Bears at the Border
How immigration and tariff policies affect the animals that roam between the U.S. and Mexico.
OCTOBER 7, 2025
“Active trap, active trap!” That’s the midnight shout that shakes me from deep sleep into utter concentration. As I pull on my boots and switch on the light, I mentally check off the things I need for the capture: measuring tape, notebook, scale, tools, satellite collar. In under five minutes, the whole team — two biologists and a veterinarian — is inside the truck, hearts racing, eyes straight ahead. There’s a bear in the trap.
Just a few kilometers away, a black bear sniffs and studies the device tethering it to a tree. With a daintiness at odds with its 120 kilos, the bear extricates its wrist from the tie and calmly takes its leave. The bear’s tracks are the only evidence of its route. An infrared camera documents both its escape and our arrival. Our faces betray the disappointment of discovering the empty trap.
The black bear — one of four bear species found in the Americas — exists in Mexico, the U.S. and Canada. The southernmost individual on record lives in the Sierra Gorda of Querétaro, just 200 kilometers from Mexico City, while the northernmost populations wander the Arctic coasts in northern Canada and Alaska.
The specimen we’ve failed to capture is an adult black bear whose home is a mountain range running from north to south on the border between the United States (in Arizona and New Mexico) and our country, Mexico (in the states of Chihuahua and Sonora). We’d hoped to fit the bear with a satellite collar and monitor its movements; we’re particularly interested in studying its reaction to the highway and recent construction of the border wall. Presumably it’s a Mexican bear, because we detected its presence on this side of the wall — but where was the bear born, here or there? Does it often visit the neighboring country to the north?
The black bear — one of four bear species found in the Americas — exists in Mexico, the U.S. and Canada. The southernmost individual on record lives in the Sierra Gorda of Querétaro, just 200 kilometers from Mexico City, while the northernmost populations wander the Arctic coasts in northern Canada and Alaska. These black bear populations have dropped and grown over centuries of hunting and conservation programs. In this way, thousands of bears coexist in a mosaic of forests, mountains, highways, farms, cities, and residential complexes.
The species’ common name is deceptive, because black bears can be cinnamon-colored, dark brown, and even blond. Only in the southeastern U.S., though, are there black bears with different colors of fur. No one knows exactly why these chromatic variations take place, but it’s believed that lighter colors help them cope with sun exposure and make them less conspicuous in open, arid terrain. Judging by the hairs caught in the honey and mango we used to lure bears into the trap, we know that the escaped individual is chocolate colored.
Several days later, I get up at 6 a.m. and use a radio antenna to check on the traps. A quick beep-beep alerts me that something has activated the trap from which Houdini, as we nicknamed the crafty bear, eluded us three nights prior. After an hour and a half, Houdini wakes up discombobulated: The bear been anesthetized, measured, sampled, and fitted with a collar that will send us its precise geolocation every two hours for the next couple of years.
The map is almost impressionistic, with darker shadows indicating their favorite spots: cool ravines and oak groves where they devote themselves to leisurely exploratory walks to finding food.
The relationship between humans and black bears is different in every country and varies by region. Hunting them is permitted in certain U.S. states and Canadian provinces. However, in Mexico — where the bear population is not as dense and forest habitats have dramatically diminished — they’re protected as an endangered species. Social attitudes toward black bears fluctuate between admiration, tenderness, and fear. Our perception of their animality intensifies when they walk on all fours; that’s when we mark an Aristotelian distance between us and them. But when they rise up on their hind legs and deftly use their front paws to open cars, trash cans or something else, the species barrier blurs: They look more like us, which stirs our empathy. The interspecies overlap of intelligence and agility is so apparent that, in places where bears and people coexist, it’s hard to design garbage cans that bears can’t open without making them indecipherable to a scatterbrained human.
After two capturing seasons, we manage to fit more bears with tracking collars. Over time, the dots marking their location on the map allow us to trace the routes between places visited by each individual. The map is almost impressionistic, with darker shadows indicating their favorite spots: cool ravines and oak groves where they devote themselves to leisurely exploratory walks to finding food. Less-frequented areas are lighter in color. These tend to be areas where they’re more exposed; the bears cut across them briskly and don’t stop to sniff around.
Immobility is another key part of a bear’s life: During the cold months, when there isn’t as much food to be had, they seek refuge among the boulders or fallen trunks and sink into a deep slumber that can last for entire weeks. Gerónimo, one of the largest males we captured in the first season, patrols a vast area of 400 square kilometers, including woods with abundant food (depending on the season), various water sources and cold slopes for hibernating. One day, we saw Gerónimo moving north. The Mexico-U.S. border was less than 2 kilometers away, and there’s no wall in that section of New Mexico. It’s wide open to non-humans. Although Gerónimo may be the most powerful animal in these mountains, the bear is also cautious; it fears people and machines. Federal Highway No. 2, which connects Tijuana and Ciudad Juárez, stood in his way. Car traffic, engine noise and the glare of the headlights eventually dissuaded it from crossing the asphalt barrier. Some 150 meters south of the highway, the bear turned around and headed back into the mountains.
In a world without humans, bears mostly worry about other bears. Black bears used to coexist with brown bears, a much larger and more aggressive species whose presence prompted them to act with caution. To avoid their fiercer relatives, black bears opted for harsher terrain and a more varied diet, less dependent on the meat consumed and locations frequented by brown bears. But precisely because brown bears are more combative and less afraid of humans, the 20th century’s predator-eradication campaigns killed every last brown bear in the valleys and mountains in the southern U.S. and northern Mexico.
One morning, I check the map of recent movements and see onscreen that Winni, a young adult male, has set out to explore new terrain. In just four days, the bear has crossed a valley of desert grassland and two highways before he reached the Sierra de Cananea, over 60 kilometers east from where we captured it. These sorts of expeditions are known as dispersion movements. In the bears’ world, young males undertake the longest journeys in search of females, traveling farther than the older males’ strictly patrolled perimeter.
Their patches of habitat and their water sources are diminishing; their feeding timeline has grown increasingly erratic, and more barricades are being built all the time, limiting their freedom of movement.
The coordinates of Winni’s voyage marked a nearly straight east-to-west line. I wonder why the bear chose to head in this direction. Does it know that the neighboring country also has bears in its mountains? And does it already know that if it had gone north, it would have run into the highway less than 3 miles away — and probably the wall, too, just over a mile beyond it? The bear made its decision and found forests stocked with everything a bear could need. But considering the distance between the two mountain ranges, there were also ill-fated days when the bear saw only grasslands: no mountains in sight. I can’t stop thinking about the bear-faith that led it to cross an ocean of meadows, hoping to find mountain-islands on the other side.
The year 2025 has just begun and it’s winter on the border. On my computer screen, I see that none of the bears we’re monitoring has moved in recent weeks. They’re hibernating in some woodsy hideout. Donald Trump has just reclaimed the presidency of the U.S., and it seems inevitable that he’ll keep building the border wall that will completely block the corridor connecting the Sierra Madre Occidental with the mountains of Arizona and New Mexico. Multiple habitat analyses show that this mountain corridor is the most important way to keep the two countries’ bear populations connected. The bears’ behavior is also affected by climate change — for example, the megadrought currently afflicting this region. Their patches of habitat and their water sources are diminishing; their feeding timeline has grown increasingly erratic, and more barricades are being built all the time, limiting their freedom of movement. This is a serious problem for bears and other species dependent on crossing vast areas to survive. The scenario points to the question at the heart of our research: Which ravines, mountain passes and barriers are most harmful to bears on the move?
Although no bear has yet been bold enough to cross the federal highway or venture into the U.S., there are undoubtedly black bears we could call “border bears.” Just like wolves, bison, pronghorns, prairie dogs, beavers, and monarch butterflies, these bears are on the list of epic species inhabiting North America — which means that any immigration and tariff-related threats and decisions made by the region’s countries invariably affect them as well. With the imposition of trade tariffs, the price of steel, semiconductor chips, and avocados goes up. Meanwhile, the energy costs involved in finishing the wall will take a brutal toll on wild species.
There will be consequences: The black bear populations of Mexico and the U.S. will be more isolated than ever. What’s more, border bears will be in even greater peril. After all, their lives depend on the amount of rain, the abundance of acorns, and whether the Department of Homeland Security dynamites mountains to build a wall, shrinking their habitat in the process.
I return to the mountains, where the bears are sleeping. I listen closely to the murmur of the water, the rustle of last autumn’s dry leaves crunching underfoot. I focus harder, as if trying to hear the bears breathing as they hibernate up the slope. I go back to the city and make sense of what I heard. The beep-beep comes through loud and clear. I understand the message, and it needs to be shouted from the rooftops to wake everyone up. Active trap, active trap!
This piece was originally published by Revista de la Universidad de México.
✺ Published in The Dial
