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Don't Fence Me In: Pronghorn in West Texas

pronghorngrant
photograph courtesy Borderlands Research Institute

Pronghorn are a species unique to North America. Their bodies and instincts are exquisitely adapted to life on the West Texas prairies. They're swifter than the wind, and tawny as the grassland itself.

But those grasslands are changing. And pronghorn are facing new threats and pressures.

Pronghorn are the fastest land animal in North America. They can run 60 miles an hour. Speed is in a very real sense what they are.

Dr. Ryan O'Shaughnessy studies pronghorn at the Borderlands Research Institute in Alpine. Every part of a pronghorn's body contributes to its speed, he says.

“Enlarged trachea, enlarged lungs, enlarged kidneys, enlarged nasal passages – which really allow them to get all that good oxygen into the lungs and motor across the landscape. Because of the way their muscles have adapted, they need to run to keep themselves healthy.”

A four-day-old fawn can outrun a horse, and no predator can compete in speed with a mature pronghorn. However, that wasn't always the case.

Before the Ice Age extinctions, about 12,000 years ago, three pronghorn species inhabited western North America – and the creatures evolved alongside an even faster predator: the American cheetah.

Let northerners follow the sun. In the West, where sunshine is plentiful, following the rain is a more adaptive skill. Through a mechanism unknown to science, pronghorn can track rainfall across vast landscapes. Days after an isolated storm soaks a patch of prairie, pronghorn will arrive, to dine on new shoots as they emerge.

“They would travel huge distances across the landscape, basically just following the rain. We don't know how it is they were able to know where and when the rainfall is falling, but they seem to know. Just like the Serengeti I guess, with the wildebeest out there. They know where the rain is, and they could track it perfectly. They would be right there – getting the best of the best.”

In Texas, pronghorn are found from the Panhandle and the Llano Estacado to the Big Bend. Historically, most of the West Texas herd has been recorded in the Trans-Pecos.

But around 2010, researchers confirmed a sharp decline in the Trans-Pecos herd. Population dropped from 17,000 in the mid-80s to fewer than 3,000 in 2011.

In response, landowners and concerned citizens formed the Trans-Pecos Pronghorn Working Group. They partnered with the BRI, and Texas Parks and Wildlife, to study the decline.

What they found, O'Shaughnessy says, was spiking predation.

Coyote and bobcat populations have surged as predator-control practices in the Trans-Pecos have changed. The BRI found that bobcats and coyotes were killing 70 percent of pronghorn fawns. The BRI has worked with landowners to reduce predator populations.

Another factor in the decline – fences. Pronghorn evolved on unbounded prairies. Unlike deer, pronghorn cannot leap a fence. Such barriers restrict pronghorns' ability to evade predators and find the forage they need. The BRI witnessed this captivity when they placed GPS collars on pronghorn to track their movements on an hourly basis.

“And when you pull them up on a map there's just a straight line. You can see these pronghorn disperse, and where there's a fence it's like a brick wall. So that really spearheaded our motivation to get out there and do some fence modifications.”

Like raising the bottom portion of a barbed-wire or net-wire fence to at least 18 inches, which allows pronghorn to crawl beneath it. Partnering with landowners, the BRI has modified hundreds of miles of fence in the Trans-Pecos.

The working group has relocated pronghorn from the Panhandle to supplement the Trans-Pecos herd, and numbers have rebounded from their 2011 low.

But climate appears to be an overarching pressure on pronghorn. Through wet years and drought, West Texas has grown steadily drier during the last 30 years. Fawns need grass for concealment, and drier conditions reduce that cover. Food sources diminish. And in drought, when jackrabbits and quail grow scarce, bobcats and coyotes increasingly prey on fawns.

And climate change is likely to intensify aridity in West Texas, further imperiling the pronghorn.

The BRI, and their landowner partners, hope they can offset these pressures – and insure that, in West Texas, the antelope continue to play.

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.