Trachypithecus cristatus

Geographic Range

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 oriental
  • native native

Habitat

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 tropical
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest
• rainforest rainforest
• scrub forest scrub forest

• Wetlands
• swamp swamp

• Other Habitat Features
• agricultural agricultural

Physical Description

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.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike
• male larger

Reproduction

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 polygynous
• cooperative breeder 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.

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

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 altricial
• precocial precocial
• male parental care male parental care
• female 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

Lifespan/Longevity

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.

Behavior

The behavior of T. cristatus is not well known. Like many primates, T. cristatus is a social species. Individuals form groups consisting of one male and 9 to 48 females, depending on the location. Juveniles usually disperse from their natal group at maturity. Being diurnal, the majority of activity for this species is from sunrise to sunset. Trachypithecus cristatus is a very shy species. Individuals are occasionally seen in the vicinity of human settlements, but retreat quickly if they feel threatened.

Trachypithecus cristatus travels primarily via brachiation, although individuals may walk on the ground when traveling with the group. They show a low level of aggression within the social group. Sociosexual, gestural, and vocal interactions are the common features of the social relationships of these monkeys. This may be due to the abundance of food in their habitat and their feeding behavior of facing toward the tree while eating. These both decrease the frequency of interaction with other members of the group, resulting in less need for tight group cooperation.

Although the species is fairly peaceful, there is occasionally conflict with neighboring groups of the same species over territory. Many times, the groups will live in peace with each other in close proximity after the initial conflict. There is some aggression within groups, and this may be related to sex. Generally, there are only intraspecific conflicts. Trachypithecus cristatus tends to co-exist comfortably with other species such as Macaca fascicularis that inhabit the same regions.

• Key Behaviors
• arboreal arboreal
• scansorial
• diurnal diurnal
• motile motile
• nomadic nomadic
• sedentary sedentary
• territorial territorial
• social social

Home Range

Because this is a nomadic species, silvered leaf monkeys travel about 200 to 500 meters throughout their territory daily. The male of the group leads the females while guiding them with vocalizations. The territory a group occupies averages 43 hectares.

Communication and Perception

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 visual
• tactile tactile
• acoustic acoustic
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

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.

• Primary Diet
• herbivore herbivore
  • folivore folivore

• Plant Foods
• leaves
• seeds, grains, and nuts
• fruit
• flowers

Predation

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.

Ecosystem Roles

Like most other members of their genus, T. cristatus feeds on young leaves. However, their impact on their ecosystem is unknown.

Economic Importance for Humans: Positive

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.

Economic Importance for Humans: Negative

Negative impact on humans is unknown and unlikely due to the rarity of these animals and the infrequency of interaction with humans.

Conservation Status

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.

Other Comments

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.

Additional Links

Encyclopedia of Life

Contributors

Christine Bedore (author), Michigan State University, Barbara Lundrigan (editor, instructor), Michigan State University, Nancy Shefferly (editor), Animal Diversity Web.

References

Furuya, Y. 1961. The Social Life of Silvered Leaf Monkeys (Trachypithecus cristatus) . Primates , 3(2): 41-60.

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Groves, C., V. Weitzel. 1985. The Nomenclature and Taxonomy of the Colobine Monkeys of Java. International Journal of Primatology , 6: 399-409.

Groves, C. 2001. Primate Taxonomy . Washington: Smithsonian Institution Press.

Harper, D. 2001. "Online Etymology Dictionary" (On-line). Accessed February 28, 2005 at http://www.etymonline.com .

Medway, L. 1970. The Monkeys of Sundaland: Ecology and Systematics of the Cercopithecids of a Humid Equatorial Environment. Pp. 513-554 in Old World Monkeys: Evolution, Systematics, and Behavior . London: Academic Press.

Medway, L. 1969. The Wild Mammals of Malaya . London: Oxford University Press.

Nowak, R. 1999. Walker's Mammals of the World . Baltimore: Johns Hopkins University Press.

Roonwal, M. 1977. Primates of South Asia: Ecology, Sociobiology, and Behavior . Cambridge: Harvard University Press.

Streck, E. 2002. Predator Sensitive Foraging in Thomas Langurs. Pp. 76 in Eat or Be Eaten: Predator Sensitive Foraging Among Primates . Cambridge: Cambridge University Press.

2001. Colobine Monkeys. Pp. 380-391 in Encyclopedia of Mammals , Vol. 2, 2 Edition. New York: Andromeda Oxford Limited.

Wisconsin Regional Primate Research Center, University of Wisconsin, Madison. 2004. "Primate Info Net" (On-line). Accessed February 24, 2005 at http://pin.primate.wisc.edu/ .