The Human Evolution Blog

(A longer discussion of Animal Vocabulary can be found in my book.)

Who would have thought that Prairie Dogs, seen by many as nothing but hole-digging nuisances, would have a rich vocabulary? Professor Con Slobodchikoff has spent nearly 30 years studying these small rodents and he spoke with me about the many things his research group has discovered.

Professor Slobodchikoff didn’t set out to work with Prairie Dogs at all. He set up his research lab at Northern Arizona University studying a small flightless beetle that sprays noxious chemicals on would-be predators. Suddenly, Slobodchikoff developed a severe allergy to those secretions. This forced him to halt his work and seek other research subjects for his budding career, a risky move for a junior faculty member on the tenure track.

“My entire research career was going down the drain!” says Slobodchikoff.

As he pondered his next move, he looked out the window in rural Arizona and saw some prairie dogs scurrying about.

Slobodchikoff began with the prairie dogs by studying what he knew best: predator-prey relationships. It wasn’t long before he noticed what others had already documented: prairie dogs warn each other when they see a predator. He observed prairie dogs make chirping sounds when they spotted a predator and how other dogs then responded by taking cover in their burrows, responding to the calls that others had made, rather than because they had seen the predator themselves.

He also noticed that the behaviors of the prairie dogs did not always follow the same pattern. He noticed that when a prairie dog sounds the alarm when she spots a hawk, the other dogs respond by running to their burrow holes and diving deep down inside the tunnels immediately. However, when a prairie dog spots a coyote and makes a call, the other dogs run to the entrance of the burrow, but do not dive down. Instead, they stand at the entrance and look around. The question he asked was, “How did the dogs know which predator was threatening when the look out gave the signal?”

To answer this, he and his team watched the prairie dogs and, every time a predator appeared in the field, they took audio recordings of the sounds the prairie dogs made. They then took the recordings back to the lab, converted them to sonograms, and analyzed them statistically. They found that the prairie dogs make a different alarm sound for different kinds of predators!

To test their hypothesis, Slobodchikoff’s team performed “playback experiments” in which they set up loudspeakers, played recorded calls, and observed if the listening prairie dogs responded appropriately. (I have previously written about this clever kind of experiment as it was performed by Dorothy Cheney and Robert Seyfarth with vervet monkeys. Plenty of others have, also.

Slobodchikoff’s team has documented distinct calls for four different threats: coyote, hawk, domestic dog, and humans. Importantly, each discovery they made was tested vigorously using sophisticated statistical tests and large sample sizes. In fact, Dr. Slobodchikoff told me that his work is often held to a higher standard than other articles in the same journals because of intense and apparently unfounded skepticism of his results. Simply put, many in the scientific community are hostile to the notion that animals are sophisticated. I asked Dr. Slobodchikoff if humans could discriminate these various alarm calls.

“Yes, it’s actually fairly easy, and I’ve been able to train others to tell apart the various calls.”

Here is a nice video of a prairie dog making a chirp:

Dr. Slobodchikoff also told me that they have evidence that the prairie dogs also have specific calls for cats and badgers, as well as non-predator cows and pronghorn antelope. These results have not been published yet because they are still gathering data until they reach those large sample sizes that the journals require of his work.

“This animal language business is very dicey as far as many scientists are concerned,” says Slobodchikoff.

That there are calls for non-threatening animals, such as antelopes, calls into question whether these are really predator alarm calls, per se. The calls of prairie dogs could just be informative referential communication. The presence of antelope, for example, is useful information to share with the pack. Antelopes are a sign of safe conditions, since antelopes and prairie dogs are preyed upon by some of the same predators.

There’s more. Slobodchikoff and his students also noticed that the calls for different individual animals, say, coyotes, were not always exactly the same. Some differences appeared consistent, meaning that the prairie dogs would “call” a particular human by a specific version of the human-call each and every time that they would see him or her, and that this call was unique and easily distinguishable (using the sonograms) from the calls for other humans. It was almost as if each individual was given a “name,” a specific call that identified them uniquely.

It turns out that what was actually happening was that the the prairie dogs were encoding descriptive information about the animal they are referring to. For example, they don’t just shout, “Hey, there’s a dog over here!” They say, “Hey, there is a BIG dog over here.” Some of the descriptors that they have documented include colors and size. Slobodchikoff is sure that there is more they have yet to decipher.

Again, his work is held to very high standards by the community, requiring his team to perform elaborate experiments in which humans approach wearing shirts of different colors and so on. It strikes me that the demands of his skeptics have actually done him, and all of us, a favor: his discoveries are conducted with such intense experimental and statistical rigor that the conclusions are pretty much beyond any reasonable doubt.

Another descriptor that prairie dogs can use is that of the speed of approach of an animal. For example, if a coyote is merely walking nearby, that is a very different threat level than a coyote that is running in hot pursuit of its next meal. Accordingly, the prairie dogs can signal this with alterations in how they make the coyote call. If the chirps are expressed in increasing frequency (tone) and rate, the coyote is running. If the chirps slow down, the coyote is merely walking nearby. This element of tonality in prairie dog calls is reminiscent of some Asian and Native American languages, such as Mandarin, that incorporate tone as important aspects of pronunciation.

Some of the other prairie dog “words” are perplexing. Slobodchikoff’s team displayed cardboard cutouts of squares, triangles, and circles. Sure enough, the dogs produced distinct calls for each which were further modified with descriptors for the color and overall size of the cutouts. There is no way to know if the dogs already had words for these shapes or if they were invented de novo. Either way, the clear theme is that vocal-auditory communication in prairie dogs appears more and more complex the more that it is studied.

Dr. Slobodchikoff told me a particularly fascinating story that demonstrates this complexity. One of his research assistants approached the prairie dogs wearing a blue shirt. As always, the dogs alerted each other to his presence and general appearance. This call became the “name” for this individual, something like “tall blue human,” and it was used each time he was spotted. Then, the research assistant approached with a gun and fired it in the air. (Prairie dogs are frequently the victims of human shooters who consider them a pest.)

In response, the prairie dogs altered the “name” they had given this person. The new name presumably encoded the danger he posed because the prairie dogs reacted to the individual as they would a strong threat. However, the prior descriptors were still present in the new name, including that of the blue shirt. Apparently, his name went from “blue human” to “dangerous blue human,” or something along those lines, and it stayed that way long after he put down the gun. “When that person appeared, [he] was subsequently labeled with that particular sound element, even though he never [again] had a gun through the course of the experiment, which was about a month,” says Slobodchikoff.

Another interesting anecdote: Slobodchikoff’s team once observed two prairie dogs fighting. In the midst of the battle, the combatant that was increasingly on the losing end suddenly started making the coyote alarm call. This sent his opponent scurrying to his burrow. There was no coyote. It was a false alarm call, a dishonest distraction perpetrated as an act of desperation by a prairie dog badly losing a fight. Deception, calculation, diversion: we are way beyond simple predator alarm calls.

As if all this linguistic complexity wasn’t dramatic enough, there is one more twist on the language of prairie dogs: there are regional dialects. Slobodchikoff’s team has done most of their work on one community of prairie dogs, but of course they eventually expanded their horizons to see if other communities used the same sounds in the same ways. They found that they did, but they also found regional differences.

The regional differences held up to statistical scrutiny, meaning that they weren’t just noise in the analysis, but consistent “dialects” of the prairie dog vernacular. Convincingly proving this point, the researchers found that the degree of difference between the various communities was directly proportional to their distance from one another. This is a perfect analogy for human language dialects. Take, for example, the various English accents on the island of Britain: as a general rule, geographic distance is proportional to linguistic variance.

Prairie dogs speak with nouns, adjectives, and adverbs, and they do so creatively, precisely, and with regional accents. They communicate with each other to communicate danger, safety, and even to deceive. Sure sounds like language to me.

To learn more, read Dr. Slobodchikoff’s book on animal communication.

     -NHL