Gibbons whisper predator warnings

New research shows that the gibbons of Thailand have a complex language made up of hundreds of soft ‘hoo’ calls that change when different predators approach

Though famous for their noisy shouts, gibbons also use whispers to share information. Each soft call is produced in response to a specific event like spying a predator, finding food or meeting a neighbour.

Researchers followed gibbons from their first morning movements until they found their evening sleeping tree. Their ‘hoo’ calls were recorded and researchers noted the responding events. Individual calls were made in different contexts, including warning others about various types of predator.

The main gibbon predators are big cats and predatory birds. Their warning calls differed depending on what type of predator was approaching. Bird warnings were shorter and quieter. In fact, warning whispers concerning birds were below the typical hearing threshold of raptors, making sure airborne predators wouldn’t be tipped off about the location of the gibbons.

This whisper system contains calls that vary between contexts. Just like human speech, the gibbons produced unique calls and there were significant differences between males and females. When encountering a neighbour, males vocalised and interacted, but females generally ignored others. Even pitch differed between males and females, with males having higher pitched voices. This is highly unusual in the animal kingdom and further study of gibbon language will help decode more and more of this ape’s secrets.

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