Spectacled Langur (Trachypithecus obscurus)
The spectacled langur is one of many species of leaf-eating monkeys. For this reason it is sometimes referred to as the dusky or spectacled leaf monkey. There are leaf-eating monkeys in both Asia (e.g. spectacled langur) and Africa (e.g. colobus monkeys).
Physical Description: The spectacled langur is one of the largest primates at Monkeyland. They are mostly dark grey-black in colour with lighter grey on their chests and the top of their heads. Spectacled langurs are named for the white rings around their eyes that look like they are wearing glasses or �spectacles�. They also have white skin around their mouth. The rest of their face is black. Interestingly, infants are orange when they are born! By 9 months of age infants change to the grey-black colour of adults. Female head and body length in this species is 425-595 mm and tail length varies from 635-813 mm. Females weigh approximately 4,994-8,626 g. Male head and body length is 420-675 mm and tail length is 570-790 mm. Males weigh around 6,129-9,080 g. The adult spectacled langur brain weighs 67.6 g.
Habitat: The spectacled langur is only found in Thailand and parts of the Malay Peninsula. Spectacled langurs live in primary forest (mature and untouched), secondary forest (regenerated), lowland forest (altitude below 1 km) as well as submontane and montane forest up to 1,828 m. Spectacled langurs are arboreal and quadrupedal. Their movement consists mostly of walking or running and leaping. Spectacled langurs travel 0.95 km per day on average. Their home range has been reported to be as large as 33 hectares.
Diet: Leaf-eating monkeys like the spectacled langur have specialized teeth for chewing leaves. In fact, over half of their diet is leaves (58%). It can be difficult to provide captive leaf-eating monkeys with the correct diet, but at Monkeyland it�s easy since they have many trees to choose from! Another major component of their diet consists of seeds and fruit (35%). Spectacled langurs eat both ripe and unripe fruit. They have bacteria in their stomachs which allow them to eat unripe fruit and seeds that would otherwise be inedible or toxic. This specialized stomach also allows them to absorb the cellulose in leaves. Spectacled langurs will eat flowers as well and particularly enjoy figs. They generally feed in the tall canopy at heights of 25-50 m. Spectacled langurs feed for about 4 hours a day on average.
Life History: Gestation in spectacled langurs is approximately 150 days. Litter size is usually one, although twins are born occasionally. One observational study of a single captive male spectacled langur characterized the mother-infant relationship throughout the first year of life. The first 20 days of life are marked by a high level of maternal care. The infant first explores itself and its environment between days 21-70 of its life. After this time the infant begins to socialise with its group members. There is a period of play lasting from days 71-240. This is followed by a juvenile or sub-adult period and eventually adulthood. Due to limited study, the lifespan of wild spectacled langurs is unknown.
Associations: The spectacled langur associates with siamangs (Hylobates syndactylus).
Social Structure: Spectacled langurs live in either single male/multi-female or multi-male/multi-female groups. Males will defend their females rather than their territories. The average group size varies from 10-17 individuals. Like black and white ruffed lemurs, the group subdivides into parties to feed in the day.
Communication: Males play a very important role in communication. They will often sit higher in trees than females to scan for predators. If a danger is seen, males give a �whoo� call as a warning. Often they will follow with a honk call known as �chengkong� (a descriptive name for the way it sounds). This honk call is so distinctive, spectacled langurs are known as �chengkong� in Malay. Honking is also used to keep group members together. Occasionally honking may be used to communicate about territory between groups, but spectacled langurs are not traditionally territorial like other primates. There is also a �long call� but its meaning is not understood. Spectacled langurs use visual contact as well to communicate with group members.
Other Behaviour: In addition to being watched by mom, infants are also �babysat� by other females. The scientific term for this is allomothering. Overall, spectacled langurs do not show much aggression and are known to be a very tolerant species. However, they do appear to be dominant over most other primate species at Monkeyland. They will often monopolize the feeding platforms. Captive studies have shown that after any aggressive events, these langurs are extremely good at reconciling their differences, which they do by embracing, grooming or presenting their hind-quarters!
Conservation: Spectacled langurs are listed as Lower Risk/Least Concern by the IUCN. Langurs are threatened by deforestation and the trade in wild meat. The population of spectacled langurs was estimated to have declined from 305,000 to 155,000 from 1958 to 1975, and habitat loss due to human population growth has sharply intensified in the last decades. Organisations such as the Dusky Langur Conservation & Community Centre are working to protect this species through ecotourism and voluntourism programmes (tourists who volunteer their services) focused on langur observation, rehabilitation and education. To read more about this work and other special projects in Thailand, please visit http://www.ecoexplorethailand.com.
Did You Know? There are two spectacled langurs at Monkeyland named Calick & Cory. Both are males and they are always found together or in close proximity. There has never been a report in the wild of a male-only group of spectacled langurs, but keeping animals in �bachelor groups� is a common occurrence in zoos. Calick & Cory came from a large bachelor group at a European zoo.
Arnold, K. & Barton, R.A, (2001) Postconflict behaviour of spectacled leaf monkeys (Trachypithecus obscurus). I. Reconciliation. International Journal of Primatology, 22(2), 243-266.
Curtin, S.H. (1980). Dusky and banded leaf monkeys. In In Malayan Forest Primates: 10 Years of Study in the Tropical Rain Forest. Plenum Press: New York, 107-145.
Eco Explorer Thailand. The Dusky Langur Project. <http://www.ecoexplorerthailand.com/The%20Dusky%20langur%20Project.html>. Accessed 2007 January 6.
Eudey, A. & Members of the Primate Specialist Group 2000. Trachypithecus obscurus. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 16 July 2006.
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Rowe, N. (1996). The Pictorial Guide to the Living Primates. Charlestown, Rhode Island: Pogonias Press.
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