Nature Notes; In Pronghorn Restoration, Biologists Keep A Close Watch

The blue of the sky contrasts with the gold of the landscape below, as pilot Cade Woodward dips and circles his plane above the Marfa Plateau. It’s a treat for any West Texan – a bird’s-eye view of where the grasslands meet the Davis Mountains – but this is not a recreational flight.

On a spring outing, Woodward and biologist Nan Nourn are tracking pronghorn. It’s part of the effort – now five years old – to prop up a struggling pronghorn population in these Trans-Pecos grasslands.

The Trans-Pecos once had the state’s largest pronghorn herds. But by 2010, scientists had confirmed an alarming decline – the population fell from 17,000 in the mid-80s to just 2,200. Herds north of Interstate 10 – in Hudspeth and Culberson counties – were holding their own, but biologists were concerned especially about thinning herds near Marathon and Marfa.

To address the issue, a partnership was formed. It was called the Trans-Pecos Pronghorn Working Group, with landowners, Texas Parks and Wildlife and the Borderlands Research Institute in Alpine. The group conducted its first relocation in 2011, moving scores of pronghorn to the southern Trans-Pecos from the Texas Panhandle, where herds are robust.

It was a dramatic process. Pronghorn were captured with net guns fired from helicopters, and loaded in trailers for an all-night trip across the state.

The timing couldn’t have been worse – 2011 turned out to be the driest year on record. And that April, the Rock House Fire altered the landscape, burning up more than 300,000 acres in the Marfa Plateau and Davis Mountains.

Only 20 percent of the translocated animals survived. It was a disaster. But later relocations have been more successful. Close to 80 percent survived a 2013 relocation, and 70 percent survived in 2014.

Now, scientists from the Borderlands Research Institute, or BRI, have a better sense of the threats pronghorn face.

It’s true – a drying climate is a huge pressure on the animals. But biologists have identified two more immediate factors: predation, and fencing. Unlike deer, pronghorn are reluctant to jump a fence. Even though an adult pronghorn can easily outrun a coyote, it can get pinned down against a fence. And coyotes can decimate fawns.

Wildlife managers are working to reduce coyote populations. Another solution is to raise the bottom of a fence up to 18 inches, allowing pronghorn to crawl beneath. Working with landowners, the BRI has modified hundreds of miles of fence in the Trans-Pecos.

In January 2016, biologists relocated 112 pronghorn from the Panhandle to an area northwest of Marfa. Seventy of the animals were equipped with radio collars.

Nourn is pursuing a master’s degree with the BRI. In February, he tracked the pronghorn in weekly flights. He’s now flying twice a month. He said aerial monitoring is important.

“For translocation, you’re essentially releasing an animal into a new home, a new habitat, and it’s important to follow up with that,” Nourn said. “We want to know how they’re moving in their new home, to see if they’re moving around a lot – or if they’re playing nice with neighbors, if they’re getting along with new pronghorn. We’re interested in seeing those kinds of interactions. Hopefully the information we gain will let us know improvements we can make in the future, if we have more translocation efforts.”

Flying west from the Alpine airport, Nourn and Woodward scan for signals from the collars. Woodward has been a pilot for more than 15 years, and he specializes in wildlife surveys and tracking.

“Basically what we do is we’ve got two antennas, one on each wing of the aircraft,” Woodward said, “and we have a receiver on board that we store all of the animals’ frequencies on that receiver. We’ll initiate the scan, and we’ll scan through all of those frequencies. And we’ll start on an area, usually the previous known location of that animal is where we start. We’ll just fly back and forth over that area until we pick up a signal.”

Once a signal is detected, Woodward flies in close to locate the pronghorn visually. Nourn records a GPS location for the animal.

So far, the flights indicate the newcomers are adjusting well. They’ve mixed in with resident animals. The collars emit a “mortality signal” when an animal has died, and biologists examine the site to determine the cause of death. About 10 percent have been lost – mostly to coyotes. Several animals died from the stress of relocation.

From the air, it’s easy to see how the human footprint intersects with wildlife habitat. The animals’ range is essentially defined by the highways that surround them.

The restoration effort has improved. Remember that initial herd number – 2,200? Well, in spring 2015, Trans-Pecos populations had increased to more than 4,000. But it’s a long-term project – and a long way from 17,000. But specialists like Woodward and Nourn will continue to keep a watchful eye.

Nature Notes is underwritten by the Dixon Water Foundation and is produced by Marfa Public Radio in cooperation with the Sibley Nature Center in Midland, Texas. This episode was written by Andrew Stuart.

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