An Analysis of the Organization of Vocal Communication in the Titi Monkey Callicebus moloch

Abstract

Vocalizations of titi monkeys were recorded from 6 groups at 2 sites in the llanos of Colombia during 8 mo. of study. Frequency and temporal measurements from spectrograms of recordings, and differences in their patterns of use, were used to characterize call types. Animals repeat calls to form phrases, and combine phrases to form sequences. The 6 sequence types, defined by different transition probabilities between phrases, varied in proportion in different contexts. To examine the effect of order of phrases on response, artificially constructed sequences were played back to subject groups. Hierarchical and sequential mechanisms are discussed as generators of vocal sequences, and comparisons with models of human language are drawn.