In group-living primates, vocal communication is critical for social interactions, maintaining contact with group members, avoiding confrontations with individuals in other groups, and evading predators. For this study, we investigated the vocalization patterns of wild woolly monkeys from the Tiputini Biodiversity Station in Amazonian Ecuador. We combined behavioral data previously collected in 2014 and 2015 on four groups of woolly monkeys and coupled that data with audio recordings captured opportunistically from the same individuals over a six-week study period in summer 2019. We tabulated nearly 10,000 vocalizations emitted by focal animals between 2014 and 2015. A majority of these vocalizations (92.8%) were classified as short to medium distance contact calls. Adult females, with and without dependent offspring, vocalized significantly more often than small adult males, but not more often than large adult males. Examining the occurrence of vocalizations among groups at 5-minute intervals, we found that larger groups vocalized significantly more often than smaller groups. Together these data emphasize the importance of vocal communication to maintain group cohesion in a habitat with limited visibility. We are currently analyzing the recordings collected in 2019. Specifically, we are inspecting the acoustic structure of different call types (e.g., contact calls, alarm calls, and those indicative of agonistic and affiliative behavior), as well as identify individual variation and plasticity of various call features (e.g., duration and frequency). Very few studies have investigated the vocalizations of woolly monkeys, and only two have recorded variation and analyzed call structures in wild populations. By identifying when particular vocalizations are used, by who, and under what contexts, we may better understand which factors were important in the evolution of our own communication and development of human language.
Author: Amber Warren
Faculty Advisor: Dr. Kelsey Ellis, Department of Anthropology
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