Delacour’s langur (Trachypithecus delacouri)

Also known as: white-rumped black langur
Synonyms: Trachypithecus francoisi delacouri
KingdomAnimalia
PhylumChordata
ClassMammalia
OrderPrimates
FamilyCercopithecidae
GenusTrachypithecus (1)
SizeMale head-to-body length: 57 – 62 cm (2)
Female head-to-body length: 57 – 59 cm (2)
Mail tail length: 82 - 88 cm (2)
Female tail length: 84 – 86 cm (2)
Male weight: 7.5 – 10.5 kg (2)
Female weight: 6.2 – 9.2 kg (2)

Classified as Critically Endangered (CR) on the IUCN Red List 2007 (1), and listed on Appendix II of CITES (3).

Found only in north-central Vietnam, Delacour’s langur is one of the rarest and most endangered primates on Earth (4) (5). This striking black and white coloured langur is distinguished from other black Asian langurs by its characteristic white lower back and outer thighs (2). As a result of this distinctive colouration, the Vietnamese frequently refer to this species as “Vooc Mong Trang”, meaning ‘the langur with white trousers’. The white cheek hairs are also slightly longer than in other black Asian langurs (2) and the thickly furred tail is unique among this genus (4). Newborns differ from adults, being brownish in colour (6), with more white fur on the head (7). Feet and hands in this species are slim and the thumb is reduced (7).

Endemic to north-central Vietnam (4).

This arboreal langur lives in tropical forests around limestone cliffs (known as karst forest) (1) (7). While occupying trees during the day, Delacour’s langur will usually come down to the ground at night to sleep in the caves of limestone cliffs (7).

Delacour’s langur has a unimale social system, in which the small group consists of one male, multiple females and their offspring, numbering a total of only three to six individuals (6) (7). The remaining males form all-male bands, from which individuals will eventually invade unimale groups to replace the leader. Males reach reproductive maturity at five years, females at four. A reproductive peak exists between January and June and, after a gestation period of 170 to 200 days, females usually give birth to a single offspring (2).

This diurnal species has a predominantly folivorous diet (7) but will also feed on shoots, fruit, flowers and bark (2). Like other members of the Colobinae subfamily, Delacour’s langur has evolved a complex stomach and enlarged salivary glands to aid the digestion of tough leaf material (7).

With as few as 270 to 300 estimated individuals remaining in 19 isolated populations, and 14 of these populations predicted to disappear in the next decade, Delacour’s langur is dangerously close to extinction (1) (8). During the 1990s, when Vietnam opened itself up to the international community and the Chinese economy started to boom, traders and poachers moved in to utilise Vietnam’s biodiversity (4). Poachers killed this langur not only for meat, but also for bones, organs and tissues that are used in traditional medicines (8). Hunting has reduced in recent years with increasing legal protection but continues to pose a significant threat. Habitat loss is also a danger to this species, with the World Conservation Monitoring Centre of the United Nations Environment Programme (UNEP-WCMC) estimating that a total of 30,000 hectares of forest are destroyed each year in Vietnam (4). The clearing of forests to accommodate human commercial and residential growth continues to separate the remaining populations of Delacour’s langur, which are now at risk of becoming too small to be viably sustainable (2). Sixty percent of Delacour’s langurs occur in isolated populations of fewer than 20 individuals. The loss of these sub-populations, and consequently 60 percent of the whole population, is feared likely in the near future without management, strict regulations and law enforcement (5).

Four areas where Delacour’s langurs are protected include: Cuc Phuong National Park, Pu Luong Nature Reserve, Hoa Lu Cultural and Historical Site, and the recently-established Van Long Nature Reserve, which is believed to contain the largest remaining population of around 70 individuals (5) (8). Unfortunately, protected areas often suffer more from poaching than unprotected areas because their dense population of wildlife is seen as more profitable (2). Thus, conservation groups are working to increase the level of protection and law enforcement within these protected areas. The Van Long Nature Reserve is now well guarded by rangers, largely funded by the Frankfurt Zoological Society. The Pu Luong Nature Reserve also employs a large number of rangers, which are helping to save the small remaining populations (8). These are encouraging steps towards helping the survival of Delacour’s langur, listed as one of the 25 most endangered primates in the world (8). Recent commitments by the Vietnamese government and several international conservation organisations to do more to protect Delacour’s langur have greatly increased the chances of saving this rare and remarkable species (2).

For further information on Delacour’s langur see:

Authenticated (03/12/2005) by Matt Richardson, independent primatologist and writer.

  1. IUCN Red List of Threatened Species (June, 2008)
    http://www.iucnredlist.org
  2. Nadler, T., Momberg, F., Dang, N.X. and Lormee, N. (2003) Leaf Monkeys: Vietnam Primate Conservation Status Review 2002 – Part 2. Fauna and Flora International Vietnam Program and Frankfurt Zoological Society, Hanoi, Vietnam. Available at:
    http://www.fauna-flora.org/docs/vietnam_primate_status_review2002_part2.pdf
  3. CITES (June, 2008)
    http://www.cites.org
  4. bbc.co.uk - Science and Nature (November, 2005)
    http://www.bbc.co.uk/nature/animals/features/153index.shtml
  5. IUCN/SSC Primate Specialist Group: The World’s 25 Most Endangered Primates 2006 – 2008 (June, 2008)
    http://www.primate-sg.org/T25full07.htm
  6. Richardson, M. (2005) Pers. comm.
  7. The Primata (November, 2005)
    http://www.theprimata.com/trachypithecus_delacouri.html
  8. Wildlife at Risk (June, 2008)
    http://www.wildlifeatrisk.org/index.php?lang=en&id=6&subid=5