How Biologists Plan To Save Endangered Sonoran Pronghorn

Jul 29, 2015

Pronghorn once roamed North America by the millions, but human activity fragmented the species into four distinctive types, one of which makes its home in the desert Southwest.

The Sonoran pronghorn is light, fast and adapted for life in the desert, but just over a decade ago they were all but wiped out due to a severe drought. Now, efforts to help the endangered animal make a comeback are proving successful.

It’s early — just after sunrise — and Lydia Morton drives her white truck across a rugged desert road on the Kofa National Wildlife Refuge in southwestern Arizona.

A few sleek, tawny-colored animals that resemble African antelope (but are unrelated) approach her from the other side of a long black fence.

“The does are a lot lighter," Morton said. "And the bucks have these big cheek patches."

Though her internship with the U.S. Fish and Wildlife Service, Morton is part of a team tasked with caring for this animal, the Sonoran pronghorn. Wildlife managers visit this breeding pen daily.

Other interns are filling feeders with alfalfa and checking water supplies. These are simple tasks with a big payoff. After decades of human encroachment on the Sonoran pronghorns’ territory and a severe drought in 2002, there were fewer than two dozen Sonoran pronghorn in the U.S.

The Sonoran pronghorn adapted to desert life, but that doesn’t mean they are immune to drought.

Jim Atkinson is a wildlife biologist and the Sonoran pronghorn recovery coordinator with U.S. Fish and Wildlife Service. He calls the 2002 drought “a wake-up call.”

“If we continued to do as we were, with basically a hands-off approach to management, we could possibly lose the animal," Atkinson said.

If we continued to do as we were, with basically a hands-off approach to management, we could possibly lose the animal. - Jim Atkinson, U.S. Fish and Wildlife Service

Much more is now known about how to manage the animals. Representatives from Fish and Wildlife Service, Arizona Game and Fish, Border Patrol and other organizations in the U.S. and Mexico collaborated on a 320-page recovery plan outlining the history of the species and its present and future challenges.

The recovery plan describes steps to take so that Sonoran pronghorn can handle another catastrophic year like 2002, if it happens. The new document updates the previous plan published in 1998.

Now, biologists provide watering stations for the pronghorn, supplemental food and irrigation to encourage forage plant growth.

“And these are just measures to tide the animals until periods of the year when favorable conditions return," Atkinson said.

In 2014, for example, the hot, dry months before the monsoon season meant a tough year for desert creatures, including pronghorn.

“The pronghorn were using the waters pretty heavily, and they were using supplemental feed where we had it put out. And that kind of bridged a pretty tough spot for them," Atkinson said.

However, this year was much easier for the Sonoran pronghorn, Atkinson said, because the May and June rains meant the desert vegetation did not dry out as much.

Breeding programs have also helped. Back in 2003, biologists created a fenced-in area dedicated to Sonoran pronghorn at Cabeza Prieta National Wildlife Refuge, 30 miles north of the U.S.-Mexico border. Some Sonoran pronghorn were gathered in Mexico to supplement the population and allow for greater genetic diversity. The enclosed pens allow supervised breeding and protect the animals from predators.

By 2007, the recovery team began releasing healthy, young animals back into the wild. Sonoran pronghorn are now released annually, with breeding taking place at both the original Cabeza Prieta site and the Kofa pen.

The Kofa Sonoran pronghorn breeding pen was built in 2011 to help re-establish the population north of Interstate 8, one of the modern man-made hurdles the Sonoran pronghorn encounter. Cars traveling on roads can collide with the animals or separate does from fawns. The animals can also get stressed by the traffic and then move to areas where food or habitat is less than ideal.

Both pens produce about 30 to 40 animals for release each year, nearly double the number of animals in the entire U.S. population just 13 years ago. Now, there are about 250 free-roaming Sonoran pronghorn. Atkinson said a strong population base will help the Sonoran pronghorn endure future drought and other threats.

In the fall, the recovery team will begin establishing a third population in Arizona on the Barry M. Goldwater range, east of Highway 85. The team hopes their efforts will lead to the removal of the Sonoran pronghorn from the endangered list by 2035.

The Fish and Wildlife Service is seeking public comment on the draft recovery plan for the Sonoran Pronghorn until Aug. 3. The recovery plan is expected to be finalized by next year.