INTRODUCTION
Birds (Aves) are endothermic vertebrates characterized by feathers, toothless beaked jaws, hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight yet strong skeleton Their bodies are covered with feathers and equipped with wings, which serve functions such as flight, temperature regulation, and display With approximately 9,000 species classified into 24 orders and 146 families, birds represent the most diverse class of endothermic vertebrates, encompassing both mammals and birds Vietnam is renowned for its rich bird diversity, hosting a total of 848 species, including 12 endemic species such as the Annam partridge, which are easily observable and identifiable due to their diurnal activity.
The avian diversity includes notable species such as the Arborophila merlini, Chestnut-eared laughingthrush (Garrulax Konkakinhensis), Collared laughingthrush (Garrulax yersin), Edwards’ pheasant (Lophura edwardsi), Golden-winged laughingthrush (Garrulax ngoclinhensis), Grey-crowned crocias (Crocias langbianis), Orange-breasted laughingthrush (Garrulax annamensis), Pale-throated wren-babbler (Spelaeornis kinneari), White-throated wren-babbler (Rimator pasquieri), Vietnamese Greenfinch (Carduelis monguilloti), Vietnamese Cutia (Cutia legalleni), and Black-crowned Fulvetta (Alcippe klossi); among these, nine species are rare or accidental sightings Importantly, 43 species within this group are classified as globally threatened, underscoring the need for targeted conservation efforts (birdlist.org).
Ngoc Linh (Quang Nam) Nature Reserve, located in Tra Leng, Tra Don, Tra Tap, Tra Cang, and Tra Linh communes in Nam Tra My District, Quang Nam Province, is a vital habitat for diverse bird species and endemic flora and fauna Positioned on the eastern side of Mount Ngoc Linh, this reserve shares its western face with Ngoc Linh (Kon Tum) Nature Reserve in Kon Tum Province The reserve is renowned for its high levels of endemism, supporting plant species such as Pinus dalatensis and Panax vietnamensis that are unique to Vietnam Additionally, it is home to the recently discovered endemic mammal, the Annamite Muntjac (Muntiacus truongsonensis), and hosts notable bird species like the Golden-winged Laughingthrush, highlighting its importance for biodiversity conservation in Vietnam.
(Garrulax ngoclinhensis), whose known global range is restricted to the central Annamites
Ngoc Linh (Quang Nam) Nature Reserve is designated as part of the Kon Tum Plateau Endemic Bird Area (EBA), owing to the presence of the Golden-winged Laughingthrush and three other restricted-range bird species, making it Vietnam's newest EBA as identified by Tordoff et al (2000) Additionally, combined with adjacent regions of Ngoc Linh (Kon Tum) Nature Reserve, the site qualifies as an important Bird Area (IBA), highlighting its significance for avian conservation (Tordoff et al., 2002) The reserve hosts a diverse bird population, with 194 species across 33 families and 11 orders, underlining its rich avifaunal biodiversity.
10 species in Red book Vietnam; 8 species in IUCN; 09 species in Decree 32
Ngoc Linh Nature Reserve in Quang Nam province has been the focus of numerous bird species studies, including research by Tordoff et al (2000, 2002) and Le Trong Trai (1999) However, most of these surveys were conducted over a decade ago, highlighting a significant gap in current avian data for the area.
Ngoc Linh Nature Reserve faces significant challenges in monitoring its biodiversity due to its vast area and numerous high mountains Traditional bird survey methods often encounter limitations, leading to inaccurate data and complicating conservation efforts Additionally, some survey techniques may harm the bird populations Conducting research under adverse weather conditions or at night further hampers data collection, posing difficulties for investors and conservationists alike.
Effective management of endangered bird species relies on detailed information about their distribution and abundance, which is often difficult to obtain Since many bird species communicate through sounds, automated sound recorders offer a practical solution for long-term, low-effort data collection This emerging method uses autonomous acoustic recorders combined with specialized software to automate the detection, classification, and analysis of bird calls Widely available and efficient, these recorders enable large-scale monitoring of bird populations, especially when integrated with custom call detection algorithms, streamlining conservation efforts and enhancing data accuracy.
2013) This method was used in many researches on bird in many other different countries However, it is not a common method in Vietnam
To obtain more accurate information on the presence and distribution of bird species in Ngoc Linh Nature Reserve, I initiated a comprehensive research study This effort aims to provide reliable data on avian biodiversity within this protected area, supporting effective conservation strategies.
“Application of automatic recorder and sound analysis in surveying the presence and distribution of targeted bird species in Ngoc Linh Nature Reserve, Quang Nam province”
STUDY GOAL AND OBJECTIVE
Goal
Applying automatic recorder and sound analysis method in surveying birds, providing information for the study and protection of bird species in Ngoc Linh Nature Reserve, Quang Nam Province.
Objectives
1 Determining the presence of targeted bird species in Ngoc Linh Nature Reserve, Quang Nam Province
2 Determining the distribution of targeted bird species in Ngoc Linh Nature Reserve, Quang Nam Province.
STUDY SITES AND METHODOLOGY
Selection of study site
Ngoc Linh Nature Reserve covers an area of 18,430 hectares, with coordinates 15°00'
Ngoc Linh Nature Reserve, located in Tra Leng, Tra Don, Tra Tap, Tra Cang, and Tra Linh communes in Nam Tra My district, Quang Nam Province in Central Vietnam (15°15' N, 107°56'–108°07' E), boasts exceptional biodiversity compared to other Vietnamese national parks The reserve offers diverse natural conditions that support a wide range of plant and animal species, including many endemic and Red-Listed species It is renowned for its unique flora, particularly its upper montane forests and the nationally famous endemic medicinal plant, Vietnamese Ginseng (Panax vietnamensis), highlighting its ecological and medicinal importance (Tordoff et al., 2000).
Figure 3.1 Map of Ngoc Linh Nature Reserve a Geographical condition
Ngoc Linh Nature Reserve is located in Kon Tum Plateau which is a dominant mountain range including a series of sharp peaks compared with other areas in the Central
Ngoc Linh Nature Reserve features a rugged highland terrain characterized by relatively isolated mountain blocks, with slopes typically ranging from 40° to 45°, and reaching up to 60°-65° in the northern regions The highest peak, Ngoc Linh Mountain, stands at 2,598 meters above sea level, complemented by other notable peaks such as Ngoc Lepho (2,070 m) and Ngoc Pa (2,251 m) located in the east-south of the reserve Erosion has influenced the landscape, resulting in an average slope that declines to between 900 and 1200 meters in the north-western part of the reserve (Tordoff et al., 2000).
The area features two main river systems: the Tranh River and Leng River, with the Tranh River originating in the southern part of the reserve and flowing north into the Thu Bon River, an important waterway in Quang Nam Province Leng River, a tributary of the Tranh River, originates from the northwest of Ngoc Linh Nature Reserve These river and stream systems are short, narrow, steep, and fast-flowing, making them susceptible to soil erosion, especially in areas with low forest cover During the rainy season, sudden and frequent floods cause riverbank erosion and damage irrigation infrastructure, while in the dry season, most rivers dry up, posing challenges for agriculture and domestic water supply for local communities (Tordoff et al., 2000).
Ngoc Linh Nature Reserve features four major soil types essential to its ecosystem, including Highland Alitic Humus Soil, Feralit Humus Soil, Feralit Soil, and River and Stream Alluvial Soil These diverse soils support a rich variety of plant and animal life, highlighting the ecological significance of the reserve Understanding the distribution of Highland Alitic Humus and Feralit soils is crucial for conservation efforts, as they influence vegetation growth and soil fertility Meanwhile, River and Stream Alluvial Soil plays a vital role in maintaining the hydrological balance and supporting local biodiversity within Ngoc Linh Nature Reserve.
Highland Alittic Humus Soil is typically found at elevations above 2,000 meters above sea level and in regions where temperatures stay below 15°C Despite having a thin aeolian and soil layer, this soil remains humid due to a thick upper humus layer—approximately 50 cm in most areas and over 1 meter thick on Ngoc Linh peak Covering about 7,600 hectares, this soil type accounts for 15.4% of the total area within the Nature Reserve.
Feralite Humus soil is typically found at elevations between 1000 to 2000 meters above sea level, where the climate remains humid and cool with annual temperatures ranging from 15°C to 20°C This soil type is characterized by a significant accumulation of humus, indicating rich organic matter Additionally, Feralite Humus soil exhibits acidic and impermeable properties, making it distinct in its environmental and chemical composition.
Feralit Soil, found at elevations from 500 to 1,000 meters above sea level, accounts for 21.2% of the total land area in Ngoc Linh Nature Reserve This soil type is classified into Yellow and Red Feralite Soil on magmatic acidic rocks in lowland areas, as well as Brown and Red Feralite Soil on magmatic alkaline and neutral rocks in the same elevation zone Additionally, Yellow and Red Feralite Soils occur on metamorphic rocks and clay slate within the lowlands, highlighting the diverse geological distribution of Feralit Soil across the reserve.
Alluvial soil, formed by deposits of alluvium along riverbanks and streams, is typically found at the foot of mountains or hills This soil is characterized by its grey, brown, and porous texture, making it highly fertile and ideal for agricultural cultivation Its abundant nutrients and good drainage properties contribute significantly to successful farming practices in these regions.
The study site is situated in a remote mountainous region lacking any weather stations Key climatic characteristics of the Ngoc Linh Nature Reserve in Tra My District are summarized in the accompanying table, providing representative data essential for understanding the reserve's environmental conditions.
Table 3.1 Meteorological data from weather station in Tra My district
Meteorological data Weather station in Tra My district
Months of maximum rainfall September, October, November, December
Rainy season April to January
Dry season February to March
Ngoc Linh Nature Reserve features a humid tropical climate influenced by varying altitudes from 500 to 2598 meters above sea level, creating diverse climatic conditions The region experiences average annual temperatures between 22°C and 25°C, while rainfall varies significantly with elevation, reaching up to 4,000 mm at Ngoc Linh Peak These high rainfall levels can lead to storms and flooding during the rainy season, whereas the dry season often results in severe water shortages in the western parts of the reserve.
Research in Ngoc Linh Nature Reserve identified 385 plant species across 260 genera and 120 families, based on studies conducted in 1996 and 1998 Among these, 45 species are threatened, with 16 listed on the IUCN Red List and 34 included in the Red Book of Vietnam The reserve hosts a diverse range of flora, including 238 timber species, 169 medicinal plants, and 78 ornamental species.
Table 3.2 Plants found in Ngoc Linh Nature Reserve, Quang Nam
In Ngoc Linh Nature Reserve, there are 9 endemic plant species of Vietnam They are
Panax vietnamensis, Pinus dalatensis, Amentotaxus poilanei, Cinnamomum balansae, Alchornea annamensis, Baccaurea silvestris, Bulbophyllum evrardii, Otochilus fuscus and
Ngoc Linh's flora comprises 26 plant families, including Asteraceae, Orchidaceae, Rutaceae, Poaceae, Fagaceae, Moraceae, Euphorbiaceae, Araliaceae, Myrsinaceae, Cyperaceae, Lauraceae, Rosaceae, Fabaceae, and others The region's rich biodiversity features a diverse array of species, with a notable dominance of trees from less species-rich families such as Fagaceae, Lauraceae, and Hamamelidaceae, contributing significantly to the unique ecosystem of Ngoc Linh.
Pinus kesiya is a widespread conifer species found in both monospecific stands and mixed forests Although the forest composition includes other conifers such as Pinus dalatensis, Dacrycarpus imbricatus, and Keteleeria evelyniana, these species are less diverse but tend to form particularly large specimens, highlighting the ecological significance of Pinus kesiya in these ecosystems.
The Araliaceae family encompasses numerous valuable medicinal plant species, including the endemic Ngoc Linh Ginseng, which is highly prized in traditional medicine Due to over-exploitation, Ngoc Linh Ginseng has become endangered in recent years, highlighting the urgent need for sustainable conservation efforts Understanding the diversity of both medicinal plants and local fauna is crucial for preserving these vital natural resources.
In Ngoc Linh Nature Reserve, there are some surveys revealing a total number of 306 vertebrate species, including 52 mammal species, 190 bird species, 41 reptile species and 23 amphibian species
Table 3.3 Vertebrate species recorded in Ngoc Linh Nature Reserve
Ngoc Linh Nature Reserve features four main types of forest according to Thai Van Trung's 1978 classification: high montane broadleaf evergreen forest, medium to high montane broadleaf evergreen forest, low montane broadleaf evergreen forest, and secondary forest These diverse forest types contribute to the rich vegetation cover of the reserve, supporting its unique ecosystem.
Ngoc Linh Nature Reserve has a considerable forest cover area that makes up 88% of the total area of this reserve The primary forest has significant proportion with approximately
Research methodology
In Ngoc Linh Nature Reserve, Quang Nam Province, automatic recorders were strategically placed across four habitat types, as outlined in Table 3.5, to monitor wildlife activity Site selection was based on topographic conditions and consultations with reserve staff to ensure accurate placement A total of 11 survey sites were established, with GPS coordinates marked and recorded for precise location tracking.
Each recorder, equipped with microphones on both the left and right sides, was securely attached to a tree to capture bird songs effectively Recordings were automatically saved to disk every 30 minutes, ensuring data preservation even if batteries ran out unexpectedly To maintain continuous operation, batteries were replaced weekly The recording process spanned 19 days, from June 4 to June 23, 2016, providing extensive data on local bird vocalizations.
Figure 3.8 An automatic recorder was attached to a tree in Ngoc Linh Nature Reserve
Table 3.5 Characteristics of study site in Ngoc Linh Nature Reserve
Medium to High Montane Broadleaf Evergreen Forest
Medium to High Montane Broadleaf Evergreen Forest
Medium to High Montane Broadleaf Evergreen Forest
Medium to High Montane Broadleaf Evergreen Forest
The location of 11 study sites in Ngoc Linh Nature Reserve was described in this map below:
Figure 3.9 Map of study sites in Ngoc Linh Nature Reserve
Birdsong signals exhibit significant variation across multiple dimensions, including frequency range, pitch modulation speed, vocabulary size, syllable duration, and overall song duration Each bird's song is represented by a unique spectrogram, a visual tool that illustrates the spectrum of frequencies present in its calls Spectrogram analysis is essential for studying and differentiating bird vocalizations, providing valuable insights into their communication patterns and species identification.
Figure 3.10 illustrates spectrograms displaying various discrete sound units, highlighting four distinct categories: (a) constant frequency signals exemplified by the Mountain Scops Owl, (b) frequency modulated whistles represented by the Large Scimitar Babbler, (c) broadband signals with varying frequency components seen in the Buff-breasted Babbler, and (d) segments featuring strong harmonics observed in the Golden-breasted Fulvetta These spectrograms provide insights into the diverse acoustic signatures of different bird species, essential for species identification and bioacoustic studies Understanding these spectral patterns enhances our ability to analyze bird communication and ecological behavior through visual sound analysis.
Recording data was analyzed by RAVEN software (Cornell Lab of Ornithology) to detect the spectrogram of each species Recognizers for calls generated in RAVEN
Targeted species consist of 21 bird species, divided into 5 orders and 9 families that are showed in the following table:
Table 3.6 List of targeted bird species in Ngoc Linh Nature Reserve
No Species name Scientific name Family name Order name
1 Oriental Bay Owl Phodilus badius Tytonidae Strigiformes
2 Mountain Scops Owl Otus spilocephalus Strigidae Strigiformes
3 Indian Scops-owl Otus bakkamoena Strigidae Strigiformes
4 Brown Wood Owl Strix leptogrammica Strigidae Strigiformes
5 Collared owlet Glaucidium brodiei Strigidae Strigiformes
6 Great Eared-nightjar Eurostopodus macrotis Caprimulgidae Caprimulgiformes
7 Large Scimitar Babbler Pomatorhinus hypoleucos Timaliidae Passeriformes
8 Golden babbler Stachyris chrysaea Timaliidae Passeriformes
9 Grey-throated babbler Stachyris nigriceps Timaliidae Passeriformes
10 Pin-striped tit-babbler Macronous gularis Timaliidae Passeriformes
11 Golden-breasted fulvetta Alcippe chrysotis Sylviidae Passeriformes
12 Grey-hooded fulvetta Alcippe cinereiceps Sylviidae Passeriformes
13 Rufous-winged fulvetta Alcippe castaneceps Pellorneidae Passeriformes
15 Mountain Fulvetta Alcippe peracensis Pellorneidae Passeriformes
16 Buff-breasted Babbler Trichastoma tickelli Pellorneidae Passeriformes
17 Stripe-throated Yuhina Yuhina gularis
18 Crested Argus Rheinardia ocellata Phasianidae Galliformes
20 Bar-backed partridge Arborophila brunneopectus Phasianidae Galliformes
21 Red-headed trogon Harpactes erythrocephalus Trogonidae Trogoniformes
Available sample songs of these species were adopted from Scharringa (2005) So I used this program to compare these spectrograms with the available spectrogram of these bird species
Before analyzing the recordings, I selected those with a recognition score above 40% and a quality score above 0, indicating their suitability for bird identification The score, ranging from 0.00% to 100.0%, reflects how well the recording matches the bird recognizer model, while the quality score, ranging from 0.00 to 99.99, indicates the clarity of the signal (Mieke et al., 2014) Additionally, spectrograms were required to display both vertical and horizontal axes for accurate interpretation To ensure meaningful data, only 30-minute interval recordings taken between 3 AM and 9 AM at study sites were included, aligning with the active behavior period of the targeted bird species.
To ensure accurate comparison, the spectrograms of the two correlating recordings must share the same frequency, specifically 24,000 Hz Therefore, I chose to use Audacity software to standardize the frequency of both recordings to this same value, ensuring consistent and reliable analysis.
Figure 3.13 The process of converting spectrogram’s frequency by Audacity software
3.2.2.2.The process of correlation configuration
I compared two recordings—a 30-minute interval recording and a targeted bird recording—using correlation configuration to identify similarities When the correlation analysis revealed an upward trend in specific segments, I focused on listening and analyzing those intervals to determine their significance By examining key features such as frequency range, pitch modulation speed, vocabulary size, and syllable duration of each sonogram, I assessed whether the recordings matched, providing insights into bird identification and behavior.
This process determined the name of bird species After that, I could know where they live by the locations I put the automatic recorders
Table 3.7 Data sheet is used to collect information in each study site
No Species name Day Time of detection
Data analysis method
3.3.1 Determining the composition of detected bird species
Based on data collected from automatic recorders and compared with the bird checklist of Vietnam from Vo Quy-Nguyen Cu (1995), as well as the IUCN Red List of Threatened Species (2016) accessed through www.iucnredlist.org, a comprehensive list of bird species detected in Ngoc Linh Nature Reserve has been established.
Table 3.8 The list of detected bird species by using automatic recorders
No Species name Scientific name
3.3.2 Determining the distribution of detected bird species
Analysis of recorder data from 11 diverse habitat sites revealed the specific locations where various bird species are present By comprehensively defining ecological variables influencing habitat suitability, we identified key factors affecting bird presence across different environments These findings were systematically compiled into a detailed table, providing valuable insights into habitat-bird species associations for targeted conservation efforts.
Table 3.9 Bird distribution in different habitats in Ngoc Linh Nature Reserve
High Montane Broadleaf Evergreen Forest
Medium to High Montane Broadleaf Evergreen Forest
Low Montane Broadleaf Evergreen Forest
Based on the biological characteristics of bird species and particular habitat of each location I explained their distribution.
RESULT
Sounds of targeted bird species
The study revealed that recordings from site 3 and site 4 were of low quality, primarily due to adverse weather conditions or technical issues with the recorders Consequently, no bird sounds were detected from these recordings, highlighting the impact of environmental and technical factors on data reliability.
Table 4.1 The comparison between the sonogram of detected birds and the sonogram of sample targeted birds
The sonogram in the recording
Bird species exhibit specific active periods for vocalization, which are closely related to their behaviors such as foraging and sleeping patterns During the survey window from 3:00 to 9:00 AM, the active times of detected birds have been documented and summarized in the accompanying table Understanding these temporal activity patterns is essential for effective bird monitoring and conservation efforts.
Table 4.2 The active time during surveying time (3.00-9.00 AM) of each detected bird species
The active time during surveying time (3.00-9.00 AM)
9 Pin-striped tit-babbler 6.30 – 7.00 AM
Several bird species, including the Mountain Scops Owl, Collared Owlet, Red-headed Trogon, Mountain Fulvetta, Buff-breasted Babbler, Golden-breasted Fulvetta, and Pin-striped Tit-Babbler, typically sing or call at dawn, establishing their presence early in the day In contrast, species like the Golden Babbler and Crested Argus usually begin vocalizing later in the morning, during the daytime Understanding these variations in bird vocalization times can enhance birdwatching experiences and aid in species identification.
Presence of targeted bird species in Ngoc Linh Nature Reserve
A total of 21 target bird species were detected in Ngoc Linh Nature Reserve, Quang Nam, involving 9 bird species classified into 4 orders and 5 families These species inhabit various habitat types within the reserve, as identified using RAVEN software The detailed findings are summarized in Table 4.3.
Table 4.3 List of detected bird species in Ngoc Linh Nature Reserve
No Species name Scientific name Family name Order name Current status
Crested Argus Rheinardia ocellata Phasianidae Galliformes Near
Otus spilocephalus Strigidae Strigiformes Least
3 Collared owlet Glaucidium brodiei Strigidae Strigiformes Least
Harpactes erythrocephalus Trogonidae Trogoniformes Least
Alcippe peracensis Pellorneidae Passeriformes Least
Trichastoma Tickelli Pellorneidae Passeriformes Least
Golden babbler Stachyris chrysaea Timaliidae Passeriformes Least
Alcippe chrysotis Timaliidae Passeriformes Least
Macronous gularis Timaliidae Passeriformes Least
The study revealed that bird species such as the Mountain Scops Owl, Collared Owlet, Crested Argus, Red-headed Trogon, and Golden Babbler exhibited higher presence frequencies compared to other species in the Ngoc Linh Nature Reserve In contrast, targeted species like the Mountain Fulvetta, Buff-breasted Babbler, Golden-breasted Fulvetta, and Pin-striped Tit-Babbler were detected only irregularly, highlighting their sporadic occurrence in the area.
The distribution of detected bird species
We have a table showing the distribution of detected birds in three communes in Ngoc Linh Nature Reserve:
Table 4.4 Distribution of detected birds in different communes in Ngoc Linh Nature Reserve
Communes in Ngoc Linh Nature Reserve Tra Tap Tra Linh Tra Leng
Tra Tap commune boasts the highest diversity of bird species within Ngoc Linh Nature Reserve, accounting for 8 species, the largest percentage among surveyed areas In contrast, Tra Linh and Tra Leng communes each contribute only 3 bird species, representing a smaller proportion of the total detected species This variation highlights Tra Tap's significant role in avian biodiversity conservation within the reserve.
Figure 4.1 Spatial distribution map of detected birds in Ngoc Linh Nature Reserve
4.3.2 Distribution in relation to habitat
Bird species require essential natural conditions such as food sources, water, shelters, and safety for their survival and growth Different bird species are adapted to specific habitats, with some environments rich in particular resources like insects, which are vital for many birds Natural selection favors species that adapt effectively to their habitats, influencing their distribution patterns across various environments Understanding these habitat-resource relationships is crucial for conserving the areas that many birds depend on for food and shelter Research into these ecological dynamics is essential for effective bird conservation and habitat protection efforts.
Table 4.4.The distribution of detected bird species in different habitats in Ngoc Linh
High Montane Broadleaf Evergreen Forest
Medium to High Montane Broadleaf Evergreen Forest
Low Montane Broadleaf Evergreen Forest
The Ngoc Linh Nature Reserve hosts diverse bird species across multiple habitats Notably, a significant number of birds, including the Crested Argus, Red-headed Trogon, Mountain Fulvetta, Buff-breasted Babbler, and Pin-striped Tit-babbler, can thrive in two different habitat types The Golden Babbler uniquely inhabits three types of forest within the reserve, showcasing its adaptability Additionally, the Mountain Scops Owl is capable of living across all four habitats in Ngoc Linh, highlighting the ecological diversity of the area This distribution underscores the rich avian biodiversity and habitat versatility within Ngoc Linh Nature Reserve.
DISCUSSION
The presence of birds in Ngoc Linh Nature Reserve, Quang Nam province and the
High detection rates of 10 bird species, such as Crested Argus, Mountain Scops Owl, Collared Owlet, and Red-headed Trogon, may be attributed to their loud vocalizations that can be heard from long distances Notably, the Pin-striped Tit-Babbler's high vocal volume and density in Ngoc Linh Nature Reserve make it easier to detect these birds in this area These findings suggest that both the distance from vocalization sources to automatic recorders and bird density significantly influence detection rates In contrast, 11 species across four families were not recorded or detected by Raven software, likely due to low-quality recordings, their absence during the recording period, or if they do not inhabit the study sites Factors such as playback timing, bird behavior, and habitat proximity also contribute to detection success.
Differences in active time during surveying are primarily influenced by bird behaviors For instance, owls are typically active at dawn, while remaining inconspicuous in daytime roosts Similarly, crested argus exhibit pheasant-like behaviors, foraging on the ground during the day and resting on high branches at night.
Using automatic recorders is an effective survey method for bird species that do not vocalize regularly, as it reduces human disturbance and allows for natural bird behavior This approach is particularly advantageous in remote, untouched areas where access is difficult, requiring only deployment and retrieval of devices, often without specialized training Data analysis is simplified for species with recognizable vocalizations, further enhancing efficiency Additionally, using automatic recorders significantly lowers survey costs by decreasing time and effort; for example, traditional surveys can take up to 6 hours daily, whereas automated methods reduce this to just two visits totaling approximately 2 hours, with data analysis taking around 1.5 hours per device per day—leading to potential time savings of up to 42%.
Factors affect the distribution of targeted bird species in Ngoc Linh Nature Reserve,
5.2.1 Factors affect spatial distribution of targeted bird species
The bird species distribution in Ngoc Linh Nature Reserve varies across communes, with Tra Tap having the highest diversity, recording eight species In contrast, Tra Linh and Tra Leng communes each have only three species, partly due to differences in the number of automatic recorders deployed—six in Tra Tap, three in Tra Linh, and two in Tra Leng This variation in recorder deployment significantly influences the observed spatial distribution of bird species within the area.
5.2.2 Factors affect the distribution of targeted bird species in four different habitats
Bird species that are considered the most typical and common for a habitat can also be found in other habitats at times due to their frequent movement during feeding, nesting, mating, and resting Additionally, the proximity of different habitats makes it easy for bird species to appear in various environments, reflecting their dynamic and adaptable nature.
The survey indicates that bird species distribution in Ngoc Linh Nature Reserve, Quang Nam Province, is influenced by various factors such as food availability, shelter, temperature, moisture, and human activity levels Higher elevations host fewer bird species, as colder temperatures at these altitudes negatively affect metabolic processes and energy exchange in birds, leading most species to avoid such habitats.
The diversity of flora and bird species in various habitats are proportionally related, indicating that higher plant diversity corresponds with greater bird diversity Notably, the Medium to High Montane Broadleaf Evergreen Forest exhibits the highest plant species diversity, with 8 species across 5 families, resulting in the greatest overall bird diversity within this habitat Conversely, the Secondary Vegetation habitat shows the lowest diversity, with only one plant species and one bird family Further habitat-specific details will be provided below.
5.2.2.1 High Montane Broadleaf Evergreen Forest
Using RAVEN software, three bird species representing 33.3% of the detected avifauna were identified within this habitat, spanning two families that account for 40.0% These species include the Mountain Scops Owl from the family Strigidae, and the Golden Babbler and Pin-striped Tit-babbler from the family Timaliidae This indicates that the forest habitat supports a relatively small number of bird species and families compared to Medium to High Montane Broadleaf Evergreen Forest, where diversity is notably higher However, the proportion of bird species in High Montane Broadleaf Evergreen Forest is greater than in Secondary Vegetation, highlighting differences in avian diversity across forest types.
The habitat’s high elevation (above 1,700m ASL) is a key factor influencing its characteristics Since birds are endothermic, maintaining a warm body temperature, they are generally not suited to cold environments, which can negatively impact their metabolism Additionally, the limited plant diversity in this habitat, primarily consisting of a few broadleaf trees and conifers, reduces the available food resources and shelter for bird species, further explaining their distribution patterns.
Additionally, trees in this forest type exhibit stunted and xerophytic morphology due to strong winds, low nutrient availability and periods of drought It impacts negatively on birdlife
5.2.2.2 Medium to High Montane Broadleaf Evergreen Forest
This forest is home to the highest diversity of bird species, with 8 species representing 88.9% of the total bird population, spanning across 5 different families Notable species include the Crested Argus, Mountain Scops Owl, Collared Owlet, Red-headed Trogon, Mountain Fulvetta, Buff-breasted Babbler, Golden Babbler, and Pin-striped Tit-babbler Its rich biodiversity makes it an ideal habitat for birds, offering ample food sources and nesting opportunities, thereby supporting their survival and reproduction.
The Medium to High Montane Broadleaf Evergreen Forest in Ngoc Linh Nature Reserve is the richest habitat, characterized by a dense bushy canopy and a complex forest structure This forest type boasts a diverse and abundant flora species composition, making it a vital ecological zone within the reserve.
Secondly, this forest type is distributed far from habitation leading to low levels of disturbance with human impact limited to hunting and non-timber forest product collection
The temperature at this elevation tends to be more stable and suitable for a wider variety of bird species, making it a preferable habitat compared to the High Montane Broadleaf Evergreen Forest.
5.2.2.3 Low Montane Broadleaf Evergreen Forest
The Low Montane Broadleaf Evergreen Forest habitat hosts a significant proportion of bird species, with 7 species representing 77.8% of the total, across 5 families This number is twice as many as found in the High Montane Broadleaf Evergreen Forest, highlighting its importance for avian biodiversity in montane ecosystems.
Despite nearby communities leading to significant deforestation for agriculture, a substantial area of the rich Low Montane Broadleaf Evergreen Forest remains intact, providing an ideal habitat for diverse bird species The forest's plant diversity across multiple families supports the needs of various bird populations, offering ample nesting sites and food sources Notably, the canopy cover exceeds 85%, which is higher than in Medium to High Montane Broadleaf Evergreen Forests, creating an optimal environment for birds Additionally, the relatively warm temperatures at this elevation further enhance the habitat's suitability for a wide variety of avian species.
The Low Montane Broadleaf Evergreen Forest provides a vital habitat supporting diverse bird species, including the Crested Argus, Mountain Scops Owl, Red-headed Trogon, Mountain Fulvetta, Buff-breasted Babbler, Golden Babbler, and Golden-breasted Fulvetta These species thrive due to the favorable environmental conditions of the area To ensure the conservation of this rich biodiversity, the local government should implement effective measures to expand and protect this critical forest habitat Preservation efforts are essential for maintaining the ecological balance and supporting bird populations in this region.
This habitat hosts the smallest proportion of bird species, representing only 11.1%, and includes a single bird species from one family, accounting for 20.0% The Mountain Scops Owl, the only bird species found in this type of forest, belongs to the Strigidae family Notably, this owl is also relatively widespread across multiple habitats, highlighting its adaptability.
Local farmers practice rotational swidden cultivation in Ngoc Linh Nature Reserve, leading to extensive secondary vegetation that significantly disrupts bird habitats Although the area contains scrub and scattered broadleaf trees, over-exploitation and repeated burning have depleted soil fertility, reducing grassland areas and narrowing the natural habitat for birds As a result, this habitat has become less suitable for avian species to live and nest, due to the ongoing negative impacts from local agricultural activities.
CONCLUSION 39 REFERENCES
Using automatic recorders and RAVEN software, we detected the sounds of 9 out of 21 target bird species, including the Mountain Scops Owl, Collared Owlet, Crested Argus, Red-headed Trogon, Golden Babbler, Mountain Fulvetta, Buff-breasted Babbler, Golden-breasted Fulvetta, and Striped Tit-Babbler.
The frequency of bird occurrences varies among species, with some birds like the Mountain Scops Owl, Collared Owlet, Crested Argus, Red-headed Trogon, and Golden Babbler appearing frequently across multiple recordings In contrast, other bird species are only recorded a few times, indicating different patterns of vocal presence and prevalence in the studied habitats.
During the survey conducted between 3:00 AM and 9:00 AM, various bird species exhibited different active periods Notably, species such as the Mountain Scops Owl, Collared Owlet, Red-headed Trogon, Mountain Fulvetta, Buff-breasted Babbler, Golden-breasted Fulvetta, and Pin-striped Tit-Babbler are known to call or sing predominantly in the morning, indicating peak vocal activity during dawn hours Conversely, species like the Golden Babbler and Crested Argus display distinct vocalization behaviors, either singing or calling at different times of the morning, highlighting diverse temporal activity patterns among bird species in the survey area.
While the number of bird species in Tra Tap commune makes up the largest percentage
(8 species) in total number of detected bird species, the number of those in Tra Linh and Tra Leng commune contributes a small proportion with three species in each commune
Medium to High Montane Broadleaf Evergreen forests host the highest percentage of bird species and families among four forest types, highlighting their rich avian diversity In contrast, Secondary Vegetation contributes the smallest proportion of bird species, indicating lower avian diversity in these areas Additionally, Low Montane Broadleaf Evergreen Forest and High Montane Broadleaf Evergreen Forest rank second and third in bird community diversity, respectively, underscoring their significance for bird conservation and biodiversity.
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BirdLife International Vietnam Programme and the Forest Inventory and Planning Institute
2 Tordoff, A W ed., 2002, “Directory of important bird areas in Vietnam: key sites for conservation” Hanoi: BirdLife International in Indochina and the Institute of Ecology and
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Human-Wildlife Surveys: An Example Using Nightjars"
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12 Waddle et al, 2009,“Ecacy of automatic vocalization recognition software for anuran monitoring” Herpetological Conservation and Biology
13 http://birdlist.org/vietnam.htm
Data in 9 study sites is described in the following tables:
Table 1 Bird song detected in site 1 in village 4, Tra Leng commune
No Species name Day Time of detection
Table 2 Bird song detected in site 2 in village 4, Tra Leng commune
No Species name Day Time of detection
Table 3 Bird song detected in site 5 in Village 4, Tra Linh commune
No Species name Day Time of detection
Table 4 Bird song detected in site 6 in Tra Tap commune
No Species name Day Time of detection
Table 5 Bird song detected 7 in Village 4, Tra Tap commune
No Species name Day Time of detection
Table 6 Bird song detected in site 8 in Village 4, Tra Tap commune
No Species name Day Time of detection
Table 7 Bird song detected in site 9 in Village 2, Tra Tap commune
No Species name Day Time of detection
Table 8 Bird song detected in site 10 in Village 4, Tra Tap commune
No Species name Day Time of detection
Table 9 Bird song detected in site 11 in village 2, Tra Tap commune
No Species name Day Time of detection