The purple-faced langur (Semnopithecus vetulus), also known as the purple-faced leaf monkey, is a species of Old World monkey that is endemic to Sri Lanka. The animal is a long-tailed arboreal species, identified by a mostly brown appearance, dark face (with paler lower face) and a very shy nature. The species was once highly prevalent, found in suburban Colombo and the "wet zone" villages (areas with high temperatures and high humidity throughout the year, whilst rain deluges occur during the monsoon seasons), but rapid urbanization has led to a significant decrease in the population level of the monkeys. It had traditionally been classified within the genus Trachypithecus but was moved to the genus Semnopithecus based on DNA evidence indicating that is it more closely related to the gray langurs. In Sinhala, it is known as ශ්රී ලංකා කළු වඳුරා [kalu ʋaⁿd̪uraː] (Sri Lanka black monkey).
Description In the purple-faced langur, males are usually larger than females. Males measure 50 to 67.1 cm (19.7 to 26.4 in) in head-body length with a tail of 67 to 85.1 cm (26.4 to 33.5 in). Females possess a head-body length 44.7 to 60 cm (17.6 to 23.6 in) and tail length of 58.9 to 82 cm (23.2 to 32.3 in). The pelage may generally vary from blackish to grayish. The species tends to have whitish to gray short 'trousers' rounded off by purplish-black faces with white sideburns. Part of the back is covered with whitish fur, and tail is also furred with black and white mixed colors. The feet and hands are also purplish-black in color. Size varies among the subspecies. Typically adults will weigh somewhere between 3.1 and 11.4 kg (6.8 and 25.1 lb), averaging about 7.08 kg (15.6 lb). The smallest subspecies (S. v. nestor) commonly weighs between 3.8 and 6 kg (8.4 and 13.2 lb). Average weight from other subspecies has been recorded up to 7.8 kg (17 lb) in females and 8.5 kg (19 lb) in males with some exceptionally big langurs weighing up to perhaps 18 kg (40 lb). Among the primates that live in Sri Lanka, it is somewhat smaller than the tufted gray langur despite leading males of the group of purple-faced langurs often being larger than the tufted gray langur that lived together in the habitats. In the subspecies known as the "bear monkey" (S. v. monitcola) usually has a darker coat and usually sports a heavy mustache. In this species, the hair of crown directed backwards throughout, not radiating. it lacks the crest of tufted gray langurs and has hair on the crown no longer than on temples and nape. Purple-faced langurs have a rump that is pure white or whitish gray.
Subspecies According to the Mammals of Sri Lanka, the 4 subspecies are recognized as follows.
Southern lowland wetzone purple-faced langur, Semnopithecus vetulus vetulus – "Color varies greatly. Black upper torso, light brown cap, well defined silvery rump patch that extends to legs. Prominent white whiskers. Tail is also white colored. Many white morphs are observed in this subspecies. They can be all-white to partly white leucistic." Western purple-faced langur or north lowland wetzone purple-faced langur, Semnopithecus vetulus nestor – "It is the smallest of all subspecies. Upper torso dark grayish brown with light grayish brown rump patch, darker grayish brown legs and white cap." Dryzone purple-faced langur, Semnopithecus vetulus philbricki – "Largest subspecies. Grayish brown torso, ill-defined grayish rump patch, dark cap. Prominent white cheeks with tufts. Exceptionally long slimy tail." Montane purple-faced langur or Bear Monkey, Semnopithecus vetulus monticola – "Dark gray brown coat. Large but ill-defined grayish rump patch. Prominent white cheek tufts, light brownish gray cap. Fur long and shaggy due to habitat they live is cold." All four recognizable subspecies exhibit different cranial and pelage characteristics, as well as body size. The western purple-faced langur is one of the 25 most endangered primates in the world. Most groups of langurs contain only one adult male. A possible subspecies called Semnopithecus vetulus harti is recognized, but not yet given validity. This subspecies is known from some skins found from Jaffna peninsula and north of the Vavuniya. Uniquely, this subspecies has yellowish golden hair on its scalp and a golden sheen to its fur. Other than these differences, anatomy and all the other aspects are similar to the Semnopithecus vetulus philbricki. Although traditionally classified within the genus Trachypithecus based on morphological similarities, DNA and vocal evidence suggests that the purple-faced langur actually is more closely related to the gray langurs of the genus Semnopithecus.
Habitat and status The purple-faced langur is found in closed canopy forests in Sri Lanka's mountains and the southwestern part of the country, known as the "wet zone". Only 19% of Sri Lanka consists of forested areas. This habitat has decreased from 80% in 1980 to ~25% in 2001. Currently, this range has decreased to below 3%. The range consists of the most densely populated lowland rainforest areas of Sri Lanka. Deforestation has resulted in the langurs home ranges to be exposed to direct sunlight. Purple-faced langurs are most often found in small and widely scattered groups. Ninety percent of the langurs range, now consists of human populated areas. Populations are critically low within and between sites. Threats to this species include infringement on range by croplands, grazing, changing agriculture, road production, soil loss/erosion and deforestation, poisoning from prevention of crop raiding, and hunting for medicine and food. Its range has constricted greatly in the face of human encroachment, although it can still be seen in Sinharaja, Kitulgala, Kandalama, Mihintale, in the mountains at Horton Plains National Park or in the rainforest near the city of Galle.
Behaviour and ecology
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