The fence is a serious environmental threat and endangers wildlife.  By cutting off components of the habitat, the fence diminishes gene flow and reduces the ability for survival, or creates remnant populations that are too small to sustain the species.1 Counter-intuitively, even certain winged species which fly low to the ground would be at risk. Climate change is forcing more migrations, and this would also prevent animals from carrying those out.2 This has been so lightly regarded by U.S. officials that at one point Mexico actually threatened to file a claim with the International Court of Justice.3  1Goldstein, Rob. "US-Mexico border fence putting wildlife at risk of extinction."  2Marshall, Jessica. "U.S.-Mexico Border Fence May Snag Wildlife."  3Magee, Megan. "The U.S.-Mexico Border Wall: An Environmental And Human Rights Disaster."