White-thighed surili (Presbytis siamensis)

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White-thighed surili fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
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White-thighed surili description

Like other Presbytis species, the white-thighed surili (Presbytis siamensis) is a medium-sized, slenderly built monkey with a long tail, a short muzzle and relatively long fur ^{(3) (5) (6)}. The top of its head and its back tend to be a dark greyish-brown, while the underside of the body, including the undersides of the tail, legs and arms, tends to be a lighter pale grey to white. There is also a large whitish patch on the outside of the legs, from which the white-thighed surili gets its name ^{(2) (3)}. The hands, feet, and outer half of the white-thighed surili’s tail are black ⁽²⁾

The white-thighed surili’s face is characterised by poorly developed brow-ridges ^{(3) (6)} and indistinct pale rings around the eyes, with the rest of the facial skin being dark grey to blackish ⁽²⁾. As in other Presbytis species, there is a crest of fur on the head ^{(3) (5) (6)}. Infants are lighter in colour than the adults, with just a dark cross-shaped pattern up the back and across the arms ⁽²⁾.

The white-thighed surili was previously considered to be a subspecies of the banded surili (Presbytis femoralis) ^{(1) (3)}, but the banded surili is generally darker on the upperparts and lacks the contrasting white outer thighs ⁽²⁾. However, the taxonomy of these species is in need of further study ⁽¹⁾.

Also known as

pale-thighed langur, pale-thighed surili, white-thighed langur.

Synonyms

Presbytis amsiri, Presbytis catemana, Presbytis dilecta, Presbytis femoralis cana, Presbytis femoralis paenulata, Presbytis femoralis rhionis, Presbytis femoralis siamensis, Presbytis nigrimanus, Presbytis nubigena.

Size

Head-body length: 41 - 69 cm ^{(2) (3)}

Tail length: 58 - 85 cm ⁽³⁾

Weight

5 - 6.7 kg ⁽³⁾

White-thighed surili biology

Like other Presbytis species, the white-thighed surili is a diurnal forest dweller ⁽⁶⁾, with a diet consisting of leaves, flowers, fruit and seeds ^{(5) (6) (9)}. The proportion of fruit and seeds in its diet is quite high compared with most other species in its genus ⁽⁹⁾. As in other members of the Cercopithecidae family, the white-thighed surili’s stomach is divided into a series of chambers ^{(2) (5)}, allowing leafy material to be more easily broken down and toxins in the leaves to be neutralised ⁽²⁾.

The white-thighed surili is well adapted to living in the trees, although it may also spend time on the ground ^{(5) (6)}. The home range of this species is estimated to be around 24 hectares ⁽⁹⁾, although this may vary depending on the habitat ⁽⁵⁾.

Although little information exists on the social dynamics of the white-thighed surili, it is likely that it is similar to that of closely related species. Group size of Presbytis species usually ranges from a few individuals to occasionally over 100, and each group will normally consist of one sexually mature male and numerous females ^{(5) (6)}. There are also likely to be some lone males and all-male groups, and some of these males may attempt to take over a group of females or split some of the females from it ⁽⁶⁾.

Relatively little is currently known about the breeding behaviour of the white-thighed surili, but in Presbytis species in general the female gives birth to a single young at a time ⁽⁶⁾ and all adult females in a group help care for the infants ⁽⁵⁾. On reaching maturity, young males typically leave the group in which they were born ⁽⁶⁾.

White-thighed surili range

There are a number of recognised subspecies of the white-thighed surili, which inhabit various areas on and around the southern tip of Southeast Asia. The range of this species includes Peninsular Malaysia and parts of southern Thailand, north-eastern Sumatra (Indonesia) and various islands in the Riau Archipelago ^{(1) (3) (7) (8)}.

White-thighed surili habitat

The white-thighed surili lives in a variety of different forest types, including forests in lowlands and hills ⁽²⁾, swamp and lowland wet forest, and even disturbed areas such as plantations and orchards ^{(1) (2)}.

White-thighed surili status

The white-thighed surili is classified as Near Threatened (NT) on the IUCN Red List ⁽¹⁾ and is listed on Appendix II of CITES ⁽⁴⁾.

The subspecies Presbytis siamensis cana (Lyon’s pale-thighed langur), Presbytis siamensis paenulata (Chasen’s pale-thighed langur) and Presbytis siamensis siamensis (Malayan pale-thighed langur) are classified as Near Threatened (NT) on the IUCN Red List, while Presbytis siamensis rhionis (Bintan Island pale-thighed langur) is classified as Data Deficient (DD) ⁽¹⁾.

White-thighed surili threats

The loss of extensive tracts of forest in Southeast Asia poses a significant threat to the white-thighed surili, as it does for many species in the same area. Deforestation and the dramatic increase in oil palm plantations have caused widespread environmental damage, resulting in extensive habitat loss for the white-thighed surili. Hunting is also a problem, albeit a smaller one ⁽¹⁾.

White-thighed surili conservation

The white-thighed surili is likely to occur in a number of protected areas across its range ⁽¹⁾, and any international trade in this monkey should be carefully controlled under its listing on Appendix II of the Convention on International Trade in Endangered Species (CITES) ⁽⁴⁾.

The unclear taxonomic relationships between some members of the Presbytis genus, in particular between the white-thighed surili and the banded surili (P. femoralis), make a taxonomic review of these species necessary so that appropriate conservation actions can be determined ⁽¹⁾.

View information on this species at the UNEP World Conservation Monitoring Centre.

Find out more

Find out more about primate conservation:

• IUCN/SSC Primate Specialist Group:
  http://www.primate-sg.org/
• Mittermeier, R.A. et al. (2009) Primates in Peril: The World’s 25 Most Endangered Primates 2008-2010. IUCN/SSC Primate Specialist Group, International Primatological Society, and Conservation International, Arlington, VA. Available at:
  http://data.iucn.org/dbtw-wpd/edocs/2009-067.pdf

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Glossary

Diurnal

Active during the day.

Genus

A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.

Home range

The area occupied by an animal during routine activities, which is not actively defended.

Subspecies

A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

Taxonomy

The science of classifying organisms, grouping together animals which share common features and are thought to have a common ancestor.

References

1. IUCN Red List (January,2013)
   http://www.iucnredlist.org/
2. Francis, C.M. (2008) A Field Guide to the Mammals of South-East Asia. New Holland Publishers (UK) Ltd, London.
3. Macdonald, D.W. (2006) The Encyclopedia of Mammals. Oxford University Press, Oxford.
4. CITES (February, 2013)
   http://www.cites.org/
5. Ankel-Simons, F. (1999) Primate Anatomy: An Introduction. Academic Press, San Diego, California.
6. Nowak, R.M. (1991) Walker’s Mammals of the World. The Johns Hopkins University Press, Baltimore and London.
7. Brandon-Jones, D., Eudey, A.A., Geissmann, T., Groves, C.P., Melnick, D.J., Morales, J.C., Shekelle, M. and Stewart, C.-B. (2004) Asian primate classification. International Journal of Primatology. 25(1): 97-164.
8. Groves, C.P. (2005) Order Primates. In: Wilson, D.E. and Reeder, D.M. (Eds.) Mammal Species of the World. A Taxonomic and Geographic Reference. Third Edition. The Johns Hopkins University Press, Baltimore.
9. Kamilar, J.M. and Paciulli, L.M. (2008) Examining the extinction risk of specialized folivores: a comparative study of colobine monkeys. American Journal of Primatology, 70: 816-827.