As we continue along the path to a warmer world, a vast, global migration is happening. The habitats animals have evolved to occupy are on the move, and to survive, each species must follow. This mass migration is set to ramp up in the future with huge implications for the animals and humans that depend on them for their livelihoods. At the same time, walls, fences, and fortifications are being constructed along borders under the auspices of national security. Designed to stop the flow of human migrants, they may prevent animals from crossing too. Without mitigation efforts and international cooperation, many species will come under increasing pressure and are at risk of dying out.
By 2012, over 13% of the world’s international boundaries already had some form of physical barrier installed, and demand continues to rise. These structures fragment habitats, degrading the connectivity between landscapes and splitting populations apart. Barriers can stop animals from finding a mate, prey, or water, or from exchanging genetic information to sustain healthy populations in the wild.
The US-Mexico wall, if completed, would render impossible the migration of endangered animals between the two countries, such as the Mexican grey wolf and the Sonoran pronghorn. This would weaken already threatened populations and could lead to their eventual demise. Winged animals are vulnerable too: low-flying pygmy owls and the Quino checkerspot butterfly would also struggle to pass, several reports have found. While progress has now been halted under the Biden administration, construction works have already caused widespread and deep ecological damage, says Laiken Jordal, Borderlands Campaign Manager for the Center for Ecological Biodiversity. “We know it’s horrific, we know it will cause localized extinction of some species...but the true lasting effects of this project, a lot of them are still unknown,” he says.
Toward the end of the century, the specific climate niche of a startling number of species will have moved to a different country.
The problem is by no means limited to North America, however. Around the world, new barriers are rising at political borders. New research published in the Proceedings of the National Academy of Sciences analyzed the combined impact of climate-driven animal migration and the growing presence of border fortifications. A team of researchers led by Mark Titley at Durham University modeled the impacts of climate change on animal migration patterns and how the shifting ecological boundaries would overlap with political ones. They discovered that toward the end of the century, the specific climatic niche of a startling number of species will have moved to a different country. While most animals are not aware of political boundaries, huge problems can arise.
“Our simulations show that species will move generally towards the poles and to higher altitudes as the climate changes,” says Titley. “For the US-Mexico border, this means the vast majority of cross-border movement is projected to be northward from Mexico into the USA,” he says.
Titley’s research examined the niches of over 12,700 species of birds and most terrestrial mammals. The team then compared the results to projections of how environmental ranges would change under the four carbon emissions scenarios used by the Intergovernmental Panel on Climate Change (IPCC). The findings were combined with spatial data on national boundaries around the world, including fortifications currently under construction.
Under the highest rate of carbon emissions, the researchers found that by the year 2070, around 35% of mammals and 29% of birds would have over half of their climatic niches in new countries. Over half of the modeled animals would have more than a fifth of their new niche beyond a current national boundary. “In some regions, particularly where governance and cross-border collaboration are already weak and human pressures are high, this will be challenging,” the authors write. Most of the movement is expected in central and eastern Africa, in the Himalayas, the western Amazon region, between China and Russia, and on the US-Mexico border.
Even with no physical barrier, animals may still migrate into new jurisdictions with completely different conservation levels. Fortifications add further difficulties. The US-Mexico border has already shrunk populations of pumas and coatis, research has found. Border fencing in Central Asia appears to be impeding ungulate migrations. Razor-wire fencing set up on the border between Slovenia and Croatia in 2015 has killed herons and ungulates, such as red deer and wild boar. Overall, fortified borders intersected with the ranges of 18.5% of all non-flying mammals surveyed, the PNAS study found. Borders that could be particularly damaging ecologically include the fence being set up between India and Myanmar and fences on the frontier between China and Russia.
Jordal says they are already noticing a northward shift of habitat of a range of species at the US-Mexico borderlands. “As habitats shift, for wildlife it’s like they're having the rug pulled out from under them, and if they want to survive they’ll have to stay on it as it moves,” he says. “But now they’ll be met with this impassable thirty-foot high metal wall stopping them from tracking their habitats as climate change progresses. We certainly expect to see dead animals on the south side of the wall if they haven’t been able to access cooler habitats to the north,” Jordal says.
The impacts on each species will depend on how much suitable climate remains on the side it is trapped on. If this dwindles, and escape is impossible, many populations could decline and eventually die out. “Even if their populations are reduced to smaller sizes but not fully lost, it can be a big problem as it makes them increasingly vulnerable to other threats like habitat loss, hunting, or random weather events,” Titley says.
International cooperation, though often challenging to achieve, is critical to tackling shared ecological threats.
There are several mitigation efforts that could help. Where there are no barriers, ecologists can ensure habitats are still connected between countries. Neighboring countries can create trans frontier conservation areas, which provide habitat continuity across political borders. These are already being trialed in Africa, says Titley, where a cooperation between national parks in Uganda, Rwanda, and the Democratic Republic of the Congo has led to an increase in the local gorilla populations. Yet the study found the largest effects of climate-driven climate migration to be in countries with lower GDP and governance levels, which may complicate conservation efforts in the areas that need it most.
Where border barriers exist, thoughtful design could go a long way to help animals cross them. “This could include smaller gaps to allow small-bodied animals to pass through, or larger openings in ecologically important places where human migratory pressures are low,” Titley says.
As with many of the consequences of climate change, addressing the source is by far the most effective solution. “It's important to remember there's no substitute for deep and swift cuts to greenhouse gas emissions that are driving climate change, and therefore these animal movements, in the first place,” Titley says.
*Richard Kemeny is a freelance science journalist from the UK. He writes about archaeology, earth sciences, biology, ecology and the environment. Follow him on Twitter @rakemeny.