Decoding acoustics of Colobinae primates inhabiting the canopy of the Congo Basin rain forest

Bc. Ema Cehelská

Diplomová práce

Abstract:

Vocal signals are an important component of communication of most non-human primates and are commonly used for monitoring elusive species. Passive acoustic monitoring is a promising method for studying and surveying Bouvier’s red colobus (Piliocolobus bouvieri) whose recently rediscovered populations are at a risk of decline due to illegal hunting. This thesis presents the results of the first-ever acoustic study of P. bouvieri, and focuses on the analyses of the vocal repertoire, contextual use of calls, vocal individuality, call detection distance, and the potential for automated detection, which provides foundational information for future acoustic monitoring system. Audio and video recordings were obtained during 15 recording sessions of a single population of P. bouvieri in Ntokou-Pikounda National Park. Vocalization samples were manually extracted, and their attributes were quantified in 24 acoustic variables. Linear discriminant analysis and hierarchical clustering of 520 high-quality samples supported the division of the vocal repertoire into four distinct call categories, namely “wheet”, “nyow”, “chirp-nyow”, and “chirp”, with gradation between call types. Adult males were shown to be the primary vocalizers in social groups and the only ones to produce wheet calls. Vocal behavior was observed in a wide range of contexts and the production of wheet calls was connected to locomotion. The analysis of vocal individuality showed significant variability of nyow calls of adult males on an inter-individual and intra-individual level. Detection distance of calls was estimated to 268 ± 30 m for wheets and 112 ± 30 m for nyow calls based on the comparison of audio recordings captured by static and mobile AudioMoth automated recording units. The possibility of automated call detection was explored using a customized Band-Limited Energy Detector from Raven Pro software on audio captured by AudioMoths. The comparison with manual detection showed low precision (31.49%) and sensitivity (30.32%) of the detector to nyow calls. This thesis contributes to broadening the knowledge of the complexity of vocal expression within the Piliocolobus genus by presenting the results of the first-ever analysis of P. bouvieri vocal expression. Furthermore, it provides a necessary reference for designing a system of future passive acoustic monitoring of this endangered species.

Keywords

vocalization, repertoire, Piliocolobus bouvieri, individuality

Jazyk práce: angličtina

Datum vytvoření / odevzdání či podání práce: 31. 3. 2026

Obhajoba závěrečné práce

• Vedoucí: Mgr. Tomáš Jůnek, Ph.D.
• Oponent: Markéta Gloneková, externi

Česká zemědělská univerzita v Praze

Fakulta životního prostředí

Magisterský studijní program:
Aplikovaná ekologie