A new study on wild Borneo orangutans shows they hold leaves in front of their mouths when calling to create a deeper pitch and ward off predators.

When researching distress calls made by the apes the team found that primates resemble the sound of a bigger ape by lowering their voice with a leaf.

Borneo orangutans, hunted by snakes, leopards and tigers, create distress calls with a sharp intake of breath between pursued lips, known as a “kiss-squeak”. The call informs a predator he has been spotted, and is performed in one of three ways: just with lips, with a hand in front, or a leaf.

“The maximum frequency (Hz) of the kiss-squeak using leaves was the lowest of the three,” Co-author Madeleine Hardus explained. “As kiss-squeaks in orangutans are related to body size, this showed that the ones using leaves exaggerated orangutans’ size by lowering the sound frequency.”

“Because it is very rare and difficult to get a full view of an orangutan in its rainforest habitat, this could be very advantageous, since a potential predator will have to rely more on sounds than sight in these conditions,” she continued.

Evolutionary psychologist and chimpanzee expert Professor Andrew Whiten of St Andrews University explained that the kiss-squeak is a socially learned trick, and that apes can also discover how to use tools by watching and imitating others.

Moreover, Madeleine Hardus explained the importance in the findings: “This study clearly indicates that the abilities of great ape communication have been traditionally undervalued and that there may be traces of language precursors in our closest relatives, the great apes.”

Via BBC News

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