In a rainforest in Uganda, a male chimpanzee runs toward a tree, letting out loud, grating screeches. It grabs the large root and bangs its feet rhythmically against the flat wooden surface.
“If you hit [the roots] really hard, with a hand or a foot, it resonates and makes this big deep, booming sound that travels through the forest,” Catherine Hobaiter, a primatologist from the University of St. Andrews in Scotland says to BBC Inside Science’s Victoria Gill.
Scientists have known about this drumming behavior for years. But now, research published last week in Animal Behaviour suggests that each individual male has a unique drumming pattern he uses to broadcast information—such as where he is and what he’s doing—across long distances while traveling.
“We could often recognize who was drumming when we heard them; it was a fantastic way to find the different chimpanzees we were looking for,” Hobaiter, the paper’s senior author, tells the BBC. “If we could do it, we were sure they could, too.”
The research team recorded 273 long-distance communications between eight chimpanzees. They examined the acoustic structure of the animals’ drumming bouts, noting aspects like duration, number of beats, time between beats and timing of accompanying vocalizations—also called pant-hoots.
They found that the chimps drummed most frequently while traveling and when in smaller groups. Drumming produced during travel showed differences between individuals, suggesting that the sounds “might serve to recruit or maintain contact with distant group members,” write the authors.
In short, the behavior works “like chimp social media,” says lead author Vesta Eleuteri, a cognitive biologist at the University of Vienna in Austria, in a statement. “Indeed, we also found that chimpanzees drum more often when they’re alone or in small groups. This means that they drum to know where others are and decide whether to join them or not.”
Likewise, the chimps hid their signature sounds when they weren’t traveling and didn’t want to share their identity, per the study. This could be useful for avoiding confrontation from higher-ranking individuals or competitors who may approach and challenge them.
Michael Wilson, a chimpanzee researcher at the University of Minnesota who was not involved with this paper, tells the Agence France-Presse that the study's methodology was sound, but he isn’t “completely convinced” the animals’ drumming is distinctive enough to consistently differentiate between all individuals, saying further research is needed.
This new understanding could help solve a long-standing mystery: why chimps greet each other but don’t seem to say goodbye when parting, the authors say.
"The chimps might not need to say goodbye, because they're effectively able to keep in touch while they're away," Hobaiter tells the BBC. "These long-distance signals give the chimps a way to check in with one another. That might help us to understand one of these things that we thought was a real difference between chimps and humans—and help us to understand why that difference might have come about."