Silvery Lutung
Encyclopedia
The silvery lutung 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
.
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.
Females range from 46 to 51 cm (18.1 to 20.1 ) in head-body length, with an average weight of 5.7 kilograms (12.6 lb) and a tail length of 67 to 75 cm (26.4 to 29.5 ). Males are slightly larger, from 50 to 58 cm (19.7 to 22.8 ) in length, with an average weight of 6.6 kilograms (14.6 lb) and a tail length of 67 to 75 cm (26.4 to 29.5 ).
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 ruminant
s. 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.
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. The latest analysis confirms the presence of only two subspecies:
However, some older sources, such as Mammal Species of the World
, still distinguish the silvery lutungs of the Natuna Islands as a separate subspecies, designated T. c. vigilans.
, 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. 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.
Local predators able to feed on silvery lutungs include leopard
s, tiger
s, dhole
s, and some large snakes. Binturong
s, civet
s, and various other small carnivores are probably able to feed on infants.
Silvery lutungs are unusually susceptible to human diseases, including AIDS
, and have therefore been widely used in medical research.
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.
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.
in the wild, and may survive up to nine years after last giving birth.
The female gives birth to a single young after a gestation
period of 181 to 200 days. The young weigh about 400 grams (14.1 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. The young are sexually mature almost as soon as they finish weaning, and, on average, females first give birth at 35 months of age.
Silvery lutungs have lived up to 31 years in captivity.
, although silvery lutungs have also been reported to produce hybrids with Phayre's leaf monkey
, generally considered to belong to a different species group.
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.
by the IUCN, and is listed in Appendix II of CITES. 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.
Old World monkey
The Old World monkeys or Cercopithecidae are a group of primates, falling in the superfamily Cercopithecoidea in the clade Catarrhini. The Old World monkeys are native to Africa and Asia today, inhabiting a range of environments from tropical rain forest to savanna, shrubland and mountainous...
. It is arboreal, living in coastal, mangrove, and riverine forests in Peninsular Malaysia
Peninsular Malaysia
Peninsular Malaysia , also known as West Malaysia , is the part of Malaysia which lies on the Malay Peninsula. Its area is . It shares a land border with Thailand in the north. To the south is the island of Singapore. Across the Strait of Malacca to the west lies the island of Sumatra...
, Sumatra
Sumatra
Sumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the sixth largest island in the world at 473,481 km2 with a population of 50,365,538...
, and Borneo
Borneo
Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....
.
It is the type
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
of its species group
Species group
A species group is an informal taxonomic rank into which an assemblage of closely related species within a genus are grouped because of their morphological similarities and their identity as a biological unit with a single monophyletic origin.-Use:...
.
Description
The silvery lutung is a medium sized monkeyMonkey
A monkey is a primate, either an Old World monkey or a New World monkey. There are about 260 known living species of monkey. Many are arboreal, although there are species that live primarily on the ground, such as baboons. Monkeys are generally considered to be intelligent. Unlike apes, monkeys...
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.
Females range from 46 to 51 cm (18.1 to 20.1 ) in head-body length, with an average weight of 5.7 kilograms (12.6 lb) and a tail length of 67 to 75 cm (26.4 to 29.5 ). Males are slightly larger, from 50 to 58 cm (19.7 to 22.8 ) in length, with an average weight of 6.6 kilograms (14.6 lb) and a tail length of 67 to 75 cm (26.4 to 29.5 ).
Like other langurs, the silvery lutung has a large three-chambered stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
to digest the cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
found in its herbivorous diet. This allows for fermentation of food, and has some similarities with the stomach of ruminant
Ruminant
A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...
s. The intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large 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.
Distribution and habitat
The silvery lutung is found across BorneoBorneo
Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....
and Sumatra
Sumatra
Sumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the sixth largest island in the world at 473,481 km2 with a population of 50,365,538...
, as well as in parts of the south-western Malay peninsula
Malay Peninsula
The Malay Peninsula or Thai-Malay Peninsula is a peninsula in Southeast Asia. The land mass runs approximately north-south and, at its terminus, is the southern-most point of the Asian mainland...
, the Natuna Islands
Natuna Islands
The Natuna Islands archipelago is located in the Natuna Sea in the larger Tudjuh Archipelago, off the northwest coast of Borneo. The islands are administratively part of the Riau Islands province of Indonesia and are the northernmost non-disputed island group of Indonesia...
, and other nearby islands. It inhabits mangrove
Mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
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. The latest analysis confirms the presence of only two subspecies:
- Trachypithecus cristatus cristatus - Borneo, Sumatra, Natuna Islands
- Trachypithecus cristatus selangorensis - Malay Peninsula
However, some older sources, such as Mammal Species of the World
Mammal Species of the World
Mammal Species of the World, now in its 3rd edition, is a standard reference work in zoology giving descriptions and bibliographic data for the known species of mammals.An updated Third Edition of Mammal Species of the World was published late in 2005:...
, still distinguish the silvery lutungs of the Natuna Islands as a separate subspecies, designated T. c. vigilans.
Diet and ecology
The silvery lutung is a specialist folivoreFolivore
In zoology, a folivore is a herbivore that specializes in eating leaves. Mature leaves contain a high proportion of hard-to-digest cellulose, less energy than other types of foods, and often toxic compounds. For this reason folivorous animals tend to have long digestive tracts and slow metabolisms....
, 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. 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.
Local predators able to feed on silvery lutungs include leopard
Leopard
The leopard , Panthera pardus, is a member of the Felidae family and the smallest of the four "big cats" in the genus Panthera, the other three being the tiger, lion, and jaguar. The leopard was once distributed across eastern and southern Asia and Africa, from Siberia to South Africa, but its...
s, tiger
Tiger
The tiger is the largest cat species, reaching a total body length of up to and weighing up to . Their most recognizable feature is a pattern of dark vertical stripes on reddish-orange fur with lighter underparts...
s, dhole
Dhole
The dhole is a species of canid native to South and Southeast Asia. It is the only extant member of the genus Cuon, which differs from Canis by the reduced number of molars and greater number of teats...
s, and some large snakes. Binturong
Binturong
The Binturong , also known as the Asian Bearcat, the Palawan Bearcat, or simply the Bearcat, is a species of the family Viverridae, which includes the civets and genets. It is the only member of its genus...
s, civet
Civet
The family Viverridae is made up of around 30 species of medium-sized mammal, including all of the genets, the binturong, most of the civets, and the two African linsangs....
s, and various other small carnivores are probably able to feed on infants.
Silvery lutungs are unusually susceptible to human diseases, including AIDS
AIDS
Acquired immune deficiency syndrome or acquired immunodeficiency syndrome is a disease of the human immune system caused by the human immunodeficiency virus...
, and have therefore been widely used in medical research.
Behaviour
Silvery lutings 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 ha (49.4 to 106.3 ), although these may overlap with those of neighbouring groups. During the day, individuals may travel up to 500 metres (1,640.4 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.The social structure of silvery lutungs is matrilineal and harem
Harem (zoology)
The term harem is used in zoology to describe the social organization of certain herbivore species, such as those in the Hominidae and Equidae families, into groups of females and young surrounding a single dominant male...
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.
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.
Reproduction
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. 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 menopauseMenopause
Menopause is a term used to describe the permanent cessation of the primary functions of the human ovaries: the ripening and release of ova and the release of hormones that cause both the creation of the uterine lining and the subsequent shedding of the uterine lining...
in the wild, and may survive up to nine years after last giving birth.
The female gives birth to a single young after a gestation
Gestation
Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
period of 181 to 200 days. The young weigh about 400 grams (14.1 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
Weaning
Weaning is the process of gradually introducing a mammal infant, either human or animal, to what will be its adult diet and withdrawing the supply of its mother's milk.The process takes place only in mammals, as only mammals produce milk...
for 18 months, even though the biological mother stops lactating after just 12 months. The young are sexually mature almost as soon as they finish weaning, and, on average, females first give birth at 35 months of age.
Silvery lutungs have lived up to 31 years in captivity.
Evolution
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 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. However, the closest living relative of the silvery lutung may be the Javan lutungJavan Lutung
The Javan lutung, Trachypithecus auratus also known as the ebony lutung and Javan langur, is an Old World monkey from the Colobinae subfamily. It is most commonly glossy black with a brownish tinge to its legs, sides, and "sideburns". It is found on and endemic to the island of Java, as well as on...
, although silvery lutungs have also been reported to produce hybrids with Phayre's leaf monkey
Phayre's Leaf Monkey
Phayre's leaf monkey , also known as Phayre's langur, is a species of lutung found in Southeast Asia. The species epithet commemorates Arthur Purves Phayre....
, generally considered to belong to a different species group.
Fossils of the species are known from the late Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
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.
Conservation
The silvery lutung is classed as Near ThreatenedNear Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
by the IUCN, and is listed in Appendix II of CITES. Its habitat is heavily threatened throughout its range by logging
Logging
Logging is the cutting, skidding, on-site processing, and loading of trees or logs onto trucks.In forestry, the term logging is sometimes used in a narrow sense concerning the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard...
and the development of oil plantations. The species is also threatened by hunting for meat and by capture for the pet trade.