INTRODUCTION
Background
Vietnam, located in Southeast Asia, spans an area of 331,689 km² and stretches 1,600 km from north to south along the eastern coast of Indochina, with altitudes ranging from sea level to 3,143 m at Mount Phan Xi Păng The country boasts rich biodiversity, with numerous newly discovered species, but faces challenges as many endangered species are threatened by deforestation, hunting, and land encroachment Notably, the northern region is home to several critically endangered primates, including a gibbon species found only in six provinces of north-central Vietnam.
Gibbons, part of the Hylobatidae family, are among the most endangered primates in Vietnam, with their populations declining faster than other primate species (Geissmann et al., 2001) These arboreal apes inhabit the tropical rainforests of Southeast Asia (Geissmann, 2000a), and hunting has significantly impacted their numbers, leading to suppressed populations even in areas with intact habitats, indicating that hunting is a primary threat Additionally, there is a lack of sufficient data on gibbon species in certain regions of central Vietnam (Nadler et al., 2007a).
Monitoring programmes are crucial for assessing the population status of conservation-concern species, particularly gibbons, which face numerous challenges These programmes play a significant role in prioritizing conservation actions by evaluating species problems and estimating total population sizes Through effective monitoring, we can track changes in gibbon populations within specific regions and identify potential threats to their survival Understanding population sizes is essential for research focused on species interactions, highlighting the importance of monitoring in conservation efforts.
2 abundance but also used to estimate density, and by extension population size, if certain assumptions are upheld (Stokes et al., 2010)
Monitoring gibbon species presents significant challenges due to the limitations of traditional methods, which often fail to provide accurate survey data This lack of precise information complicates conservation efforts (Vinh et al., 2010) Effective management of gibbons necessitates comprehensive details on their distribution and abundance, information that is frequently difficult to acquire.
Gibbons inhabit the upper canopy of broadleaf evergreen forests, making them highly arboreal creatures that are rarely seen on the ground (Sarma et al., 2013) Their swift movements in the treetops make visual detections challenging, particularly during short surveys (Vinh et al., 2010) To minimize human impact on their behavior, the use of automatic recorders in the field allows for the study of gibbon singing without direct human interaction (Muñoz-Delgado et al., 2004).
Using automatic sound recorders for surveys offers several advantages, including their effectiveness in monitoring animals that do not vocalize daily This method minimizes human disturbance compared to traditional survey techniques, making it particularly useful in challenging environments where field specialists are not required Additionally, the recordings can be easily analyzed using RAVEN PRO 1.4 sound analysis software, which allows for the creation of spectrograms and measurement of various vocal attributes.
Researchers advocate for automatic recording as the most effective method for collecting field data on animals Automated acoustic monitoring is particularly valuable for studying diverse groups of sound-producing animals and enables the detection of elusive, rare, and threatened species (Collen et al., 2009; Burbidge, A 2017).
Gibbons are known for their loud and elaborate songs, making them easily detectable with automatic recorders Since gibbons do not call every day, using autonomous recorders for monitoring is an efficient method for species observation This approach combines automated acoustic analysis with field surveys, utilizing commercially available recorders and custom call detection software Many researchers have adopted this method due to its effectiveness in studying gibbon populations.
Vietnam is home to numerous national parks and nature reserves that boast a diverse range of gibbon species Among these, the Khe Nuoc Trong proposed nature reserve stands out as a vital area for biodiversity and conservation, encompassing a 20,000-hectare section of Annamese Lowland Forest in Quang Binh Province, located in north-central Vietnam This reserve is part of a larger 82,700-hectare forest area that extends into Quang Tri Province Protecting the Khe Nuoc Trong forest is projected to sequester around 50,000 tonnes of carbon dioxide (CO2) annually over the next 30 years, highlighting its significance in environmental conservation efforts (Viet Nature, 2018).
The Khe Nuoc Trong proposed nature reserve is a critical habitat for numerous endangered species, primarily due to habitat degradation and loss This reserve is home to the Critically Endangered Sunda Pangolin (Manis javanica) and three species of Endangered primates: the Red-shanked Douc (Pygathrix nemaeus), the Southern White-cheeked Gibbon (Nomascus siki), and the Ha Tinh Langur (Trachypithecus hatinhensis) (Merriman et al., unpublished; Viet Nature, 2018).
The Khe Nuoc Trong proposed nature reserve has been the focus of various studies on its avian species and diverse flora and fauna (Tuong et al., 2018; Viet Nature, 2018; Merriman et al., unpublished) Additionally, research on the rare southern white-cheeked gibbon is limited within this area However, the reserve faces significant challenges in monitoring its biodiversity due to its expansive size and complex mountainous terrain Traditional surveying methods for gibbon species may also present various limitations.
Investors often struggle to obtain accurate information, especially when conducting research under unfavorable conditions To enhance the understanding of gibbon occurrence and distribution in the Khe Nuoc Trong proposed nature reserve, I have decided to undertake this study.
„„Identifying the occurrence and distribution of southern white cheeked-gibbon (Nomascus siki) using autonomous recorders: A case study in the Khe Nuoc Trong proposed nature reserve‟‟
Goal
To add information on the occurrence and distribution of southern white-cheeked gibbon (Nomascus siki) in Khe Nuoc Trong proposed nature reserve by using autonomous recorders.
Specific objectives
The specific objectives of this study are:
To determine the occurrence of southern white-cheeked gibbon in Khe Nuoc Trong proposed nature reserve by using autonomous recorders
To determine the distribution of southern white-cheeked gibbon in Khe Nuoc Trong proposed nature reserve by using autonomous recorders.
Research questions
Where is the occurrence of southern white-cheeked gibbon in the study site?
Where is the distribution of southern white-cheeked gibbon in the study site?
LITERATURE REVIEW
Occurrence and distribution
Occurrence, as defined by Friedmann & Regenbrecht (2001), is a subjective experience shaped by immersive virtual reality technology, reflecting the degree of a user's presence in a virtual environment Suzuki and Critchley (2012) suggest that this sense of occurrence arises from effectively managing the discrepancy between anticipated and actual sensory experiences.
Understanding the distribution and abundance patterns of organisms is crucial in ecology and wildlife conservation (Krebs, 1972) Distribution refers to how organisms are spread across an area or shared among a group These patterns can change over time due to variations in overall abundance and individual movements between habitats Distributional consistency, which includes both spatial and temporal aspects, enables researchers to measure how consistently a population is distributed across various sites while accounting for fluctuations in regional abundance (Heath et al., 2012).
Gibbon in Vietnam
In Vietnam, all gibbon species belong to the crested gibbons of the genus Nomascus, which are found across the country, ranging from the northern regions down to Ho Chi Minh City.
Six species of gibbons in Vietnam are classified as endangered or critically endangered according to the IUCN Red List of Threatened Species (IUCN, 2017) These primates are recognized in Vietnam's Red List (2007) and are protected under various governmental decisions aimed at conserving the country's rare primates, including Decision 32 (2006), Decision 170 (2013), and Decision 538 (2017) by the Prime Minister, which outlines urgent conservation activities through 2025 and a vision for 2030 Gibbons, belonging to the family Hylobatidae, are not monkeys but rather apes (Hominoidea), making them more closely related to humans They are the only apes inhabiting the Asian mainland and, like all apes, lack an external tail (Geissmann et al., 2013).
According to Eames and Robson (1993), the presence of primates in an area is typically assessed through interviews with local residents, yet there is currently no population estimate for gibbons in Vietnam, and their distribution remains unclear The southernmost confirmed records are from Quang Binh Province (Nhat, 2002), with significant populations located in Phong Nha-Ke Bang and Pu Mat National Parks (Ha et al., 2005) Notably, Pu Mat National Park has experienced a population decline of approximately 40% between 1999 and 2004 In Dak Rong Nature Reserve, Quang Tri Province, a minimum of 25 gibbon groups has been identified (Ha, 2004), though the systematic status of gibbons in this region still needs further investigation (Nadler et al., 2007a) Gibbons, which inhabit various locations across Vietnam, live in groups led by a male, comprising females and young, with the male responsible for the group's protection (Fuentes, 2000).
According to Rawson et al (2011), a new taxonomy for Vietnam gibbons was introduced, identifying seven species of Nomascus, with six species located in Vietnam and the others distributed across Cambodia, Laos, and China This classification report is the most comprehensive resource on Vietnam gibbons to date For clarity, we will refer to the scientific and English names of the Vietnam gibbons as outlined by Rawson et al (2011), with a detailed list of the six subspecies provided in Table 1.1.
Table.1.1 List of Vietnamese gibbons
No Scientific Name English Name
1 Nomascus concolor Western black gibbon
2 Nomascus nasutus Eastern black gibbon
3 Nomascus leucogenys Northern white-cheeked gibbon
4 Nomascus siki Southern white-cheeked gibbon
5 Nomascus annamensis Northern yellow-cheeked gibbon
6 Nomascus gabriellae Southern yellow-cheeked gibbon
Distribution of Southern white-cheeked gibbon in Vietnam
The Southern white-cheeked gibbon, found in southern Lao PDR and north-central Vietnam east of the Mekong River, primarily inhabits Phong Nha-Ke Bang and Pu Mat National Parks Historically, its range extended across five provinces in north-central Vietnam, with distribution limits at the Ca River and Bach Ma National Park; however, the northern limit remains uncertain, and undetected populations may still exist in these reserves Classified as one of Vietnam's most endangered primates, the Southern white-cheeked gibbon faces significant threats from habitat loss, degradation, and fragmentation due to deforestation and the expansion of rubber plantations from the 1960s to the 1980s.
The southern white-cheeked gibbon, N siki, has a restricted range, primarily in Vietnam, where it faces significant threats from hunting and ongoing population decline Despite insufficient data to quantitatively assess its trends, large populations still exist in forested areas, particularly in Quang Binh Province and along the Laos border N siki is found in Ha Tinh, Quang Binh, and Quang Tri Provinces, with documented populations in six sites, including two protected areas (Phong Nha-Ke Bang National Park and Bac Huong Hoa Nature Reserve), two proposed nature reserves (Khe Ve and Giang Man), and two state forest enterprises (Truong Son and Khe Giua) Since the first Vietnam status review of gibbons in 2000, considerable new information on the taxonomy, distribution, and ecology of N siki has emerged.
The southern white-cheeked gibbon has been recognized as a distinct species, previously classified as a subspecies of the northern white-cheeked gibbon (Nomascus leucogenys) (Geissmann, 2000a) It is one of the most endangered primates in Vietnam (Geissmann et al., 2003; Nadler et al., 2007b), with Khe Nuoc Trong proposed nature reserve being a crucial habitat that showcases original biodiversity (Ha, 2007) However, hunting is prevalent in this area, and there are no recent records of the southern white-cheeked gibbon's occurrence and distribution The species is classified as critically endangered in Vietnam's red list and globally endangered on the IUCN red list (Geissmann et al., 2001).
Vocalization of gibbons
Gibbons are known for their loud and complex vocalizations, making them easily detectable in their habitats (Geissmann, 1993) Utilizing automatic recorders to capture these calls is an effective method for monitoring gibbon populations, as it leverages the distinctive volume of their sounds (Brockelman, 1987; Brockelman and Srikosamatara).
1993) In wildlife survey people use different automatic acoustic recorders to record the sounds of animals because some animals do not produce sounds all the day
The study commenced with a survey at the designated site, followed by the installation of automatic acoustic recorders in the field These recorders are mounted on trees or suspended in the canopy to capture animal sounds Compared to traditional methods, automatic acoustic recorders provide a cost-effective solution that enhances the reliability of wildlife surveys (Zwart et al., 2014).
Geissmann and Orgeldinger (2000b) discovered that the role of duetting varies among gibbon species, leading to the possibility that a correlation between duetting and its specific functions may not be evident when comparing different species.
Cross-species comparisons may not yield correlations for the functions of duetting, even among duetting species Gibbons exhibit stable and stereotyped vocalizations, with males and females producing short phrases that are generally less stereotypic than their great-calls While female great-calls remain consistent throughout a song bout, males progressively build their phrases, starting with simple notes Notably, gibbons can recognize and respond to the great-calls of other species All gibbon species utilize a diverse array of note types, with crested gibbons (genus Nomascus) demonstrating the highest level of sex-specificity in their vocal repertoire.
10 Figure.1.1 Male and female spectrograms of the six crested gibbon species of Vietnam (Hallam et al 2011)
Nomascus spp exhibit a distinct song structure compared to other gibbons, with adult females producing only great call phrases or their fragments, while adult males create fully developed phrases featuring three different note types As part of the Hylobatidae family, crested gibbons (Nomascus) are one of four primary taxonomic groups, distinguished by unique morphologic, anatomic, karyologic, and vocal traits Their singing behavior showcases several unique characteristics that differentiate them from other gibbon species.
According to Nhat, (2002) acoustic analysis could confirm the concordance between song structure and phylogenetic relationships as obtained from mitochondrial sequence data Significant differences are found between the songs of
N nasutus, N concolor and the four southern species, N leucogenys, N siki, N annamensis and N gabriellae Although latter four species revealed only subtle differences in their songs, a detailed acoustic analysis was able to discriminate significantly between them This relation was positively correlated with their genetic relatedness found by recent molecular studies In many cases, species could be distinguished by directly inspecting the spectrograms of their songs (Wich et al.,
Acoustic analysis does not allow us to determine the ancestral origin of crested gibbons due to a lack of evidence regarding which song structure is the most primitive However, significant differences in song structure were observed between the northernmost and southernmost species, with a gradual transition noted among them.
Wich et al (2002) found that gibbon song vocalizations serve as unique vocal fingerprints for individual identification However, it remains unproven whether gibbons utilize these vocal differences to distinguish between songs from neighbors and non-neighbors While classification accuracy is high among individuals within the same site, it decreases when data from multiple sites are combined This aligns with findings by Sun et al (2007), which suggest that increased individual numbers can lead to more classification errors Using vocalization software, we analyzed the song structure of gibbons to determine the total number of individuals present.
12 of gibbons per group The sonograms could help to distinguish between the songs of male, female or juvenile white-cheeked crested gibbons (Thinh et al., 2010).
Calling time of gibbon
Gibbons are known for their early morning singing, often starting before dawn and continuing for approximately 10.30 minutes (Leighton, 1987; Geissmann et al., 2007) During these singing bouts, which typically occur from their sleeping trees, neighboring groups interact by responding to each other's calls, marking their territory boundaries (Tenaza, 1976; Xue-feng & Wu-jing, 2008) This behavior highlights the social dynamics of gibbons as they approach one another while singing.
Gibbons are known for their unique vocal behavior, where mated pairs create harmonious duets, as highlighted by Konrad and Geissmann (2004) Their singing typically occurs for up to one hour before sunrise, marking it as their primary activity during nighttime (Cheyne et al., 2008) According to Fan et al (2009), these song bouts last between 7 to 15 minutes Since gibbon groups do not vocalize daily, multiple survey days are necessary to effectively detect nearly all gibbon groups (Brockelman, 1987; Jiang et al., 2006).
Factors effecting gibbon call
Studying primate vocalizations is crucial for understanding their evolution, environmental responses, and social behaviors, as well as for developing vocalization-based surveys Primates adapt their behaviors based on various environmental factors, including light intensity, temperature, and precipitation Gibbons, for instance, sing daily throughout the year, with singing frequency influenced by seasonal changes and fruit availability Research indicates that gibbons tend to sing less on rainy days, supporting the hypothesis that rainfall inhibits their singing activities.
The frequency of gibbon singing varies among different populations and is influenced by factors such as population density, resource availability, sexual activity, and weather conditions However, most gibbon species engage in duets nearly every day.
2005) Groups of Hylobates significantly reduced calling when disturbed by loggers In Indonesia, where air quality varies seasonally with forest fires,
Hylobates albibarbis reduced singing during months of intense atmospheric smoke
Johnson et al (2003) discovered that gibbons typically sing when it is not raining, with cloud cover below 50% and minimal wind While it is acknowledged that various factors, such as weather, human disturbance, and local topography, can influence gibbon singing, there is limited research on how astronomical cues, light intensity, and air quality impact their vocalizations (Cheyne 2008; Cheyne et al., 2008).
Delgado et al (2004) suggest that human interactions can impact primate behavior, yet their study on wild gibbons, which had no direct contact with humans, minimized this influence on singing behavior Interestingly, they observed no reduction in observer-directed threats throughout the study; in fact, one group notably increased these threats, often displaying them without fear at distances of just 1 to 2 meters from observers (Crofoot et al., 2010).
Using of automatic recorder
Gibbons inhabit the upper forest canopy and are highly sensitive to human presence, making them difficult to observe during short surveys Their distinct and loud song bouts can be used for detection, as they do not require visual contact like movement in the canopy Human interactions can alter primate behavior, but utilizing automatic recorders in the field minimizes direct human contact, thereby reducing potential impacts on gibbon singing behavior.
Gibbons are elusive and challenging to observe in their natural habitat, making the use of directional microphones for recording their songs an effective field method This approach allows researchers to identify gibbon populations without disturbing them, facilitating easier study of individual groups in the dense tropical rainforests (Geissmann et al., 2003) Vocal recognition proves to be a valuable tool for surveying the critically endangered Northern white-cheeked gibbons (Nomascus leucogenys), as demonstrated by recent recordings in Vietnam (Vinh et al., 2010).
Hutto & Stutzman, (2009); Crofoot et al., (2010) suggested autonomous acoustic recorders offer an alternative not subject taxonomy of the biases of field surveys
Acoustic recorders offer a cost-effective solution for wildlife monitoring by eliminating the need for an observer, allowing for data collection in hard-to-reach habitats while minimizing disturbance and temporal bias through extended sampling These devices provide quicker and more efficient data acquisition compared to traditional human survey methods A study comparing nightjar detection through conventional human surveys and bioacoustic recordings demonstrated that automated bioacoustic recorders are superior for field data collection (Zwart et al., 2014).
Wild gibbons are known for their songs, which can be heard over distances greater than 1 km However, various factors can complicate accurate estimates, even for experienced researchers To effectively study the vocal functions and behavioral responses of entire family groups rather than just individuals, all-occurrence sampling was employed (Brockelman, 1987; Brockelman and Srikosamatara).
Infrequent vocalizations allowed for the accurate monitoring of multiple individuals simultaneously regarding their target behaviors Vocalization studies were exclusively conducted in captive settings, as wild vocalizations were seldom detected due to the significant distance between primates and observers.
Researchers advocate for the use of automatic recording as the most effective method for collecting data on animals in their natural habitats This approach aims to establish a remote monitoring system for sound-producing species through autonomous recording units that capture soundscapes Compared to traditional survey methods, automated acoustic monitoring offers numerous advantages, including the ability to study diverse taxonomic groups and detect elusive, rare, and threatened species (Collen et al., 2009; Burbidge, A 2017).
The fixed-point method effectively estimates gibbon population densities by monitoring their loud morning songs from designated listening points, making it suitable for a variety of terrestrial and aquatic habitats, including remote and rugged areas (Jahn et al., 2017; Brockelman, 1987; Brockelman and Srikosamatara, 1993) This approach also supports presence-absence surveys and the estimation of species richness and population density.
METHODS
Study area description
The research focuses on the Khe Nuoc Trong proposed nature reserve in Quang Binh Province, North-central Vietnam, situated near the Laos border at coordinates 17°55′18′′N to 17°3′34′′N and 106°32′31′′E to 106°48′27′′E This area is part of a larger 82,700 ha tract that extends into neighboring Quang Tri Province (Tuong et al., 2018).
The region features the foothills of the Annamite Mountains, with elevations exceeding 1,000 meters above sea level in the west Spanning an area of 19,898 hectares, the site is primarily covered by a diverse array of tree species typical of lowland evergreen-broadleaf forests Additionally, it is connected to the Bac Huong Hoa Nature Reserve in Quang Tri province to the south (Tuong et al., 2018).
Khe Nuoc Trong proposed nature reserve, located in the southern part of the Truong Son Important Bird Area (IBA) identified by Birdlife International Vietnam Programme in 2002, is a vital habitat for the Annamese Lowlands Endemic Bird Area's unique flora and fauna This site qualifies as an IBA under criteria A1 due to the presence of globally threatened species like Edwards’s Pheasant and Crested Argus, A2 for its restricted-range species, and A3 for biome-restricted species (Tuong et al., 2018) The predominant land cover is diverse forest, featuring lowland evergreen-broadleaf trees and a rich biodiversity that supports many endemic species (Merriman et al., unpublished) Additionally, it is recognized as the lowest continuous land in Vietnam, preserving a significant area of forest.
The lowland moist tropical evergreen forests, as identified by Tuong et al (2018), are home to white-cheeked gibbons, whose presence in the region has been recorded for several years However, a comprehensive study on the species' status in this area remains lacking Below, figure (3.1) presents images of the flora surveyed in the region.
Figure.3.1 Flora images of the KNT proposed nature reserve (Field data)
The villages in the vicinity of Khe Nuoc Trong proposed nature reserve is Ho Rum
In the regions of Ha Lec, An Bai, and surrounding areas, there are 68 households with approximately 300 residents, 78 households with 346 individuals, and 38 households housing 171 people, respectively However, these communities face challenges as numerous outsiders, including individuals from other provinces and even across the border from Laos, come to exploit the forest's resources.
Figure.3.2 Elevation map of Khe Nuoc Trong proposed nature reserve, Quang Binh
Province, Vietnam in May 2018 (Abu Bakar)
Field survey
Gibbons are known for their loud, patterned songs, which can be heard over distances greater than 2 km, making them detectable during their early morning singing sessions before and after dawn The duration of these song bouts ranges from 15 to 30 minutes, varying by species and environmental conditions To effectively monitor gibbon populations, researchers employed automatic recorders in the field, utilizing the fixed point count method to capture their calls from designated recording posts A field survey was conducted from April 14 to May 11, 2017, over 27 days, during which 53 recording posts were established to collect data on gibbon vocalizations.
Figure.3.3 Elevation map of recording posts in the Khe Nuoc Trong proposed nature reserve in May 2017 (Abu Bakar)
Recording posts were strategically placed 500 to 1000 meters apart, depending on the terrain of the study area, primarily in the western and central regions of the proposed nature reserve Automatic SM3 recorders (Wildlife Acoustic) were affixed to trees to capture gibbon calls, with the precise coordinates of each recording post documented and saved using GPS technology.
Figure.3.4 SM3 (Wildlife Acoustic) automatic recorders was attached to the trees in Khe Nuoc Trong proposed nature reserve (Field data)
In the Khe Nuoc Trong proposed nature reserve eight compartments were selected
The total surveyed area of the Khe Nuoc Trong proposed nature reserve encompasses 5,353.2 hectares, with specific habitat areas detailed in Table 3.1.
Table.3.1 Area of each sub-zone in the study area
In 53 recording posts, 16 recording posts were surveyed for one day, 12 were surveyed for 2 days and 25 were surveyed for three days Picture and other activities were minimized from which disturbance occur The set up date and collection date of the each recording post is shown in (Appendix 1)
Selecting the right season for gibbon field surveys is crucial, as weather significantly influences their vocal activity The dry season is optimal for conducting these surveys, as gibbons vocalize more frequently during this time (Rawson, 2004) Various factors impact gibbon vocalization (Cheyne et al., 2008), with poor weather or rain leading to reduced calls; thus, clear and sunny conditions are ideal for observing gibbon calls, particularly in the mornings To ensure reliable density estimates, survey periods should provide a 90% probability of detection (Brockelman, 1987) Daily weather conditions and forest types were meticulously recorded at each sampling site Each site was sampled for 1-3 consecutive days, with continuous sound recordings throughout the day Recordings were saved to a disk and compressed at half-hour intervals, and memory disks and batteries were replaced when moving between sample sites.
Data analysis and vocalization analysis Method
The analysis of recording data was conducted using RAVEN PRO 1.5 software from the Cornell Lab of Ornithology, focusing on the spectrogram of gibbons A four-hour time interval from 5 AM to 9 AM was selected for analysis, as this period is optimal for observing gibbon singing behavior.
To assess gibbon populations, the recording site's coordinates, along with the starting and ending times of detected gibbon calls, were analyzed This process enabled the identification of distinct groups and individuals in the area If the starting and ending times of the calls differed, two separate groups were recognized; conversely, if the calls occurred simultaneously at different recording posts, they were classified as a single group.
Group identification is essential in this survey, as duets that occur simultaneously or overlap in time can be easily differentiated into distinct groups The identification process involved analyzing the timing and coordinates of the calls Additionally, the specific day of singing and the duration of gibbon calls were recorded, detailing how long each pair sings throughout the day Each recording was cataloged with a recorder ID, coordinates, and compartments for further analysis (see Appendix 4).
3.3.2 Effect of weather on the singing behavior of gibbons
The singing behavior of gibbons is significantly influenced by weather conditions A survey conducted in April and May 2017 revealed that April had mostly sunny days, with only two rainy days, creating ideal conditions for gibbons to sing In contrast, May, being a monsoon month in Vietnam, experienced frequent rain, which greatly affected gibbon vocalizations Gibbons tend to sing less or not at all during rainy days, highlighting the importance of weather in their singing habits.
Vocalization analysis
Crested gibbons, residing in the upper canopy, are challenging to observe directly but are renowned for their elaborate and loud vocalizations (Geissmann, 1993) The song structures vary among species, allowing researchers to identify the number of males, females, and juveniles within gibbon groups using vocalization analysis software Distinct sonograms enable the differentiation of songs among male, female, and juvenile white-cheeked crested gibbons Utilizing RAVEN PRO 1.5 Software from the Cornell Laboratory of Ornithology, researchers can generate spectrograms to count individuals and assess minimum population density Adult females produce a recognizable great call, while males emit a multi-modulated call featuring a sequence of notes Both sexes engage in duet songs, characterized by vigorous interactive displays, while young gibbons often call alongside their parents, facilitating their identification in sonograms (Thinh et al., 2010) This specific song structure allows for easy differentiation between the sexes based on their unique sonograms.
3.4.1 Duet calls songs of Southern white-cheeked gibbon:
Gibbons exhibit unique song structures that allow for the differentiation of species and sex, with notable studies highlighting the distinct vocalizations of Nomascus (Geissmann, 2002) The Southern white-cheeked gibbon, in particular, has a unique song structure compared to other gibbon species Their duet calls, performed by mated pairs, begin with the male singing first, followed by the female harmonizing with his melody This collaborative singing showcases the intricate communication patterns of these primates.
In the analysis of the 23 male song, the male pauses his singing to incorporate a multi-modulated phrase that complements the end of the female's great call (Figure 3.5) The distinct differences in the sonograms of the male and female calls are clearly identifiable, as discussed in the following sections.
Figure.3.5 Duet call of the Sothern white-cheeked gibbon, great call is female call and short call is male call (Hallam et al., 2011)
3.4.2 Female song of Southern white-cheeked gibbon
Adult female Southern white-cheeked gibbons exclusively produce great calls, which consist of three distinct phrases The great call starts with long, slowly increasing frequency notes known as oo notes (fa), followed by bark notes (fb), and concludes with twitter notes (fc) (Geissmann, 2000a; Konrad and Geissmann, 2004) The initial phase of the great call is characterized by these unique fa notes, also referred to as oo notes in this study.
During a great call, note durations and intervals progressively decrease, leading to a transition from elongated notes to short, rapidly increasing frequency notes known as bark notes Following the peak of this acceleration, bark notes diminish into a twitter The great call is characterized as a female call phrase (Konrad and Geissmann, 2004).
3.4.3 Male song of southern-white cheeked gibbon
Adult male Southern-white cheeked gibbons (Nomascus siki) produce a complex song characterized by three distinct note types: ma, mb, and mc The song begins with a deep, resonant boom note (ma), which is typically delivered as a single note This is followed by the staccato note (mb), creating a dynamic contrast within the song's structure.
The male song features distinct staccato notes, characterized by 24 continuous repeated sounds A key element is the multi-modulated phrase (mc), which includes rapid and steep frequency modulations Adult males typically deliver this phrase, known as the coda, at or shortly after the peak of the female great call phrase Throughout a complete song bout, male phrases evolve, starting with long, minimally modulated notes that serve as precursors to the multi-modulated phrases As the song progresses, these phrases become increasingly modulated, incorporating boom notes and staccato phrases (Konrad and Geissmann).
RESULT
Gibbon calls detected
From 53 recording posts 26 calls of southern white-cheeked gibbon were detected from recordings in the proposed nature reserve In 53 recording posts, no gibbon calls were detected from 7 recorders and from 45 recording posts gibbon songs were detected The earliest song bout was started at 5:15am and the late song was started at 7:45 am No gibbon call was heard before 5:15am and after 7:45am The highest percentage of song bouts time in the morning is from 5:30am to 6:30am with the percentage of 70% calls detected in this time (Figure 4.1)
Figure.4.1 Frequency distribution of the start time of gibbon song bouts
In the Khe Nuoc Trong proposed nature reserve, 26 calls from southern white-cheeked gibbons (Nomascus siki) were recorded, primarily in the western and central regions Due to time constraints, other areas of the reserve were not surveyed Most recording posts captured gibbon calls, often detecting multiple groups due to overlapping territories and the close proximity of the posts, with a maximum of two groups recorded from a single post.
Weather has also an effect on the singing behavior of gibbons From the 27 days of recordings survey, 8 days were recorded with rain and 19 days were recorded with
Rain significantly impacts gibbon calling behavior, with gibbons singing less during rainy days compared to sunny ones During the study, gibbons started their calls later on rainy days, with only three to four duet calls lasting 4-7 minutes Out of eight rainy days analyzed, gibbon calls were detected on only three days, while no calls were heard on five days Over a 27-day survey period, 30% of the days were rainy, highlighting the correlation between rainfall and gibbon vocalization The results are visually represented in a percentage graph comparing rainy and non-rainy days.
Figure.4.2 Percentage graph of the rain and no rainy days in the survey
Distribution of gibbons in Khe Nuoc Trong proposed nature reserve
Nomascus siki has been identified in the Khe Nuoc Trong proposed nature reserve, which boasts a higher gibbon population compared to other regions in north central Vietnam These gibbons thrive in less disturbed forest areas with minimal human interaction The broadleaf evergreen forest within the reserve provides an ideal habitat, as gibbons inhabit the upper canopy of trees.
Per ce n tage o f r ai n an d n o r ai n y d ay s
Rainy and no rainy days of the survey in the April and May 2017
Figure.4.3 Elevation and comparative map of the gibbon with forest type in Khe
Nuoc Trong proposed nature reserve in May 2017 (Abu Bakar)
The study area is characterized by evergreen broadleaf forests, primarily consisting of medium and rich forest types Out of 53 recording sites, 46 were identified as medium forest and 8 as rich forest Gibbons inhabit both forest types, but the majority are found in medium forests due to the limited availability of rich forests Medium forests dominate the landscape, covering a larger portion of the study area compared to rich forests.
Figure.4.4 Elevation and forest type map of the surveyed area with recording posts in the Khe Nuoc Trong proposed nature reserve in May 2017 (Abu Bakar)
In the nature reserve, medium forest dominates the landscape, comprising 85% of the area, while rich forest accounts for only 15% This significant difference highlights the prevalence of medium forest over rich forest within the reserve.
Figure.4.5 Percentage graph of the surveyed area forest in the Khe Nuoc Trong proposed nature reserve
Our research has revealed a significant population of southern white-cheeked gibbons within the proposed nature reserve, highlighting its importance as a suitable habitat compared to other regions in central Vietnam The distribution of these gibbons is primarily concentrated in the western and central areas of the reserve, as illustrated in Figure 4.6.
Figure.4.6 Elevation and distribution map of gibbon in the KNT proposed nature reserve in May 2017 (Abu Bakar)
Per ce n tage o f for e st
Rich and medium forest in the surveyed area
Gibbon detection was conducted across six compartments of the Khe Nuoc Trong proposed nature reserve (515, 516, 517, 532, 534, 535) Compartments 516 and 517 exhibited the same percentage of gibbon calls, while the other compartments showed varying percentages The highest detection rate was in compartment 335, with seven gibbon calls, accounting for 27% of the total, whereas compartment 532 recorded the lowest with only one gibbon call, representing 4%.
Table.4.1 Percentage graph of the gibbon call detected in each compartment
S no Compartments Percentage of call detected
Structure of gibbon group
Gibbon groups can be identified through their distinct spectrograms, with the southern white-cheeked gibbon exhibiting a unique vocalization pattern The female produces the great call, while the male contributes a short call phrase, resulting in a harmonious duet Additionally, juvenile and sub-adult gibbons vocalize alongside their parents Analysis of the sonograms reveals the composition of gibbon groups, including males, females, and juveniles (see Table 4.2 and Appendix 5).
Table.4.2 Structure of the gibbon calls with recorded time
Group structure Recording call Time Recorder
Sub- Adults Total Start End
Calls Date Group structure Recording call Time
Analysis of field data revealed 26 distinct calls from the recordings, with the start and end times of the gibbon call group detailed in Table 4.2.
In a study of gibbon vocalizations, 26 calls were detected, comprising 24 duet calls involving males, females, and sub-adults, along with two solo male calls This led to the identification of 26 gibbon groups, including two solitary males, with most groups consisting of one male and one female Notably, one group featured one male and two females, while four groups included juveniles, and two groups were composed solely of males, resulting in an average group size of three (95% CI 2.11) The study revealed that males constituted 47% of the population, females 45%, and juveniles 7%, indicating a higher number of males than females The distinct song structures and spectrograms of the southern white-cheeked crested gibbon facilitated easy identification of the groups.
In a duet call, 33 sub-adult males initiate with a short phrase known as the boom note, which is subsequently joined by a female call This interaction culminates with the female's great call, followed by the male adding a multi-modulated phrase, creating a harmonious duet.
Figure.4.7 Duet call of the southern white-cheeked gibbon from recording site at
The southern white-cheeked gibbon's female responds to the male's booming call by adding her own vocalization, which follows his initial sound After she incorporates her call, the male briefly pauses, allowing the female to produce a distinct great call composed of 8 to 12 notes.
Figure.4.8.Female sonogram of Southern white-cheeked gibbon from recording site at 4:47am
The Southern white-cheeked gibbon male produces a distinctive short call phrase that includes three key components: the boom note, staccato note, and multi-modulated note The male begins its song with the boom note, which is complemented by the female's great call At the conclusion of the female's great call, the male adds a multi-modulated phrase, creating a harmonious vocal display.
Fre q u en cy Fre q u en cy
Figure.4.9 Male sonogram of the southern white-cheeked gibbon from recording site at 5:35am
DISCUSSION
Occurrence and distribution of white-cheeked crested gibbon in KNT proposed nature
The study confirmed the presence of the southern white-cheeked gibbon in the proposed nature reserve, clarifying previous uncertainties about the gibbon species in the area Data collection revealed that this species inhabits the broadleaf evergreen forest within the reserve Each gibbon species can be identified by distinct sonogram forms, with the duet call initiated by the male and joined by the female The male pauses his song during the female's great call, concluding with his own multi-modulated phrase.
Gibbons primarily sing in the early morning hours, with calls recorded between 5:00 AM and 9:00 AM In this study, the earliest call was noted at 5:15 AM, while the latest occurred at 7:45 AM on a rainy day, with the majority of calls happening between 5:30 AM and 6:30 AM The longest call duration was 19 minutes, with an average of 9 minutes and a minimum of 4 minutes during rainy conditions These findings align with Geissmann et al (2007), which reported that gibbon song bouts typically occur early in the morning, lasting about 10.3 minutes, with the earliest song starting at 5:22 AM and the last at 8:44 AM Notably, 53% of all songs began before 6:00 AM, with a median duration of 7 minutes.
Weather significantly influences gibbon calling frequency, with rain leading to a marked decrease in their vocalizations During a recent survey, it rained for eight days, and gibbon calls were detected on only three of those days, lasting between four to six minutes and consisting of just four to six duet calls This is in stark contrast to sunny days, where gibbons sing more frequently On the rainy days when calls were heard, they began later in the morning, specifically between 7:00 AM and 7:45 AM Supporting this observation, Cheyne (2008) found that during his study of 34 rainy days, no singing was recorded on 27 of those days, indicating that gibbons sing significantly less during rainy conditions.
Gibbons typically do not sing based solely on temperature, as their singing behavior is not influenced by minor temperature fluctuations Instead, the primary factor affecting their singing is rain, which can make them cold by getting them wet Therefore, rainy conditions are likely the main trigger for gibbons to begin singing.
Gibbons tend to sing less on rainy days, supporting our initial hypothesis and aligning with previous research Rainfall is frequently recognized as a significant factor that inhibits gibbon singing due to its impact on the audibility of their calls Additionally, prior rainfall has been shown to decrease the likelihood of singing the next morning Studies have also indicated that strong winds combined with rainfall further diminish the probability of gibbon calls Overall, our findings confirm that rain significantly affects gibbon singing behavior.
In the proposed nature reserve, 26 gibbon calls were detected, indicating a higher population compared to other studies, likely due to the area's broadleaf evergreen forest, which provides an ideal habitat for gibbons This forest type, characterized by a rich and medium canopy, remains largely undisturbed by human activities, allowing gibbons to thrive They prefer living in the upper canopy of these forests, which are essential for their arboreal movement The findings suggest that gibbons inhabit the broadleaf evergreen forest areas in the western and central parts of the nature reserve, covering approximately 44,824 hectares Notably, no signs of threats such as shooting or tree cutting were recorded, highlighting the area's suitability for gibbon conservation.
From 53 recording posts 26 gibbon calls were detected from 8 compartments of the proposed nature reserve The finding of this study is contrast with the finding of (Ha, 2007) who investigated 12 gibbon groups in their respective study because of having threats to the gibbon The population of gibbons in the nature reserve is higher than some other protected areas because the forest provides a good habitat The forest in the proposed nature reserve is broadleaf evergreen forest and provides
37 a good source of food for gibbons In Kon Cha Rang Nature Reserve ( Vinh et al.,
In 2010, research identified 21 gibbon groups, aligning with previous findings by Geissmann et al (2007), who noted eight groups with solitary individuals Gibbon populations are influenced by habitat quality; areas that are suitable and undisturbed by human activities tend to support larger populations Additionally, weather conditions significantly affect gibbon vocalizations, making it crucial to select optimal weather for surveys to ensure accurate data collection.
The maximum number of gibbons observed in a group was three, with a 95% confidence interval of 2.11 This finding aligns with the research by Le Xuan Canh et al (2008), who reported a group of three southern white-cheeked gibbons in the Khe Giua state forest enterprise in Quang Binh province, central Vietnam.
The typical group composition of the southern white-cheeked gibbon consists of an adult male, an adult female, and their sub-adults This finding aligns with previous studies, such as Ha et al (2011), which reported groups of 3 to 4 individuals However, in the Nakai-Nam Theun National Protected Area, Nanthavong (2013) observed an average group size of 4, which is greater than my findings Additionally, Geissmann et al (2007) identified one adult male and one to three great-call-singing individuals, likely including adult females and immature members In contrast, my observations revealed only one adult male, one adult female, and one sub-adult Other surveys, like Vinh et al (2010), also noted groups consisting of one male and one female.
Research indicates variability in gibbon group structures, influenced by factors such as the presence of new pairs or sub-adults leaving to find mates The southern white-cheeked gibbon typically comprises males, females, and sub-adults, yet its specific group structure remains largely unknown, according to the IUCN Red List My study observed a lower group structure compared to other research, potentially due to the young age of the infants, which may affect their vocalization.
38 birth after a long period of time Weather has also effect on the singing of the gibbon so maybe be because of weather condition
The proposed nature reserve is home to a significant population of the endangered Southern white-cheeked gibbon, listed on the IUCN Red List To ensure their survival, it is crucial to protect their habitat from human disturbances Our study, focused on the western and central areas of the reserve, indicates that gibbons may also inhabit other regions, highlighting the need for further research to conserve their habitat and that of other wildlife in the reserve.
CONCLUSION
During a 27-day survey at the Khe Nuoc Trong proposed nature reserve, 26 southern white-cheeked gibbon calls were recorded The study involved 53 recording posts, with gibbon calls detected at 46 of them, while 7 posts showed no gibbon activity The total surveyed area was 53,532 hectares, of which 44,824 hectares were identified as suitable habitat for gibbons.
The Khe Nuoc Trong proposed nature reserve, located in the western and central regions of Vietnam, is home to 26 groups of gibbons Notably, the population of southern white-cheeked gibbons in this reserve is higher than that found in other areas of central Vietnam, highlighting its significance for the conservation of this species.
Weather significantly influences gibbon singing behavior, with adverse conditions such as rain leading to reduced vocalization Consequently, gibbons are less likely to be detected during acoustic surveys in poor weather A field survey conducted in April and May 2017 revealed that while April experienced minimal rainfall, May was dominated by rain due to Vietnam's monsoon season.
In 27 days of the survey, 8 days were recorded with rain and 19 days were recorded with no rain
The study area consists entirely of broadleaf evergreen forest, providing an ideal habitat for gibbons Within this region, 15% of the forest is classified as rich forest, while 85% is categorized as medium forest Among the eight compartments studied (515, 516, 517, 532, 533, 534, 535, and 536), compartment 515 recorded the highest percentage of gibbon calls at 27%, whereas compartment 532 had the lowest at just 4%.
The gibbon population in the proposed nature reserve surpasses that of several other regions Our survey focused on the western and central sections of the reserve, highlighting the need for further research to protect the habitat of this species and other wildlife, as well as to develop effective conservation strategies.
Firstly, I would like to express my sincere gratitude to my advisor Assoc Prof Dr
I would like to express my heartfelt gratitude to Assoc Prof Dr Vu Tien Thinh of Vietnam National University of Forestry for his unwavering support throughout my Master’s research His patience, motivation, and vast knowledge were invaluable during the research and writing of my thesis Dr Thinh's open-door policy provided me with guidance whenever I faced challenges or had questions While he encouraged me to take ownership of my work, he also expertly directed me whenever I needed assistance I truly appreciate his readiness to help me throughout this entire research process.
I would like to express my gratitude to Mr Tran Van Dung and Nguyen Hai Ha from the Department of Wildlife at Vietnam National University of Forestry for their valuable insights and encouragement Their challenging questions inspired me to expand my research and explore various perspectives.
I would like to extend my heartfelt gratitude to my parents and friends for their unwavering support and encouragement during my academic journey and the process of researching and writing this thesis This achievement would not have been possible without their invaluable assistance Thank you.
Agmen, F.L., 2014 Conservation strategies for Delacour‟s langur (Trachypithecus delacouri) in Vietnam: Behavioural comparisons and reviewing a release
Bartlett, T.Q., 2015 The Gibbons of Khao Yai: Seasonal Variation in Behavior and
Brockelman, W., 1987 Methods of surveying and sampling forest primate populations Primate conservation in the tropical rain forest 23–62
Brockelman, W.Y., Srikosamatara, S., 1993 Estimation of density of gibbon groups by use of loud songs American Journal of Primatology 29, 93–108
Burbidge, A, 2016 Use of sound recording devices in wildlife survey Science and
Conservation Division: Departments of parks and wildlife
Cọsar, C., Byrne, R., Young, R.J., Zuberbỹhler, K., 2012 The alarm call system of wild black-fronted titi monkeys, Callicebus nigrifrons Behavioral Ecology and Sociobiology 66, 653–667
Cheyne, S.M., 2008 Effects of meteorology, astronomical variables, location and human disturbance on the singing apes: Hylobates albibarbis American
Journal of Primatology: Official Journal of the American Society of Primatologists 70, 386–392
Cheyne, S.M., Thompson, C.J., Phillips, A.C., Hill, R.M., Limin, S.H., 2008
Density and population estimate of gibbons (Hylobates albibarbis) in the
Sabangau catchment, Central Kalimantan, Indonesia Primates 49, 50–56 Collen, B., Loh, J., Whitmee, S., McRAE, L., Amin, R., Baillie, J.E., 2009
Monitoring change in vertebrate abundance: the Living Planet Index Conservation Biology 23, 317–327
Coudrat, C., Nanthavong, C., Ngoprasert, D., Suwanwaree, P., Savini, T., 2015
Singing patterns of white-cheeked gibbons (Nomascus sp.) in the Annamite
Mountains of Laos International Journal of Primatology 36, 691–706
Crofoot, M.C., Lambert, T.D., Kays, R., Wikelski, M.C., 2010 Does watching a monkey change its behaviour? Quantifying observer effects in habituated wild primates using automated radiotelemetry Animal Behaviour 80, 475–
Dooley, H.M., Judge, D.S., Schmitt, L.H., 2013 Singing by male and female Kloss gibbons (Hylobates klossii) in the Peleonan Forest, Siberut Island, Indonesia Primates 54, 39–48
Eames, J.C., Robson, C.R., 1993 Threatened primates in southern Vietnam Oryx
Erkert, H.G., 2003 Chronobiological aspects of primate research Field and laboratory methods in primatology Cambridge University Press, Cambridge 252–270
Fan, P., Ni, Q., Sun, G., Huang, B., Jiang, X., 2009 Gibbons under seasonal stress: the diet of the black crested gibbon (Nomascus concolor) on Mt Wuliang, Central Yunnan, China Primates 50, 37
Fan, P.-F., Fei, H.-L., Luo, A.-D., 2014 Ecological extinction of the critically endangered northern white-cheeked gibbon Nomascus leucogenys in China
Fuentes, A., 2000 Hylobatid communities: changing views on pair bonding and social organization in hominoids American journal of physical anthropology
Geissmann, T., 2002 Duet-splitting and the evolution of gibbon songs Biological
Geissmann, T., 2000a Vietnam Primate Conservation Status Review 2000: Part 1:
Gibbons Fauna & Flora International, Indochina Programme
Geissmann, T., 2000b Gibbon songs and human music from an evolutionary perspective The origins of music 103–123
Geissmann, T., 1993 Evolution of communication in gibbons (Hylobates spp.)
PhD thesis, University of Zurich
Geissmann, T., Bohlen-Eyring, S., Heuck, A., 2005 The male song of the Javan silvery gibbon (Hylobates moloch) Contributions to Zoology 74, 1–25 Geissmann, T., Dang, N.X., Lormée, N., Momberg, F., 2003 Status review of gibbons in Vietnam Asian Primates 8, 10–12
Geissmann, T., Grindley, M., Ngwe, L., Saw, S., Thet, N., Saw, B., Momberg, F.,
2013 The conservation status of hoolock gibbons in Myanmar Gibbon Conservation Alliance, Zürich, Switzerland
Geissmann, T., Hoang, T.D., Trung, L., Tallents, L., 2007 A brief survey for crested gibbons in Bach Ma National Park, central Vietnam Gibbon J 3, 43–
Geissmann, T., Orgeldinger, M., 2000a The relationship between duet songs and pair bonds in siamangs, Hylobates syndactylus Animal Behaviour 60, 805–
Geissmann, T., Orgeldinger, M., 2000b The relationship between duet songs and pair bonds in siamangs, Hylobates syndactylus Animal Behaviour 60, 805–
Geissmann, T., Thanh, V.N., Xuan, T., NAM, V., 2001 Preliminary results of a primate survey in northeastern Vietnam, with special reference to gibbons Asian Primates 7, 0–4
Ha, N.M., 2007 Survey for southern white-cheeked gibbons (Nomascus leucogenys siki) in Dak Rong Nature Reserve, Quang Tri Province, Vietnam
Ha, N.M., Hoang, T.M., Anh, P.T., Hung, L.M., Son, N.T., Van Dat, N., Huy, D.Q.,
2005 Status of white cheek-crested gibbon (Nomascus leucogenys) in north central of Vietnam Center for Natural Resources and Environmental Studies, Hanoi, Vietnam
Ha, N.M., Tuoc, D., Dung, L.V., 2011 A survey of white-cheeked gibbons
(Nomascus leucogenys) and large mammals (Mammalia) in Xuan Nha
Nature Reserve and Sop Cop Nature Reserve, Son La Province Centre for Natural Resources and Environmental Studies, Hanoi, Vietnam
Hallam, C., Roos, C., Hammerschmidt, K., 2011 Concordance between vocal and genetic diversity in crested gibbons BMC evolutionary biology 11, 36 Harding, L.E., 2012 Nomascus leucogenys (Primates: Hylobatidae) Mammalian
Harrison, M.E., Cheyne, S.M., Sulistiyanto, Y., Rieley, J.O., 2007 Biological effects of smoke from dry-season fires in non-burnt areas of the Sabangau
43 peat swamp forest, Central Kalimantan, Indonesia Presented at the Carbon- climate-human interaction on tropical peatland Proceedings of The International Symposium and Workshop on Tropical Peatland, Yogyakarta, pp 27–29
Heath, J.P., Montevecchi, W.A., Esler, D., 2012 A Method for Quantifying
Consistency in Animal Distributions Using Survey Data PloS one 7, e44353 Huaiqing, D., Huamei, W., Jiang, Z., 2016 Sound spectrum characteristics of
Eastern Black Crested Gibbons North-Western Journal of Zoology
In the study by Hutto and Stutzman (2009), a comparison of point-count results between human observers and autonomous recording units was conducted, highlighting the effectiveness of technology in ornithological research Similarly, Jahn et al (2017) demonstrated that automated sound recognition can enhance our understanding of the behavioral ecology of tropical birds, showcasing the potential of innovative methods in wildlife studies.
Jenny Merriman, Pham Tuan anh, Trai Le Trong, Roger Safford, n.d Khe Nuoc
Jiang, X., Luo, Z., Zhao, S., Li, R., Liu, C., 2006 Status and distribution pattern of black crested gibbon (Nomascus concolor jingdongensis) in Wuliang Mountains, Yunnan, China: implication for conservation Primates 47, 264–
Johnson, A., Singh, S., Duangdala, M., Chanthasone, B., Namsombath, T.,
Hedemark, M., 2003 A preliminary survey for gibbon and other primates in the Nam Ha National Protected Area, Lao PDR
Konrad, R., Geissmann, T., 2004 Vocal diversity and taxonomy of the crested gibbons (genus Nomascus) in Cambodia
Krebs, C.J., 1972 The experimental analysis of distribution and abundance
Ecology New York: Harper and Row
Le Xuan Canh, T.R., Hai, D.T., Timmins, R., 2008 Trachypithecus hatinhensis In:
IUCN 2008 2008 IUCN Red List of Threatened Species
Downloaded on 19 January 2009 The IUCN Red List of
The eastern black crested gibbon (Nomascus nasutus), a critically endangered species, has been rediscovered in China, highlighting the urgent need for conservation efforts Research by Lok et al (2008) provides preliminary insights into the population size, ecology, and conservation status of this species, emphasizing the importance of territoriality and monogamy in gibbon societies as discussed by Leighton (1987) These findings underscore the significance of habitat preservation and targeted conservation strategies to protect the future of the eastern black crested gibbon.
Muủoz-Delgado, J., Corsi-Cabrera, M., Canales-Espinosa, D., Santillỏn-Doherty,
A.M., Erkert, H.G., 2004 Astronomical and meteorological parameters and rest–activity rhythm in the Spider monkey Ateles geoffroyi Physiology & behavior 83, 107–117
Nadler, T., Long, H.T., Thanh, V.N., Roos, C., Hai, D.T., Duc, H.M., Dang, N.X.,
Covert, H.H., Streicher, U., Workman, C., 2007a Vietnamese Journal of Primatology
Nadler, T., Thanh, V.N., Streicher, U., 2007b Conservation status of Vietnamese primates Vietnamese Journal of Primatology 1, 7–26
Nanthavong, C., 2013 Chanthalaphone, N., 2013 Singing behaviour and population estimates of the endangered southern white-cheeked gibbon
(Nomascus siki) in nakai-nam theun national protected area, Lao pdr
Nature, Viet., 2018 Progress report to Selective Asia – February 2018
Nhat, P., 2002 Primates of Vietnam Hanoi: Agriculture Publishing House
Rawson, B., 2004 Vocalisation patterns in the yellow-cheeked crested gibbon
(Nomascus gabriellae) Conservation of primates in Vietnam 130–136
Rawson, B.M., Clements, T., Hor, N.M., 2009 Status and conservation of yellow- cheeked crested gibbons (Nomascus gabriellae) in the Seima Biodiversity Conservation Area, Mondulkiri Province, cambodia, in: The Gibbons Springer, pp 387–408
Rawson, B.M., Insua-Cao, P., Ha, N.M., Thinh, V.N., Duc, H.M., Mahood, S.,
Geissmann, T., Roos, C., 2011 The conservation status of gibbons in Vietnam Fauna & Flora International/Conservation International, Hanoi, Vietnam 13–116
Sarma, K., Kumar, A., Krishna, C.M., Tripathi, O., Gajurel, P., 2013 Ground feeding observations on corn (Zea mays) by eastern hoolock gibbon
Schubert, T., Friedmann, F., Regenbrecht, H., 2001 The experience of presence:
Factor analytic insights Presence: Teleoperators & Virtual Environments 10, 266–281
Seth, A.K., Suzuki, K., Critchley, H.D., 2012 An interoceptive predictive coding model of conscious presence Frontiers in psychology 2, 395
Stokes, E.J., Johnson, A., Rao, M., 2010 Monitoring wildlife populations for management Wildlife Conservation Society and the National University of Laos, Vientiane
Sun, G., Huang, B., Guan, Z., Geissmann, T., Jiang, X., 2011 Individuality in male songs of wild black crested gibbons (Nomascus concolor) American journal of primatology 73, 431–438
Tenaza, R.R., 1976 Songs, choruses and countersinging of Kloss‟ gibbons
(Hylobates klossii) in Siberut Island, Indonesia Zeitschrift für
Tuong, N.X., Le Trong Trai, Nghia, H.V., 2018 The Avifauna of the Khe Nuoc
The Proposed Natural Reserve in Quang Binh Province, Central Vietnam, is highlighted in a 2010 population survey of white-cheeked crested gibbons conducted by Van Ngoc Thinh, L.V.H., Dung, N.T., and Roos, C This survey covers both Ke Go Nature Reserve in Ha Tinh Province and Khe Net Proposed Nature Reserve in Quang Binh Province, underscoring the significance of these areas for biodiversity conservation The research was supported by Fauna & Flora International, Conservation International, and the German Primate Centre in Hanoi, Vietnam.
Van Ngoc Thinh, M.A., Thanh, V.N., Roos, C., 2010 A new species of crested gibbon, from the central Annamite mountain range Vietnamese Journal of Primatology 1, 1–12
The article by Van Ngoc Thinh et al (2010) explores the unique vocal characteristics specific to crested gibbons (Nomascus spp.), highlighting the importance of these traits in understanding their behavior and conservation needs Published in the book "Conservation of Primates in Indochina," edited by T Nadler, BM Rawson, and Van Ngoc Thinh, this research emphasizes the role of vocalizations in the social dynamics of gibbons, contributing to ongoing conservation efforts in Vietnam.
Vinh, L.Q., Thinh, V.T., Hai, D.T., Huy, D., Manh, N., Trinh, B., 2010 Survey of
Northern Buff-cheeked Crested Gibbon (Nomascus annamensis) in Kon Cha Rang Nature Reserve Fauna and Flora
Vu Tien, T., Le Thi, D., Tran Van, D., Nguyen Thi, H., Nguyen Chi, T., Dong
Thanh, H., Nguyen Dac, M., Giang Trong, T., Nguyen Huu, V., Thao A, T.,
2017 Application of automatic recorder and sound analysis in surveying the presence and distribution of bird species in Ngoc Linh nature reserve, Quang Nam province
Vu, T.T., Tran, V., Giang, T.T., Nguyen, H., Nguyen, D., Nguyen, C., Doherty, P.,
2016 A mark-recapture population size estimation of southern yellow- cheeked crested gibbon Nomascus gabriellae (Thomas, 1909) in Chu Yang sin National Park, Vietnam Asian Primate Journal 6, 33–42
Wich, S., Assink, P., Becher, F., Sterck, E., 2002 Playbacks of loud calls to wild
Thomas langurs (Primates; Presbytis thomasi): the effect of familiarity
Zwart, M.C., Baker, A., McGowan, P.J., Whittingham, M.J., 2014 The use of automated bioacoustic recorders to replace human wildlife surveys: an example using nightjars PloS one 9, e102770 https://iucnredlist.org/
Appendix.1 Data of the recording posts in Khe Nuoc Trong proposed nature reserve
No ID recorders X Y Elevation Date to set up
No ID recorders X Y Elevation Date to set up
No ID recorders X Y Elevation Date to set up
Slope Weather Temp Collection Weather Temp
1 SM305135 TXB mount side 6-May-2017 69 gloomy 24 5/7/2017 sunny 27
2 SM305135 RTB mount side 7-May-2017 281 sunny 30 5/9/2017 sunny 28
3 SM305188 TXB mount side 9-May-2017 259 rainy 28 5/7/2017
4 SM305188 RTB mount side 6-May-2017
5 SM305188 RTB mount side 7-May-2017 68 sunny 30 5/9/2017 no rain
6 SM305135 RTB mount side 9-May-2017 177 rainy 28 5/7/2017 sunny 28
7 SM30537 RTB mount side 6-May-2017 250 24 5/7/2017 sunny 26.5
8 SM30537 RTB mount side 7-May-2017 80 sunny 30 5/9/2017 gloomy 20.5
APPENDIX.2 Data of the recording posts of Khe Nuoc Trong proposed nature reserve with forest type, weather, slope and temperature
Slope Weather Temp Collection Weather Temp
9 SM30537 RTB mount side 9-May-2017 90 tiny rain 29 5/7/2017 no rain 24.5
10 SM304785 rich forest mount side 6-May-2017 40 sunny 30 5/7/2017
11 SM304785 mount side 7-May-2017 140 sunny 30 5/9/2017 rainy 21
12 SM304785 RTB mount side 9-May-2017 252 rainy 28 5/7/2017 sunny 28.5
13 SM30537 RTB mount side 2-May-2017 250 sunny 30 5/2/2017 sunny 27
TXN (near road) mount side 2-May-2017 57 no rain, windy 29 5/2/2017 gloomy, fog 23
TXN (near road ) mount side ( HCM road) 2-May-2017 19 no rain, windy 29 5/2/2017 windy, light sunny 24
16 H4N TXB top, peak 3-May-2017 sunny 24 5/3/2017 sunny 28
Slope Weather Temp Collection Weather Temp
17 M-305135 TXB mount side 2-May-2017 45 sunny 29.5 5/4/2017 25
18 SM304785 2-May-2017 330 sunny 29 5/2/2017 windy , light sunny
19 SM304785 RTB mount side 2-May-2017 79 sunny 29 5/4/2017 21
20 SM305135 RTB Top, Peck 28-Apr-2017 90 rainy 22.5 4/29/2017 21
21 SM305135 TXB mount side 29-Apr-2017 91 gloomy 26.5 5/1/2017 21
22 SM 304785 RTB mount side 28-Apr-2017 73 rainy 27 4/29/2017 21
23 SM 304785 RTB mount side 29-Apr-2017 175 sunny 29.5 5/1/2017 24
24 H4N TXB mount side 30-Apr-2017 170 no rain 27 4/30/2017 24
25 H4N TXB mount side 1-May-2017 170 windy, no 27 5/1/2017 25
Slope Weather Temp Collection Weather Temp rain
26 SM305188 TXB mount side 28-Apr-2017 12 rainy, fog 22 4/29/2017 24
27 SM305188 TXB mount side 29-Apr-2017 159 shade, no rain, no sun
28 SM 30537 RTB top, peak 28-Apr-2017 fog, rainy 22 4/29/2017 sunny 28
East mount side 29-Apr-2017 90 fog, gloomy 23 5/1/2017 sunny 28
TXB soil mount mount side 19-Apr-2017 60 sunny 26.5 4/21/2017 28
TXB soil mount mount side 21-Apr-2017 123 27 4/23/2017 sunny 26
Slope Weather Temp Collection Weather Temp
32 SM305135 TXB mount side 23-Apr-2017 91 25.5 4/25/2017 rainy
33 SM305135 TXB mount side 14-Apr-2017 145 shady 23 4/15/2017 no rain
34 SM30537 TXB mount side 14-Apr-2017 145 rainy, fog 20 4/14/2017 27
35 SM305135 TXB mount side 17-Apr-2017 0 no rain 22.5 4/17/2017 21
36 SM305135 TXB mount side 17-Apr-2017 136 sunny 28 4/19/2017 24
37 SM305135 RTB mount side 21-Apr-2017 275 light sunny 26 4/23/2017 sunny 27
East mountain side 23-Apr-2017 270 fog, gloomy 23 4/25/2017 rainy 21
39 SM 30537 RTB mount side 17-Apr-2017 sunny 28 4/17/2017 23.5
Slope Weather Temp Collection Weather Temp
40 SM 30537 RTB mount side 17-Apr-2017 270 light sunny 23 2/19/2017
(TXB) mount side 14-Apr-2017 tiny rain 21 4/14/2017
43 SM305188 near road 14-Apr-2017 tiny rain 21 4/14/2017
44 SM304785 near road mount side 14-Apr-2017 fog, tiny rain 21 4/14/2017
45 SM305135 near road mount side 14-Apr-2017 190 tiny rain, fog 20 4/14/2017
46 H4N TXB mount road 18-Apr-2017 sunny 24 4/18/2017
Slope Weather Temp Collection Weather Temp
49 H4N TXG mount road 20-Apr-2017 windy, no rain 24 4/20/2017
50 SM30537 TXG mount road 14-Apr-2017 102 no rain 26 15/4/2077
51 SM305188 TXB mount road 17-Apr-2017 252 sunny 28 4/17/2017
52 H4N TXB mount road 17-Apr-2017 sunny 28 4/17/2017
53 SM305188 TXG mount road 17-Apr-2017 sunny 28 4/17/2017
54 SM305188 TXG mount road 19-Apr-2017 sunny 25 2/21/2017
55 SM305188 TXB mount road 21-Apr-2017 sunny 27 4/23/2017
56 SM305188 TXB mount side 23-Apr-2017 170 no rain
57 H4N TXG mount side 21-Apr-2017 sunny, 26 4/21/2017
Slope Weather Temp Collection Weather Temp windy
58 H4N TXB mount side 24-Apr-2017 174 tiny rain 21 4/24/2017
59 H4N mount side 26-Apr-2017 sunny, windy 24
60 SM 304785 rich forest mount side 19-Apr-2017 130 sunny 25 4/21/2017
61 SM 304785 RTB mount side 21-Apr-2017 130 sunny 27 4/23/2017
62 SM 304785 rich forest mount side 23-Apr-2017 40 sunny 25 4/25/2017
TXG= rich forest, TXB= Medium forest, RTB= Medium forest
Appendix.3 Summary table of gibbon call detected in Khe Nuoc Trong proposed nature reserve from the recordings posts
Days of gibbon call heard
Day1 Day 2 Day3 Starting date Ending date
1: Gibbon detected on the day of the investigation
0: No gibbon detected on the day
Blank: Recorder was not activate
Appendix.4 Summary of gibbon calls recorded during the survey
Time of call Date of recordings Recording Id Compar tments Starting Ending
Time of call Date of recordings Recording Id Compar tments
Appendix.5 Sonogram of 20 different groups calls of southern white-cheeked gibbons from the recording of Khe Nuoc Trong Proposed nature reserve
Sonogram.1 Two females and one male Sonogram.2 One male and one female Time:5h:46-6h:04 Time:5h:35-5h:51
Sonogram.1 One females and one male Sonogram.2 One male and one female Time:6h:11-6h:28 Time:5h:41-5h:57
Sonogram.1 One females and one male Sonogram.2 One male and one female Time:5h:46-6h:04 Time:5h:33-5h:51
Sonogram.1 One females and one male Sonogram.2 One male and one female Time:5h:43-6h:03 Time:5h:18-5h:39
Sonogram.1 One females and one male Sonogram.2 One male and one female Time:5h:47-6h:07 Time:5h:50-6h:06
Sonogram.1 One females and one male Sonogram.2 One male and one female Time:5h:46-6h:05 Time:5h:37-5h:56
Sonogram.1 One females and one male Sonogram.2 Male, femaleand sub-adult Time:5h:37-5h:57 Time:6h:05-6h:19