Marmoset monkeys listen and understand conversations between other marmosets

People are constantly observing and evaluating interactions by third parties to decide with whom they want to communicate in the future. But it is difficult to measure what information animals get when they eavesdrop on vocal interactions between specifications: if they understand such conversations, they do not necessarily display behavioral expressions that can be easily observed. To overcome this obstacle, anthropologists from the University of Zurich compiled a study combining call simulations, thermography methods and behavioral preferences.

Using thermal imaging, the researchers were able to non-invasively measure temperature changes in the faces of marmoset monkeys to quantify subtle emotional responses. “We were able to use this technique to show that the marmosets did not view the vocal interactions between specifications as the mere sum of the single call elements, but rather holistically experienced it as a conversation,” says first author Rahel Brügger, Ph.D. . candidate in the Department of Anthropology of the University of Zurich.

Distinction between dialogues and monologues

An animal experiencing an increase in emotional arousal will show a decrease in facial surface temperature, especially in the most exposed regions, namely in the nose. Measurement of the emitted infrared radiation by means of thermography makes it possible to record these changes. For their study, the researchers used playback of vocal exchanges between marmosets as well as calls from individual animals that were not involved in an interaction. They play the corresponding playback from a hidden speaker and use thermography to measure the monkeys’ reactions to the different simulations. “It showed that the response to call interactions was significantly different from the response to individual calls,” Brügger said. “Marmoset monkeys can therefore distinguish a dialogue between persons from a pure monologue.”

Preference for employees

In the simulations, the researchers also distinguished between collaborative and competitive interactions. After the monkeys heard the different interactions, they were given the opportunity to approach the sources of the sounds. The researchers noted that the marmosets prefer to approach the simulated specifications that were involved in a collaborative interaction with a third party.

This preference fits in with the social system and the natural behavior of these small Brazilian new world monkeys who are cooperative breeders and depend on the cooperation of their group members. “This study contributes to the growing evidence that many animals are not only passive observers of interactions with third parties, but that they also interpret them,” concludes the latest author and professor of anthropology at UZH, Judith Burkart. “In addition, our study shows that thermography can help reveal how these social interactions are perceived by nonverbal subjects.”