On Trails (13 page)

As Huxley argued, the same pattern underlies all scientific progress; best guesses are ventured, which, over time, become better guesses. Thus a trail grows—a hunch is strengthened to a claim, a claim splits into a dialogue, a dialogue frays into a debate, a debate swells into a chorus, and a chorus rises, full, now, of clashes and echoes and weird new harmonies, with each new voice calling out:

This way . . .

This way . . .

This way . . .

CHAPTER 3

S
TRANGE CREATURES
paced the pale autumn grass. Out the left window of our Land Rover stood a trio of wildebeests. Out the right: a muscled cluster of elands. The truck slowed to a crawl. Up ahead ambled a flock of mountain goats, clotting the road. As we crept forward, a nearby giraffe craned down and peered through our windows with the slow, sleepy eyes of a courtesan.

Beside me, in the driver's seat, was Nidhi Dharithreesan, a biologist specializing in the herd behavior of large mammals. She pointed out the more obscure species—gnu, oryx, kudu, addax, waterbuck—whose names reminded me of characters in a science fiction novel. Over the months she had spent watching these animals, she had formed lovingly frank opinions about each: White rhinos are “sweet,” but zebras are “assholes.” Elephants will “tear up everything” if given the chance. Male kudus, like boys at their first school dance, are more interested in performing elaborate mating displays than in actually mating.

I had met Dharithreesan at the Swarm Lab in Newark, where
she was finishing her PhD. Alongside her insect-obsessed colleagues, her interest in swarms of giant furry beasts was somewhat unusual. However, she informed me that there was a great deal of overlap between their work and hers: Mammals, like insects, aggregate on a massive scale, share information, and create highly efficient networks of trails. If you were to step into a hot-air balloon and float high above the Serengeti during the annual great wildebeest migration, the herds of ungulates would resemble nothing so much as an invasion of safari ants.

By studying insects, I had learned that trails can function as a form of external memory and collective intelligence. Bugs benefit from trails because they are tiny and small-brained but nevertheless must manage huge, complex tasks. But why, I wondered, do we big-brained, highly individualized land mammals—the greatest class of walkers in the known universe—feel the need to trail after one another? Why not walk alone, utterly free?

It can be tough to puzzle out why other animals do what they do. Between humans and the rest of the animal kingdom lie near-­insurmountable psychic and linguistic barriers. And yet humans have always been peculiarly curious about what motivates other animals, and whether those motivations resemble our own. I have yet to find a culture on Earth that does not speculate about the interior lives of our animal brethren. And for good reason: our survival often depends on it. To understand the psychology of their prey, many indigenous hunting societies perform magical rites, including ritual trances, sacrifices, ceremonial dances, various forms of fasting, even self-mutilation. Driven by that same basic question, Western scientists perform elaborate experiments and concoct dazzlingly complex computer models. The understanding we've sought and the bonds we've formed with other animals have, over millions of years, made humans—all of us, from the gazelle hunters of the Kalahari to the cat fanciers of Tokyo—into who we are today.

Traditionally, humans have learned to empathize with other species in three distinct ways. Perhaps most commonly, we have bonded with animals by living alongside them: housing them, feeding them, breeding them, and herding them from place to place, until we attained a kind of loose symbiosis. Conversely, we have also learned about them by hunting and killing them, which produces a wholly different kind of mind-meld—the cold empathy of the predator. And most recently, we have begun studying them: cataloguing what they eat, tracking where they travel, testing how they react, and modeling how they organize themselves.

This is how I found myself sitting in a Land Rover beside Dharithreesan. I had decided to spend some time trying out each of these oldest forms of cross-species communication: watching, herding, and hunting. (Naturally, I began with the one that intimidated me least.)

In all three of these pursuits, I would learn that trails provide a helpful (if narrow) portal into the minds of other animals. Despite what we sometimes imagine, the animal world is not a rigidly compartmentalized place, like a child's coloring book, with zebras on one page, giraffes on another, and lions on the next. Animals are all intermixed, interdependent. Flocking and stalking, they follow one another across landscapes. And in those places where their most vital needs overlap, trails inevitably appear.

Human animals are not excluded from this collaborative process; the earliest humans no doubt relied on the paths of other land mammals, just as many modern roads overlay old game trails. By following in the footsteps of other animals, we have learned to intuit their intentions. Expert trackers, it is said, begin to identify themselves with their quarry; this inclination allows them to follow trails that intermittently vanish, and even to experience the same sensations the animals felt as they walked—the prick of a thorn in a paw, the soft give of warm sand under hoof—a process that is sometimes referred to as “becoming the animal.”

We may not be able to read other animals' minds, but we can read their trails. In learning to do so, we have become recognizably human: hunting animals, we sharpened our intelligence and invented some of our earliest technologies; herding animals, we reaped the reliable luxuries of milk and meat, leather and wool; harnessing animals, we tilled fields, transported goods, and built cities; and studying animals' wisdom, we have increased our own. That long, slow waltz across continents—as humans and animals clashed, meshed, and, ultimately, began to prop one another up—would in time transform us all.

PART I

Watching

A sugary rain began to sift down as Dharithreesan and I watched the animals enact the mundane chores of being alive. An addax delicately scratched an itch on his back with one long curved horn. A baby antelope wobbled beside its mother, who bent down, stuck her nose up under the calf's hind legs, and licked its rear. The calf looked over at us, blissfully unabashed.

Staring at these herds of striped and spotted ungulates, I could almost be fooled into believing that we were on a safari in some far-off veldt, if it weren't for certain discordant details: the high steel fences, the cartoonish faux-wood sign reading
AFRIKKA
, and, most jarring of all, in the distance, the swooping steel scribbles of roller coasters. In fact, we were in an enormous outdoor zoo—­reportedly “the largest drive-through safari outside of Africa”—­attached to the Six Flags Great Adventure theme park in suburban New Jersey, less than a two-hour drive down the turnpike from New York City. The safari park was introduced in 1974, alongside attractions like the world's biggest hot-air balloon and the world's
largest teepee. It now contains over twelve hundred animals from six continents, including a sizable population of African herd animals.

Dharithreesan set up a camera on a tripod on her windowsill to film the animals' movements. She began jotting notes in a field journal: date, time, temperature, weather conditions, and any notable behavior. She was in the preliminary stages of a multiyear campaign to tag the park's African ungulates with GPS-enabled collars. The data would be transmitted wirelessly to a receiving station then relayed to the Swarm Lab, where it would eventually help solve the riddle of why mammals form herds.

One of the most prominent explanations, which she hoped to test, was called the “many eyes theory.” The more eyes a herd has, this theory holds, the more likely it is to detect a predator or a new source of food. By taking turns scanning the plains, more herd members are free to graze in peace. Many African ungulates—zebras, wildebeest, gazelles, antelopes—tend to live in mixed herds, perhaps because the strengths of one species make up for the deficiencies of another. Zebras, for example, are nearsighted, but have excellent hearing, while giraffes and wildebeest have keen long-range vision. By herding together, they increase their chance of spotting (or hearing) the approach of a stalking lion.

Dharithreesan planned to test this theory by installing electronic collars on all the ungulates, which would track not only each animal's location, using GPS, but also employ gyroscopes and accelerometers to record which direction its head was pointing. Scientists have so far conducted only a few studies like this on the dynamics of mixed-­species herds. The logistics were staggering, Dharithreesan told me. “You can't really do this type of study in the wild, because there's just too much space; we don't have the resources,” she said. “And you can't quite do it in a laboratory setting, because these animals
are
huge
.” Fortunately, the owners of Six Flags Great Adventure had unwittingly built the ideal scientific testing ground.

Out in the wild, scientists often sacrifice this kind of granular data for a much broader scope. With the rise of satellite technology, humans have suddenly acquired a god's-eye view of how animals move across vast stretches of land. Previously, to track a group of animals in the wild, scientists had to tag them with radio collars and then, using jeeps equipped with special antennas, chase after the tagged animals. Now with GPS collars, researchers can tag an animal, let it roam for months, and then download the collar's data either manually or, increasingly, wirelessly. This new technology—paired with ever more detailed satellite imagery—is revealing how groups of mammals create and pass down migration routes from generation to generation. Some of the oldest of these migratory routes, like those of Canadian mountain sheep, likely stretch back tens of thousands of years.

A few years ago, an ecologist named Hattie Bartlam-Brooks attached GPS collars to a group of zebras in Botswana's Okavango Delta to track their grazing patterns. At the time, it was widely believed that the zebras never left the delta, so when a large number of the zebras disappeared from sight at the onset of the rainy season, Bartlam-Brooks assumed they had been eaten by lions. Then, six months later, the tagged zebras reappeared. When Bartlam-Brooks recovered their collars and downloaded the data, she discovered that the zebras had somehow walked halfway across the country, to feed on the sprouting grasses of the Makgadikgadi salt pan.

By reading through old hunters' and explorers' records, she learned that a large zebra migration had once existed along that same route, but it had been severed when the Botswanan government installed hundreds of miles of veterinary cordon fences in 1968. One of these fences blocked the zebras' migratory route for decades before
the government finally dismantled it in 2004. Since the fence stood for thirty-six years, and the average lifespan of a zebra is only twelve years, no living zebras could have possibly remembered making that trip. But then, I wondered, how could the zebras have known where to go?

When I spoke to Bartlam-Brooks on a long-distance call to Botswana, she quickly ruled out my first guess: there was no grassy runway—as I had imagined—that lured them across the country. Instead, they had to pass over hundreds of miles of dry Kalahari scrub. The study's coauthor, Pieter Beck, explained that migrations, by definition, involve not only long distances, but also high stakes: in a migration, there is always a considerable “energetic cost” to the journey. Every voyage is a gamble. (This may explain why not all the zebras ended up taking the trip. Even among zebras, there are bold and timid individuals.)

Because the cost of unsuccessful exploration is so high, successful migration routes are precious and hard-won. Older herd members teach the routes to their children, passing them down as a kind of traditional knowledge. But like all traditions, migratory routes are delicate. Once a route is disrupted, it rarely reemerges. What Bartlam-Brooks had apparently uncovered was a rare instance of a species reviving their ancestral lifeway.

But still I wondered:
How?
I pushed Bartlam-Brooks to venture a guess.

Her answer surprised me. She said that her hunch was that, through a series of exploratory walks, the zebras might have followed a chain of elephant trails that led them from water source to water source all the way to the salt flats.