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King of the Mountains: Desert Bighorn Sheep in West Texas

photograph courtesy of Borderlands Research Institute

The reintroduction of desert bighorn sheep into West Texas is one of the great wildlife success stories in the state, and in the country.

Bighorn used to roam in Texas, but by 1960, they were gone. Now, bighorn are found in mountain ranges from the Rio Grande to the northern Trans-Pecos, and the herd is more than 1,500 strong. As bighorns return, scientists are learning more about this majestic creature.

Before 1880, bighorn roamed in 15 mountain ranges in West Texas, and scientists estimate the population at 2,500 or more.

In 1987, Texas Parks and Wildlife reintroduced bighorn at Elephant Mountain Wildlife Management Area, south of Alpine. The population flourished. Working with private landowners, the agency has transported sheep to other ranges.

Bighorn populations are now established in Black Gap Wildlife Management Area, in the Bofecillos Mountains in Big Bend Ranch State Peark, in the Van Horn Mountains, at Nine Point Mesa and, most recently, in the Sierra Vieja, south of Valentine. The Sierra Diablo Mountains, and the adjacent Beach and Baylor ranges, north of Van Horn, sustain 800 animals.

Building on its success, Texas Parks and Wildlife is working aggressively to return bighorns to as much of their historic range as possible.

Dr. Louis Harveson is the director of the Borderlands Research Institute in Alpine, which is assisting in the bighorn restoration effort. Harveson said that to see these animals, in the Texas environments to which they're so finely adapted, is a powerful experience.

“The first release that I went to – it was a religious experience,” Harveson said. “It was absolutely impressive to see them get up the side of the mountain. They stopped for a second – and [it] was just jaw-dropping. It's an impressive sight, and just an honor to be part of that program.”

The mountains of Far West Texas are forbidding terrain. But desert bighorn are drawn to the region's jagged ridges and steep mountain slopes.

Bighorn's hooves are uniquely elastic and concave. In rugged terrain, they're peerless in their agility. Mountainsides become their sanctuary.

“They need cover,” Harveson said, “and cover doesn't come in the form of brush, it comes in the form of topography. They're almost always running uphill as they're spooked. They need ridges – a cascade, stair-step type of mountain range. Sixty percent slope or better – that's pretty steep stuff. They have an uncanny ability to navigate through that, and elude their predators.”

The BRI has placed radio collars on hundreds of bighorns. The collars provide their locations on an almost hourly basis. With this data, the institute has developed a picture of how bighorns use habitat.

The sheep stick to higher elevations, and rarely venture far from the steepest slopes. The BRI has found that ewes – or female sheep – generally stay within 250 yards of steep slopes. Rams – male sheep – roam a bit more, but typically stay within 300 yards of escape cover.

For most of the year, ewes and rams live separately. Rams may linger together in groups as large as 15 or 20, while ewes gather in areas of prime forage.

Bighorns are lords of the mountain, and they're picky eaters. The BRI has found that grass comprises only about 10 percent of the bighorn diet. Sheep avoid common plants like creosote and mesquite. Chamiso, goosefoot and ephedra are favorites. The lambs rely especially on seasonal forbs that spring up after summer rains.

The bighorn rut typically begins in late September or October. The rams compete – in dramatic fashion. They charge head-first into one another, from distances of 20 feet or more. The collisions continue until one ram retreats.

“Early on it's practice, they're playing with their buddies,” Harveson said. “But then it gets pretty serious as the females come into estrus, and it's usually the dominant males, those that are higher up the pecking order, typically with larger horns – they're the ones that do the majority of the breeding.”

Coyotes, bobcats and eagles feed on bighorn lambs. But a mature bighorn faces one main predator – the mountain lion. In one relocation project, the BRI placed radio collars on 78 sheep in the Bofecillos Mountains. At least seven fell prey to lions.

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.