Fortified walls marking national borders are preventing hundreds of wild animals from migrating in an attempt to escape the effects of climate change, according to a paper published in the Proceedings of the National Academy of Sciences (1). This is the first time researchers have assessed the impact of man-made fences and walls, specifically at border locations, to find out that these structures often restrict animal migrations. These limitations are becoming increasingly alarming as animals need to move more to avoid extreme weather conditions.
Researchers from Durham University, UK, mapped the climatic niche – area with appropriate temperature and precipitation for a species – for over 12,000 species of terrestrial mammals and birds. Using computer simulations, they then projected where these habitats would be in 2070.
Worryingly, if we continue to emit greenhouse gasses as we’ve been doing until now, these areas are going to change dramatically in only 50 years. The authors showed that 35% of mammals and 29% of birds would have significant changes in the area where they can live, even reaching countries where they are not currently found. To put it simply, about a third of all species analysed will be obliged to find a new home due to climate change. According to the researchers, this is most likely to happen in the Amazon rainforest and tropical Andes, around the Himalayas, and in some parts of Central and Eastern Africa.
Here lies the problem: for animals to find a new location, they often need to cross between different countries. In many cases, borders between nations are marked by heavy structures and more are popping up all the time. The British team found over 32,000 km of border walls around the world that can stop large numbers of animals from searching for more hospitable conditions.
Animals can deal with natural obstacles. In fact, mountain ranges and water crossings offer a chance to adapt and increase natural diversity. Man-made barriers, however – such as international border walls – have the opposite effect. These barriers destroy habitats, split up populations and stop migrations. Of all the barriers analysed, the researchers found that walls between Mexico and US, Russia and China, as well as new fences being erected between Myanmar and India are likely to be the most problematic, potentially affecting over 700 species of mammals. Just as an example, the Mexico/US border may block travels for 120 species, such as the Mexican wolf, the jaguar and the opossum.
To allow animals to travel freely, barriers need to be as permeable as possible. This could include, for example, tunnels or openings to allow animals to cross the border between countries. However, this can only happen with bilateral cooperation, particularly in the areas most affected, which will likely see massive increases in animal migrations. Priorities in this area include developing appropriate legislation, correctly identifying what species are on the move, and sharing knowledge and resources between countries.
The authors also urged world leaders to seize the opportunity at the next COP26 meeting in Glasgow to commit to ambitious reductions in greenhouse gas emissions to avoid considerable losses in biodiversity. “Species all over the planet are on the move as they respond to a changing climate. Our findings show how important it is that species can move across national boundaries through connected habitats to cope with this change”, said Professor Stephen Willis. “If we’re serious about protecting nature, expanding transboundary conservation initiatives and reducing the impacts of border barriers on species will be really important – although there’s no substitute for tackling the greenhouse gas emissions at the root of the issue.”
(1) Titley M, Butchart S, Jones V, Whittingham M, and Willis S (2021) Global inequities and political borders challenge nature conservation under climate change. PNAS, 118 (7) e2011204118; https://doi.org/10.1073/pnas.2011204118