Vocal repertoire of free‐ranging adult golden snub‐nosed monkeys (Rhinopithecus roxellana)

Abstract

Vocal signaling represents a primary mode of communication for most nonhuman primates. A quantitative description of the vocal repertoire is a critical step in in‐depth studies of the vocal communication of particular species, and provides the foundation for comparative studies to investigate the selective pressures in the evolution of vocal communication systems. The present study was the first attempt to establish the vocal repertoire of free‐ranging adult golden snub‐nosed monkeys (Rhinopithecus roxellana) based on quantitative methods. During 8 months in Shennongjia National Park, China, we digitally recorded the vocalizations of adult individuals from a provisioned, free‐ranging group of R. roxellana across a variety of social‐ecological contexts. We identified 18 call types, which were easily distinguishable by ear, visual inspection of spectrograms, and quantitative analysis of acoustic parameters measured from recording samples. We found a great sexual asymmetry in the vocal repertoire size (females produced many more call types than males), likely due to the sex differences in body size and social role. We found a variety of call types that occurred during various forms of agonistic and affiliative interactions at close range. We made inference about the functions of particular call types based on the contexts in which they were produced. Studies on the vocal communication in R. roxellana are particularly valuable since they provide a case about how nonhuman primates, inhabiting forest habitats and forming complex social systems, use their vocalizations to interact with their social and ecological environments.

A natural history of Chlorocebus dryas from camera traps in Lomami National Park and its buffer zone, Democratic Republic of the Congo, with notes on the species status of Cercopithecus salongo

“…Contact calls were the most frequent vocalizations in the dryas monkey footage. Forest‐dwelling primates rely on vocal signals as a primary mode of communication due to low visibility in their habitat (Fan et al, 2018). Therefore, these short, single element calls likely facilitate group cohesion while moving through dense vegetation.…”

Individuality in coo calls of adult male golden snub-nosed monkeys (Rhinopithecus roxellana) living in a multilevel society

“…Specifically, we observed that the resident males uttered coo calls towards the direction of their unit members that were out of sight during unit/group movement in the dense forest. Sometimes, the unit members responded vocally to these vocalizations (Fan et al 2018). The resident males would continuously emit coo calls if their unit members did not catch up.…”

“…Vocalizations were collected at a sampling rate of 44.1 kHz (16 bit) using a Tascam DR44-WL digital recorder connected to a Sennheiser ME 66 directional microphone at distances within 10 m to the monkeys. For the DCS group, we selected one adult male as the subject on an observation day (08:00–18:00) and recorded his coo calls using 5-min focal animal sampling (Fan et al 2018). We then rotated to another on the next day.…”

“…Coo calls are one of the most frequently occurring call types in adult R. roxellana and likely function to maintain contact in various contexts including group movement, foraging, and resting (Fan et al 2018). The spectrogram of coo calls is characterized by few frequency modulations and rich harmonic patterns (Fan et al 2018), and the dense harmonic structure should highlight the formants, making these vocalizations well suited for individual discrimination (Charlton et al 2009b; Owren and Rendall 2001). Here, based on the source-filter theory, we investigated the individuality in coo calls of adult male R. roxellana .…”

“…However, to date, it is not yet known whether and how vocal signals of R. roxellana (and the genus of snub-nosed monkeys in general) can convey information of individual identity. Coo calls are one of the most frequently occurring call types in adult R. roxellana and likely function to maintain contact in various contexts including group movement, foraging, and resting (Fan et al 2018). The spectrogram of coo calls is characterized by few frequency modulations and rich harmonic patterns (Fan et al 2018), and the dense harmonic structure should highlight the formants, making these vocalizations well suited for individual discrimination (Charlton et al 2009b; Owren and Rendall 2001).…”