Udomlux Suwanvecho. Behavioral study of maturation of white-handed gibbons (hylobates lar) at Khao Yai National Park, Thailand. Master's Degree(Environmental Biology). Mahidol University. Mahidol University Library and Knowledge Center. : Mahidol University, 1997.
Behavioral study of maturation of white-handed gibbons (hylobates lar) at Khao Yai National Park, Thailand
Abstract:
A field behavioral study of the white-handed gibbons (Hylobates lar) was carried out in the Khao Yai National Park, Thailand, from November 1995 to July 1996. The goal of the research was to study the maturation process and to evaluate the roles of subadults in their social groups. The research was focused on the differences between animals in proportion of time they spent in social behavior and the social interactions of subadults with other individuals. Earlier studies indicated that subadults are peripherized by the adults after reaching maturation, and automatically excluded from their groups. The findings from this study show that subadults are not peripherized as soon as believed. Instead, they remained with their family for several years even after maturation, and played positive roles in their groups. The maturation process of subadult females was rarely observed in the wild. It was generally believed that subadult females received the same level of antagonistic behavior from the female adults as subadult males did from male adults. However, the subadult female in this study had closer relationship with the adults and was not observed to be subject of aggression, while the subadult males received frequently antagonistic behavior from adult males. This phenomenon can be explained by the extra pair copulation and the kin-ship theory. Reciprocal benefits are believed to exist between adults and subadults that remained in a group after maturation. Two major benefits that subadults contribute to breeding adult pairs observed in this study are: (1) aid in territorial defense and; (2) improved physical and social development of juveniles through playing and grooming.