The wall stretched as far as I could see, both east and west.

Made of steel, it rose at least twelve feet above the ground and penetrated an unknown distance beneath the surface. The bars were almost touching. No person could get through it, much less a vehicle. To all intents and purposes, it completely separated the land, people and wildlife on either side of the wall.

The wall is located on the border separating the United States and Mexico, about twenty miles east of El Centro, California. I don't know the exact date the wall was erected but know it was not present prior to 2002.

It is not the purpose of this column to comment on the social and political implication of this barrier that is, in many respects, reminiscent of the wall that once separated East and West Berlin during the Cold War. Rather, my thoughts are directed at implications for desert animals that no longer move freely across the border.

Generally speaking, wildlife populations thrive best when their movements, migrations and emigrations are unrestricted. Put more simply, individuals of any species are most likely to thrive when they can go where they want, when they want. This maximizes opportunities to find the best food resources, discover places to hide from predators and inclement weather, and, most importantly for long-term survival, breed with unrelated members of their species. Animals whose populations are restricted in their movements by barriers have less chances of doing these things and are thus at greater risk of declining in numbers or becoming extinct. As we humans continue to expand our impact on Earth, artificial barriers to animal dispersal have an exponential negative effect on the survival of nearly all species.

In abbreviated form, this was one of my thoughts as I stared at the enormous steel wall and bars that towered in front of me—and not really that far from my home.

Though I saw no person searching for a way to get into the United States, I saw coyote tracks on the U.S. side of the wall running parallel to it. It looked to me like the coyote had been looking for a way to get into Mexico. But the steel columns are to too close to each other and I doubt that even a jackrabbit, much less a kit fox or badger, could have squeezed through. The wall is indeed a barrier not only to humans but to many species of desert mammals as well.

I don't think anyone would disagree that large numbers of illegal immigrants find their way into the U.S. each year. But it is hard for me to believe that significant numbers wander miles on foot across one of the hottest and sandiest desert regions on planet Earth to sneak into the U.S. Considering the potential negative impact on desert animals, why not erect a much less expensive barrier that blocks vehicles rather than wildlife?

The photograph accompanying this column shows a vast vehicle barrier that blemishes the U.S./Mexico border in New Mexico. It would be next to impossible for any vehicle to penetrate the barrier but a medium-size mammal can easily move through it. Even deer, pronghorn and bighorn, large mammals known to occur along the border, can fit through it as well.

Cornett is a desert biologist and author of Wildlife of the Southwest Deserts.

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