Effects of habitat disturbance and hunting on the density and the biomass of the endemic Hose’s leaf monkey Presbytis hosei (Thomas, 1889) (Mammalia: Primates: Cercopithecidae) in east Borneo

Hose’s leaf monkey Presbytis hosei is endemic to Borneo and occurs only in tall forest. In recent decades Borneo has lost a large part of its forest cover, mostly in low-lying coastal regions. Large intact tracts of forest remain in the interior, but these are by and large inhabited by tribes that subsist in part by hunting. The combined effects of habitat disturbance and hunting on the densities and biomass of Hose’s leaf monkey were studied in Kayan Mentarang National Park in Borneo’s far interior. Over four months, data on densities and hunting were collected by transect walks in four forest types. Hose’s leaf monkeys were hunted to deter crop-raiding, for their meat, and to obtain bezoar stones (visceral secretions used in traditional medicine). Hose’s leaf monkeys occurred in single male groups of 7-8 individuals in densities from 0.8 to 2.3 groups km-2. Densities of Hose’s leaf monkeys were positively correlated with certain vegetation characteristics, e.g. tree height and height of first bough, and negatively correlated with distance to the nearest village. Biomass of Hose’s leaf monkeys declined considerably as a result of habitat disturbance and hunting from 92 kg km-2 in primary hill forest inside the reserve to 38 kg km-2 in old secondary forest and 31 kg km-2 in young secondary forest near villages. A review of the few studies conducted on the effects of habitat disturbance and hunting on Hose’s leaf monkeys reveal inconsistent trends in biomass and density responses.