Do you remember being taught not to speak with your mouth full? Well this would have been bad advice for a gorilla.
Recent research has shown that gorillas utter a range of distinctive sounds when feeding, and that these flexible food-associated vocalisations could be a mechanism for controlling the activities of a gorilla group. They may even offer insights into the evolution of human language.
Eva Maria Luef and Simone Pika from the Max Planck Institute for Ornithology in Germany, teamed up with Thomas Breuer from the Wildlife Conservation Society in New York to study two free-ranging groups of habituated western lowland gorillas (Gorilla g. gorilla) in the Mondika Research Centre in the Republic of Congo.
By analysing caller identities, vocalisation patterns and the behavioural contexts in which they occurred, the researchers discovered that these distinctive sounds were usually made by an individual male.
Furthermore, they were associated with particular types of food, and only occurred when the gorillas were actually in the process of eating.
Previous studies on chimpanzees and bonobos have shown that those primates also use a distinctive set of food-associated vocalisations, and that they sometimes use them to advertise the discovery of food to other members of the group.
But the feeding sounds of gorillas are too quiet to travel very far, and are only made when the group is already busy tucking in. So for gorillas, the sounds must serve a different function.
The researchers suspect they could be a way for the senior gorillas to inform the rest of the group that it is time to feed—as a kind of group coordination strategy. When the sounds stop, the group knows that they are about to move off and do something else.
“Food-associated calling could represent a form of collective decision-making in the feeding context and allow group members to coordinate their feeding activities,” the researchers explain in an article published in PLoS ONE. “It seems that, while many other primates use their food-associated calls to alert others, gorillas and chimpanzees may use theirs to inform the other members of the fact that they are in the process of feeding.”
Clues to human language
Ultimately, insights into the development of food-associated vocalisation within the primate lineage may have something to teach us about the origins of human language. This repertoire of feeding sounds seems to be used more flexibly by primates than other more rigid patterns of vocalisation, and it might therefore be shaped through learning.
If so, this could point to a channel for evolutionary change—a mechanism that might have made the development of more complex language possible in ancestral humans.