Primate Rescue Center

Monkey Creates 6-Word ‘Language’

Erika Fleury April 28, 2015

Male species of a West African monkey communicate using at least these six main sounds: boom-boom, krak, krak-oo, hok, hok-oo and wak-oo.

Key to the communication by the male Campbell's monkey is the suffix "oo," according to a new study, which is published in the latest issue of the Proceedings of the Royal Society B.

By adding that sound to the end of their calls, the male monkeys have created a surprisingly rich "vocabulary" that males and females of their own kind, as well as a related species of monkey, understand.

The study confirms prior suspected translations of the calls. For example, "krak" means leopard, while "krak-oo" refers to other non-leopard threats, such as falling branches. "Boom-boom-krak-oo" can roughly translate to, "Watch out for that falling tree branch."

"Several aspects of communication in Campbell's monkeys allow us to draw parallels with human language," lead author Camille Coye, a researcher at the University of St. Andrews, told Discovery News.

For the study, she and her team broadcast actual and artificially modified male Campbell's monkey calls to 42 male and female members of a related species: Diana monkeys. The latter's vocal responses showed that they understood the calls and replied in predicted ways.

They freaked out after hearing "krak," for example, and remained on alert as they do after seeing a leopard.

In addition to "krak," other root calls are the "boom," as well as hok (crowned eagle) and wak, with a meaning that hasn't yet been confirmed. These are root "words" that the monkeys vary with the "oo" suffix. "Hok" by itself, for example, refers to the bird of prey, but "boom boom hok-oo hok-oo" appears to signify claiming of territory.

While the researchers are still reserving the word "language" and related terms for humans, they have identified five ways in which Campbell's monkey calls are similar to our way of communicating.

Campbell's monkey, image courtesy Camille Coye / Discovery News

First, it's now known that these monkeys engage in conversations. "The call exchanges between individuals follow a conversational rule," Coye explained. "An individual gives a call and then, after a short silence of less than one second, another answers, just as we do when discussing with others."

Secondly, there is evidence for "vocal convergence," or development of something akin to accents and other connected ways of expression among monkeys that have strong relationships with each other.

Further, the monkey calls have distinct meanings, and suffixes are added to change those meanings. Finally, the calls include what's known as "proto-syntax," meaning that the order of the calls and suffixes is significant. For example, "oo-krak" would be just as puzzling to a monkey as "ed-educate" would be to people who might have meant to say "educated."

In a separate study led by researcher Karim Ouattara, who also was a co-author of the new paper, the scientists concluded that "the Campbell's monkey call system may be the most complex example of proto-syntax in animal communication known to date."

Aside from learning more about our fellow primates, Coye said that the goal of this and similar studies "is to understand which abilities existed before language, abilities which may have been the ground of language evolution."

Both Ouattara and Coye are quick to point out, however, that Campbell's monkeys have very limited control over their vocalizations when compared to humans. This is due to anatomical differences, such as the monkey's less mobile tongues and lips, reduced airflow control, and larynxes that are positioned much higher in the trachea, limiting possible motion.

So far, most research on Campbell's monkey communication has focused on male alarm calls. These monkeys live in harems, with males spending much of their time alone while females literally hang out together. The females have their own alarm calls and at least eight social calls, which the researchers are analyzing now.

- Discovery

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