Socioecology of white-headed langurs (Presbytis leucocephalus) and its implications for their conservation

A study on the socioecology of white-headed langurs (Presbytis leucocephalus) was undertaken in Bapen Reserve, China, between December 1996 and September 1998. White-headed langurs occur on clumps of limestone hills in four counties in Southwest Guangxi. Due to the heavy pressure of human population, flat ground surrounding the groups of hills is largely lost to agricultural use and tree felling, thus the habitat of white-headed langurs is fragmented into several patches. In addition to habitat fragmentation, tree felling is another serious conservation issue that is often ignored in conservation management. White-headed langurs are endemic to this area thus it is necessary to investigate the effects of these human activities on their survival. The objective of this research was therefore to provide recommendations for improving the conservation management of white-headed langurs. A survey was carried out on the overall population size in Bapen Reserve. Five groups of hills were surveyed. Data showed that local extinction has been occurring for a long time, due to habitat destruction and hunting. However, a drastic population decline has taken place over the past ten years. Most langurs were found in a hill-group in which the Reserve staff members often patrol. The langur population in this hill-group was defined as the main population pool of the Reserve. Further detailed sampling in the main population pool showed a much higher population density compared to other hill-groups. Langurs preferred large areas of continuous habitat. A similar survey was carried out in Longgang Reserve, Ningming County, which indicated a high population density in the central area of that reserve where the habitat has been much less disturbed by humans. In the area of the main population pool, data were collected on climate, distribution of vegetation patches, plant species richness, phenology of food plant species, feeding ecology, range use and group dynamics of langurs. Habitat quality was classified according to the extent of human disturbance. Results showed that a large amount of mature leaves were available year round. Young leaves maintained a low level of availability, but disappeared almost completely in the winter of 1997. Rainfall was seasonal and was linked to the production of fruits and young leaves. Vegetation was mainly distributed on the lowest 40% of the hills. Behavioural data showed that the activity of white-headed langurs was restricted to the hills by the distribution of vegetation. Langurs fed mostly on less common plant species. These were more likely to occur in the higher quality habitat, for which different langur groups competed. As a consequence, only the langur groups living in 50% of the higher quality habitat area produced offspring. Langurs fed intensively on young leaves. Compared to other colobine species, white-headed langurs were extremely folivorous. The home ranges of langur groups were smaller in higher quality habitat and well defended. Adult males seemed to compete for habitat to attract females. Intergroup spacing was maintained by loud calls accompanied by jumping about by breeding males. A bisexual group was composed of one adult male, several adult females, and their offspring. In the main study area of this research, only a few males made a genetic contribution to the next generation in the observation period from September 1997 to September 1998. With further habitat degradation, the number of breeding males may decrease further, which may accelerate extinction of the whole population of langurs in Bapen Reserve. Based on these findings and conservation issues in Bapen Reserve, some recommendations are provided for improving langur conservation management. The goal is to avoid extinction of the Bapen population of langurs in the foreseeable future. Options for in situ and ex situ conservation action are recommended. In situ action is classified into three phases: short-term action is to stop the current trend of population extinction and habitat degradation immediately. Medium term action is to increase the area of high quality habitat, and then allow the langur population to recover. In addition to white-headed langurs, other wild plants and animals will also benefit from these objectives.