Macaques take turns while chattering

When polite people talk, they take turns speaking and adjust the timing of their responses on the fly. So do wild macaques, a team of Japanese ethologists reports.

Analysis of 20-minute vocal exchanges involving 15 adult female Japanese macaques (Macaca fuscata) revealed that the monkeys altered their conversational pauses depending on how quickly others answered, the researchers report in a study in an upcoming issue of Current Zoology.

It’s unclear whether the monkeys were actually talking in any way analogous to how humans converse. While macaques have the vocal equipment to form humanlike words, their brains are unable to transform that vocal potential into human talk (SN Online: 12/19/16). The primates instead communicate in grunts, coos and other similar sounds.

But the length of pauses between those grunts and coos closely match the length of pauses in human chats, says coauthor Noriko Katsu of the University of Tokyo.

The researchers analyzed 64 vocal exchanges, called bouts, between at least two monkeys that were recorded between April and October 2012 at the Iwatayama Monkey Park in Kyoto, Japan. The team found that the median length of time between the end of one monkey’s calls and the beginning of another’s was 250 milliseconds — similar to the average 200 milliseconds in conversational pause time between humans. That makes the macaques’ gaps between turns in chattering one of the shortest call-and-response pauses yet measured in nonhuman primates.

The quick response time suggests the macaques are not calling out in habit, but are taking turns and coordinating their vocalizations, says Isaac David Schamberg, a primatologist at Harvard University who was not involved in the study.

“Monkey vocalizations are not static and automatic; they’re dynamic and conversational,” Schamberg says. Vocal pauses were also reported in marmosets in a 2013 study published in Current Biology, but with much longer gaps averaging three to five seconds.

The new study highlights an “area in which monkey vocalizations, studied in their social context, function in some ways like human speech,” says Robert Seyfarth, a primatologist at the University of Pennsylvania who wasn’t involved in the study. Understanding primates’ vocal patterns could help reveal “the conditions under which language might have evolved from the prelinguistic communication of our ancestors.”