LANGURS AND LEAF MONKEYS OF SOUTHEAST ASIA: SPECIES, CHARACTERISTICS, BEHAVIOR

LANGURS

Indochinese grey langur

Langurs are mostly leaf-eating, tree-residing, forest-dwelling monkeys. They are regarded as among the most arboreal of all Old World monkeys. They are active throughout the tree canopy and can be found in both primary and secondary forests. They rarely come to the ground. When they do it is mainly to gain access to mineral sources. The stomachs of monkeys in the Colobinae subfamily are large and multi-chambered. The forestomach hosts bacteria with cellulose-digesting abilities, allowing these mammals to process leaves and plant fibers.

Leaf monkeys and langurs are in the subfamily Colobinae, which is part of the family Cercopithecidae (Old World monkey), which has a wide geographical distribution throughout Asia and Africa. Leaf monkeys and langurs are scattered over a wide area in India, Southeast Asia and Indonesia. They are mainly diurnal (active during the day). They eat crops as well as leaves and and some prefer fruit and flowers and may migrate a great distance to gain access to fruit. Some species never descend from trees except to get water during the middle of the dry season.

Most langurs are grayish, brownish or blackish, with paler underparts. Some have light colored markings on their head or stripes on their thighs. Langur adults weigh from five to eight kilograms and have a head and body length of 42 to 61 centimeters (16.5 to 24 inches) and a tail length of 50 to 85 centimeters (20 to 33.5 inches) .

Langur bodies are adapted for tree life. They have long tails, a slender body, strong slender hands, and well developed fingers. Although langurs eat leaves their primary sources of nutrition come from fruits and seeds. On a daily basis they range through the forest between 500 and 800 meters to forage.

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Langurs of Southeast Asia (Trachypithecus Genus)

Most langurs and leaf monkeys in Southeast Asiain Southeast Asia, belong to the genus Trachypithecus. Trachypithecus is a genus of Old World monkeys containing species known as lutungs, langurs, or leaf monkeys. They range across much of Southeast Asia from northeast India to southern China, Borneo into Indonesia, and are found in Vietnam, Myanmar (Burma) Thailand, Java, and Bali). [Source: Wikipedia +]

Trachypithecus was recognized as a separate genus by Eudey in 1987, but occasionally it is still considered a subgenus or synonym of Presbytis or of Semnopithecus. Among the species recognized in the genus are: François’ langurs (Trachypithecus francoisi) Trachypithecus vetulus, T. johnii, T. geei, T. pileatus, T. phayrei, T. cristatus, T. auratus, and T. obscurus. There is some debate over whether Trachypithecus leucoscephalus is a subspecies of François’ langur or a distinct species. Recent DNA research suggests that it may be distinct. [Source: Lauren Ris, Animal Diversity Web (ADW)]

Langurs and leaf monkeys in the Trachypithecus genus have a slim body with a long tail. Their fur varies in color, depending on the species, from black and grey to orange yellow. Many species have skin markings and a brighter lower surface. The hair on their head is often compared to a hood. Their arms are very short in comparison to the feet and their thumbs are also somewhat shorter. The inner surfaces of the hands and feet are hairless so that their fur does not get caught when reaching into branches. These monkeys range in length from of 40 to 80 centimeters and weigh from five to 15 kilogramss, with males generally being larger than females. A bulge over the eyes and other details, primarily in the head, differentiate it from the surilis. +

Christine Bedore wrote in Animal Diversity Web: Colobines have a long tail, and dense fur. Also common to colobines is an under-bite in which the lower jaw projects out further than the upper jaw. The genus Trachypithecus is distinguished from other colobines by its prominent nasal bones, a well-developed coronal crest, and poorly developed brow ridges. There is also a reduction in the size of the first digit (thumb) facilitating the brachiating (using the arms to swing from branch to branch) movements they utilize. The fore and hind limbs are more equal in length than most other cercopithecid (Old World monkey)s (Old World monkeys), or Old World Monkeys, suggesting that the group previously occupied a more terrestrial habitat. [Source: Christine Bedore, Animal Diversity Web (ADW)]

Behavior of Trachypithecus Langurs

Annamese langur

Langurs and leaf monkeys in the Trachypithecus genus live in forests, often preferring rain forests, although occasionally they are also found in secluded mountain forests. They spend the largest part of the day in the trees, where they crawl along the branches on all fours, although they can also jump well from tree to tree. They are diurnal, although more active in the early mornings and the afternoon. They are primarily eat leaves, fruits, and buds. To digest the tough leaves, they developed a multichambered stomach. +

Langurs and leaf monkeys in the Trachypithecus genus live in groups of five to 20 animals, mostly in harems, i.e. a single male with several females. Young males leave their birth group when fully mature, often forming bachelor groups. If a new male takes over a harem, defeating and scaring off the harem leader, he often kills the children of the group. Langurs and leaf monkeys in the Trachypithecus genus are territorial, with loud shouting to defend their territories from other langurs and leaf monkeys, resorting to force if the outsiders are not scared off. They have a common repertoire of sounds with which they warn group members. Also, mutual grooming plays an important role. +

Usually a single offspring is born after a seven-month gestation period. Newborns usually have a golden-yellow fur. The mother shares responsibilities of rearing the young with the other females ("aunties") of the harem. They hand the young around, play with it, carry it, and cuddle it, while the mother searches for food. If the mother dies, another female adopts the young animal. Young are weaned in the latter half of their first year, and reach full maturity at 4 to 5 years. The life expectancy is estimated at 20 years. +

Langurs and Leaf Monkey Species in Southeast Asia

Annamese Langurs (Trachypithecus margarita, Elliot, 1909) are gray in color. They live in Southeast Asia. They are 40–76 centimeters (16–30 inches) long, with a 57–110 centimeter (22–43 inch) tail. They live in the forest and eat leaves, flowers, and fruit. They are endangered. Their numbers are unknown. Their population is declining.

Capped Langurs (Trachypithecus pileatus, Blyth, 1843) are gray in color. There are three subspecies: 1) T. P. brahma; 2) T. P. pileatus; 3) T. P. tenebricus. They live in South Asia. They are 40–76 centimeters (16–30 inches) long, with a 57–110 centimeter (22–43 inch) tail. They live in the forest and eat leaves, seeds, and fruit, as well as flowers, buds, bark, and caterpillars. They are vulnerable. Their numbers are unknown. Their population is declining.

Dusky Leaf Monkeys (Trachypithecus obscurus, Reid, 1837) are brown in color. There are seven subspecies. They live in Southeast Asia. They are 42–61 centimeters (17–24 inches) long, with a 50–85 centimeter (20–33 inch) tail. They live in the forest and eat leaves, shoots, fruit, and seedlings. They are endangered. Their numbers are unknown. Their population is declining.

Germain's Langurs (Trachypithecus germaini, A. Milne-Edwards, 1876) are gray in color. They live in Southeast Asia. They are 40–76 centimeters (16–30 inches) long, with a 57–110 centimeter (22–43 inch) tail. They live in the forest and rocky areas and eat leaves, fruit, and flowers. They are endangered. Their numbers are unknown. Their population is declining.

Indochinese Black Langurs (Trachypithecus ebenus, Brandon-Jones, 1995) live in Southeast Asia. They are 40–76 centimeters (16–30 inches) long, with a 57–110 centimeter (22–43 inch) tail. They live in the forest, rocky areas, and caves and eat leaves, as well as fruit, vines, and flowers. They are endangered. Their numbers are unknown. Their population is declining.

Indochinese Grey Langurs (Trachypithecus crepuscula, Elliot, 1909) are gray in color. They live in Southeast Asia. They are 40–76 centimeters (16–30 inches) long, with a 57–110 centimeter (22–43 inch) tail. They live in the forest, inland wetlands, and rocky areas and eat leaves, flowers, and fruit. They are endangered. There are only 2,400–2,500 of them. Their population is declining.

capped langur

Silvery Lutungs are (Trachypithecus cristatus, Raffles, 1821) gray in color. There are two subspecies: 1) T. c. cristatus; and 2) T. c. vigilans. They live in Southeast Asia. They are 46–56 centimeters (18–22 inches) long, with a 63–84 centimeter (25–33 inch) tail. They eat leaves, as well as fruit, seeds, shoots, flowers, and buds . They are vulnerable. Their numbers are unknown. Their population is declining.

Tenasserim Lutungs (Trachypithecus barbei, Blyth, 1847) live in Southeast Asia. They are 40–76 centimeters (16–30 inches) long, with a 57–110 centimeter (22–43 inch) tail. They live and eat leaves, flowers, and fruit. They are vulnerable. Their numbers are unknown. Their population is declining.

Laotian Langurs (Trachypithecus laotum, Thomas, 1911) are black and yellow monkeys. They live in Laos. They are 40–76 centimeters (16–30 inches) long, with a 57–110 centimeter (22–43 inch) tail. They live in the forest and rocky areas and eat leaves, flowers, and fruit. They are endangered. Their numbers are unknown. Their population is declining.

Phayre's Leaf Monkeys (Trachypithecus phayrei, Blyth, 1847) are gray in color. There are two subspecies: 1) T. P. phayrei; and 2) T. P. shanicus. They live in Southeast Asia (in green). They are 40–76 centimeters (16–30 inches) long, with a 57–110 centimeter (22–43 inch) tail. They live in the forest and eat leaves, as well as bamboo shoots. They are endangered. Their numbers are unknown. Their population is declining.

White-thighed suriliare (Presbytis siamensis, S. Müller & Schlegel, 1838) are gray in color. There are four subspecies: 1) P. s. cana; 2) P. s. paenulata; 3) P. s. rhionis; and 4) P. s. siamensis. They live in Southeast Asia. They are 42–61 centimeters (17–24 inches) long, with a 50–85 centimeter (20–33 inch) tail. They live in the forest and eat fruit, seeds, and leaves. They are not threatened. Their numbers are unknown. Their population is declining.

Popa Langurs (Trachypithecus popa, Roos et al., 2020) live in Myanmar. They are 40–76 centimeters (16–30 inches) long, with a 57–110 centimeter (22–43 inch) tail. They live in the forest and eat leaves, flowers, and fruit. They are critically endangered. There are only 130–180 of them. Their population is declining.

Langurs and Leaf Monkey Species in Vietnam

Germain's langur (Indochinese Lutung)

Cat Ba Langurs (Trachypithecus poliocephalus, Pousargues, 1898) are gray in color. They live in Cát Bà Island, Vietnam (in purple). They are 40–76 centimeters (16–30 inches) long, with a 57–110 centimeter (22–43 inch) tail. They live in the forests and caves and eat leaves, flowers, and fruit. They are critically endangered. There are only 30–35 of them. Population increasing

Delacour's Langurs (Trachypithecus delacouri, Osgood, 1911) are gray in color. They live in Northern Vietnam. They are 40–76 centimeters (16–30 inches) long, with a 57–110 centimeter (22–43 inch) tail. They live in the forest, rocky areas, and caves and eat leaves, flowers, and fruit. They are critically endangered. There are only 240–250 of them. Their population is declining.

Hatinh Langurs (Trachypithecus hatinhensis, Dao, 1970) are black monkeys. They live in Vietnam. They are 40–76 centimeters (16–30 inches) long, with a 57–110 centimeter (22–43 inch) tail. They live in the forest, rocky areas, and caves and eat leaves, as well as fruit, vines, and flowers. They are endangered. Their numbers are unknown. Their population is declining.

François’ Langurs

François’ langurs (Trachypithecus francoisi) are also known as François’ leaf monkeys, capped leaf monkeys, brow-ridged langurs, lutungs, Tonkin leaf monkeys, white side-burned black langurs and black leaf monkeys. These primates were first described by M. Francois, the French Consul at Lungchow, Kwangsi, China, who found specimens on cliffs along the Longkiang River. He observed flocks of small black monkeys with long tails and black heads. The species was first officially described by Pousargues in 1898 from specimens collected in Longzhou, southern Guangxi Province in China. [Source: Lauren Ris, Animal Diversity Web (ADW) /=]

François’ langurs are found only in southern Guangxi province in China, northern Vietnam, and west-central Laos. They inhabit densely forested and limestone areas of tropical lowlands and forest valleys and have a head and body length of between 40 and 76 centimeters (16 and 30 inches) and a tail between 57 and 110 centimeters (22.4 and 43 inches) in length and weigh between 4.2 and 14 kilograms (9.2 and 31 pounds). Sexual Dimorphism (differences between males and females) is present: Males are larger than females. /=\

François’ langurs are primarily herbivores (primarily eat plants or plants parts), and folivores (eat mainly leaves). Animal foods include insects. Among the plant foods they eat are leaves fruit. They fead mainly on foliage, especially mature leaves, as well as some fruit and occasional insects. This low protein, high fiber diet requires a modified digestive system.

According to Animal Diversity Web: François’ langurs have small heads and lack cheek pouches. The tail is long, straight, and black with a white tip. Forelegs are much shorter than hind legs with hairless hands and feet that allow easy grasping of branches. Thumbs are well-developed, opposable, and significantly shorter than the thumbs of Presbytis. Fur varies from uniformly brown, black, or dark gray with a white stripe running from the corner of the mouth to the ear. White is also present in a crest above the eyes, resembling eyebrows, a feature which distinguishes them from species in the genus Presbytis. Young are golden yellow with a black tail, another feature that distinguishes these monkeys from the black young of Presbytis. /=\

On the International Union for Conservation of Nature (IUCN) Red List François’ langurs are listed as Endangered. On the US Federal List they are classified as Endangered. In CITES (Convention on International Trade in Endangered Species of Wild) they are in Appendix I, which lists species that are the most endangered among CITES-listed animals and plants.

Threats to the species include habitat loss to the expansion of agriculture, fuelwood harvesting, warfare, logging, and hunting.François’ langur has been used in researching retroviruses that infect a variety of nonhuman primates and can be transmitted to exposed humans. The species is also hunted for its believed medicinal value. /=\

François’ Langur Behavior

Francois' langur

François’ langurs are arboreal (lives mainly in trees), diurnal (active during the daytime), motile (move around as opposed to being stationary), sedentary (remain in the same area), territorial (defend an area within the home range), social (associates with others of its species; forms social groups), and have dominance hierarchies (ranking systems or pecking orders among members of a long-term social group, where dominance status affects access to resources or mates). These monkeys are very agile in trees and good at leaping from tree to tree. They inhabit home ranges of about 157 hectares and the average daily range is about 1,000 meters. Population density per square kilometer is less than 45. [Source: Lauren Ris, Animal Diversity Web (ADW) /=]

François’ langur groups tend to be small with six to 30 members. Each group is led by a single male and generally has twice as many females as males. Most individuals live in one-male groups of three to 10 individuals. Males typically maintain their territories through loud vocalization and displays. They periodically fight for dominance of a group. When a new male takes over a group he often kills all the young. Females have their own hierarchy system and appear to initiate social activities in the group.

Relationships within the group have been poorly documented due to the difficultt of see the species in their arboreal environment. According to Animal Diversity Web: However, female-female affiliative behavior, allogrooming, sitting close to one another, as well as alloparental care have been observed. Groups generally exist peacefully; however, the leading male may experience territorial encounters with the males of other groups and may be ousted by an outside male. Little is know about the communication of François’ langur but they could be similar to the vocalizations and visual displays that have been observed in other members of the their genus.

François’ Langur Mating, Reproduction and Offspring

François’ langurs are polygynous (males having more than one female as a mate at one time). They are also cooperative breeders (helpers provide assistance in raising young that are not their own). They engage in year-round breeding although breeding peaks in autumn and winter. Females are capable of producing young annually. Most births result in one offspring. The estrous cycle is 24 days.[Source: Lauren Ris, Animal Diversity Web (ADW) /=]

According to Animal Diversity Web: It is common among colobines for females to initiate sexual behavior, and François’ langur is no exception.However, they are somewhat of an exception among other species in the family in that the social structure involves primarily one-male groups, in which one male mates with multiple females.

The gestation period lasts six to seven months. Young are born fully furred and are fairly active. Males and females become sexually mature after four or five years. Among primates with similar social structures, females provide the bulk of parental care. They groom, carry, and protect their young. However, males may also play some role in carrying, provisioning and protecting young. The most important parental role of males may be to protect young from potentially infanticidal rival males. /=\

Phraye’s Leaf Monkey

Phayre's leaf monkeys (Trachypithecus phayrei) range from Eastern India to Southern China, including parts of Thailand and Vietnam. They traditionally lived in forests but are now found in a variety of habitats due to human disturbance within their range. They usually reside in mixed evergree-deciduous primary and secondary forests. In thick evergreen forests, these monkeys can be found 15 to 50 meters above the ground. Outside primary and secondary forests, they depend on bamboo and small shrubs and can sometimes be found along stream banks containing thick bamboo forests. [Source: Wayne Cantwell, Animal Diversity Web (ADW) /=]

The head and body length of Phayre's leaf monkeys range from one to 1.3 meters (3.5 to 4.3 feet). The tail of these monkeys constitutes 68 percent of their overall length, ranging from 65 to 86 centimeters (25.6 to 34 inches). Sexual Dimorphism (differences between males and females) is present: Sexes look a little different and females are longer. While males range from one to 1.1 meters in length, females range from 1.15 to 1.3 meters. The average weight of a male is 7.4 kilograms; for females its 6.2 kilograms.

The three subspecies of Phayre's leaf monkeys — 1) T. p. phayrei, 2) T. p. crepusculus and 3) T. p. shanicus — have slightly different colorations. In general, Phayre’s leaf monkeys are dark grayish-blue in color with some brown on their back and are mostly brownish-white on their front. The upper arms, legs, and tail are silvery-grey in color. The head and tail are darker than the rest of the torso. The area around the lips and eyes are white. Young Phayre’s leaf monkeys have yellowish colored fur until about three months of age when the fur begins to change. Adult Phayre's leaf monkeys also have slightly longer hair on the top of their head. Male Phayre's leaf monkeys can be distinguished from females in the field is by observing differences between ocular markings. In males, the white ocular rings around the eyes are parallel to the side of the nose, resulting in a black strip uniform in width. In females, the white ocular rings around the eyes bend inwards toward the nose causing more of black triangular shape. /=\

Phayre’s leaf monkeys are primarily folivores (eat mainly leaves). They have been know to eat leaves from approximately 80 different species of plants. Due to the considerable about of leaves in their diet, Phayre's leaf monkeys have highly adapted stomachs, necessary to digest cellulose and denature the toxins found in leafy materials. Phayre's leaf monkeys also eat bamboo shoots when tree foliage is not as abundant.

On the International Union for Conservation of Nature (IUCN) Red List Phayre’s leaf monkeys are listed as Endangered. In CITES (Convention on International Trade in Endangered Species of Wild) they have no special status. Habitat loss and fragmentation are the biggest threats to these animals. It is estimated that 1,300 individuals currently exist in the wild. Their populations are isolated throughout their range. Phayre’s leaf monkeys may still be hunted for food by local people. They are also poached for their gall stones — which are used for medicinal purposes — particularly around salt springs. Young may be taken by large tree snakes and raptors. Conservation efforts have focused on limiting slash and burn agriculture and increasing the amount of protected land.

Phayre's Leaf Monkey Behavior and Communication

Phayre's leaf monkeys are arboreal (lives mainly in trees), scansorial (able to or good at climbing), motile (move around as opposed to being stationary), sedentary (remain in the same area), territorial (defend an area within the home range) and social (associates with others of its species; forms social groups). Wayne Cantwell wrote in Animal Diversity Web: Phayre's leaf monkeys have home ranges from 10 to 100 hectares, with very little overlap among groups. The size of the range depends heavily on the distribution and abundance of food. If food resources are limited, larger groups will increase the size of their home range in search of food. Although range is mainly determined by group size, group size is heavily limited by social stress. Stress limits population size and thus home range in three ways: stress reduces a female’s ability to conceive and carry an infant to term; stress can lead to immunosuppression making individuals more susceptible to disease and therefore death; and stressed Phayre’s leaf monkeys may disperse, leaving their group, which puts them at a greater risk of death.[Source: Wayne Cantwell, Animal Diversity Web (ADW) /=]

Phayre's leaf monkeys are very shy and typically flee when threatened. They spend over 75 percent of their time feeding within tree tops. This species rarely leaves the safety of the trees, leaving only if their requirements are not met or to negotiate gaps in the canopy. Phayre's leaf monkeys are strongly territorial, against other groups of the same species, although sympatric groups of other species may share the same territory. /=\

Groups of Phayre's leaf monkeys vary in size from eight to 22 members. One dominant male rules the group, composed of three to six adult females, and a mixture of sub-adults, juveniles, and infants. Females tend to be closely related to each other and rarely leave the troop. Their roles and level of dominance amongst females are not clearly defined. Adolescent males leave the troop at about three years of age before they reach sexual maturity, preventing males from challenging the dominant male of or mating with females e within their natal group. Outcast males may join other solitary males, becoming nomadic (move from place to place, generally within a well-defined range), in search of breeding females or the opportunity to challenge a dominant male in order to establish his own troop. Dominant males protect their territory from troopless males. If an intruding male wins an encounter, the dominant male is then outcast, and the newcomer gains breeding rights. /=\

Phayre's leaf monkeys communicate with vision and sound and sense using vision, sound, touch and chemicals usually detected with smell. Both males and females use vocal calls for a variety of reasons. Adult males use a loud "kah kah kah" call when alarmed. A softer "whoo" call is used when adult males detect a predator within the area. The "cheng-kong" call is emitted by the dominant male to bring the group together. When a dominant male must defend its territory, a "loud call" is used, which is a high pitched roar against intruders. Young Phayre's leaf monkeys will emit a distress call when they fall from the treetops. Femals also use a “lost call” in an attempt to locate lost newborns. This call has also been heard from Phayre's leaf monkeys in the presence of deceased newborns. /=\

Phayre's Leaf Monkey Mating, Reproduction and Offspring

Phayre's leaf monkeys are polygynous (males having more than one female as a mate at one time). They breed intermittently throughout the year, but births generally occur in March and April. The average number of offspring is one. According to Animal Diversity Web: The mating system of Phayre’s leaf monkeys is similar to that of spectacled langurs, Troops of Phayre’s leaf monkeys have one dominant male that breeds with multiple females. Because adolescent males leave the troop before reaching sexual maturity, males do not challenge the dominant male of or mate with females within their natal group. [Source: Wayne Cantwell, Animal Diversity Web (ADW) /=]

Outcast males may join other solitary males, becoming nomadic (move from place to place, generally within a well-defined range), in search of breeding females or the opportunity to challenge a dominant male in order to establish his own troop. Dominant males protect their territory from troopless males. If an intruding male wins an encounter, the dominant male is then outcast, and the newcomer gains breeding rights. The new dominant male may kill young from the previous male, effectively permitting earlier copulation with females.

The average gestation period is 205 days. The age in which young are weaned is around 12 months. Males reach sexual maturity at three to four years of age. Phayre's leaf monkeys invest considerable energy in raising their young. Newborns nurse for almost a year, which greatly increases chance of survival. Mothers are the main caregivers as they feed, protect and groom newborns. It is not uncommon for older female siblings of a newborn to provide minimal care in the absence of the mother. Adolescent Phayre's leaf monkeys tend to keep some contact with their mothers, even after she gives birth to additional offspring. When young Phayre's leaf monkeys fall to the ground, they call out in distress to their mother. In most instances, the mother or an older sibling descend to retrieve it. In the case that an infant is lost from the troop the mother gives a "lost call" in hopes of locating the lost newborn./=\

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Text Sources: Animal Diversity Web animaldiversity.org ; National Geographic, Live Science, Natural History magazine, David Attenborough books, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The New Yorker, Time, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.

Last updated December 2024