What do humans, dolphins, elephants and marmosets have in common? The answer has just been given in the journal Science. An Israeli team reports that, in small South American monkeys, each individual has a vocal "label" used by fellow monkeys to address it, a property previously reserved only for the other three mammals.
David Omer's laboratory at the Hebrew University of Jerusalem recorded exchanges between captive individuals, with or without the possibility of seeing each other. They then used artificial intelligence methods to analyze these vocalizations, in particular the little cries known as "phee calls." They found that by these calls alone, it was possible to detect who an individual was addressing; that two related marmosets used the same call to address a third; and that, conversely, a monkey responded more to a fellow monkey using its "name." The Israeli researchers now intend to study other monkey species in greater detail using these new methods.
The study didn't stop there. It highlighted the social nature of learning this language: monkeys learn the rudiments from their parents. The scientists also observed that individuals engage in dialogue, or at least take turns expressing themselves – a rare skill in animals. The Israeli researchers were unable to "crack" the code used by the monkeys. It is not yet known what encodes the identity of an interlocutor in phee calls (duration, pitch, intensity...). But the article was nevertheless judged "very convincing" by Emmanuel Chemla, linguist and director of research at CNRS (École normale supérieure Ulm), a specialist in animal language, who was not involved in the study.
The French researcher pointed out, however, that while the overall results could be perfectly explained by the presence of a name in the vocalizations, other "slightly different" reasons could also contribute to the results observed. "For example, if a marmoset is particularly agitated, everyone might address it, trying to calm it down," he explained. "If an individual is dominant, everyone will speak to it with respect, and so on. This can be detected by the intonation taken, but it doesn't mean a name has been spoken."
The Israeli researchers do not use the term "name" in their article. But they do believe they have identified an "individual sound label," far removed from the single positioning call previously attributed to phee calls. This peculiarity may have arisen in marmosets because of their particular way of life: small communities in particularly dense canopies.
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