Effects of anthropogenic disturbance on group densities of Thomas' langurs ( <scp> <i>Presbytis thomasi</i> </scp> ) within a lowland tropical forest, north Sumatra

Ecosystems around the globe are facing irreversible impacts due to climate change, habitat destruction, hunting, and an ever-increasing human population. Estimating densities of species across their geographical range helps us understand natural variation anthropogenic effects on assess effectiveness existing conservation measures. Various methods have been used produce accurate precise population density estimates, each with associated limitations. Acoustic surveys for producing loud calls become common ease use, low cost, reduced timescale. Relative many other mammal taxa, primate studied extensively, a wealth data socioecology behavior, but most species, estimates over large ranges still lacking. We acoustic spatial capture–recapture model estimate group unhabituated Thomas' langurs (Presbytis thomasi), endemic Indonesian island Sumatra, 60 km2 area lowland dipterocarp forest. then assessed if vegetation structure distance from habitation affected estimates. Estimates differed almost threefold between survey locations (from 2.79 8.08 groups/km2); there was no clear relationship forest structure, significantly positive habitation, increase 0.38 groups/km2 every km distance. Although large-scale logging within Sikundur region ceased ~30 years ago, continue detrimental area.