MORPHOLOGY:
The average body mass for an adult male douc langur is around 10.9 kilograms, and for the female it is around 8.2 kilograms. The douc langur has a sacculated stomach to assist in the breakdown of cellulose. The douc langur`s hind limbs are longer than the forelimbs. The infant douc langur has a pelage coloration where the face is black with two light stripes beneath the eyes, the top of the head is reddish-black, and the back is light chestnut in color with a black line along the back. The arms and legs of the infant are chestnut-reddish-brown, and the color is brighter on the legs than on the arms. The hands and the feet of the infant are black, and the tail is whitish with a gray tip. The neck and the tail root of the infant are chestnut and the ventral side is a pale chestnut color. White round spots near the rump patch develop on males at about 8 months, and this can be used to tell males from females.
This species has three subspecies each having differing pelage colorations:
Pygathrix nemaeus nemaeus: The legs of this subspecies are maroon from the knee to the ankle, with the thighs, fingers, and toes black. The tail and the genital region of this subspecies are white. The body of this subspecies is gray with agouti hairs of black, white, and gray. The arms have a white coloration from the elbow to the wrist, with the upper portion of the arms being gray. The cheeks have long, white hair, and the two frontal bands over the eyes are dominated by red over black. The area of the face around the eyes is colored reddish yellow. The perineum of this subspecies is white, and males have a circular white spot found on either side of the white rump patch. The scrotum of the male is white. Pygathrix nemaeus nigripes: The hindlimbs of this species are black and the forelimbs and the body are gray, except for the fingers. The tail is white. The chest is a lighter gray than the rest of the body. The cheek has short, white hair, and the two frontal bands over the eyes are dominated by black over red. The area of the face around the eyes is colored black. The perineum of this subspecies is white, and males have a circular white spot found on either side of the white rump patch. The male has a blue colored scrotum.
Pygathrix nemaeus cinerea: The upper and lower legs of this subspecies are gray agouti with black feet. The chest, perineum, rump patch, and tail are white. The arms are gray with black colored fingers. This subspecies has a neck that is white except for a small band that is orange but mostly black that runs into black shoulders. The cheeks have medium to long and white hairs. The face and lips are white with orange between the eyes and on the nose. The facial skin is yellow-brown. The frontal band is black with gray agouti hair on the head.
RANGE: The douc langur is found in the countries of Cambodia, Laos, and Vietnam. This species was once thought found in Hainan, China, but new evidence suggests that perhaps it does not occur on the island. In Vietnam the douc langur is found from Tay Ninh province to Nghe An province. Red-shanked douc langurs (Pygathrix nemaeus nemaeus) are found in Bach Ma National Park, and black-shanked douc langurs (Pygathrix nemaeus nigripes) are found in Nam Bai Cat Tien National Park in Vietnam. Both the red and black-shanked douc langurs are found in Kong Cha Rang, Kon Khi Kinh, and Mom Ray Nature Reserves. On the Hon Nga-Cong Troi-Bi Doup Massif, Vietnam the douc langur occurs primarily below 1500 meters.
In Laos, this species ranges to the eastern border of Vietnam, south to the Cambodian border, north to the Nam Chat catchment, and west to the Mekong River. This species lives in primary and secondary rainforests and gallery forests. In Vietnam, the douc langur is found in the mid to upper levels of the canopy. In Laos the douc langur lives in evergreen and semi-evergreen broadleaf forests.
Black-shanked douc langurs in Cambodia were found to live in closed-canopy forested hills and riverine forests in the extensive dry dipterocarp forest.
This species has three subspecies each having differing ranges:
Pygathrix nemaeus nemaeus: This subspecies is found in north and central Vietnam. This subspecies also occurs in Laos.
Pygathrix nemaeus nigripes: This subspecies is found in central and southern Vietnam. This subspecies also occurs in Cambodia.
Pygathrix nemaeus cinerea: This subspecies occurs in the central highlands of Vietnam.
ECOLOGY:
The douc langur is a folivorous species, but it also consumes fruit, buds, flowers, and bamboo shoots. The diet of the douc langur is composed of 82% leaves and petioles, 14% fruits (unripe and seeds), and 4% flowers. The douc langur species consumes leaves that contain high fibroid matter. Leaves consumed also are predominately small, young, and tender. The douc langur prefers to eat fruit that is unripe and also fruit from the fig tree (Ficus). This species does not drink water rather it derives water from the food it eats. The douc langur tends to show a hand preference when feeding, but this differs for each individual, some favoring the right hand, some using the left hand. Food sharing has been observed to occur between individuals. The douc langur is an arboreal and diurnal species. Their group sizes range from 4-5 individuals near areas of heavy human population (Homo sapiens), and 20-25 individual near areas of low human population.
Humans are the major predator of the douc langur. Douc langurs are killed by humans for food and for target practice. In areas of Vietnam that defoliants were used in times of war, the birth rate of this and other endemic animal species has gone down.
LOCOMOTION: The douc langur moves through the forest quadrupedally. Groups move through the forest canopy along established routes. Movement of the group is led by the adult male(s) with females and infants in the center and juvenile males bringing up the rear. Adult males will sometimes brachiate back and forth when threatening a disturbance to the group. Jumping is common by all individuals of the group except for infants. Jumps start like a dive with the arms over the head and legs propelling the individual. When jumping individuals will land feet first.
SOCIAL BEHAVIOR: The social system of the douc langur varies between a unimale and a multimale-multifemale system depending upon the location. Single individuals of both sexes are seen in the forest. In groups there is usually a ratio of two females to one male. Females have a higher tendency to groom males in multimale groups than in unimale groups. A dominance hierarchy was found to exist amongst group members in captivity. In captivity aggressive interactions were found to be rare, much like other colobine monkeys. Females and males disperse from the group. Food sharing has been observed by group members where one individual will break off part of a branch with leaves and give it to another group member.
Immature group members tend to play more than adults. Social play consists of running, climbing, jumping from place to place, jumping up and down in one place, hanging, and swinging from overhead supports. Contact between individuals during play consists of touching, pulling, mouthing, wrestling, and chasing. Adult social play is usually accompanied by playface, with individuals grimacing during playface. Social play tends to occur after eating and before resting. The most popular times for play are late mornings, early afternoons, and just before resting at night.
VOCAL COMMUNICATION:
growl: This call is a low-pitched, low-intensity, guttural-type vocalization. The duration of this call is typically one second. This call may be uttered singly or in series of two or three followed by a pause, then a repeat of the series. This call can occur during feeding or during the stare display. When emitted during stare, this call serves to communicate threat. This call was found to be only emitted by adults. This call might be the "threat-warning bark" described by Lippold.
twitter: This call encompasses a range of faint, difficult to localize sounds. The softest form of this call consists of a faint, slightly squeaky, bird-like twittering. This call sounds like the "maiow" of a cat, Felis sp., at high intensities. This call is often accompanied by grimace. This call occurs in a response to stare, during sparring, and preceding social grooming. This is a submissive signal, allowing an individual to approach another without getting a hostile response.
OLFACTORY COMMUNICATION:
VISUAL COMMUNICATION: stare: This is when an individual will focus a fixed stare with fully-opened eyes on another individual. The eyebrows are raised, the scalp drawn back slightly, and sometimes, the jaw thrust forward when performing this pattern. The thrusting of the jaw consists of a single forward thrust followed by a relaxed retraction, but this may be repeated several times during the course of the display. This behavior tends to occur with an external disturbance of the group. This is also associated with growling, twittering, grimacing, or sparring within the group. The receiver of this display will respond with avoiding the sender or grimacing and twittering.
grimace: This is when an individual will hold the eyes and mouth open, with having the lips drawn back to reveal the teeth. This display is directed at another individual in response to stare, during sparring, preceding social grooming, and during social play. This is a submissive signal made during an agonistic encounter and as a distance-reducing mechanism during social grooming and play. During social grooming this behavior is performed by the individual who is approaching. When this behavior pattern occurs during play, a playface always accompanies it.
playface: This is when an individual close the eyelids exposing the very pale blue of the lids. This behavior is performed by adults during social play. Grimace can occur with this display. This behavior is sometimes maintained when moving towards a potential play partner.
sexual invitation display: This is where the jaw is thrust forward and the head is shaken sideways with small, jerky movements. Also during this display the eyebrows are raised and lowered several times and the upper eyelids are momentarily lowered. This display is directed at a member of the opposite sex, with the same display given as a response. Copulation occurs after the performance of this display, with the display being maintained while the female is presenting and during the act of copulation.
presenting: This is where the female will flex all four limbs and press the ventrum against the substrate. The head is kept raised and the base of the tail is raised slightly with the rest of it hanging down during this display. The perineum is oriented towards a male. This display serves to communicate the willingness to copulate on the part of the female.
TACTILE COMMUNICATION:
social grooming: This is when one individual grooms another and is used to reinforce the bonds between individuals. Parasites, dead skin, and other foreign materials are removed by either or both hand and mouth. On infants the areas that receive the most attention are the anogenital region, the face, and the ears. On adults the areas that receive the most grooming attention are the head, neck, face, and arms. This behavior is common amongst adult females, and juvenile females spend a large amount of time grooming adult females, infants, and peers, but never adult males. Most grooming occurs before rest periods.
sparring: This includes slapping, grabbing, or pulling of the fur of a conspecific. This behavior could just be a single slap. This can involve two to four participants. This pattern serves to communicate agonistic behavior.
REPRODUCTION:
The douc langur gives birth to a single offspring. During estrus the perineum swells and reddens and this condition persists throughout a pregnancy. The menstrual cycle for this species is 28-30 days. In captivity the mean interbirth interval was found to be 22 months and the gestation period to be between 180 and 190 days. Most births in captivity were found to occur between January and August, ahead of the fruiting season. In captivity it was found that females show a food preference for leaves when pregnant. Infant transfer between females has been observed in captivity. Infants are carried ventrally by their mother as well as other group members.
Sex begins with the sexual invitation display, where the jaw is thrust forward and the head is shaken sideways with small, jerky movements. Also during this display the eyebrows are raised and lowered several times and the upper eyelids are momentarily lowered. This display is directed at a member of the opposite sex, with the same display given as a response. Copulation occurs after the performance of this display, with the display being maintained while the female is presenting and during the act of copulation. It has been observed that the females always solicited copulations. Every copulation sequence is preceded by presenting, but not every display of presenting leads to copulation. Females will remain in the presenting posture during copulation. The male will mount the female by placing the hands on the female`s hips and leaning over so that the ventral surface (chest) is in contact with the female`s dorsal surface (back). The male`s feet are firmly placed on the substrate when mounting. The inside of the male`s hindlimbs are in contact with the outside of the female`s hindlimbs in the mounting position. The male will thrust 1-30 times at a rate of one to two thrusts per second. When thrusting is finished, the male will sit up behind the female with the hands resting on the female`s back. Copulation is generally single mount for the douc langur although double mount sequences have been observed. Social grooming often follows a copulation sequence. Juvenile males have been observed in captivity to attempt copulations with varying degrees of success. Copulatory behavior for the douc langur occurs from the day before until three days after the estrus peak of the female. Copulations still will occur when the female is pregnant.
When a female is ready to give birth, the female will become restless and touch the vaginal area frequently and alternate between stretching and squatting on the substrate. The female will grasp the infant as it emerges and pull it towards the ventrum. When the arms of the infant are freed, they will grab hold of the female`s fur, aiding in their own delivery. Females will lick their newborns after birth and inspect the face, ears, and genitals. Newborns are born with eyes wide open. In a captive observation of giving birth, the female was found not to eat the placenta after it was discharged from the body. When infants suckle they do not have any preference of their mother`s nipple, but they will change from one nipple to another. When the infant sleeps, it is held upright by the mother and sometimes the infant will hold a nipple in its mouth when it sleeps.
