Bridging Barriers: Sonoran Researchers Seek Wildlife-Friendly Highway Crossings

By Kendal Blust
Published: Tuesday, October 1, 2019 - 5:05am
Updated: Friday, April 24, 2020 - 1:59pm

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Researchers stand on the edge of Mexico’s Highway 2 as semi-trucks zoom past. They’re just outside the little town of Imuris, Sonora. Here ocotillos, organ pipe cactus and mesquites, bright green from the summer rains, line the road as it winds through the Sierra Azul mountains.

Cocóspera Valley
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Rolling hills in the Sierra Azul mountains near the town of Imurís, Sonora.

When the road clears, the researchers sprint across the cracked two-lane highway about 35 miles south of the Arizona. border. Then scramble down into a drainage beneath the roadway to check a camera trap tucked into the narrow tunnel.

“We want to know which species are using the drainages, and which drainages see the most activity,” says Cecilia Aguilar, a road ecologist with the Seattle-based nonprofit Wildlands Network.

Aguilar is working on a years-long project monitoring roadkill and camera traps along the highway from Imurís to Sonora’s eastern border with the state of Chihuahua to understand where, how and which animals cross the highway — and if they make it.

Every year, more than 2,000 animals, from beavers and skunks, to black bears and coyotes are hit by cars on this section of the highway. But many animals will take passages under, around or over the road if they're available. So Wildlands Network is advocating for wildlife friendly highway crossings to be added to sections of Highway 2 that are under expansion.

“The highway is one of the main barriers — the other is the border wall,” Aguilar says.

Crossing the highway
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Cecilia Aguilar checks for cars as researchers prepare to cross the highway on July 28, 2019, during a study of wildlife crossings in Sonora, Mexico.

They bisect an important wildlife corridor through the Sky Islands in Arizona and Sonora where endangered species like jaguars and ocelots are known crisscross the border.

“But it won’t happen if there is a border wall in between, if there is a big highway in between,” says Juan Carlos Bravo, director of Western and Mexico Programs for Wildlands Network.

“People in Arizona have been increasingly excited about the notion of jaguars,” he says.

But re-establishing jaguar and ocelot populations in the United States requires connectivity between Arizona and Sonora. And Sonora’s few black bears rely on a larger population in Arizona for survival.

Wildlands and other organizations have put a lot of effort into studying and mitigating damage created by border fence construction. But Bravo says Wildlands also wants to mitigate this other barrier — the highway.

“The idea is to focus mostly on underpasses,” he says, because they are already a necessary part of road infrastructure.

researchers inspect a tunnel
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Researchers in 2019 inspect a tunnel under Mexico's Highway 2 that animals use to cross the road.

Rather than building new infrastructure, existing drainages just need to be reconfigured and fencing put up along the highway to direct animals to safe crossings.

But protecting wildlife in this region will also mean constructing some overpasses for larger animals less likely to cross under the road, Bravo says.

“The number of black bears in the region I think merit that investment, the occasional jaguar that passes through,” he says. “And it must be noted that most of the jaguars that have reached Arizona have actually crossed through this corridor.”

Wildlands is working with transportation authorities to push for wildlife crossings as part of planned highway expansions.

Cecilia Aguilar
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Cecilia Aguilar tries to identify animal markings in a wash under Mexico's Highway 2.

He’s also pushing for policy change.

Legislation requiring wildlife crossings on Mexican highways has been introduced at both the state and federal levels. So far only the state of Chihuahua has passed a law.

But Bravo thinks shy of a law, changing the perspective of road engineers who plan highways will also help provide safer infrastructure for wildlife. That’s why Wildlands has been holding road ecology conferences and talking to engineering students about the work researchers are doing on wildlife crossings.

“The young engineers were just so fired up by this idea. It was just fantastic, they were like, ‘How do we make this mandatory?’ ‘Are there any laws that make this mandatory?’” Bravo says.

He thinks that’s a hopeful sign.

Looking To The Future

Back on the highway, researchers arrive at the El Aribabi conservation ranch to check camera traps just off the road in Sonora’s Cocóspera valley.

Luis Ernesto Robles and his family are in the yard enjoying a cloudy afternoon when the researchers pull up. They’ve owned the ranch for generations.

camera trap
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Researchers change the batteries on a camera trap that monitors how animals cross Mexico's Highway 2 in northern Sonora.

“We know highways are necessary,” Robles says. “The problem is the way they’re building them.”

He says roadways cause a lot of damage in this region.

“And the expansion, it’s going to destroy everything. I’m convinced of that,” he says.

But researcher Ricardo Félix says new road projects can also be an opportunity for positive change.

“We see this as an opportunity,” he says.

Money and resources budgeted for the highway expansion open up the possibility of constructing wildlife crossings, too.

He’s optimistic.

“When I  the presence of all these different animals on the cameras, it's always exciting, even the most common animals," he said. "It's just exciting to know that they're there and they're using the drainages."

Every shot of coyotes, deer or bobcats crossing under the highway gives him hope, he says, that with safe passages, wildlife will continue to thrive in this region.

Cecilia Aguilar
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Cecilia Aguilar looks out the car window on the way to inspect a camera trap near Mexico's Highway 2 just outside the town of Imurís, Sonora on July 27, 2019.
Ricardo Félix
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Ricardo Félix drives a team of researchers to camera traps hidden along Mexico's Highway 2 to study animals crossing in drainages under the road on July 27, 2019.
Camera trap
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Ricardo Félix checks a camera trap on July 27, 2019.
camera trap
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Researchers check a camera trap near Mexico's Highway 2 on July 27, 2019.
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Researchers take cover from the rain before heading out to check camera traps that monitor animals crossing a major highway in northern Sonora.
cars on the highway
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Cars pass under a huge painting of the Virgin Mary on a cliff face on Mexico's Highway 2.
field notes
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Ricardo Félix takes notes while checking camera traps on Mexico's Highway 2.
camera trap
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Ricardo Félix adjusts a camera trap in a drainage under Mexico's Highway 2 near Imurís, Sonora on July 28, 2019.
researchers hiking to cameras
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Researchers hike down from the highway to check camera traps hidden in tunnels under the road.
Highway 2
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Mexico's Highway 2 winds through the Sierra Azul mountains outside the town of Imurís, Sonora.
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Researchers pause to rest and jot down some data after checking a camera trap near the highway on July 28, 2019.
paw print
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Cecilia Aguilar uses a ruler to determine what kind of animal left paw prints in a wash under Mexico's Highway 2.
Cecilia Aguilar and Ricardo Félix
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Cecilia Aguilar and Ricardo Félix discuss their findings after checking camera traps just on Highway 2 on July 28, 2019.
Cecilia Aguilar and Ricardo Félix
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Cecilia Aguilar and Ricardo Félix look over their notes after checking camera trap on Mexico's Highway 2 on July 28, 2019.
Camera trap
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A camera trap attached to a post near Mexico's Highway 2 in northern Sonora snaps photos of animals that use a drainage under the road to cross the highway.