HATINH LANGUR

Trachypithecus hatinhensis

Geographic Distribution and Habitat
The Hatinh langur is endemic to Vietnam—a Southeast Asian country about the same size as New Mexico—and to the People’s Democratic Republic of Laos. Although Hatinh langurs are not actually gibbons, locals often refer to them as long-tailed or black gibbons.

These elusive creatures inhabit the dense Annamite mountain range limestone forests, and sightings have been reported on the north central coast of the country in the Quang Binh Province. The largest population is thought to reside in that region, in the Phong Nha–Ke Bang National Park, which is inscribed on the UNESCO World Heritage List. In 2005, another population was identified in the rural district of Huong Hoa in the Quang Tri Province near the border with Laos. 

Climate in the region consists of two seasons. The dry season starts in April and lasts through the month of August. Temperatures average 99 degrees F (37 C) but can reach 104 degrees F (40 C) in July and August. The rainy season spans the months of September through March and is marked by sudden storms that often cause landslides between September and November.

The landscape is rugged, unique, and dramatically beautiful with sharp peaks that can reach altitudes of 7,000 ft (2,100 m) and steep slopes descending into valleys that are covered in dense broadleaf forests. The soil is slightly alkaline, rich in calcium carbonate and magnesium. It is thin and porous with many sinkholes and large caves. In fact, there are more than 400 caves in Quang Binh Province alone.

Hatinh langur range, IUCN 2020

Size, Weight, and Lifespan
Hatinh langurs are quite large and weigh on average between 13 and 17 pounds (6–8 kg), with males being a bit heavier and sometimes weighing as much as 19 pounds (9 kg).

Males’ head-to-body length averages 22–23 inches (56–59 cm) long, whereas females are a bit shorter with an average length of 21–22 inches (54–57 cm). Both males and females have a long tail that measures an additional 30–35 inches (78–90 cm).

Appearance
These elegant langurs are long, thin, and muscular with a lustrous black pelage covering their entire body and tail. The band of white fur that grows out of their cheeks looks like a delicate stroke of paint, giving them a very distinguished appearance. It extends above and behind their round ears onto the nape of their neck. Their soft oval face is topped by a spiky tuft. Their eyes are brown and their nostrils are slanted downward. They have five digits on their hands and feet allowing them to be quite dexterous.

What Does It Mean?

Limestone:
Hard sedimentary rock that is mainly composed of calcium carbonate and is often used in construction.

UNESCO World Heritage Sites:
Landmarks or areas legally protected by an international convention administered by the United Nations Educational, Scientific and Cultural Organization. These sites are considered of outstanding cultural and natural value for the world.

Visit the Glossary for more definitions

Diet
The diet of Hatinh langurs is mostly composed of foliage, but they also consume fruit. They sit in the trees, plucking leaves with their hands one by one, and they chew on them for a long time—thereby breaking the leaves into small pieces before swallowing. The leaves are further decomposed by microbes in the gut to extract the nutrients these primates need. Thorough chewing is thought to make the digestion process easier. This behavior is different than that of other leaf monkeys who don’t chew as much and rely exclusively on their digestive tract to break down food.

Behavior and Lifestyle
Hatinh langurs are diurnal and arboreal. Since they dwell in dense forests and rarely come out in the open, they can be difficult to observe in the wild, but scientists report that they seem to prefer cliffs facing west or southwest—perhaps because these are warmer than other cliffs. The langurs establish their sleeping sites in small limestone caves and holes, where they are sheltered from rain, cold, and predators. Unlike other species, they tend to use the same sleeping areas for many years. This is evidenced by the presence of urine and feces stains left at the entrance of the caves by the langurs when they relieve themselves at night. They do not sleep in groups; rather, each adult retires in its own cave or crevice for the night. It is rare for two individuals to share their sleeping space, unless they are mother and infant.

Hatinh langurs prefer walking to suspensory locomotion, although they do opt for the latter means of locomotion when they need to travel long distances, facilitated by swinging from branch to branch. When climbing trees, they pull their body up with their arms and when descending, they do so head first. Youngsters spend more time suspended from one or two arms than adults do.

Fun Facts

​Limestone or karst formations found in the Phong Nha-Ke Bang National Forest are the oldest in Asia and were formed 400 million years ago. These formations led to the creation of underground rivers and many caves—some of which are dry, others terraced or suspended.

Daily Life and Group Dynamics
Hatinh langurs live in groups of 5 to 30 individuals, with an average group size of 15, depending on the quality of their environment. The distribution of the group depends on food availability, the presence of predators, and human hunters. The smallest groups are composed of one male and three to four females with their immature offspring.  

Adult males produce loud vocalizations upon waking up, and it is probable that the dominant male is the first out to lead the way when the group leaves the sleeping area at dawn to go foraging for a few hours. At around 4 PM, they travel in a single line along the cliffs and head back toward the sleeping area. Then they hang out in the vicinity of the sleeping caves for a couple of hours to play, relax, and interact with one another. They retire for the night between 6 PM and 7 PM, depending on when the sun sets.

Communication
Langurs communicate with body posture and touch—for instance, adult females often hug one another. They also vocalize. It would seem they utter a sequence of three “huut huut” calls to tell the group it is time to travel back to the sleeping site. Adult males also use alarm calls to warn the group when danger in near; they usually post themselves on top of a rock or high branch to look out for predators.

Reproduction and Family
Hatinh langurs can reproduce at any time throughout the year. However, most births occur during the spring and summer months when temperatures are high and food is abundant. Females give birth to one yellow infant—the body of whom darkens after two months and turns completely black after three—although the head remains orange for a while and is the last to change color. Infants nurse and are totally dependent on their mothers until they mature and become independent.

Ecological Role
Like most primates, Hatinh langurs are important seed dispersers. 

Conservation Status and Threats
The Hatinh langur is listed as Endangered and appears on the International Union for Conservation of Nature’s (IUCN) Red List of Threatened Species (IUCN, 2015). Their natural habitat is classified as being of “significant concern” in the Phong Nha-Ke Bang National Park Conservation assessment.

In the past, Hatinh langurs dwelled in forests of the Nghe An, Hatinh, and Quang Binh provinces; however, surveys conducted since 1998 indicate that the species is now mostly present in Quang Binh province, with some smaller groups in Quang Tri province. There isn’t any recent census, but it is estimated that the Hatinh populations have decreased by 50% in the last 35 years.

The Hatinh langurs’ natural predators include the yellow-throated marten—a fearless mammal also known as the kharza—but the main threats to the species are humans. In fact, entire groups of Hatinh langurs have been wiped out over the years. These animals are shot or captured with snares to provide meat for luxury restaurants frequented by a wealthy clientele who experience the consumption of wildlife as a symbol of high social status. Their body parts are also used in “traditional” medicines as they are thought to treat all kinds of ailments.

Habitat fragmentation, which is caused by human activities, is making dispersal difficult for surviving individuals to join other groups and thereby limits their opportunity to breed successfully, as well as negatively impacting the genetic diversity crucial to species survival. Large and numerous areas of forest are cleared to make room for rubber plantations, timber harvesting, mining, road construction, as well as a booming tourist economy and the construction of vacation resorts. Although tourism is a great source of revenue, it also generates pollution due to the use of motorized vehicles, including boats, as well as plastic and other non-biodegradable refuse that ends up in lakes and rivers.

To compound the problem of unregulated construction at the expense of endemic species conservation, Vietnam’s national parks do not offer the protection one would expect for these animals either. Park rangers, whose salaries are low, often help poachers capture animals destined for the illegal but very lucrative wildlife trafficking. So much so, that the places advertised as eco-tourism heavens cannot offer the sightings of the extraordinary animals visitors are coming to see, despite the fact that Vietnam is still considered one of the richest countries for its biodiversity.

Conservation Efforts
The Hatinh langur is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES) list of species. It is protected under the wildlife protection law (Government of Vietnam) and appears in the Red Data Book of Vietnam (Ministry of Science, Technology, and Environment).

In 2017, the Prime Minister approved the “Conservation Action Plan for Primates,” offering a glimpse of hope for Hatinh langurs and the region. This plan was developed after the 25th Congress of the International Primatologist Society hosted in Hanoi three years earlier. It is vetted by the Vietnam Administration of Forestry (VNFOREST) and the Ministry of Agriculture and Rural Development (MARD). The goals are for the government and local populations to cooperate and ensure that primate populations are self-sustaining, both inside and outside protected areas. The plan also calls for actions such as the eradication of illegal hunting, enforcement of the law, and conservation education.

In parallel, conservationists are advocating for the expansion of the Phong Nha-Ke Bang National Park to include the northwestern limestone forested areas. They recommend surveys to map the limestone forests and better assess the remaining populations of Hatinh langurs. They outline the necessity to evaluate the threats to the species and develop a longterm conservation strategy.

Finally, various national and international non-profit groups are also active in situ and are vital for the survival of the Hatinh langurs and other native endangered species. The Endangered Primate Rescue Center is a good example. This organization is dedicated to research and the rescue of langurs, gibbons, and lorises captured for the pet trade. They nurse them back to health and, if conditions permit, return them to the wild. When releasing Hatinh langurs in the forest, staff of the Endangered Primate Rescue Center equip the animals with tracking devices and follow their progress—ensuring that the primates are able to adequately find food resources and thrive.

Other groups active in the region, like Education for Nature Vietnam, concentrate on public outreach, criminal investigations, and education, and offer economic incentives to local people, without whom all efforts would be in vain.

References:​​

  • IUCN Red List
  • Some Observations on the Hatinh langur, Trachypithecus laotum hatinhensis (), in North Central Vietnam – (Centre for Natural Resources and Environmental Studies (CRES), Vietnam National University, Hanoi, V) –  Nguyen Manh Ha 
  • youtube.com – Spotting rare monkey – hating langur (Trackypithecus hatinhensis) in central Vietnam
  • The New York Times (4/1/2019) – Vietnam’s Empty Forests – Stephen Nash
  • Anthropology Now (vol.9, #2, September 2017) – Primates of Vietnam – Conservation in a Rapidly Developing Country – Herbert H. Covert, Hoang Minh Duc, Le Kha Quyet with Andie Ang, Amy Harrison-Levine and Tran Van Bang
  • www.epcr.asia – Endangered Primate Rescue Center – Three Endangered Hatinh Langurs Successfully Released (July 9, 2016)
  • Journal of Forestry Science and Technology no.2 – 2018 – Status and Social Organization of Hatinh Langur (Trachypithecus hatinensis) in Dong Hoa and Trach Hoa Communes Forest, Quang Bihn Province — Dong Thanh Hai, Thao A. Tung 
  • IUCN World Heritage Outlook – Phong Nha-Ke Bang National Park 2020 Conservation Outlook Assessment
  • Learning the Ropes: The Ontogeny of Locomotion in Red-Shanked Douc (Pygathrix nemaeus), Delacour Langur (Trachypethicus delacouri), and Hatinh Langurs (Trachypethicus hatinhensis). Positional Behavior – Catherine Workman and Herbert H. Covert
  • ​​Vietnamese Journal of Primatology – Conservation Status of Vietnamese Primaes – Tilo Nadler, Vu Ngoc Thanh and Ulrike Streicher.

Written by Sylvie Abrams, April 2021