Gibbons are the opera stars of the monkey world, a study has shown.
They use the same vocal techniques as human sopranos singing at London's Royal Opera House or La Scala in Milan, scientists have learned. Just like a trained diva whose voice can fill an auditorium, a gibbon is able to make itself heard across two miles of dense forest.
Researchers in Japan carried out a unique experiment in which helium gas was used to make gibbon voices higher pitched.
They found that the animals amplify the higher sounds using the mouth and tongue to alter the shape of the upper vocal tract. Exactly the same technique is used by professional human singers.
Dr Takeshi Nishimura, from the Primate Research Institute at Kyoto University, said: "The complexity of human speech is unique among primates as it requires varied soft sounds made by the rapid movements of vocal tracts. Our speech was thought to have evolved through specific modifications in our vocal anatomy. However, we've shown how the gibbons' distinctive song uses the same vocal mechanics as soprano singers, revealing a fundamental similarity with humans."
The monkeys use their songs to communicate with neighbours and potential mates in dense jungle where visibility is poor.
Dr Nishimura's team studied a white-handed gibbon from Fukuchiyama City Zoo in Kyoto. The scientists compared 20 recordings of the animal's calls made in normal air with 37 made in a helium-enriched atmosphere.
The sounds revealed how gibbons consciously manipulate their vocal cords and tract to produce their distinctive songs.
"The lowest frequency of harmonics is amplified in a gibbon's song when performed in normal air," said Dr Nishimura. "However, in a helium-enriched atmosphere the tuning of the vocal cord vibration and the resonance of the vocal tract are altered as the gas causes an upward shift of the resonance frequencies."
The findings appear in the American Journal of Physical Anthropology.