For stretches of the border between Arizona and Mexico, a security barrier stands about 15 feet high, meant to thwart illegal immigration and smuggling. But where this barricade cuts through protected wildlife areas, it’s hindering native predators -- just not humans. The fence appears to have little impact on human travel, says a new report in the scientific journal PLOS ONE, although it’s restricting the territory of pumas and the raccoon-like coatis.

A coati captured on the researchers' camera. All images courtesy of Jamie McCallum

A group of biologists from the University of Bristol deployed 36 cameras in national wildlife refuges and other reserves along the border, set to snap photos of animals that passed by. The images revealed that, for most mammals -- including humans and more resilient species such as deer -- a nearby barrier had little impact.


But more fencing meant fewer pumas, who may have left in search of wider spaces to roam. And it wasn’t only the big cats that were affected -- coatis have a limited ability to travel, the scientists note. Just how much of an impact it has is uncertain, but the barrier, they write, may be leading the coati toward a “possible collapse in population.”


The researchers also point to other studies to highlight that the infrastructure of boundary security “has little or no effect” on the attitude of people looking to cross international borders. And illegal immigration through wildlife reserves, unfortunately, harms the local habitat. A 2004 study in a California national forest estimated that for every 1,000 people who entered the U.S. illegally, 110 pounds of trash was left behind. (That’s the equivalent of about 3,500 empty soda cans.)


As it stands, the intermittent barrier “delivers the worst of both worlds for biodiversity,” the scientists write -- no defense from human travelers, and fewer resources for the animals meant to be protected.