Abstract Species of the genus Trachypithecus normally live in groups of less than 20 individuals composed of only one adult male and several adult females (one-male unit). While Indochinese gray langurs (T. crepusculus) live in one male group and multi-male group with less than 30 indiviudals in northeastern Thailand, the conspecific populations in Wuliang Mountain, Yunnan live in large group with up to more than 100 individuals. So far, little is known on detail of the social structure of Indochinese gray langurs in Wuliang Mountain. We studied the social structure of a large habituated group (>70 individuals) of Indochinese gray langurs in Dazhaizi, Wuliang Mountain between September 2012 and July 2015. We selected adult males as focal animal randomly, and then recorded the behavior for other individuals who proximity to the focal male within 5m by 10 minutes interval scanning. Restricted by difficulty of individuals identification, we could only accurately identify age-sex classes of all members staying within 5 m with the focal male in 594 scans in which at least one individual was observed. In 44.2% scans, there was at least one adult male remaining within 5 m to the focal male, with an average of 0.62 ± 0.85 adult males. In 32.5% scans, there were both adult male(s) and adult female(s) remaining within 5 m to the focal male. Most notability, higher frequency (60.0%) and more males (0.93 individuals) were observed surrounding the focal male within 5 m during feeding compared to moving and resting. Our results suggested that the study group did not live in multi-level society that composed of several one-male units and all male units, but live in multimale-multifemale group. Our results also demonstrated that tolerance between adult males in this group was high, especially during feeding. Up to 18 individuals feeding within 5 m to the focal male suggested that food resources were abundant in Wuliang Mountain, at least during certain seasons, which partly explained why Indochinese gray langurs could live in such large groups in the area. We provided preliminary results of social structure of Indochinese gray langurs in Wuliang Mountain which will benefit to better understanding of diversity and evolution of social system of langurs in the future.
LUO Xu E-mail: email@example.com；
CUI Liangwei E-mail: firstname.lastname@example.org；
FAN Pengfei E-mail: email@example.com