Comparison of Grooming Income between OMUs of Rhinopithecus bieti

Grooming behavior is the main way for non-human primates to maintain social relations. The income of grooming can reflect the role and social ranks of individuals in the group. In order to understand the impact of individual social roles and grades on grooming income of Rhinopithecus bieti within in one male multi-female units (OMU), during July-August 2018 and February-August 2019, the data of grooming behavior and aggressive-yielding behavior of R. bieti group in Baima Snow Mountain National Nature Reserve were collected, and the grooming income and influencing factors of males and females were analyzed. The results showed that 32.3% of adult individuals in the breeding unit of R. bieti were rewarded with grooming rounds, and the average grooming time was 302 ± 255 s (n = 96). There was no difference in grooming income of dominant males among the breeding units with the same number of females (Z = 4.59, P = 0.20). In the male female bout pairs, the grooming income of male was higher than those of female (T = −6.138, df = 58, P < 0.01), but there was no difference in grooming income between difference grades female as they groomed male (Z = −1.54, P = 0.12). The grooming income of high grade female was higher than low grade female grooming income (T = −3.467, df = 36, P < 0.01) within OMU. Therefore, the grooming income of dominant males in OMU of R. bieti was higher than that of females in the multi-level society, and there was no difference in grooming income in OMU of the male grooming income with the same number of adult females. The grooming income of high grade females was higher than that of low grade females, which indicated that the grooming income of R. bieti was influenced by social roles (dominant male) and grades within OMU.