Institute of the Environment 2017

Studying the Shy Sonoran Pronghorn

Monday, February 23, 2015

The endangered Sonoran pronghorn once ranged widely in Arizona, California, and Sonora, Mexico. Now, according to the U.S. Fish and Wildlife Service (USFWS), only about 160 free-ranging animals live in the U.S., with an additional 434 living in Mexico.

David Christianson, an assistant professor in the School of Natural Resources and the Environment, wants to know why their numbers are low. With funding from the USFWS, Christianson is studying the impacts of humans on the spry tan and white ungulates.

Hit hard by drought, most of the U.S. Sonoran pronghorn live relatively close to the U.S.-Mexico border in Organ Pipe National Park, Cabeza Prieta National Wildlife Refuge, and the Barry M. Goldwater Air Force Range. The fastest mammal in North America, pronghorn are easily spooked by cars, airplanes, and people.

“The hypothesis from the Fish and Wildlife Service is that border activity is part of the reason that pronghorn numbers have declined, which has prompted attempts at recovery using captive breeding,” says Christianson, who joined the UA as part of a campus-wide environmental hiring initiative coordinated by IE.

Because observing the elusive animals can be difficult, Christianson and his graduate students spend long hours in the field and also rely on data from motion-sensing cameras they’ve set up near existing water and feeding troughs. “We can test if the frequency of use by pronghorn is affected by the frequency of use by humans,” he says. “From what we see on cameras, most human activity is associated with border traffic, as well as from personnel from the various federal agencies.”

While it’s likely that humans have some impact on the pronghorn, Christianson says it’s too early in his study to gauge the extent. “The question is whether or not that effect is significant at all to the survival and reproduction of the species and, if so, what is the magnitude of that effect,” he says.  

Understanding that effect, Christianson says, will help land managers make better decisions aimed at conserving the endangered pronghorn.

Report from the Field

By Stephanie Doerries, 2014 Carson Scholar and PhD student, School of Natural Resources and the Environment

A typical field day starts one to three hours before sunrise. Our goals are to locate Sonoran pronghorn from an observation point, conduct a behavioral observation, and collect fecal samples while avoiding disturbance to pronghorn. We often rely on radio-telemetry to help us locate animals. Hopefully, we time our hike to an appropriate observation point so that we are visually scanning for pronghorn by sunrise. 

Once we locate a group of pronghorn, we record key behaviors such as grazing, browsing, grooming, fighting, and drinking, as well as any interactions with other species, including humans. Within a few days, we also collect one scat sample for each individual observed. On our way back to the field house, we usually stop at one or more of our 67 motion-sensing cameras to conduct routine maintenance and collect images for classification.

My favorite field days are when I find a group of unmarked pronghorn with fawns. One morning, I observed a fawn come running out from behind some vegetation pursued by a coyote. Two does cut the coyote off and chased it more than 500 meters away from the group. Because fawn recruitment is the most important variable impacting Sonoran pronghorn population growth, confirmed fawn survival (for an hour, at least) is encouraging for recovery.