The common marmoset is a certified chatterbox. The small, South American monkey uses an array of chirps, whistles and trills to defend its territory, flag the discovery of food, warn of impending danger and find family members hidden by dense forest foliage.
Marmosets also use distinct calls to address different individuals, in much the same way that people use names, new research suggests. The findings make them the first nonhuman primates known to use name-like vocal labels for individuals.
Until this year, only humans, dolphins and parrots were known to use names when communicating. In June, however, scientists reported that African elephants appeared to use names, too; researchers made the discovery by using artificial intelligence-powered software to detect subtle patterns in the elephants’ low-pitched rumbles.
In the new study, which was published in Science last month, a different team of researchers also used A.I. to uncover name-like labels hiding in the calls of common marmosets. The discovery, which is part of a burgeoning scientific effort to use sophisticated computational tools to decode animal communication, could help shed light on the origins of language. And it raises the possibility that name-bestowing behavior may be more widespread in the animal kingdom than scientists once assumed.
“I think what it’s telling us is that it’s likely that animals actually have names for each other a lot more than maybe we ever conceived,” said George Wittemyer, a conservation biologist at Colorado State University who led the recent elephant study but was not involved in the marmoset research. “We just never were really looking properly.”
Marmosets are highly social, forming long-term bonds with their mates and raising their offspring cooperatively in small family groups. They produce high-pitched, whistle-like “phee calls” to communicate with other marmosets who might be hidden among the treetops. “They start to exchange phee calls when they lose eyesight of each other,” said David Omer, a neuroscientist at the Hebrew University of Jerusalem who led the new study.
Scientists have previously shown that these phee calls contain information about the identity of the monkey making the call, theorizing that the sounds can help the monkeys find one another in the forest.
For the new paper, scientists studied 10 captive marmosets from three family groups, analyzing the phee calls between different pairs of monkeys. Two monkeys at a time were brought to a study room and placed in separate enclosures. The marmosets were allowed to see their conversational partners briefly before a curtain was placed between them.
The researchers recorded the phee calls the marmosets made after the curtain came down, ultimately amassing a database of nearly 54,000 calls. They then fed the calls into a machine learning system, which was able to detect differences between the calls directed at individual monkeys. Based on acoustic features alone, the system was able to predict which monkey a particular call had been addressed to. “It was way above chance, which means that the information was there about the receiver identity,” Dr. Omer said.
And when the scientists played the recorded calls back to the animals, they found that marmosets were more likely to respond to calls containing their “names” than they were to calls without them. “Monkeys can actually perceive this information and respond correctly,” Dr. Omer said.
But those results led to a new question: Had each marmoset devised its own unique names for its compatriots? Or had all the monkeys somehow converged on the same name for each individual?
The answer, the researchers found, was somewhere in between. Marmosets in the same social or family group tended to use similar names to address any given marmoset, but there were differences in the names used by each group. The results suggest that the marmosets learn names from others in their groups. (Two of the three groups in the study were composed of monkeys that were not biologically related, so genetics cannot fully explain the differences, the researchers noted.)
Dr. Wittemyer said that he was stunned by the findings, noting that marmosets are “kind of a run-of-the-mill primate in terms of cognitive ability.” But the results are “really convincing,” he added.
So far, all of the animals known to use names are highly social, group-living creatures. It may be those traits that help give rise to naming behavior.
When it comes to marmosets, “individual relationships are really fundamental to who they are,” Dr. Wittemyer said. “It makes sense in this context that names could be really useful.”
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