Orangutan Long Call Degradation and Individuality Over Distance: A Playback Approach

Researchers have documented individual vocal recognition in several primate species but do not know whether the changes in acoustical parameters that might occur over distance influence the informational content of a call that relates to individuality. Accordingly, we performed playback experiments using male orangutan long-distance calls (long calls) and rerecorded them at increasing distances from the source. We aimed to determine 1) which acoustical parameters changed over distance and 2) whether the percentage of calls that a discriminant analyses would assign to the correct individual would change over distance. High-frequency harmonics were attenuated and lost with increasing distance, but other parameters did not change. The percentage of calls assigned to the correct individual did not change over distance, indicating that even though there are some acoustical changes over distance the opportunity for other individuals to recognize the caller remains similar until ≤300 m, which was the maximum distance at which we rerecorded calls. Extending similar experiments to other primate species and other taxa, while subsequently conducting experiments to assess whether individual discrimination by receivers is indeed based on relatively stable acoustical parameters, would forward our understanding of acoustic communication.