The Prairie Dog's Implicature

Speranza

Can Prairie Dogs Talk

Can prairie dogs talk?

 

An Arizona biologist believes that their sounds should be considered language – and that someday we’ll understand what they have to say.

 

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.”

 

By the late 1990s, Slobodchikoff had transitioned from studying paper sonograms to generating computer-based statistical analyses of the frequency, duration and harmonic structure of prairie-dog vocalizations. Based on such analyses, he said that the most crucial distinctions between prairie dogs’ calls are not in length or the number of discrete chirps but rather in the amplitudes of overlapping sound waves in each call — the composite of which is essentially their tone. Slobodchikoff makes an analogy to Mandarin: The word ma can mean “horse,” “mother” or “to scold,” depending on its intonation. Whereas the tone of human speech is typically determined by a fundamental frequency and just three or four overtones layered on top, prairie dogs can have six or seven audible overtones mingling in a single call. Slobodchikoff thinks that by modifying these harmonics and combining them in different ways, prairie dogs form original descriptive phrases: dog big yellow fast; human small blue slow.

Why would a prairie dog need such specific information? “My guess is that these descriptions evolved to recognize and remember predators with different appearances and hunting strategies,” Slobodchikoff says. Coyotes, for example, have varying proportions of black, gray, white, red and yellow in their fur. “One coyote might walk into a colony relatively nonchalant,” Slobodchikoff explains. “Some will charge a prairie dog. Others lie down at a burrow, waiting for up to an hour to pounce.” Indeed, some of Slobodchikoff’s studies support the idea that prairie dogs remember individuals. In one experiment, black-tailed prairie dogs — one of the five prairie-dog species in North America — distinguished human trespassers by height and T-shirt color and further produced a signature call for a person who repeatedly fired a 12-gauge shotgun into the ground.

All this evidence, Slobodchikoff insists, elevates prairie-dog alarm calls from the level of mere “communication” into the realm of language. “Calling it communication sets up that us-versus-them divide,” he says. “I don’t think there is a gap. I think it all integrates in there. You can go to Barnes & Noble and pick up book after book that says humans are the only ones with language. That cheats our understanding of animal abilities and inhibits the breadth of our investigation. I would like to see people give animals more credence, and I think it’s happening now, slowly. But I would like to push it along a little faster.”

Slobodchikoff’s research is one of the longest and most comprehensive studies of highly complex animal communication in the wild, without training or inducement of any kind. Yet his peers disagree about the merits of his work, in part because they disagree more generally about methodology. Some scientists worry that Slobodchikoff’s studies, especially the early ones, are too small and depend too much on unreliable techniques. “The statistical approach he uses can be treacherous,” says Julia Fischer of the German Primate Center in Göttingen. “It tends to pick up patterns that might not be there. If you redo his analysis with modern techniques, I’m not sure how strong it would be.” Fischer belongs to one of two unrelated research groups that recently cast doubt on some aspects of the 1980 vervet-monkey studies: Based on a reanalysis of the original data and fresh experimentation, the two groups argue that the vervet calls are not as clear-cut as they have been viewed and that the monkeys ignore playbacks just as often as they respond to them appropriately.

Other researchers counter that Slobodchikoff’s techniques are sound and widely used and that reluctance to embrace his research owes more to prejudice than empiricism. “It seems to me that some people don’t trust Con because what he has found is outside what they are willing to accept,” says James Hare, a biologist at the University of Manitoba who studies ground squirrels. “But when you look at it all scientifically, I can’t really pick apart his methods. He presents compelling evidence of fine-grained communication about color, shape and size. I think language is a perfectly reasonable thing to call it.”

The Yale University linguist Stephen Anderson says the idea that prairie dogs have language is ludicrous. The essence of language, he argues, is not a set of symbols or phrases but rather syntax: the ability to systematically combine symbols into an infinite array of sentences. I asked him what an animal would have to do to meet the minimum requirements for language. He replied that if you showed a parrot a fruit that it had never seen before, a pineapple, for example, and it said, “My, that looks spiky, so I don’t think I want to eat it,” that might be sufficient.

Because the fundamental nature of language is so intangible, because there is no agreed-upon way to determine its existence, it is easy to continually dismiss new evidence of ostensible animal language as inadequate — intriguing, but not quite good enough. Contrast that with the firm scientific consensus that tool use is far more prevalent in the animal kingdom than previously realized: Chimpanzees fashion twigs into dipping sticks for termites and honey; sea otters store rocks in “armpit pouches,” using them to crack open seashells; and octopuses tote coconut shells to use as shields. No other animal makes Black & Decker power drills, yet we do not deny the legitimacy of their crafts. Why should language be so different?

Setting such disputes aside, Slobodchikoff’s ongoing study is lacking in one critical aspect: It is unfinished. “I have great respect for the prairie-dog work, but so far there is no evidence that the most nuanced information is meaningful to this species,” says Zuberbühler, the researcher who studied Campbell’s monkeys. Slobodchikoff’s playback experiments demonstrate that different predator-alarm calls trigger distinct escape responses, but so far he has not been able to link the acoustic variations that ostensibly encode color, shape and so on to any observable behavioral differences. Without such evidence, he cannot rule out the possibility that some of the discrepancies in the alarm calls are an inadvertent byproduct of prairie-dog physiology — an increased sensitivity to a certain color or shape invoking a more forceful rush of air through the vocal tract, for instance — and that the animals do not recognize such differences or use them to their advantage. Perhaps part of what Slobodchikoff deems prairie-dog language is just useless prattle. This is the gaping pitfall of his field: Can we ever know, definitively, that another species is saying what we think it’s saying?

In Flagstaff, Slobodchikoff and I spent some time searching for his former study sites. One had been converted into a baseball diamond, another into a cow pasture and others into parking lots and landscaped highway shoulders. At one point we drove to an alpine meadow strewn with the white discs of morning glory and bordered by ponderosa pines. Just about a month earlier, Slobodchikoff saw prairie dogs here. Now the grass was still and silent. Dozens of brown mounds rose from the ground, covered in vegetation, like village ruins reclaimed by a jungle.

When Slobodchikoff started studying prairie dogs in the late 1970s, there were about 50 healthy colonies within a 30-mile radius of his university. It was easy to repeatedly study the same colonies over long periods of time. There are just a few hamlets left in and around Flagstaff. “Something is happening to prairie dogs,” Slobodchikoff says. “They’re disappearing all over.”

Before 1800, as many as five billion prairie dogs lived throughout the Great Plains in colonies that collectively spanned more than 100 million acres. Today, by some estimates, the five prairie-dog species inhabit as little as one to two million acres total. Much like the bison, prairie dogs have declined in part because of sanctioned mass slaughter — not for their meat or fur but simply to eliminate what many people consider a pest. Ranchers have long held that cattle cannot thrive alongside prairie dogs because the two creatures compete for pasture. Studies suggest that such competition is generally negligible; it takes hundreds of prairie dogs to eat as much grass as a single cow. There is also a persistent notion that horses and cattle break their legs by tripping in prairie-dog burrows, though evidence is scant.

Around 1900, another major threat to prairie dogs arrived on the West Coast. Trade ships from Asia brought rats infested with Yersinia pestis, the bacterium that causes plague. Using fleas as an initial vector, Y. pestis didn’t just trigger an epidemic of plague in San Francisco; it escaped into the wild, eventually establishing itself in more than 76 mammal species. Prairie dogs are one of the most susceptible. Plague can wipe out an entire colony in a week, in part because they are so intimate and close-quartered.

 

Shortly before I visited, plague was detected in the alpine meadow surrounding us. Slobodchikoff explained that despite the efforts of conservation groups, such as the Prairie Dog Coalition and Habitat Harmony, very few colonies are vaccinated or shielded from hunting and mass poisoning. Prairie dogs have hardly any federal or state protections. “People see them as vermin that spread disease,” Slobodchikoff said. (In truth, prairie dogs die far too quickly from plague to be a major vector.) “Most people would be more than happy if we got rid of every single one.”

There are certain animals that we love, defend and even revere precisely because of their sentience, because they seem to possess minds similar to our own. After Jane Goodall and Dian Fossey brought the intelligence and kinship of chimpanzees and gorillas into the limelight, increasing resources were channeled into saving the great apes from habitat destruction and poaching. Following John Lilly’s research and writing on dolphin communication in the 1960s, the cetaceans gained an almost cultlike following. Most recently there has been increasing backlash against the captivity of elephants and orcas, highly communal and empathic species.

Nothing of the sort has happened for prairie dogs. If Slobodchikoff is right about their language — to say nothing of all the other undeciphered clucks, yawps and bellows on Earth — then we will have been the cause of, and the indifferent witness to, the annihilation of a species that helped transform our understanding of animal minds. To recognize that we are not alone, that we share our world with other conscious, thinking, speaking beings, requires us to sacrifice a great deal of ego. At the same time, it folds us, palpably and inextricably, into the fabric of a much grander universe. As it stands, our greatest chance of achieving such a breakthrough may not require radio telescopes or interstellar travel but rather a new appreciation for a raucous rodent in our vast grassy backyard. Assuming, that is, that we don’t lose — or invent — anything in translation.

Just as we were leaving the barren colony in Flagstaff, Slobodchikoff spotted a lone prairie dog in the distance, standing upright in the classic sentinel fashion. We fumbled for our binoculars and peered through the passenger window.

 “Can you see him?” Slobodchikoff said. I said, “Show me again where you pointed.” He did. At first, I thought it must have run off. Then I found it: Just the right shape and color but eerily angular and statuesque.

“I’m not sure that’s a prairie dog,” I told Slobodchikoff. He craned his neck to re-examine the scene. “You’re right,” he said, lowering his binoculars. “It’s a rock.”