A mountain gorilla rises and hammers its chest to signal a mate or scare off an enemy, but the drums echoing in the forest could also reveal details of their physique, according to a study released Thursday.
Unlike the croak of a frog or the growl of a lion, the beating of the mountain gorilla’s chest is unusual because it is not vocalization but rather a form of physical communication that can be both seen and heard.
This display – mostly by silverback males banging their chests with cupped hands – is seen as a way to attract females and intimidate potential rivals.
But the researchers wanted to know if the sound of the drum, which can carry for a kilometer through the rainforest, also conveys information about the breast drummer.
They observed and recorded 25 adult male mountain gorillas monitored by the Dian Fossey Gorilla Fund in Volcanoes National Park, Rwanda and found that the larger gorillas produced chest beats with lower peak frequencies than the larger ones. small.
“In other words, chest beats are an honest signal of body size in mountain gorillas,” said Edward Wright, of the Max Planck Institute for Evolutionary Anthropology, who led the study.
Previous research had shown that size matters for silverback gorillas – larger males are more dominant and have better reproductive success than smaller ones, he told UKTN.
Scientists believe chest pounding may allow gorillas to send a signal that allows potential mates or rivals to judge their size even without seeing them.
“As a male gorilla, if you want to assess the competitive ability of a rival male, it may be safer to do it from a distance,” Wright said.
He added previous research showing that larger dominant males lead groups with more adult females suggests that females, who are known to move between gorilla bands, may be influenced by size.
These transfers are usually done in person when the groups meet and the men bang their chests to announce their prowess.
But Wright said more research is needed to show that men and women actually judge body size by listening to chest beats.
‘Power and strength’
To study the relationship between the size of wild gorillas and the resonance of their chest drums, researchers first had to measure them – without getting too close.
To do this, they used lasers. By projecting two beams a set distance at the animal and then taking a photo, researchers could use lasers as a scale to measure areas of its body.
They also had to be patient in recording the gorilla’s chest beats, which occur in short bursts about once every five hours.
“You have to be in the right place at the right time,” Wright said.
But when they were, he says, the sound and the spectacle are awesome.
“As a human you definitely have the feeling of power and strength,” he said.
In the end, the researchers were able to use recordings of 36 heartbeats made by six of the men to measure their duration, number of beats and audio frequencies and compare them to their body size.
The study, published in the journal Scientific Reports, found a correlation between the size of the animal and the sonic frequency of the drum sound, but found no connection with the length of time they spent beating their breasts. or the number of beats.
He also found “a significant amount of variation” in the breast beats of different males, Wright said.
But each gorilla didn’t vary their style of drumming much, he said.
“This suggests that chest beats may have individual signatures, but more research is needed to examine this,” he said, adding that some colleagues in the field say they can guess which silverback is beating. the chest just from the sound.
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