A scientist based in Scotland claims to have found the first evidence of a common language shared by different animal species.
The calls, which are understood by monkeys and birds, were discovered by Klaus Zuberbühler, a psychologist at St Andrews University.
According to Zuberbühler, animals and birds can communicate complex ideas not just to their peers but across species.
The findings have been heralded as a significant breakthrough in the quest to discover the origins of human language and proof that the ability to construct a complex form of communication is not unique to man.
Zuberbühler made the discovery after spending months observing the calls of Diana monkeys in the Tai Forest in Ivory Coast, in west Africa.
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He and his colleagues recorded thousands of monkey calls and spent hundreds of hours listening to the animals' noises. They noticed that the monkeys adapted their calls to change the meaning to warn one another about different threats or opportunities. For example, the sight of a leopard prompted a "krack" alarm call. However, when they merely repeated calls made by other monkeys they added an "oo".
The researchers found that the calls could be understood by other species of monkey as well as by some birds.
"What our discovery showed is that [the alarm calls] were far more complex [than we had thought]," said Zuberbühler. "They were conveying information that was contextual, self-aware and intelligent.
"We then tried playing these calls back to other monkeys and they responded in ways that showed they knew the meaning. What's more, the same calls would be recognised by other species like Campbell's monkeys. So they are communicating across species.
"And since then we have found that hornbill birds can understand these calls and they too can understand all the different meanings."