Delacour's langur: where and when to see them

Delacour's langur is a highly threatened leaf-eating monkey found only in a small part of northern Vietnam. Its black body contrasts dramatically with broad white patches around the rump and thighs, often described as white shorts. Remaining groups inhabit fragmented limestone landscapes rather than the country's general coastal forests. Hunting and habitat loss have reduced its range severely, making protection of each surviving population important to the species' future.

Size

55–62 cm head-body length

Weight

7–10 kg

Lifespan

Not reliably established

Status

Critically Endangered

Groups commonly include an adult male, several females and their young, although composition varies. They move between limestone ledges and patches of vegetation, balancing with long tails as they cross broken terrain. Feeding and resting occupy much of the day because leaves require prolonged processing. Cliffs provide sleeping refuges, and alarmed animals can retreat into difficult terrain. Infants have bright orange coats that gradually change as they mature. Communication involves a range of vocalizations, including alarm calls and contact calls between group members. Langurs are predominantly diurnal, spending their days foraging and resting, typically retreating to cliff crevices or caves at night.

• The species occurs naturally only in Vietnam.
• Newborns are orange rather than black and white.
• Its long tail is used for balance, not for grasping branches.
• A specialized stomach allows microbes to help break down leafy food.

The cooler, relatively drier months often make northern Vietnam's inland excursions more comfortable. Langurs are resident, not seasonal visitors, and visibility depends on their movements and permitted routes. Mist, rain and heat can all affect distant cliff observation. Morning hours often provide the best opportunities for spotting langurs as they emerge from sleeping sites to feed. Clear, calm weather allows for better viewing of these arboreal primates across the often distant and rugged terrain.

Steep limestone karst with remaining forest, scrub and cliff vegetation is essential habitat. Some populations occupy karst rising beside inland wetlands and agricultural land. These are specialized inland landscapes, not routine coastal wildlife stops, and access may be tightly managed. The species is highly specialized to the limestone karst, making it a critical indicator of habitat health in these unique ecosystems. Its reliance on these specific geological formations means it is often found in isolated, fragmented populations.

Leaves dominate the diet, supplemented by shoots, fruit and other plant material according to availability. A complex stomach supports microbial fermentation of fibrous food. Feeding choices reflect the patchy vegetation available on limestone hills and within surviving forest fragments. They exhibit selective feeding, often preferring young leaves which are easier to digest and contain fewer toxins. This dietary specialization underscores their vulnerability to habitat changes impacting preferred food plants.

Common name

Delacour's langur

Scientific name

Trachypithecus delacouri

Animal group

Mammals

Size

55–62 cm head-body length

Weight

7–10 kg

Lifespan

Not reliably established

Status

Critically Endangered

Identification

Its broad white rump-and-thigh patches distinguish it from other Vietnamese black langurs, including François' langur, which instead has conspicuous white cheek stripes. The extent and prominence of the white rump and thigh patches can vary slightly between individuals and age classes. These distinctive white markings provide camouflage against the pale limestone cliffs in some lighting conditions.