09/10/2026
Along the Arizona border, a female mountain lion was filmed squeezing through a tiny opening in the steel border wall, then waiting as her three spotted cubs followed. The opening measured just 8.5 inches wide and 11 inches tall. Researchers call them “cat doors,” and for some wildlife, they offer one of the few ways through the barrier.
Between August 2022 and July 2024, researchers from Sky Island Alliance and Wildlands Network deployed 36 wildlife cameras along 100 miles of the Arizona–Sonora border. They recorded 9,240 wildlife events involving 20 species, comparing older vehicle barriers with approximately 70 miles of 30-foot steel bollard wall.
At the older barriers, 65% of wildlife interactions resulted in successful crossings. At the taller wall, that figure fell to just 9%. Researchers documented no successful crossings by bears, deer, or wild turkeys during the monitoring period.
The four-inch gaps between the steel posts allowed smaller animals, including bobcats, foxes, hares, raccoons, and skunks, to squeeze through. Larger mammals faced a much greater obstacle.
The 13 cat doors offered some relief. Mountain lions, javelinas, and coyotes were 16.7 times more likely to cross when they encountered one of these openings. Although designed for smaller wildlife, the openings also proved usable by mountain lions, demonstrating how determined animals could navigate the barrier.
However, the passages remain extremely scarce, averaging roughly one opening every five and a half miles along the wall. Animals searching for a route across may travel long distances before finding one.
Published in Frontiers in Ecology and Evolution in November 2024, the study highlighted a significant conservation concern: small wildlife passages can help certain species, but larger animals need more frequent and accessible crossings.
For the mountain lion mother and her cubs, a tiny opening provided a way forward. For countless other animals, the towering steel wall remains an almost insurmountable obstacle.
Image is for illustration purposes only.
Source: Harrity et al. (2024), Frontiers in Ecology and Evolution; Sky Island Alliance; Wildlands Network; Sierra Club; High Country News; Courthouse News.