Integrating population surveys and population viability analysis to evaluate and guide future rhesus macaque (Macaca mulatta) contraceptive programs in Hong Kong

Rapid urbanization exacerbates human-wildlife conflict, particularly affecting synanthropic species, such as rhesus macaques (Macaca mulatta) in Hong Kong, who frequently venture into urban areas. To mitigate negative human-macaque interactions, the Agriculture, Fisheries and Conservation Department of the Hong Kong Government implemented a multipronged approach, which includes a long-term contraceptive program, regular population surveys, and a ban on intentional feeding. In this study, we described the contraceptive program implemented since 2009, conducted systematic population surveys to examine population trends and analyzed data to evaluate the effectiveness of the program since its commencement. We also conducted population viability analysis (PVA) to predict population trends under different sterilization intensities to inform future contraceptive efforts. We sterilized 1,923 individuals endoscopically. We found that the macaque birth rate dropped from 59% to 31% within 3 years of program implementation, then the birth rate and population size remained relatively stable over time. To achieve a stable macaque population, the PVA suggests sterilizing 80–100 individuals per year. Sensitivity analysis reveals that macaque populations are most sensitive to adult survivorship, while birth rate has low elasticity but relatively high sensitivity, both of which are lower than adult survivorship. This result underscores the importance of managing food availability. Overall, our results suggest that continued implementation of the sterilization program and feeding bans are essential for controlling population growth and achieving human-macaque coexistence, with long-term success requiring a multifaceted, adaptive management approach integrating contraception, resource management, behavior modification, and ongoing evaluations.