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.
Geographic range and habitat
The red-shanked douc is native to Indochina; Vietnam, southern Laos, and possibly northeastern Cambodia, east of the Mekong river. In Laos, red-shanked doucs occur from the southern Nam Ghong Provincial Protected Area to the central-north part of the country. 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. In Vietnam, the species lives between Nghệ An and Gia Lai provinces, from 18°29'N to 14°21'N. The Sơn Trà Nature Reserve on Sơn Trà Mountain in central Vietnam holds the greatest Vietnamese population with approximately 700–1300 individuals. The Phong Nha – Kẻ Bàng National Park is also an important Vietnamese site for the species. 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.
Red-shanked doucs are found in evergreen, semi-evergreen and occasionally limestone forests, up to in elevation. Their home range is approximately and they have a core area of , with a smaller range in the dry season of and a larger range in the wet season of . There are weak correlations between precipitation, temperature, and diet and home range but not enough to draw conclusions from them. Males of all ages have a white spot on both sides of the corners of the rump patch, and red and white genitals.
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Red-shanked douc langur (Pygathrix nemaeus) male Son Tra.jpg|Male
Red-shanked douc langur (Pygathrix nemaeus) female Son Tra.jpg|Female
Red-shanked douc langur (Pygathrix nemaeus) juvenile Son Tra.jpg|Juvenile
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Behavior
This monkey communicates using facial expressions. It has a specific "play face" with the mouth open, teeth partially bared and chin thrust forward. Sometimes, it closes its eyes and paws blindly towards another douc without regard for the hazards of doing so when up a tree. 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.
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.
Group composition
thumb|Group of red-shanked doucs
Red-shanked doucs live in multilevel, fission-fusion societies in one-male/multi-female or multi-male/multi-female groups with a male-to-female ratio of 1.0:1.63 and an adult-to-young ratio of 1.1:1.0. The bands contain a mean of 18 individuals in a mean of 2.7 units per band and a mean of 6.5 individuals per unit. Both males and females have their own hierarchies and males are dominant to females. Both males and females will eventually leave the group they were born into.
Red-shanked doucs fuse overnight and fission during mornings and early afternoons.
When they travel by foot, their tail will usually hang down. 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. 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. 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.
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.
Mating and development
Mating
thumb|hybrid with [[Rhesus macaque (Macaca mulatta)]]
In captivity, female red-shanked doucs reach sexual maturity at four years old and males at four years and eight months.
Births occur year-round but peak between August and October and again between February and April. The gestation period lasts between 165 and 210 days, resulting in the birth of a single offspring or very rarely, twins. Like all other doucs, they do not have cheek pouches.
Conservation
In 2000, the IUCN Red List of Threatened Species classified the red-shanked douc langur as endangered.