The vocal repertoire of adult male blue monkeys (Cercopithecus mitis stulmanni): A quantitative analysis of acoustic structure

Abstract

Vocal signals are key elements in understanding species' behavior, sociality, and evolution. Quantified repertoires serve as foundations for investigating usage and function of particular signals, and also provide a basis for comparative analyses among individuals, populations, and taxa to explore how entire signal systems evolve. This study presents a descriptive catalogue of all vocal signals used by adult male blue monkeys (Cercopithecus mitis stuhlmanni). During 12 months in the Kakamega Forest, Kenya, I observed and digitally recorded vocal behavior of 32 adult males across a variety of socioecological contexts. From recordings, I measured 18 temporal-frequency parameters. Undirected ordination and hierarchical cluster analysis identified six distinct call types regularly used by males: ant, boom, ka, katrain, nasal scream, and pyow. Cross-validated discriminant function analysis supported the classifications. The repertoire is best described as discrete, though some gradation occurs between pyows and ants. Summary of acoustic structure and exemplar spectrograms are provided for each call type, along with preliminary examination of socioecological contexts in which they were produced. Discussion addresses repertoire structure, similarity to other taxa, and potential for functional inferences.