SILVERY LUTUNG

Trachypithecus cristatus

Geographic Distribution and Habitat
The silvery lutung, also known as the silvered leaf monkey or the silvered langur, is found in Brunei, Indonesia and Malaysia. They may occur on Batam in the Riau Archipelago as well.

Silvery lutungs prefer dense forests; however, their habitat varies depending on the region they inhabit. In the Malayan Peninsula, they live in mangrove and sub-coastal forests, whereas in Java and Sumatra they live in the trees of inland forests. They are also found in bamboo forests, swamp forests, and, occasionally, plantations.

Silvery lutung geographic range. Map: IUCN, 2020

Size, Weight, and Lifespan
Male silvery lutungs average 14.5 lb (6.6 kg) and females average 12.6 lb (5.7 kg). Body length in males ranges from 20.6 to 22 in (52.4–56 cm). Female body length ranges from 18.3 to 19.5 in (46.5–49.6 cm). Silvery lutungs have long tails, sometimes measuring longer than their body length.

In the wild their average lifespan is 20 years and in captivity they are known to live up to 31 years.

Appearance
The pelage color of silvery lutung monkeys is dark gray; the tips of their hair is a lighter gray, which gives them an overall silvery effect. The ventral portion of the tail and the groin are a yellowish color. Their face is black and the black hair atop their heads sweeps upward into a point. There are slight variations in hair color, including brown, brownish-gray, or black. Although adult males are slightly larger than adult females, it can be difficult to visually distinguish between the sexes. One visible differentiator is white patching on the interior flanks of females.

As is typical among colobine monkeys, the lower jaw projects out further than the upper jaw. The genus Trachypithecus can be distinguished from other colobines by their prominent nasal bones, a well developed sagittal crest, and recess brow ridges.

The size of their thumbs is reduced, which makes it easier for them to use brachiating movements while traveling throughout their forest habitats. Their fore and hind limbs are almost equal in length, which is unique for an Old World monkey. This suggests that they may have previously occupied a more terrestrial habitat.

Newborns have orange hair, and white hands, feet, and faces. Within a couple of days of birth an infant’s face turns black, just like an adult’s. Their hair changes to the adult color within 3 to 5 months.

What Does It Mean?

Bilophodont:
Molars that have four cusps that are oriented in parallel rows, which resemble ridges. This trait is a common characteristic of Old World monkeys. 

​Brachiation:
Also called arm swinging, it’s a form of arboreal locomotion in which primates swing from tree limb to tree limb using only their arms.

Cellulose:
Molecule found in plant matter that gives structure and strength to the cell walls of plants and provides dietary fiber.

Folivorous:
Having a diet that consists of leaves.

Mangrove: 
A mangrove refers to two different things: a tidal swamp ecosystem found in tropical deltas, estuaries, lagoons or islands, and the characteristic tree species populating this ecosystem. 

Old World monkey:
Monkeys native to Africa and Asia.

Sacculated:
Having a series of different sections. For example, langurs have sacculated stomachs (i.e., stomachs with three sections).

​​Ventrum:
The stomach or belly area, the outside lower surface of the torso.

Visit the Glossary for more definitions

Diet
The silvery lutung is a folivorous species, feeding on leaves, leaf buds, ground plants, and vines. They also consume various fruits, seeds, flowers, and shoots. They prefer to eat immature leaves over mature ones since immature leaves contain fewer lignin and tannins that may upset their stomachs. They have also been observed to eat clay, which may serve as a natural antacid. Their stomachs are sacculated, or have sack-like compartments that contain bacteria and enzymes to break down plant cellulose.

Silvered leaf monkeys have adapted pointed cusps on portions of their teeth, known as transverse ridges, which are referred to as bilophodont.

Due to the low nutritional quality of their diets, silvery lutungs are slow-moving, less energetic monkeys.

Behavior and Lifestyle
Silvery lutungs live a mostly arboreal lifestyle in the trees. They are diurnal, which means that most of their activities are accomplished during the daylight hours, up until sunset. They occasionally descend to the ground, but only to travel from place to place. They are quite shy, especially when in the vicinity of humans. When they feel threatened, they quickly retreat back into the trees.

While traveling through the trees, silvery lutungs brachiate, swinging by their arms from limb to limb. When traveling on the ground or walking and climbing through the trees, they do so quadrupedally. Walking is typically a group activity.

Silvery lutungs are a fairly peaceful species and have low levels of aggression toward one another in their social group. Some suggest the low levels of aggression are associated with the abundance of food in their habitat and the manner in which they feed. Since they face toward a tree while eating, less social cooperation is required. These factors decrease the need for interaction between individuals of the group.

Occasional conflicts arise between groups, mostly over territory. These conflicts usually occur in areas in which home ranges overlap. Males chase away males from other groups. Other fighting behaviors include slapping, pulling, and biting. Adult males emit loud vocalization calls when neighboring groups come in contact with each other. They share habitat and live harmoniously with other primate species, such as long-tailed macaques.

Social play primarily occurs between juveniles and infants of both sexes; however, all age groups have been observed participating in play. Wrestling and locomotor play are the most common forms of play. Locomotor play is when an individual swings from branches or drops to the ground from branches, but in a repeated motion like a circuit. Play fighting also occurs among juvenile males and sub-adult males.

Daily Life and Group Dynamics 
Silvery lutungs have a uni-male social structure. This means that groups consist of a single adult male, several adult females, juveniles, and infants. All-male social groups, known as bachelor groups, also exist. Sometimes individual males are on the search for a new troop. A male from an all-male group or a single male will challenge the male of a uni-male (male/female) group in the hopes of taking over leadership of that group. If the challenger male wins, he may kill the defeated male’s infants and chase off the sub-adult males of the group.

Group sizes can range from 9 to 51 individuals. Right before sunrise, groups set out to forage throughout their territory, traveling 656–1,640 ft (200–500 m) daily. The adult male of the group leads the females by guiding them with vocalizations (a “kwah” sound). During the late morning, individuals rest. Juveniles and infants prefer to stay close to adult females when resting. Silvered leaf monkeys also travel right before sunset. All group members retreat to a single tree to sleep at night.

Fun Facts

Silvery lutungs make at least 13 different vocalizations.

Silvery lutungs are susceptible to human diseases, including AIDS, and thus have been widely used in medical research. 

Communication
Researchers describe the silvery lutung as expressionless, solemn, and slow-moving. Although they are somewhat quiet, they have various vocalizations. A “ku” sound is emitted by infants when they are in a happy state. A “ho” sound is used by young males and females over short distances to address each other. “Ku-ku” calls are uttered by adult females while greeting each other. In addition, they have alarm calls, territorial calls, fear calls, and threat calls.

This species also communicates tactilely through social grooming and embracing. Other non-vocal communication includes yawning to communicate tension or excitement, branch shaking, head shaking, and chasing.

Reproduction and Family
Silvered leaf monkeys invest a great deal of time into their offspring. They are polygynous, which means one male mates with more than one female. To attract a mate, a female makes side-to-side motions with her head. Females usually give birth to one infant per year. There is no defined season for copulation; however, births peak from December to May.

Infants are born well-developed and possess a strong grip for holding onto their mother. Mothers nurse their young for several months after birth. Mothers will care for the young of other mothers in their group and will even allow them to nurse. This is called allomothering. Females and males both teach their young, play with them, and protect them. Infants usually approach males to be carried and to play.

Newborns have orange hair, and white hands, feet, and faces.
Within a couple of days of birth an infant’s face turns black, just like an adult’s. Their body hair changes to the adult color within three to five months.

Ecological Role
Silvery langurs feed on young leaves and occasionally on fruits, the seeds of which are then dispersed throughout the forest. This makes them important to the reforestation and biodiversity of their ecosystem.

Conservation Status and Threats
The International Union for Conservation of Nature’s Redlist of Threatened Species categorizes the silvery lutung as Vulnerable (IUCN, 2015). Due to extensive habitat loss within their range, their populations are decreasing. Land clearance, especially for palm oil plantations, and forest fires are a huge threat in Malaysia and Borneo. In Sarawak, silvery lutungs are hunted for meat. In Sumatra, they are heavily traded and are captured and sold for the pet trade. 

There are a few common predators of silvery lutungs found throughout the forest including snakes, tigers, leopards, and jackals. Thus, they stay in the treetops for added protection.

Conservation Efforts
The silvery lutung is listed on the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) Appendix II. They are found throughout at least four protected areas, which include Bukit Barisan Selatan National Park and Gunung Leuser National Park in Indonesia, and Bako National Park and Taman Negara National Park in Malaysia; they may occur in Tanjung Puting National Park, Indonesia, as well.

​References:

  • https://eol.org/pages/311196/data
  • http://animalia.bio/silvery-lutung
  • https://www.iucnredlist.org/species/22035/9348474
  • https://animaldiversity.org/accounts/Trachypithecus_cristatus/#8bad7a7825b9aaa8aa370dde5942a2c4
  • http://www.theprimata.com/trachypithecus_cristatus/
  • Bernstein, I.S. 1968. The Lutong of Kuala Selangor. Behaviour, 32, 1-16.
  • Furuya, Y. 1961. The Social Life of Silvered Leaf Monkeys (Trachypithecus cristatus) . Primates, 3(2): 41-60.
  • Harding LE. 2010. Trachypithecus cristatus (Primates: Cercopithecidae). Mammalian Species 42(862):149-165. 
  • Nowak, R. 1999. Walker’s Mammals of the World. Baltimore: Johns Hopkins University Press.
  • Wolf, K. and Fleagle, J.G. 1977. Adult Male Replacement in a Group of Silvered Leaf-monkeys (Presbytis cristata) at Kuala Selangor, Malaysia. Primates, 18, 949-955.