Orang-utans are cunning communicators
Apes modify their gestures depending on human response
When orang-utans want a human to hand over a tasty treat, they use a similar strategy to that used in the game 'charades', say researchers. They repeat signals that work, and modify those that don't, revealing surprisingly sophisticated communication skills.
Non-verbal communication of this kind has already been seen in chimpanzees, and there is plenty of anecdotal evidence that orang-utans are similarly gifted.
"Talk to any zookeeper and they'll tell you they can communicate with the orang-utans, and the orang-utans can communicate with them," says Richard Byrne of the University of St Andrews in Scotland. "But the big question is whether the animal is communicating intentionally or simply responding to learned symbols."
Byrne and his colleague Erica Cartmill investigated the communicative powers of six female orang-utans in British zoos. Each ape's keeper sat outside its cage with two buckets containing food that was either desirable (such as bananas) or undesirable (such as celery).
For 30 seconds, the orang-utan tried to express her preference, while the keeper sat silently. The keeper then gave the ape the desirable food, half the desirable food or all of the undesirable food, and waited silently for another minute.
The three outcomes correspond to the experimenter's level of understanding — full, partial or none — of the orang-utan's goal, says Byrne. "The experimenter pretended not to understand what the animal wanted — something a zookeeper would never normally do."
All but one of the orang-utans stopped signalling when they were given all the desirable food, and several retreated into their cages. "After they received the desired food, most were busy eating," says Byrne. "I don't know what happened with that one individual, perhaps it was extremely greedy."
When they were partially understood, the orang-utans repeated their previous gestures in the hope of getting the rest of the desirable food. When given undesirable food, they tried new gestures and stopped using those that had apparently not been understood.
"The responses showed that the orang-utans had intended a particular result, anticipated getting it and kept trying until it got it," says Cartmill. "They made a clear distinction between total misunderstanding and partial misunderstanding. The result is that they are understood more quickly."
"This is a tremendously exciting study," says psychologist David Leavens of the University of Sussex, UK. "It shows that orang-utans can communicate with a human experimenter and make tactical decisions about how to communicate. It's an unprecedented finding."
The work may also contribute to our understanding of how human language evolved, says Byrne. "There must have been a time when our ancestors had no more language than chimps or orang-utans do today. By looking at orang-utans, which communicate in quite a rich way but possess nothing like the complexity of spoken language, we can look for clues about how human ancestors may have behaved."
- Cartmill, E. A. & Byrne, R. W. Curr. Biol. 17, 1-4 (2007).