Matt WalkerEditor, Earth News
Female gorillas clap their hands to get the attention of male silverbacks and infants.
The discovery in the forests of central Africa is only the second time the behaviour has been recorded in wild western lowland gorillas.
It suggests that the great apes use hand-clapping to communicate over long distances and keep the family group together.
The discovery is published in the journal Primates.
"What struck me most was how it was conducted in such a controlled and deliberate manner while in a bipedal position; much like a human would hand clap," says Ammie Kalan of Oxford Brookes University, in Oxford, UK.
"A female was able to exert control over her infant's behaviour by hand-clapping. Which did remind me of a human mother."
Kalan and colleague Hugo Rainey of the Wildlife Conservation Society observed the gorillas at the Lac Tele Community Reserve Project in the Republic of Congo.
Alerting silverbacks
Captive male and female gorillas occasionally clap their hands, either to display enthusiasm or to attract the attention of human keepers.
More than 25 years ago, Diane Fossey observed hand-clapping in a single wild mountain gorilla, a different species. But this female acquired and lost the behaviour again within four years.
Twenty years ago, primatologist J Michael Fay saw western lowland gorillas in the Central African Republic hand-clapping, which he believed to be an alarm response to human observers.
Kalan and Rainey recorded hand-clapping among four separate groups of western lowland gorilla living in the Likouala swamp within the Lac Tele Community Reserve.
In all, they observed five adult females clapping their hands. Four were mothers with infants present. Each time the female clapped her hands twice in rapid succession in front of her body.
On two occasions, the females clearly clapped their hands to alert a male silverback to the presence of the human observers.
In response, one silverback tried to intimidate the observers, while on the second occasion a silverback hiding 10m away behind a tree produced a loud roar, then drummed on the buttress roots and beat his chest.
Group cohesion
Another time, after Kalan's and Rainey's research team startled three females in a tree, they heard them hand-clap five times in succession, with at least one minute between each.
"We believe they were attempting to contact the silverback even after we were no longer posing a threat," says Kalan.
They also saw a mother suddenly clap her hands at her infant, who stopped playing, while other adults stopped foraging. They all then followed the mother's gaze, who was looking at the researchers. The whole group moved away shortly after.
"It's a form of gestural communication that has largely been overlooked by gorilla researchers," says Kalan.
"It's used as a form of long distance communication with the silverback, even when humans are not posing an immediate threat, as well as to get the attention of group members. The hand clap allows the gorillas to maintain group cohesiveness."
Kalan and Rainey's research also supports the idea that gorillas might develop different ways to communicate depending on the varying culture of each group.
http://news.bbc.co.uk/earth/hi/earth_news/newsid_8027000/8027622.stm
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