On 5 January 2024, state wildlife officials in Arizona confirmed the presence of a previously unidentified jaguar in the Huachuca mountains near the Mexican border, making it the third individual recently seen in Arizona, and only the eighth in total to be documented in the United States for nearly 30 years.
Jaguars once ranged across almost the entire southern half of the US, as far north as Colorado and eastward to Louisiana. There’s no ecological reason why they wouldn’t have thrived as far east as Florida, where they would have enjoyed an ideal habitat – though there are no known fossil records there since the Pleistocene, so the Mississippi River possibly acted as a natural geographical barrier.
These jaguar individuals – most likely vagrant males – appearing in Arizona and New Mexico would ordinarily be an early sign that the species is beginning to recolonise its northern range. However, any such recolonisation faces a range of anthropogenic obstacles, including highways, hostility from the ranching industry, and more immediately and importantly, a heavily fortified and impenetrable US-Mexico border, which the UN has called the world’s deadliest overland migration route.
National borders target vulnerable migrants
National borders are perhaps just lines on a map, but their physical demarcation with fencing, walls and militarised policing has increased dramatically over the last several decades. Since 1990, EU and Schengen area states have built border walls with greater length than six Berlin Walls, largely with the intention of denying entry to vulnerable migrants from the neighbouring territories, with a callous indifference to human rights.
The borders that Poland and Lithuania share with Belarus and which mark the eastern edge of the EU, for instance, are particularly impenetrable. In recent years, the far-right Belarussian government under Putin-aligned President Lukashenko has been dangling the possibility of entry into Europe to asylum seekers mainly from the Middle East, before simply dumping them at the border, hoping to provoke a crisis for the EU. In response, Poland’s Law and Justice government built a heavily policed wall from which migrants are simply pushed back into Belarus. People are then stuck in migrant camps in Belarus, starving and even freezing to death during winter – a deadly route.
National borders don’t just keep people out
In this misery, the wildlife tends to get overlooked, but these border walls undoubtedly inflict serious ecological obstacles. This same Belarus-Poland border runs straight through the middle of the Białowieża forest, one of the largest areas of old growth primeval forest remaining in Europe and home to an extraordinary array of creatures, including bison, wolves, lynx, wild boar, and tens of thousands of invertebrate species.
The wall is likely to prevent the recolonisation of the ecosystem by brown bears from Belarus, of which a few vagrant individuals have recently been seen there, just like the jaguars in the US. It will also fragment populations of existing wildlife and prevent dispersal and migration, reducing the genetic diversity of populations. Footage of bears trying to cross the wall is astonishing and heartbreaking.
Similar threats are posed by the border wall in the US. Even without physical barriers, pronghorn antelopes were already sensitive to disturbance caused by border patrol activity. With walls and fencing into the bargain, many other species with cross-border populations are also similarly affected, even including species of amphibians and reptiles with small geographic ranges, some of which are listed as threatened.
Border infrastructure tends to be most detrimental to flightless species, but not exclusively. At the US-Mexico border, the ferruginous pygmy owl, whose populations are naturally sparse and patchy, is unable to easily cross walls or fences as they fly very low to the ground. In Białowieża, the border wall is over five metres high and this is sufficient to impede low-flying grouse.
The situation may deteriorate with climate change
These threats will likely grow worse as the climate changes, and as many species move in response. A recent study estimated that under a high emissions scenario, by 2070, around 35% of mammals and 29% of birds globally will have more than half of their geographic ranges in countries where they’re not currently found. This means their distributions, as predicted by climatic conditions, will want to shift across borders. Unfortunately, there are few ways to mitigate the problems involved without removing the physical barriers, which in any case are usually expensive and ineffective solutions to the different crises created by political decisions.
Apropos the jaguars, whose movements are blocked due to the border wall, there are proposals for an alternative reintroduction into the mountainous forests spanning Arizona and New Mexico, areas which could easily support a viable population. However, unless the border became more permeable, the long-term genetic health of this population would require periodic translocation of new individuals from further south. It is, however, doubtful whether regular translocations across borders could be practical or sustainable for all species affected.
The important point is that, during our biodiversity crisis, made all the worse by climate change, physical barriers across national borders must be reduced, made more permeable, or removed. Some might want to echo the words of a former US president: ‘Mr. Biden, tear down that wall!’