Annamese Langur, Trachypithecus margarita
ANNAMESE LANGUR
Trachypithecus margarita
Geographic Distribution and Habitat
The Annamese langur, also known as the Elliot’s silvery langur, is found in eastern Cambodia within the provinces of Ratanakiri and Mondulkiri, southern Laos, and south-central Vietnam. They are the most scarce monkey species in Laos, while their largest populations are found in Cambodia.
Within their range, they are found in lowland forests, evergreen and semi-evergreen forests, mixed deciduous forests (those with trees which lose their leaves during the dry season), riparian forests (those close to a body of water), and gallery forests (those formed along riverbanks that flow into otherwise open areas, such as deserts or savannas).
The Annamese langur was once considered a subspecies of the Indochinese silvered langur (T. germaini). As a result of a 2008 study of the genus’s genetics, coupled with the fact that the former species has a lighter fur color than the latter, the Annamese langur was classified as a separate species.
Size, Weight, and Lifespan
The Annamese langur has a head-body length of 16-30 inches (40-75 cm), with a non-prehensile tail (not used for grabbing or grasping, but rather, to balance among the tree branches) that ranges in length between 22-43 inches (57-110 cm). Exact measurements of their weight have not been recorded, but those of their genus range from 11-33 pounds (5-15 kg), with males generally being larger than females. This likely difference in weight between genders, along with a whiteish patch around the pubic region of females, are examples of sexual dimorphism (noticeable physical differences between genders).
Their lifespan is not known, but it is likely to be similar to that of other langurs, at around 20–25 years in the wild.
Appearance
The Annamese langur has a slim build and is covered in thick, pale gray fur. The abdomen and throat are a lighter shade of gray compared with the rest of the torso, as are the legs and underside of the tail. This contrasts with their black forehead, forearms, hands, and feet. Their gray face is marked with a pale ring around each of their copper eyes. The fur on the top of the head forms a hood or cap, giving them a furry “hat” of sorts.
Babies, meanwhile, differ dramatically in coloration from the adults. They have a glossy golden-orange fur coat, with a white face, hands, and feet! After a few months, their coloration changes to that of the adults, starting with the head, hands, and feet.
Diet
The diet of the Annamese langur is similar to that of others in their genus. They are primarily folivores (leaf-eating), and supplement their diet with flowers and, especially, juicy fruit!
In terms of exact metrics, based on one study, the Annamese langur’s diet has been reported as consisting of 54.4% young leaves, 29.9% fruit, 7.7% flowers, and 7.1% mature leaves.
As is the case with other langurs of their genus, many of the leaves the Annamese langur eats are tough and contain plenty of cellulose (the primary chemical that forms the main structure of plants). To combat this, they have a multi-chambered stomach to help digest this material. In addition, It is also likely that like other members of their genus, they also spend a decent portion of their day resting so digestion can run smoothly.
Behavior and Lifestyle
Much regarding the behavior and lifestyle specifically of the Annamese langur is unknown, due to the lack of studies (and their secretive nature). Information however, can be inferred from other langur species.
The Annamese 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 to eat soil (and, when undisturbed, juveniles may spend their time playing on the forest floor).
As is the case with other langurs, much of their activity is dedicated to caring for infants and feeding. Other activities performed during the day include playing, grooming, resting, vocalizing, and traveling around their territory.
Besides humans, natural predators of the Annamese langur include leopards and large snakes. Similar to other members of their genus, the Annamese 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 sleeps in designated sleeping trees.
Grey adults, but orange babies!? Yes! Scientists have theorized several reasons as to why baby langurs of the genus Trachypithecus are so brightly colored. Three dominant theories are camouflage from predators 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).
Similar to their behavior and lifestyle, information on the Annamese langur’s daily routine and group dynamics is seriously lacking. Once again, most of the information can be inferred from other langur species in the Trachypithecus genus.
If we look at their close relative, the Indochinese gray langur, it’s possible that, like them, Annamese langur troops are comprised of several families. One study on the Annamese langur found a troop consisting of 61 individuals (!) with multi-male and multi-female social organization. Based on information about the Indochinese gray langur, it’s likely that one male among the troop is the dominant male, while the rest of the group consists of adults of both genders and their young offspring. Dispersal patterns of male and female Annamese langurs from their natal troop are unknown and require further study.
From one study focusing on the Annamese langur, home range size can reach 632 acres (256 ha), and is typically larger in the dry season when compared to the rainy season, likely because of varying availability of food. The high canopy section of the forest habitat is most frequently used, although juveniles use the mid-canopy more frequently than adults. In addition, langurs prefer mixed deciduous forests during the rainy season but avoid them during the dry season, possibly due to a lack of canopy in which to hide from predators and feed.
They are sympatric (occur in the same area) as douc langurs (genus Pygathrix), which consists of three species: the black-shanked douc langur (P. nigripes), the gray-shanked douc langur (P. cinerea), and the red-shanked douc langur (P. nemaeus).
Once again, due to the severe lack of studies on the Annamese langur (along with their elusive nature), information regarding their communication repertoire is virtually unknown. More studies by wildlife biologists are necessary to discover the langurs’ full repertoire of expressions.
If we once again look at the Indochinese gray langur, vocalizations include loud, staccato calls used to intimidate and scare away a rival or potential predator. Males might curl their upper lip and bare their canine teeth to add a truly frightening display to this threat. When a predator is spotted, they may “cough” to warn others. To call out to other members of the troop, langurs emit throaty, reverberating chirps. Squeaks often accompany their daily activities. Finally, after a big meal, these leaf-eating langurs often belch—just like humans (excuse them!)
Mothers are likely to attentively groom their young, reinforcing the ever-important parent-child bond.
The mating system of langurs varies. Societies can be monogamous (exclusive male-female mating partners); polygynous (males mate with multiple females), or polyandrous (females mate with multiple males). Once again, information regarding the reproductive lives and care for young among the Annemese langur is severely lacking, and must be inferred from closely related langur species. These monkeys just won’t stop being a mystery, will they!?
Like other langurs, adult females give birth after a seven-month gestation (pregnancy) period to one (rarely two) young. Looking at the Indochinese gray langur:
• Reproductive maturity for females is between 3 and 5 years of age.
• Births occur year-round, but peak between November and April.
• A mother’s inter-birth interval (time period between births) is about two years, assuming her previous infant survives.
As is the case with other langurs, females initiate copulation (sexual contact) by presenting their anogenital region to a prospective male partner. It’s also possible that all members of a family group help to raise the young.
As fruit-eaters, Annamese 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 Annamese langur as Endangered (IUCN, 2015), appearing on the IUCN Red List of Threatened Species.
Major threats to the Annamese langur’s survival include habitat loss due to land use changes (especially in eastern Cambodia and the Central Highland in Vietnam), hunting, use in traditional medicine, and the pet trade.
In Laos, suitable habitats for the Annamese langur have largely been converted for agriculture; any remaining suitable habitat is fragmented and has been under severe hunting pressure. The demand for langur bones in Vietnam as part of traditional medicine has likely driven more intensive hunting of the Annamese langur in the past few decades.
The Annamese 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.
In Vietnam, the Annamese langur is legally protected under Appendix 1B of Decree 32 (2006) and Appendix I of Decree 160 (2013) under the name of Trachypithecus villosus. They may be found in the following protected areas: Cat Tien, Yok Don, Chu Mom Ray, and Kon Ka Kinh National Parks, Ta Kou Nature Reserve and Chu Prong Proposed Nature Reserve.
In Cambodia, the Annamese langur is legally protected under Chapter 10 of the Forestry Law (2002), and within protected areas managed by the Ministry of Environment under the Protected Area Law (2008). They may be found in the following protected areas: Virachey National Park, Veun Sai Forests, Mondulkiri Protected Forest, Lomphat Wildlife Sanctuary, Phom Prich Wildlife Sanctuary, Seima Protection Forest, Phom Nam Lyr, and Snoul Wildlife Sanctuaries.
In Laos, the Annamese langur is considered “At Risk”, and is legally protected under the ‘Prohibited’ category of the list of threatened species, and the Wildlife and Aquatic Law (2007). They may be found in the following protected areas: Dong Phou Vieng, Xe Bang Nouan, Xe Pian, and Dong Hua Sao National Biodiversity Conservation Areas, and Bolaven Southwest Proposed National Protected Area.
Ultimately, PLENTY of conservation actions are needed if the Annamese langur has any chance of surviving extinction. These include: further site/area protection, resource and habitat protection, habitat and natural process restoration, species and harvest management, ex-situ conservation (i.e., outside of their natural habitat) of the species, captive breeding, and additional education, awareness, and communications regarding the species. No surprise here, but additional research is needed on the Annamese langur’s population size, distribution and trends, life history and ecology, and threats to their survival. Conservation planning needed includes a species action/recovery plan and area-based management plan(s). Finally, additional monitoring of the Annamese langur’s habitat, harvest level, and population trends is required as part of the long list of needs for the Annamese langur to bounce back from the current path to extinction.
- https://www.bioexplorer.net/animals/mammals/monkeys/annamese-silvered-langur/
- https://en.wikipedia.org/wiki/Annamese_langur
- https://en.wikipedia.org/wiki/Riparian_forest
- https://en.wikipedia.org/wiki/Trachypithecus
- https://www.gbif.org/species/5786349
- https://www.iucnredlist.org/species/39875/210372003
- https://www.researchgate.net/profile/Alvaro-Gonzalez-Monge/publication/320923721_The_Socioecology_and_the_Effects_of_Human_Activity_on_It_of_the_Annamese_Silvered_Langur_Trachypithecus_margarita_in_Northeastern_Cambodia/links/5a901173aca27214056103f4/The-Socioecology-and-the-Effects-of-Human-Activity-on-It-of-the-Annamese-Silvered-Langur-Trachypithecus-margarita-in-Northeastern-Cambodia.pdf
Written by Sienna Weinstein, June 2024