Environmentalists are concerned that Trump's wall will disrupt wildlife corridors
Beautiful jaguars and ocelots along with wolves and migratory birds will suffer if millions of tons of concrete scar the wild desert country between the United States and Mexico.
Up to 111 endangered animals and plants are feared to be imperilled if their habitat is bulldozed and built over. It could also see the millions of dollars in eco-tourism lost.
Cutting a dividing line between the two countries will destroy vital wildlife corridors in the one of the most unique wildernesses left on the planet.
There is no reason to sacrifice the health of wildlife for such political grandstanding
The borderlands are the only place where big cats from South America hunt in the same habitats as North American black bears.
With the new president laying the foundation stones for the $15 billion (£12 billion) wall by declaring that it will be funded by a 20 per cent tax on Mexican imports, conservationists have responded by threatening to fight President Trump's "Stone Age" plans every inch of the wall as it meanders across Texas, New Mexico, Arizona and California.
The Center for Biological Diversity based in Tuscon is highlighting the threat to America's most powerful big cat, the jaguar, which has recently been re-discovered north of the Mexican border.
Jaguars are among the animals which are under threat from the border wall
Camera trap images of jaguars in Arizona have only emerged in recent months, after an absence of big cat sightings north of the border for many years.
Ocelots, a much smaller but equally impressive wild feline, have also been enjoying a renaissance, with the first den being discovered in Texas last month in 20 years.
The Great Wall of Trump would be the death knell for the cats' recovery, say critics.
Mexico Wall: Trump gives the go ahead
Thu, January 26, 2017
The structures, fences and walls that mark the border between the United States and Mexico as President Donald Trump reiterates his promise to build a wall along the U.S. border with Mexico.
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Combo with images of the border fence between Mexico and the U.S. taken in the states of Sonora and Baja California, Mexico, and in the states of Arizona and California, U.S., between July 2, 2016 and January 25, 2017.
Kierán Suckling, executive director of the Center for Biological Diversity, said: "Donald Trump continues to cling to his paranoid fantasy of walling off the US-Mexico border, regardless of the harm it would do to border communities and wildlife.
"We already know that walls don't stop people from crossing the border, but Trump's plan would end any chance of recovery for endangered jaguars, ocelots, and wolves in the border region."
The CBD says billions of dollars have already been spent building and maintaining hundreds of miles of border wall, with "little to no" environmental oversight, and yet Homeland Security officials have testified it is no more than a "speed bump" for people trying to get into the USA.
The wall idea has come under fire form conservationists who claim it won't help immigration problems
Mr Suckling said: "Like many of Trump's ideas, this one has nothing to do with reality.
"By any measure the US-Mexico border is more secure now than it's ever been. There is no reason to sacrifice the health of border communities and wildlife for such political grandstanding.
"The border region is home to a rich diversity of living beings. It's a place where north and south meet and overlap: the only place in the world where jaguars and black bears live side by side. It's this diversity that makes us strong, not some wasteful, immoral wall.
The Rio Grande river is one of the most popular wildlife areas on the planet
"We will not stand by while Trump creates a Berlin Wall on America's border. We'll fight this Stone Age proposal in every way we can, and, if necessary, put our bodies in front of the bulldozers."
A provisional report from the US Fish and Wildlife Service published last year has warned that a 2,000-mile wall with 1,000ft development either side would impact on 111 endangered species, 108 migratory birds as well as wildlife refuges and protected wetlands.
The Rio Grande Valley running through Texas is also one of the most popular wildlife tourist venues on the planet, with birdwatchers alone spending $460 million (£360 million) to see such colourful species as green jays, ringed kingfishers and kiskadees.