Operational sex ratio (OSR) is the ratio of the number of sexually mature males to the estrous females, which is used to predict the intensity of sexual selection. During the mating season (August－December 2007), we studied reproductive and aggressive behaviors in sexually mature male Tibetan macaques (
Macaca thibetana
) in two troops (YA
1 and YA
2) at Huangshan, China. The behavioral data were collected by focal animal sampling, ad libitum sampling and continuous recording. The purpose is to discuss the impact of OSR on mating competition of male Tibetan macaques. The OSR of YA
1 was 0.4:1, and the OSR of YA
2 was 0.9:1. The male-biased in OSR of YA
2 was higher than YA
1. The sexually mature males of high rank in YA
1 troop showed higher rates of reproductive behaviors than the males in YA
2: genital-inspecting, grimace, sexual chase and mating, respectively (P<0.01). The sexually mature males of middle rank in YA
1 troop showed higher rates of reproductive behaviors than the males in YA
2: genital-inspecting, grimace, sexual chase (P<0.01). The sexually mature males of middle rank in YA
1 troop also showed higher rate of mating behavior than the males in YA
2 (P<0.05). However, there was no significant difference in reproductive behaviors between sexually mature males of low rank in two troops. The sexually mature males of high rank in YA
2 troop showed higher rate of aggressive behavior than the males in YA
1 (P<0.01). The sexually mature males of middle rank in YA
2 troop showed higher rate of aggressive behavior than the males in YA
1 (P<0.05). The sexually mature males of low rank in YA
1 troop didn’t show any aggressive behavior. These results suggested that the intensification of male-biased in OSR can lead to the decrease of reproductive behaviors and the increase of aggressive behavior of male Tibetan macaques. The intensity of mating competition of sexually mature males in YA
2 troop was stronger than the males in YA
1. Our results support the prediction of the impact of OSR on mating competition by sexual selection theory.
