PLoS ONE 11, e0144197 (2016)

Western lowland gorillas ‘sing’ and ‘hum’ while consuming preferred foodstuffs, report Eva Maria Luef and colleagues, who investigated the vocalizations of two free-ranging groups of Gorilla gorilla gorilla at Mondika Research Centre in the Republic of Congo. Luef et al. provide the first detailed analysis of wild gorilla vocalizations. Although other gorilla species have been found to vocalize during other activities, western lowland gorillas seem to do so only while they eat.

Over the course of the study, the two gorilla groups followed by the researchers fed on 41 different plant species and 2 insect species, producing calls while consuming 18 of the plant species and both insect species. Seeds of Gilbertiodendron dewevrei and Annonidium mannii fruits were preferred by both groups, but calls were most frequently associated with aquatic vegetation and seeds. Calls were most frequently associated with the two plant species G. dewevrei and Pteleopsis hylodendron — recordings of these ‘songs’ accompany the paper online. They also found that males more often produced calls than females, and adults called more than juveniles.

The low volume of the calls makes it unlikely that they are produced for long-distance communication or food advertising, note the authors. Instead, the vocalizations could just notify others that the individual is eating, or, as in other gorilla subspecies, to convey well-being.