The tallest panels of border wall between the U.S. and Mexico stand about three stories high. On the ground, the partitions have a long and troubled record of blocking natural waterways and severing wildlife migration corridors, but the environmental impacts don’t stop there.

When the sun goes down, the wall’s ecological footprint expands up and out, with lights reaching into the sky and illuminating cross-border habitats. Most of that illumination is concentrated near population centers and ports of entry, but with the flip of a switch, that could easily change.

According to a new survey, federal contractors have placed nearly 2,000 stadium-style lights in southern Arizona alone in recent years, imperiling some of the most ecologically complex and celebrated public lands in the United States.

In a report published Tuesday, the Center for Biological Diversity, an Arizona-based environmental organization, revealed the placement of more than 1,800 lights on federal land in the Sonoran Desert between 2019 and 2021, including wildlife preserves that are home to at least 16 threatened or endangered species. The new lights are not yet in use, and according to the report’s authors, they never should be.

“The scientific record clearly shows that artificial light at night can have costly, even deadly effects on a wide variety of species including amphibians, reptiles, birds, mammals, insects and plants,” the group said. “High-intensity lighting in these priority conservation areas would be devastating to the rich biodiversity of southern Arizona and northern Sonora, Mexico.”

The Center for Biological Diversity documented the placement of lighting in several of the most famed ecosystems of the American Southwest, including the Cabeza Prieta National Wildlife Refuge, Organ Pipe Cactus National Monument, the San Pedro Riparian National Conservation Area, and the San Bernardino National Wildlife Refuge.

Together, the four parcels provide a habitat for hundreds of species of birds and an astonishing number of ecosystem-sustaining insects, while also featuring some of the only U.S.-Mexico jaguar migration corridors on the planet, all of which depend on dark skies to survive and thrive.

“The entire purpose of the wildlife refuges where these lights are is contradicted by the actions of CBP.”

The Center for Biological Diversity’s findings mark the latest example of the mission of the Department of Homeland Security — especially Customs and Border Protection — colliding with that of federal agencies mandated to protect public lands and wildlife. Those collisions have been particularly acute in Arizona, where CBP has blown apart national monuments and wildlife refuges and desecrated sacred Native American heritage sites to make way for wall construction.

“The entire purpose of the wildlife refuges where these lights are is contradicted by the actions of CBP,” Russ McSpadden, the Center for Biological Diversity’s borderlands advocate and lead author of the report, told The Intercept. “It’s outrageous that they built these. These are some of the most important conservation lands in North America.”

A map of the border wall lighting infrastructure at Organ Pipe Cactus National Monument, San Pedro River National Conservation Area, Cabeza Prieta National Wildlife Refuge, San Bernardino Valley, and San Bernardino National Wildlife Refuge.

Image: Curt Bradley/Center for Biological Diversity

The expansion of Arizona’s border wall lighting began in 2019 under former President Donald Trump. The additions created a major hurdle for officials at the Organ Pipe Cactus National Monument, who were in the middle of applying for certification with the International Dark-Sky Association for recognition of the monument’s unique lack of light of pollution.

Monument Superintendent Scott Stonum, in a statement to Arizona Luminaria, a Tucson-based news outlet, said the National Park Service “provided comments at the request of CBP concerning potential impacts and suggested mitigations” at the time of the expansion. The service’s “concerns included potential impacts to natural and cultural resources: disturbance of archeological sites, disruption of wildlife corridors, wilderness values, scenic vistas, night-sky, and others.”

In a call with reporters last year, CBP officials outlined a series of construction projects related to the border wall, from repairing gates and roads to filling gaps. New lighting was not included in the contracts for the “remediation” work, officials said in September, adding that the agency was “currently evaluating the operational requirements for lighting across the southwest border” and “looking at the technology available that may help reduce the need for light.”

Whether CBP’s position holds 10 months later is unclear; the agency did not respond to a request for comment by publication. The Center for Biological Diversity’s report, however, shows that whether new lighting goes up or not, the infrastructure is already in place in southern Arizona to do significant environmental harm.

“If they ever switch the lights on, you’d be able to see this huge linear line of lights from space.”

The group’s investigation began after McSpadden called several of Arizona’s federal land management offices and learned that they had no idea how many lights CBP had placed in their jurisdictions. He began making trips to the border and counting lights on the wall, then cross-checked those counts with public records requests and follow-up calls with federal officials.

“The biodiversity in these regions is off the hook and they built it right across federally designated critical habitat, habitat for at least 16 endangered species,” McSpadden said. “If they ever switch the lights on, you’d be able to see this huge linear line of lights from space.”

Flood lights illuminate the U.S. border fence with Mexico at dusk near Nogales, Ariz., on June 22, 2011.

Photo: John Moore/Getty Images

Contrary to the desolate desert images of the popular imagination, the ecosystems of southern Arizona are among the most vibrant on the planet.

“Half of all breeding bird species in North America are known to use the San Pedro River corridor,” the Center for Biological Diversity noted, “along with 82 species of mammals and 43 species of reptiles and amphibians.”

A single game camera along the river documented more than 1,100 instances of wildlife crossing through the borderlands in a three-year period. The travelers included badgers, bobcats, javelina, mountain lions, raccoons, and multiple species of skunk and deer.

Additionally, the report added, “the borderlands between Arizona and Sonora, Mexico, contain some of the highest diversity of insects in the world.” According to one study cited by the group, “the highest diversity of bee species anywhere on Earth exists within just six square miles of San Bernardino Valley, including the San Bernardino National Wildlife Refuge.”

“Turning on the existing border lighting infrastructure at Organ Pipe and Cabeza Prieta would be devastating for lesser long-nosed bats.”

The insects provide food for the area’s world-famous bird and bat populations. Lesser long-nosed bats in particular, which migrate by the thousands over the border wall each summer, are key pollinators for Arizona’s iconic saguaro cacti. They are also prone to significant behavioral disruptions when confronted with giant beams of light.

“Turning on the existing border lighting infrastructure at Organ Pipe and Cabeza Prieta would be devastating for lesser long-nosed bats, shooting a massive wall of light into the sky stretching dozens of miles,” the Center for Biological Diversity reported.

The danger was one of many cited in the report. Others manifested in aquatic habitats, such as the famed Quitobaquito Springs on Organ Pipe, where threatened and endangered species like the Sonoyta turtle and the Quitobaquito pupfish are barely clinging to existence.

The impacts on the desert’s smallest creatures would have cascading effects on the ecosystem’s largest and most iconic animals, the report added, including endangered populations of jaguar and ocelot that still roam the borderlands: “Exposure to artificial lighting has been demonstrated to substantially change behavior patterns of rodents and prey species, thereby altering predator-prey relationships and diminishing hunting opportunities for carnivores.”

Lighting up the borderlands “would worsen the already devastating harm caused by border walls,” the report argued, “further altering behavior patterns and degrading habitat.”