1
Background
The Laotian Langur (Trachypithecus laotum), a member of the Old-World Monkeys in the Cercopithecidae family and Colobinae sub-family, is recognized as a leaf-eating monkey within the Trachypithecus genus Recently, this species has been classified as Endangered by the IUCN Red List and is included in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora.
2020) It is also totally protected under the Lao Wildlife and Aquatic Law; it is classified as Category I “Prohibited” species list under the name Trachypithecus laotum (MAF, 2021)
The Laotian Langur, an endangered colobine monkey endemic to Laos, is primarily found in the karst forest habitats of Khammouan and Bolikhamxay Provinces This species is restricted to limestone forests in central Laos, particularly within the Nam Kading National Protected Area and Phou Hin Poun National Protected Area, along with surrounding protected areas As part of the francoisi superspecies group, the Laotian Langur shares its habitat with other endangered species such as the Hatinh Langur and Black Langur Currently, its distribution covers less than 5,000 km², and its population is declining due to habitat loss and hunting Furthermore, this species remains one of the least studied in the region, with limited surveys conducted to understand its ecology and behavior.
PHP-NPA, located in northwestern Khammouane Province, is home to the largest wild population of T laotum, a key mammal species for conservation and a flagship species of the reserve Despite its ecological significance, the last survey on Langurs in PHP-NPA was conducted a decade ago, leaving a gap in current data regarding their population, distribution, and conservation status This lack of updated information hinders effective conservation efforts for the Langur within this protected area.
In response to the need for updated information on the Laotian Langur, I conducted a six-month field study in the PHP-NPA from July to December 2020 This research aimed to assess the population, distribution, threats, and conservation status of this endemic species The findings are intended to aid NPA management authorities and local communities in Khammouane Province in developing effective conservation programs to protect the remaining Laotian Langur population and to support further research initiatives in PHP-NPA.
Aim of this research
This study aims to gather essential data regarding the status, distribution, and threats faced by the T laotum species, serving as a foundation for its long-term conservation in the designated study area.
Objectives
This study aims to specifically study:
1) Population (abundance, group size, group composition and age-sex composition) of the T laotum;
2) Distribution (based on elevation, vegetation, distance) of the Langur;
3) To identify the current threats to the species and their habitats and;
4) To provide recommendations for further conservation and research about
T laotum in PHP-NPA, Khammouane Province, Lao PDR.
Scope of the study
This study was conducted in PHP-NPA in Khammouane Province, Lao PDR from July to December 2020 I studied about the population, distribution and conservation of the Laotian Langur (Trachypithecus laotum).
4
Primates
The Asian primate taxonomy published in 2014 has been recognized 119 species and 183 taxa of non-human primates to occur in 22 Asian countries Of the
113 Asian primate species have been assessed, 17 (15%) are Critically Endangered,
45 (40%) are Endangered and 25 (22%) are Vulnerable (Roos et al., 2014) The most endangered genera are Rhinopithecus, Pygatrix, Nasalis, Simias, Hylobates, Nomascus, Symphalangus and Pongo (Roos et al., 2014)
Asia is home to a diverse range of primate species, with Indonesia leading the count at 58-59 species, followed by Vietnam with 25, Malaysia with 24-25, and China with 22-26 Other notable countries include India (21), Laos (20-22), Myanmar (18), and Thailand (18) (Roos et al., 2014) The number of primate species is expected to rise, particularly with the recent discovery of new Loris species in Vietnam, highlighting the ongoing importance of biodiversity research in the region.
As of September 5, 2020, the IUCN Primate Specialist Group identifies several primate species native to Asia, including 23 species from the Lorisidae family (2 genera), 3 species from Tarsiidae (3 genera), 146 species from Cercopithecidae (8 genera), 29 species from Hylobatidae (4 genera), and 6 species from Hominidae (1 genus) For a comprehensive list of these Asian primate species, please refer to Annex 1.
Figure 1: Confirmed and unconfirmed primate species in Asia (2014)
2.1.2 Primates and their conservation status in Laos
Laos, officially known as the Lao People's Democratic Republic (Lao PDR), is renowned for its rich biodiversity, housing some of the world's most endangered terrestrial and aquatic ecosystems (World Bank, 2020) This Southeast Asian nation serves as a crucial habitat for a diverse array of non-human primates, featuring six genera across three families and an estimated 20-22 species (Roos et al., 2014; MAF).
Laos is home to a diverse range of primate species, including two species of Slow Loris (Bengal and Pygmy) from the family Lorisidae, five species of Macaques (Northern Pig-tailed, Assamese, Stump-tailed, Long-tailed, and Rhesus) from the genus Macaca, and six species of Langurs (Germain’s, Annamese, Indochinese Grey, Laotian, Hatinh, and Black) from the genus Trachypithecus Additionally, the country hosts two species of Doucs (Red and Grey-shanked) from the genus Pygathrix, two species of Gibbons (Pileated and Lar) from the genus Hylobates, and four species of Gibbons (Western Black Crested, Southern White-cheeked Crested, Northern Yellow-cheeked Crested, and Northern White-cheeked Crested) from the genus Nomascus Notably, Laos is recognized for its eight Langur species, including the endemic Laotian Langur (T laotum) and the world's largest population of Red-shanked Doucs (P nemaeus) Three species of limestone Langurs, T laotum, T ebenus, and T hatinhensis, are specifically adapted to the limestone forest habitats in central Laos.
The IUCN Red List has recently assessed the conservation status of all primate species in Laos, designating four as Critically Endangered (CR), eleven as Endangered (EN), three as Vulnerable (VU), one as Near Threatened (NT), and one as Least Concern (LC) Additionally, these primates are included in the CITES listings, with ten species classified under Appendix I, nine under Appendix II, and two species not listed.
Table 1: Primate species in Laos and conservation status
Family Common name Scientific name IUCN Nat CITES Lorisidae
Loris Bengal Slow Loris Nycticebus bengalensis EN [P] I
Pygmy Slow Loris Nycticebus pygmaeus EN [P] I Cercopithecidae
Northern Pig-tailed Macaque Macaca leonina VU [P] II
Assamese Macaque Macaca assamensis NT [P] II
Stump-tailed Macaque Macaca artoides VU [P] II
Long-tailed Macaque Macaca fascicularis VU [P] II
Rhesus Macaque Macaca mulatta LC [P] II
Trachypithecus Germain's Langur Trachypithecus germaini EN [P] II
Family Common name Scientific name IUCN Nat CITES
Annamese Langur Trachypithecus margarita EN [P] -
Laotian Langur Trachypithecus laotum EN [P] II
Hatinh Langur Trachypithecus hatinhensis EN [P] II
Black Langur Trachypithecus ebenus EN [P] II
Red-shanked Douc Langur Pygathrix nemaeus CR [P] I
Grey-shanked Douc Langur Pygathrix cinerea CR [P] I
Hylobates Pileated Gibbon Hylobates pileatus EN [P] I
Lar Gibbon Hylobates lar EN [P] I
Southern White- cheeked Gibbon Nomascus siki CR [P] I
Northern White- cheeked Gibbon Nomascus leucogenys CR [P] I
IUCN: LC = Least Concern; NT = Near Threatened; VU = Vulnerable; EN Endangered and CR = Critically Endangered
CITES: Appendix: I, II, - = not listed
Nat = National conservation status; [P] = Category I "Prohibited Species"
Study species
Colobine monkeys, belonging to the subfamily Colobinae, encompass a diverse range of 59-78 species across up to 10 genera These Old World primates inhabit various forest and woodland ecosystems in Africa and Asia In Asia, colobines are represented by seven genera, including Pygathrix, Rhinopithecus, Nasalis, Simias, Presbytis, Trachypithecus, and Semnopithecus.
The genus Trachypithecus is the most diverse and widely distributed group among Asian colobines, found primarily in Southeast Asia, extending from Bhutan and Assam in India to Bangladesh, Myanmar, Thailand, Cambodia, Laos, Vietnam, and Southern China Additionally, these species inhabit significant areas of the Sundaland region, including the Malay Peninsula, Sumatra, Borneo, Java, and several smaller islands Currently, there are 20 recognized species within the Trachypithecus genus.
2013; Roos 2021; Roos et al., 2014, 2019a; Rowe & Myers, 2016, Zinner et al.,
2013), but until recently, different classifications with generally lower species numbers and varying species assemblies have been proposed (Brandon-Jones, 1984,
1995, 1996; Brandon-Jones et al., 2004; Groves, 2001; Roos et al., 2007)
The genus Trachypithecus, which recently contains 20 species (Roos et al.,
The genus Trachypithecus is classified into four species groups based on genetic, phenotypic, ecological, and behavioral differences and similarities The T pileatus group includes three species: T pileatus, T geei, and T shortridgei, while the T francoisi group comprises seven species: T francoisi, T delacouri, T ebenus, and T hatinhensis.
T laotum, T leucocephalus and T poliocephalus), the T cristatus group contains six species (T cristatus, T auratus, T gernaini, T margarita, T mauritius, and T selangorensis), and the T obscurus group contains four species (T obscurus, T barbei, T crepusculus and T phayrei) (Anandam et al., 2013; Zinner et al., 2013;
Genetic studies indicate that the T pileatus group was the first to diverge, followed by the T francoisi group, while the T cristatus and T obscurus groups are the most recent divergents (Roos et al., 2014; Rowe and Myers, 2016; Roos, 2021; Roos et al., 2019; Roos and Zinner).
2021) However, I found that there are about 35 species names within this genus and one new described as new species (see Table 2) from Myanmar (Roos et al.,
The genus Trachypithecus, commonly known as Langurs, comprises slim monkeys with long tails, typically weighing between 5 to 10 kg Males are generally larger than females, and all species are diurnal, primarily using quadrupedal locomotion, although some are skilled leapers Langurs are primarily florivorous, feeding on leaves, and they inhabit forested areas They usually form social groups consisting of one male and multiple females, ranging from 5 to 20 individuals Notably, all Langur species give birth to bright orange infants, which gradually darken in color within a few months.
Table 2: List of the genus Trachypithecus species with IUCN conservation status
Common Name Scientific Name IUCN
Trachypithecus auratus VU (Setiawan et al.,
2 Tenasserim Langur Trachypithecus barbei VU (Nadler, 2021)
4 Silvered Langur Trachypithecus cristatus VU (Meijjaard and
4.1 Sunda Silvered Langur Trachypithecus cristatus cristatus
Trachypithecus delacouri CR (Nadler et al.,
Trachypithecus francoisi EN (Nadler et al.,
8 Golden Langur Trachypithecus geei EN (Das et al., 2020c)
9 Germain's Langur Trachypithecus germaini EN (Duc et al., 2021)
11 Laotian Langur Trachypithecus laotum EN (Coudrat et al.,
Common Name Scientific Name IUCN
12 White-headed Langur Trachypithecus leucocephalus CR (Bleisch and Long,
Trachypithecus margarita EN (Eudey and Ang,
14 West Javan Langur Trachypithecus mauritius VU (Setiawan et al.,
15 Dusky Langur Trachypithecus obscurus EN (Boonratana et al.,
Langur Trachypithecus obscurus carbo EN (Boonratana et al.,
Langur Trachypithecus obscurus styx VU (Boonratana et al.,
16 Phayre's Langur Trachypithecus phayrei EN (Bleisch et al.,
17 Capped Langur Trachypithecus pileatus VU (Das et al., 2021a)
Capped Langur Trachypithecus pileatus durga VU
Common Name Scientific Name IUCN
18 Cat Ba Langur Trachypithecus poliocephalus CR (Rawson et al.,
20 Shortridge's Langur Trachypithecus shortridgei EN (Long and Htun,
21 Popa Langur Trachypithecus popa - (Roos et al., 2020)
The Laotian Langur, scientifically known as Trachypithecus laotum, is often referred to as the Lao Langur or Laotian Langur This primate is also recognized by other names, including Laotian Black Langur and White-browed Black Langur, as noted by Timmins and Boonratana in 2008.
The "Khang Lao," also known as "Khoung" by local villagers, is an endangered leaf-eating monkey belonging to the Cercopithecidae family and Colobinae subfamily of Old World monkeys This unique species is endemic to Laos, highlighting its significance in the region's biodiversity.
From the 1960s to the 1990s, this taxon was regarded as monotypic and conspecific with Trachypithecus fransoisi (Steinmetz et al., 2011) Various subsequent classifications of this Langur have emerged, but they lack sufficient primary information to support their validity Consequently, it has been proposed as a distinct species.
Trachypithecus laotum (Roos et al., 2007) to contain also the subspecies T l hatinhensis with Trachypithecus auratus ebenus as provisionally synonymous with
T l hatinhensis and T hatinhensis cannot be resolved without additional primary information I follow an updated Asian primate taxonomy (Roos et al., 2014) which referred to T laotum as a distinct species (Fig 2)
The Laotian Langur is characterized by its glossy black fur, a hairless dark face, a black crest on its head, and white markings on its cheeks and forehead Adult males are larger than females, while sub-adults share the same fur color but are intermediate in size between adults and juveniles Juveniles exhibit a mix of colors, including black, yellowish, and white, whereas infants are orange The black coloration of the Laotian Langur resembles that of the Black Langur (T ebenus) and the Hatinh Langur (T hatinhensis).
Figure 2: Scientific classification of the Laotian Langur
Figure 3: Appearance of the adult Laotian Langur ( T laotum )
The Laotian Langur is known only from Bolikhamxai and Khammouan Provinces, central part of Lao PDR (Le and Campbell, 1994, Ruggeri and Timmins,
The study species, T laotum, is found in the NKD-NPA, Nam Sanam Provincial Protected Area, and PHP-NPA, with notable populations reported in the northern and central regions of PHP-NPA in Khammouan Additionally, this species has been observed in the corridor leading to Nakai-Nam Theun National Park and in the Khamkheut district near Lak Sao, as noted in studies by Steinmetz et al (2011) and Roos et al (2014).
Province (Nadler, 2009; Phiapalath, 2010) At present, the known extent of occurrence of the Langur is smaller than 5000 km 2 and occurs in fewer than five locations (Coudrat et al., 2020) (Fig 4)
Photo credit: Dr Phaivanh Phiapalath
Figure 4: Geographic range of T laotum
Currently, there is a lack of reliable data on the population status of the Laotian Langur, with estimates not yet established, although it is deemed abundant within its habitat Large groups, sometimes consisting of up to 25 individuals, have been observed a few kilometers from villages Notably, a significant portion of their occupied range extends beyond these distances and appears to be untouched by human activity However, the Laotian Langur population is experiencing a drastic decline due to habitat loss and human disturbances.
Between 1994 and 2010, several groups of Laotian and Black Langurs were observed in the PHP-NPA, with a notable sighting of a single male and a group comprising 14 adults and subadults, along with three yellow juveniles Previous surveys documented a total of 19 groups within this protected area (Nadler, 2009; Phiapalath, 2010; Steinmetz et al., 2011).
The IUCN is currently conducting projects in the PHP-NPA, where approximately 100 individuals and around 37 groups of vocalizing Langurs have been documented (Phiapalath, 2010) During patrolling efforts, additional encounters with this species may also be recorded.
The Laotian Langur, a leaf-eating monkey, primarily inhabits karst forest ecosystems in central Lao PDR, thriving in steep terrains such as limestone karsts and non-calcareous escarpments These monkeys are often found on rocky surfaces within semi-evergreen forests and open scrub areas, relying on the rocky landscape for their survival They have been observed at elevations ranging from 160 to 900 meters, although their upper altitude limit remains unknown and is likely to be significantly higher Historically, Laotian Langurs have been recorded in groups of 15 to 25 individuals, with smaller groups of 4 to 8 also noted.
Study area
2.3.1 Phou Hin Poun National Protected Area
Designation and current status of the NPA
The PHP-NPA, located in northwestern Khammouane Province in central Lao PDR, spans an area of 150,000 hectares It lies between latitudes N17°26’–18°05′ and longitudes E104°25’–105°10′ Established as one of the original 18 National Conservation Areas (NCBAs) in Laos on October 29, 1993, through Prime Minister Decree No 164, it currently stands as one of the 26 National Protected Areas in the country.
In 2023, six new National Parks were declared, with several newly established NPAs, including one of two NPAs located in Khammouane Province, alongside Khounxe-Nongma NPA.
The protected areas in the Lao PDR national system are categorized as Category VI "Protected Area with Sustainable Use of Natural Resources" under the IUCN framework, allowing for village presence within designated controlled use zones (WCS, 2012) This system marks the beginning of a long-term initiative aimed at sustainably managing and enhancing valuable resources (DoF, 2015) The legal framework governing these National Protected Areas in Lao PDR is designed to support this management process.
- Decree 164/PM on the establishment of the Lao PDR Protected Area System
- Regulation on the Management of National Biodiversity Conservation Areas, Wildlife and Aquatic Animals Law (2007)
- Decree 134/PM on Conservation Forest (2015)
- Phou Hin Poun National Protected Area Collaborative Management Plan (2022-
- Other sectoral plans which may impact on the objectives of the NPA
The Forestry Law 2019 defines a protected area as a designated space for the conservation of nature, safeguarding plant, aquatic, and wildlife species, as well as preserving forest ecosystems These areas hold significant value for nature, history, culture, tourism, the environment, education, and scientific research (Vorlachith, 2019).
Therefore, all PAs in Laos play an important role in biodiversity conservation including PHP-NPA (Fig 5)
Figure 5: Phou Hin Poun National Protected Area in wet season
The NPA is situated in the western Khammouane Province of Lao PDR, bordered by Highway 12, Highway 13, Highway 8, and the Nakai Plateau, with geographical coordinates ranging from N17°26’ to N18°05′ and E104°25’ to E105°10′ (MAF, 2000) This protected area encompasses portions of six districts: Hinboun, Thakhek, Mahaxai, Yommalath, Nakai, and Khoukham.
The park's boundaries are defined by the Nam Hinboun River to the north and northwest, extending along the limestone massif in the west, and the Nam Don River in the southwest They continue along Highway 12, just before reaching Yommalath town, and then trace the depression between the Nakai Plateau and the limestone until they meet the Nam Hinboun River.
The site is strategically linked to several significant areas, including the Phou Hai National Protection Forest, which serves as a vital corridor between the PHP-NPA and Nakai-Nam Theun National Park to the southeast Additionally, it connects to the Phou Nok Kok Provincial Protection Forest and the Nam Sanam-Phou Pha Marn Provincial Protected Area, both of which are associated with the Nam Kading NPA to the north.
The PHP-NPA Management Office, in collaboration with the IUCN-BCEM project and the World Bank's Lao Landscape and Livelihood initiative, will update the boundaries of the NPA as part of the five-year management plan established by the Department of Forestry in 2022.
Figure 6: Location of Phou Hin Poun National Protected Area
The PHP-NPA stands out among protected areas in Laos, specifically within the Central Indochina Limestone region, alongside Hin Nam No National Park It safeguards a representative sample of the western biogeographic limit, preserving its associated biodiversity and ecological values The area features diverse forest types, including semi-evergreen, vine and bamboo, mixed deciduous, and deciduous dipterocarp forests, as well as vital wetland habitats These ecosystems are crucial for supporting populations of globally and nationally significant species such as Laotian Langurs, Black Langurs, Assamese Macaques, Southern White-Cheeked Gibbons, Asian Elephants, Tigers, and Serows.
The PHP-NPA is a rich biodiversity hotspot, hosting 113 mammal species, 160 bird species, 81 reptile species, 47 amphibian species, and 145 fish species (MAF, 2000) Among its remarkable inhabitants are 41 bat species, with Tham Houay Si cave serving as a habitat for 22 of them (Robinson and Webber, 2000) Notably, the Laotian Rock Rat (Laonastes aenigmamus) was identified here, a unique species so distinct that it was placed in its own family, later linked to a family previously believed to be extinct.
Saxatilomys paulinae, represents a new genus of the Murinae subfamily, the Old-
Mammals known to live in PHP-NPA include the Giant Muntjac (Muntiacus vuquangensis), the Assam Macaque (Macaca assamensis), Laotian Langur
Phou Hin Poun National Biodiversity Conservation Area (NBCA) is home to a diverse array of wildlife, including the Trachypithecus laotum, Southern White-Cheeked Gibbon (Nomascus siki), and the Black Giant Squirrel (Ratufa bicolor) Notable bird species in this region include the Grey Peacock-Pheasant (Polyplectron bicalcaratum), Hill Myna (Gracula religiosa), Red-collared Woodpecker (Picus rabieri), Sooty Babbler (Stachyris herberti), Bare-faced Bulbul (Nok hualon), and Wreathed Hornbill (Rhyticeros undulatus).
The vegetation of PHP-NPA is influenced by its tropical savanna climate and rugged karst terrain, with over 50% of the landscape consisting of rocky outcroppings The area primarily features dry evergreen forest and scrubland, with only 16% of the NPA covered by forest—11% mixed deciduous and 5% evergreen (Robinson and Webber, 2000) Notable rare flora species in PHP-NPA include Diospyros embryopteris, agarwood (Aquilaria sp.), dragon’s blood (Dracaena sp.), and rosewood.
(Dalbergia cultrata) as well as orchid species
The PHP-NPA spans parts of six districts: Thakhek, Hinboun, Khounkham, Nakai, Yommalath, and Mahaxay, encompassing a total of 115 villages and over 64,000 residents who rely on the area's natural resources (Phiapalath et al., 2012) Among these, 89 villages are situated within or adjacent to the PHP-NPA, while surrounding communities also utilize forest resources from the region The area is home to diverse ethnic groups, including the Lao Loum subgroups such as Kaleung, Tai Bo, Tai Sam, and Meuy, as well as Lao Theung groups like Makong (Kwa, Tro subgroup), predominantly found in the eastern part of the NPA (MAF, 2000).
Methods for primate studies
Various methods exist for conducting animal censuses, including direct techniques like mark-recapture, point counts from fixed locations, and strip transects that survey specific habitat areas Among these, line transects are widely recognized as the most effective approach for surveying forest-dwelling primates, such as Langurs This method involves counting all visible animals from a predetermined line traversing the forest, facilitating comprehensive data analysis Consequently, I reviewed the methodologies pertinent to limestone Langur studies conducted in Vietnam, China, and Lao PDR.
In Lao PDR, the line transect method is commonly employed to survey primate species This technique is essential for gathering data on the distribution and threats facing primate species, including T ebenus and T hatinhensis.
Hin Nam No National Park (Minh et al., 2019) Similar, this method also previously has been used to study on distribution and threats of Red-shanked Douc (Phiapalath,
In Nakai-Nam Theun National Park, researchers employ a combination of methods, including camera trapping, to survey the Red-shanked Douc (Coudrat et al., 2012) Additionally, line transects are utilized to monitor key species such as Langurs, gibbons, macaques, and douc Langurs in Hin Nam No National Park (Vongkhamheng, 2014; Coudrat and Nanthavong, 2015; Coudrat, 2016).
In Vietnam, the line transect method is a widely used technique for studying the group sizes and structures of diurnal primates Due to the area's steep terrain and inaccessibility, surveyors adapted their approach by walking along the contour lines at the mountain's base instead of using straight transect lines (Hai and Tung, 2018) This method has proven effective in assessing the occurrence and population abundance of monkeys in Phong Nha Ke Bang National Park, as highlighted in studies by Haus et al (2009b) and Long et al (2011).
In China, various methods were employed to collect data on the distribution and status of the White-headed Langur, primarily through on-site daytime observations in designated areas and conducting interviews (Huang et al.).
In 2002, researchers employed line transect methods and sleeping-site counts to conduct a population census of the Langur at Longrui Karst Hills (Wang et al., 2005) However, these methods were not applicable for surveying T francois in Guangxi Province due to the challenging accessibility of the limestone outcrop habitat and the uneven distribution of this Langur group (Li et al., 2007).
To investigate the population, distribution, and threats facing the Laotian Langur in PHP-NPA, I employed the line transect method (Brockelman and Ali, 1987) Due to the challenging terrain, I utilized existing local trails as transects for surveying the Langurs instead of establishing straight lines.
23
Study area
I conducted a study on the population, distribution, and conservation of the Laotian Langur within the PHP-NPA, located in northwestern Khammouane Province, Laos This region, positioned between 17°26’–18°05′N and 104°25’–105°10′E, was designated as one of the original 18 Lao National Biodiversity Conservation Areas (NBCA) in 1993 through Prime Minister Decree 164 Previously known as Khammouane Limestone NBCA, it now encompasses approximately 225,000 hectares of stunning karst formations at an elevation of 180 meters.
The PHP-NPA, covering 150,000 hectares, is situated at an elevation of 850 meters and features mature forests in its valleys and depressions (Timmins, 1997; Siphandone, 1993) This area is home to the largest population of Laotian Langurs in the country, with flat depressions contrasting the surrounding topography, often containing primary and secondary mixed deciduous/semi-evergreen forests (Steinmetz et al., 2011) However, human activities have fragmented the Langur habitat, as settlements and agricultural fields encroach upon the karst rock bases, leading to significant habitat loss The central part of PHP-NPA, particularly the TPZ, has the highest quality forest, covering approximately 351 km², which is about 15.6% of the park area (Brakels, 2019b) The survey areas were chosen for their pristine habitats, flat terrain, and accessibility The wet season spans from June to October, with peak rainfall in August (mean = 476.3 mm) and October (436 mm), while the driest months are December (16.3 mm) and February (19.7 mm), averaging 149.8 mm monthly (Souwideth et al., 2021) The study area is divided into four sectors: Konglor-Natan, Konglor, Buamlou, and Kuankacha.
Figure 7: Map of study area
Materials and equipment
In my studies, I utilized various equipment and tools for data collection, including field data collection forms, maps, and writing instruments such as pens and pencils Additionally, I equipped myself with waterproof bags and clothing, along with essential camping gear like sleeping bags, hammocks, flashlights, and first aid kits A smartphone was also an integral part of my data collection process.
The article highlights essential equipment for field research, including the Huawei P9 smartphone, Vixen New FORESTA HR 10x50 WP binoculars, Nikon P950 digital camera with a 2000 mm zoom, Garmin 62s GPS device, and Uni-T LM 1000M rangefinder Additionally, it mentions the inclusion of a Lao primate guide, photographs of primates in the study area, and provisions of food and water for the survey team.
Figure 8: Tools and equipment are used for field data collection
In addition, I also used my personal laptop Acer Nitro 5 and installed open- source software QGIS version 3.14 and Microsoft Office Excel 2016 in my laptop for data analysis in this study.
Data collection
The study's data collection involved two key phases: conducting interviews with staff from the District Agriculture and Forestry Offices (DAFOs) and local residents, alongside performing forest transect walks in the study area.
- First phase was conducted to interview the staffs at DAFOs in Khammouane Province and local people live in and around the PHP-NPA
The second phase involved selecting survey areas, determining the equipment to be used, establishing study camps, and designing transects for the systematic surveying and documentation of the population, distribution, and threats to T laotum in the designated study area.
From 27 th July to 3 rd August 2020, I interviewed 31 people (29 men, 2 women) (Fig 9) They were 14 peoples belonging to the staff of six District Agriculture and Forestry Offices (DAFO, i.e., Thakhak, Khounkham, Hinboun, Nakai, Yommalath and Mahaxay), and 17 villagers, including three from Ban Natan (Nakai district), six from Ban Konglor (Khounkham district), three from Ban Buamlou, one from Ban Bo Neng and four from Ban Kuankacha (Hinboun district)
I conducted standardized interviews with local residents to assess the presence of primates in their villages To facilitate this process, I utilized a smartphone to display photos of various primate species, including the Laotian Langur (T laotum), black Langur (T ebenus), southern white-cheek gibbon (Nomascus siki), stump-tailed macaque (Macaca arctoides), and Assamese macaque (Macaca assamensis) During the interviews, we referred to each species by their local names: Laotian Langur as khoung, black Langur as khong, gibbon as tha nee, Assamese macaque as ling kang, and stump-tailed macaque as ling nar daeng Each participant answered ten specific questions to provide insights into the primate populations in their areas.
During a two-hour interview with DAFO staff across three districts (Khounkham, Nakai, and Hinboun) and villagers at survey camps, all eight DAFO interviewees accurately identified the Laotian Langur However, two DAFO staff in Yommalath recognized another species, T ebenus, but mistakenly believed it to be the same as T laotum In Thakhek, two DAFO members misidentified the Langurs while correctly identifying gibbons, and in Mahaxay, two staff members were unfamiliar with the Laotian Langur In contrast, all villagers successfully identified the Laotian Langur and were knowledgeable about its vocalizations, sleeping sites, and some of the plant species it consumes.
Figure 9: Interview staffs at District Agriculture and Forestry Offices
Therefore, I and survey team members used the information gathered from the interviewees to define the areas of the potential presence of T laotum in the
PHP-NPA We established the field survey team to identify the areas to be carefully surveyed in each district
Eleven study camps were established to investigate the population and distribution of Laotian Langurs within the PHP-NPA, primarily located in the central Total Protection Zone The selection of these camps was based on terrain accessibility, proximity to water sources, and the feasibility of walking transects Two camps were set up in the village, while the remaining nine were situated in forested areas.
Table 3: Description of the study camps and transects
Survey sector No Study camp Latitude Longitude Altitude
Survey sector No Study camp Latitude Longitude Altitude
The length of a trail is determined using GPS tracking tools, which only account for one direction of the journey; the return trip is not included in the measurement to avoid double counting.
Figure 10: Study camp locations at study area
Figure 11: Survey camps and team
Key: a = Camp 4, b = Camp 8 and c = Camp 9, d = Camp 10
The field survey team, comprising 18 members, was led by a main researcher responsible for overseeing the research and managing the survey team It included one representative from the Provincial Agriculture and Forestry Office for field coordination, four field assistants from DAFO, and 12 villagers from four different villages who served as field guides and provided food and water for the team, with some also acting as rangers Detailed descriptions of the survey team's activities along each transect are provided in Table 4.
Table 4: Survey teams and transects walked Sector Survey transects (trail) and Team
Trail 1-3: Johnny, Lianphet, Kongla and 2 village rangers from Ban Konglor
Trail 4-5: Johnny, Lianphet and 2 villagers from Ban Natan
Trail 6: Johnny, Lianphet, and 2 villagers from Ban Konglor
Trail 7: Johnny, Lianphet, Kongla, Kalason and 3 village rangers from Ban Konglor
Trail 8-9: Johnny, Lianphet, Kongla, and 5 villagers from Ban Konglor
Trail 10: Johnny, Lianphet, and 2 villagers from Ban Konglor Trail 11: Kongla, and 3 villagers from Ban Konglor
Trail 12: Johnny, Lianphet, Kongla, and 5 villagers from Ban Konglor
Trail 13: Johnny, Lianphet and 2 villagers Trail 14: Kongla, 3 villagers from Ban Konglor Trail 15: Johnny, Lianphet, Kongla and 5 villagers from Ban Konglor
Trail 16: Johnny, Lianphet, Balame, and 3 villagers from Ban Buamlou (Khampoun (DAFO), Peter Brakels from IUCN and rangers joined the team)
Trail 17: Johnny, Lianphet, Balame, and 3 villagers from Ban Buamlou
Trail 18: Johnny, Lianphet, and 3 villagers from Ban Kuankacha Trail 19: Balame, Khampoun and 3 villagers from Ban Kuankacha Trail 20: Johnny, Lianphet, and 3 villagers from Ban Kuankacha Trail 21: Johnny, Lianphet, and 3 villagers from Ban Kuankacha
During the dry season in the PHP-NPA, survey teams struggle to find drinking water, making fieldwork particularly challenging To mitigate these difficulties, our team initiated the survey during the wet season from July to October However, we encountered several challenges due to unfavorable weather conditions.
Due to heavy rainfall, we were unable to conduct continuous surveys of the Langurs from August to October as originally planned, as traversing the karst areas became hazardous Consequently, we postponed our work schedule and resumed field surveys in December 2020 For a detailed overview of our activities, please refer to Annex 3 – Working Schedules.
In our field survey, we aimed to implement line transect methodology as outlined by Brockelman and Ali (1987) However, the challenging limestone terrain in PHP-NPA made it impractical to follow a straight transect line Consequently, we utilized existing local trails as alternative transects for our surveys.
During our fieldwork, we covered a total of 64.1 km across 21 transects, conducting 2 to 10 surveys per sector between 7:00 AM and 5:00 PM Due to the lack of water sources for our survey team during the dry season, we restricted our fieldwork to the wet season, specifically from August to October 2020 However, adverse weather conditions, including heavy rainfall that posed risks in karst areas, forced us to postpone our schedule, ultimately completing the surveys between August 13 and December 17, 2020.
In the study area, visibility was consistently similar across all four sectors, with a mean detection distance of approximately 150-200 meters for direct sightings and 300-400 meters for calls For each observed Langur group, we meticulously recorded the number, sex, and age of individuals, along with GPS coordinates, altitude of sighting spots (meters above sea level), time of sighting, and estimated distance from observers Age classification of the Langur individuals was determined based on body size, fur color, and the presence of sexual organs.
Adult males are much larger in body size, with visible penis and with the breast being fully covered by fur
Adult females are noticeably smaller in size, characterized by their visible breasts and absence of a penis Subadult individuals resemble their adult counterparts in size and features, but are medium-sized Juveniles exhibit a range of fur colors, varying from yellowish or orange to black and white.
In contrast, the adults are black in the body and black and white in the head In addition, the juveniles are normally spending their time nearby the adult females
Data analysis
The data and information of the study on population, distribution and threats of the Laotian Langur were processed and analyzed by Microsoft Excel and QGIS software
Group size of the study species
The study analyzed the group size of the species by counting the number of individuals or groups recorded in each survey sector, including Konglor-Natan, Konglor, Buamlou, and Kuankacha, as well as the total number of individuals or groups within the entire study area.
Group composition of the Laotian Langur
The study of Laotian Langur group composition involved classifying individuals into four categories: adults (male and female), sub-adults (male and female), juveniles (male and female), and infants The analysis focused on counting the number of each category observed in various groups within the study area.
The age classes of Langur individuals were classified based on body size, fur color, and sexual characteristics Adult males are significantly larger, displaying visible penises and fully fur-covered breasts, while adult females are smaller with prominent breasts and no penis Sub-adults resemble their adult counterparts in size, but are intermediate in body size Juveniles exhibit a range of fur colors, from yellowish or orange to black and white, with their bodies and tails being yellowish to black and heads featuring three colors In contrast, adults have a predominantly black body and a black and white head Juveniles typically stay close to adult females, while infants have orange or gold fur and are carried by their mothers The age-sex composition data was analyzed based on the number of individuals in each class identified within the study sector.
Estimate abundance of the Laotian Langur
The Encounter Rate (ER) index was utilized to assess the relative abundance of the Laotian Langur population in the study area, following the methodology outlined by Rovero et al (2006) This analysis focused exclusively on the Laotian Langurs detected within the study sites of the NPA, measuring the number of groups heard or observed per kilometer of transect walked Data regarding Langur groups identified in each survey sector, along with the total length of transects, were processed using Microsoft Excel 2016 The encounter rate was calculated based on a specific formula, ensuring accurate representation of the species' presence in the area.
N = Total number of Langur groups detected/observed in study area (groups)
L = Total transect walk in the study area (km)
Figure 12: Age-sex class of the Laotian Langur
Note: a = adult male, b = juvenile (left) and adult female (right), c = sub-adult, d juvenile
I registered an account on https://search.asf.alaska.edu to download the terrain-corrected ALOS PALSAR Digital Elevation Model (DEM) products, featuring a resolution of 12.5 meters for the Phou Hin Poun National Protected Area The DEM dataset, along with two shapefiles detailing the study area and GPS coordinates of the detected Langur group, was processed using QGIS software (Fig 13).
Figure 13: Raster (DEM) and GPS coordinates shapefiles
The DEM raster file was reclassed into four categories based on the level of elevation of the study area as following Table 5:
Table 5: Description of the elevation intervals at the study area
1 >250 Low (High vegetation and humidity)
2 250-500 Medium (Moderate vegetation and temperature)
3 500-750 High (Less vegetation and high temperature)
4 0.1 Bare soil, rock, sand, water body Low
2 0.2-0.5 Sparse vegetation/moderate vegetation dense Moderate
3 0.6-9 High dense of forest/vegetation cover High
Figure 14: A raster file of NDVI in study area
In my research, I utilized the GPS coordinate layer alongside the NDVI layer in QGIS to analyze the distribution of Langur groups based on elevation By estimating values from the NDVI raster files, I was able to accurately assess the NDVI values at the specific locations where the Langurs were observed This involved measuring the distance from the observer's position to the animals and leveraging Google satellite imagery to enhance the precision of my estimations.
Distribution based on nearest village distance
In this study, two shapefiles were utilized: one representing the village locations within and around the study area, and the other containing GPS coordinates of the study species (Fig 15) These shapefiles were analyzed using the "Distance to Nearest Hub" tool in QGIS software to determine spatial relationships.
Figure 15: Location of villages and study species GPS coordinate
The survey identified various threats to the habitats of the Laotian Langur and other species, including camps, logging, hunting activities, and poaching To assess these threats, the frequency of threat signs was recorded in relation to the total distance surveyed in each sector The Encounter Rate Index was calculated using Microsoft Excel 2016, with the formula ER = N/L, where ER represents the encounter rate, N denotes the total number of threat signs observed, and L signifies the total transect distance walked in kilometers.
I utilized QGIS software to map the GPS coordinates of recorded threats to the habitat of the Langur in the study area.
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RESULTS
Interviewees from Hinboun, Khounkham, and Nakai reported the presence of the Laotian Langur in their districts, while those in Yommalath and Thakhek expressed uncertainty regarding its existence there Despite suspicions that both Laotian and black Langurs may inhabit these latter districts, there is no solid evidence to confirm this Additionally, DAFO teams have verified that the Laotian Langur is absent in the Mahaxay district Table 7 provides a summary of the interview results by village, highlighting identified threats and the perceptions of interviewees concerning the species' population status.
Table 7: Occurrence and population status of primate species in PHP-NPA District Village Occurrence Population Interviewee
Pheepaeng T laotum, N siki, Macaque sp Decreased DAFO staff
Huana T laotum, N siki, Macaque sp Unknown DAFO staff
T laotum, N siki, Macaque sp Unknown DAFO staffs; villagers
T laotum, N siki, Macaque sp Decreased Villagers
Bo Neng T laotum, Macaque sp Decreased Villagers
T laotum, N siki, Macaque sp Decreased DAFO staffs; villagers
Or T laotum Decreased DAFO staffs
Kateup T laotum, N siki, Macaque sp., serow sp
Natan T laotum Macauqe sp Decreased DAFO staffs
Kuam Sam T laotum Unknown DAFO staffs
Vanghin T laotum Unknown DAFO staffs
Yommalath Kuanphan T ebenus, Macaque sp., maybe
Doi T laotum, N siki, maybe T ebenus
Phalaem T laotum, N siki, maybe T ebenus
During our study, we covered a distance of 64.1 km, observing a mean encounter rate of Langur groups—both seen and heard—at 0.432 ± 0.38 km⁻¹ Notably, encounter rates were significantly higher in the Buamlou sector compared to other areas.
Figure 16: Transects walked at study area
Estimate relative abundance of the T laotum
During our survey, we covered 14.9 km in the Konglor-Natan sector, detecting 5 groups of approximately 17 individuals, and 32.8 km in the Konglor sector, where we identified 7 groups with around 22 individuals Additionally, we explored 5 km in the Buamlou sector, finding 5 groups with about 6 individuals, and 11.4 km in the Kuankacha sector, where we detected 2 groups consisting of roughly 2 individuals Overall, I recorded both directly observed and heard Langur groups, estimating a total of 19 groups with approximately 47 individuals The highest encounter rate was noted in the Buamlou sector at 1 group/km, followed by Konglor-Natan at 0.34 group/km, Konglor at 0.21 group/km, and Kuankacha at 0.18 group/km The average encounter rate throughout the study was 0.43 group/km walked.
Table 8: Description of survey sites and transect lengths
Survey sector Trails/Transect Length (Km)
Trail 3: Poung Ta Thid Pha 2.6
Trail 9: Ang Nam Ta Ngon 2.5
Buamlou (5 km) Trail 16: Kouan Pang 3.1
Table 9: Laotian Langur encountered on transects walked in each sector
Encounter Rates (Groups Per km Walked)
The survey included both directly observed Langur groups and those identified by their vocalizations However, it was not feasible to ascertain the size, sex, or age of the individuals within these groups.
In the study area, Laotian Langur groups varied in size from 2 to 6 individuals, with the largest group (Group no 7) observed at the Ang Ta Ngon site in the central part of the TPZ of the NPA Conversely, the smallest group (Group no 1) was found at Tham Kuay in the Konglor-Natan sector A total of 35 individuals from nine groups were directly observed across the Konglor-Natan and Konglor sectors, revealing a composition of 68.57% adults (both male and female), 28.57% sub-adults, and a single juvenile, with no infants recorded The average group size of the T laotum in this area was 3.38 individuals per group.
Table 10: Record of group size of the Laotian Langur at study area
Coordinate (GPS) WGS 84 UTM Zone 48 N Adult SA JU IF Total
Key: SA = Sub-adult, JU = Juvenile, IF = Infant
Figure 17: Group size of the Laotian Langur
Figure 18: Group size of the Laotian Langur at survey sectors
I spent about 537 minutes or approximately 9 hours to observe nine groups of Langurs at study area (average 1 hour per group for direct observation) In total,
35 individuals in 9 groups were recorded Within 9 group, I found that 8 individuals were adult male, 12 was adult female and 4 adult Langurs (from Group 6 and Group
8) could not identify their sex because they flee away when the survey team encountered them, 10 was sub-adult and one was juvenile (Table 11) Based on direct observation I found that the majority composition of the Langur was mainly one male multi female groups which account for 57.14% (n=7), follow by one male one female group was 28.57% (n=7) and multi-male multi-female group was 14.28% (n=7) (Fig 19)
Table 11: Record of group composition of the Laotian Langur
AM AF SA JU IF Composition
Key: AM = Adult male; AF = Adult female; SA = Sub-adult; J = Juvenile; I= Infant; M-F
= One male with one female; M-MF = one male with multi-female; MM-MF = multi-male with multi-female, n/k = not known
Figure 19: Group composition of the Laotian Langur
This study focuses on identifying the age and sex of adult Langurs, specifically adult males and females, within the observed groups However, the sex of sub-adult, juvenile, and infant Langurs could not be determined due to challenges in observing their sexual characteristics.
G R O U P C O M P O S I T I O N O F T H E L A N G U R during the field survey Therefore, I classified sub-adults (both male and female), juvenile and infant Langurs as non-adults and adult-male and female Langurs as adults
In a study of Langur populations, it was observed that 68.57% were adults, comprising 24 individuals, while 31.42% were non-adults The average ratio of adult males to adult females was found to be 1.41:1.71 within groups, and the ratio of adult to non-adult Langurs was 2.66:1.22 Specifically, Group 1 contained one adult male and one adult female; Group 2 had one adult male, two adult females, and two juveniles; Group 3 included one adult male, two adult females, and one sub-adult; Group 4 consisted of one adult male and two adult females; and Group 5 comprised one adult male, one adult female, and one sub-adult Further details for Groups 6 and 8 were also noted.
At the Pha Soung site, I observed two adult Langurs and one sub-adult, while Group 8 consisted of two adult Langurs and one sub-adult In Group 7, I recorded two adult males, two adult females, and two sub-adult Langurs Additionally, Group 9 included one adult male, one adult female, two sub-adult Langurs, and one juvenile.
Table 12: Age-sex composition of the Laotian Langur
No Location AM AF AM:AF A NA A:NA Total
Key: AM = Adult male; AF = Adult female; A = Adult male and females; NA = non-adult (sub-adult male and female + juveniles + infants)
Figure 20: Age-sex composition of the Laotian Langur groups
4.1.2.2 Distribution of the Laotian Langur
The study area exhibited an elevation range of 32 m to 930 m above sea level, with data collected from 27 locations where Langur groups were identified This included 8 designated sleep sites, 10 areas where Langur calls were heard, and 9 locations where the groups were directly observed along the transects The elevation of all sleep sites varied significantly, as illustrated in Figure 21.
The study identified ten Langur group locations, with elevations ranging from 200 m to 670 m, and direct observations of these groups revealed elevations between 226 m and 607 m Consequently, the detected locations and sleep sites of the Langurs varied from 200 m to 670 m Notably, 50% of the sleep sites (n=8) were documented within this elevation range.
NUM B E R OF INDI VI DUA L
Adult male Adult female Adults Non-adults
37.5% (n=8) at low elevation (>250 m) and 12.5% (n=8) at high elevation (500-750 m) but did not encounter any sleeping site of the Langur at very high elevation (250 m) and 11.1% (n=9) at high elevation (500-750 m) There were on Langurs were observed at very high elevation (