Indochinese Silvered Langur, Trachypithecus germaini
INDOCHINESE SILVERED LANGUR
Trachypithecus germaini
Geographic Distribution and Habitat
The Indochinese silvered langur, also known as Germain’s silver langur or the Indochinese leaf monkey, is native to Southeast Asia, particularly Thailand, Myanmar, Cambodia, Laos, and Vietnam. Vietnam’s population has drastically declined, and in the past 50 years, there have been very few sightings. The species has several areas of greater relative abundance, rather than a continuous distribution, in the Lao PDR. Although it is widely distributed in Cambodia, its abundance varies from common to scarce. Keo Seima Wildlife Sanctuary in Cambodia has a constant population of 1,487, making it one of the rare locations with a population estimate. The species is widespread in Thailand, where numerous protected areas support sizable populations.
In the geographical areas mentioned, Indochinese silvered langurs inhabit lowland terrestrial habitats, preferring evergreen and semi-evergreen, riparian, gallery, and deciduous forests from sea level up to 1,967 feet (600 m). They are not commonly found at high elevations or hilly areas.
Categorized under the subfamily Colobinae of the larger family Cercopithecidae of the Afro-Eurasian monkeys, the Indochinese silvered langur has had a controversial taxonomic history. It was once considered the same species as the silvered langur (Trachypithecus cristatus) and the Annamese langur (Trachypithecus margarita). Advances in morphological and genetic studies, however, have led to their separation into distinct species. Today, Indochinese populations found west of the Mekong River (in Vietnam, Cambodia, Laos, Thailand, and Myanmar) are recognized as the Indochinese silvered langur (T. germaini), while those east of the Mekong (in Vietnam, Cambodia, and Laos) are classified as the Annamese silvered langur (T. margarita).
Size, Weight, and Lifespan
Adults have an average combined head and body length of 21.7 in (55 cm) with a tail length of around 28 in (78 cm). Females are slightly smaller than males, and adults weigh an average of 14.3–15.4 lb (6.5–7 kg).
The lifespan of this species is not well known, but likely to be similar to other langurs at around 20–25 years in the wild.
Appearance
Adult Indochinese silvered langurs, as their name suggests, are covered in a thick, dark silvery coat. They have dark, bare faces and silvery-gray crests atop their heads, with their faces surrounded by a halo of long hair. The belly is a lighter silver than the rest of the torso, as are their legs and the underside of the tail. They have dark hands and feet and no eye-rings, unlike other closely related langur species.
They also have long, hook-like fingers and reduced thumbs, which make it easier for them to swing from branch to branch. This form of movement requires less energy than climbing, running, or leaping, an important adaptation since their specialized digestive system already demands a high amount of energy. The small thumb is an adaptation to their forest habitat, allowing a secure grip while still making their hands efficient for this type of movement.
Infant Indochinese silvered langurs are very easy to identify as they have a startlingly bright golden-orange pelage, contrasting sharply with the adults’ silvery gray coloring. They are also born with white faces, hands, and feet, although these start to darken within a few days. After a few months, this orange pelage starts to become silvered until the juveniles have the same coloring as adults. Scientists have proposed a number of theories as to why these infants should be bright orange, with one of the more popular hypotheses suggesting that the bright color helps adults in the group locate the infants in dense forests.
Diet
The Indochinese silvered langur is a careful eater with a menu that changes with the seasons. Most of its diet is made up of tender young leaves, which are easier to digest and sweeter than tough, older ones. Fruits, flowers, and buds add variety, especially when the forest is in bloom. In total, these monkeys feed on more than 50 different plant species, but they return again and again to a handful of favorites like figs and Phyllanthus reticulatus. They have also been observed eating mushrooms (mycophagy) and soil (geophagy) sometimes.
Scientists discovered that the langurs are picky for a reason: the plants they choose tend to have less of the hard-to-digest fibers and bitter chemicals that make some leaves unappetizing. In fact, their favorite foods have more natural sugars and less woody material, giving them the energy they need to leap through the forest canopy. By shifting their diet between wet and dry seasons, the silvered langurs show just how finely tuned they are to the rhythms of their environment.
Behavior and Lifestyle
The daily life of the Indochinese silvered langur is mostly calm and unhurried. Almost half of their day is spent resting (47%), while another large share is devoted to feeding (44%). Most of their day is spent resting because their herbivorous diet, rich in fibrous leaves, requires long periods of rest so they can ruminate, similar to how cows digest their food. The rest of their time is spent moving through the forest (5%), especially on tree limbs since they are an arboreal species, and grooming one another (4%).
The langurs divide their time across different layers of the forest, spending most hours in the understory (54%), considerable time on the forest floor (29%), and less in the high canopy (17%). The understory offers the best mix of food and safety. Time spent on the forest floor is linked to their preference for more digestible vegetation such as grasses and young shrub leaves, which are richer in protein and lower in fiber compared to mature leaves. They also occasionally visit the ground to collect bark, soil, or fallen fruits. Indochinese silvered langurs sometimes spend entire afternoons searching for mushrooms on the forest floor despite other primates overlooking them because they provide little energy and are hard to digest. Once gathered from the forest floor, the langurs carry the fungi up into the trees to eat in safety. On rare occasions, they also dig up moist soil and consume it to help supplement dietary minerals, neutralize toxins from leaves, or soothe digestive problems. The canopy is used less often since it provides fewer of their preferred foods.
Their use of space also changes with the weather. They are more likely to visit the forest floor on sunny days. In rainy weather, they retreat upward into the canopy, where branches provide shelter.
They also follow a clear rhythm to their day: feeding peaks in the early morning (around 8 a.m.) and again in the late afternoon (3–5 p.m.), when temperatures are cooler and leaves and fruits are fresher. Midday, when the heat is strongest, is mostly devoted to resting in the shade, which also aids digestion of their fibrous diet. Interestingly, when feeding increases, resting and grooming decrease, showing how their activities are carefully balanced around food availability, temperature, and weather conditions.
Orange Babies: Infants are born with bright orange fur, which makes them stand out in the group. Scientists think this helps adults spot and protect them more easily.
Monkey ‘Cows’: Like cows, these langurs have a complex stomach that allows them to ferment and digest tough, fibrous leaves. They even ruminate (chew cud) during their long resting periods.
Leaf Connoisseurs: Out of more than 50 plants in their diet, they carefully choose leaves that are softer, sweeter, and easier to digest, avoiding the tough and bitter ones.
Quiet Neighbors: Unlike many monkey species, silvered langurs are not very noisy. They rely more on close social bonds, grooming, and staying near each other than on loud calls. They occasionally emit loud calls, such as the sharp “khek khek” vocalization. But these are not frequent and are usually used in specific contexts, like alarm calls, maintaining group cohesion, or signaling to outsiders.
Weather Watchers: They adjust their position in the forest depending on the weather, spending more time on the ground during sunny days and climbing higher during rain.
Shy but Social: Groups can be quite large, sometimes up to 50 individuals, but they remain gentle and rarely show aggression.
Indochinese silvered langurs live in multi-male, multi-female groups that can number from seven to over 50 individuals, often breaking into smaller subgroups throughout the day in a fission-fusion pattern.
Like other folivorous primates, their lifestyle is shaped by their diet: because leaves are tough to digest, langurs must spend long periods resting (47% of their day) to allow for rumination, with feeding taking up almost as much time (44%). As a result, overt social behaviors such as grooming make up only a small portion of their activity (4%). Yet this does not mean they are unsociable. On the contrary, they spend nearly one-fifth of the day (18%) sitting in close proximity to one another, actively seeking companionship by resting within reach of group members.
They mostly groom on sunny days and do not groom during rainy weather, likely because rainwater would easily get onto the skin and make the experience uncomfortable.
Unlike some other primates, scientists have not observed play, but this could be because the populations they studied were independent (subadults or adults) rather than juveniles (young, dependent offspring who are most likely to engage in play).
Agonistic behaviors among the Indochinese Silvered langur are rare, a phenomenon consistent with patterns across leaf-eating monkeys. Leaf-eating monkeys do not fall into conflict because leaves are abundant and widely available, and are harder to monopolize than fruit, which reduces competition.
Together, these patterns show how diet, weather, and group composition shape the rhythm of their daily life and the quiet, harmonious nature of their social world.
Langurs communicate through a variety of modalities, including postures, gestures, and vocalizations. The loud call of the Indochinese silvered langur has been described as a “khek khek.” Other species of langur use at least 20 vocalizations, and it’s very likely that, with further investigation, a wide vocal repertoire will be revealed for this species.
An Indochinese silvered langur is mature and ready for mating at the age of 3-4 years. After a gestation period of about 196 days, a mother gives birth to a single infant. While breeding is not seasonal, bright orange infants are most often born between November and May.
Females probably mate with more than one male and give birth to a single infant who clings to her for the first few months of life. As the infant grows older and its orange pelage begins to turn to silver, it will become more independent and spend more and more time away from its mother. It is likely that, like other langur species, females of this species are philopatric and stay in their birth group for life. It is also likely that males leave their birth group around the age of sexual maturity.
It is thought that males who take over a troop kill infants through a phenomenon known as infanticide, as is the case in other closely related langur species. Infanticide forces females into estrus because they no longer have a child to care for. This increases a male’s reproductive success when he takes over a new troop.
Indochinese silvered langurs contribute to the health and balance of their forest habitats. As primarily leaf-eaters, they “prune” the over 50 species of trees that make up their diet and encourage new growth. They also help regulate plant growth and composition, shaping which species thrive within the understory and canopy.
As they eat fruits, they also act as occasional seed dispersers, aiding forest regeneration and plant diversity.
At the same time, langurs form part of the prey base for predators such as carnivores and large birds of prey, linking them into the broader food web.
Finally, because they depend on intact, continuous tracts of forest, the presence of healthy langur populations serves as an indicator of overall ecosystem health.
The Indochinese silvered langur is currently classified as Endangered by the International Union for Conservation of Nature (IUCN, 2015). Major threats to this species include habitat loss due to land use and hunting for bush meat, the pet trade, and use in traditional medicine. Deforestation and habitat degradation are major threats in Cambodia and Vietnam, with land converted for projects such as rubber plantations and the construction of dams. Limestone quarrying in Vietnam has also destroyed the habitat of half of the largest subpopulation in the karst areas of Kien Giang Province. Much of the population is split into small, isolated populations, which exacerbates the already severe threats to this species. Many individuals currently held in zoos in Vietnam are believed to have been captured from wild populations.
The Indochinese silvered langur is included in the Convention on International Trade in Endangered Species (CITES) Appendix II and is afforded some legal protection across its range. Hunting of this species is banned within Cambodia, but this law is rarely enforced.
Within its range, this species has been recorded in several protected areas in each country. However, further protections will be required to halt the decline in its population, including habitat protection and enforcing hunting bans. For instance, an educational program in Cambodia has aimed to aid long-term primate conservation by empowering local children living around Kbal Spean and Phnom Kulen national park to protect the country’s primates against detrimental anthropogenic influences on primates and their habitat. In 2017, the species population was reported to have increased in two protected areas, Phú Quốc National Park and Kiên Lương Karst Area, demonstrating the importance of conservation efforts.
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Written by Brenda Awuor, Aug 2025