GRAY-SHANKED DOUC LANGUR
Geographic Distribution and Habitat
The gray-shanked douc langur (Pygathrix cinerea) is endemic to the Central Highlands forests of Vietnam and possibly to a small area of Cambodia. They reside mostly in dense evergreen rainforests in the lower parts of mountains, between 3,000 to 4,300 feet (900–1,300 m) above sea level. They can also live in degraded forests.
Gray-shanked douc langurs were previously thought to be a subspecies of red-shanked douc langurs (P. nemaeus), or sometimes as a hybrid of red-shanked douc langurs and black-shanked douc langurs (P. nigripes). Currently, the scientific community believes that these three species—gray-shanked, red-shanked, and black-shanked douc langurs—are the only three that make up their genus, Pygathrix.
Size, Weight, and Lifespan
Females weigh about 18 pounds (8.2 kg) on average and are about 22 inches (56 cm) long, not including their tails which are about the same length. Males are slightly larger at 24 pounds (10.9 kg) and 23 inches (59 cm) long. Gray-shanked douc langurs can live 24 years or more in captivity. Their lifespan in the wild is not known.
Gray-shanked douc langurs are particularly striking primates. They possess long arms and legs that adapt them well to their lives in the trees. They have a bit of a potbelly as well—perhaps surprising for such an athletic animal! They are covered in gray hair over most of their bodies, and it lightens slightly on their bellies. Their bare-skin face is orange from the nose up, and white on the bottom half. They have white beards that splay out around the bottoms of their faces. Below their beard, they have a bib of orange hair on their chests. Gray-shanked douc langurs can be differentiated from the other douc langurs by their gray arms and legs, which are red and black, respectively, on their red-shanked and black-shanked cousins. Besides their slight size difference, males and females look identical.
Gray-shanked douc langurs are folivorous, meaning that their diet primarily consists of leaves. About half of their food intake is made up of young leaves, about 10% mature leaves, and the rest is composed of fruits, seeds, and flowers. They eat from at least 166 species of plant, although mulberry, beech, and myrtle trees are particular favorites. Their diet is heavily influenced by the time of year, with fruits being consumed much more often in the wet season, and young leaves being the primary source of nutrition in the dry season. Gray-shanked douc langurs don’t drink water, as they get all the hydration they need from the foods they eat.
Behavior and Lifestyle
Mostly arboreal, gray-shanked douc langurs live most of their lives in the trees, only occasionally coming to the ground. They move about by jumping and brachiating—that is, swinging from branch to branch. They sometimes hang by their arms from branches while eating leaves. Because their diet consists largely of young leaves, they need to be extremely agile in order to reach the ends of branches where the newest leaves grow.
They spend a large portion of their day—about 40% of it—resting, with about a quarter each spent on socializing and traveling. The remainder of their time, about 10%, is spent eating. In the dry season, they spend less time resting and more time moving, as they need to travel longer distances to find food.
There is evidence that gray-shanked and red-shanked douc langurs hybridize in a small area of their range. However, they are still considered distinct species because the hybridization is confined only to a small area.
“Douc” is an ancient Vietnamese word believed to mean “monkey.”
Gray-shanked douc langurs can be found in a variety of group dynamics. The most common arrangement is for one or two males to be grouped with multiple females. However, sometimes these smaller groups come together to form a large, multi-male multi-female group. Bachelor groups, composed entirely of adult males, are also found. Males have a dominance hierarchy among themselves, and males are dominant to females. Social interactions among one another are very complex, and they have been observed interacting in a variety of different ways, including playing, aggression, and grooming. Not only does grooming serve the practical purpose of parasite removal, it also helps to strengthen bonds within the group. They usually groom each other just before settling down to sleep for the night.
Gray-shanked douc langurs have extremely varied methods of communication. Visual communication includes body postures and facial expressions. This may include stares, playful expressions, and grimaces. Though grimaces look a bit like a wide smile to a human, they are used to indicate submission. Stares can communicate aggression, or simply curiosity. Body postures also include sexual displays, like a female presenting herself to a male to indicate that she is receptive to mating. Verbal communication can include growls, which serve as warnings, and twitters, which are voiced when an individual is being submissive. Tactile communication can include grooming as well as aggressive behaviors like slapping, grabbing, and pulling.
Gray-shanked douc langurs have a courtship ritual that may be initiated by either sex. An individual selects a member of the opposite sex and thrusts their jaw towards them, while shaking their head from side to side. At the same time, they raise and lower their eyebrows and slightly close their eyes. If the other individual is receptive, they perform the same movements. This back-and-forth may be repeated until the female presents herself for copulation. Around 180 days later, a single infant is born. Mothers are the primary caregivers of their young, although they are sometimes helped by other members of the social group. It is unknown when weaning or independence occurs in the offspring.
The most significant predator of gray-shanked douc langurs is humans, but natural predators exist as well and likely include birds of prey and large cats. The langurs may also help to disperse seeds from the fruits they consume.
The International Union for Conservation of Nature lists the gray-shanked douc langur as Critically Endangered (IUCN, 2015), appearing on the IUCN’s Red List of Threatened Species. Sadly, their population has dropped by more than 80% over the last 36 years—or three generations—largely due to deforestation, hunting for meat and medicine, and collection for the pet trade. In the past, their population was also negatively impacted by the Vietnam War. Their current total population is estimated at under 2,000 individuals, with specific estimates ranging from 550 to 1,700 individuals. Because these threats are not subsiding, it is believed that the population loss will continue, possibly at an even faster pace, over the next few decades without immediate and substantial conservation action.
Forests in the Central Highlands region of Vietnam are being lost at an alarming rate. Annually, almost 25,000 acres (10,000 ha) of forest are lost due to logging, conversion to agricultural fields, hydropower stations, and construction of roads. Not only is outright habitat loss a major concern but the development of roads and other infrastructure results in a more fragmented habitat as well. In addition to the threats from habitat loss and fragmentation, gray-shanked douc langurs are also hunted for food and traditional medicine. Their natural defense mechanism against predators relies primarily on freezing and hiding rather than fleeing, which unfortunately makes them rather easy targets for human hunters. They are also vulnerable to snares when they come to the ground. In addition to being hunted, they are also collected for the pet trade.
Additionally, Vietnam is often considered to be one of the most heavily impacted countries by climate change. It is threatened by more frequent and intense droughts, floods, storms, and landslides. These changes are causing untold impacts to Vietnam’s ecological systems, and will further stress highly endangered species. Species with narrow distributions, like gray-shanked douc langurs, are particularly susceptible to the effects of climate change. Models have shown that as the climate changes, gray-shanked douc langurs will move to the center of their already small range, effectively making it even smaller. Areas in the northern and western parts of their range with prime habitat now are predicted to become less suitable by 2050 and possibly unsuitable by 2070.
Gray-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. They are also federally protected under Vietnamese wildlife protection laws.
Nine subpopulations of gray-shanked douc langurs, which comprise about half of their global population, live in unprotected forests. Four subpopulations, about 600 individuals in total, live in protected forests in Kon Ka Kihn National Park, Kon Chu Rang Nature Reserve, Ngoc Linh National Park, and Song Thanh Nature Reserve. Kon Cha Rang Nature Reserve and Kon Ka Kinh National Park are particularly high priority protected areas as they contain habitat that will likely remain suitable for the species in the future as the climate changes. Unfortunately, hunting and habitat protection laws are not universally enforced. There is a captive breeding program for this species at the Endangered Primate Rescue Center in Vietnam, as well as conservation education programs offered at Kon Ka Kinh National Park that aim to bring awareness of gray-shanked douc langurs and other endangered species. Organizations like GreenViet are working to conserve unprotected langur habitat in Vietnam.
The highest priority conservation goals for gray-shanked douc langurs involve protecting the subpopulations that do not live in protected areas, conducting surveys to learn more about these subpopulations, establishing a corridor between Kon Ka Kinh National Park and Kon Chu Rang Nature Preserve to allow animals to travel between the two areas, creating monitoring programs within protected areas, and conducting education programs to further educate the public about the value of this highly endangered species.
- Long, H. T. 2020. Feeding behaviour and diet of grey-shanked douc langurs (Pygathrix cinerea) in Kon Ka Kinh National Park, Vietnam. Vietnamese Journal of Primatology 3(2): 59-83.
- Tuan, B. V., N. A. Tam, T. H. Vy, et al. 2019. Discovery of isolated populations of the ‘Critically Endangered’ grey-shanked douc langur (Pygathrix cinerea) in Quang Nam Province, Vietnam. Vietnamese Journal of Primatology 3(1): 19-25.
- Vu, T.T., Tran, D.V., Tran, H.T.P. et al. 2020. An assessment of the impact of climate change on the distribution of the grey-shanked douc Pygathrix cinerea using an ecological niche model. Primates 61: 267–275. https://doi.org/10.1007/s10329-019-00763-8
Written by K. Clare Quinlan, June 2023