Gibbon Songs: Understanding the Evolution and Development of This Unique Form of Vocal Communication

Abstract

Gibbons, as well as the siamang, are small apes with an extraordinary high diversity in distinctive loud calls, commonly referred to as ‘songs’, unusual among primate lineages. Analogous to bird songs, gibbon songs have a sequential structure organized from single vocal utterances with species and sex specificities. These specialized vocal communications are comparable with human speech and are not found in other apes. However, how their songs have evolved is not well understood. This contribution attempts to argue the tentative hypothesis that socio-ecological factors enhance auditory-dominant communication systems in gibbons by reviewing recent studies on specialized patterns of development and production mechanisms of gibbon songs. Unlike other singing vertebrates, gibbon mothers and daughters simultaneously sing (co-sing) female-specific songs, and mother-daughter co-singing interactions likely contribute to song development. Moreover, remarkable sound propagation of songs is achieved by a specialized vocalism of formant tuning , analogous to human soprano singing. It is plausible that both of these specializations would be adaptive responses to environmental pressures within their socio-ecological background, such as arboreality , brachiation , high degree of sociality , small body size , and long-lasting mother-offspring bonding.