Dissertation Research: Signal Content and Function in Wild Male Orangutan Long Calls

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Despite previous long-term behavioral studies, a full understanding of the social organization and reproductive strategies of orangutans has been difficult to achieve due to their extended life histories, large home ranges, predominantly arboreal lifestyles and semi-solitary natures. Because adult individuals are normally dispersed and visibility is limited within their rainforest habitats, long distance vocalizations are likely to play an important role in regulating individual relationships and social interactions, including reproduction. There is already strong and consistent behavioral and experimental evidence for an intra-sexual spacing function, but additional hypotheses such as mate attraction or protection against sexual coercion have not been tested rigorously. It is also not yet clear if reliable assessment cues are encoded in acoustic features and calling patterns or if listeners can recognize individual males and associate a signaler's identity with past performance. This research aims to test predictions for the signal content of male long calls, examine potential functions and assess possible determinants of variation in calling behavior among Bornean and Sumatran populations. Using field recordings, focal animal sampling and carefully controlled playback experiments, this study intends to examine acoustic variation in male long calls, the patterns of calling behavior by males and behavioral responses in relation to the listener's social context, reproductive status and familiarity with the calling male. The signal content of male orangutan long calls has important repercussions for understanding female mate choice and the nature of inter-individual relationships in this endangered species.