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Wednesday, May 4, 2016

Gorilla's Hum Is a Do-Not-Disturb Sign

Written by Steve Mirsky & Daisy Yuhas

If a socially prominent gorilla is in the midst of a meal, it may hum or sing to tell others nearby that it's busy at the moment and will get back to you later.

Listen to the podcast here.

Full Transcript

This is a short edition of Science Talk, the podcast of Scientific American, for February 29, 2016. I’m Steve Mirsky.
[Rumbling sound]

Dolby Sound in a theater showing Jurassic World?
[Rumbling sound]

The engine of Fat Boy Harley-Davidson?
[Rumbling sound]

What is really is is a gorilla. A male gorilla humming in the middle of a meal.

“We know from studies on chimpanzees and bonobos that great apes produce certain vocalizations while they’re feeding, so-called food associated calls. And our study wanted to investigate whether gorillas do the same.”

Eva Luef, with the Max Planck Institute in Germany.

“Our study focused on food calls of gorillas in the Republic of Congo in the Djéké triangle. There are two habituated gorilla groups, habituated means that they are used to humans around them. Tourists come there and researchers can get as close as seven meters to the gorillas. This allowed us to record quiet vocalizations that the gorillas produced…

“So we recorded the food calls of two habituated gorillas groups, and we found that they produce two distinct vocalizations during feeding. They’re termed humming and singing. The terms have been chosen by researchers before us. Dian Fossey described the vocal repertoire of mountain gorillas, and she heard them hum and sing.”

Listen closely for an example of another gorilla producing the vocalization the researchers call singing. [Singing sound]

“But no systematic studies were ever conducted on the humming and singing, before ours. So our study is the first one that looked at which calls are used during which feeding instances in gorillas. So we recorded all foods that were eaten by the gorillas and all sounds that it produced during eating those foods. And we found that it was males, so blackbacked and silverback males were the most frequent callers.

“This is not surprising as adult males are usually the most frequent callers concerning any gorilla vocalization. And then we found that the food calls were produced when they were feeding on certain foods. So aquatic vegetation or seeds elicited a lot of food calls, and insects for instance they never called when they were eating insects like termites or ants.”

The study, by Luef and Simone Pika at the Max Planck Institute and Thomas Breuer with the Wildlife Conservation Society is in the journal PLOS ONE. [Eva Maria Luef, Thomas Breuer and Simone Pika, Food-Associated Calling in Gorillas (Gorilla g. gorilla) in the Wild]

“We believe that the food calls have a social function in gorillas. That they may signal to listeners that an individual is busy eating at the moment. Silverback males have a special role in gorilla society, and they’re the leaders of the harem group. And they are most often the ones making group decisions, so when the silverback sits and eats the others eat as well, and he gets up and starts to move and travel in the forest, and the others follow him.

“So it makes sense for the silverback to signal to his group mates that he’s still eating and then signal that he has finished eating when he stops calling. A similar function has been ascribed to chimpanzee food calls. So they have a social function as well.

“We think that great ape food calls are important to study as they can tell us about the evolutionary history of human vocal abilities. Gorillas, like any great ape, they’re closely related to humans. And what they can do with their vocal apparatus and how they use their vocalizations can tell us a lot about how this may have evolved in early humans.

“As a follow-up project to this one, we are planning to study the exact form of singing. How the gorillas compose their food songs and whether they possess a certain repertoire of song notes, which they combine in their little food songs. That would be more similar to human language because humans are able, have a certain repertoire of sounds we can make and we combine them into words and different languages. So if gorillas could do the same with their songs that would just be amazing.”

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