In Big Bend, a border wall could divert bears, bighorn sheep from a comeback trail

BIG BEND NATIONAL PARK, Texas — Some people call it the Great Wall of Mexico, though no one labored to build it.

A wall of mountains — two nearly overlapping walls, really — hugs the Mexican side of the Rio Grande, leaving an arduous crossing for even the hardiest of would-be migrants through the Big Bend country.

Rangers in the U.S. national park and an adjacent Texas state park say the only crossers who appear up to the challenge are the four-footed kind who need no papers.

Burros. Bears. Bighorns.

The latter two — black bears and desert bighorns — are Texas natives that were wiped out but have returned to a small slice of their former Lone Star habitats.

SEE ALSO: Back from the brink, the Sonoran pronghorn now roam an increasingly political landscape

The bighorns have survived with considerable help from the state, from volunteers, and from donor populations in Arizona and other southwestern states.

The bears wandered north across the river on their own in the late 1980s, and have since delighted visitors with their summer ramblings for piñon nuts and acorns in the park’s wooded Chisos Mountains.

“Big Bend has simply been more whole,” said Raymond Skiles, a National Park Service biologist.

Uncertainty about a new border wall — the artificial kind — makes him wonder how whole the park will remain. Both the bears and the bighorns are isolated from other U.S. populations and depend on genetic interchange with animals across the river in Mexico.

RELATED: How a border wall could drive the jaguar extinct in America

The bears fluctuate in numbers between about one dozen and three dozen, depending on drought or other conditions. Their freedom to mingle with the source population 25 miles south in Mexico’s Sierra del Carmen keeps the population healthy.

“We feel like the future of these animals should be a transboundary population,” Skiles said.

Mountains deter people, not wildlife

In places in and around Big Bend, it’s hard to picture a border wall. At Santa Elena Canyon, the lazy Rio Grande slices through rock, creating a cliff that might meet the definition of what President Donald Trump means when he sometimes says mountains and rivers preclude the need for walling off the entire 2,000-mile border.

Just downstream, though, American tourists wade the river, sometimes ignoring the warning signs and reaching the south bank so they can say they touched Mexico. Farther down still, a sloping flat between the Chisos and the river marks the bears’ transboundary route.

READ MORE: Ocelots try to survive in a world that barely knows they exist

It would be possible to build a barrier across those flats, or perhaps to build one on the desert north of the park. But Skiles sees no point. In 40 years of living here, he said, he has never seen a migrant or smuggler pass through illegally.

That could be because the crossing would require humping across dozens of miles of mountainous Mexican territory without any paved roads. Upstream of the Sierra del Carmen, the Sierra Ponce run east and west for more than a hundred miles, creating a towering scarp on the south side of Big Bend Ranch, a state park near the national park.

These are the mountains state park ranger-archaeologist Tim Gibbs calls the “Great Wall.” They deter people, but not hooved animals. The park’s bighorns linger in the mountains on either side.

“The Rio Grande is just a border for humans,” he said. “But the animals don’t know that.”

'We owe it to the species'

Plano resident Bethany Ross floated with her family last year past lupines and yuccas and through mountain shadows in the state park. After coming off the river, she looked up at the cliffs and said she couldn’t imagine a border wall there.

“It seems like they’d be doing engineering feats all along,” she said. “I don’t think they could do it on the cheap.”

Farther upstream in West Texas, a wall becomes easier to envision. So does an illegal crossing in the rolling hills and mesas, as the border snakes closer toward El Paso.

Out there, on an arid knob in the Van Horn Mountains last spring, dozens of volunteers joined state wildlife officials to build a gravity-fed watering trough with two 2,500-gallon tanks and corrugated metal sheets to catch and funnel rain into them.

SEE ALSO: Balancing border security with conservation is not easy

The idea is to water the transplanted sheep in these private hills so they don’t have to descend from protected rock outcrops and become vulnerable to mountain lions. Surrounding land uses also dried some of the area’s natural springs, which would have supported native sheep herds before they disappeared from Texas in the last century.

“We owe it to the species,” said Froylan Hernandez, desert bighorn restoration director for Texas. “They were here at one time and it’s because of man that they were no longer here.

“It was a void in the niche.”

The Texas Bighorn Society has put more than $2 million into restoring wild sheep, mostly on private ranch lands with lots of volunteer hours.

“Sheep are just an exciting species,” society president Jim Payne explained. “There are a whole lot of Texans who don’t even know there (once) was sheep in Texas.”

Past president Kathy Boone has hunted other bighorn species in Canada and wants to bring that wilderness experience home. Hunting the sure-footed creatures is physically exhausting but puts a hunter in touch with nature, she said.

SPECIAL REPORT | THE WALL: 2,000-mile journey in shadow of border wall

“It’s pristine. It’s addictive,” she said. “It’s wild country.”

Payne said he wants future Texans to see their native wildlife, whether they hunt or not. He said he wonders how a border wall would affect the effort.

Wildlife migration the best hope

From the hilltop where volunteers welded and bolted the watering station in place, yellow ridges studded with prickly pear and ocotillos extended toward the river and Mexico.

“The Rio Grande is a barrier on the map,” Payne said, but only on the map. “Without a doubt, sheep cross. They can swim the river and they do.”

In fact, that international migration is the best hope for isolated Texas sheep to maintain connections to other populations. To the north, their mountain range peters out into New Mexico and Texas Panhandle prairies.

Elsewhere in the Southwest, a Mexican connection is less crucial. In Arizona, sheep populations likely would remain comparatively robust with the connections they have internally or with neighboring states.

READ MORE: Building a different kind of wall to revive a dying landscape

Parts of Arizona’s sheep range, such as the Tinajas Altas Mountains on the Barry M. Goldwater Air Force Range, are rugged border crossings.

"They cannot build a wall over the Tinajas Altas mountain range,” said John Hervert, a biologist at the Arizona Game and Fish Department. “I mean, it's a wall in itself.”

If the government did manage to erect a wall, though, he said it could block bighorn migrations without having severe effects on the Arizona herd.

In Texas, though, genetic exchange will become important as the herds grow, Texas biologist Hernandez said.

“We look at it from a landscape level,” he said, “not just a Texas issue or a United States issue.”

Republic reporter Alex Devoid contributed to this report.

Environmental coverage on azcentral.com and in the Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow the azcentral and Arizona Republic environmental reporting team at OurGrandAZ on Facebook, Twitter and Instagram.