BLACK-SHANKED DOUC LANGUR
Geographic Distribution and Habitat
The black-shanked douc langur is one of three species of douc langurs (the red-shanked and the gray-shanked are the other two) and is found only in eastern Cambodia and southwestern Vietnam, residing in primary and secondary monsoon forests and rainforests, from medium to high altitudes.
Cambodia’s Mondulkiri province is home to the largest population of these endangered monkeys, with an estimated 42,000 individuals living in the Seima Biodiversity Conservation Area. Additional populations live throughout the Phnom Prich Wildlife Sanctuary and in the Mondulkiri Protected Forest.
By contrast, Vietnam hosts only fragmented populations of the species, with the largest population of black-shanked douc langurs estimated at 500 to 700 individuals.
Size, Weight, and Lifespan
Head-to-body length for black-shanked-douc langurs is 21 to 25 in (55 to 63 cm). Their tail is the longest of the douc species, adding another 26 to 33 in (66 to 84 cm).
Males are a bit larger than females, weighing about 24 lb (11 kg); females weigh about 17 lb (8 kg).
Black-shanked doucs are reported to live up to 30 years.
What Does It Mean?
Incapable of grasping (opposite of prehensile: capable of grasping).
Visit the Glossary for more definitions
The different species of douc langurs can be distinguished by the color of their legs, or shanks.
As with the red-shanked and gray-shanked douc langurs, Nature has given the black-shanked douc langur a striking appearance and an almost alien beauty. Dark, almond-shaped eyes and a hairless heart-shaped face are characteristic of doucs. But instead of a golden-colored face—like that of red-shanked and gray-shanked doucs—Nature used a different brush to color the face of black-shanked douc langurs, painting it blue-gray and drawing yellow rings around the monkey’s eyes. Long, white whiskers frame the face and tickle the chin. The monkey inhales the scents of the forest through tiny nostrils that peek out from a flat muzzle. Hands and feet are black.
A wide, dark band of fur extends across the forehead and reaches downward to the shoulders before fading to gray across the back and forelimbs, palest on the monkey’s underside. Legs (shanks) are black. A white triangle of fur marks the base of the monkey’s long, tasseled tail, which is also white. Males can be identified from females by a white circle that dots either side of their rump—and by their blue scrotum and bright pink penis.
Like all doucs, black-shanked douc langurs are herbivores with a fondness for leaves (which also makes them folivorous). Young, tender leaves are their preference; however, depending on the season, they will also eat shoots, buds, seeds, flowers, and unripened fruit. (Ripened fruit gives the monkeys a tummy ache.) A multi-chambered stomach uses bacteria to break down the cellulose in the leaves through the biological process known as fermentation. These monkeys receive their water requirement through their diet, but they are also known to lick the morning dew from leaves.
Behavior and Lifestyle
Active during daylight hours, black-shanked douc langurs (like all langurs) are diurnal. They spend most of their time in the forest canopy (making them arboreal). Unlike red-shanked and gray-shanked douc langurs, however, black-shanked douc langurs have been reported to descend to the ground on infrequent occasions.
Like other douc langurs, black-shanked douc langurs jump from branch to branch, pushing off with their legs, and landing feet first on the next branch. Or they propel themselves forward, swinging from branch to branch by their elongated arms (known as brachiation). They use their long, nonprehensile tails for balance.
Daily Life and Group Dynamics
Black-shanked douc langurs live in multimale/multifemale groups, with females outnumbering the males. 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 are more typical. Group size can also fluctuate when members disperse for a specific purpose, such as foraging, and then regather at the end of day (this leaving-and-coming-together phenomenon is known as fission-fusion society).
Black-shanked douc langurs are extremely social primates. Individuals play together, travel together, and groom one another.
Social partners of the same approximate age engage in daily play. As expected, play is especially popular with the young. During their first few months of life, young langurs spend their playtime hopping, running, jumping, and climbing.
If a foraging group should encounter another group in its travels (black-shanked douc langur home ranges overlap), opposing males threaten one another by slapping their hands against their thighs.
Social grooming sessions (known as allogrooming) can last up to an hour and typically occur before the monkeys’ afternoon nap or bedtime. Come nightfall, they sleep in carefully selected large trees that provide a thick, protective canopy. Mothers and infants sleep together.
Douc is an ancient Vietnamese word thought to mean monkey.
The black-shanked douc langur, along with the red-shanked and gray-shanked douc langur, belongs to the subfamily of Old World leaf-eating monkeys known as Colobinae.
Previously classified as a subspecies of the genetically similar red-shanked douc langur, only recently has the black-shanked douc langur received due recognition, and respect, as a distinct langur species.
These leaf-eating monkeys don’t typically engage in much conversation. They allow their facial expressions and postures to convey their mood or intent. To initiate play, for example, black-shanked douc langurs throw back their head and slightly open their mouth. To warn a potential foe to keep away, a male will glare intently at his subject, while thrusting his head and shoulders back in an intimidating posture. And to express her romantic interest in a male partner, an adult female will stare at him intently, with her mouth closed and chin jutted out. Moving her head gently from side to side, she holds her gaze while approaching the male and crouches beside him. If the male is receptive to the female’s overtures, he will return her love-struck gaze and the couple will engage in copulation.
Black-shanked douc langurs will break their silence, however, if they perceive a threat, emitting loud alarm calls, or barks, to alert others in the group. (An unfortunate side effect of their fright can induce “panic diarrhea.”)
The time spent allogrooming is an important tactile activity that establishes strong social bonds not only between mothers and their infants, but between all members of a group.
Reproduction and Family
Black-shanked douc langurs have no defined breeding season. Females give birth to a single infant every one to three years, after a gestation period of 180 to 190 days. During her pregnancy, a mom-to-be will keep calm and quiet, scaling back on her social activity.
Mothers are the primary caregivers of their infants; however, others in the group also help with infant care—known as alloparenting—so that new moms have some time to themselves, to rest and eat unencumbered by a baby on their lap. Alloparenting is also important in helping to integrate the young into the group. Occasionally, adult females in a group behave aggressively toward one another.
Juvenile males may leave their birth groups, traveling in nonbreeding bachelor groups, before creating or finding a new group to join.
Black-shanked douc langurs disperse seeds of the fruits they eat through their feces, helping to nourish the ecosystem in which they live.
Conservation Status and Threats
The black-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. Their primary threats include hunting for traditional folkloric “medicine” and bushmeat consumption, as well as forest habitat loss and fragmentation due to legal and illegal logging, conversion for agriculture, and construction of roads and hydroelectric dams.
This species is undergoing a very rapid decline. Scientists estimate a population decline of more than 80% over the last 3 generations (36 years). This decline is predicted to continue at the same rate or slightly higher in the next 3 generations.
Humans present the greatest threat to this species. These monkeys are hunted for their flesh and also for their body parts, which are used in folkloric medicines. Habitat loss due to human encroachment and the exotic pet trade also endanger the species’ survival.
Vietnam’s population of black-shanked douc langurs (along with red-shanked and gray-shanked douc langurs) suffered a decline resulting from the Vietnam War. 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.
As populations of black-shanked douc langurs become increasingly fragmented, the monkeys are forced to engage in inbreeding, resulting in a lineage that is less robust and less genetically viable.
Black-shanked douc langurs are 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.
The Endangered Primate Resource Center (EPRC) rescues and rehabilitates doucs, along with other endangered and critically endangered primates, in Vietnam.
Other conservation organizations dedicated to saving the langurs include the Douc Langur Foundation and the Vietnam Primate Conservation Program.
Although black-shanked douc langurs are difficult to keep in captivity, captive black-shanked douc langur breeding programs at the San Diego and Cologne Zoo have proven successful.
Many thanks to Hoang Minh Duc, PhD, Specialist in Natural and Rural Systems Management Southern Institute of Ecology (SIE), Ho Chi Minh City, Vietnam, for providing and allowing us to use his beautiful photos of the black-shanked douc langur.
Written by Kathleen Downey, June 2017. Conservation status updated Jul 2020.