Con Slobodchikoff and I approached the mountain meadow slowly, obliquely, softening our footfalls and conversing in whispers. It didn’t make much difference. Once we were within 50 feet of the clearing’s edge, the alarm sounded: short, shrill notes in rapid sequence, like rounds of sonic bullets.
We had just trespassed on a prairie-dog colony. A North American analogue to Africa’s meerkat, the prairie dog is trepidation incarnate. It lives in subterranean societies of neighboring burrows, surfacing to forage during the day and rarely venturing more than a few hundred feet from the center of town. The moment it detects a hawk, coyote, human or any other threat, it cries out to alert the cohort and takes appropriate evasive action. A prairie dog’s voice has about as much acoustic appeal as a chew toy. French explorers called the rodents petits chiens because they thought they sounded like incessantly yippy versions of their pets back home.
On this searing summer morning, Slobodchikoff had taken us to a tract of well-trodden wilderness on the grounds of the Museum of Northern Arizona in Flagstaff. Distressed squeaks flew from the grass, but the vegetation itself remained still; most of the prairie dogs had retreated underground. We continued along a dirt path bisecting the meadow, startling a prairie dog that was peering out of a burrow to our immediate right. It chirped at us a few times, then stared silently.
“Hello,” Slobodchikoff said, stooping a bit. A stout bald man with a scraggly white beard and wine-dark lips, Slobodchikoff speaks with a gentler and more lilting voice than you might expect. “Hi, guy. What do you think? Are we worth calling about? Hmm?”
Slobodchikoff, an emeritus professor of biology at Northern Arizona University, has been analyzing the sounds of prairie dogs for more than 30 years. Not long after he started, he learned that prairie dogs had distinct alarm calls for different predators. Around the same time, separate researchers found that a few other species had similar vocabularies of danger. What Slobodchikoff claimed to discover in the following decades, however, was extraordinary: Beyond identifying the type of predator, prairie-dog calls also specified its size, shape, color and speed; the animals could even combine the structural elements of their calls in novel ways to describe something they had never seen before. No scientist had ever put forward such a thorough guide to the native tongue of a wild species or discovered one so intricate. Prairie-dog communication is so complex, Slobodchikoff says — so expressive and rich in information — that it constitutes nothing less than language.
That would be an audacious claim to make about even the most overtly intelligent species — say, a chimpanzee or a dolphin — let alone some kind of dirt hamster with a brain that barely weighs more than a grape. The majority of linguists and animal-communication experts maintain that language is restricted to a single species: ourselves. Perhaps because it is so ostensibly entwined with thought, with consciousness and our sense of self, language is the last bastion encircling human exceptionalism. To concede that we share language with other species is to finally and fully admit that we are different from other animals only in degrees not in kind. In many people’s minds, language is the “cardinal distinction between man and animal, a sheerly dividing line as abrupt and immovable as a cliff,” as Tom Wolfe argues in his book “The Kingdom of Speech,” published last year.
Slobodchikoff thinks that dividing line is an illusion. To him, the idea that a human might have a two-way conversation with another species, even a humble prairie dog, is not a pretense; it’s an inevitability. And the notion that animals of all kinds routinely engage in sophisticated discourse with one another — that the world’s ecosystems reverberate with elaborate animal idioms just waiting to be translated — is not Doctor Dolittle-inspired nonsense; it is fact.
Like “life” and “consciousness,” “language” is one of those words whose frequent and casual use papers over an epistemological chasm: No one really knows what language is or how it originated. At the center of this conundrum is a much-pondered question about the relationship between language and cognition more generally. Namely, did the mind create language or did language create the mind? Throughout history, philosophers, linguists and scientists have argued eloquently for each possibility. Some have contended that thought and conscious experience necessarily predate language and that language evolved later, as a way to share thoughts. Others have declared that language is the very marrow of consciousness, that the latter requires the former as a foundation.
In lieu of a precise definition for language, many experts and textbooks fall back on the work of the American linguist Charles Hockett, who in the 1950s and ’60s proposed a set of more than a dozen “design features” that characterize language, like semanticity — distinct sounds and symbols with specific meanings — and displacement, the ability to speak of things outside your immediate environment. He acknowledged that numerous animal-communication systems had at least some of these features but maintained that only human language boasted them all. For those who think that language is a prerequisite for consciousness, the unavoidable conclusion is that animals possess neither.
To many biologists and neuroscientists, however, this notion smacks of anthropocentrism. There is now a consensus that numerous species, including birds and mammals, as well as octopuses and honeybees, have some degree of consciousness, that is, a subjective experience of the world — they feel, think, remember, plan and in some cases possess a sense of self. In parallel, although few scientists are as ready as Slobodchikoff to proclaim the existence of nonhuman language, the idea that many species have language-like abilities, that animal communication is vastly more sophisticated than Hockett and his peers realized, is gaining credence. “It’s increasingly obvious just how much information is encoded in animal calls,” says Holly Root-Gutteridge, a bioacoustician at the University of Sussex. “There’s now a preponderance of evidence.”
In the 1990s, inspired in part by Slobodchikoff’s studies, the primatologist Klaus Zuberbühler began investigating monkey vocalizations in the dense and cacophonous forests of the Ivory Coast in Africa. Over the years, he and his colleagues discovered that adult male Campbell’s monkeys change the meaning of their screeches by combining distinct calls in specific sequences, adding or omitting an “oo” suffix. Krak exclusively warns of a leopard, but krak-oo is a generalized alarm call; isolated pairs of booms are a “Come this way!” command, but booms preceding krak-oos denote falling tree branches. Studies of songbirds have also uncovered similar complexity in their communication. Japanese great tits, for example, tell one another to scan for danger using one string of chirps and a different set of notes to encourage others to move closer to the caller. When researchers played the warning followed by the invitation, the birds combined the commands, approaching the speaker only after cautiously surveying the area. In the South Pacific, biologists have shown that humpback-whale songs are neither random nor innate: rather, migrating pods of humpback whales learn one another’s songs, which evolve over time and spread through the ocean in waves of “cultural revolution.” And baby bottlenose dolphins develop “signature whistles” that serve as their names in a kind of roll call among kin.
With the help of human tutors, some captive animals have developed especially impressive linguistic prowess. Dolphins have learned to mimic computer-generated whistles and use them as labels for objects like hoops and balls. A bonobo known as Kanzi communicates with a touch-screen displaying hundreds of lexigrams, occasionally combining the symbols with hand gestures to form simple phrases. And over the course of a 30-year research project, an African gray parrot named Alex learned to identify seven colors, five shapes, quantities up to eight and more than 50 objects; he could correctly pick out the number of, for instance, green wooden blocks on a tray with more than a dozen objects; he routinely said “no,” “come here” and “wanna go X” to get what he desired; and on occasion he spontaneously combined words from his growing vocabulary into descriptive phrases, like “yummy bread” for cake.
Slobodchikoff’s studies on prairie dogs have long hovered on the periphery of this burgeoning field. Unknown to Slobodchikoff, around the same time that he began recording prairie-dog alarm calls in Flagstaff, Peter Marler, the renowned animal-communication expert and one of Slobodchikoff’s former professors, was working on a similar study, one that would eventually redefine the field. In the spring of 1977, Marler sent Robert Seyfarth and Dorothy Cheney — a young husband-and-wife duo of primate scientists — to Amboseli, Kenya, to study the alarm calls of small silver-haired monkeys known as vervets. Earlier research had hinted that vervet monkeys produced different vocal warnings for different predators: a kind of bark to warn of a leopard; a low-pitched staccato rraup for a martial eagle; and a high-pitched chutter for a python. Seyfarth and Cheney decided to further investigate these findings in a controlled field experiment.
The two scientists hid a loudspeaker in the bushes near different groups of vervets and played recordings of their alarm calls, documenting the monkeys’ responses. Even in the absence of actual predators, the recordings evoked the appropriate escape strategies. Leopard-alarm calls sent monkeys scampering into the trees. When they heard eagle-alarm calls, they looked up and took cover in the bushes. In response to the warning for snakes, the primates reared up on their hind legs and scanned the ground. Contrary to the consensus of the time, the researchers argued that the sounds animals made were not always involuntary expressions of physiological states, like pain, hunger or excitement. Instead, some animals systematically used sounds as symbols. In both academia and the popular press, vervet monkeys became celebrated mascots for the language-like abilities of animals.
While the vervet research won acclaim, Slobodchikoff’s remained frustratingly sidelined. Marler, Seyfarth and Cheney worked for the well-staffed and moneyed Rockefeller University in New York; Slobodchikoff conducted his studies on a shoestring budget, compiling funds from the university’s biology department, very occasional grants and his own bank account. Slobodchikoff did not collect enough data to formally present his research at a conference until 1986. And it was not until 2006 that he published a study with the same kind of playback techniques that Cheney and Seyfarth used in Kenya, which are essential to demonstrating that an animal comprehends and exploits the variation in its calls. Although many scientists attended Slobodchikoff’s talks at conferences and spoke with him about his research in private, they rarely referenced his studies when publishing their own. And despite a few news stories and nature documentaries, prairie dogs have not secured a seat in public consciousness as a cognitively interesting species.
It did not take long for Slobodchikoff to master the basic vocabulary of Flagstaff’s native prairie dogs. Prairie-dog alarm calls are the vocal equivalent of wartime telegrams: concise, abrupt, stripped to essentials. On a typical research day, Slobodchikoff and three or four graduate students or local volunteers visited one of six prairie-dog colonies they had selected for observation in and around Flagstaff. They usually arrived in the predawn hours, before the creatures emerged from their slumber, and climbed into one of the observation towers they had constructed on the colonies: stilted plywood platforms 10 feet high, covered by tarps or burlap sacks with small openings for microphones and cameras. By waiting, watching and recording, Slobodchikoff soon learned to discriminate between “Hawk!” “Human!” and so on — a talent that he says anyone can develop with practice. And when he mapped out his recordings as sonograms, he could see clear distinctions in wavelength and amplitude among the different calls.
He also discovered consistent variations in how prairie dogs use their alarm calls to evade predators. When a human appeared, the first prairie dog to spot the intruder gave a sequence of barks, which sent a majority of clan members scurrying underground. When a hawk swooped into view, one or a few prairies dogs each gave a single bark and any animal in the flight path raced back to the burrow. (Slobodchikoff suspects that, because of a hawk’s speed, there’s little time for a more complex call.) The presence of a coyote inspired a chorus of alarm calls throughout the colony as prairie dogs ran to the lips of their burrows and waited to see what the canine would do next. When confronted with a domestic dog, however, prairie dogs stood upright wherever they were, squeaking and watching, presumably because tame, leashed dogs were generally, though not always, harmless.
Something in Slobodchikoff’s data troubled him, however. There was too much variation in the acoustic structure of alarm calls, much more than would be expected if their only purpose was to distinguish between types of predator. Slobodchikoff arranged for various dogs — a husky, a golden retriever, a Dalmatian and a cocker spaniel — to wander through a prairie-dog colony one at a time. The recorded alarm calls were still highly variable, even though the intruders all belonged to the same predator class. “That led me to think, What if they are actually describing physical features?” Slobodchikoff remembers. What if, instead of barking out nouns, prairie dogs were forming something closer to descriptive phrases?
To find out, he became a participant in his own experiment. Slobodchikoff and three colleagues paraded through two prairie-dog colonies dressed in either jeans and white lab coats, or jeans and variously colored shirts: blue, gray, orange, green. The prairie dogs produced highly similar alarm calls for each person in the lab coat, except for one especially short researcher. But they chirped in very different ways for most of the different colored shirts. In a related experiment, three slender women differing in height by just a bit meandered through a prairie-dog habitat dressed identically except for the color of their T-shirts. Again the animals varied their calls. And in another study, prairie dogs changed the rate of their chirping to reflect the speed of an approaching human.
If prairie dogs had sounds for color and speed, Slobodchikoff wondered, what else could they articulate? This time, he and his colleagues designed a more elaborate test. First they built plywood silhouettes of a coyote and a skunk, as well as a plywood oval (to confront the prairie dogs with something foreign), and painted the three shapes black. Then they strung a nylon cord between a tree and an observation tower, attached the plywood figures to slotted wheels on the cord and pulled them across the colony like pieces of laundry. Despite their lack of familiarity with these props, the prairie dogs did not respond to the cutouts with a single generalized “unknown threat” call. Rather, their warnings differed depending on the attributes of the object. They unanimously produced one alarm call for the coyote silhouette; a distinct warning for the skunk; and a third, entirely novel call for the oval. And in a follow-up study, prairie dogs consistently barked in distinct ways at small and large cardboard squares strung above the colony. Instead of relying on a fixed repertory of alarm calls, they were modifying their exclamations in the moment to create something new — a hallmark of language Hockett called “productivity.”