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Impact of monkey-human relationships and habitat change on Semnopithecus vetulus nestor in human modified habitats


Jinie D. S. Dela

No. 45, Gunatilleke Mawatha, Etambagoda, Panadura, LK
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Semnopithecus (Trachypithecus) vetulus nestor,(Family: Cercopithecidae, Sub-family Colobinae) the western purple-faced langur of Sri Lanka, is currently recognized as one of the world’s 25 most endangered primate taxa as much of the free-ranging populations of this subspecies are found in human modified areas. Accordingly, this paper seeks to identify and assess the impact of monkey-human relationships on S. vetulus nestor, in areas where monkeys and humans co-occur, and to ascertain threats to these langur populations living outside natural forests.

Monkey-human conflicts were investigated in 1985 during a census of langurs at seven sites in and around Panadura and Piliyandala. More detailed data were gathered through direct observation of two habituated free ranging groups of S. vetulus nestor in home gardens and rubber monocultures at two study sites in Panadura and Piliyandala during a systematic study from 1985–1987. This was followed by opportunistic observations during 1987 – 1992 at the Panadura site. A questionnaire was administered to householders at these two sites in 1987, and habitat change was monitored periodically thereafter until 2006 at both sites.

The study revealed that loss of canopy cover due to habitat destruction was the most significant threat to S. vetulus nestor in human modified environments, followed by hunting, which varied in intensity at different sites. Live capture of monkeys as pets was not a threat at any of the investigated sites. Langurs caused damage to crops and tiled roofs, and were considered pests by 47.5% and 82.4% of householders at the two main study sites. Despite this, there was high tolerance towards langurs by householders at both study sites during the 1987 survey; less than 10% of the householders wanted monkeys destroyed; and fewer were willing to do so themselves. Most people at each site (63.1% and 55.6% at Panadura and Piliyandala respectively) harassed or chased monkeys only if they caused crop or roof damage. At both sites, food competition-mainly for human edible fruit-was the main cause of conflict, followed by roof damage.

The study sites exemplify scenarios in non-forested areas in the densely populated geographic range of S. vetulus nestor. This study, therefore, underscores the precarious existence of this Critically Endangered langur in human–modified habitats, which are vulnerable to change. Ensuring the survival of S. vetulus nestor requires addressing the major challenges of establishing linkages between isolated forest fragments in its range and maintaining adequate canopy cover and food trees in the main forest and modified habitats without further delay.

Keywords: Habitat fragmentation, human modified habitats, monkey-human conflicts, Semnopithecus vetulus nestor.


J.Natn.Sci.Foundation Sri Lanka 2011 39 (4): 365-382

How to Cite: Dela, J.D.S., 2011. Impact of monkey-human relationships and habitat change on Semnopithecus vetulus nestor in human modified habitats. Journal of the National Science Foundation of Sri Lanka, 39(4), pp.365–382. DOI:
Published on 30 Dec 2011.
Peer Reviewed


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