Although the chest-beating of male gorillas is a common behavior, its purpose still isn't entirely understood. Now, however, scientists believe it may serve as a means of acoustically indicating the size of the apes' bodies – needless to say, bigger is better.
The findings are based on a recently published study, in which scientists from Germany and the US observed 25 wild male mountain gorillas in Rwanda's Volcanoes National Park. The observation period lasted from January of 2014 to July of 2016.
Not only were the sounds of the animals' chest beats recorded, but the size of their bodies was also non-invasively measured via a technique known as photogrammetry. It was found that the larger the individual, the lower the audio frequencies were in its chest beats. This could be due to the size of air sacs located near the apes' larynx – these are of course larger in larger gorillas, so they produce a deeper sound.
The scientists now theorize that by scrutinizing the acoustics of one gorilla's chest beats, other male gorillas can decide if it's worth trying to challenge that individual for social dominance, while females can decide if he would make a good, robust mate.
It was also noted that the number of beats per chest-beating session – and the duration of those sessions – varied significantly between individual gorillas. Such unique patterns may serve as a sort of personal signature, allowing male gorillas to announce their presence and identify one another from a distance.
The study involved scientists from Germany's Max Planck Institute for Evolutionary Anthropology, the US-based Dian Fossey Gorilla Fund International, and The George Washington University in Washington, DC. It is described in a paper that was recently published in the journal Scientific Reports.
Source: Max Planck Institute