New barriers along the U.S.–Mexico border would threaten scores of unique plant and animal species.
At a section of the border wall in Arizona, two javelina turn back after walking 100 yards along the barrier searching for a place to cross. The wall here bisects the San Pedro River, a wildlife corridor and one of the state’s last free-flowing rivers.
LOOK SOUTH TOWARD THE RIO GRANDE RIVER from a spot off U.S. 281 in Texas and you’ll see nothing but greenery—palo verde, acacia, granjeno, honey mesquite and other native trees and shrubs—stretching all the way to the horizon. The air on an early spring day echoes with the calls and songs of dozens of birds, including mourning doves, great kiskadees, plain chachalacas and Altamira orioles—the latter three species found nowhere else in the United States except the southernmost tip of Texas near the Mexican border.
A 100-acre island of habitat amid a sea of highways, houses, farms and other developments, this parcel of land, dubbed Monterrey Banco, is one of 115 separate tracts—totaling more than 100,000 acres—that make up the Lower Rio Grande Valley National Wildlife Refuge. Created in 1979, the refuge was established to protect, restore and create corridors between isolated remnants of the region’s dwindling forests and scrublands. In 1988, the U.S. Fish and Wildlife Service (FWS) added Monterrey Banco to the refuge and, for the past three decades, FWS staff have worked to bring native vegetation back to what once was agricultural land. Animals followed the plants. Biologists have recorded more than 110 wildlife species in the tract, including the Texas indigo snake and Texas tortoise, both listed by the state as threatened.
But all is not well in this small sanctuary. To see why, just glance over your shoulder, where a nearly 20-foot-tall, concrete wall looms. Built during the George W. Bush administration, this close-to-mile-long barrier is one of dozens of sections of border wall that were constructed during the early 2000s. Some segments, like this one, are made of concrete while the majority consist of tall, steel-bollard fencing. Taken together, the barricades run along 650 miles—or nearly a third—of the U.S.–Mexico border. To conservationists, they are both eyesores and threats to biodiversity. Gesturing toward the Monterrey Banco wall last spring, Jim Chapman, vice president of the nonprofit Friends of the Wildlife Corridor, said: “If you wanted to design a structure that has the maximum negative impact on wildlife, it would be this.”
According to an internal FWS memo dated March 2011, the barrier has indeed hurt wildlife. Its construction, along with clearings beside it, destroyed and fragmented habitat. More dramatically, when a 2010 hurricane left several feet of standing water in the refuge for more than six months, animals that could not fly or swim away were trapped and drowned—including many Texas tortoises whose shells were found after the water receded. While a levee had long stood at the same location (the wall was built on top of it), “wildlife can get over a gently sloping levee but not a sheer vertical wall,” Chapman says.
In recent years, border wall building had wound down due to lack of interest and funds. But following the 2017 inauguration of President Donald Trump, the barriers are back in play, with the Lower Rio Grande Valley the first region in the crosshairs. This March, Congress passed and the president signed an appropriations bill that provides funding for 33 miles of new walls in the valley. Because building on private land can be problematic—owners often sue when the government tries to seize their property—construction is expected to begin on federal land, namely more of the precious parcels that make up the Lower Rio Grande Valley National Wildlife Refuge.
Already, agriculture and urbanization have consumed more than 96 percent of the valley’s native habitats. Some ecosystems have been especially hard hit. Just 3 percent of the region’s Tamaulipan thornscrub forests remain intact and even less of its riparian forests. Meanwhile, the valley continues to be one of the nation’s fastest-growing regions, with tens of thousands of new people added to its population every year.
Despite such losses, the Lower Rio Grande Valley remains one of the biologically richest regions in the country thanks to its location where the temperate zone meets the Tropics. Hundreds of plant and animal species found nowhere else in the United States make their homes here. In addition, two major migratory bird flyways converge in the region, funneling in millions of songbirds, raptors, shorebirds and waterfowl each spring and fall to join resident “specialty” birds such as green jays, great kiskadees and Altamira orioles. Ornithologists have recorded more than 530 bird species in the valley, a larger number than in any area of equal size north of Mexico.
Not surprisingly, the valley also attracts legions of birdwatchers. According to a 2011 Texas A&M University study, nature tourism—primarily birding—contributes $463 million annually to the local economy. Located near several birding hotspots, the Alamo Inn B&B, for example, hosts more than 1,200 visitors a year. “Ninety-five percent of our guests are birders,” says innkeeper and guide Keith Hackland, who adds that his bird-loving visitors so far have come from 40 different countries and every U.S. state.
In future budgets, the president hopes Congress will appropriate enough funds to build a continuous wall along the entire 1,989-mile border. Such a massive barricade would slice through some of the continent’s most iconic and biodiverse habitats, from Pacific and Gulf of Mexico shorelines to the majestic Sonoran Desert to some of North America’s last undeveloped grasslands.
The wall’s effects on borderland wildlife also would be wide-ranging. “Barriers like border walls can interfere with the ability of animals to meet their daily needs, make seasonal migrations or disperse to new areas,” says National Wildlife Federation Chief Scientist Bruce Stein. “In addition, the capacity of many species to survive in the face of warming temperatures will hinge on their ability to move unimpeded to follow shifts in climate.”
According to a 2016 FWS analysis, more than 100 federally listed endangered species, from obscure plants to black-footed ferrets, could be impacted by a completed wall. In an editorial published this July in BioScience, 18 prominent Mexican and U.S. biologists say the wall could harm more than 1,500 native species whose ranges are bisected by the border. They and more than 2,800 other scientists have signed a petition in opposition to the wall.
Though more than 600 miles of barriers already are on the ground, “there are surprisingly few peer-reviewed scientific studies of their biological effects,” says University of Texas at Austin biologist Norma Fowler. To synthesize that research, she and her colleagues conducted a literature review of scientific publications. Reporting their results this April in Frontiers in Ecology and the Environment, the scientists wrote that “expanding the physical barriers along the southern border of the U.S. will have substantial negative effects on wild species and natural ecosystems.” Those effects range from habitat fragmentation and loss (between 4.8 and 7.3 acres lost per mile of new wall) to ecosystem degradation due to “edge effects” (from pollution, floodlights, traffic and changes in water drainage, for example).
The most obvious impact of walls on wildlife is when an animal is stopped dead in its tracks. Since the first walls went up, observers have reported a variety of creatures blocked by the barriers, from mule deer, javelina and cottontail rabbits to lizards, toads and snakes. Even wings do not guarantee safe passage. In a study published in 2010 in Conservation Biology, researchers from the University of Arizona reported that the endangered ferruginous pygmy-owl rarely flies more than 13 feet above the ground.
For some animals, daily survival depends on crossing the border. That critical point hit home for writer and photographer Krista Schlyer a decade ago when she was flying in a small plane above New Mexico and spotted “a ragtag band of transboundary bison.” The bisons’ water source is in Mexico, but the grass they eat is on the U.S. side. “It was one of those lightbulb-goes-on-in-your-head moments,” says Schlyer, who since then has dedicated her career to documenting wildlife and habitats of the borderlands.
Less obvious impacts on wildlife can be just as devastating. Particularly vulnerable, scientists say, are rare species with small populations. “Obstacles to movement across the border may inhibit the exchange of genes with larger populations, resulting in inbreeding and, eventually, extinction,” Stein says, citing desert bighorn sheep, Sonoran pronghorn and the Quino checkerspot butterfly as species at risk.
In South Texas, the endangered ocelot is an example of a species already suffering the consequences of inbreeding. According to wild-cat expert Michael Tewes at Texas A&M University–Kingsville, fewer than 80 ocelots—split into two isolated populations—remain in the United States. For more than 20 years, he says, the cats have been forced to inbreed, with the resulting loss of genetic diversity posing a threat to their survival. One goal of the Lower Rio Grande Valley National Wildlife Refuge had been to create habitat corridors that one day would allow U.S. ocelots to breed with members of larger populations in Mexico. The new walls “will shut down that possibility,” Fowler says.
Fowler, a plant ecologist, adds that rare plants in the border region also are threatened. Some species, including the endangered Zapata bladderpod and threatened whiskerbush cactus, “will have walls built on top of them,” she says. Others rely on animals that cannot get past walls as pollinators or seed dispersers. “It’s important to realize that it’s not just birds and mammals at risk,” Fowler says, “but also plants and the functioning of entire ecosystems.”
Scientists like Fowler question why the country would put so much at risk for a structure unlikely to solve problems at the border. According to a 2017 Government Accountability Office study, Customs and Border Protection has been unable to provide evidence that walls improve border security. And longtime local observers say the changing nature of illegal immigration makes a wall irrelevant. Most unauthorized crossers now, they say, are families coming to the border to turn themselves in, seeking asylum.
There’s also a strong economic argument against border walls. Massive spending on such barriers can rob funds from proven border-security tools such as aircraft and patrol boats. New technologies offer even more promise. Combining high-tech equipment such as underground pressure sensors, radar, drones and seismic detectors can create a virtual wall far more proficient than any physical barrier. “Unlike physical walls, such approaches have little wildlife impact,” says NWF President and CEO Collin O’Mara. “We have more-effective and less-harmful solutions today than what the Chinese came up with thousands of years ago.” More than 60 members of Congress agree and have signed bipartisan legislation that would “ensure the most practical and effective technologies are deployed on the border, a win for wildlife and the nation,” he adds.
When this issue went to press in mid-August, Congress was debating whether to include additional money for wall building in the 2019 budget. Meanwhile, construction on funded barriers in Texas was expected to begin by this winter. But activists like Schlyer have not given up. Unlike the previous round of wall construction, she notes, Congress has funded new walls but not required they be built, so opponents are organizing protests, letter-writing campaigns, lobbying trips and other activities. They also are going to court to challenge 2005 legislation that gave the government authority to waive environmental laws, including the U.S. Endangered Species Act, if those laws might slow down border wall construction.
As cause for continued hope, activists cite one thing that was not in the 2018 budget: Among the first places new walls had been planned was Santa Ana National Wildlife Refuge, a 2,088-acre sanctuary sheltering some of the Lower Rio Grande Valley’s last uncut forests. Thanks to protests and pressure on local congressional representatives, Congress excluded from the budget any funds for barriers through the refuge. “Putting a wall through Santa Ana became politically toxic,” explains Scott Nicol, cochair of the Sierra Club’s Borderlands Team in Texas.
The challenge now, he and other opponents say, is to amplify the energy that spawned that victory. “We proved it is possible,” says Schlyer. “Now we need people across the country to write letters, pick up their phones and take to the streets to say they are opposed to building this wall.”
Citing adverse impacts to wildlife ranging from Sonoran pronghorn to Gould’s turkey, the National Wildlife Federation passed a resolution in 2017 opposing “construction of a continuous wall along the U.S.-Mexico border.” Calling the barrier “one of the biggest potential ecological disasters of our time,” the resolution’s author, Gabe Vasquez, director of community relations for NWF affiliate New Mexico Wildlife Federation (see this issue's Working for Wildlife), said the wall also could harm outdoor recreation. “Nobody wants to hunt or fish in an active construction site,” he says, “but that’s what this administration proposes to create along 2,000 miles of our southern border.”
Laura Tangley is senior editor of National Wildlife.
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