I know in places with big animals, like Botswana, building vast fences screwed up the herd migrations.
Are there any animals along the Mex-US border that would be cut off from their normal habitat? Coyotes or tortoises or such?
You’re thinking of the Alaskan pipeline, where it killed all the deer. They got to the pipe and couldn’t cross over to the fresh grass.
No, no, no, and no.
A border fence would only interfere with the normal migration of illegal immigrants, and the Alaska pipeline is beloved by the caribou because it stays warm all winter and they can snuggle up to it.
The Alaska Pipeline is 800 miles long. Approximately 380 miles of it is buried. The remaining 420 miles above ground has almost 600 animal crossing locations.
Not true. Sonoran pronghorn antelopes (already listed as a federally endangered species and mountain lions are among the large animals that move back and forth across the border. Large animals that require huge areas of land are usually the most effected when a significant barrier is put in place - in many cases, freeways.
An additional problem can be caused if fence construction destroys habitat - for example, the border runs right into the Tijuana River National Estuarine Research Reserve, home to many endangered species and a significant fraction of California’s remaining ~8% salt marshes (compared to 1850).
Some citations of concern around the environmental impact of a border fence:
http://www.ombwatch.org/article/articleview/3091/1/308
www.fas.org/sgp/crs/homesec/RS22026.pdf (WARNING: PDF)
That’s not to say that we couldn’t figure out some arrangement that would let us create an effective barrier to humans but not so much to migrating animals, but the issue does exist.
You build a fence that will keep human beings out. It’ll have to be of the same nature to keep all but flying animals out. Include the personell, equipment, housing, and other outbuildings necessary for bulding, maintaining, and patrolling the fence, especially in the extremely isolated portions of the fence, it just gets worse.
A little MPSIMS, but jaguars also cross the border into New Mexico and Arizona.
What the hell are you talking about? Deer don’t live anywhere near the Alaska Pipeline (though moose and caribou do). Deer also generally don’t eat much grass, being browsers.
Actually I’m thinking much more along the lines of a “virtual fence” idea which consists sensors that allow border patrol personnel to keep better track of what’s going on at the border. The agents will most likely ignore wild animals (and domesticated ones too, most likely 
). Some parts where a physical fence would be less damaging would be alright.
Expensive? Yes, but IMHO, a better solution - besides, I think trying to physically fence in the whole border is a little bit too much anyway.
Wow. I just had a vision in my head.
Furry convention meets Mexican man-smuggling operation.
“Here, kitty kity…”
“No hablo ingles…”