'Pyow-pyow': how the putty-nosed monkey tells its friends there's a leopard coming

A troop of monkeys in west Africa has been found to use different combinations of calls to convey different meanings in what is believed to be one of the first experimental demonstrations of rudimentary language ability in wild animals.

The putty-nosed monkeys living in Nigeria were already known to use different alarm calls to warn each other about the presence of predators, but now scientists have found that their linguistic ability goes a step further.

Male putty-nosed monkeys are able to combine different types of alarm calls to indicate their identity, what they have seen and whether they intend to flee – and all of this information is recognised by other members of the troop, a study has found.

Klaus Zuberbühler, of St Andrew's University, said his research into wild putty-nosed monkeys demonstrated that their linguistic ability shows intriguing similarities with human speech, in that they can combine sounds to convey various meanings. "In linguistics, 'morphemes' are usually defined as the smallest meaningful units in the grammar of a language. Our research revealed some interesting parallels in the vocal behaviour of forest monkeys and this feature of human language," he said.

The monkeys have two basic alarm calls – "hacks" and "pyows", and they use them to warn each other about different predators – for example, a "pyow-pyow" signals a leopard. Dominant male monkeys are also able to combine "hacks" and "pyows" into a unique sequence that conveys important information, such as "I am about to travel, follow me", according to Dr Zuberbühler, who, with his colleague Kate Arnold, carried out the study published in the journal Current Biology.

The scientists proved their theory by playing audio tapes of "pyow-hack" sequences made by a dominant male and observing the reactions of other troop members. The behaviour of the monkeys followed the scientists' predictions – for instance, that they would all move in response to the signal to travel.

"What we showed is that it was this call sequence alone that was sufficient to trigger group travel," Dr Zuberbühler said. "Most primates are limited in the number of signals they can physically produce due to their lack of tongue control. The only way to escape this constraint may be to combine the few calls they have into more complex sequences.

"In other words, it may be harder for non-human primates to evolve large repertoires than to evolve the ability to combine signals. Hence, the evolution of combinatorial signalling may not be driven by too many signals, but rather by too few."

The ability to combine different sounds or vocalisation was believed to be an important step in the evolution of human language. According to this theory, at some point it became more economical to combine existing elements of communication, rather than adding new ones, because the repertoire was already too large.

But, Dr Zuberbühler said: "Our research shows these assumptions may not be correct. Putty-nosed monkeys have very small vocal repertoires, but nevertheless we observe meaningful combinatorial signalling."

Listen to the calls of the putty-nosed monkey:

Monkey speak

* The study of the putty-nosed monkey was carried out in the Gashaka Gumti National Park in Nigeria.

* Naturalists observed the animals using two distinct alarm calls – "pyow" and "hack" – in non-random sequences.

* Further studies revealed that the monkeys were using different combinations of calls to express various specific meanings.

* These include: hack-hack-hack-hack: "There's an eagle over there!"

* Pyow-hack-hack-pyow-pyow-pyow: "I've seen a leopard, let's move away!"

* Hack-hack-hack-pyow-hack-hack-hack-hack-hack "There's an eagle over there, let's move away!"

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