Quick Facts Conservation status, Scientific classification ...

Red-shanked douc[1]
Conservation status
Critically Endangered  (IUCN 3.1)[2]
CITES Appendix I (CITES)[3]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Primates
Suborder:	Haplorhini
Infraorder:	Simiiformes
Family:	Cercopithecidae
Genus:	Pygathrix
Species:	P. nemaeus
Binomial name
Pygathrix nemaeus (Linnaeus, 1771)
Red-shanked douc range

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The red-shanked douc (Pygathrix nemaeus) is an arboreal and diurnal Old World monkey belonging to the Colobinae subfamily. They are endemic to Laos, Vietnam, and Cambodia. They are known for their bright colors and exhibit sexual dimorphism through their body size. The species has been declared critically endangered by the International Union for Conservation of Nature, with the main threats being: hunting, habitat loss and pet trade. They are one of three species in the genus Pygathrix, the other two being the black-shanked (P. nigripes) and gray-shanked (P. cinerea) doucs.

Red-shanked doucs live in fission-fusion, multilevel societies that have a mean of 18 individuals per band. They are folivorous and consume mainly Acacia pruinescens, Ficus racemosa, Millettia nigrescens, Zanthoxylum avicennae and Castanopsis ceratacantha. Their four-chambered stomachs that allow for bacterial fermentation help them with their high-fiber diet.^[4]

The red-shanked douc is native to Indochina; Vietnam, southern Laos, and possibly northeastern Cambodia, east of the Mekong river.^[5] Before 1967, the douc was completely unstudied.^{[citation needed]} It is the only douc species that inhabits all three countries of Indochina.^[6] In Laos, red-shanked doucs occur from the southern Nam Ghong Provincial Protected Area to the central-north part of the country.^[5] Laos is believed to have the largest population of red-shanked doucs, with Nakai-Nam Theun National Protected Area in central Laos having the most individuals of approximately 4,420 groups, followed by the Hin Namno National Protected Area.^[7] In Vietnam, the species lives between Nghe An and Gia Lai provinces, from 18°29'N to 14°21'N.^[6][8] The Son Tra Nature Reserve in central Vietnam holds the greatest Vietnamese population with approximately 700–1300 individuals.^[9] The Phong Nha – Kẻ Bàng National Park is also an important Vietnamese site for the species.^[6]

There was one observation of the red-shanked doucs in Cambodia by Rawson and Ross in 2008 in the Ratanakiri Province at the border of Vietnam.^[10] There was a report of a red-shanked douc specimen that was given to the Staatliches Museum by the Dresden Zoological Garden who had said that it originated in Hainan, China but the zoo records no longer exist so it remains uncertain.^[11]

Red-shanked doucs are found in evergreen, semi-evergreen and occasionally limestone forests, up to 1,600 metres (5,200 ft) in elevation.^[6] They are arboreal and spend most of their time in the forest canopy, including to sleep.^[10] They occasionally get on the ground to drink water or eat dirt that contains minerals.^{[citation needed]} According to an ecological niche model, red-shanked doucs can live between approximately 14°N to 21°N.^[12] Their home range is approximately 36 hectares (89 acres) and they have a core area of 8 hectares (20 acres), with a smaller range in the dry season of 24 hectares (59 acres) and a larger range in the wet season of 33 hectares (82 acres).^{[clarification needed][13]} There are weak correlations between precipitation, temperature, and diet and home range but not enough to draw conclusions from them.^[13]

Like other Doucs, the red-shanked douc is a long, slender monkey. The male has a head and body length of 55–82 centimetres (22–32 in) with a tail that measures 56–74 centimetres (22–29 in), and the female is between 60–63 centimetres (24–25 in) long with a tail that measures 44–60 centimetres (17–24 in) long. Males weigh 8.6–11.4 kilograms (19–25 lb), and females 6.6–10.5 kilograms (15–23 lb).^[13]

The red-shanked douc are among the most colorful primates. They are considered "Queen of primates" thanks to their distinctive and unique appearance.^{[citation needed]} They have agouti hair on their crown, temples, inner thighs, ventral coat, nape of the neck, back, triceps and lateral sides of their arms. Their crown is silver, their temples are red hair and their foreheads are black. They have white whiskers that are approximately 12 cm long for adult males. Their eyes have a high axis. The fur on their cheeks and on their throat is white. Their collar is orange with black from one shoulder to the other. Their face is a yellow-brown color and they have light blue eyelids. Their inner arms and inner, lateral and back thighs are black while their lower legs are a vibrant red. Their abdomen and back are silver yet their sacral area is white. Both feet and hands are black as well as their nipples. Their tails are white and are oftentimes equal in length to their head and body length.^[13]

The coloration gradually becomes less vibrant and having smaller red patches with more southern latitudes.^[5] In Nam Ghong Provincial Protected Area in Laos, red-shanked doucs only have small red patches around their ankles.^[13]

Although minor, the red-shanked doucs are sexually dimorphic with respect to body size but not coloration.^[13] There is a slight difference in rump markings between males and females; the male has round white spots above the triangle of white on his rump, while the female does not.^[14] Males of all ages have a white spot on both sides of the corners of the rump patch, and red and white genitals. ^{[citation needed]}

This monkey communicates using facial expressions. It has a specific "play face" with the mouth open, teeth partially bared and chin thrust forward.^{[citation needed]} Sometimes, it closes its eyes and paws blindly towards another douc without regard for the hazards of doing so when up a tree.^{[citation needed]} A fixed stare is a threat display. A grimace with the mouth open and the teeth exposed is a submissive gesture given in response to a stare and is also used to initiate grooming or play. The red-shanked douc has a low-pitched growl that is given as a threat, and a short, harsh distress squeal. During adult play, they perform an eyelid display where they blink their eyes open and closed to show their light blue eyelids.^[15]

They are a fairly peaceful species and agonistic behavior has been very rarely reported. In the San Diego Zoo, researchers observed that in the instances where there was agonistic behavior, it only lasted a few seconds and did not result in injury.^[15] Grooming lasts up to an hour and is most commonly found between adult females. In captivity, young red-shanked doucs groom and care for infants, showing signs of alloparental care.^[13]

The activity budget of wild red-shanked doucs is rest at 35.3%, movement at 28.6%, socializing at 21.7%, feeding at 13.7% and self-grooming at 0.7%.^[16]

In captivity, red-shanked doucs use brachiation for almost half of their locomotion whereas, in the wild, arm-swinging accounts for an average of 18% of locomotion. Juveniles use arm-swinging the most (34.3%), followed by subadults (21.7%), adult females (17.6%), adult females carrying infants (15.5%), and then adult males (9.8%). This showed that with increased body weight there is a decreased amount of brachiation.^[18]

When they travel by foot, their tail will usually hang down.^[19] Like all other Old World monkeys, its tail is not prehensile. It uses its tail solely for balance, and it uses its arms and legs to move through the forest along established routes.^{[citation needed]} When on the move, the group is led by adult males, with juvenile males bringing up the rear and the females and infants staying safe in the middle.^{[citation needed]} This douc is an aerial specialist, moving high up in the canopy. It is very agile and frequently makes breath-taking leaps of up to 6 meters (20 feet), leaping with its arms outstretched over its head, pushing off with its legs and landing on two feet.^{[citation needed]}

When the group is untroubled, the red-shanked douc will move noisily from branch to branch through the forest, crashing through foliage, swinging under branches and leaping with two feet together, displaying its remarkable sense of balance. But when a group is disturbed, by either a predator or other dangers, it can flee silently through the trees, away from danger. If it is startled, it may produce loud barks and rush around the trees slapping branches with its hands and feet.^{[citation needed]}

Red-shanked doucs are highly folivorous. In the Son Tra Nature Reserve found they consume 54.8% buds and young leaves, 22.6% mature leaves, 3.7% leaf petioles and 18.9% other plant parts. Per month, they found that the red-shanked doucs consumed a mean of 18 species per month and a total of 226 species consumed altogether. Out of the 226 species, there are five species that were eaten 47-82% of the time: Acacia pruinescens, Ficus racemosa, Millettia nigrescens, Zanthoxylum avicennae and Castanopsis ceratacantha. Red-shanked doucs are selective feeders and flexible eaters because of their ability to eat a wide variety of food in all seasons. Fruit is consumed mainly in the morning, which is common amongst leaf-eating monkeys as this is where they derive their energy for the day.

They have different eating patterns during the wet season and the dry season both in what they eat and in the parts of the plants that they eat, although it is not a drastic change. Figs however, are consumed all year long and make up 16-36% of their diet. It is the second most commonly consumed plant by the monkeys and they eat the fruit, leaves and flowers.^[17]

They eat peacefully together, not quarreling over food, and have been known to share their food with others. Often, they will share the same clump of foliage and may even break pieces off and hand them to each other, a type of active generosity that is rare among Old World monkeys.^[22] Like all other doucs, they do not have cheek pouches.^[23]

In 2000, the IUCN Red List of Threatened Species classified the red-shanked douc langur as endangered.^[20] In 2020, the IUCN updated their classification of the species to critically endangered, due to the population’s continual decline. It was also listed in the Vietnam Red Book in 2007. In 2019, the Vietnamese prime minister classified them as a high-risk species that needs protection, in Decree 06.^[9] The species is listed in CITES I, which prohibits commercial international trade.^[3] More than half of the species has been lost in the past 30–40 years.^{[citation needed]}

The main threat to the red-shanked douc is from hunting. Their meat is used for food, traditional medicine, and for international sale or trade.^[7] Local people often hunt the species for consumption, pets, or making glue.^{[citation needed]} Although hunting of the species is technically illegal, it is not strictly enforced and has little effect.^[5] In the Dong Ampham National Protected Area in Laos, on the border with Vietnam, local hunters have estimated that approximately fifty red-shanked doucs are killed each year.^[5] From 2015 to 2018, the Bach Ma National Park Forestry Protection department in Vietnam confiscated 13 kg of red-shanked douc meat.^[9] Their behavioral characteristics are believed to make the species particularly easy to hunt.^[6] Vietnam has the highest hunting levels of the species.^[5]

Their other main threats are pet trade, habitat fragmentation, creation of agricultural land, and military installations.^[5][8]

With Laos having the biggest population of red-shanked doucs, the country has been marked as being the most important for the species' conservation.^[5] A study conducted by Camille N. Z. Coudrat et al. stated that the best approach to conserving the monkeys is to focus on the largest populations, specifically in Laos.^[5] At present, there is no conservation effort in that country.^[7] There have been efforts to breed red-shanked doucs in captivity since the late 1960s, but they are difficult to keep in zoos due to factors such as their diet, so currently^[when?], there are only 33 individuals in captivity worldwide.^[17][20]

Habitat loss in Son Tra due to development plans poses a high risk to the monkeys.^{[citation needed]} Historically, Son Tra had a military installation, so many animals in the region were shot as practice targets.^[8] Currently, the red-shanked doucs in Son Tra Nature Reserve are protected by the army, police and forest protection departments of Da Nang and Son Tra.^[17]