Douc is Vietnamese for "monkey"
The doucs or douc langurs make up the genus Pygathrix, which consists of these 3 species:
Red-shanked Douc, Pygathrix nemaeus
Black-shanked Douc, Pygathrix nigripes
Gray-shanked Douc, Pygathrix cinerea
These colobine Old World monkeys, native to Southeast Asia, have an extremely striking appearance. The Red-shanked Douc characteristically has bright maroon legs and reddish patches around the eyes. In contrast, the Grey-shanked Douc is less vibrant, with speckled grey legs and orange markings on the face. Both have dappled grey bodies, black hands and feet and white cheeks, although the cheek hairs of the Red-shanked Douc are much longer. The Black-shanked Douc has black legs. Their long hind limbs and tail allow these monkeys to be wonderfully agile in their treetop habitat.
Even though they are known as "douc langurs", they are in fact more closely related to the Proboscis Monkey and snub-nosed monkeys, than to any of the langurs. They are part of the Colobinae subfamily of the Cercopithecidae family.
All the species have a white tail, but P. cinerea and P. nemaeus have a tassel at the end, while the P. nigripes tail is longer with a nearly absent tassel. Male P. nemaeus have a pink penis and a white scrotum as do P. cinerea, while P. nigripes have a blue scrotum and red penis (Nadler et al. 2003). In P. nemaeus, both sexes have a triangle of white pelage around the base of the tail above which males, but not females, have round white spots. This feature can be used to determine the sex of individuals.
Wild douc langurs spend a majority of their time arboreally, moving through quadrupedal and brachiation locomotion; traveling single-file through established pathways. P. nemaeus are not often seen on the ground, however wild P. nigripes have been seen on the ground and may spend up to 20% of their day terrestrially. P. nemaeus in captivity primarily move through their environment through brachiation (46%) and quadrupedal walking and running. Wild P. nigripes move quadrupedally (61%), through leaping (17%), by brachiating (10%), climbing (8%) and dropping (4%) (Rawson 2006). Horizontal jumps in wild P. nemaeus are also seen, with individuals landing feet first.
In general, douc langurs of all species are found in eastern Indochina, east of the Mekong River; found in Vietnam (P. cinerea, P. nemaeus, P. nigripes), Laos (P. nemaeus), and Cambodia (P. nigripes) (Timmins & Duckworth 1999; review in Nadler et al. 2003). Roughly, from the north to south, the species of Pygathrix are arranged parapatrically starting with the P. nemaeus, then P. cinerea, and with P. nigripes at the southern end of the generic distribution (Nadler et al. 2003). However, the exact boundaries between all species are unclear and also confounded by the presence of possible hybrid forms and often large gaps in confirmed populations (Nadler et al. 2003). P. nemaeus are the only douc langurs found in Laos, and are found as far north as the center of the country. They range through the central and southern reaches of the country east into Vietnam and south to the Cambodian border (Timmins & Duckworth 1999; Nadler et al. 2003). In Vietnam, the northern limit of P. nemaeus is confirmed as far north as the Pu Mat National Park and south to the Kon Ka Kinh Nature Reserve, but its limits are unclear (Timmins & Duckworth 1999; Nadler et al. 2003). P. nigripes occurs as far north as the Kon Ka Kinh Nature reserve and as far south as the Cat Tien National park. P. cinerea occurs in Vietnam between the distributions other two species, and is present or probably present in the Quang Nam, Gia Lai, Quang Ngai, Binh Dinh, and Kon Tum Provinces (Nadler et al. 2003; Long 2004). The only species that occurs in Cambodia is P. nigripes, with confirmed sightings in the Ratanakiri province and the Mondulkiri Province (reviewed in Nadler et al. 2003).
Both P. nemaeus and P. nigripes occur sympatrically at the Kon Cha Rang Nature Reserve in the Gia Lai Province, Vietnam (Lippold 1998). Douc langurs can live sympatrically with a number of other non-human primates as well. For example, at the Cat Tien National Park in southeastern Vietnam, P. nigripes, is found with pygmy loris (Nycticebus pygmaeus), macaques (Macaca mulatta, M. fascicularis, M. arctoides), silvered langurs (Trachypithecus germaini), and yellow-cheeked crested gibbons (Nomascus gabriellae) (Polet et al. 2004).
It is estimated that there are only 600-700 P. cinerea remaining (Mittermeier et al. 2007; but see also Ha 2004).
Douc langurs are only found in forest habitats. These include old-growth and secondary broadleaf evergreen forest, montane rainforest, wet/dry forests, tropical and semi-tropical evergreen rainforest, submontane and montane evergreen forest, secondary moist forest, monsoon forests, valley forests, sclerophyll evergreen forest, semi-evergreen forest, seasonal lowland forests, and mixed semi-evergreen, mixed humid evergreen forest, and mixed deciduous forest (Lippold 1995; 1998; 1999; Timmins & Duckworth 1999; Lippold & Vu 2002; Ha 2007; Hoang et al. 2009). Douc langurs may also be able to survive in more heavily disturbed forest habitats as well (Ha Thang Long pers comm. cited in Nadler et al. 2003). There are reports of P. nigripes as well as P. nemaeus as high as 1500 meters (4921.3 feet) above sea level and as low as sea level (Eames & Robson 1993; Timmins & Duckworth 1999; Nadler et al. 2003; Ha 2007). Reports at very low altitudes are rare, however, this is nearly meaningless as much suitable habitat at lower altitudes has been cleared and douc langur rarity may be an artifact of extensive human land use and forest clearance (Timmins & Duckworth 1999).
At Phuoc Binh, a douc langur study site in south Vietnam, the average rainfall is over 200 cm (78.7 in), with average highs at 38.8°C (101.8 °F) and lows at 14.2°C (57.6 °F) (Hoang et al. 2009). Across Vietnam (a habitat of all three Pygathrix species), average temperatures range from 27°C (80.6 °F) in south Vietnam grading to an average of 21°C (69.8 °F) in the north of the country. Mountainous areas typically receive more rainfall than in the rest of the country and there are three yearly monsoon seasons (Lippold 1998).
Douc langurs are herbivorous and predominately folivorous (Nadler et al. 2003). In one study in south Vietnam, P. nigripes consumed a range of 152 species of plant, with leaves (especially young leaves) predominating in all seasons, and a lesser reliance on fruit and flowers. At this study site on a year-round basis, P. nigripes consumed leaves (54.6%), fruits (19.8%), seeds (9.6%), flowers (14.6%), and other foods (1.5%). Food consumption changed somewhat between the wet and dry seasons, with more fruit eaten in the wet season than in the dry, and correspondingly fewer flowers and leaves in the wet season than in the dry season. The species also drinks water while on the ground. P. nemaeus mostly eat leaves (especially newly grown), but also eat buds, flowers and fruit. Based on feeding time, P. nemaeus eat leaves (82%), fruit and seeds (14%), and flowers (4%).
Wild P. nigripes spend their days on average resting (62%), feeding (27%), traveling (6%), engaged in social behavior (3%) and in other activities (2%). There are peaks in activity, including feeding and traveling early and late in the day. Social behaviors include grooming, inter-group aggression, copulation and allomothering.
In captivity, P. nemaeus spend their day resting and sleeping (54%) and feeding (23%). In the wild, most of the P. nemaeus day is spent moving between food sources and eating, with time also spent sleeping, grooming, or playing.
The home range of P. nemaeus is estimated at 1.5-3.5 km² (0.6-1.4 mi²). More than one species of douc langur may live sympatrically, as is the case at Kong Cha Rang, Vietnam, where P. nemaeus and P. nigripes are both found.