Gibbons of North East Thailand make hoo sound like humans

Photo issued by BioMed Central of a gibbon, as scientists are fathoming out the secret language of gibbons. Image by Esther Clarke/PA Wire

Scientists are fathoming out the secret language of funky gibbons.

The Asian apes are renowned for their loud musical songs, but also produce distinctive soft calls known as “hoos”.

Now new research has shown that they use these whispers to communicate specific information about events such as foraging, meeting neighbours, or types of predator.

Scientists believe they could provide valuable clues to the evolution of human speech.

Lead researcher Dr Esther Clarke, from the University of Durham, said: “These animals are extraordinarily vocal creatures and give us the rare opportunity to study the evolution of complex vocal communication in a non-human primate.

“In the future, gibbon vocalisations may reveal much about the processes that shape vocal communication, and because they are an ape species, they may be one of our best hopes at tracing the evolution of human communication.”

The scientists spent almost four months tracking lar gibbon groups around the forests of north-east Thailand.

Scientists are fathoming out the secret language of gibbons. Image by Esther Clarke/PA Wire

The apes were usually followed from the first morning encounter until they had located their evening sleeping tree. During this time, the researchers recorded their hoos and noted the event that elicited the response.

From the recordings, they extracted more than 450 hoo sounds which were subjected to computer analysis.

Gibbons reliably produced individual hoo calls in different communication contexts, including foraging, predator detection, encountering neighbours, and “duet” songs performed by mated pairs.

Subtle hoo variations also occurred within a particular situation, for instance to distinguish between different types of predator, the scientists found.

Responses to a range of predators including leopards, tigers, pythons and raptors – birds of prey – were investigated. As well as observing the apes’ reactions to real predators, the researchers also presented them with fake model predators in realistic poses.

Raptor hoos were distinctively less intense, shorter, and lower in pitch than other calls. They were also below the frequency range where eagles and other raptors hear best, suggesting that they were designed to avoid attracting the attention of the birds.

Tiger and leopard hoos were similar, indicating that both animals were perceived as belonging to the same “big cat” class.

While both gibbon sexes shared much the same hoo calls, those of females were lower in pitch, which is unusual among mammals. Females also typically did not produce hoo sounds when encountering neighbours, while males actively interacted with the gibbons next door.

The study, published in the journal BMC Evolutionary Biology, is said to be directly relevant to the on-going debate about the evolution of human speech.

Experts believe the ability to produce calls that are context-specific is necessary for human-like communication.

Gibbon hoo variation may have strong parallels with human speech, in which parameters such as pitch can be important carriers of meaning, say the scientists.

(Press Association)