Orangutans Play Charades to Get Food

Aug. 2, 2007 — Frustrated orangutans resorted to playing a makeshift game of charades in order to obtain favorite foods that were intentionally withheld by researchers, according to new research in Current Biology.

Since charades relies upon an awareness of what others both understand and do not comprehend, scientists now believe that orangutans, and probably all other apes, have the ability to adjust their communication strategies to get their points across.

"This reaction to another's state of mind is an essential component of human language and the charades-like strategy illustrates how an individual in a prelinguistic society might still have been able to communicate their desires effectively," lead author Erica Cartmill told Discovery News.

Cartmill and colleague Richard Byrne, both researchers in the University of St. Andrews School of Psychology, presented six captive zoo orangutans with two of their favorite food treats — wheat bread and bananas — along with two of their least favorite, "yucky" foods — celery and leeks.

The orangutans eagerly displayed interest in their food faves by pointing at them, or by trying to capture the scientists' attention through cage banging, clapping, swinging, waving and even blowing sputtered raspberries. Some of the large apes actually tried to trade celery and leeks for the bread and bananas.

To complicate matters for the orangutans, the researchers pretended to either not understand some of the apes' gestures, or none of them at all. The testers did this by handing over only small portions of the desired treats, or by giving the large apes the foods they did not want.

At first the exasperated orangutans communicated their displeasure by spitting or throwing the celery and leeks at the researchers. When partially understood, however, they narrowed their signal choices to only those that seemed to be working. Just like charades, if the onlookers seemed fully perplexed, the apes then switched strategies by utilizing completely different gestures than those that apparently failed.

Byrne told Discovery News that these gestures do not necessarily have "word-like meanings." Instead, they are more context-specific.

As an example, he said a person may wave his or her arms, but that could mean any number of things, such as "hello," "goodbye," a mimic of bird wing flapping or even "I'm drowning," depending on the situation.

Cartmill added that while some apes have been taught simple sign language skills, "The orangutans in our study were all using natural gestures and had never been taught specific signs for different objects. The gestures they used varied from individual to individual."

William Hopkins, a scientist working at the Yerkes National Primate Research Center, led a somewhat similar study on chimpanzees.

Hopkins and his team found that the chimps emitted "vocalizations as attention-getting signals" in the presence of a human standing in front of them holding a banana. Like the orangutans, the chimps also clapped, banged, blew raspberries and more to communicate with the fruit holders.

While the chimp researchers did not test the animals for their reactions under situations of partial misunderstandings, the scientists did find that chimps can "generate novel communicative signals, which is a hallmark of human linguistic communication."

While no researcher in either study would support the idea that apes possess full language skills, they do now suspect the roots of early language development may have existed in our ape ancestors.

Byrne said, "The significance of our work is in showing how ancient is the ability to understand other individuals' understanding, part of the 'theory of mind,' and a crucial part of using language."