Why Do Male Gorillas Beat Their Chests?

They're communicating key information to rival males and potential mates.

silverback gorilla beating chest
Silverback gorilla beating his chest.

Dian Fossey Gorilla Fund

Male gorillas convey a lot of information when they beat their chests, a new study finds.

Gorillas usually stand on both feet and beat rapidly on their chests with their hands cupped. It was long presumed they were doing this to intimidate rival males while attracting females.

“Gorillas use chest beats to communicate with one another. For a long while, we speculated that this impressive signal conveys information about competitive ability, but we were not sure,” study first author Edward Wright from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, tells Treehugger.

Calling the chest beat of gorillas “among the most emblematic sounds in the animal kingdom,” researchers set out to analyze exactly what type of information those motions and noises communicate. They published their findings in the journal Scientific Reports.

The researchers collected information on 25 wild, adult male silverback gorillas from 10 social groups in Volcanoes National Park in Rwanda. The gorillas — all were being monitored by the Dian Fossey Gorilla Fund — were all accustomed to human observers. The study took place between January 2014 and July 2016.

“First, we measured their body size, which is not an easy feat," says Wright. "You cannot go up to a wild gorilla with a measuring tape."

He adds: “We used a non-invasive technique called the parallel laser method, which involves projecting two parallel lasers separated by a known distance onto the gorillas and taking a photograph (at a minimum distance of seven meters). The distance between the lasers is then used as a scale to measure several body parts of interest.”

Then, they recorded chest beats using a directional microphone and recorder.

“This was particularly challenging as gorillas do not chest beat very often (around once every five hours) and you need to be at the right place at the right time,” Wright says.

What Chest Beats Communicate

The researchers captured a total of 36 chest beat sound recordings from six different males. They focused on aggressive displays involving chest beats that were directed at members of the same species. They used this data to calculate a chest beat rate for each male gorilla.

“We were able to show that mountain gorilla chest beats convey reliable information regarding the body size of the chest beater. Indicating that the chest beat is an honest signal of body size,” Wright says.

In earlier research, his team showed that larger males are more dominant than smaller males when in groups with many males. They also found body size correlates with reproductive success.

“Being large is really key for male gorillas,” Wright says.

In this new study, the team discovered body size is reliably conveyed to other gorillas through chest beats. Larger male gorillas emitted chest beats with lower peak frequencies than smaller male gorillas.

“This is really important as we think it is very likely that rival males will use this information to assess the size of the gorilla chest-beating. This will help them decide whether to initiate, escalate, or retreat in contests. You don't want to pick a fight with a larger male, as you will likely lose,” he says.

“The risk of injury, and even death, is considerable in these large powerful animals," Wright adds. "We think that chest beats play an important role in these conflicts such that most contests are resolved without the need of physical fighting. Females, on the other hand, are likely to use the body size information transmitted in chest beats in their choice of mates."

View Article Sources
  1. Wright, Edward, et al. "Chest Beats as an Honest Signal of Body Size in Male Mountain Gorillas (Gorilla Beringei Beringei)." Scientific Reports, vol. 11, no. 1, 2021, doi:10.1038/s41598-021-86261-8