Socio-sexual changes in female long-tailed macaques following sterilization by tubectomy (Bali, Indonesia)

Thriving urban primate populations often create conflicts with humans, calling for special management measures. To control the growth of a high-density population of long-tailed macaque (Macaca fascicularis) in Ubud Monkey Forest (Indonesia), female sterilization by tubectomy started in 2017, a method keeping intact hormonal functions. However, their new reproductive state and the absence of new infants could impact the sterilized females’ behavior and their position in the social group. Our study compared the socio-sexual behaviors and the centrality index of sterilized females with control (intact) females and evaluated intra-individual temporal variation over three years (2017-2019). Using proximity scan and focal data (565 hrs.) of 48 adult females, we predicted that sterilized females continuously cycling would be more sexually active than control females, which could also increase female competition. GLMMs showed that sterilized females were more proceptive than controls two years after sterilization, but became less attractive for males over time. Sterilized females expressed more agonistic behaviors than control ones. Finally, their social centrality within their groups declined significantly over time, probably due to the absence of new infants, known to cement social relationships in female macaques. This study suggests that tubectomy as a management strategy, although keeping female hormonal functional integrity, still could induce changes in social dynamics. Further long-term analyses should precise the patterns of social dynamics’ modification and provide support to management decisions.