The effect of tropical forest modification on primate population density and richness

Agricultural expansion is increasingly forcing primates to exist within heavily modified landscapes. To assess the long-term viability of these populations, robust monitoring is required, however the cryptic nature of primates and sparse distribution often makes collecting sufficient data to produce precise density estimates challenging, particularly within disturbed areas. Here, I undertook a pilot study assessing the feasibility of using occupancy modelling as a state variable for monitoring six diurnal primate species, the Sabah Grey Langur (Presbytis sabana), red leaf monkey (Presbytis rubicunda), long tailed macaque (Macaca fascicularis), pig tailed macaque (Macaca nemestrina), Bornean gibbon (Hylobates muelleri) and orangutan (Pongo pygmaeus morio), using direct observations within a heavily modified landscape in Borneo. Low detection rates led to high levels of uncertainty and using simulations to extrapolate these results to the maximum survey effort available for a main study, revealed no single study design would provide precise estimates (SE