A High-Speed Gamble

A railroad project in the Mojave could significantly harm desert bighorn sheep. Wildlife crossings could help.

Drivers barreling along Interstate 15 in Baker, California may not realize they’re driving by what’s called the “Lonesome Triangle” — a sweeping desert landscape in the Mojave framed by I-15 to the north and I-40 to the south. Within this vast, biodiverse desert are dry lake beds, ancient cinder cones, Joshua tree forests, sand dunes, and rugged mountain ranges. The Mojave National Preserve’s wildlife is equally as diverse as the landscape. Kit foxes, mountain lions, bobcats, coyotes, desert bighorn sheep, and a variety of birds and reptiles, including the desert tortoise, are some of the wildlife found here.

While the company building the high-speed rail through the Mojave has said it will repair existing tunnels that would allow animals to pass under the train tracks, it has not included a plan for land bridges that would provide bighorn sheep a path to move freely over the railroad. Photo by Bill Sloan.

Working as a park ranger at Mojave National Preserve, I watched industrial scale solar projects and freeways destroy wildlife habitat. The latest threat to this fragile ecosystem is an $8-billion-dollar railroad project that would run along the center of I-15 through the Mojave Desert from Victorville, California to Las Vegas, Nevada. High walls and barbed wire on either side of this proposed high-speed rail would block bighorn sheep and other wildlife from crossing the tracks. Habitat loss from encroaching development, climate change, and disease are already pushing bighorn sheep to the brink. Their survival hinges on the ability to move. For them, the high-speed rail could be a matter of life or death.

I remember my first encounter with desert bighorn sheep in the spring of 2007. I drove 11 miles south of Baker, California, away from the truck stops and fast food joints dotting the congested I-15 corridor. Driving down a rutted dirt road west toward Zzyzx, a protected area of the preserve, I unrolled my window, breathed in the creosote, and scanned the expansive dry lake bed — a sea of brown framed by jagged mountain ranges. Then I saw them: four bighorn ewes, heads bent, their curved, narrow horns jutting out, as they drank from a puddle. I stopped, turned off the engine, and watched them. After about five minutes, they leapt up a nearby cliff face, rocks tumbling in their midst as they disappeared from view. That memory stays with me.

Wildlife biologist Bill Sloan also has a special connection to bighorn sheep. He has been studying bighorn at national parks throughout the Southwest for over 40 years. He divides his time between California’s Death Valley and Joshua Tree national parks in the winter and spring and Utah’s Canyonlands, Arches, and Capitol Reef national parks in the summer and fall. Sloan has participated in numerous sheep captures and monitoring projects throughout the Southwest. Wildlife corridors, he believes, are essential pathways for connectivity for bighorn sheep.

“100 years ago, there was a metapopulation of bighorn sheep — many populations that were genetically connected in the Mojave Desert,” he said. “The building of interstates 15, 40, and 10 fragmented bighorn sheep habitat. Populations became isolated.”

map of california bighornsheep

Today, there are two subspecies of desert bighorn sheep in California spread across three primary herds. A small population of sheep, known as the Sierra Nevada bighorn, live in the Eastern Sierra in the Owens Valley and in parts of Sequoia Kings Canyon and Yosemite national parks. Disease and overhunting caused their historically high numbers to plummet, which led to their federally endangered status. Additional populations are scattered in pockets throughout the West. One herd roams in the rugged Peninsular Ranges, which run south from Mount San Jacinto, California all the way to the distant border of Mexico’s Baja California. This population is also federally endangered. They’re the same species as the bighorns that live in eastern California, and parts of Arizona, Utah and Nevada. This last herd is not currently endangered, but faces mounting threats, including from the proposed railway.

While the project developer has said it will repair existing tunnels that allow animals to pass under the interstate, it has not included a plan for wildlife crossings, or land bridges, that would provide bighorn sheep a path to move freely over the railroad.

Out of the many sheep Sloan has tracked using GPS collars, he’s never observed one using an underpass. “I’ve observed kit foxes, coyotes, desert tortoises, and bobcats traveling through underpasses, but never bighorn sheep. Underpasses are dark and confining, so sheep can’t use their keen eyesight to spot predators like mountain lions. This is why overpasses or wildlife corridors need to be part of this project.”

Conservationists are pushing for three wildlife crossings to be included in the project. The corridors would help these bighorn reestablish their traditional genetic population, especially at Zzyzx. One crossing would link the southern and the northern Soda Mountains. This is a natural transportation route for bighorn sheep where they have, sometimes, been killed attempting to cross 1-15. In addition to helping mitigate the impacts of the rail project, wildlife corridors would help protect sheep from vehicle collisions when they attempt to cross a freeway.

“The corridors would provide a safe pathway for the sheep to travel north from the Soda Mountains to the Avawatz Mountains, and genetically continue the movement northward through mating with other sheep,” Sloan says.

Studies of two new wildlife crossings on Highway 93 in Wells and Contact, Nevada show that corridors greatly benefit wildlife. From 2011 to 2014, the Nevada Department of Transportation estimated over 85 percent of the mule deer population used at least one of the two wildlife crossings. These studies found the number of deer struck by vehicles decreased dramatically — up to 50 percent during each migration season — benefitting the animals and the motorists. These corridors continue to protect both wildlife and people.

The study of Highway 93 wildlife corridors focused on mule deer, but all types of animals benefit from them. Remote-sensor cameras have captured mountain lions, coyotes, bobcats, bighorn sheep, and other wildlife making use of the bridges.

Sloan notes that “mycoplasma ovipneumoniae, a type of pneumonia spread from domestic sheep to desert bighorn, may infect more sheep as animals congregate and interact with other populations. But the long-term benefits of wildlife corridors far outweigh the potential for spreading disease. They help establish wildlife connectivity, thereby strengthening bighorn sheep’s gene pool.”

As climate change intensifies, springs and other water sources evaporate and food sources shrink. Drought conditions adversely affect water quality and the nutritious value of plants that sustain desert animals. Wildlife corridors not only provide a path for food and water, but potential mates. This helps bighorn sheep and other wildlife diversify their gene pool, increasing their odds for survival.

A high-speed rail without wildlife crossings along the I-15 corridor is not sustainable for desert wildlife. It’s not a gamble worth taking.

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