INDOCHINESE SILVERED LANGUR
Geographic Distribution and Habitat
Also known as Germain’s langur, the Indochinese silvered langur is found in Eastern Asia, west of the Mekong river. They are distributed across a large part of Cambodia, as well as parts of Vietnam, Laos, Thailand, and Myanmar.
This species inhabits a range of forested habitats, including lowland, semi-evergreen and evergreen forests, karst forests, mangroves, and seasonally flooded forests. They occur from sea level up to 1,967 feet (600 m).
Their taxonomy is still debated and some scientists argue that there are two subspecies of Indochinese silvered langurs: T. g. caudalis, occurring in Northern Vietnam, and T. g. germaini, living throughout the rest of their range.
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.
Adult Indochinese silvered langurs, as their name suggests, are covered in a thick dark silvery coat. They have dark 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.
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 and care for the infants.
Langurs are also known as leaf monkeys and with good reason. Young leaves make up the majority of these primates’ diet, with Indochinese silvered langurs known to eat at least 58 plant species. The digestive systems of langurs are specially evolved to digest leaf matter; they have multi-chambered stomachs filled with gut microbes that help in breaking down leaves. In addition to the leaves, they also eat fruits, flowers, and buds.
Behavior and Lifestyle
Indochinese silvered langurs are more active in the early mornings and afternoons than in midday. They spend large portions of their time feeding and resting. Other periods are spent traveling and engaging in social behaviors, such as grooming. There tend to be low rates of agonistic behaviors among langurs, which scientists hypothesize is due to their folivorous diet. Since leaves are spread out, rather than clumped together like fruits, primates that feed on leaves generally have less competition over food sources.
While adults are a dark gray, newborn infants are born bright orange, making them easy to spot in the forest
Langurs have evolved specialized stomachs and gut biomes, allowing them to digest their diet made up primarily of leaves.
Indochinese silvered langurs exhibit a multi-male, multi-female social structure, similar to other langurs. They also exhibit a fission-fusion group structure, whereby members of the groups do not spend all their time together but break up into smaller groups throughout the day. Group size ranges from seven to more than 50, indicating a degree of flexibility in the demographics of the groups.
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.
Females of this species probably mate with more than one male and give birth to a single, bright orange infant who clings to her for the first few months of life. As the infant grows older, and its pelage begins to turn to silver, they will become more independent and spend more and more time away from their 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 male infanticide—the killing of an infant by a male—occurs in these langurs, as it does in closely related langur species. Infanticide increases a male’s reproductive success when he takes over a new troop of females.
Indochinese silvered langurs feed primarily on young leaves, which means they have an important impact on forest growth. As they pull the young leaves from the plant, they “prune” the tree and encourage new growth. Since this species feeds on upwards of 50 plant species, they are likely to have a significant impact on the forests that they inhabit.
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 bushmeat, 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. 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.
This species 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.
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Written by Jennifer Botting, PhD, May 2021