Border fences to stop illegal immigration are a threat to wildlife, with animals in border areas in Texas and California especially vulnerable, a study says. Researchers at the University of Texas say most at risk of extinction are smaller populations of wildlife that occur in more specialized habitats, and among them are four species listed as threatened globally or by both the United States and Mexico. The animals include the Arroyo toad, the California red-legged frog and the jaguarundi wild cat, a university release said Tuesday. "Our study is the first comprehensive analysis of threats to species across the entire U.S.-Mexico border," researcher Jesse Lasky said. "The scale at which these fences stretch across the landscape is large, so it's important for us to also have a large- scale view of their effects across the continent." When barriers, including border fences and roads, separate the ranges of these animals their ability to move is limited, which makes them more vulnerable to events such as hurricanes or fire, which can wipe out an entire population, he said. Some species in California have barriers that block as much as 75 percent of their ranges, the researchers said. The U.S. Department of Homeland Security is exempt from environmental regulations when building security infrastructure, which now includes almost 750 miles of fences and migration barriers on the border, the UT release said. "The U.S.-Mexico border spans regions of extraordinary biological diversity as well as intense human impacts," UT biology Professor Tim Keitt said. "Loss of biological diversity can have negative impacts on the ecosystem services that are the basis of our life-support system."