Distribution of Capped Langurs (Trachypithecus pileatus) in Bhutan

Bhutan is a biodiversity hotspot and home to seven primate species, including the langur species Trachypithecus geei, T. pileatus, and Semnopithecus shistaceus. Despite the already declining populations, with predictions for another 30% decline over the next 36 years, little research has been conducted on capped langurs (T. pileatus). To provide baseline data on the distribution of capped langurs in Bhutan, I mapped reported sightings of capped langurs using GPS data collected in the field by Bhutanese staff of the Ugyen Wangchuck Institute for Conservation and Environment Research (UWICER). I calculated total langurs recorded, overall mean, median, and modal group sizes, total number of groups recorded per district, total number of individuals per district, and recorded the adult to young, adult male to adult female, and adult female to young ratios. I used additional spatial data provided from UWICER to analyze environmental factors potentially influencing group sizes and ratios. Results showed variation in number of groups and mean group sizes between the districts. The district of Samdrupjongkhar, situated in southeastern Bhutan, had 21 mapped capped langur locations with an average group size of 4 individuals. The northern district of Lhuentse had only one mapped capped langur location with a group size of 11. Land use and cover type showed no effect on overall group size. Variation in a capped langur groups’ proximity to landscape features (road, river, settlement) showed an effect on group size, however an effect was not found for group demographics