A gibbon's song can be heard from over three kilometres away. Image: Kitch Bain/Shutterstock.
Singing apes on helium use the same techniques as professional sopranos.
The voices of Dame Joan Sutherland or Maria Callas might not be the first sounds that come to mind if you hear a white-handed gibbon (Hylobates lar) sing. But the gibbons’ unique song is produced using the same techniques that these great sopranos would have employed on stage.
Living in dense forest canopy with poor visibility, the gibbons have to make loud calls to protect their home range or communicate mate candidates. And soprano singing meets these requirements without any great modifications on anatomy or physiology, according to Dr Takeshi Nishimura from Kyoto University in Japan. “Such (an) ecological and social requirements forced gibbons using a soprano technique to produce their pure-tone and loud voices.”
Nishimura and his colleagues discovered the use of these techniques while examining how the gibbons produce their pure tones at such impressive volumes. They studied the song of a white-handed gibbon in Fukuchiyama City Zoo in northern Kyoto, first recording 20 calls in a normal air atmosphere. They then recorded another 37 songs in a helium-rich atmosphere.
Why helium? Well, Nishimura says that as gibbons make pure-toned vocal sounds, standardised acoustic analyses cannot examine the properties of such sounds. However, helium increases sound velocity and resonance frequency. “The helium gas (modifies) the property of resonance with little effects on the source property,” he explains. “Thus, helium experiments are necessary for understanding the acoustical mechanism of the gibbon singing.”
The results, published in the American Journal of Physical Anthropology, indicate that the gibbons can consciously manipulate their vocal cords and tract to produce their songs. So, as in humans, acoustic sound originates from the larynx and is controlled by a filter, determined by the shape of the supralaryngeal vocal tract, allowing humans to form speech and the gibbons to sing.
A closer examination revealed that the gibbons’ techniques bear a remarkable similarity to the complex vocal abilities that, in humans, can only be mastered by professional sopranos. The fact that the gibbons can adopt these difficult techniques with minimal effort suggests that the physiological foundation in human speech is not unique.
Instead of being the result of evolutionary modifications, humans probably share the same biological fundamentals of vocalisation as other primates and simply acquired another of its sophisticated forms in speech. “It is hoped that this study will encourage researchers in various research fields to conduct further investigations of primate vocalizations and that such empirical evidence will lead to a deeper understanding of the evolution of speech and language,” Nishimura says.
