U.S.-Mexico Border Fence Hinders Wildlife, Study Says

Humans aren’t the only ones whose movement will be obstructed by sections of the U.S.-Mexico border fence currently under construction. According to scientists, the barrier will pose a major risk for wildlife.

Ecosystems running along the U.S.-Mexico border range from coniferous forests near the Sierra Madre Occidental to deserts in the Colorado River Valley, but 1125 kilometers of fencing proposed in U.S. Law 109-367 (otherwise known as the Secure Fence Act of 2006) will cut many of these bionetworks in half, drastically limiting the movements of wildlife.

Researchers from the University of Arizona and University of California-Berkeley conducted a case study of travel patterns of desert bighorn sheep and Ferruginous Pygmy-Owls, two species representative of wide-ranging mammals and nonmigratory birds respectively. The study, published online in Conservation Biology on June 23, used GPS telemetry collars and radio transmitters to track the two species in the Sonora area of Northern Mexico and Arizona, a region with one of the largest networks of protected land in North America.

According to the study’s findings, pygmy-owls on average fly approximately 4.5 feet above the ground; only 23 percent of their flights above 13 feet. This poses a major concern since the US-Mexico border fence is on average 13 feet high. The owls were taken off Arizona’s endangered species list in 2006, but conservationists continue to worry about the sustainability of the current population. Scientists of this latest study argue that the border fence will limit reproduction and genetic sharing from southern pygmy-owl communities, two factors vital for the Arizona-based population’s revival.

As far as the border fence’s impact on wide-ranging mammals, genetic analyses found there is a high level of genetic flow between the desert bighorn sheep populations of Sonora and Arizona, a fact that researchers point to as a reason for the need for transboundary movement. The study’s GPS tracking also revealed that the sheep travel the shortest distance between two places, no matter the terrain or passage difficulty, which would render specialized wildlife crossings in the fence relatively useless in helping to stimulate bighorn movement between the countries.

Lastly, researchers also noted the potential threat of increased physical barriers, lighting, vehicle traffic, human activity, and land degradation on wildlife populations.

The study shied away from debating controversial questions, like whether there should be a U.S.-Mexico fence at all, offering up suggestions to encourage wildlife movement between the Sonora and Arizona instead. Ideas include increasing vegetation, particularly tall tree stands, for nonmigratory birds to launch from for long-distance flights and building crossing structures or fence gaps (although researchers did acknowledge the difficulty these would pose in the whole purpose of trying to keep humans from crossing the border).