GRAY-SHANKED DOUC LANGUR
Geographic Distribution and Habitat
The gray-shanked douc langur is one of three species of douc langurs (the red-shanked and black-shanked are the other two) and is found only in fragmented populations of Vietnam’s central highlands, high in the forest canopy. Home range for this extremely rare monkey includes the provinces of Quang Nam, Quang Ngai, Binh Dinh, Kon Tum, and Gia Lai. Some speculation suggests that the species might also extend to the neighboring countries of Laos and Cambodia.
Size, Weight, and Lifespan
Body length in all three douc langur species is about 22 to 30 inches (56 to 76 cm). Gray-shanked douc langurs are similar in size to red-shanked langurs and slightly larger than black-shanked douc langurs; their tails are about the same length as their bodies. Tail length in black-shanked douc langurs, however, exceeds that of gray and red-shanked douc langurs by about 4 inches (10 cm).
Males are slightly larger than females, with the adults weighing about 24 lbs (10.9 kg). Adult females weigh about 18 lbs (8.2 kg).
Lifespan for captive gray-shanked douc langurs has been documented at 24 years; lifespan in the wild is not well documented, however.
The different species of douc can be distinguished by the color of their legs, or shanks.
With dark, almond-shaped eyes, a golden almost-heart-shaped hairless face framed by a forest of long, white whiskers—like that of an old man who fell asleep and forgot to shave for 100 years—tiny nostrils peeking out from a flat nose, a horizontal stick of a mouth, and a white beard adorning a sturdy white chin, gray-shanked douc langurs evoke a startling alien beauty.
A wide black band extends across their forehead, and they wear a modest, fluffy gray fur crown. Their speckled gray coat is accented by a wide orange fur collar with a black border, arms and legs are a speckled gray, and their underside is a pale shade of gray to almost white. Hands and feet are black. Their tails are nearly equal in length to their total head and body length and end in a thin tassel.
Gray-shanked douc langurs are herbivores with a particular fondness for leaves, making them folivorous. Young, tender leaves are their preference. Plant buds, fruit (especially unripened fruit), seeds, nuts, and flowers are also on their menu. They receive their water requirement through their diet.
Behavior and Lifestyle
Spending all their time exclusively in trees, gray-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 (an activity known as brachiation); 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 gray-shanked douc langur, along with the red-shanked and black-shanked douc langur, belongs to the subfamily of leaf-eating monkeys known as Colobinae.
Gray-shanked doc langurs are genetically similar to red-shanked douc langurs; however, they are considered different species due to their different biological features.
Social groups of 4 to 15 individuals are the norm. Before the species became threatened, however, groups as large as 50 individuals had been observed. Males are the dominant sex, even though the female-to-male ratio in a group is two to one.
Communication includes touch, visual signals, and vocalizations. Group grooming, for example, is not just about picking parasites from one another; this tactile communication, usually occurring before bedtime, is an important act of social bonding. Time is made for play, too, particularly with the youngsters, again, strengthening social bonds. A play face is the visual signal that a member wishes to engage in playful activities. Sparring, however—behavior that has group members slapping or aggressively grabbing one another— helps to establish social boundaries. A stare down might precede an act of sparring, but staring can also indicate curiosity. Sparring may be accompanied by growling, which indicates a threat or a warning. A grimace, accompanied by a soft “twitter” sound, indicates submission.
The courtship face has its own facial expressions and postures. With jaw thrust outward, a sideways shake of the head, and jerky movements, a member indicates his or her desire to mate with another.
Males interested in a particular female will give her “the look”—eyebrows raised and lowered several times while briefly lowering their upper eyelids. If a female is receptive to her suitor’s charm, she will return a similar expression—flirtatiously batting her eyes (to call in a suggestion of human primate behavior)—as she presents herself to the male. Flexing all four limbs and pressing her belly flat against a surface (likely a tree limb or trunk), she will raise her tail and face her backside toward her male suitor.
Females are considered sexually mature between 4 and 5 years old.
Gray-shanked douc langurs breed once a year, and this activity occurs when seasonal fruits are abundant. After a 165- to 190-day gestation period, a female gives birth to a single infant. A mother will assist in her own baby’s delivery by pulling the baby out. Newborns weigh between 1 lb (.5 kg) to 1.5 lbs (.7 kg). Most babies are born between January and August.
Mothers are the primary caregivers for their infants, carrying them around and nursing them until they become independent (weaning age has not been documented, however). To help out these new moms, other members of the group will sometimes carry the babies, giving moms a break.
Gray-shanked douc langurs disperse seeds of the fruits they eat through their feces, helping to nourish the ecosystem in which they live.
The gray-shanked douc langur is classified as Critically Endangered by the International Union for Conservation of Nature, appearing on the IUCN Red List of Threatened Species (IUCN, 2015). This highest threat level means that the species faces an “extremely high risk of extinction in the wild.”
Populations of gray-shanked douc langurs continue to decrease, and the species is listed as one of the world’s 25 most endangered primates. Less than 1,000 individuals remain in the wild.
Humans present the greatest threat to this species, through hunting, habitat destruction (for logging and agriculture), and the exotic 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.
And in 2012, three Vietnamese soldiers were thrown out of the army after they tortured and brutally killed two gray-shanked douc langur monkeys before uploading their heinous act to Facebook. The gruesome images sparked immediate worldwide outrage. Speculation is that the soldiers purchased the critically endangered primates for $57 from local wildlife smugglers. Eight more soldiers were reprimanded, and three local villagers were arrested for their role in hunting and capturing the monkeys.
The gray-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 gray-shanked douc langur the highest protection status under its Wildlife Protection Law.
Nevertheless, several conservation groups are working to save the gray-shanked douc langur from extinction and to preserve this monkey’s habitat, home to 24 primate species—25 percent of which are found nowhere else in the world.
These groups include the World Wildlife Fund, working to conserve natural ecosystems through the Greater Mekong Program.
The Frankfurt Zoological Society has conducted several studies on the species in the wild and has provided subsequent recommendations for the creation of Species Protection Areas. The society also works with the Endangered Primate Rescue Center, which operates an ongoing captive breeding program. This program incorporates an education component to raise awareness and reverence for the species.
And the main objective of the Vietnam Primate Conservation Program, a project initiated by the Frankfurt Zoological Society, is to protect the country’s langur species.
The Douc Langur Foundation is a locally based organization that takes direct action, including rescuing doucs who have been captured, disarming wire hunting snares, raiding markets and restaurants that sell the flesh of doucs, and raiding private homes where homeowners are illegally keeping langurs.
Written by Kathleen Downey, May 2017