Shouting monkeys show surprising eloquence
Monkeys string sounds together to create meaning.
It may not be exactly poetry, but a species of monkey has demonstrated an unsuspected level of articulacy. Researchers working in Nigeria have found that putty-nosed monkeys can use their two warning calls as 'building blocks' to create a third call with a different meaning. It's the first example of this outside humans, say the researchers.
Putty-nosed monkeys (Cercopithecus nictitans) live in family groups, usually led by a dominant male who keeps a wary eye out for their two main enemies — leopards and eagles. A circling eagle will cause a male to warn his troop by making a series of calls called 'hacks', whereas a lurking leopard will prompt him to shout out a string of 'pyow' sounds. Different predators require different warnings because the treetops are generally the safest place to hide from a leopard, but staying under cover is more advisable when an eagle is around.
These two calls seem to be the only sounds in the putty-nosed monkey's repertoire. Researchers had observed that the monkeys sometimes use these calls in an apparently non-meaningful way: to yell at a fellow monkey, for example, without communicating a specific message.
But now zoologists have realized that at least one combination of these sounds has its own distinct meaning: up to three pyows followed by up to four hacks seems to mean 'let's move on'. This call sequence is given both in response to the presence of predators or simply as a sign to head for new terrain.
"Whenever a male gave these sequences the group would move on and leave," says Klaus Zuberbühler of the University of St Andrews, UK, who carried out the research in Nigeria's Gashaka Gumti National Park with his colleague Kate Arnold.
The team discovered this unknown ability in the putty-nosed monkeys when playing them recordings of either a leopard's growl or an eagle's shriek, to investigate their response. As expected, the monkeys usually produced the corresponding warning call.
But the monkeys also produced puzzling strings of pyow-hacks, which at first the researchers dismissed as simple mistakes. Then they realized that the monkeys tended to move in response to these calls, leading the researchers to suspect that they have a distinct meaning.
By tracking the movements of one particular group, they confirmed that the monkeys were significantly more likely to move on if the male produced a pyow-hack call. The researchers present their discovery in this week's Nature1.
This is the first example in the wild of a non-human using building blocks to create forms of communication, says Arnold. Although chimpanzees have been led to use rudimentary 'language' in the lab, they are usually taught by humans.
The trick is a handy way for putty-nosed monkeys to expand their vocabulary, Arnold adds. "Monkeys can't learn new calls," she explains. "But if they can combine calls, their repertoire might not be quite so limited."
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- Arnold K.& Zuberbühler K.Nature, 441. 303 (2006).