Orangutans mime to get message across
Just like humans, orangutans will resort to mime to get their message across, scientists report.
A team from Canada found the great apes would sometimes use elaborate gestures to explain what they meant.
They mimed the action of being scratched to get an itch attended to, and enacted opening a termite nest to prompt a partner to do just that.
The study, published in Biology Letters, suggests ape communication is more complex than was thought.
The researchers uncovered the primates' propensity for mime by looking through 20 years of observational studies that had been carried out on orangutans in Borneo.
These animals had all previously been captive, but were now living free or partly free in the forests.
The team found 18 cases where orangutans had been spotted performing mimes.
Professor Anne Russon, from Glendon College at York University in Ontario, Canada, said: "When I observed the events, yes, I was surprised - in the sense that it was very unusual and in one case their behavior seemed, at the time, entirely bizarre and way out of character."
Give us a clue
Some of these gestures were quite complicated.
One orangutan, Kikan, had injured her foot, and had been helped by a conservationist who dug out a small stone and then dripped latex from the stem of a fig leaf on to the wound to seal it.
A week later, Kikan attracted the same conservationist's attention and then picked up a leaf and re-enacted her treatment.
Professor Russon said: "She's not asking for anything, which is the most common aim observed of great ape communication, but appears simply to be sharing a memory with the person who helped her when she hurt her foot.
"It shows her understanding of how events had unfolded in a particular situation, which was very complex."
Often, the primates resorted to mime after other methods of communication had failed.
An orangutan called Cindy spotted a conservationist using an umbrella. On spying the contraption, she held out her open hand, as if to gesture that she wanted it.
When she was not given the umbrella, she then picked up a leaf and held it over her head, mimicking the person holding the umbrella. She then offered the branch to the conservationist and tried to take the umbrella in return, revealing the motive behind her performance.
The researchers said that while miming in orangutans seemed to be rare, it did tell us more about how the great apes communicated.
In their paper, Anne Russon from Glendon College in Toronto, Canada, and Kristin Andrews from York University, also in Toronto, wrote that the complex "pantomimes" showed some of the properties of natural language.
Professor Russon saidd: "Orangutans, and other great apes have more sophisticated communicative abilities than currently believed.
"Pantomime has been proposed as the basis for the evolution to language because it broadens the range of messages that individuals can send - basically, anything you can act out. It allows you to create the sentence-like message: 'You do action X using tool Y on object Z'.
"This is a powerful communication tool indeed."
Apes that ape
Previously, scientists thought that mime was such a sophisticated form of communication that only humans were able to do it.
But more recent studies have shown that some captive great apes could also act out messages, such as Koko, a language-trained gorilla, who would roll a ball of imaginary clay in her hands to express the word clay.
Other research has hinted that wild chimpanzees may also mime. For example, a female chimp has been spotted acting out to her daughter how best to hold a stone in order to crack a nut.
The fact that orangutans now too seem to mime supports the case that great ape communication is far more complex that was originally imagined.
Scientists say that finding out more about how our primate cousins communicate may also help us to better understand how human language evolved.