Copulation behavior within one-male groups of wild Rhinopithecus roxellana in the Qinling Mountains of China

Abstract

This study was conducted using focal animal sampling on the west ridge group of the Sichuan snub-nosed monkey (Rhinopithecus roxellana) located in the Zhouzhi National Nature Reserve on the north slope of the Qinling Mountains, from 8 July 2003 to 24 May 2004. The difference in the average frequency of copulations for each focal male for each month was significant (F=3.068, P=0.016, one-way ANOVA test) with the majority of copulations occurring between September and November. Duration of intromission ranged from 2 to 39 s, with a mean of 16.0+/-0.4 s. Females initiated 627 courtship attempts (96.2%), while males only initiated 3.8%. Both adult females (72.8%) and sub-adult females (27.2%) were involved in sexual interference acts. Females who gave birth in 2004 performed more sexual interference acts than would be expected by chance in the reproductive period of 2003 (X2=13.73>X2(0.005,2), df=2, P<0.005). Male response to female interference was equally divided into "solicitor mounting" and "interrupter mounting". The resident males of one-male units were not observed to mount both the solicitor and the interrupter or mount neither following female solicitation interruptions. Three post-conception copulations were also observed in this study. These results suggest a skewed sexual competition, with multiple females competing for a single male, which was shown by courtship attempts and female interference.