RED-SHANKED DOUC LANGUR
Geographic Distribution and Habitat
Of the three douc langur species—gray-shanked, black-shanked, and red-shanked—the red-shanked douc langur is the only one recorded in three countries of Indochina: Vietnam, Laos, and Cambodia. They live in evergreen, semi-evergreen, and limestone forests up to 5,200 feet (1,600 m) and spend most of their time in the middle to upper levels of the canopy.
In Vietnam, red-shanked doucs inhabit a region from Nghe An to Kon Tum Province. In Laos, their range extends from the Nam Ghong Provincial Area to the central northeast. Their Cambodian distribution is much less clear, as sightings are rare and difficult to corroborate. In 2018, researchers captured photographs of red-shanked doucs in Cambodia’s Virachey National Park, but this area lies on the border of Laos and Cambodia, so it is possible that the doucs were crossing over from Laos. Nonetheless, experts think northern Cambodia probably hosts some red-shanked doucs.
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. Their lifespan is about 25 years. Red-shanked doucs are sexually dimorphic; that is, their size and appearance vary with their gender.
The male has a head-to-toe body length of 22–32 inches (55–82 cm) with a tail that measures 22–29 inches (56–74 cm). The female is slightly smaller, reaching 24–25 inches (60–63 cm) with a tail that measures 17–24 inches (44–60 cm) long. Males weigh 19–25 pounds (8.6–11.4 kg), and females 15–23 pounds (6.6–10.5 kg).
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.
Interestingly, their eponymous red shanks may not always be red beyond light speckling. The doucs photographed in Cambodia showed little red on their thighs, aside from one individual with red feet. However, these doucs may have been hybridized offspring of red-shanked and gray-shanked doucs.
Red-shanked doucs depend mainly on buds and young leaves, and they supplement their diet with flowers, fruits, seeds, and bark. 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 for in manners, often sharing their meals with others in their group.
Recent studies on their feeding patterns reveal that they use hundreds of different plant species as food sources, suggesting that red-shanked doucs are more seasonally and dietarily flexible than previously believed. This flexibility may explain why they’re able to succeed in several different types of habitats. They have been observed sharing food with each other, a rare behavior among Afro-Eurasian primates—however, it’s worth noting that this behavior was observed in captive douc langurs.
Behavior and Lifestyle
Red-shanked doucs live almost entirely in the trees, where their long arms and tails make it easy for them to swing or leap between branches. Juvenile doucs rely heavily on brachiation—swinging like Tarzan—while mature doucs prefer to jump with two feet since brachiation becomes more tiring as they grow older and heavier. There are few reports of agonistic behavior in doucs; they appear to be mostly peaceful. Much of their day is spent foraging or socializing, with the rest dedicated to resting.
“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.
After sleeping through the night and waking shortly after sunrise, red-shanked doucs spend most of the day foraging and feeding. At night, doucs “fuse” into a larger group that usually “fissions”—separates—into smaller units during the morning and early afternoon. This group type is referred to as a “fission-fusion” society. Fission tends to correlate with greater activity, as well as increased vigilance and vocalizations. Limited data suggest that sub-units are stable—that is, their members do not fluctuate regularly. However, it is unclear whether sub-units tend towards certain sets of individuals. Researchers in the Son Tra Nature Reserve recorded one-male units, pair-bonded units (one male, one female), and multi-male units. Their work suggests that vocalizations may be used to coordinate activities between the separated sub-units of the larger group.
Fused groups range from 30–50 individuals, though groups in regions that are highly impacted by human activities and habitat loss are often much smaller. Group size also may shrink when less food is available. One or two adult males are typically the group leaders, and other members follow their movements through the canopy. When the group moves, females and infants stay in the center, while juvenile males take up the rear. Groups opt for higher ground when sleeping to avoid predators. Females sleep with their offspring.
During social periods, red-shanked doucs (mainly adults) groom each other; some data suggests that females prefer to groom males. Juvenile doucs may engage in chase play or (occasionally) rough play. Antagonistic behaviors are rare across all age classes. There are occasional reports of dominant males chasing subordinate males away from females, but fighting is extremely uncommon.
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 affection. 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 the 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 eat lots of leaves, fruit, and flowers. Consequently, they disperse seeds throughout their home ranges. They are also a source of food for certain birds of prey, snakes, and carnivorous mammals.
The International Union for Conservation of Nature lists red-shanked douc langurs as Critically Endangered (IUCN, 2015), appearing on the IUCN Red List of Threatened Species.
The population of red-shanked douc langurs has been halved in the last forty years through a combination of illegal hunting, habitat loss, and war effects. Laos has been especially impacted—the country hosts the largest group of red-shanked doucs, but conservation efforts in the area are negligible.
Hunting for subsistence and medicinal use is currently their greatest threat—their behavioral patterns make them a particularly easy target, and regulations on hunting are notoriously difficult to enforce. Between 2015–2018, Vietnam’s Bach Ma National Park Forestry Protection Department confiscated 28 pounds (13 kg) of red-shanked douc meat. Habitat loss is another major problem. Much of the doucs’ natural habitat in Vietnam has been cleared for human use in the post-war period as Vietnam’s population has risen. Notably, habitat loss and hunting form a vicious cycle for red-shanked doucs, wherein the fragmentation of langur habitats increases access by hunters to their remote forest homes.
Additionally, the Vietnam War had a detrimental impact on langur populations. Their habitats were bombed and sprayed with Agent Orange, a highly toxic defoliant; soldiers also 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. Laos, home to the largest population of red-shanked douc langurs in the world, has taken virtually no steps to regulate langur hunting and habitat destruction. Some experts have argued that conservation efforts should be focused on Laos and Vietnam, where the largest confirmed populations live.
Several organizations are working to protect and restore langur populations. The Greater Mekong Programme, developed by the World Wildlife Fund, has led efforts to monitor populations, organize ecological research, improve park management, and provide technical assistance to combat wildlife trade in collaboration with the governments of Cambodia, Laos, and Vietnam. The Douc Langur Foundation employs local people in langur habitats to eradicate snares and traps and confiscate healthy live langurs found in markets, restaurants, and private homes. Project Anoulak, the Southern Institute of Ecology, and the Endangered Primate Rescue Center all also focus on the red-shanked douc langur—the latter group runs a captive breeding program to restore the species.
Written by Eli Elster, April 2023