Chimpanzees use over 400 “words” when combining calls.

(ORDO NEWS) — Chimpanzees are howling. They squeak. They bark. And sometimes they scream, then they grunt, then they bark, and then they scream, and all this in a row.

According to a study published today in the journal Communications Biology, this series of expressions can have their own meaning, almost like a chimpanzee phrase.

During 2019 and 2020, Tatiana Bortolato, a PhD student at the Max Planck Institute for Evolutionary Anthropology in Germany, monitored and recorded 46 adult chimpanzees in Tai National Park in Ivory Coast from dawn to dusk.

After recording 900 hours of primate sounds, she and her colleagues from France and Switzerland sat down to analyze the structure of these sounds.

Biologists have known before that chimpanzees build their calls out of several separate sounds, almost like letters: grunts, hums, barks, screams and roars.

They can either spit out one sound, or “hum” them, inhaling between beats. These sounds are used to communicate in the jungle, making them especially inviting for people trying to understand chimpanzee speech.

To figure out whether primates string intentional phrases up their pants, a team of linguists needed to find out if certain sequences occur more often than they would by pure chance.

It turned out that chimpanzees especially like several combinations: good-panto-ground, good-panto-hoot, and pant-panto-creek. Sometimes they combined two separate “units” into much longer phrases – two-thirds of the primates made five-part calls. By combining letters, chimpanzees had about 400 calls in their vocabulary.

It’s possible that even more subtle building blocks were missed in the study, as chimpanzees use sounds that are superficially similar to humans but are used in a wide variety of situations. For example, it is possible that the buzz in response to the appearance of a predator has a subtly different tone from the buzz at a meeting of relatives.

Bortolato and her colleagues also did not figure out what the phrases they wrote down meant. However, it is possible that the order of the sequences matters: Certain chimpanzee sounds tended to appear at the beginning of phrases, while others were always at the end.

But even without the Siamese Rosetta Stone, the mixed and matched nature of the calls is the basis for a more complex vocal system reminiscent of language.

If a chimpanzee can only make six sounds, he won’t be a great conversationalist, even to other members of his species. (Adult English speakers typically have tens of thousands of words at their disposal.) This study shows that chimpanzees have enough vocal repertoire to convey something meaningful.

To date, chimpanzees have the most modular vocalizations of all the studied representatives of the animal world.

Some other primates such as Madagascar’s indri lemurs combine notes into couplets or three-lines. And the rock hyrax, a tiny, rat-like relative of the elephant, can change the order of sounds in its call. But chimpanzees and humans are the only ones able to simultaneously add to their playlist and shuffle it.

The next step in understanding whether chimpanzees have what we mean by “language” is to find out if they organize phrases into so-called “hierarchical structures” – the way humans organize words into sentences and sentences into phrases.

As the authors of Communications Biology note, deciphering even one call of another kind is a very laborious process. If animals speak in phrases, we simply did not have time to catch them.


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