Delacour’s Langur – Trachypithecus delacouri – (Osgood, 1932)

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Science name: Trachypithecus delacouri – (Osgood, 1932)

Taxonomic:  Animalia>> Chordata>> Mammalia>> Primates >> Cercopithecidae >> delacouri

Species status: Endemic ; IUCN status: CR (Critically Endangered Species)

Description:

Physical Characteristics:
Delacour’s Langur has thick, coarse black fur with a distinctive white patch extending from its flanks to its thighs. It has a prominent black crest of hair on its head and a long, bushy tail that helps with balance while climbing. Females can show variation in fur color during pregnancy and lactation, where the white area on their flanks turns brownish.

Newborns have a golden-yellow coat, which darkens over time to match the adult coloration. At about four months old, juveniles transition to a black coat with white thighs. By the time they reach maturity at about three years, their appearance closely resembles that of adult langurs.

Distribution and habitat:

Altitude:
Trachypithecus delacouri is found at elevations up to 1,000 meters above sea level.

Range:
This species is endemic to north-central Vietnam, inhabiting a very restricted area of about 5,000 km². The species’ range spans the provinces of Ninh Binh, Nam Ha, Hoa Binh, and Thanh Hoa, primarily along limestone mountain ranges. Its area of occupancy (AOO) has been reduced from 400 km² before 2000 to less than 300 km² due to habitat loss and population decline.

Habitat:
Delacour’s Langur thrives in karst limestone forests, often in subtropical/tropical moist lowland and montane forests. These areas provide a variety of shelters such as caves and crevices, which are especially important for staying warm in the winter. They have been observed in primary forests as well as secondary growth in limestone areas. Their diet primarily consists of young and mature leaves, making them folivores.

Behaviour and ecology:

Social Structure:
Delacour’s Langur lives in social groups typically composed of one dominant male and multiple females, along with their offspring. The average group size is about 10 individuals, although groups of up to 17 have been recorded. Bachelor groups of 2-4 young males have also been observed. Groups may exhibit territorial behaviors and defend their home range, which can span between 20 and 50 hectares. In cases where two males are present in a group, they are often relatives, such as brothers or a father-son pair.

Feeding Habits:
This species is primarily folivorous, with around 80% of its diet consisting of leaves, especially young leaves (60%) and mature leaves (20%). They have also been known to eat seeds, flowers, and fruits. Delacour’s Langur does not consume insects. Their diet is adapted to high-protein, low-fiber vegetation, which is abundant in their limestone forest habitat.

Reproduction:
Females reach sexual maturity at about four years of age, while males mature around five years. The gestation period lasts between 180 and 196 days, and females typically give birth to a single infant. The breeding season occurs from December to August. Infants are born with golden-yellow fur, which gradually darkens as they grow.

Conservation and status:

IUCN Red List Category and Criteria:
Trachypithecus delacouri is listed as Critically Endangered under criteria A2cd; C2a(i), meaning the species has experienced a severe population decline due to habitat loss and hunting, and its remaining population is fragmented and at high risk of extinction.

Population Trend:
The population is decreasing, with an estimated 240-250 mature individuals remaining. The species is severely fragmented into 19 subpopulations, none of which exceeds 25 individuals. Van Long Nature Reserve is the only site with a relatively stable population of 164-191 individuals.

Threats:
Major threats to Delacour’s Langur include hunting for traditional medicine and meat, as well as habitat loss due to limestone quarrying, agriculture, and deforestation. These activities have reduced the species’ range and population size dramatically over recent decades.

Conservation Actions:
Delacour’s Langur is protected by law in Vietnam, listed in the Vietnam Red Data Book and included in Appendix II of CITES. Conservation efforts have focused on protecting the species in Van Long Nature Reserve, where education programs and community involvement have led to some population recovery. However, other populations continue to decline, and habitat protection, enforcement of anti-poaching laws, and habitat restoration are critical for the species’ long-term survival.