Boom! Hok! A monkey language

Hok hok hok! (Hey,crowned eagle!)

Very good. You have mastered half the vocabulary of the Campbells monkey,a fellow primate that lives in the forests of the Ivory Coast. The adult males have six types of call,each with a specific meaning,but they can string two or more calls together into a message with a different meaning.

Having spent months recording the monkeys calls,a group led by Klaus Zuberbühler of the University of St. Andrews in Scotland argues that the Campbells monkeys have a primitive form of syntax.

This is likely to be a controversial claim because despite extensive efforts to teach chimpanzees language,the subjects showed little or no ability to combine the sounds they learned into a sentence with a larger meaning. Syntax,basic to the structure of language,seemed be a uniquely human faculty.

Still,species like gibbons and whales make complex vocalisations in which the order of the sounds seems to have some effect on their meaning,though it is hard to say what. Zuberbühlers team reports deciphering some of the Campbells monkeys communication system in The Proceedings of the National Academy of Sciences.

Krak is a call that warns of leopards in the vicinity. The monkeys gave it in response to real leopards and to model leopards or leopard growls broadcast by the researchers. The monkeys can vary the call by adding the suffix -oo: krak-oo seems to be a general word for predator,but one given in a special contextwhen monkeys hear but do not see a predator,or when they hear the alarm calls of another species known as the Diana monkey.

The boom-boom call invites other monkeys to come toward the male making the sound. Two booms can be combined with a series of krak-oos,with a meaning entirely different to that of either of its components. Boom boom krak-oo krak-oo krak-oo is the monkeys version of Timber!it warns of falling trees.

There is yet another variation on this theme,Zuberbühlers team reports. Into the Timber! call,the Campbells monkeys insert a series of up to seven hok-oo calls. The combined call indicates the presence of other monkey groups and is heard most often when the monkeys are on the edge of their home range.

The meaning of monkey calls was first worked out with vervet monkeys,which have distinct alarm calls for each of their three main predators: the martial eagle,leopards and snakes. But the vervets did not combine their alarm calls to generate new meanings.

If the Zuberbühler teams observations are correct,the Campbells monkeys can both vary the meaning of specific calls by adding suffixes and combine calls to generate a different meaning. Zuberbühler said he planned to play back recordings of given calls to the Campbells monkeys and to test from their reactions whether he had correctly decoded their messaging system.