Whether it is gorillas or young human males trying to show their bravado, you have surely heard about “chest beating”. But does it really mean what we think it does? Now we finally know. A team of international researchers have shown that chest beats reliably indicate the body size of the chest beater. Body size indicates competitive ability in gorillas. Therefore this information is likely to be crucial for rival males, as well as females in influencing mate choice.
Gorillas usually stand bipedally and rapidly beat their chests with cupped hands in rapid succession. Chest beating is a unique sound because is it not a vocalization, like frogs croaking, but rather it is a form of gestural communication that can be both heard and seen. The emanating drumming sound can be heard over one kilometer away. The presumed function of gorilla chest beats is to attract females and intimidate rival males.
Researchers recorded chest beats and used a technique called photogrammetry to non-invasively measured body size of adult male wild mountain gorillas monitored by the Dian Fossey Gorilla Fund in Volcanoes National Park, Rwanda. They found that larger males emitted chest beats with lower peak frequencies than smaller ones. In other words, chest beats conveyed information regarding the body size of the chest beater.
What this means
Body size is a key attribute in many animals as it often reflects fighting or competitive ability. Previous research by this team showed that larger males were more socially dominant and more successful in terms of reproduction than smaller males.
Rival males are likely to attend to the body size information transmitted in chest beats as it allows them to assess the competitive ability of the chest beater, this will help them decide whether to initiate, escalate or retreat in aggressive contests with them. Females on the other hand, are likely to use this information in their choice of potential mates.
Journal reference: Edward Wright, Sven Grawunder, Eric Ndayishimiye, Jordi Galbany, Shannon C. McFarlin, Tara S. Stoinski & Martha M. Robbins. Chest beats as an honest signal of body size in male mountain gorillas (Gorilla beringei beringei), Scientific Reports, 08 April 2021. Max Planck Institute for Evolutionary Anthropology. Overview