Wild Sheep Showdown in West Texas: As Aoudad Boom, Scientists See a Threat to Native Wildlife
photograph courtesy Borderlands Research Institute. Bighorn sheep vanished from West Texas due to overhunting and disease. Their restoration here is one of the state’s marquee conservation stories.
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.
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Desert bighorn sheep
Characteristics
Desert bighorn sheep are stocky, heavy-bodied sheep, similar in size to mule deer. Weights of mature rams range from 115 to 280 pounds (52 to 127 kg), while ewes are somewhat smaller. Due to their unique concave elastic hooves, bighorn are able to climb the steep, rocky terrain of the desert mountains with speed and agility. They rely on their keen eyesight to detect potential predators, such as mountain lions, coyotes, and bobcats, and they use their climbing ability to escape.
Both sexes develop horns soon after birth, with horn growth continuing more or less throughout life. Older rams have curling horns measuring over three feet long with more than one foot of circumference at the base. The ewes’ horns are much smaller and lighter and do not tend to curl. After eight years of growth, the horns of an adult ram may weigh more than 30 pounds. Annual growth rings indicate the animal’s age. The rams may rub their own horns to improve their field of view. Both rams and ewes use their horns as tools to break open cactus, which they consume, and for fighting.
Desert bighorn sheep typically live for 10–20 years. The typical diet of a desert bighorn sheep is mainly grasses.When grasses are unavailable, they turn to other food sources, such as sedges, forbs, or cacti.
Desert adaptations
The desert bighorn has become well adapted to living in the desert heat and cold and, unlike most mammals, their body temperature can safely fluctuate several degrees. During the heat of the day, they often rest in the shade of trees and caves.
Southern desert bighorn sheep are adapted to a desert mountain environment with little or no permanent water. Some may go without visiting water for weeks or months, sustaining their body moisture from food and from rainwater collected in temporary rock pools. They may have the ability to lose up to 30% of their body weight and still survive. After drinking water, they quickly recover from their dehydrated condition. Wildlife ecologists are just beginning to study the importance of this adaptive strategy, which has allowed small bands of desert bighorns to survive in areas too dry for many of their predators.
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Aoudad Sheep in Palo Duro Canyon
A herd of fascinating non-native North African barbary sheep roam the canyon, but they are seldom seen in the state park.
The sheep (who, per their DNA, are really more closely related to wild goats) are well-adapted to arid, rugged landscapes like Palo Duro Canyon. The story is that they were introduced to Texas in the 1940’s by ex-GI’s who had served in North Africa in WWII and realized the aoudad’s potential as a game animal in our state. Like most introductions of non-native species, the aoudad sheep did not calmly cooperate and follow the plan. They escaped, and are now more populous in Texas than in their native areas of Africa.
The introduction of the Palo Duro Canyon herd was deliberate. They were first placed in our part of Texas in 1957, when 31 were released southwest of Claude in Armstrong County (the eastern part of the canyon area). Thirteen more were released near Quitaque (the southern end of the canyon area of West Texas, where Caprock Canyons State Park is located). I don’t know the exact count of sheep in Palo Duro Canyon now, but they are still very hard to spot and harder to photograph in the actual state park.
The secret to seeing and photographing these sheep is to understand that they have been fed deer corn by people in the area for years. The most famous of these sheep people was the late Fred Beatty. His story was told on Texas Country Reporter in 2014. https://youtu.be/L0x0o43lrDY. Other neighbors continue to feed them, just not as consistently as Fred did. So if you are looking for aoudad sheep, don’t look in the state park. Make friends with the locals and then look for aoudads on the ranches and neighborhoods nearby.
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