Selangor Silvery Langur, Trachypithecus selangorensis
Selangor Silvery Langur
Trachypithecus selangorensis
Geographic Distribution and Habitat
The Selangor silvery langur is found along a strip on the western coast of Peninsular Malaysia. This strip includes portions of the states of Johor, Negeri Sembilan, Selangor, Melaka, Perak, and Kedah, and even the capital city of Kuala Lumpur! Within this range, they are found in riparian forests (forests next to a body of water), mangroves, and occasionally, human plantations.
The country of Malaysia is a tropical one, with high humidity, uniformly high temperatures year-round, PLENTY of rainfall, and occasional monsoons.
The Selangor silvery langur was once classified as a subspecies of the silvery lutung (T. cristatus). As of 2013, they have been recognized as separate species by primatologists due to genetics as well as differences in their whiskers. Selangor silvery langurs have long, straight whiskers, while those of the silvery lutung are forward-curled, forming a semi-circular shape resembling a mussel’s shell.
Size, Weight, and Lifespan
The Selangor silvery langur has a head-body length ranging from 16-30 inches (40-76 cm), and a tail length ranging between 22-43 inches (57-110 cm). There is no specific data on their weight, but their close cousin, the silvery lutung, has an average weight of 13 pounds (5.7 kg) for females, and 15 pounds (6.6 kg) for males. As with all other langurs, there is slight sexual dimorphism (noticeable physical differences between genders), with males being larger than females.
The life expectancy of the species is unknown, but that of members in the genus Trachypithecus is estimated at 20 years.
Appearance
The Selangor silvery langur has a slim build, with a uniformly gray, furry body and black face, hands, and feet. Their distinctive (and distinguished) gray mustache is long and straight, while their eyes are a striking copper color. The long tail is non-prehensile (not used for grabbing), but is rather used for balancing in the trees of the forest habitat.
Babies, meanwhile, differ dramatically in coloration from the adults. They have bright orange fur with white faces, hands, and feet. Over the first three to five months of life, their coloration changes to that of the adults, starting with the head, hands, and feet.
Diet
The Selangor silvery langur is primarily folivorous (leaf-eating), with up to 91% of its diet consisting of leaves! The remaining portion of their diet is made up of fruit, flowers, seeds, buds, bark, and young shoots.
Many of the leaves they eat are tough and contain plenty of cellulose (the primary chemical that forms the main structure of plants), so like other members of their genus, the Selangor silvery langur has a multi-chambered stomach to help digest this tough material. They also spend a decent portion of their day resting so digestion can run smoothly.
Behavior and Lifestyle
The Selangor silvery langur is diurnal (active during daylight hours), being most active in the early morning and afternoon. They are also arboreal, preferring to spend most of their time in the trees, where they move on all fours (quadruped) along the branches. Like other langurs, they also have great climbing abilities and can leap from tree to tree. Groups may descend to the ground on occasion, and when undisturbed, play among individuals (especially juveniles of both sexes) occurs on the forest floor.
Much of their activity budget is dedicated to caring for infants and feeding. Other activities performed during the day include playing, grooming, resting, vocalizing, and traveling around their territory.
Studies on natural predators of the Selangor silvery langur are few and far between, but based on their range, and known predators of other species within the Trachypithecus genus, leopards and some large snakes likely make the list. Similar to other members of their genus, the Selangor silvery langur likely avoids these predators by sounding an alarm call followed by beating a hasty retreat, as well as by sleeping in tall trees at night. Speaking of sleeping, they do not construct sleeping nests. Rather, the troop spreads out between a couple of sleeping trees within 66 feet (20 m) of each other.
Grey and black adults, but orange and white babies!? Yes! Scientists have theorized several reasons as to why baby Selangor silvery langurs (along with those of other Trachypithecus langur species) are so brightly colored. Three dominant theories are camouflage within their forest habitat, the ability to be easily found by Mom should the little ones wander off, and to encourage alloparenting (taking care of a baby that isn’t one’s own).
Human habituation: The Selangor silvery langurs at Bukit Malawi (a fort in the town of Kuala Selangor, and a popular local tourist attraction) are among the few wild leaf monkey populations to have experienced continual habituation to humans. They will sometimes willingly climb on and touch visitors, and even approach and beg for food!
Selangor silvery langurs live in troops ranging between 11 to 38 individuals, including a single dominant adult male, multiple adult females, and their juvenile offspring. One study however, found that the Selangor silvery langur was more likely than most langurs to live in groups with more than one adult male. In some cases, after a younger male deposed the dominant male of the troop, the former dominant male was allowed to stay. In other cases, new young adult males were allowed to join a troop without challenging the dominant male. Finally, in other cases, younger males (presumably the dominant male’s sons) were allowed to stay with the troop for some time after reaching adulthood. More typically, upon reaching adulthood, young males are kicked out of the troop by the dominant male, upon which these bachelors search for a new troop to join. Similarly-aged males also tend to leave their natal troop together without any drama from the dominant male and join new troops together. Troops are territorial, with little overlap between the territories of neighboring troops. Upon spotting a rival troop, males defend their territory by sounding various warning and threat calls, and, if that’s not enough to keep the peace, they’ll attack!
The home range of the Selangor silvery langur ranges between 49.4-106 acres (20-43 ha), and during their daily routine, troop members travel 0.12-0.31 miles (200-500 m) per day.
The Selangor silvery langur has been observed peacefully associating with the long-tailed macaque (Macaca fascicularis), although mother langurs with infants tend to avoid the macaques to protect their young. Another study found that the two species sometimes travel together, and even occasionally feed in the same tree. Other species the Selangor silvery langur has been observed cohabitating with include the dusky langur (T. obscurus), the white-thighed surili (Presbytis siamensis), and the Raffles’ banded langur (P. femoralis).
By far the most popular (and fun) forms of communication for the Selangor silvery langur are play and grooming. Members of both genders participate in play, and play is especially seen among juveniles and even infants. Grooming typically involves two monkeys but sometimes can include three or four individuals. Not only does grooming rid the langurs of parasites, but the soothing activity also reinforces social bonds among troop members.
Posturing and gesturing have also been observed among Selangor silvery langurs, especially among females who are trying to catch the dominant male’s attention for breeding. At times of distress, Selangor silvery langurs prefer to hug it out, embracing one another for reassurance and comfort.
Finally, Selangor silvery langurs, like other langurs, are BIG chatterboxes! They have a varied and complex vocalization repertoire:
• Adult females greet others with a “ku ku” sound.
• Young members of both genders emit a “ho” to address others.
• “Ki”, “gyu”, and “kie” are all exclamations of fear or surprise made by both genders.
• An alarm call sounds like “snick”.
• Adult males use “guu” and “gyu” as threatening noises, while “gua gua gua” are used when on the attack. Young and adult males use “cha cha”, “chue chue”, or “ge ge” as warnings against intruders. Males also use a two-note, inhale-exhale vocalization during and after a territorial conflict with other males.
• Infants and juveniles emit a “ku” sound when content, and “gya gya gya”, “chu”, “chii”, or “chu chu chu” when asking for milk or when they’re VERY unhappy.
• The dominant male emits a “kwah” sound to get the troop moving, especially to start the daily foraging trip.
Very little is known with regard to the reproduction and maturation of the Selangor silvery langur and has to be inferred from other closely related species. With that, as is similar to other langurs, the Selangor silvery langur is likely polygynous (males mate with multiple females). Females give birth to a single baby per year (though twins, while rare, can happen), and one study indicated that births do not show a seasonal pattern. It is likely that, similar to other langurs, there is no seasonal breeding period, as well.
If we look at the dusky langur, a relative of the Selangor silvery langur, when infants reach one month of age, their confidence begins, as does their learning to climb and play. This may also be when Selangor silvery infants begin to eat solid foods. To help their tiny tummies digest, Mom will chew the leaves for them, using her specialized saliva to break down the plant material. After two months, the young will begin to engage in social activities, like play and grooming, with other group members. Further studies are needed to confirm all of this probable information with regard to the Selangor silvery langur, however. The genus Trachypithecus has a gestation period lasting seven months.
What is known for certain is that males have not been observed to initiate mating. Rather, females will approach the male to solicit mating, using rhythmic side-to-side head movements, as well as presenting their hindquarters. When it comes to caring for infants, it’s a family affair! Everyone helps out in caring for the offspring, even Dad! Mothers will care for the young of other mothers in the troop and will even allow them to nurse (a process known as allomothering or alloparenting). Infants are weaned from their mom within the latter half of their first year and reach full maturity at four to five years of age.
As fruit-eaters, Selangor silvery langurs aid in the regeneration of their forest habitats by dispersing seeds through their feces as they move around the habitat. They also play a role in pollination. Like bees and butterflies, they collect pollen from flowers when drinking nectar. They then deposit the pollen on each flower they visit, thereby pollinating the plants. Finally, as a prey species, they also play a role in feeding local predators within their range.
The International Union for Conservation of Nature lists the Selangor silvery langur as Near Threatened (IUCN, 2021), appearing on the IUCN Red List of Threatened Species.
The primary threats facing the Selangor silvery langur are hunting by humans (the motivation for which has not been documented), and habitat loss due to land clearances and forest fires. These land clearances are likely for the conversion of the land to agricultural space (i.e., plantations), as well as [continued] expansion of human settlements and recreational areas to cater to locals and the tourism industry.
In addition, despite occurring along populated areas of the Malaysian Peninsula, there is a lack of research regarding the species, particularly on their life history.
The Selangor silvery langur is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival.
The species is found in protected areas of Peninsular Malaysia, specifically the Kuala Selangor and Bukit Nanas Nature Reserves. In order to prevent the species from moving further to endangerment and extinction, proper land and water protection and management must be enforced. Furthermore, additional research is needed on their population size, distribution, trends, life history and ecology, threats to their survival, additional conservation actions, and the reason(s) for their being targeted by hunters.
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- https://animalia.bio/selangor-silvered-langur
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- https://www.britannica.com/place/Malaysia/Climate
- https://www.dpz.eu/en/info-center/knowledge/biodiversity-research/selangor-silvery-langur.html
- https://en.wikipedia.org/wiki/Bukit_Malawati
- https://en.wikipedia.org/wiki/Selangor_silvered_langur
- https://en.wikipedia.org/wiki/Trachypithecus
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Written by Sienna Weinstein, June 2024