How Roadkill Became an Environmental Disaster

To save Brazil’s giant anteaters, scientists are grappling with one of the planet’s most transformative forces: roads.

Among Salvador Dalí’s many obsessions—sex, time, death, himself—one of the longest-lasting was giant anteaters. The Spanish painter began sketching the creatures around 1930, and decades later strolled the streets of Paris with a leashed live specimen. A surrealist couldn’t have chosen a more appropriate pet. Massive front claws force anteaters to walk on their knuckles, giving them the shuffling gait of a gorilla holding a fistful of steak knives. Entirely toothless, Myrmecophaga tridactyla possesses a two-foot-long tongue, an organ so prodigious that it’s anchored to the sternum and furls, Fruit Roll-Ups–style, into its owner’s tubular mouth. Anteaters use their tongue to probe anthills and termite mounds like moths at an orchid, lapping up prey with a sticky lacquer of saliva. These sieges are brief, ending when the insects flee or sting. Giant anteaters are thus rotational grazers, endlessly circuiting their bug-filled pastures. A few termites here, a few there, and by day’s end they’ve slurped down 30,000 bugs.

To wander in the 21st century, unfortunately, is to court death. The giant anteater’s range, which runs from Honduras to Argentina, is bisected by BR-262, the highway that cuts across the Brazilian state of Mato Grosso do Sul as it winds from the Bolivian border to the Atlantic Ocean. Along the way, the road knifes through two ecosystems: the Pantanal, Earth’s largest tropical wetland, and the Cerrado, the savanna that covers more than 20 percent of Brazil. Eucalyptus, iron, cattle, and cocaine pulse through this infrastructural aorta, transported in trucks against which soft-bodied, naive animals stand no chance. Researchers who have tallied BR-262’s roadkill consider the highway Brazil’s deadliest, and one of the worst in the world.

When I drove BR-262 with a Brazilian wildlife veterinarian named Mario Alves one dry morning in July, we found that it had claimed yet another giant anteater. The victim, six feet from her long snout to her massive tail, lay sprawled on the shoulder in a state of advanced decomposition. Her fur sloughed from her sun-blackened skin. Botflies whirred. Alves knelt, scissors in his gloved hand, and snipped the tip of one ear, stuffing the scrap into a vial for genetic analysis. I ogled the long broom of a tail, the appendage that this anteater had once wrapped around herself and her pup like a blanket against the chilly Cerrado nights. Now it was limp.

The anteater’s pennantlike tail furnishes its Portuguese name—tamanduá-bandeira, the flag anteater. It also provides the moniker of the research initiative that had brought us to BR-262: Projeto Bandeiras e Rodovias, or Anteaters and Highways, a multipronged examination of how Brazil’s metastasizing road network affects one of its most charismatic mammals.

I’d joined Alves, who used to manage the initiative, for two days of roadkill surveys along 112 miles of BR-262, a road that lays bare the brutal costs of infrastructure. (Alves took a job at a Colombian zoo soon after my visit, though he still manages Bandeiras e Rodovias’ social-media accounts.) In addition to two more giant anteaters, we also came across the leathery husk of a smaller anteater known as the southern tamandua, the shattered armor of a six-banded armadillo, and the mangled remains of a capybara. We saw crushed seriemas, birds that stomp their prey with crimson legs. We drove over the scattered plating of caimans, crocodilians drawn to bask on hot asphalt, and the torn plumage of Rupornis magnirostris, a raptor whose too-apt common name is the roadside hawk. We counted two raccoons and seven crab-eating foxes and a lump of meat that Alves could only categorize as “indeterminate mammal.” And this was the slow season. In the antipodean summer, from December to March, so many carcasses litter BR-262 that Alves takes twice as long to complete his rounds.

At one point, as we bent over the putrescent corpse of another tamanduá-bandeira, I asked Alves—a laid-back hipster whose body is a canvas for animal tattoos, an anteater among them—if quantifying roadkill upset him. He shrugged.

“I’m sad about the situation,” Alves said. “Not about each animal that I see. Or I would be”—he glanced skyward, casting for an English phrase—“under depression.”

If the study of roadkill has a birthday, it’s June 13, 1924—the day a biologist named Dayton Stoner and his ornithologist wife, Lillian, pulled away from their home in Iowa City. The couple were bound for a field station to do some bird banding, but they didn’t get far before noticing that their route was strewn with “a considerable number of dead animals, apparently casualties from passing motor cars.” Commercial car radios were nearly six years away; road-trippers had to entertain themselves somehow. Dayton and Lillian concocted a morbid game to pass the time: “an enumeration and actual count” of the dead. The list ultimately ran 225 animals long, including 19 flickers, 18 ground squirrels, 14 garter snakes, 12 cottontails, two weasels, one woodchuck, and 53 red-headed woodpeckers. The automobile, Dayton Stoner later cautioned in Science, “demands recognition as one of the important checks upon the natural increase of many forms of life.”

The past century has vindicated Stoner’s concern. Roads, scientists have written, have surpassed hunting to become “the leading direct human cause of vertebrate mortality on land.” The most cited estimate pegs America’s roadkill toll at 1 million critters a day. While most are culled from the ranks of the superabundant—squirrels, raccoons, those infernal white-tailed deer—for rarer species, roadkill can represent an existential threat. One study identified 21 threatened or endangered species, from the Houston toad to the Florida panther, that are jeopardized by the four-wheeled menace.

As a conservation issue, roads are a paradox. They mediate humanity’s most conspicuous interactions with wildlife—I would wager that more Americans have seen a flattened opossum than a live one. Yet roads are also so ubiquitous, they’re practically invisible, their harm dismissed as the unavoidable price of modernity. When Wyoming and Idaho proposed to let hunters shoot roughly two dozen grizzly bears in the Greater Yellowstone Ecosystem in 2018, the scheme was slammed by hundreds of thousands of furious petition-signers. That the U.S. Fish and Wildlife Service has described roads as “the most imminent threat to grizzly habitat today,” however, doesn’t inflame the citizenry. Quoth the sage John Oliver: “Infrastructure isn’t sexy.”

Lately, though, roads have begun to receive their scientific due. In the late 1990s, a Harvard professor named Richard Forman coined the term road ecology, the study of how “life change[s] for plants and animals with a road and traffic nearby.” The constant threat of violent death is the most obvious change, but roads are insidious for other reasons. Alaska’s oil roads repel migrating caribou and cleave tundra habitat, while researchers in Idaho have found that merely playing the rumble of traffic through speakers is enough to deter migrating warblers. In the Democratic Republic of Congo, elephant poachers trundle down logging tracks; in Southeast Asia, deforestation linked to road building endangers a fifth of the region’s land-dwelling mammals. White-crowned sparrows born near roads produce more stress hormones. Black bears’ heart rates speed up when they prepare to cross. Roads even bend evolution’s arc, shortening swallows’ wings so they can better dodge 18-wheelers.

Road ecology has become an especially vital field in Brazil, where unsurpassed biodiversity is fractured by the planet’s fourth-longest road network. The Brazilian biologist Alex Bager, the inventor of a citizen-science roadkill app called Sistema Urubu—the Vulture System—has estimated that cars strike more than 400 million Brazilian animals annually. And while highway construction has slowed in most fully developed countries, Brazil is in the throes of explosive infrastructural growth. The nation has built or repaired thousands of kilometers of highway in the past decade, and its asphalt spiderweb is forecast to soon expand by 20 percent—enough, Bager has written, to “cause the (additional) loss of half a billion vertebrates annually.”

And that was before the 2018 election of Jair Bolsonaro, a far-right development fanatic who campaigned on new Amazonian highways. Bolsonaro shows every sign of making good on his promises: No sooner did he assume office than his infrastructure minister, Tarcísio Gomes de Freitas, announced the government’s intent to goose agricultural exports by signing $27 billion in private highway-construction contracts. A bill being considered by the country’s Chamber of Deputies would eliminate environmental licensing on road-maintenance projects, fast-tracking the paving of dirt highways. Freitas’s devotion to infrastructure is so fierce, it’s inspired a grandiose sobriquet: “Paver General of the Republic.”

All this shovel-rattling has conservationists on edge. In June, researchers warned that the widening of BR-101, Brazil’s longest highway, could doom the endangered golden lion tamarin, a resplendently furred monkey endemic to the country’s Atlantic Forest. Likewise in jeopardy is the maned wolf, an elegant canid that sports a black ruff and an apricot pelt. Although maned wolves are seldom killed, their low population densities and slow reproduction lend outsize significance to each casualty. Clara Grilo, a Portuguese road ecologist who spent three years in Brazil, has calculated that 20 to 30 percent of some maned-wolf populations may be run down each year.

“The expansion of roads in Brazil is important for the quality of life of the people,” Grilo told me. “The thing is, how will they do it? Is there enough legislation to protect wildlife? I’m not sure.”

Anteaters and Highways is the brainchild of Arnaud Desbiez, a fast-talking French biologist who has lived in Brazil for the past 15 years. I met Desbiez at a buffet in Campo Grande, Mato Grosso do Sul’s capital, where, over caipirinhas and feijoada, he untangled the project’s history. Desbiez, who grew up working as a keeper at a French zoo, first came to Brazil to complete his doctorate on piglike mammals called peccaries. Once in South America, he fell in love twice: first with Patricia Medici, a Brazilian tapir biologist, and then with giant armadillos—secretive, armored burrowers that grow as large as German shepherds.

“The giant armadillo is my disease; it’s my virus,” Desbiez told me, his gray beard split by a beatific smile. “Don’t get me talking about giant armadillos, because it’s going to ruin all the anteater conversation.”

In 2013, Medici and Desbiez, Brazil’s road-ecology power couple, began monitoring roadkill to determine how Mato Grosso do Sul’s highways were harming the state’s wildlife, especially armadillos. To Desbiez’s surprise, their surveys didn’t turn a single giant armadillo. What they found instead were anteaters, anteaters, and more anteaters—124 altogether, a staggering figure for a species whose global population has been estimated, albeit imprecisely, at 5,000.

“Nobody was doing anything about giant anteaters and roadkill,” Desbiez recalled incredulously. “When I looked at the [International Union for Conservation of Nature] Red List, it didn’t mention roadkill as a threat.” (It does now.) Giant armadillos and giant anteaters happen to be the two largest surviving Xenarthrans, an ancient mammalian superorder that once included rhino-size glyptodonts and elephantine ground sloths. No subject fires Desbiez up like armadillos, but a giant-anteater study would be the next best thing.

The resultant project, launched in 2017, is one of road ecology’s most comprehensive ventures. Every two weeks, its technicians tabulate roadkill of all species along more than 1,300 kilometers of Brazilian highway; since the project’s inception, Anteaters and Highways’ staff have driven far enough to circle the Earth almost twice, and counted twice as many dead animals as the Bronx Zoo houses live ones. They’ve also affixed satellite collars to 44 anteaters to study highways’ influence on movement; installed camera traps to figure out how roads affect population densities; and necropsied 59 slain anteaters, collecting everything from lymph nodes to skin parasites in order to determine whether living near highways impairs health. A social scientist, Mari Catapani, has even interviewed more than 200 truck drivers to investigate the rumor that truckers consider anteaters unlucky and flatten them on purpose. (Before you despair at human depravity, Catapani told me that the rumor is mostly false: Only one driver has copped to targeting anteaters. Snakes are another story.)

Although these multifarious studies will take a while to bear fruit, the project’s early roadkill data are alarming. Nearly 600 giant anteaters have been found dead since 2017, which is likely a severe underestimate of the total killed. Who knows how many carcasses are dragged away by scavengers before they can be counted, or how many mortally injured anteaters crawl off to die in the brush?

Giant anteaters are conspicuous animals—big, bold, and fond of loitering on treeless savannas. Their visibility creates the impression of abundance: João Jose, the amiable manager of the Santa Lourdes ranch, told me that he sees them daily. Even so, giant anteaters are in rapid decline throughout their range, and are already gone from much of Central America and parts of Brazil and Argentina. Their sluggish reproductive rates don’t help: A single anteater pup gestates for six months, then clings for another six to its mother, splayed across her back like a saddle. Kill enough precious females, Desbiez said, “and the road could really be acting as a sink.”

If Anteaters and Highways has discovered a saving grace, it’s that males fall victim to vehicles twice as often as females, perhaps because they roam more widely. While cars can apparently slow the growth of an anteater population, they can’t extinguish it altogether. But in concert with other threats—habitat loss, pesticide poisoning, the occasional slaying by a superstitious ranch hand—roadkill can produce catastrophe. “When you add other impacts, that can cause local extinction,” Desbiez said. “Roadkill is kind of the last straw.”

The morning after our grim survey of BR-262, Mario Alves took me on a happier mission. “Today,” he announced as we drove into the rising sun, “we will catch Evelyn.”

Alves first apprehended Evelyn, a giant anteater named for a Rodovias e Bandeiras donor, in August 2018 and outfitted her with a tracking collar that monitored her whereabouts for a year. Now the time had come to recapture Evelyn and find out what she’d been up to. The day was cloudless, the broad-skied Cerrado a world away from the Amazon’s jungles. We drove through endless campo sujo, or “dirty fields,” sere scrubland whose horizons were broken by gnarled trees and rust-colored termite pillars. The land’s harshness concealed abundance: The Cerrado is the most biodiverse savanna on Earth, home to 4,000 endemic plants and a third of Brazil’s flora and fauna. The most evident organisms, though, were human commodities—bone-white cattle, walls of non-native eucalyptus, and lime-green tracts of sugarcane, the latter destined to become biofuels that would power vehicles whose existence would, somewhere on the planet, justify more roads.

Alves turned onto a dirt road, then into a pasture, nudging his Mitsubishi through recalcitrant Zebu cows whose dewlaps rippled as they stepped aside. Landowners in the Cerrado are required to leave 20 percent of their parcels undeveloped (in the better-loved Amazon, they must protect up to 80 percent) and Alves beelined for an ungrazed thicket overrun by spiky caraguata plants. Tatiane Bressan Moreira, another veterinarian, unfolded an antenna to listen for our quarry’s collar, which transmitted GPS points and a radio signal. After a moment, we heard it: a faint metronomic clicking.

Zoe van Djik

Satisfied that Evelyn was nearby, Alves drew a cocktail of sedatives from a tackle box overflowing with syringes, creams, tubes, and swabs. Then he turned to me.

“What do you want to do?” he asked. “Do you want to take pictures, or do something … adventurous?”

“Adventurous,” I said.

From the truck bed, Alves extracted two long-handled dip nets, contraptions I’d last seen used to land salmon on Alaska’s Kenai River. He handed me one.

“You will help me to catch Evelyn.”

I examined the flimsy net, whose rim had begun to detach from its handle, and recalled a paper I’d read, ominously titled “Human Death Caused by a Giant Anteater (Myrmecophaga tridactyla) in Brazil.” Anteaters are docile creatures that, in captivity, are wont to give their keepers warm hugs; this homicidal individual had, in its defense, been provoked by hunting dogs. Still, the phrase severe bleeding in the left inguinal region sticks with you.

“I’m, uh, not very fast,” I said.

Alves wouldn’t let me off. “You don’t need to be fast. You must be like a hobbit. Very quiet.”

Considering that yesterday I’d strolled face-first into an air conditioner, raising such a lump on my cabeça that Alves had texted his ex-girlfriend, a physician, for a consult, I wasn’t sure why he judged me capable of Frodoish stealth. But okay. Hobbit.

“She will not attack,” Alves whispered as he snuck into the brush. “But when she’s in the net, don’t approach her.”

Minutes passed. The radio ticked. Trucks droned down the inescapable BR-262, a quarter-mile distant. I crept through the undergrowth, net raised, fearing and hoping that I’d see Evelyn’s kielbasa-like snout poking warily above the caraguata. I needn’t have worried: A crash in the bushes to starboard signified that Alves had made first contact. When I caught up with him a minute later, he was doubled over, hands on his thighs, net on the ground. And beside him, straining against the mesh, was Evelyn.

So alien are anteaters, so cobbled together from components with no real analogue in Animalia, that it was hard at first to discern where Evelyn began. I experienced her as a collection of parts: tubiform, velvety snout. Curved claws, as large and as hard as gardening tools. Fanned bustle of a tail, its hair coarse as straw. Stunning swatch of black fur, trimmed in white, that wrapped around her chest and down her flank like a racing stripe. The sight of her decaying, road-killed compatriots, I realized, had no more prepared me for her beauty than an art-history class readies you for the Louvre.

One tranquilizer injection later, Evelyn lay unconscious and ready for processing. Alves and Moreira worked with swift surety: duct-taping her formidable claws, cutting off her collar, shielding her face with a sock. Her body radiated the not entirely unpleasant smell of a horse stable in need of a thorough mucking. Unfurled and slack, her purplish tongue perfectly explained her taxonomic suborder: Vermilingua.

The next 30 minutes passed by in a blizzard of data collection. There was a heart rate to monitor, feces to gather, fur samples to clip. Had she reproduced before? Her teats said yes. Was she pregnant? Her belly, palpated, said no. Alves produced a razor and shaved one leg to collect blood from her femoral artery. (He would have preferred to tap the jugular, but anteaters, weird even beneath the skin, hide the vein under enormous salivary glands.) And this was a relatively tame workup: Were Evelyn male, they would have taken a semen sample with a device called an electro-ejaculator. “We would collect their souls if we could,” Alves deadpanned.

From a road-ecology standpoint, though, the most revealing information wasn’t stored in Evelyn’s body at all. Rather, it was in her collar, which had recorded her coordinates every 20 minutes for the past year. Although preliminary tracking suggested that Evelyn didn’t cross BR-262 during her daily peregrinations, Alves and Desbiez couldn’t be sure until they’d downloaded the data.

If collaring anteaters has revealed anything, it’s that bravery is deadly. Take Ben, an anteater captured in May 2018. Unlike the prudent Evelyn, Ben was fearless, traversing the highway every few days on his feeding rounds. When he turned up dead three months later, Alves was saddened but not surprised. The same fate befell Christoffer, the project’s most foolhardy anteater, who averaged two crossings every three days.

Yet excess timidity is, in its own way, as harmful as undue boldness. Anteaters—like mule deer and spotted salamanders, wildebeest and pocket mice—are compelled to roam: to forage, to mate, to escape competition. When traffic impedes migration, populations can splinter, each dwindling cluster marooned on an island of habitat within a developed sea. In Southern California, cougars are so isolated by insuperable freeways, they breed with their own offspring; in Montana, I-90 shatters the contiguity of the Northern Rockies’ grizzly bears. Collisions may be road ecology’s most obvious concern, but fragmentation is roadkill’s pernicious twin.

The same holds true for anteaters: In a 2018 study, Clara Grilo and others found that habitat fragmentation by roads posed a graver threat than direct mortality. Whether BR-262 is truly fracturing the Cerrado’s connectivity isn’t certain; Alves and Desbiez hope the collars will reveal the answer. But it’s clear that giant anteaters find themselves in a bind: Either cross roads and face inevitable death, like Ben, or restrict your movements to avoid them, like, perhaps, Evelyn. When she finally trotted off at the end of her ordeal, grunting in irritation, I couldn’t help but pity her—still alive, yes, but her world circumscribed by pavement.

How, then, to reduce fragmentation? The de rigueur solution is the installation of wildlife crossings, networks of underpasses and bridges that allow creatures to scamper beneath or over roadways unimpeded. First developed in France, where they’re known as passages à faune, wildlife crossings reached their apogee in Canada’s Banff National Park, where 50 miles of roadside fencing, 38 underpasses, and six overpasses have reduced roadkill by more than 80 percent and permitted more than 200,000 traversals by creatures from wolverines to boreal toads. Fueled by data from Banff and similar projects, crossings have proliferated around the planet. Today underpasses shepherd elephants beneath Kenyan highways, overpasses connect pangolins in Singapore, and bridges usher Christmas Island’s crabs from forest to beach.

Wildlife crossings have gained ground in Brazil, too. The week after visiting Bandeiras e Rodovias, I flew east to São Paulo state to meet Fernanda Abra, the director of a consultancy, ViaFauna, that helps highway managers design crossings. Abra grew up in the small city of Bauru, the daughter of parents who would rather spend Carnival fishing than partying. During a government internship in 2007, she glimpsed a page of roadkill data and instantly felt appalled. She found an article about wildlife underpasses and showed it to her boss, who agreed to incorporate them in a road-relicensing plan. During our days together, Abra proved to be a certifiable road-ecology zealot, constantly pulling over to chase tapirs away from traffic, scoop snakes off the pavement with sticks, and snip the whiskers from dead jaguarundis for DNA analysis.

“I don’t miss one opportunity to talk about roadkill,” she told me proudly. “If they call me to talk about roadkill at a baptism, I go.”

When she’s not evangelizing, Abra spends much of her time monitoring crossings to see whether animals are using them, and if not, how they might be improved. On our way to inspect one underpass, she showed me a video she’d compiled from motion-activated cameras. A parade of nocturnal trekkers—pumas, armadillos, anteaters—slunk in grayscale through a large culvert. (If she’d wanted, Abra could have shown me clips of equally wild human visitors—police chases, defecating motorists, and, needless to say, roadside sex.)

When we clambered down an embankment to the underpass, we discovered, to Abra’s frustration, that thieves had pried open a locked case and absconded with the camera. Even lacking fresh video evidence, though, the crossing seemed to be working. I stooped and followed Abra into the dim tunnel. At just five-and-a-half-feet high, the passage would have been too low for white-tailed deer, but it was just right for Brazil’s more diminutive fauna. A maze of tracks meandered over the sandy floor. “This looks like a canid, because we have the nails,” Abra said, crouched in the dirt. Cars purred faintly overhead, travelers through a harsh surface-world far from the underpass’s cavernous comforts.

Yet this underpass also serves people, and not just fans of highway-side coitus. According to São Paulo’s highway police, roadkill—or wildlife-vehicle collisions, in the bloodless verbiage of highway managers —causes 2,600 car accidents each year, nearly a fifth of which injure or kill drivers. From 2005 to 2014, 115 drivers died statewide in animal-related crashes. The most common culprits—or victims, depending on your perspective—were capybaras, giant rodents prone to blundering across highways in herds. “You don’t die when you roadkill one capybara,” Abra said. “You die when you roadkill the whole group.”

Wildlife collisions are as expensive as they are dangerous, costing São Paulo $14 million a year. Under Brazilian law, road managers can be sued for damages by drivers who suffer collisions. More than conservation, then, safety—and liability—has motivated road managers to install fences and crossings. Abra recalled showing maned-wolf roadkill statistics to one engineer. He replied that maned wolves were beautiful animals, and their deaths indeed tragic. “But when people get killed by hitting capybaras,” he added, “that’s what will make the changes.”

Capybara collisions, for all the trouble they cause, are relatively easy to prevent. The semiaquatic mammals follow predictable riverine corridors, allowing highway managers to narrowly focus their fencing efforts along a handful of perilous streams. Giant anteaters, by contrast, traipse the landscape willy-nilly, crossing highways seemingly at random rather than at reliable hot spots. Abra will soon begin analyzing Anteaters and Highways’ collar data to determine whether fences and underpasses might be applicable in Mato Grosso do Sul, but she’s not sure if a signal will emerge from the noise. Giant anteaters: vexing to the last.

One of the primary challenges of practicing road ecology is definitional: It’s hard to say where its purview ends. Name an ecological problem—suburban sprawl, poaching, unchecked wildfire—and it’s worsened by the access that roads provide. Take deforestation: Roads make harvesting timber possible, expanded logging operations require more roads, and around and around we go. That’s as true in Alaska’s Tongass National Forest, where Donald Trump’s administration is seeking to revoke roadless protections to permit new logging, as it is in the Amazon, where Bolsonaro hopes new roads will bring the region under governmental control and thwart conservation. It’s no coincidence that, even as Amazonian deforestation fell in the mid-2000s, it spiked along BR-163, a largely dirt highway that’s vital to soybean exporters—and which Bolsonaro and private agribusiness intend to pave. “The best thing you could do for the Amazon,” the Brazilian scientist Eneas Salati has said, “is to bomb all the roads.”

Often, practicing road ecology means knowing when a road shouldn’t be carved at all. Fernanda Zimmermann Teixeira, an ecologist at Brazil’s Federal University of Rio Grande do Sul, pointed out to me that no amount of eco-friendly engineering can blunt the habitat destruction that will follow the paving of certain Amazonian tracks. It occurred to me that, in a tragic twist, wildlife crossings and fences could even become a form of green-washing, a cynical tactic for laundering a harmful road’s environmental reputation. “We cannot talk only about mitigation—you have to talk about avoiding roads,” Teixeira said. “Passages won’t make any difference if we change the whole land use and burn everything.”

Yet new routes are coming, whether we’re prepared or not. The International Energy Agency has estimated that more than 15 million miles of new road lanes will be built by 2050, nearly 90 percent of them in the developing world—a trend the ecologist William Laurance calls an “infrastructure tsunami.” Many of the regions slated for massive road networks—Sumatra, Central Asia’s steppe, the Peruvian Amazon—harbor our planet’s most intact habitat.

Conservationists have staved off some especially frightening projects: A highway that would sunder the Serengeti’s wildebeest migration lies dormant, fought to a standstill by local activists. But the Hydra only sprouts new heads, forcing scientists into hard decisions. “The way I see it, many of these roads are going to be built whether we like it or not,” Rodney van der Ree, an Australian road ecologist who often consults with foreign governments, told me. He recently helped persuade officials in Myanmar (also known as Burma) to add underpasses to a highway that could disrupt the movements of leopards, tigers, and elephants. “From a biodiversity standpoint, they shouldn’t build the road at all,” van der Ree said, “but at least it’s a better outcome than it was.”

Brazil’s long-neglected savanna is among the many ecosystems in the crosshairs of development. The Cerrado, whose name means “closed,” was once judged worthless, its soils too acidic for farming. Then, in the 1970s, farmers began dosing it with lime and fertilizer; today it’s being cleared twice as fast as the Amazon. Roads have played a part, too. Take MS-040, an erstwhile dirt highway in Mato Grosso do Sul that was surfaced several years ago. “When they paved MS-040, the price of land went up and people started investing more,” Arnaud Desbiez told me. As a result, low-intensity cattle pastures, which afford decent wildlife habitat, are being supplanted by lucrative monocultures.

“Once you bring in the monocrops—soy, corn, sugarcane—that’s it for anteaters,” Desbiez lamented.

It’s easy, now that I’m back at my desk a stone’s throw from I-90, to denounce the tsunami. But of course, I eat produce trucked in from California; I rely on America’s marvel of an interstate highway system to reach family and hospitals and restaurants and airports and fishing holes. Roads are surely contributing to the Cerrado’s undoing, but the cane plantations I saw in Brazil seemed no more biologically sterile than the American Midwest’s cornfields—which, after all, were made possible by 20th-century road projects intended to “get the farmer out of the mud.” Roads pose the same queasy moral conundrum as climate change: Having profited wildly from a century of infrastructural growth, can the developed world deny other countries the benefits of connectivity?

One afternoon, Alves and I paid a visit to Flavio Gomes da Silva Filho, the transportation secretary of Aquidauana, to discuss that quandary. Aquidauana, a city of about 50,000, bridges the transition between the wet Pantanal and the dry Cerrado, and, like many ecotones, it’s rich in life. Capybaras and anacondas swim in its ponds; anteaters have been known to break into its hotels. Silva Filho struck me as a reasonable advocate for this urban nature. In his white-walled office, he flicked through cellphone photos from the city’s “Yellow Month,” a grisly campaign dedicated to driver-safety education in general and animal avoidance in particular. In one especially gnarly shot, an actor, face splattered in blood, rests his forehead against a shattered windshield—the imagined result, perhaps, of veering to avoid an anteater encountered at an unsafe speed.

Even so, Silva Filho was cautiously optimistic about new roads planned for the region, chief among them an extension that would connect Aquidauana with the Interoceanic Highway, a 1,600-mile artery through the Amazon that exacerbated deforestation practically from the moment of its completion in 2010. With Alves translating, Silva Filho told me that he hoped the road would be built with wildlife in mind, as it would cut through important habitat—but also that it would expedite travel and encourage development. Our own species grows ever more mobile and connected, others ever more isolated and trapped. The new roads, Silva Filho said, were “pretty good news for the city.”