Vocal diversity and taxonomy of white-cheeked crested gibbons

Abstract

Previous research suggests that gibbon song repertoire is genetically determined and song characteristics are useful for assessing systematic relationships. The taxonomy and distribution of crested gibbons (genus Nomascus) had not been studied previously. In addition, crested gibbons face several threats to extinction such as habitat loss, the pet trade, the domestic and international trade of wildlife, and unsustainable harvest of wildlife for subsistence consumption. Additionally, rice field expansion and poaching pose significant threats to gibbons and their habitats, especially because most populations are very small. I studied vocal diversity among different wild populations of Nomascus in Vietnam and Laos to assess their taxonomic relationships and to examine whether their vocal patterns correspond to forms previously described. Linear discriminant analysis, classification trees, and multidimensional scaling revealed distinct populations based on song characteristics and species (or subspecies) boundary locations were recognized. In addition, population sizes in different areas were estimated based on vocal analysis. The recognition of previously unknown diversity within Nomascus and ability to locate potential species boundaries aided in implementation and adaptation of gibbon conservation strategies and the development of gibbon management plans for protected areas. In addition, this project improved the monitoring of a poorly known and understudied ape, by working with provincial staff and local people.