Wild gorillas often "sing" or "hum" while eating, presumably as a sign that the food is tasty.  In human language, such calls may translate to "mmmm" or "yummy." This behavior, researchers say, is most common among adult male gorillas.

In the latest study from the Max Planck Institute for Ornithology and the Wildlife Conservation Society, researchers tracked two wild western lowland gorilla populations in the Republic of Congo. They then recorded and analyzed the singing and humming calls that gorillas of different ages and sexes made when consuming various foods. 

Overall, researchers found adult males make such eating sounds much more frequently than females, and the type of food greatly influenced their calls, too. For instance, aquatic vegetation, flowers, and seeds led to a high likelihood of call production, while eating insects yielded the lowest probability and rate of calling.

Males, including the dominant silverbacks, tend to vocalize more frequently, as females and younger individuals are generally at a higher risk of predation and thus behave more quietly, according to a news release. 

While the calls are not loud enough to be a "dinner bell," or rather a "food advertisement signal," researchers suggest they could "represent a form of collective decision-making in the feeding context and allow group members to coordinate their feeding activities."

Previous studies have observed similar social behaviors in birds and mammals, including chimps and bonobos. 

"Similar to the function of food-calls in chimpanzees, gorillas may call to let their group mates know when it is time to finish eating," Dr. Eva Maria Luef, one of the study researchers, explained in the release. "Silverback males may have to call more frequently since they are often the ones initiating changes in group activity."

Researchers note their findings, recently published in the journal PLOS ONE, require further study to determine the full communication abilities of gorillas and how they may have contributed to the evolution of vocalizations among other primates -- including humans, who can often be caught singing to themselves when content. 

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