The red-shanked douc (Pygathrix nemaeus) is an arboreal and diurnal Old World monkey belonging to the Colobinae subfamily.

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 folivorous and consume mainly Acacia pruinescens, Ficus racemosa, Millettia nigrescens, Zanthoxylum avicennae and Castanopsis ceratacantha.

[4] The red-shanked douc is native to Indochina; Vietnam, southern Laos, and possibly northeastern Cambodia, east of the Mekong river.

[6] In Laos, red-shanked doucs occur from the southern Nam Ghong Provincial Protected Area to the central-north part of the country.

[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.

[clarification needed][13] There are weak correlations between precipitation, temperature, and diet and home range but not enough to draw conclusions from them.

[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.

[5] In Nam Ghong Provincial Protected Area in Laos, red-shanked doucs only have small red patches around their ankles.

It has a specific "play face" with the mouth open, teeth partially bared and chin thrust forward.

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.

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.

[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%.

[citation needed] Red-shanked doucs fuse overnight and fission during mornings and early afternoons.

[10] Mating is initiated by both sexes jutting their jaw forward, raising and lowering their eyebrows, shaking their head and squinting their eyes.

Red-shanked doucs are selective feeders and flexible eaters because of their ability to eat a wide variety of food in all seasons.

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.

[23] In 2000, the IUCN Red List of Threatened Species classified the red-shanked douc langur as endangered.

[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.

[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.

[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?

[17][20] Habitat loss in Sơn Trà due to development plans poses a high risk to the monkeys.

[citation needed] Historically, Sơn Trà had a military installation, so many animals in the region were shot as practice targets.