This species occurs in Malaysia (troughout the Malay Peninsula along with a few small adjacent islands), southern Myanmar (including the Mergui Archipelago), and southwestern Thailand (including adjacent islands). It is found north to 15°10?N in Myanmar and Thailand (Groves 2001).

T. o. obscurus
Found on Peninsular Malaysia, north to about Perlis (Groves 2001).

T. o. flavicauda
Found in northern Peninsular Malaysia, southern Myanmar (including James, Kisseraing, and King Islands in the Mergui Archipelago) and southwestern Thailand (including Koh Lak Island). On the mainland found from Perlis north to the northern border of the species? range (Groves 2001).

T. o. halonifer
Restricted to Penang Island, Malaysia (Groves 2001).

T. o. carbo
Found off the western coast of Malaysia and Thailand, specifically on Terutao and Dayang Bunting Islands, and on Langkawi Island (Malaysia) (Groves 2001).

T. o. styx
Occurs on East Perhentian Island and, possibly, adjacent eastern coastal Malaysia (Groves 2001).

T. o. seimundi
Occurs on Phangan Island (Pennan Island), Thailand; may possibly occur in adjacent eastern Thailand as well (Groves 2001).

T. o. sanctorum
Restricted to Zadetkyi Kyun (St. Matthew Island) in the Mergui Archipelago (Myanmar) (Groves 2001).

Dusky leaf monkeys are found primarily on the Malay Peninsula, including southern Burma and parts of Thailand. They also inhabit the islands of Langkawi, Penang, and Perhentian Besar.

Biogeographic Regions: oriental (Native )

Dusky leaf monkeys are widely variable in color. Their upper parts may be any shade of brown, grey, or black, whereas the under parts, hind legs, and tail are paler. The face is grey and is often marked with a patch of white fur located around the eyes and mouth.

The hands and feet are capable of grasping and closely resemble those of humans. The palms and soles are hairless and usually black. The fingers of dusky leaf monkeys are well developed, but are distinct because of their opposable thumb. The nonprehensile tail varies in length and fur coverage from short and hairless, to long and hairy.

Head and body length ranges from 42 to 61 cm, and tail length from 50 to 85 cm. There are no significant morphological differences between males and females except that males tend to be slightly larger and heavier than females. On average, a healthy adult male weighs 7.4 kg, whereas a healthy adult female weighs approximately 6.5 kg.

Newly born dusky leaf monkeys are bright yellow or orange in color, and have a pink face; the fur changes to a greyish color within six months.

Range mass: 5 to 9 kg.

Range length: 42 to 61 cm.

Habitat and Ecology

Systems

• Terrestrial

Dusky leaf monkeys can be found in a wide range of habitats. Being arboreal forest dwellers, they prefer dense forests with tall trees.

Terrestrial Biomes: taiga ; forest ; rainforest

The diet of these monkeys consists of young leaves, shoots, and seedlings. They feed from 87 different species of trees, ingesting both leaves and fruit. In general, a dusky leaf monkey eats up to 2 kg of food per day.

These monkeys can be maintained, in captivity, on sweet potato shoots, lettuce, cabbage, kangkong, grean beans, maize, carrots, and soft fruits. Meat was refused, but certain insects were occasionally accepted.

Plant Foods: leaves; seeds, grains, and nuts; fruit; flowers

Primary Diet: herbivore (Folivore )

These monkeys are likely to be important predators of folliage. They may help to disperse seeds. To the extent that they serve as prey for other species, these monkeys may affect local food webs.

Ecosystem Impact: disperses seeds

Information on predation of these monkeys is not available. Because they are arboreal, it is likely that they do not have many predators. Possible predators are large carnivores, snakes, and raptors.

Details on communication in these monkeys are scant. However, we know that they use vocalizations to protect their territories from other members of the species. Like other primates, tactile communication (e.g. grooming, playing, mating, aggression) and visual communication (e.g. facial expressions and body postures) are probably both inmportant in these monkeys.

Communication Channels: visual ; tactile ; acoustic

Perception Channels: visual ; acoustic

Another monkey in the same genus, Trachypithecus cristatus, is reported to have lived over 31 years in captivity. It is likely that T. obscurus is similar. Lifespan in the wild is probably lower than in captivity.

Average lifespan

Status: captivity: 25.0 years.

Average lifespan

Sex: female

Status: captivity: 15.3 years.

Maximum longevity: 33.9 years (captivity)

There is no information available regarding the mating system of dusky leaf monkeys. However, the social system typically involves groups with only one or two males. In other primate species, this social organization is typically associated with polygynous breeding. It is reasonable to assume that this species is like other similar primates in this respect.

Mating System: polygynous

Breeding in dusky leaf monkeys is intermittent and not always seasonal. Births usually take place during the months of January, February, and March, but have been documented to occur during the summer months as well. Typically one young is born. The gestation period is, on average, 145 days.

Females have a menstual cycle lasting approximately three weeks. Oestrus is often accompanied by a swelling of the genitalia.

The normal interbirth interval is about 2 years.

Sexual maturity is reached between 3 and 4 years of age.

Breeding interval: These monkeys reproduce every two years.

Breeding season: These monkeys breed intermittantly throughout the year.

Range number of offspring: 1 to 2.

Average number of offspring: 1.

Average gestation period: 145 days.

Range age at sexual or reproductive maturity (female): 3 to 4 years.

Range age at sexual or reproductive maturity (male): 3 to 4 years.

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization ; viviparous

Average birth mass: 300 g.

Average gestation period: 145 days.

Average number of offspring: 1.

Research on the parental behavior of these monkeys is lacking. However, we may assume that they are like other primates in that the mother provides the bulk of the parental care. She grooms, protects, and feeds the newborn. The role of the father in parental care is not known.

There is no information available regarding the weaning age of dusky leaf monkeys. It is known, however, that the newborn monkey is fully furred and active.

Parental Investment: precocial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Protecting: Female); extended period of juvenile learning

The following is a representative barcode sequence, the centroid of all available sequences for this species. 

 
There are 2 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
 

Download FASTA File

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 2
Species: 2
Species With Barcodes: 1

There is very little information about the status of dusky leaf monkeys. I found no published estimates of how many monkeys currently exist.

Dusky leaf monkeys are confined within a relatively small area of southeast Asia. It is probable that these forested areas are under threat of development or logging. Therefore, there is reason to believe that the species is threatened to some extent because of habitat loss, but there are no studies to support this.

US Federal List: no special status

CITES: appendix ii

IUCN Red List of Threatened Species: near threatened

Population

Population Trend

Major Threats

Conservation Actions

Dusky leaf monkeys are generally restricted to primary forests. Therefore, it is unlikely that they contribute to any serious agricultural (or other) problems that would adversely affect humans.

It is probable that dusky leaf monkeys are hunted for food by the human population, since a large number of primates are hunted as sources of food throughout Asia.

Positive Impacts: food