Eight years ago, while flying 800 feet above the grasslands of southern New Mexico, an unlikely observation changed the course of my life. As I was leaning out the window of a small Cessna above the border of the United States and Mexico, a cold March wind roared through the plane and I could just barely make out the excited words of wildlife scientist Rurik List Sánchez:
“There they are, at the border!”
Bison! We had been searching for them all morning and the day before, and we spotted them just as they were jumping from Mexico to the United States, over a barbed wire border fence that ran between their main food and water resources. I had come to write a story about these unique trans-border bison for Wildlife Conservation magazine, and by slim chance had happened to witness their international journey in real-time. Research in Mexico had shown that this bison band—one of six free-ranging herds left in North America—had been making this journey almost daily for the past half-century as the herd labored to survive the trials of life in an arid land. Spotting them at the border itself had made the long trip from my home in Washington D.C. worth it.
But as I watched those bison, my excitement was tempered by the fear that their greatest trial awaited them on a near horizon. The beginnings of the U.S.-Mexico border wall were already being designed and constructed elsewhere on this 2,000-mile border. How long would it take that barrier to reach this remote grassland and divide the bison’s pond and pasture?
I had followed border policy and wall construction, though not closely, but in an instant as I watched those bison cross the border, the real-world consequences that would follow the building of a border wall came home to me. From that moment, I began to gear my working life toward telling their story, and the stories of all the other countless creatures on the U.S.-Mexico border that would be facing the fallout of this sudden barrier.
There is, for all living things, a breaking point, where cumulative challenges overwhelm the ability to adapt.
The predicament of those bison, and the thousands of other wild species on the border, is just one example of an infinity of barriers that we construct continually through the lives of other creatures. Barriers are all around us.
This reality was brought home to me a couple of days ago, while sitting in my house on the northeastern edge of Washington D.C., shortly after I returned from the Texas shooting of this “Think Like a Scientist” film on barriers. I had received a text from a neighbor: “There’s a vulture feeding frenzy in your front yard!” By the time I looked outside the vultures were gone, but on the road just beyond my front walk sprawled an eviscerated Virginia opossum, killed by a car in the night. I knew this neighborhood opossum and was saddened by his ignoble ending. But there was something more.
The two events, with bison and opossum, though long separated by time and space, were fundamentally linked. Two very important forces often dictate the actions and aspirations of all living things: the need to move, and the obstacles that stand in the way.
There have always been natural obstacles to the movement of plants and animals: climate, mountain ranges, oceans, but the pace of change with these obstructions offers a chance to adapt and therefore often ignites the flames of natural diversity. Human-wrought barriers however, whether they are suburban roads or international border walls, tend to have the opposite effect: They are sudden, defy nature’s logic, and, though some species may see benefits, the overall impact erodes biological diversity.
What was once a natural factor in the survival of plants and animals has become touched by the chaotic hand of human industry.
A cleared forest, a fence, a diverse meadow replaced by monoculture, even the invisible line drawn where a protected landscape like a wildlife refuge transitions into commercial property: All can pose abrupt challenges to survival.
In the borderlands land managers and wildlife biologists are grappling with the fallout of these challenges: a herd of pronghorn dying out on the Arizona border because all the breeding males were trapped on the Mexican side of the barrier; an increase in bobcat deaths on roads in South Texas after border wall construction fragmented their habitat and sent them searching for food, water, and mates.
I imagine the life of my local opossum, the trials that tested his survival, and the death that ultimately came on a suburban street. My neighborhood is filled with barriers, from fences, roads, and buildings, to less noticeable obstructions like bright street lighting that hinders the movements of shy nocturnal creatures, and monocultures of grass that offer little in the way of food resources or cover. Opossum have fared better than most in navigating the maze of our urban world. The IUCN Red List categorizes the species as “Least Concern” because of their adaptability to our fragmented world. But recent surveys done by wildlife biologists in Washington D.C. show opossum populations are declining.
There is, for all living things, a breaking point, where cumulative challenges overwhelm the ability to adapt. In Washington D.C., barriers laid down over centuries have helped reduce the region’s biodiversity to a hardy handful. In the borderlands, political climates are already taking a toll on wildlife as artificial barriers rise in a landscape that has until now been relatively free of them. And in the world at large, human-wrought barriers and obstructions are always rising and falling, appearing and disappearing.
In an era of climate change, what was once a natural factor in the survival of plants and animals has become touched by the chaotic hand of human industry. This nebulous barrier, and how it plays out in the world of wild things, is anybody’s guess. Some scientific models have predicted that in the next 50 years one-third of Earth’s species could go extinct due to humanity’s epic reconfiguring of our planet and its atmosphere. And various models have predicted big climatic shifts for both the borderlands and Washington D.C.—extended drought for the borderlands, intense heat for D.C. From the climate perspective, one of the greatest determinants for the future of the borderlands bison, my local opossum, and indeed all wild species, will be their ability to move and find suitable habitat as climate chaos shakes out. Physical barriers may ultimately prove decisive factors in an extinction crisis.
And human consciousness and care are the fulcrum on which all else rests.