Scientists found gorillas fight their chests to show how tall and fearful they are

Male gorillas fight their chest as an acoustic indicator of their body size and ability to compete against their rivals and females, as revealed by an international study published today by the magazine ‘Scientific reports‘of Nature.

The work has revealed the hidden significance of the iconic blows to the chest of mountain gorillas, including the largest and most competitive specimens. they emit lower sound frequencies, i.e. lower pitched sounds, so the gorilla’s size is encoded in the sound message.

The research, led by Edward Wright and Martha Robbins, of the Max Planck Institute for Evolutionary Anthropology, was followed by Professor of the Faculty of Psychology at the University of Barcelona (UB) Jordi Galbany, as well as experts from the Dian Fossey Foundation, George Washington University and Goethe University in Frankfurt.

Researchers have found a correlation between the body size of gorillas and the frequency of sounds characteristic of their chest thrusts.

According to the study, this visual and acoustic signal reliably indicates the bodily dimensions of gorillas to their social group – males and females – and also other gorillas from neighboring groups.

The work studied a dozen social groups of mountain gorillas in the Rwanda Volcanoes National Park, East Africa, a small and well-known habitat thanks to the American primatologist Dian Fossey.

the mountain gorilla (Gorilla beringei beringei, one of the African great apes that inhabits the volcanic slopes of the Albertina fault, it is an endangered subspecies of which less than 1000 specimens remain in Bwindi Impenetrable Forest National Park (Uganda) and the Virunga Mountains, between the Democratic Republic of Congo, Uganda and Rwanda.

Until now, the beatings were thought to be associated with competition between men and the process of group selection by women, but the type of information communicated was still unknown.

The work confirms that the strategy of the thorax strikes is a reliable indicator of the body size of gorillas and reveals their competitive ability vis-à-vis members of their social group and others.

According to the researchers, the anatomy close to the larynx of larger males reduces the frequency of sound these monkeys make when pounding their breasts.

Yes indeed, rival males might be intimidated by the sound of such blows –that can be heard a mile away– O they would choose to avoid fights with the sending buck, while females could use the information to choose a mate.

“Chest punching behavior is typical of adult male gorillas and has historically been described as a show of strength related to social status and threatening behavior.», Explained the professor of psychobiology at UB Jordi galbany.

“This behavior,” he added, “is the culmination of a demonstration: the gorilla begins to make vocalizations similar to short howls, stands up and runs on its legs while hitting its chest hard with the palms of the two hands alternating, producing an impressive sound, like the roll of a drum ”.

“Male gorillas strike their breasts once every twenty hours of observation, but they can do it every few minutes when they are interacting between two groups,” Galbany explained.

Researchers have also found that this behavior is more common on days when there is a female in heat.

The team recorded the hits in the gorillas’ chest to analyze various sound parameters (duration, number of hits, frequency of emission) and studied the back width of each animal using non-invasive photogrammetric techniques, work in which Galbany was directly involved during four years of fieldwork in the Volcanoes National Park.

“Other species of great apes can also communicate at a distance using non-vocal acoustic signals, such as chimpanzees, which use the buttresses of trees as a drum and emit a wide range of communication signals with different durations and characteristics.” , Galbany pointed out. .

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