Secrets of gibbon 'speech' decoded

Scientists have deciphered the secrets of gibbon “speech” – discovering that the apes are sophisticated communicators employing a range of more than 450 different calls to talk to their companions.

The research is so significant that it could provide clues on the evolution of human speech and suggests that other animal species could speak a more precise language than has been previously thought, according to lead author Dr Esther Clarke of Durham University.

Her study found that gibbons produce different categories of “hoo” calls – relatively quiet sounds that are distinct from their more melodic “song” calls.

These categories of call allow the animals to distinguish when their fellow gibbons are foraging for food, alerting them to distant noises or warning others about the presence of predators.

In addition, Clarke found that each category of “hoo” call can be broken down further, allowing gibbons to be even more specific in their communication.

A warning about lurking raptor birds, for example, sounds different to one about pythons or clouded leopards – being pitched at a particularly low frequency to ensure it is too deep for the  birds of prey  to hear.

The warning call denoting the presence of tigers and leopards is the same because they belong to the same class of big cats, the research found.

Clarke says that she set out to analyse the loud and conspicuous songs that gibbons are mainly known for. But sitting in the forests of north-east Thailand she began to notice distinct variations – and patterns – in the way that the quieter calls were being used.

The discovery that gibbon communication is far more sophisticated than previously thought has implications across the animal kingdom, she says.

Gibbon hoo calls were first identified in the 1940s, yet their intricacies have gone largely unanalysed because they are so quiet and virtually indistinguishable to the human ear.