The Meaning of Gorilla Chest Thumping

By, Astute Africa Safaris

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Gorilla chest thumping

The meaning of gorilla chest thumping is multifaceted, serving as a crucial form of nonvocal communication among gorillas, particularly adult males known as silverbacks. This behavior is an impressive display that conveys information about the individual’s body size, competitive ability, mating status, and identity, playing vital roles in social hierarchy, attracting mates, defending territory, and potentially preventing physical conflict.

Gorilla chest-beating is a real behavior that has been widely recognized, partly due to its portrayal in popular culture. While scientists have long speculated about its purpose, recent research has provided significant evidence regarding the information conveyed by this display. Unlike vocalizations such as calls or roars, chest-beating is a gestural form of communication that is both seen and heard.

When performing a chest beat, gorillas typically rise from a sitting to a standing posture and rapidly beat their chests with cupped hands, rather than balled fists. Using cupped hands helps to amplify the sound, which can travel long distances through thick rainforests, potentially more than half a mile or over one kilometer away.

Research conducted by scientists, including Edward Wright and colleagues, involved observing and recording mountain gorillas in Volcanoes National Park, Rwanda. Over 3,000 hours of observation between 2014 and 2016 allowed researchers to study hundreds of chest beats from multiple males. They used audio equipment to record the characteristics of the beats, such as frequency, number of beats, and duration. To determine the relationship between the sound and the gorilla’s physical attributes, they used techniques like analyzing photographs or using lasers to measure body size, specifically the maximum breadth of the shoulders.

The results of this research demonstrated a significant finding: larger male gorillas produced chest beats with lower peak frequencies than smaller gorillas. This correlation suggests that the sound frequency of the chest beat is related to the animal’s size, possibly because larger gorillas possess larger air sacs near their larynx. This makes chest-beating an “honest signal of competitive ability,” meaning it reliably communicates information about the individual’s physical prowess. This is analogous to other animal displays like the alligator’s rumble or the bison’s bellow.

Body size is a key attribute in gorillas, as previous studies have shown that larger males tend to be more socially dominant and have higher reproductive success. Therefore, by communicating their size through chest-beating, gorillas are also signaling their dominance and potential as a mate.

The information conveyed by chest-beating is crucial for both rival males and females. For rival males, hearing the chest beat allows them to assess the competitive ability of the chest beater from a distance, helping them decide whether to initiate, escalate, or retreat from a potential aggressive encounter. This ability to size each other up without physical confrontation is believed to be a reason why gorillas, despite their size and strength, rarely engage in damaging fights. A smaller male might be deterred by the low-frequency beat of a larger silverback, while a silverback might hear the beat of a smaller male and deem him not worth challenging.

For females, the information about body size, linked to dominance and reproductive success, is likely used in mate choice. Particularly impressive chest-beating displays might influence females when choosing a mate or even potentially lure them to a different group, although this specific aspect requires further study.

Beyond signaling size and competitive ability, chest-beating serves several other functions within gorilla social dynamics. It is used to establish and maintain dominance within the social group, with silverbacks signaling their strength and presence to deter rivals and assert authority. It also plays a role in territorial defense, with the loud sound communicating territorial boundaries to other groups and potential intruders, thereby reducing the likelihood of direct confrontation.

Chest-beating is also involved in social interactions among younger and subordinate males, who may engage in the behavior to practice social skills and gain feedback. While the research found no clear link between size/dominance and the number or duration of beats, there is variation in these aspects among males, hinting at the possibility that chest beats may have individual signatures, allowing other gorillas to identify the specific individual performing the display.

In addition to these functions, chest-beating can occur in specific contexts. It can serve as a warning sign that a gorilla perceives a threat or danger and might be about to charge. It can also be a sign of victory following a successful fight. A silverback might use chest-beating as a signal for the group members to follow him, beating his chest and then walking away. Furthermore, silverbacks may beat their chests in response to a challenge from a younger silverback, acting as a warning that could lead to the younger gorilla retreating or a physical confrontation.

Overall, gorilla chest thumping is a complex and vital form of nonvocal communication that conveys a range of information, from reliable indicators of body size and competitive ability to potential individual identity, and serves critical roles in social structure, reproduction, and conflict avoidance within gorilla groups