Polygynous Mating System and Behavioural Reason of Black Crested Gibbon ( Nomascus concolor jingdongensis  ) at Dazhaizi, Mt. Wuliang, Yunnan, China

The field research on five black crested gibbon groups, recently performed at Dazhaizi, Mt. Wuliang, Central Yunnan, China, showed that all groups in the local population consisted of one adult male, two adult females and 2-5 sub-adults, juveniles and infants. The mean group size was 6.2 in August 2003 and 6.4 in August 2005. Two sub-adult males disappeared from their natal home range and three newborns were given birth in Group 3 (G3) and G4 during this study. The two adult females in G1, G2 and G3 gave births and/or carried babies but at different times. There was no aggressive or dominating behaviour observed between the two adult females. One floating female was first seen in G3's territory on April 15, 2005. The two resident females interrupted her duet with adult male and chased her. We did not observe adult male chased this floating female and she left G3's territory 10 days later. Sub-adult males often kept distance with the family, and they often sang solo bouts in their natal territory before they dispersed. The sub-adult males and females dispersed from natal territory and two adult resident females rejected the third one, which might were the reasons why the black gibbon groups were polygyny in Dazhaizi.

Keywords
Nomascus concolor jingdongensis; Group size and composition; Social structure; Polygyny; Local population; Wuliang Mountain