December 8, 2009
Boom! Hok! A Monkey Language Is Deciphered
Boom boom! (I'm here, come to me!)
Krak krak! (Watch
out, a leopard!)
Hok hok hok! (Hey, crowned eagle!)
Very good ' you
have already mastered half the basic vocabulary of the Campbell's monkey, a
fellow primate that lives in the forests of the Tai National Park in 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
Having spent months recording the monkeys' calls in response to
both natural and artificial stimuli, a group led by Klaus Zuberb'hler of the
University of St. Andrews in Scotland argues that the Campbell's 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 vocalizations in which the order of the sounds seems to have some effect
on their meaning, though it is hard to say what. Dr. Zuberb'hler's team reports
deciphering some of the Campbell's monkey's 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 context ' when 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 monkey's version of
'Timber!' ' it warns of falling trees.
There is yet another variation on
this theme, Dr. Zuberb'hler's team reports. Into the 'Timber!' call, the
Campbell's 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,
unlike human words that can be combined in an infinite number of different
If the Zuberb'hler team's observations are correct, the
Campbell's monkeys can both vary the meaning of specific calls by adding
suffixes and combine calls to generate a different meaning. Their call system,
the researchers write, 'may be the most complex example of 'proto-syntax' in
animal communication known to date.'
Dr. Zuberb'hler said he planned to
play back recordings of given calls to the Campbell's monkeys and to test from
their reactions whether he had correctly decoded their messaging system.