| Description |
Vocalizations are used in multiple contexts for widely different functions. However, the vocalizing individual may convey more information than merely the primary context of the vocalization, including caller identity, dominance status, reproductive status, body condition, etc. Decoding these potential signals could be useful as a noninvasive research tool in conservation. We explore this possibility in the long-distance vocalization of the male orangutan, the long call, and address three questions. When do males call? Researchers must first understand the temporal call patterns of the targeted species to know when and how to study the species. By using a passive acoustic monitoring (PAM) system and direct observation, we were able to study in an unbiased manner when flanged male orangutans call. We discovered that the diurnal orangutan calls more frequently at night than during the activity period. What influences the calling behavior of individuals? Understanding if social or environmental factors influence vocal behavior is necessary to be able to disentangle the information content of vocal signals. While multiple social factors, like association with another individual, do result in a higher long call rate of male orangutans, the dominant influence on vocal behavior was food availability. We discuss how local ecology may determine to which degree each factor can influence vocal behavior. How do vocalizations vary over time? Understanding which aspects of the vocalization remain constant and which vary is key to understanding which acoustic features may encode signals that should not change, such as identity, and signals that may change, such as body condition or dominance status. We found that, while there is inter-individual variation, overall the orangutan long call is not stereotyped, and the most easily measured acoustic features do not allow reliable identification of individuals over long time periods. With current rates of deforestation around the world, conservation managers seek a less labor intensive and noninvasive method to monitor habitat condition. If researchers are able to decode acoustic signals, vocal behavior may provide a more sensitive method to monitor populations and, potentially, habitat condition. This research shows for the highly endangered orangutan clear limitations in this approach, but also highlights that habitat condition may be reflected in the calling behavior. |
