Abundance of introduced rhesus macaques (Macaca mulatta) in central Florida

Introduced non-human primates threaten native ecosystems and have the potential to transmit diseases to humans and native wildlife, but primate population management is challenging and often controversial. Rhesus macaques (Macaca mulatta), native to much of Asia, were introduced to an island in the Silver River in central Florida (Marion County, U.S.A.) in the 1930s and 40s. An initial population of approximately twelve individuals has grown and spread throughout what is now Silver Springs State Park. In 2015, the park was home to at least 176 rhesus macaques despite the removal of approximately 1000 animals over the preceding 30 years. The Silver River flows east into the Ocklawaha River, where rhesus macaques were reported as early as the 1970s. Population management or further research on the effects of rhesus macaques in Florida requires estimates of abundance, home range, and distribution, yet prior to this study the abundance and spatial distribution of the Ocklawaha groups were unknown. In this study, we evaluated minimum population size, number of groups, and minimum winter home range size of Ocklawaha River groups, and compared these metrics with the previously-studied Silver River groups. We surveyed a 52 km section of the Ocklawaha River using baited camera traps and river surveys for ten weeks. We identified six Ocklawaha River macaque groups, each containing between fourteen and 39 individuals, for a minimum abundance of 134 individuals. Minimum winter home ranges were between 3.63 and 11.89 km, measured as the linear distance between the furthest points at which a group was observed. Overall, Ocklawaha groups were smaller and had larger winter home ranges than Silver River groups, a difference likely driven by provisioning from tourists along the heavily-visited Silver River. This information is crucial for management of the central Florida rhesus macaque population and for future research regarding population growth and ecology of this invasive species.