|Species group:||T. francoisi|
|Delacour's langur range|
The Delacour's langur, or Delacour's lutung, (Trachypithecus delacouri) is a critically endangered species of lutung endemic to Vietnam. It is considered to be one of the world's most endangered primate species. It is named for French-American ornithologist Jean Théodore Delacour.
Delacour's langur is somewhat larger than its two closest relatives, François' langur and the Laotian langur, but in other respects has a similar appearance. Adults measure from 57 to 62 centimetres (22 to 24 in) in head-body length, with a tail 82 to 88 millimetres (3.2 to 3.5 in) long. Males weigh between 7.5 and 10.5 kilograms (17 and 23 lb), while the females are slightly smaller, weighing between 6.2 to 9.2 kilograms (14 to 20 lb). Their fur is predominantly black, with white markings on the face and distinctive creamy-white fur over the rump and the outer thighs, while females also have a patch of pale fur in the pubic area. Like other closely related lutungs, Delacour's langur has a crest of long, upright, hair over the forehead and crown; this is, however, somewhat taller and narrower than in other species.
Distribution and habitat
Delacour's langur is endemic to Vietnam, where it is found only in an area of around 6,000 square kilometres (2,300 sq mi) in the provinces of Ninh Bình, Hà Nam, Hòa Bình, Thanh Hóa, and Hà Tây in the north of the country. The largest surviving population is believed to be in Van Long Nature Reserve in Ninh Bình, where the monkey inhabits open forest up to elevations of 328 metres (1,076 ft), in terrain dominated by limestone karst.
Delacour's langurs are diurnal, often spending the day sleeping in limestones caves, although they will sleep on bare rocky surfaces if no caves are available. They are folivorous, without about 78% of the diet reportedly consisting of foliage, although they will also eat fruit, seeds, and flowers. It has been reported that the monkeys will eat leaves from a wide range of different plant species, indicating that their apparent dependence on limestone habitats is not related to their diet.
In previous decades, Delacour's langurs were reported to live in troops of up to thirty individuals, often including a mix of males and females, although single-male groups are more common, and some small all-male groups have also been reported. In more recent years, the typical group size seems to be much smaller, with only about four to sixteen members each. Males defend the troop's territory from outsiders, often standing watch on rocky outcrops. When potential rivals are spotted, the males in a troop initially try to intimidate them with loud hoots and visual displays, resorting to chasing and fighting if this fails. Within the group, social bonds are maintained by grooming and play.
Despite living in forested habitats, Delacour's langur is primarily terrestrial, only occasionally venturing into the trees. They swing by their hands when travelling through trees, and use their tail for balance when scrambling over steep rocky terrain, which may allow them to move more rapidly than other related lutungs.
Females give birth to a single young after a gestation period of 170 to 200 days. The young are born with orange fur, and precocial, with open eyes and strong arms. The fur begins to turn black at around four months, and the young are probably weaned at 19 to 21 months, by which time the mother is likely ready to breed again. However, the full adult coat pattern is not achieved for around three years. Females reach sexual maturity at four years, and males at five years; the total life expectancy is around twenty years.
The population of Delacour's langurs has declined rapidly in recent years. As of 2006, only nineteen populations were known, following a dramatic decline in the total population of around 20% between 1999 and 2004. Since that time, two of the populations have been extirpated, and only that in the Van Long Nature Reserve may still be large enough to remain viable.
Classified as critically endangered by the IUCN, the primary threat to the species is hunting for traditional medicine, with loss of forest habitat and the local development of tourism also being a potential risk. As of 2008, less than 250 animals were believed to remain in the wild, with nineteen in captivity.
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- Nadler, T., Xuan Canh, L., Ngoc Thanh, V. & Khac Quyet, L. (2008). Trachypithecus delacouri. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 4 January 2009.
- Mittermeier, R.A.; Wallis, J.; Rylands, A.B.; Ganzhorn, J.U.; Oates, J.F.; Williamson, E.A.; Palacios, E.; Heymann, E.W.; Kierulff, M.C.M.; Long Yongcheng; Supriatna, J.; Roos, C.; Walker, S.; Cortés-Ortiz, L.; Schwitzer, C., eds. (2009). "Primates in Peril: The World's 25 Most Endangered Primates 2008–2010" (PDF). Illustrated by S.D. Nash. Arlington, VA.: IUCN/SSC Primate Specialist Group (PSG), International Primatological Society (IPS), and Conservation International (CI). pp. 1–92. ISBN 978-1-934151-34-1.
- Harding, L.E. (2011). "Trachypithecus delacouri (Primates: Cercopithecidae)". Mammalian Species 43 (1): 118–128. doi:10.1644/880.1.
- Groves, C. (2007). "Speciation and biogeography of Vietnam's primates". Vietnamese Journal of Primatology 1 (1): 27–40.
- Workman, C. & Dung, L.V. (2009). "The chemistry of eaten and uneaten leaves by Delacour's langurs (Trachypithecus delacouri) in Van Long Nature Reserve, Vietnam". Vietnamese Journal of Primatology 1 (3): 29–36.
- Workman, C. (2010). "Diet of the Delacour's langur (Trachypithecus delacouri) in Van Long Nature Reserve, Vietnam". American Journal of Primatology 72 (4): 317–324. doi:10.1002/ajp.20785.