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To warn of dangers, tree apes use songs

Gibbons found to vary their calls

A wild gibbon was photographed singing in August 2005 at Khao Yai National Park in Thailand. (Esther Clarke/University of St. Andrews)

BANGKOK -- Wah, wow, hoo! Turns out humans aren't the only primates using songs to warn of life's dangers and travails.

White-handed gibbons in Thailand's forests have been found to communicate threats from predators by singing -- the first time the behavior has been discovered among non human primates, researchers said yesterday.

While other animals have been shown to use song to attract mates or signal danger, researchers said their study was the first to show gibbons -- a slender, tree-dwelling ape -- issuing song-like warnings to each other.

The study was published in this month's edition of the journal PLoS One, published by the Public Library of Science.

"This work is a really good indicator that non human primates are able to use combinations of calls . . . to relay new and, in this case, potentially lifesaving information to one another," said Esther Clarke, a University of St. Andrews graduate student and co author of the study.

"This type of referential communication's commonplace in human language, but has yet to be widely demonstrated in some of our closest living relatives -- the apes," she said.

Along with Klaus Zuberbuhler from St. Andrews in Scotland and Ulrich Reichard of the Max Planck Institute in Germany, Clarke spent 2004 and 2005 at Khao Yai National Park in Thailand observing groups of gibbons.

Mostly black with a white face, gibbons live in the treetops and are known for issuing elaborate hooting sounds that echo across the forest for up to a half mile to advertise pair bonds or attract mates.

To test the primates' response to danger, the team conducted a series of experiments in which they put models of predators -- snow leopards, pythons, and crested serpent eagles -- near a group of gibbons and then made audio recordings of their response.

What they found, Clarke said, is that the gibbons approached the potential predator and began warbling a series of sounds -- "wahs, wows, and hoos" -- that were picked up by other gibbons, who then repeated the calls to others.

The sounds made when encountering a predator were more chaotic and louder than those used to win over a mate, Clarke said. "Gibbons can rearrange their songs to denote different circumstances, much like we do with words," she said.

Thad Q. Bartlett, a gibbon expert at the University of Texas at San Antonio, said the findings were interesting and significant.

"From a cognitive standpoint, the claim that gibbon calls are digital is interesting because this is one of the hallmarks of human language, that is, the ability to rearrange discrete elements to create new meanings," he said in an e-mail.

Bartlett also said the findings provide further insight into the behavior of gibbons, contradicting earlier suggestions that their small social network -- a male, female, and their offspring -- was largely a result of the apes facing few threats.

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