The Delacour langur (Trachypithecus delacouri) is a species of Old World monkey that is endemic to a narrow range in north-central Vietnam and is listed as critically endangered on the IUCN Red List.
The Delacour langur belongs to the genus Trachypithecus and was for many years considered a subspecies of Trachypithecus francoisi.
Morphological Features
The Delacour langur is a primate species that is slightly larger than its morphologically close relatives. Its body fur is largely black, and its distinguishing feature is the white hairs that extend from the hip region to the outer thighs. Its face has white whiskers extending from its cheeks, and its head has a crest of erect feathers that are narrower and longer than those of other related species.
This species exhibits sexual dimorphism; males (7.5–10.5 kg) are slightly heavier than females (6.2–9.2 kg); the head-body length of both genus ranges from approximately 57 to 62 cm, and the tail length ranges from 82 to 90 cm. The tail is thick and densely furred compared to other species. Females also have a pale patch of fur or a patch of white hairs in the pubic area.
Unlike their parents, cubs are born with bright orange fur, which disappears after about four months and begins to develop into the adult black-and-white pattern around one year of age. Both genus have thickened layers of skin called ischial calluses (sit pads) covering their hip bones.
Geographic Distribution and Habitat
This species is an endemic primate to Vietnam and is distributed within a very limited area in north-central Vietnam. Its habitat is closely associated with the limestone mountain ranges of Ninh Binh, Nam Ha, Hoa Binh, and Thanh Hoa provinces. Delacour's langur prefers limestone (karst) forest habitats, primarily in the lowland areas. This habitat typically consists of broadleaf evergreen forests, but it can also occasionally be seen in secondary forest areas. Karst regions are important for the species because they provide warm shelter during the cold winter months, thanks to their caves and rock crevices.
Reproduction
These primates typically live in unimal-multifemale groups, and reproduction occurs within this social structure. Females typically reach sexual maturity at four years of age, while males mature at around five; however, females may delay mating until around six years of age to fully prepare for the physical and mental responsibilities of motherhood. The dominant male typically mates with females in the group during the mating season, which typically occurs between January and June. Gestation lasts between 170 and 200 days (approximately 6 to 7 months), and the female typically gives birth to a single offspring.
Diet
The Delacour langur is a primate whose diet is highly folivorous. Its diet consists of approximately 80% leaves, with young leaves being preferred, as they are higher in protein and lower in fiber. Their digestive system is specially developed for this diet (multi-chambered stomach). A small portion of the remaining food consists of unripe fruit, flowers, and shoots, depending on the season.
Population and Ecology
The Delacour langur is a diurnal primate. Their social structure is typically one-male, multi-female groups, with an average of ten individuals per group. Home ranges may overlap with other groups, and aggressive interactions between groups are occasionally observed.
Its population is extremely low and is declining. It is estimated that over 80% of its population has declined over the last thirty-six years (three generations). According to 2015 data, the total number of mature individuals is thought to be less than 250. The majority of the surviving population is found in the Van Long Nature Reserve, which plays a role in the species' conservation.
Threats and Conservation Efforts
The species' survival is threatened by increased hunting for traditional "medicine." This hunting pressure has led to the decline and fragmentation of many surviving populations. Another threat is habitat fragmentation and destruction; even in the protected Van Long range, limestone quarrying for cement production is disrupting the animals' natural movements.
Listed internationally on CITES Appendix II, the species is also under the highest protection level in Vietnam. The Van Long Nature Reserve was established in 2001 to protect the species. Conservation efforts are aimed at effectively protecting all existing populations and expanding the Van Long Nature Reserve to ensure the species' long-term future. Programs to reintroduce captive-bred individuals into the wild have also been implemented.
