Effects of fertility control on social dynamics of Balinese long-tailed macaques

The long-tailed macaque (Macaca fascicularis) has been recently classified as endangered on the IUCN Red List. Meanwhile, fertility control has gain influence in the wild as an alternative to culling and translocation to manage conflicts between synanthropic primates and humans. Yet, behavioral changes associated with fertility control remain poorly documented in free-ranging populations. Our study investigates socio-sexual changes after sterilization by tubectomy of female long-tailed macaques at the Ubud Monkey Forest in Bali, Indonesia. Although tubectomy preserves ovarian function and consequently limits impacts on hormone-dependent behaviors, the growing number of sterilized females over successive campaigns modifies the operational sex ratio. We
tested whether an increased proportion of available females repeatedly cycling within the group would modify the intrasexual competition in males. Through 895 hours of focal samples on 56 adult females (including 17 sterilized females) and 17 adult males over 3 years, we analyzed male grooming and sexual competitive networks, male-female grooming and sexual networks. We found the number of male competitors and the time (duration and occurrence) spent in competition with other males increased along with the number of sterilized females, especially for high-ranking males (GLMMs, α=0.05). Regarding male-female networks, high-ranking males decreased their interactions with sterilized females compared to intact females, while no changes occurred in lower-ranking males. In conclusion, tubectomy has consequences on male-female socio-sexual interactions and male-male sexual competition. Ultimately, these findings might inform appropriate management decisions fostering coexistence between synanthropic primates and humans in shared habitats.