There are a number of reasons why Donald Trump's proposal to build a wall on the US-Mexican border is kind of dumb, primarily being that nobody wants to fund such a crazy expensive operation. However, scientists have presented another reason why the border wall plan would be terrible, and it's not just for the people who may or may not have to pay for it if Trump gets elected. Photo credit: Gerald Herbert/AP
According to ecologists, a wall would cut through the ecosystem in the southwestern United States, denying species access to their environment and destroying habitats.
"The southwestern US and northwestern Mexico share their weather, rivers and wildlife," Sergio Avila-Villegas, a conservation scientist from the Arizona-Sonora Desert Museum in Tucson, told Nature. "The infrastructure on the border cuts through all that and divides a shared landscape in two."
The area is home to a wide diversity of species, including some that are endangered and need access to both nations to survive. Movement is important for the continued survival of many species and a large wall could hamper that movement.
These hypotheses are based on the kind of wall proposed by Trump (granted, there isn't a plan that goes into a lot of detail), which'll be at least 15m high and made out of precast concrete. The height of the wall alone could impact the movement of birds that either don't fly, such as roadrunners, or who fly low, such as pygmy owls. Other species like bighorn sheep -- that travel in small groups and rely on cross-border connections to survive -- would be cut off from their neighbours.
Most animals migrate to some degree, whether it's to travel to breeding grounds at certain times of the year, or to find better living conditions in the event of catastrophes. Migration specifically allows for more varied genetic diversity in certain populations that connect with species in other countries to mate. A concrete barrier that spans thousands of kilometres would cut off access for those animals.
Clinton Epps, a wildlife biologist at Oregon State University in Corvallis, was one of the authors on a 2009 study published in Conservation Biology that suggested that a barrier would have a negative effect on the pygmy owls and bighorn sheep. He also highlighted to Nature the problems black bears, jaguars and ocelots will have in the event of a border wall. Black bears in the US are particularly in danger if they can't connect with Mexican bears.
A border wall that was haphazardly placed could also cut off access to food and water sources. Mother Nature Network spoke with conservation photographer Krista Schlyer in 2011 and found that it already has in some cases, such as when she and a scientist spotted a broken-down barbed-wire fence near the border.
When we got to the ground, we visited the ranches on either side of the border to learn what we could about the bison's movements and habits. The rancher on the Mexican side of the border said the bison visited a pond on his land almost every day because it was the only year-round water source anywhere nearby. The rancher on the American side said they came to a certain pasture on his land, where there was a special kind of native grass.
A study published by the University of Texas at Austin in 2011 highlighted at least 27 species that were at risk due to a border wall. Researchers studied an area along coastal California where barriers block as much as 75 per cent of species' ranges. Most at risk are smaller populations in specialised habitats.
Experts have already noticed the toll that the existing barrier has taken on species -- the one authorised by President George W. Bush in 2006 and that spans around 1100km. Mountain lions have been spotted trying to climb over the bars, for example. However, efforts to actively study the impact of border policies on wildlife has been hampered by the danger that patrols present in the area and the unwelcoming nature for many scientists, including Sergio Avila-Villegas, who is Hispanic.
"Every time I -- a Hispanic male with dark skin and long hair -- am in the field, I get patrols, helicopters, and ATVs coming to check on what I'm doing," Avila-Villegas told Nature.
Of course, if you don't care about the conservation of wildlife, this all seems like a nonissue. Maybe we can get the mountain lions to pay for the wall, since it's going to be on their land too.