Behaviour 2019
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An Evaluation of Vocal Complexity in the Long Calls of Bornean Orangutans
Whitney Ross, Haley Kazanecki, Shyam Madhusudhana, Dena J Clink, Wendy M Erb. Center for Conservation Bioacoustics, Cornell Lab of Ornithology, Cornell University, Ithaca, New York, United States

Vocal complexity is central to many evolutionary hypotheses about animal communication; yet, quantifying and comparing complexity remains a challenge, particularly when vocal types are highly graded. We studied long calls (N=130) of Bornean orangutans (N=13) to compare call classification approaches. Previous studies described seven distinct call types within these complex vocalizations, but none quantified their discreteness or reliability of audio-visual (AV) classification. We used three approaches: 1) quantified inter-observer reliability (IOR) across 3 observers, 2) extracted 30 acoustic features using Raven Pro and WarbleR and classified call types using supervised (support vector machines) and unsupervised (affinity propagation and fuzzy c-means) approaches to identify call types and assess their discreteness, and 3) used a non-linear clustering technique (UMAP) for unsupervised clustering of raw spectrograms of calls. We found low IOR and poor classification accuracy using supervised approaches, indicating that pulse types were not discrete. We identify recommendations for future studies and discuss the evolutionary implications of these highly graded calls.