NATURE NOTES:
Wild Sheep Showdown in West Texas: As Aoudad Boom, Scientists See a Threat to Native Wildlife

photograph courtesy Borderlands Research Institute. Aoudad are native to North Africa, and compared to their ancient home, the Chihuahuan Desert is easy living. The non-native sheep are thriving in the West Texas mountains, and are a major draw for hunters here.

The return of desert bighorn sheep to West Texas is one of the state’s marquee conservation stories. These majestic animals had been eradicated here by the 1960s. Some 1,500 now roam the Texas mountains – a testament to the sustained efforts of countless wildlife managers and enthusiasts.

But there’s another wild sheep species flourishing here. Native to North Africa, aoudad, or Barbary sheep, have been present for decades. But their numbers have skyrocketed in recent years. They’re now established not only on the Trans-Pecos landscape, but in its culture and economy. Aoudad hunting is a major draw.

Aoudad could also have serious impacts on other animals here – desert bighorn, to be sure, but also mule deer, and even livestock. At Sul Ross State University’s Borderlands Research Institute, scientists are studying those impacts, and how they can be managed. And the public will have a unique opportunity to learn about this critical conservation dilemma, at the Trans-Pecos Wildlife Conference, August 4th in Alpine.

Justin French joined the BRI staff in 2020. He’s a Hill Country native with a master’s from Sul Ross and a PhD from Texas A&M.

“I’m currently the big game specialist for BRI,” he said. “All of the research projects involving anything with hooves and antlers and horns comes through me.”

At the conference, French will talk aoudad – what scientists have learned thus far, and about plans for new research.

Between 2019 and 2021, Texas Parks & Wildlife and the BRI partnered to conduct a study known as “BAM one-point-O” – for “bighorn, aoudad and mule deer.” In the Van Horn Mountains, the collaborating scientists placed GPS collars on 40 individuals of each species. The goal was to assess the impacts of aoudad on the other two “ungulates,” or hoofed mammals, in two primary areas: competition, and disease.

If you’ve had the fortune to see desert bighorns in the wild, you’ve likely witnessed their “superpower.” Bighorn can bound effortlessly up the steepest, rockiest terrain. It’s key to their survival. These sheep need exposed slopes and cliffs where they can detect and evade their main predator: the mountain lion.

Aoudad favor the same terrain. And they have an advantage, French said.

“Everything about them is tougher than most of the natives,” he said. “They’re very, very strong. They’re very, very aggressive. They’re probably a pretty tough prey item, even for a lion.”

The Chihuahuan Desert is rugged. But compared to the aoudads’ ancestral home, at the edge of the Sahara, it’s easy living. 

Aoudad are bigger and stronger than bighorn. And they’re fertile. They reach sexual maturity sooner, and typically produce two lamb “crops” – often with twins – each year, compared to one for bighorns. Aoudad are “the feral hogs of the mountains,” French said, and are well-equipped to dominate and exclude bighorn from the prime habitat.

In BAM 1.0, researcher Daniel Wilcox used GPS data to explore this dynamic. Aoudad were indeed seen to be dominating the prime terrain. But the interactions were far more complex than expected.

Aoudad and bighorn herds sometimes mingled together. Aoudad rams were seen to run off bighorn rams, commandeering bighorn ewes. The research raised as many questions as it answered, French said.

“It means it’s tough to predict what’s going to happen,” he said. “If they’re competing with aoudad, the level of aggression in those interactions, ‘antagonism’ is what we would call, probably escalates the more competition there is. But there’s no real evidence to document that. If anything, what we’ve seen is it’s tough to anticipate.”

Another researcher took up a messier project in BAM 1.0. Olivia Gray collected fresh fecal samples from the three species – to assess their diets. 

Aoudad and bighorns do indeed have shared tastes. Acacias are favored by both. And both dine on tasajillo cacti, undaunted by its dense spines. In a land of scarce resources, the overlap in diets could be bad news for bighorn.

Overhunting was one cause of the bighorn’s initial disappearance here. But another factor was disease – specifically pneumonia, transmitted by domestic sheep. Today, surging aoudad populations could pose a comparable threat.

BRI researchers recently documented pneumonia outbreaks in the Van Horns and Black Gap Wildlife Management Area. The outbreaks killed half the bighorn populations in both areas.

Those outbreaks can’t be definitively blamed on aoudad. But the pneumonia bacteria is present in aoudad here. And while fatality rates for bighorns are high, aoudad can survive the illness.

French and his colleagues are gearing up for more research – BAM 2.0. With private donations, and matching federal funds, the researchers again plan to “collar and foller” the three species. This time they’ll monitor the animals for four years, in two West Texas mountain ranges – the Chinatis and the Quitmans. 

Midway through the study, they’ll kill a substantial number of aoudad – and monitor the impacts. Bighorn ranges could become smaller, and more stable, when competition for the best territory is reduced. 

The goal is to identify the threshold where aoudad populations don’t threaten bighorn survival.

“No matter how anybody feels about aoudad,” French said, “and those opinions vary a lot, the one thing everybody agrees on is they’re not going away completely. They’re on the landscape. How many can we handle? What’s a management target we might be able to achieve?”

Toughness and fecundity are part of the aoudad’s success. But the non-native sheep also continue to be introduced here. It’s understandable. A West Texas aoudad hunt can be the hunt of a lifetime. And it might cost $5,000, compared to $100,000 for a bighorn hunt – meaning it’s within reach for more people.  

But the threat isn’t just to bighorn. As populations grow, aoudad are moving into foothills, where they compete with mule deer, and are even grazing livestock pastures.

Preliminary findings suggest that 80 percent of aoudad ewes would need to be removed each year, just to keep populations steady. It’s a daunting figure, and it’s unclear how it could be achieved.

But French said more science is needed, to understand how these non-native – if impressive – creatures are impacting Trans-Pecos ecosystems.

“The way I like to explain it is, just looking under the hood isn’t going to fix the truck,” he said. “If you’ve got a problem, you’ve got to dig into that thing. So we’re tearing the engine apart, so to speak, of how aoudad interact with these native ungulates. That’s how we’re going to figure out how to fix the problem.”

The Trans-Pecos Wildlife Conference will be held Aug. 4 and 5, at the Morgan University Center on the Sul Ross campus. Visit bri.sulross.edu to learn more, or to register.