The results showed that the biggest mountain gorillas produced sounds with lower frequencies than smaller gorillas-possibly because bigger gorillas have larger air sacs near their larynx. (See National Geographic’s beautiful photos of gorillas.) To do so, the team analyzed photographs to measure the maximum breadth of each animal’s shoulders. Finally, they searched for relationships between these variables and the gorillas’ sizes. The scientists, whose work was funded in part by the National Geographic Society, used audio equipment to record the frequencies of the chest beats, as well as the number of beats and duration of each display. They stayed at a safe distance from the animals, which have been habituated to the presence of researchers but remain highly vulnerable to human diseases. While battling biting insects and navigating the park’s rugged, mountainous terrain, the scientists observed more than 500 chest beats from 25 different males between 20. To study the behavior in never-before-seen detail, Wright and his colleagues spent more than 3,000 hours observing endangered mountain gorillas at Volcanoes National Park in Rwanda. By advertising their size, mating status, and fighting ability via sounds that can travel long distances through thick rainforests, the silverbacks are signaling would-be challengers that they better think again before starting a ruckus.

Mountain gorillas live in tight-knit family groups led by silverback males, whose authority is constantly being challenged by other males. Interestingly, while a male mountain gorilla’s hearty chest beat would seem to signal aggression, new research by Wright shows that the behavior may actually prevent violence between the massive animals, which can top out at nearly 500 pounds.

“It is an extremely impressive display,” says Edward Wright, a primatologist at the Max Planck Institute for Evolutionary Anthropology in Germany. Since King Kong first appeared on the silver screen in 1933, the fictional giant ape has exposed audiences all over the world to a very real gorilla behavior-chest-beating.īut it may surprise you to learn that while scientists have speculated about the percussive display’s meanings, actual evidence for why male gorillas sometimes pound their chests has been scarce.

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