Red-Shanked Douc Langur, Pygathrix nemaeus
RED-SHANKED DOUC LANGUR
Pygathrix nemaeus
Geographic Distribution and Habitat
The red-shanked douc langur is one of three species of douc langurs (the gray-shanked and black-shanked are the other two) and is native to Indochina, inhabiting the undisturbed evergreen, semi-evergreen, and limestone forests of east-central Laos and northern and central Vietnam. These Endangered primates make their home in the mid to upper levels of the forest canopy.
Laos hosts the largest and most stable population of red-shanked douc langurs; they live in the Nam Theun basin and its surroundings, including several protected areas. By contrast, Vietnam’s red-shanked douc langur population is smaller, having suffered significant decline due to years of human-caused destruction. However, a population of about 200 individuals, from 12 different groups, currently live at Vietnam’s Son Tra Nature Reserve.
Sightings of the species in northern Cambodia have recently been reported.
Size, Weight, and Lifespan
Like all langurs, red-shanked douc langurs are long and slender; their tails are about the same length or slightly longer than their bodies. Males are bit more hefty than the females.
Head-to-body length in males is from 21.6 to 23.6 in (55 to 60 cm). Their tails add another 23.6 to 29 in (60 to 74 cm). Males weigh between 24 and 28 lbs (10.9 to 12.6 kg).
Head-to-body length in females is about 23.6 in (60 cm). Their tails add another 23.6 in (60 cm). Females weigh between 18 and 19.6 lbs (8.2 and 8.9 kg).
Lifespan for captive red-shanked douc langurs is about 25 years.
Nonprehensile:
Incapable of grasping or gripping (opposite of prehensile: capable of grasping).
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Appearance
The different species of douc langurs can be distinguished by the color of their legs, or shanks.
Sometimes referred to as “the costumed ape,” the red-shanked douc langur is among the most colorful of primates. The monkey’s yellow-orange face and ears appear to be powdered with theatrical makeup, and the eyelids appear to be dusted with a powder-blue eye shadow. Dark, almond-shaped eyes view the world, and from a modest nose, tiny nostrils inhale the fragrance of the forest habitat. Long, white whiskers (more generous in males) adorn the chin and frame the monkey’s alien-like face. A wide black band stretches across the monkey’s forehead.
The garb of the red-shanked douc langur is strikingly stylish. Jazzing up a black-speckled gray coat that covers the back, crown of head, and upper arms is a chestnut-colored collar that separates the white neck from a black band that stretches between the shoulders. The monkey’s generous “pot belly” is a shimmery silver color. Maroon-red fur on the lower legs (shanks) leads one to think, imaginatively, that the primate may have slipped into a pair of colorful stockings. Likewise, the white fur extending the length of the monkey’s forearms is evocative of a pair of long gloves that perhaps this douc grabbed from a theatrical wardrobe. A triangle of white fur marks the base of a white tail.
Males can be distinguished from females by a white spot adorning both sides of their rump, just above the white triangle. And, if you are peeking, their genitals are red and white.
Diet
Red-shanked douc langurs are folivorous; that is, they are herbivores who specialize in eating mostly leaves. Young, tender leaves are their preference; however, they will also eat shoots, buds, seeds, flowers, and unripened fruit. They receive their water requirement through their diet.
Messy eaters, they frequently drop their food to the forest floor below. And they routinely burp. Their multichambered stomach uses bacteria to break down the cellulose in the leaves that they eat through the biological process known as fermentation, thereby creating “gassy monkeys.” But what these colorful primates might lack in dining etiquette they make up in manners, often sharing their meals with others in their group.
Behavior and Lifestyle
Spending all their time exclusively in trees, red-shanked douc langurs are an arboreal species. They live high in the rainforest canopy where they use their long arms to propel themselves from tree limb to tree limb; other times, jumping, as they forage for the best leaves to eat. After finding something tasty, they might share their meal with other members of the group in an act of langur etiquette.
These monkeys are active during daylight hours, making them diurnal. They travel in groups and appear to enjoy one another’s company. Come nightfall, they sleep in carefully selected large trees that provide a thick canopy.
“Douc” is an ancient Vietnamese word thought to mean “monkey.”
The red-shanked douc langur, along with the gray-shanked and black-shanked douc langur, belongs to the subfamily of Old World leaf-eating monkeys known as Colobinae.
Red-shanked douc langurs are genetically similar to gray-shanked douc langurs; however, they are considered a different species due to their different biological features.
Groups are composed of a mixed-gender population, with females usually outnumbering the males. Adult males, however, exhibit dominance over the females. The size of a group is influenced by a habitat’s food sources and by human disturbance, such as hunting. Although sightings of 50 individuals have been observed, smaller groups of 15 individuals, or less, are more typical. Group size can also fluctuate when members disperse for a specific purpose, such as foraging, and then regather (this leaving-and-coming-together phenomenon is known as fission-fusion).
Adult males take the lead position in a group’s foraging activities, females and infants assume the center position, and the group’s juvenile males follow at the rear.
When they are not foraging, much of a group’s time is spent digesting the food they’ve eaten, napping, and grooming one another.
Communication includes touch, visual signals, and vocalizations. Group grooming is an important tactile activity that establishes strong social bonds not only between mothers and their infants, but between all members of a group.
Facial expressions include a “play face,” identified by an open mouth, teeth partially bared, and chin thrust forward; a fixed stare, used for intimidation when conveying a threat; and a grimace, given as a submissive response to a threat and identified by an open mouth and teeth exposed (similar in appearance to the play face).
Vocalizations include low-pitched growls, used in conjunction with a threat display; and short, harsh distress squeals or “barks” when the doucs are startled. While emitting stress squeals, the doucs will simultaneously slap tree branches with their hands as they deftly move through the canopy.
When it comes to mating, both male and female doucs give one another “the look” by thrusting their jaw forward, raising and lowering their eyebrows, and shaking their head. But it is the female who makes the first move by lying face-down on a branch and then casting a coquettish look, over her shoulder, at the male object of her affections. Should he succumb to her charms, her paramour will return her stare and mount her where she lay (one or multiple times!), or he might choose a spot he considers more suitable for their copulation.
Females are considered sexually mature at about four years of age and breed every two years, giving birth to a single offspring after a gestation period of about 210 days. Births coincide with the beginning of fruiting season, when food is plentiful.
Males attain sexual maturity closer to five years of age.
Infants are born with their eyes open and instinctively cling to their mothers. Their grey fur is soft and lighter in color than adult red-shanked douc langurs and is marked by a dark stripe down the center of their back. Their faces are black with two pale strips beneath the eyes. As they grow older, their faces lighten and their bodies darken. By age 10 months, their metamorphosis is complete, and they have attained all their colors of their resplendent costume.
Mothers are the primary caregivers for their infants, carrying them around and nursing them until the infants become independent (a weaning age has not been documented, however). Some studies report that group members help out new moms with infant care, giving moms a chance to forage and feed. A study of captive red-shanked douc langurs confirms these mothers’ helpers, reporting one instance when an orphaned infant was fed by two females in a group and also looked after by a male.
Both male and female red-shanked douc langurs eventually leave their birth groups.
Red-shanked douc langurs disperse seeds of the fruits the eat through their feces, helping to nourish the ecosystem in which they live.
The red-shanked douc langur is classified as Critically Endangered by the International Union for Conservation of Nature (IUCN, 2015), appearing on the IUCN Red Lists of Threatened Species. In the last three generations, the species has experienced a population decline of more than 80 percent, due to forest loss and extensive hunting, and the grim prediction is that the population will continue to decline—at perhaps a greater pace.
Humans present the greatest threat to this species, through hunting (for food and for the monkey’s body parts, used for folkloric “medicinal” purposes), habitat destruction (for logging, agriculture, and general infrastructure development that includes roads and major highways), and the illegal wildlife/pet trade. The Vietnam War also had a detrimental impact on langur populations. In addition to having their habitat extensively bombed and sprayed with the toxic defoliant known as Agent Orange, soldiers used the monkeys for target practice.
The red-shanked douc langur is listed in Appendix I 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. However, as is often the case with endangered species, laws created to protect them are largely ignored and difficult to enforce. And in Vietnam, conservation law enforcement is extremely weak—even though the country has granted the red-shanked douc langur the highest protection status under its Wildlife Protection Law.
A captive breeding program is underway at the Endangered Primate Rescue Center at Cuc Phuong National Park in Vietnam to help preserve the species.
And the Douc Langur Foundation is a locally based organization conducting comprehensive surveys on the species to better understand the social interactions and distribution of red-shanked douc langur populations. The foundation also spearheads direct action, employing local people to remove traps and snares from the reserves and national parks; to confiscate monkeys from local markets and restaurants, where they are to be sold for their flesh; and to rescue from homes, where doucs are being illegally kept as pets. Healthy monkeys are released back to their forest habitat; if one needs medical attention, the foundation transfers the monkey to a rehabilitation center.
Through its Indochina Program, the World Wildlife Foundation (WWF) is performing vital research into the effectiveness of national parks within Vietnam and is training park rangers in effective enforcement of existing wildlife protection laws and in primate survey techniques. WWF’s Greater Mekong Program focuses on the region where douc langurs live, working with local communities and governments to help conserve rich biodiversity and natural ecosystems.
Founded in 2009 by the Frankfurt Zoological Society, the main objective of the Vietnam Primate Conservation Program is to protect the country’s langur species.
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Written by Kathleen Downey, June 2017. Conservation status updated July 2020.