The Socioecology, and the Effects of Human Activity on It, of the Annamese Silvered Langur (Trachypithecus margarita) in Northeastern Cambodia

Abstract

The Annamese silvered langur (Trachypithecus margarita) is a colobine species recently recognized as a separate species and considered Endangered by the IUCN. It lives in Indochina, east of the Mekong River. There are some studies on its morphology, distribution and diet. Information on the species’ ranging, social behavior and organization, habitat use and reproduction is scarce. The effects of human disturbance on langurs are unknown, a reason for concern given the current biodiversity crisis in the region. Information on the habitats where the species is found in the wild is scarce, with some sources conflicting. I aim to expand our current knowledge on the socioecology of T. margarita and the effects of human activities on it. Research was done at Veun Sai Siem Pang Conservation Area, Ratanakiri Province, Cambodia, from April 2013 until May 2014. An unhabituated group was followed for five days every week. Group size was estimated and their geographical position was marked every 30 minutes until the end of the day or the group was lost. Canopy layer and forest type were noted every time an individual was seen. When eating, plant part and species were identified to species level. Eight botanical transects of 5x200 meters were set up, classified by forest type and anthropic disturbance. Plants with a DBH of 12 cm or over were identified to species level. Biodiversity and Evenness indices were calculated for the habitat and each transect and compared. Langur visits to a mineral lick were recorded using camera traps. Group size, sex and age classes were counted, and morphological characters analysed for individual variability. Chainsaw numbers, length of logging in hours and distance from logging spots to the group were calculated daily. Mixed evergreen forest is more heterogeneous than mixed deciduous forest and presents more canopy layers and smaller stems. Logging tracks affect habitat structure but not diversity, while intensive logging strongly affects structure and diversity. Vertebrate populations at VSSPCA are resilient to small scale logging. T. margarita at VSSPCA are morphologically uniform. Group size is at least 61 individuals and the social organization is multi-male multi-female. Langurs associate with other sympatric species of primates at the site, especially M. leonina and P. nemaeus. Langurs fed mainly on seeds, (69% of their diet), but also ate other fruit parts; leaf consumption was low. Focus on plant parts, food species and families varied between ix seasons. Dipterocarps were highly consumed, but Willughbeia and oak trees were highly selected. Home range size reached 256 ha, being larger in the dry season than in the rainy season, likely because of different food availability. The high canopy was most frequently used, although juveniles used the mid canopy more frequently. Langurs preferred mixed deciduous forest during the rainy season but avoided it during the dry season, probably for a lack of canopy to hide and feed. Langurs were strongly affected by logging, moving higher in the canopy as intensity increased, and abandoned areas of their home range where it was most destructive. While T. margarita tolerates human disturbance, loggers target key tree groups and law enforcement must be maintained.