In the 25th year of the BBC's Natural History Unit, the second ' half of a series in 26 parts. Narrator
David Attenborough 24: Monkey Business A call given when two monkeys meet may also be heard when an individual encounters its favourite food. Is it the same call or are there two distinct calls that humans are unable to appreciate?
Pat Kuhl of Washington
University. Seattle, Peter Marler of Rockefeller University, New York,
Charles Snowdon of the University of Wisconsin, and Tom Strusacker of New York Zoological Society unravel the ' graded ' system of monkey calls.
Written and produced by MICHAEL BRIGHT BBC Bristol