Monkey calls are more sophisticated than commonly believed

A new linguistic research has revealed that the same species of monkeys located in separate geographic regions use their alarm calls differently to warn of approaching predators

Lead author Philippe Schlenker said that their findings show that Campbell's monkeys have a distinction between roots and suffixes, and that their combination allows the monkeys to describe both the nature of a threat and its degree of danger.

The combined team of linguists and primatologists at New York University analyzed alarm calls of Campbell's monkeys on two sites, the Tai forest in Ivory Coast and Tiwai Island in Sierra Leone, and notably, monkey predators on the two sites differ: the primates are threatened by eagles on Tiwai Island and by eagles and leopards in the Tai Forest.

Using transcriptions of these monkey calls gathered in field experiments involving playbacks of predator calls (e.g. eagle shrieks and leopard growls), the researchers found greater complexity in expression than previously understood as well as differences in alarm calls between the two locations.

Confirming with linguistic means some hypotheses initially made by primatologists, their analysis showed that these calls make a distinction between roots (especially "hok" and "krak") and suffixes (-oo), and that their combination allows the monkeys to describe both the nature of a threat and its degree of danger.

For instance, "hok" warns of serious aerial threats, usually eagles, whereas "hok-oo" can be used for a variety of general aerial disturbances; in effect the suffix -oo serves as a kind of attenuator.

Moreover, their results suggest that the calls are not used in the same way in the Tai Forest and on Tiwai Island, for instance, "krak" usually functions as a leopard alarm call in Tai, but as a general alarm call to warn of all sorts of disturbances, including eagles on Tiwai.

In the long term, Schlenker observes, the research should help initiate the development of a form of "primate linguistics," the application of sophisticated methods from contemporary formal linguistics to systems of animal communication.

The study is published in the journal Linguistics and Philosophy.