Western Purple-faced Langur Semnopithecus vetulus nestor Bennett, 1833 Sri Lanka (2004, 2006)

Endemic to Sri Lanka, this langur is restricted to a small area of the wet zone in the west of the country, most of which is threatened due to human activities (crops, infrastructure and industry, settlements, deforestation and forest fragmentation, and hunting). Colombo, the capital city of Sri Lanka, is in the center of its very limited range. Hill (1934) indicated that it was common around the capital, but this is no longer the case. Forest cover in Sri Lanka has declined drastically since the late 1950s, and the area of occupancy of this langur has been reduced to a highly fragmented 1,900 km˛ (Molur et al. 2003). Although still quite numerous (>10,000), the declines in numbers are expected to have been precipitous—estimated at more 80% in three generations due to urbanization and development. Western purple-faced langurs are highly arboreal and need good canopy cover, and there are possibly less than three forests that can support viable populations, none of which are protected areas set aside for conservation. The human-modified areas that sustain much of the langur population, such as gardens and rubber plantations, are under private ownership and changing rapidly due to human population expansion and development; large trees are cut down and entire forest patches are destroyed for housing and development. This severely restricts home ranges, isolating the groups, and resulting in escalated conflict with humans and low juvenile recruitment rates (Dela 1998). Long-term studies by Dela (1998) have shown that this taxon is unique in having subpopulations adapted to a diet high in mature/ripe fruit, a feature as yet unrecorded for any other colobine, and are dependent on fruits cultivated by humans. The geographical range of the species has a very high human population density, and home ranges are being compressed due to loss of tree cover. Censuses are urgently needed to identify forest areas for conservation and to better quantify the decline of subpopulations in space and time, and to provide a better understanding of their demographics (especially reproductive rates, population turnover and dispersal) in the extremely disturbed habitats where they survive today. Jinie Dela & Noel Rowe

References Dela, J. D. S. 1998. The ecology and social biology of a selected population of the western purple-faced leaf monkey (Trachypithecus vetulus nestor = Presbytis senex nestor). PhD thesis, University of Peradeniya, Peradeniya. Hill, W. C. O. 1934. A monograph on the purple-faced leaf monkeys (Pithecus vetulus). Ceylon J. Sci. (B) 19 (Pt.1): 23–88. Molur, S., Brandon-Jones, D., Dittus, W., Eudey, A., Kumar, A., Singh, M., Feeroz, M. M., Chalise, M., Priya, P. and Walker, S. (eds.). 2003. Status of South Asian Primates: Conservation Assessment and Management Plan (CAMP) Workshop Report, 2003. Zoo Outreach Organisation, IUCN/SCC Conservation Breeding Specialist Group – South Asia, Coimbatore, India. viii + 432pp. Suggested citation: Dela, J. and Rowe, N. 2007. Western Purple-faced Langur, Semnopithecus vetulus nestor Bennett, 1833. In: Primates in Peril: The World’s 25 Most Endangered Primates 2006–2008, R. A. Mittermeier et al. (compilers), p.15. Unpublished report, IUCN/SSC Primate Specialist Group (PSG), International Primatological Society (IPS), and Conservation International (CI), Arlington, VA.