The vocal repertoire of an African colobine, Colobus angolensis ruwenzorii: a multi-level society compared to congeners in stable groups

Abstract

Abstract Vocal behaviour offers a window into understanding the social life and evolution of animals. Colobine monkeys show great interspecific and interpopulation variation in their social organization and behaviour. Recent research has shown that Rwenzori Angolan colobus (Colobus angolensis ruwenzorii) differ substantially from other black-and-white colobus in forming a multi-level society. No previous research has been conducted on the communication of C. a. ruwenzorii, but the social complexity hypothesis for communication suggests that more complex societies should evolve more complex communication repertoires. Our objective was to catalogue the vocal repertoire of C. a. ruwenzorii at Nabugabo, Uganda, and to compare it with the data available on congeners regarding intergroup tolerance, vocal repertoire size, and acoustic and behavioural features of vocal communication. Vocalizations were subject to spectrographic and behavioural analysis, and a descriptive analysis of each vocalization type was made. The influence of a few environmental and social factors on calling rates was also examined. We describe five vocalizations (i.e., the snort, roar, squeak, scream and pok) and one non-vocal signal (i.e., the tongue click) in this subspecies and their contexts. Distinct alarm calls are made for dogs, and these are given more often near the edge of the forest where humans frequent. We did not find that C. a. ruwenzorii showed a greater vocal repertoire than C. guereza or C. polykomos, which do not live in multi-level societies. Further, preliminary data do not indicate greater calling rates in larger core units of C. a. ruwenzorii compared to smaller units. These findings support the view that these primates’ vocalizations tend to be relatively conserved despite large differences in social organization.