Gorillas in the wild frequently 'sing' and 'hum' during feeding and adult males call more than their younger or female counterparts, according to a study published February 24th, 2016 in the open-access journal PLOS ONE by Eva Maria Luef and Simone Pika at the Humboldt Research Group at the Max Planck Institute for Ornithology, Germany, and their colleague Thomas Breuer from the Wildlife Conservation Society in New York.
Many mammals and birds vocalize when finding or consuming certain foods. The phenomenon had been studied in chimps and bonobos, but only anecdotal evidence previously existed for gorillas. The authors of this study tracked two wild western lowland gorilla populations in the Republic of Congo, recording and analyzing the 'singing' and 'humming' calls that gorillas of different ages and sexes produced in response to various foods.
They found that adult male gorillas, including the dominant silverbacks, called the most. Females and juveniles were quieter, perhaps to reduce these vulnerable individuals' risk of predation. The researchers only observed 'singing' and humming' calls in association with food, especially while eating aquatic vegetation, flowers, and seeds. The authors suggest that this food-associated calling may be a means of expressing well-being. They also propose that it could aid group coordination and social cohesion. "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", said Dr. Luef. "Silverback males may have to call more frequently since they are often the ones initiating changes in group activity", she further explained.
The researchers only assessed 20 gorillas in the two groups, and did not analyze 'singing' and 'humming' calls separately in relation to specific foods. Nonetheless, they note that their findings provide new insight into the vocal abilities of gorillas and may provide new opportunities to investigate the development of vocal communication.
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Luef EM, Breuer T, Pika S (2016) Food-Associated Calling in Gorillas (Gorilla g. gorilla) in the Wild. PLoS ONE 11(2): e0144197. DOI: 10.1371/journal.pone.0144197