Why Do Gorillas Beat Their Chests? What the Sound Means

What does a gorilla chest beat sound like?

A gorilla chest beat is a rapid series of slaps on the chest with cupped, open hands, alternating left and right. A typical bout lasts a few seconds. The cupped hands make a hollow “pok-pok-pok” sound, a bit like drumming, rather than the thump of a fist.

In adult males the sound is deep and carries well through the forest. It can often be heard about a kilometer (0.6 mi) away. Gorillas have air sacs connected to the voice box, and some scientists have suggested that these may help the chest resonate, although this has not been firmly proven.

Chest beats are a non-vocal signal, meaning the sound is made by the body rather than the voice. Gorillas also have many calls, such as hoots, barks and contented rumbles, and chest beats often accompany them.

Chest beating as an honest signal of size

A study of wild mountain gorillas published in 2021 in Scientific Reports tested whether chest beats reveal how big a male is. Researchers working with the Dian Fossey Gorilla Fund in Rwanda recorded chest beats from adult males and measured each male’s back width from photographs, an accurate measure of body size.

They found that larger males produced chest beats with a lower peak frequency, or deeper sound, than smaller males. The length of the bout and the number and speed of beats varied from male to male but did not reliably reflect size. Because a male cannot easily fake a deeper sound, the authors concluded that the chest beat is an “honest signal” of body size, and therefore of fighting ability.

This matters because in mountain gorillas, bigger males tend to have higher rank and father more offspring. A chest beat lets a rival judge a silverback’s size from a distance, and lets females assess a potential mate, without anyone having to see him in thick vegetation.

Warning rivals and avoiding fights

The most dramatic chest beating happens when two groups meet or when a lone male approaches a group. A silverback may then perform a full display. Field biologist George Schaller, who studied mountain gorillas in the late 1950s, described it as a sequence of up to nine steps:

1. Hooting, getting faster and faster
2. Symbolic feeding, plucking a plant and putting it in the mouth
3. Rising onto two legs
4. Throwing vegetation
5. Beating the chest with cupped hands
6. Kicking out with one leg
7. Running sideways
8. Slapping and tearing at plants
9. Thumping the ground with the palms

Not every display includes every step. The point is to look and sound as impressive as possible. Fights between silverbacks can cause serious injuries from their long canine teeth, so a convincing bluff that makes a rival back down is safer for both. Most encounters end without contact.

Impressing females and keeping the group together

Chest beating is not only aimed at rivals. Observations suggest that males chest-beat more often when females in the group are ready to mate, which fits the idea that the sound advertises a male’s quality to potential partners.

Because the sound carries so far through dense forest, chest beats may also help group members and neighboring groups keep track of where a silverback is. In thick vegetation, where gorillas often cannot see one another, sound is an important way of staying in contact and keeping a safe distance from other groups.

Do female and young gorillas beat their chests?

Yes. All gorillas can chest-beat. Infants begin trying it at a very young age, often while playing, and juveniles of both sexes drum on their chests when excited, during games of chase or wrestling, or when showing off to playmates. Females chest-beat too, especially during excitement or tension, but less often than males.

Researchers think that early practice helps young gorillas learn a signal that will matter more as they grow. A young male’s chest beats get deeper and more powerful as he grows into a silverback.

Myths about chest beating

Myth: gorillas pound their chests with fists. Films and cartoons often show closed fists, but wild gorillas use cupped, open hands.

Myth: chest beating always means a gorilla is about to attack. It is usually a signal, not a declaration of war. Gorillas are generally peaceful, and displays exist largely to prevent fights. Visitors on guided gorilla treks keep at least 7 m (23 ft) away and follow rangers’ instructions, which keeps both people and gorillas calm and safe.

Myth: only silverbacks do it. Chest beating is found in gorillas of all ages and both sexes, in both the eastern gorilla and the western gorilla.

What else do we know about gorilla communication?

Chest beats are just one part of a rich communication system. Mountain gorillas use around 25 recognized calls, from soft rumbling “belches” that signal contentment to loud screams and roars of alarm. Facial expressions, postures and gestures add more information. To learn more about the leader whose chest beat is loudest of all, see What is a silverback gorilla?, or find out how strong a gorilla is.