Gorillas’ chest beats may reveal how big they are

The chest-beating of mountain gorillas could be designed to indicate size and help in assessing the fighting ability of rivals, experts believe.

Researchers found that audio frequencies of the chest beats made by larger adult silverback gorilla males were “significantly lower” than those made by smaller males.

The experts from Germany observed and recorded 25 wild gorillas at Volcanoes National Park in Rwanda and were able to calculate the body size of each gorilla by measuring the distance between their shoulder blades.

Audio recordings enabled the authors to measure the duration, number and audio frequencies of 36 chest beats made by six male gorillas.They found that the chest beats of larger males had lower peak frequencies than smaller ones.

The researchers believe that larger males may have bigger air sacs near their voice box, which may be lowering the frequencies of sound they produce while chest beating.

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Edward Wright, the first author of the study from the Max Planck Institute for Evolutionary Anthropology in Leipzig, said: “The gorilla chest beat is one of those iconic sounds from the animal kingdom, so it is great that we have been able to show that body size is encoded in these spectacular displays.”

They also believe that chest beating may also help in assessing the fighting ability of rivals. They said that female gorillas are likely to use the information to find potential mates.

Additionally, researchers observed variations in the duration and number of chest beats made by different gorillas and they were not related to body size.

The team believes these variations may allow individual gorillas to be identified across the thick forests where it can be difficult for them to see one another.

Mr Wright said: “This hints at the possibility that chest beats may have individual signatures, but further study is needed to test this.”

Additional reporting by PA