It might sound like a squeak, a kiss, and raspberry to us, but this is how some of our ginger-haired great ape cousins tell one another to "go away" or “gimme that.”
A new study led by the University of Exeter in the UK and the Borneo Nature Foundation set about to decipher the vocal calls and gestures of wild orangutans. Reported in the International Journal of Primatology, the results are essentially an orangutan-to-human dictionary.
The team headed to the forests of Borneo and documented the communication of wild orangutans (Pongo pygmaeus wurmbii), especially between mothers and their children. Over a period of two years, a total of 681 hours of video footage captured almost 1,300 different types of communication signals.
They identified 11 vocal signals and 21 physical gestures that had eight specific motives, including "acquire object" (signaller wants something), "climb on me", "climb on you", "climb over", "move away", "play change: decrease intensity", "resume play", and "stop that."
These goals were communicated through a number of different sounds, including grumbles, cries, croaks, and raspberries. Some of the calls were also surprisingly complex, such as making a “kiss squeak” but changing the noise by cupping a hand around the mouth or putting a leaf in front of their lips.
Their observations showed that juvenile orangutans tended to communicate by mostly using visual gestures, while adults used gestures and physical touching equally. However, both tended to use vocal communication more if the other orangutan was out of sight. These signals did not fall on deaf ears, either. The study estimates that up to 90 percent of the communications got a response or a reaction from their pals.
"We observed orangutans using sounds and gestures to achieve eight different 'goals' – things they wanted another orangutan to do," Dr Helen Morrogh-Bernard, from the University of Exeter and founder of the Bornean Nature Foundation, said in a statement.
"Orangutans are the most solitary of all the apes, which is why most studies have been done on African apes, and not much is known about wild orangutan gestures.
"While some of our findings support what has been discovered by zoo-based studies, other aspects are new – and these highlight the importance of studying communication in its natural context."
While previous research has started to unravel the secrets of orangutan chattering, this is one of the most comprehensive looks at complex communication in the creatures. Most researchers argue that non-human animals don't possess the ability to communicate through a true "language", although many species exhibit complex vocal communication that can be compared to language, most notably great apes and parrots. This is especially interesting for scientists who are attempting to understand the evolutionary origins of complex human speech.