Why orangutans cup their mouths to sound an alarm


Orangutans, pictured here in in the Ketambe area of Sumatra, Indonesia, learn from their elders to use alarm calls to signal distress and scare off predators.

Perry van Duijnhoven

In the forests of Sumatra and Borneo, orangutans use their hands to alter the pitch of their alarm calls to deceive predators into thinking that they’re bigger and badder, researchers posit March 18 in the Journal of Experimental Biology.

To scare off predators, orangutans produce alarm calls called “kiss-squeaks” (because that’s what they sound like), sometimes placing their hands around their lips as they call out. Simulations and recordings from the wild suggest that the hands make the call sound deeper — as if it’s coming from a larger animal. Because the behavior is learned, there’s a chance the apes might be aware that they can change the pitch of the call with their hands, the researchers speculate.

HEY THERE  At the Tuanan Orangutan Research station in Indonesia, an orangutan performs a “kiss-squeak” alarm call, first without its hands and then with its hands.

Credit: Madeleine Hardus

Helen Thompson

Helen Thompson is the multimedia editor. She has undergraduate degrees in biology and English from Trinity University and a master’s degree in science writing from Johns Hopkins University.

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