rapidly between all the food in the world and no food at all, depending on the time since the last rain," Hervert says as he drives toward the irrigation hoses on an overcast August day. He passes extensive tracts where all the bursage plants—common desert shrubs, and good pronghorn food—have died in last year’s drought, their clustered stems stark and leafless. In some places even the hardy creosote bushes are withered and dead. Yet in another area hit by a recent heavy rain, the ironwood trees and the spiny ocotillos are flush with new green leaves.

The unpredictable conditions play havoc with the pronghorn, Hervert points out. Adults can tolerate drought in early summer by eating the moist but nutrient-poor fruits of chain-fruit cholla cactus. But fawns need higher-quality food. As a result, he says, “large numbers of fawns survive the first two or three weeks, when they’re most vulnerable to predators, but then they don’t make it later if the summer rains don’t arrive. If we just leave it to chance, we can’t bank on these fawns making it to reproductive age."

To get fawns through the hard times, a collaborative team of state and federal officials began the project to enhance the food supply in the desert by adding water. They drilled a well and connected it with plastic pipe to an array of six irrigation hoses that run into small washes, feed sprinklers or fill a pool from which pronghorn can drink. All told, about three acres of desert were irrigated weekly this summer, at 60,000 gallons a pop, until the rains came.

The effects were immediate: ocotillos and ironwoods greened up, shrubs and vines bloomed in the washes. Surveys showed that at least ten pronghorn used the area. “It’s a toehold," Hervert says. By next summer, biologists plan to have five such irrigation sites in operation on the refuge and the adjacent Air Force range.

This fall construction will also begin on a nearby captive-breeding facility—a pen a square mile in extent, with a fence designed to keep pronghorn in and predators out. A few acres inside the pen will also be watered. The enclosure will be “small enough for us to control the animals, but large enough that they can move around freely and not get habituated to people, and escape from any predator that might get in," says Morgart. This winter biologists plan to capture five Sonoran pronghorn—four females and a male—from the more abundant Mexican population. The females should all be pregnant with twins. Given a reliable food source, freedom from disturbance by people and a lack of predators, the captive population could swell quickly.

“In two or three years we could have as many as 80 or 90 individuals," says Hervert, “and then we’ll have to be prepared to do something with them." Some could be released directly from the pen. Some could be shipped back to Mexico to augment the population there. And some could be used to start a new group in some other part of Arizona’s Sonoran Desert.

No one is sure how long the emergency measures will be needed, or whether the Sonoran pronghorn will pull through. At best, says Noah Matson, director of public lands for Defenders of Wildlife, these measures will buy government agencies time to implement a long-term recovery effort for the species. “We are in the emergency room now, and once the surgery is over, we need to get serious about rehabilitation," Matson says. “The agencies need to begin to make some difficult choices. If they continue the status quo, this species will either be on life support forever, or worse, will disappear from the United States."

Freelance journalist Peter Friederici lives in Flagstaff, Arizona.