Trachypithecus cristatus has different common names in different countries. In English, they are referred to as silvered leaf monkeys, whereas in India they are referred to as silvered langurs. In their endemic area of Malaya, they are called lutong.
Sir Thomas Stamford Raffles originally described the species in 1821. He gave them the name Simia cristata. The scientific name was later changed to Presbytis cristatus. The genus Presbytis has been broken into 4 new groups, including the genus Trachypithecus, in which T. cristatus is now found. The meaning of the name Trachypithecus comes from the Greek words "trach," meaning rough and "pithekos," meaning ape. Cristatus comes from the Latin word "crista," which means crest or tuft. Thus, the name was given fitting its physical characteristics.
Trachypithecus cristatus is the most silent of the colobine species. Researchers describe these monkeys as being grave, serious, expressionless, and slow moving. They make 13 different vocalizations, which are most common at dusk and dawn. They vocalize to signal conflict, fear, warnings, alarms, and salutation. In addition to these vocalizations, males make threatening calls and young call for their mothers. Although members of the species are relatively quiet, individuals also communicate nonvocally with each other in social play, grooming, and light fighting.
Communication Channels: visual ; tactile ; acoustic ; chemical
Perception Channels: visual ; tactile ; chemical
Silvered leaf monkeys are considered threatened according to IUCN RedList and are on the CITES Website, Appendix II. The species was first labeled threatened in 1996. Their status is threatened due to the habitat destruction occuring in the forests of their region for agriculture.
CITES: appendix ii
IUCN Red List of Threatened Species: near threatened
Negative impact on humans is unknown and unlikely due to the rarity of these animals and the infrequency of interaction with humans.
Many primates are hunted by humans in Asia for their flesh and the medicinal value of bezoar stones found in their intestine. Trachypithecus cristatus, however, is the exception. Other aspects of this species that may positively affect humans are unknown.
Like most other members of their genus, T. cristatus feeds on young leaves. However, their impact on their ecosystem is unknown.
Silvered leaf monkeys, as their name suggests, feed primarily on leaves, with a preference for young leaves. As herbivores, they also eat some other vegetation including fruit, seeds, shoots, flowers, and buds. Some adaptations have been made to increase efficiency of digesting and processing plant materials. The teeth have pointed cusps on their two transverse ridges, and are referred to as bilophodont. The stomach has become sacculated and contains bacteria for fermentation of the plants. The stomach is also enlarged to hold a large amount of food, given that the food they eat is nutritionally poor. They also contain large salivary glands that act to neutralize stomach acid that may cause damage if seepage from the stomach occurs.
Plant Foods: leaves; seeds, grains, and nuts; fruit; flowers
Primary Diet: herbivore (Folivore )
Silvered leaf monkeys, Trachypithecus cristatus, are found throughout Southeastern Asia and Indonesia, including the Malayan Peninsula, Borneo, Sumatra, Java, Thailand, and the Natuna Islands. One subspecies, T. c. vigilans, is found only on the Natuna Islands. The other subspecies, T. c. cristatus, is found in all areas to which the species is endemic.
Biogeographic Regions: oriental (Native )
The habitat of T. cristatus is very similar to that of other members of its subfamily Colobinae. Silvered leaf monkeys primarily inhabit dense forests, but their habitat can vary somewhat depending on the region. In Java and Sumatra, they live in the trees of inland forests, whereas on the Malaysian Peninsula, they live in the mangrove and sub-coastal forests. They have also been found in bamboo forests, on plantations, and in swamp forests. Because the monkeys are largely arboreal, they rarely leave the trees. Occasionally, they come down to the ground, but retreat quickly if there is a threat of danger.
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: forest ; rainforest ; scrub forest
Wetlands: swamp
Other Habitat Features: agricultural
The lifespan of T. cristatus has rarely been recorded. In captivity, the maximum lifespan is 29 years. Animals in the wild generally live about 20 years, although due to difficulty in making sustained observations in the wild, exact longevity in the wild is unknown.
Average lifespan
Status: wild: 20 years.
Range lifespan
Status: captivity: 29 (high) years.
Average lifespan
Sex: female
Status: captivity: 31.1 years.
Trachypithecus cristatus is similar in appearance to other colobines in that it is small in size, has 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 movements they utilize. The fore and hind limbs are more equal in length than most other cercopithecids, or Old World Monkeys, suggesting that the group previously occupied a more terrestrial habitat.
Silvered leaf monkeys get their name from the coloring of their pelage. There is some variation in the color of their fur, including brown, gray, brownish-gray, or black. No matter what the color, some hairs are gray-white and give a silver appearance. Polymorphisms are very rare; the best known is a red morph that exists in Borneo. The hands and feet are prehensile, hairless, and usually black in color. Males and females are difficult to distinguish from one another. The only visible difference is irregular white patching on the inside of the flanks of females. Males are also slightly larger than females: females are 89% of the body weight of the males.
Newborns have orange fur and white colored hands, feet, and face. The skin changes color within days of birth to black, as in the adults of this species. The orange fur changes to the adult color within three to five months.
Body length in males ranges from 52.4 cm to 56.0 cm, whereas females are typically 46.5 cm to 49.6 cm. Both sexes have a tail that is longer than their body; tail length ranges from 63 cm to 84 cm. Male body weight averages 7.1 kg and female body weight is about 6.2 kg. Newborns are about 20 cm and 0.4 kg at birth. They reach their adult size at about 5 years of age.
Range mass: 4.9 to 8.0 kg.
Average mass: Male: 7.1; Female: 6.2 kg.
Range length: 46.5 to 56.0 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes alike; male larger
Predators of silvered leaf monkeys are common predators found throughout the forests of southeast Asia, Thailand, and Indonesia, and include snakes, tigers, leapords, and jackals. The forest canopy is the safest place for T. cristatus as there are no raptors in the area that prey on arboreal monkeys. Therefore, the treetops act as protection for silvered leaf monkeys.
Known Predators:
Groups of T. cristatus are generally one-male groups in which one male defends and mates with multiple females. All-male groups as well as single males are also found. Occasionally, a male from an all-male unit or an individual male will challenge the male of a male/female group. If the challenger presides over the defending male, infanticide usually occurs. Females commonly care for young of other mothers in the group, and often even allow other young to nurse.
Mating System: polygynous ; cooperative breeder
Trachypithecus cristatus reproduction has not been widely studied, however a few facts are known. There is no limited season for copulation, although there is a birth peak from December to May when there is an abundance of food. The gestation period is 6 to 7 months, and the estrous cycle is 24 days. Females usually give birth to no more than one infant per year. Twins have occurred, but are very rare. Females reach sexual maturity at 4 years of age, whereas males mature between 4 and 5 years of age.
Breeding interval: Silvered leaf monkeys typically breed once every year.
Breeding season: Breeding does not appear to be strictly limited by season.
Average number of offspring: 1.
Average gestation period: 6 months.
Average age at sexual or reproductive maturity (female): 4 years.
Average age at sexual or reproductive maturity (male): 4-5 years.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous
Average number of offspring: 1.
Average age at sexual or reproductive maturity (female)
Sex: female: 1461 days.
There is little information available about parental care of young, however, being mammals, silvered leaf monkeys invest a great deal of time and care into offspring. Mothers nurse their young for months after birth. Females, as well as males, teach their young, play with them, and protect them from danger. However, typically infants approach males to be carried and to play. Young are well developed when born. Their eyes are open and their forearms are strong, allowing them to cling to the mother.
Parental Investment: altricial ; precocial ; male parental care ; female parental care ; pre-fertilization (Protecting: Male); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female); extended period of juvenile learning
The silvery lutung (Trachypithecus cristatus), also known as the silvered leaf monkey or the silvery langur, is an Old World monkey. It is arboreal, living in coastal, mangrove, and riverine forests in Peninsular Malaysia, Sumatra, and Borneo.
It is the type of its species group.
The silvery lutung is a medium-sized monkey with a long, non-prehensile tail. It has grey-tipped, dark brown or black fur, giving it a uniform silvery appearance. Unlike some related species, there are no paler markings on the face or body, except for a patch of whitish hair on the groin of females. A crest of fur runs along the top of the head, and the hair on the cheeks is long, often obscuring the ears. The hands and feet are hairless, with dark coloured skin, and have opposable thumbs and toes.[3]
Females range from 46 to 51 centimetres (18 to 20 in) in head-body length, with an average weight of 5.7 kilograms (13 lb) and a tail length of 67 to 75 centimetres (26 to 30 in). Males are slightly larger, from 50 to 58 centimetres (20 to 23 in) in length, with an average weight of 6.6 kilograms (15 lb) and a tail length of 67 to 75 centimetres (26 to 30 in).[4]
Like other langurs, the silvery lutung has a large three-chambered stomach to digest the cellulose found in its herbivorous diet. This allows for fermentation of food, and has some similarities with the stomach of ruminants. The intestine is unusually long, even compared to those of other langurs, and has a number of pouches along its length, which carry out further fermentation of plant matter. The teeth have grinding ridges and other modifications to allow the more efficient processing of tough leaves.[3]
The silvery lutung is found across Borneo and Sumatra, as well as in parts of the south-western Malay peninsula, the Natuna Islands, and other nearby islands. It inhabits mangrove swamps and nearby forest regions, and generally avoids travelling far from coasts or rivers.
The number and identity of subspecies of the silvery lutung is currently debated. A 2008 analysis confirms the presence of only two subspecies:[5]
The Malay Peninsula form has been subsequently elevated to a separate species, the Selangor silvered langur T. selangorensis[6]
However, some older sources, such as Mammal Species of the World,[1] as well as some much newer ones such as the 2021 edition of the IUCN Red List,[2] distinguish the silvery lutungs of the Natuna Islands as a separate subspecies, designated T. c. vigilans.
The silvery lutung is a specialist folivore, including a higher proportion of leaves in its diet than any other colobine monkey. Although it does also eat fruit, and some seeds and flowers, these comprise only 9% of the diet, and it is also able to feed on tougher and more mature leaves than any of its close relatives.[7] Because of these differences, silvery lutungs do not normally live in the same parts of the forest as other monkeys. Where other species are found in the same area, silvery lutungs are more commonly found in the middle canopy of the forest, leaving the higher branches to monkeys with a more frugivorous diet.[3]
Local predators able to feed on silvery lutungs include leopards, tigers, dholes, and some large snakes. Binturongs, and various other small carnivores are probably able to feed on infants.[3]
Silvery lutungs are unusually susceptible to human diseases, including AIDS, and have therefore been widely used in medical research.[8]
Silvery lutungs are diurnal, and travel in groups of around 9-40 individuals with one adult male and many adult females communally caring for infants. They rarely leave the trees, which provide them protection from ground-dwelling predators, and rapidly flee if threatened. Each group occupies a home range of 20 to 43 hectares (49 to 106 acres), although these may overlap with those of neighbouring groups. During the day, individuals may travel up to 500 metres (1,600 ft) through the forest, with some forming all-female subgroups that separate from the group containing the male. The entire group shelters in a single tree at night.[3]
The social structure of silvery lutungs is matrilineal and harem based. Females remain in the group for life, while males leave shortly after reaching adulthood, living in small groups of their own until they can take over an established harem. Within the group, males dominate the females, and females with young dominate those without. However, there is relatively little aggression within the group compared with some related species.
Because group ranges often overlap, different groups frequently come into contact with one another. The adult male protects his group and territory from competing males, communicating his dominance to other males via vocalizations and fighting. In the absence of males, however, females from different groups are more likely to interact peacefully. The most serious conflicts occur when a male intrudes directly on the territory of another male, which may result in the intruder displacing the resident and taking control of the group. In many other primates, such a displacement would normally be followed by the male killing any infants sired by his predecessor; although this may occur in silvery lutungs, it has not been directly observed, and may be less common than in some other species.[3]
Although less vocal than other closely related species, silvery lutungs make at least thirteen different vocalisations, with the most common being used by adult males defending their territory. Other vocalisations express fear, anger, excitement, and satisfaction, in addition to various calls made by infants.[3]
In Sabah, Malaysia, silvery lutungs have been observed in mixed-species groups with proboscis monkeys, and interspecific mating and a possible hybrid has been observed.[9] Researchers believe this may be a result of the two species being confined to a small patch of riverine forest due to deforestation in order to plant oil palm trees.[9]
Silvery lutungs breed year round, with no clear breeding season, although each female typically gives birth no more than once every 18 to 24 months.[10] The female attracts the male by making side-to-side motions with her head, and copulation may occur several times during a bout. Unusually, females have been reported to reach menopause in the wild, and may survive up to nine years after last giving birth.[3]
The female gives birth to a single young after a gestation period of 181 to 200 days. The young weigh about 400 grams (14 oz), measure about 20 centimetres (7.9 in) and are well developed, with a strong grip for holding onto the mother. Silvery lutungs are born with orange fur, and with white hairless skin on the face, hands, and feet. The skin rapidly changes to the dark adult colour, but the fur does not reach the adult pattern for three to five months after birth. The young are cared for by females communally, and are not weaned for 18 months, even though the biological mother stops lactating after just 12 months.[11] The young are sexually mature almost as soon as they finish weaning, and, on average, females first give birth at 35 months of age.[12]
Silvery lutungs have lived up to 31 years in captivity.[3]
Genetic analysis has shown that the silvery lutung probably first evolved during a rapid speciation event that occurred between 0.95 and 1.25 million years ago, during which all the living species of the T. cristatus species group evolved. Because of the relative speed and diversity of this event, the species of the group are difficult to distinguish genetically, and there is some uncertainty as to which represent genuinely distinct species.[5] However, the closest living relative of the silvery lutung may be the Javan lutung,[13] although silvery lutungs have also been reported to produce hybrids with Phayre's leaf monkey, generally considered to belong to a different species group.[3]
Fossils of the species are known from the late Pleistocene onwards, and occupy the same geographic range as today. Some of these fossils had significantly larger cheek teeth than living animals, although they have not been assigned to a distinct subspecies.[3]
The silvery lutung is classed as vulnerable by the IUCN,[2] and is listed in Appendix II of CITES.[14] Its habitat is heavily threatened throughout its range by logging and the development of oil plantations. The species is also threatened by hunting for meat and by capture for the pet trade.[15]
{{cite journal}}: CS1 maint: uses authors parameter (link) The silvery lutung (Trachypithecus cristatus), also known as the silvered leaf monkey or the silvery langur, is an Old World monkey. It is arboreal, living in coastal, mangrove, and riverine forests in Peninsular Malaysia, Sumatra, and Borneo.
It is the type of its species group.
