They hit their chest so they don’t have to hit you.
The image of King Kong hitting his chest may seem like the ultimate threat image. However, German scientists have found that gorillas strike with their sternum to avoid – rather than provoke – a fight.
In particular, pec-pounding advertises primate size, combat skill and other practical information, giving rivals a picture of what they would run into if they chose to throw down, National Geographic reported.
“We found that it is absolutely a real, reliable signal – males surrender their true size,” Edward Wright, a researcher at the Max Planck Institute for Evolutionary Anthropology, told The Guardian. He co-authored the percussion study published in Scientific Reports on Thursday.
Many have speculated that gorillas communicate size through moob banging, but “there was no data to support this claim,” said Roberta Salmi, director of the University of Georgia’s Primate Behavioral Ecology Lab.
To prove their exciting theory, Wright and his team spent 3,000 hours studying endangered mountain gorillas in Rwanda’s Volcanoes National Park, National Geographic reported.
They used audio equipment to record the chest sound frequencies, number and duration of each display in six animals between November 2015 and July 2016. They then compared these variables with the size of the specimens, which were measured by analyzing pictures of the beasts.
The researchers found that larger gorillas produced lower frequencies than their smaller counterparts, indicating that pectoral percussion was a “fair signal of competitive ability” and size, rather than an exaggerated threat display, according to the study. Think of a UFC fighter summing up their stats versus a drunkard blowing his chest at the bar.
“These are big, powerful animals that can do a lot of damage.”
Since larger body size correlated with higher social rank – and thus fighting ability – scientists deduced that transmitting it through chest patting could help gorillas avoid violence – a must in a species that grows up to 500 pounds.
“Even if you are likely to win a fight, there is still a fairly high risk factor,” explains Wright. “These are large, powerful animals that can do a lot of damage.”
“A lot of times it’s all about the rhythm on the chest and then they don’t fight,” he said, adding that little gorillas can be put off by a larger silverback, whose clapping bass is likely caused by their larger larynx sacs. Likewise, an alpha Mighty Joe Young can hear a beta monkey’s drum solo and decide they are too small to monkey with.
In addition to tailoring rivals, it could also be used to attract partners, according to the study.
The next step is to figure out how other gorillas translate the language of chest slapping.
“It will be very interesting to see how hearing heartbeats in their environment can influence their movements and decision-making about which parts of their home range to use,” said Salmi.