Purple-faced langur  (Semnopithecus vetulus)

The purple-faced langur is a long-tailed arboreal monkey endemic to Sri Lanka (4). Coat colour varies with the subspecies, but is generally brownish-black on the body and limbs, whilst the facial whiskers range in colour from white to pale brown and are directed backwards. Newborns, by contrast, possess a pale grey coat, with a brownish tinge on the crown, chest, arms and legs. The thumb of this species is markedly reduced (5). The face is greyish-black, as opposed to purple as its common name suggests (2).

Endemic to Sri Lanka (1).

Habitat varies with the subspecies, but includes montane tropical rainforest, monsoon scrub, dry evergreen forests and mature secondary, semi-deciduous and undisturbed cloud forests (1) (5). The monkey is found to an altitude of up to 2,000 m, and often inhabits areas near permanent water sources (1) (5). Where natural forest has been lost refugee populations occupy semi-urban and rural home gardens, rubber plantations and areas with adequate canopy cover (1). Although highly arboreal, this langur will move to the ground briefly where trees are lacking (5).

The purple-faced langur normally has a ‘unimale' social system, usually consisting of one resident adult male (sometimes two), one to seven adult females and a number of subadults, juveniles and infants (2) (5). All-male groups also exist, numbering from 2 to 14 individuals, which split up to forage during the day and reform at the sleeping site at night. The home ranges of all-male groups overlap the home-ranges of unimale groups, but home ranges of unimale groups almost never overlap one another. The resident male will defend his territory aggressively against other males attempting to take over the harem (5).

A single offspring is born after a gestation period of 195 to 210 days. From 12 to 20 weeks the infant becomes more independent of its mother, beginning to eat solid food and engage in social play. Weaning occurs at seven to eight months. This diurnal species is largely folivorous, but will also feed on fruit, flowers and seeds (5).

The purple-faced langur's range has contracted greatly in the face of human encroachment. Deforestation as a result of agricultural, industrial and residential development has led to habitat loss and fragmentation, and the consequent isolation of subpopulations, which impedes out-breeding and genetic diversity. From 1956 to 1993 Sri Lanka lost more than 50 % of its forests to human activities, followed by a similar rate of decline between 1994 and 2003. This species has also suffered from hunting and illegal trade of its meat and skin, with the skin used to make drums in some areas. The purple-faced langur is hunted mainly for subsistence living and trade at local village level. According to continuing trends, populations of this species are predicted to decline by more than 50 % within the next 11 to 22 years (1).

The commercial exploitation of purple-faced langurs is regulated by their listing on Appendix II of the Convention on International Trade in Endangered Species (CITES) (3). All four subspecies are also protected under the Flora and Fauna Protection Ordinance 1993, and exist in a number of protected areas (1). However, the issue of habitat loss still places these subspecies, classified as Endangered and Critically Endangered, at serious risk of extinction (1). Indeed, the Critically Endangered western purple-faced langur (S. v. nestor) was officially recognised in 2004 as one of the world's 25 most endangered primates. This subspecies requires good canopy cover, but possibly fewer than three forests currently exist within Sri Lanka that can support viable populations, and none of these are within protected areas. Furthermore, the human-modified areas that support much of the langur population, such as gardens and rubber plantations, are under private ownership and therefore unstable, changing rapidly due to human population expansion and development. Censuses are therefore urgently needed to identify forest areas suitable for conservation. Further studies are also essential to better understand the decline of sub-populations, in both space and time, in the extremely disturbed habitats where these langurs survive today (6).

For further information on the purple-faced langur see:

The Primata:
www.theprimata.com/factsheets.html

Primates in Peril: The World's 25 Most Endangered Primates 2004 – 2006:
http://portals.conservation.org/downloads/storedfile/Document/top252004final.pdf

Authenticated (10/04/2006) by Matt Richardson, independent primatologist and writer.