|Species group:||T. vetulus|
|Purple-faced Langur range|
The purple-faced langur (Trachypithecus 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.
There are four distinct subspecies of purple-faced langur:
- Southern lowland wetzone purple-faced langur, Trachypithecus vetulus vetulus
- Western purple-faced langur or north lowland wetzone purple-faced langur, Trachypithecus vetulus nestor
- Dryzone purple-faced langur, Trachypithecus vetulus philbricki
- Montane purple-faced langur or Bear Monkey, Trachypithecus vetulus monticola
All four 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.
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, in the mountains at Horton Plains National Park or in the rainforest city of Galle.
The purple-faced langur is mostly folivorous, but will also feed on fruits, flowers, and seeds. Within the human domesticated areas fruit such as jak (Arctocarpus heterophylus), rambutan Nephelium lappaceum, banana Musa sexpientum, and mango Mangifera indica consist up to 50% of its diet. The langur is adapted to get much of its nutrients and energy from complex carbohydrates found in leaves. This happens with the help of a highly specialized stomach that uses symbiotic bacteria to help digest food. Since its diet currently conists more heavily on cultivated fruits that are full of simple sugars instead of complex carbohydrates this could possibly change the gut fauna and its ability to absorb nutrients. Fruit in this area is also grown seasonally so the purple-faced langur could possibly be missing out on a fully complete diet during the off seasons of these fruit.
Loud calls are often used to distinguish between individual purple-faced langurs. The elements of a call fall into three categories: harsh barks, whoops, and residuals. Individuals can be differentiated by the number of phrases and residuals within a call. Calls occur more often in the morning mostly stimulated by neighboring groups and territorial battles. More calls occur during sunny periods than cloudy. The least amount of calls occur in the evening. Daytime calls usually aid in the defense of home ranges. The loud barking call, particularly of the highland form, can be mistaken for the roar of a predator such as a leopard. Calls of the purple-faced langur differ from those of any of the subspecies. Environmental characters impact call times as well as anthropogenic disturbance. Vocalization can be used to alert members of predators, attract mates, defend territory, and locate group members. Vocalization is extremely important for the use in conservation especially because they are very difficult to observe directly. Adult males are the most vocal among the entire group. Defensive whooping calls are also accompanied by intense visual and locomotive displays. Vocalizations are also helpful in determining taxonomic identification.
Some conservation strategies consist of improving management of the already protected areas as well as locate and protect new areas and corridors within ranges. Efforts to help increase populations may help survival. It would be beneficial to lower human-langur conflicts. Rope bridges could be established for langurs to move between ranges safely, which may decrease the crossing of power lines and roads. Replanting pine plantations with native species exploited by these langurs, could possibly increase its preferred habitat as well. Public education of conservation to the local people emphasizing compassion and kindness as well as explaining the importance and necessity of these mammals to the ecosystems overall biodiversity.
- Groves, C. P. (2005). Wilson, D. E.; Reeder, D. M, eds. Mammal Species of the World (3rd ed.). Baltimore: Johns Hopkins University Press. p. 178. OCLC 62265494. ISBN 0-801-88221-4.
- Dittus, W., Molur, S. & Nekaris, A. (2008). Trachypithecus vetulus. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 4 January 2009.
- Post-Disaster Housing Coordination Project (August 2007). "Introduction" (PDF). UN-HABITAT: United Nations Human Settlements Programme - Sri Lanka District Housing Profile (Colombo District). UNICEF. p. 3. Retrieved 28 April 2012.
- Parker, L; V. Nijman, K. A. I. Nekaris (5). "When there is no forest left: fragmentation, local extinction, and small population sizes in the Sri Lankan western purple-faced langur". Endangered Species Research 5: 29–36.
- Rudran, Rasanayagam (January 2007). "A survey of Sri Lanka's endangered and endemic western purple-faced langur (Trachypithecus vetulus nestor)". Primate Conservation 22: 139–144.
- Eschmann, C; R. Moore, K.A.I. Nekaris (2008). "Calling patterns of Western purple-faced langurs (Mammalia: Primates: Cercopithecidea: Trachypithecus vetulus nestor) in a degraded human landscape in Sri Lanka". Contributions to Zoology 81 (77).
- Bauchop, T.; Martucci, R. W. (1968). "The ruminant-like digestion of the langur monkey.". Science: 698–700.
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