Journal of Threatened
Taxa | www.threatenedtaxa.org | 26 August 2026 | 18(8): 29430–29446
ISSN 0974-7907 (Online) | ISSN 0974-7893 (Print)
https://doi.org/10.11609/jott.10447.18.8.29430-29446
#10447 | Received 09 February 2026 | Final received 11 July 2026| Finally
accepted 01 August 2026
A preliminary checklist and
seasonal diversity of wetland-associated
birds in Bajali District, Assam, India
Bidyut Kumar Das
Department of Zoology, Nalbari College, Nalbari
District, Assam 781335, India.
Editor: Aditya Srinivasulu,
Zoo Outreach Organisation, Hyderabad, India. Date of publication: 26
August 2026 (online & print)
Citation: Das,
B.K. (2026). A preliminary checklist and seasonal diversity of
wetland-associated birds in Bajali District, Assam,
India. Journal of Threatened Taxa 18(8): 29430–29446. https://doi.org/10.11609/jott.10447.18.8.29430-29446
Copyright: © Das 2026. Creative
Commons Attribution 4.0 International License. JoTT
allows unrestricted use, reproduction, and distribution of this article in any
medium by providing adequate credit to the author(s) and the source of
publication.
Funding: No funding agency or project grant was involved in the study, and the work was completed independently.
Competing interests: The author declares no competing interests.
Author details: Dr. Bidyut Kumar Das is currently serving as an assistant professor in the Department of Zoology, Nalbari College, Assam, India. He obtained his PhD degree from Gauhati University, Assam, in 2020. He completed his M.Sc. in Zoology with a specialization in Cell and Molecular Biology. He has over 13 years
of teaching experience at both undergraduate and postgraduate levels. His research interests include Conservation Biology, Ecotoxicology, and Bioinformatics. He has a special interest in field-based biodiversity studies, particularly on birds, butterflies, and fishes. His hobbies include organic farming and wildlife photography, reflecting his passion for nature and conservation.
Acknowledgements: The author is grateful to the authorities of Nalbari College, Assam, for granting permission to conduct this study and for providing necessary support and encouragement during the course of the research. The author also sincerely thank Mr. Nejib Ahmed, wildlife photographer and birdwatcher, and Mr. Prasanna Kalita, president of the environmental conservation NGO Bonyabondhu, for their valuable assistance in bird identification and for their support in various environmental and conservation-related activities.
Abstract: Wetlands sustain diverse avian
assemblages and provide indispensable habitats for resident and migratory waterbirds; however, many wetlands in northeastern India
remain inadequately documented. This study presents the first preliminary
checklist and diversity assessment of wetland-associated birds from selected
wetlands in Bajali District, Assam, northeastern
India, based on systematic point-count surveys conducted across five sites
between April 2024 and March 2025. Seasonal variations in species composition,
abundance, migratory status, feeding guilds, conservation status, and community
diversity were comprehensively evaluated. A total of 44 wetland-associated bird
species representing 14 families were recorded. Ardeidae
was the most species-rich family (10 species; relative diversity index =
22.72%), followed by Scolopacidae (7 species). Bird
abundance exhibited pronounced seasonal fluctuations, peaking during winter
(2,835 individuals), followed by monsoon (2,601), autumn (2,064), and summer
(2,009). Species richness attained its maximum during autumn and winter (44
species each) but declined markedly during the monsoon (29 species). Diversity
metrics consistently revealed greater species richness, diversity, evenness,
and community stability during the post-monsoon and winter seasons, whereas
monsoon assemblages were characterized by reduced diversity and elevated
species dominance. Resident species constituted 65.91% of the recorded
avifauna, while 34.09% were winter visitors. Most species (95.46%) were
classified as ‘Least Concern’, whereas the Lesser Adjutant and Asian Woollyneck were categorized as ‘Near Threatened’,
underscoring the conservation significance of the study area. This study
provides the first comprehensive documentation of wetland-associated birds in Bajali District and highlights the ecological importance of
its wetlands in sustaining diverse resident and migratory bird assemblages. The
findings establish a valuable reference for long-term biodiversity monitoring,
conservation planning, and sustainable wetland management in the lower
Brahmaputra floodplain.
Keywords: Abundance, avian assemblages,
biodiversity monitoring, community stability, conservation planning, feeding
guild, migratory status, seasonal variation, species richness.
INTRODUCTION
Birds significantly contribute to
ecosystem functionality through pollination, regulation of insect populations,
and modification of the physico-chemical properties
of their habitats via diverse ecological interactions (Fraixedas
et al. 2020; Basile et al. 2021). Consequently, avian species richness,
community composition, habitat utilization patterns, and population dynamics
are widely recognized as robust indicators of environmental quality, resource
availability, and overall ecosystem health (Lindenmayer
et al. 2006; Tanalgo et al. 2015). Birds occupy
multiple trophic levels within food webs and play essential roles in ecological
networks through predation, seed dispersal, scavenging, nutrient cycling, and
other ecosystem functions, thereby contributing to ecosystem stability and
resilience (Michel et al. 2020; Tobias et al. 2020; Signa et al. 2021).
Within urban landscapes, the
availability and management of large green spaces are critical for the
long-term persistence and conservation of avian assemblages (Campbell et al.
2022; Choudaj & Shaha
2023). Spatial heterogeneity in avian abundance and species richness can exert
cascading effects on both terrestrial and aquatic ecosystems, which are
ecologically linked through complex trophic pathways (Turner 2003).
Nevertheless, a marked decline in bird populations—particularly within highly
urbanized environments—has emerged as a growing ecological concern, closely
associated with increasing levels of urban development and environmental
pollution (Donaldson et al. 2007). Furthermore, climatic stability and seasonal
variability function as key determinants of avian diversity, strongly
influencing species distributions and community structure (Graham et al. 2006).
Accelerated urban expansion has
substantially transformed natural landscapes, altered ecological processes, and
modified ecosystem structure and functioning (Basu
& Das 2021; Hersperger et al. 2021). Urbanization
results in habitat loss, fragmentation, and degradation, leading to significant
reductions in the diversity of plants, insects, and vertebrate taxa, with birds
being among the most sensitive to these changes (Carrasco et al. 2018).
Mitigating the negative impacts of urban growth on biodiversity and achieving a
sustainable balance between anthropogenic development and ecological integrity
therefore constitute major objectives of contemporary urban planning and
biodiversity conservation research (Canedoli et al.
2018). As the most widespread and ecologically responsive vertebrate group in
urban ecosystems, birds serve as reliable bioindicators of environmental
conditions and biodiversity status (Shwartz et al.
2014). Given their ecological importance and contributions to human well-being
in urban environments (Fuller et al. 2007), avian-focused research is
particularly essential in regions experiencing rapid urbanization.
Wetland ecosystems are among the
most productive and biologically rich environments on Earth, yet they are
highly fragile and sensitive to disturbance (Gibbs 1993; Van der Valk 2006). These ecosystems are primarily structured by
hydrological processes, including water availability, hydroperiod, and local
water cycles, which strongly influence species composition, habitat structure,
and overall biodiversity (Urban 2004; Bronmark &
Hansson 2005). Variations in hydrological regimes regulate ecological filtering
and species assemblage patterns, making water dynamics a key driver of wetland
community organization. Freshwater wetlands, particularly lakes and riverine
systems, are of immense ecological and socio-economic importance, supporting
agriculture, fisheries, livestock, and drinking water supplies while sustaining
high biodiversity. They also provide critical ecosystem services such as flood
regulation, groundwater recharge, nutrient retention, sediment control, and
erosion mitigation (Mitsch & Gosselink
1986). However, increasing anthropogenic pressures—including agricultural
expansion, aquaculture, industrial discharge, waste disposal, land reclamation,
and dredging—have severely altered wetland structure and function, threatening
both biodiversity and ecosystem services (Balachandran et al. 2002; Naveen et
al. 2025).
Waterbirds, defined as bird species
ecologically dependent on wetlands, constitute a major faunal component of
these ecosystems. They occupy multiple trophic levels within wetland food webs
and play an important role in nutrient cycling, prey–predator regulation, and
ecosystem stability (Custer & Osborne 1977; Rajashekara
& Venkatesha 2010). Because waterbirds
respond rapidly to environmental change, their population trends and community
structure serve as reliable biological indicators of wetland health and water
quality (Grimmett & Inskipp
2007). Their assemblages are regulated by food availability, wetland size,
habitat heterogeneity, productivity, and the duration and timing of flooding
cycles (Cintra et al. 2007; Gajardo et al. 2009; Khan
2010; Cintra 2012; Rajpar 2022). Temporal factors,
such as seasonal variations, tidal cycles, and climatic conditions, influence
the quality and resource availability, thereby shaping waterbird
abundance and assemblage structure in wetlands (Khan 2010; Pandiyan
et al. 2010; Byju et al. 2025c). Wetlands containing
diverse microhabitats, such as shallow open water, marshes, mudflats, and aquatic
vegetation, generally support higher waterbird
diversity by providing essential feeding, nesting, and roosting resources (Paracuellos 2006; Manikannan et
al. 2011; Arya et al. 2014; Mathibalan et al. 2026).
In addition to natural wetlands,
agricultural and agroforestry landscapes also contribute significantly to bird
conservation, as protected areas cover only a limited proportion of land (Sundar & Subramanya 2010). Agroecosystems provide
diverse food resources, including grains, seeds, fruits, insects, and small
vertebrates, supporting avian communities that function both as crop pests and
as natural pest-control agents (O’Connor & Shrubb
1986; Borad et al. 2000; Haslem
& Bennett 2008; Asokan et al. 2009). Furthermore,
birds contribute to seed dispersal, pollination, scavenging, and nutrient
cycling, thereby enhancing ecosystem functioning in both natural and
human-modified landscapes (Dhindsa & Saini 1994;
Whelan et al. 2008; Sekercioglu 2012). Bird diversity
in agricultural systems is strongly influenced by crop type, vegetation
structure, land-use practices, and landscape composition, including the
presence of wetlands, forest patches, grasslands, and agroforestry trees (Taft
& Haig 2006; Bruggisser et al. 2010; Wretenberg et al. 2010).
Although wetland bird communities
have been studied in several ecologically important wetlands of Assam and other
parts of northeastern India, these investigations are largely restricted to
protected areas and a few well-known floodplain wetlands. Consequently, many district-level
wetlands remain poorly documented, resulting in limited knowledge of their
avifaunal diversity, community composition, seasonal dynamics, and habitat use.
Bajali District, situated in the lower Brahmaputra
valley of western Assam and adjoining the foothills of Bhutan, contains a
network of natural and human-modified wetlands that are likely to provide
important habitats for both resident and migratory waterbirds.
Despite their ecological significance, these wetlands have received little
scientific attention, and baseline information on their bird communities is
lacking. The present study was therefore undertaken to prepare the first
preliminary checklist of wetland-associated birds and document their diversity,
abundance, and seasonal dynamics in selected wetlands of Bajali
District, Assam. The findings provide baseline ecological information to
support long-term biodiversity monitoring, conservation planning, and
sustainable wetland management in this understudied region.
MATERIALS AND METHODS
Study area
Bajali District, located in the western
part of Assam, India, was formally established on 12 January 2021 following its
separation from Barpeta District, where it previously
functioned as a subdivision. The district is bordered by Baksa
District to the north, Nalbari District to the east,
and Barpeta District to the west and south. The
administrative headquarters is situated at Madan Rauta
Nagar in Pathsala. Geographically, Bajali lies between 26.7333–26.8333 °N and 91.0667–91.4000
°E, covering a total area of approximately 422.95 km² (163.30 square miles),
which is comparable in size to the country of Barbados.
Bajali District is characterized by a
heterogeneous landscape comprising low-lying alluvial plains interspersed with
gentle uplands and traversed by several minor river systems, including the Palla, Deojara, Pahumara, and Kaldia, which
render the area highly flood-prone. The district lies within Seismic Zone V,
reflecting a high level of tectonic vulnerability. Its economy is predominantly
agrarian, supported by fertile alluvial soils that sustain crops such as rice,
mustard, and a variety of vegetables. The climate is tropical monsoonal, with
hot and humid summers, heavy rainfall from May to September, and relatively
cool, overcast winters. Vegetation is dominated by wet broadleaf forests
containing sal, teak, mahogany, bamboo, and diverse
fruit-bearing species. The district also hosts ecologically significant
wetlands rich in aquatic macrophytes such as lotus and water lilies,
underscoring Bajali’s role as an important
biodiversity reservoir within the Brahmaputra Valley. Bajali
experiences a humid subtropical climate with hot, moisture-laden summers and
cool, overcast winters. Peak rainfall occurs from May to September, followed by
a mild post-monsoon period, while February–April remain comparatively dry.
Seasonal flooding of the Kaldiya and Pahumara rivers frequently results in hydrological stress
and socio-environmental disruption across the district.
Bird surveys
Surveys of wetland-associated
birds in Bajali District were conducted from April
2024 to March 2025 using the point count method (Ralph et al. 1995; Drapeau et
al. 1999; Bibby et al. 2000). A total of five-point count stations were
established across the landscape (Table 1; Image 1), spaced 1.0–2.5 km apart to
minimize the likelihood of double counting (Ralph et al. 1995). The sampling
sites were randomly selected from relatively species-rich areas, with site
selection guided by vegetation structure, food availability, and overall
habitat suitability for bird communities. The selected locations represented a
range of habitat complexes supporting varying levels of wetland-associated bird
species richness and community composition (Table 1). Surveys were conducted
two days per week, twice daily between 0600–0900 h and 1500–1700 h under
favorable weather conditions, and were postponed during periods of heavy
rainfall or strong winds to minimize observational bias. Precise GPS
coordinates were recorded for each station to ensure spatial accuracy. At each
station, observers allowed a brief acclimatization period before initiating
counts to reduce disturbance (Hostetler & Main 2001). Birds were then
recorded during a 15-minute observation period, including all individuals
detected visually or aurally within an unlimited radius (Drapeau et al. 1999;
Bibby et al. 2000). Species identification was carried out using standard field
guides (Kazmierczak 2002; Grimmett
et al. 2016; Grewal et al. 2018), based on morphological characteristics, size,
plumage, and vocalizations. When identification was uncertain, photographic and
audio records were obtained for later verification. Observations were made
using binoculars (Nikon, Monarch, 10 × 42 mm) and a spotting scope (20 × 60),
with additional documentation captured using a Nikon D7500 camera. Diversity
indices were calculated using PAST software (version 4.03). The global
conservation status of each species was determined following the IUCN Red List.
Species were classified according to their frequency of occurrence during
repeated field surveys following the classification proposed by Mackinnon &
Phillips (1993) and subsequently adopted by Byju et
al. (2024). Species recorded on 6–8 out of every 10 survey visits were
categorized as Common (C), those observed on 3–5 out of 10 visits as Uncommon
(UC), and those detected on only 1–2 out of every 10 survey visits as Rare (R).
In addition, the relative diversity of each bird family was estimated using the
relative diversity index (RDi) following Koli (2014), calculated as:
Number of species in a family
RDi = –––––––––––––––––––––––––––– x
100
Total number of species recorded
Field observations conducted
throughout the study period, together with information from standard
ornithological literature (Ali et al. 1996; Feijen
& Feijen 2008; Grimmett
et al. 2016; Billerman et al. 2022), were used to
assign all recorded bird species to seasonal occurrence categories comprising
resident species, winter visitors, and summer migrants, as well as to feeding
guilds comprising granivores, frugivores, nectivores,
insectivores, carnivores, and omnivores. Assamese vernacular names were compiled
and cross-verified using published regional sources (Gogoi
2006; Dutta 2011; Datta 2017).
RESULTS AND DISCUSSION
Species composition and seasonal
abundance of wetland-associated birds
A total of 44 wetland-associated
bird species, representing 14 avian families, were recorded from the selected
wetlands of the Bajali landscape during the study
period (April 2024–March 2025) (Table 2). The recorded assemblage comprised
both resident and migratory species occupying diverse ecological niches within
the wetland ecosystem, indicating the importance of these habitats in
supporting a taxonomically diverse avifaunal community.
Seasonal surveys conducted during
summer (pre-monsoon; March–May), monsoon (June–September), autumn
(post-monsoon; October–November), and winter (December–February) revealed
pronounced temporal variation in bird abundance (Table 3). The total abundance
was highest during winter (2,835 individuals), followed by monsoon (2,601
individuals), autumn (2,064 individuals) and summer (2,009 individuals). The
marked increase in winter abundance was primarily associated with the seasonal
arrival of migratory waterbirds, whereas relatively
lower abundance during summer reflected the predominance of resident species
prior to the onset of migration.
Seasonal fluctuations were also
evident in species richness, reflecting changes in community composition
throughout the annual hydrological cycle. Wetland habitats supported a greater
diversity of species during autumn and winter, whereas comparatively fewer species
were encountered during the monsoon. These seasonal differences indicate that
hydrological fluctuations strongly influence the availability of suitable
foraging and roosting habitats, thereby regulating the distribution and
abundance of wetland-associated birds. Similar seasonal patterns have been
reported from other wetland ecosystems in India, where post-monsoon habitat
stabilization and winter migration substantially enhance bird diversity and
abundance (Verma 2008; Nair & Krishna 2013; Kar
& Debata 2019).
Overall, the observed seasonal
variation demonstrates that the wetland bird community in the Bajali landscape is strongly influenced by annual
hydro-climatic conditions. The higher abundance recorded during winter
highlights the ecological significance of these wetlands as important seasonal
habitats for migratory waterbirds, whereas the
persistence of numerous resident species throughout the year emphasizes their
role in sustaining breeding and foraging populations under varying
environmental conditions. These findings are consistent with studies
demonstrating that seasonal abundance, species composition, and migration
dynamics of wetland birds are closely regulated by habitat quality,
hydrological conditions, prey availability, and anthropogenic disturbances,
which collectively determine habitat suitability and community structure (Ellis
et al. 2021; Jagadeesan & Pandiyan
2021; Kularatne 2021; Rashiba
et al. 2022).
Family
composition and seasonal dynamics
The wetland-associated bird
assemblage exhibited marked variation in taxonomic composition and seasonal
abundance among avian families (Image 2; Table 3). Based on relative diversity
(RDi), Ardeidae was the
most species-rich family, comprising 10 species (RDi
= 22.72%), followed by Scolopacidae with seven
species (RDi = 15.90%). Rallidae,
Charadriidae, and Alcedinidae
were each represented by four species (RDi = 9.09%),
while Ciconiidae included three species (RDi = 6.81%). Jacanidae, Threskiornithidae, Motacillidae,
and Anatidae each contributed two species (RDi = 4.54%), whereas Phalacrocoracidae,
Anhingidae, Glareolidae,
and Pandionidae were represented by a single species
each (RDi = 2.27%). The predominance of Ardeidae and Scolopacidae
indicates that the wetlands provide a broad range of shallow-water and marsh
habitats capable of supporting taxonomically diverse wading and shorebird
communities.
Pronounced seasonal variation was
evident in family-level abundance, although species within individual families
differed considerably in their numerical dominance and seasonal occurrence
(Image 3). These patterns indicate that family-level abundance was primarily
influenced by a limited number of dominant species rather than by uniform
contributions from all constituent species.
Among all families, Ardeidae remained the most abundant throughout the study
period, with abundance increasing from 758 individuals in summer to a peak of 981
individuals during the monsoon, before declining to 505 individuals in autumn and
increasing slightly to 657 individuals in winter. This dominance was largely
attributable to the Cattle Egret Bubulcus
ibis (651 individuals) and Indian Pond Heron Ardeola
grayii (624 individuals), followed by the Purple
Heron Ardea purpurea
(444 individuals). The remaining species, including the Great Egret Ardea alba (228 individuals), Medium
Egret Ardea intermedia (228
individuals), Little Egret Egretta garzetta (215 individuals), Cinnamon Bittern Ixobrychus cinnamomeus
(156 individuals), Grey Heron Ardea cinerea (155 individuals), Black-crowned Night
Heron Nycticorax nycticorax
(109 individuals), and Yellow Bittern Ixobrychus
sinensis (91 individuals) occurred in
comparatively lower numbers. The consistently high abundance of Ardeidae reflects the availability of shallow-water
foraging habitats and abundant aquatic prey throughout much of the year,
particularly during the monsoon when extensive inundation enhances feeding
opportunities for herons and egrets.
In contrast, Scolopacidae
exhibited the most pronounced seasonal variation among all recorded families.
The family was absent during the monsoon, moderately represented during summer
(91 individuals), increased substantially during autumn (290 individuals), and
attained its highest abundance during winter (415 individuals). Although the
family showed a pronounced seasonal influx, abundance was unevenly distributed
among species. The Common Snipe Gallinago
gallinago (215 individuals) was the
dominant representative, followed by the Common Greenshank Tringa
nebularia (130 individuals), Green
Sandpiper Tringa ochropus
(126 individuals), Common Sandpiper Actitis
hypoleucos (110 individuals), and Marsh
Sandpiper Tringa stagnatilis
(106 individuals), whereas Temminck’s Stint Calidris temminckii (66
individuals) and Spotted Redshank Tringa erythropus (43 individuals) were comparatively less
abundant. The complete absence of Scolopacidae during
the monsoon, followed by a substantial increase during autumn and winter,
highlights the importance of exposed mudflats and shallow wetlands created
after floodwaters recede, providing favourable
foraging habitats for migratory shorebirds.
Rallidae reached its maximum abundance
during the monsoon (446 individuals) and declined during autumn (222
individuals), winter (230 individuals), and summer (168 individuals). This
seasonal pattern was largely driven by the White-breasted Waterhen Amaurornis phoenicurus
(462 individuals) and Grey-headed Swamphen Porphyrio poliocephalus
(398 individuals), whereas the Common Moorhen Gallinula
chloropus (111 individuals), and Watercock
Gallicrex cinerea
(95 individuals) occurred less frequently. The predominance of these
marsh-dependent species during the rainy season corresponds with the expansion
of emergent vegetation and shallow inundated habitats, which provide suitable
nesting, shelter, and feeding sites.
Charadriidae was recorded throughout the
year, with abundance increasing from 179 individuals in summer to 273
individuals in autumn, followed by a slight decline to 259 individuals in
winter. Family abundance was dominated by the Red-wattled
Lapwing Vanellus indicus (460
individuals), while the Grey-headed Lapwing Vanellus
cinereus (204 individuals), Little Ringed
Plover Charadrius dubius (155 individuals), and Pacific Golden
Plover Pluvialis fulva
(76 individuals) were comparatively less abundant. Similarly, Ciconiidae reached its highest abundance during the monsoon
(238 individuals) and lowest abundance during autumn (110 individuals). The Asian
Openbill Anastomus oscitans (334 individuals) was the dominant species
within the family, followed by the Lesser Adjutant Leptoptilos
javanicus (227 individuals) and Asian Woollyneck Ciconia episcopus (150 individuals). The seasonal
occurrence of these large wading birds reflects fluctuations in water depth and
prey availability across the wetlands.
Comparable species-level
variation was also observed among the remaining families. Within Jacanidae, the Bronze-winged Jacana Metopidius indicus (271 individuals)
was more abundant than the Pheasant-tailed Jacana Hydrophasianus
chirurgus (148 individuals). In Threskiornithidae, the Black-headed Ibis Threskiornis melanocephalus
(217 individuals) slightly outnumbered the Glossy Ibis Plegadis falcinellus
(197 individuals). Motacillidae was represented
predominantly by the White Wagtail Motacilla
alba (145 individuals) compared with the Citrine Wagtail Motacilla citreola
(100 individuals). Among Alcedinidae, the White-throated
Kingfisher Halcyon smyrnensis (188
individuals) occurred more frequently than the Pied Kingfisher Ceryle rudis (175
individuals), Common Kingfisher Alcedo atthis 144 individuals), and Stork-billed
Kingfisher Pelargopsis capensis
(144 individuals). Likewise, Anatidae was
overwhelmingly dominated by the Lesser Whistling Duck Dendrocygna
javanica (624 individuals), whereas the Ruddy
Shelduck Tadorna ferruginea
(51 individuals) occurred only occasionally.
Overall, the observed
family-level patterns demonstrate that wetland bird assemblages in the Bajali landscape are strongly structured by seasonal
hydrological changes and species-specific ecological requirements. Resident
families such as Ardeidae, Rallidae,
Jacanidae, Alcedinidae, and
Anhingidae persisted throughout the year, whereas
migratory families, particularly Scolopacidae,
together with Threskiornithidae, Motacillidae,
Glareolidae, and Pandionidae,
exhibited marked seasonal occurrence, becoming most abundant during the
post-monsoon and winter periods. These findings emphasize the complementary
ecological roles of permanent wetlands and seasonally exposed mudflats in
sustaining both resident and migratory wetland bird communities, supporting
previous studies that identified seasonal habitat quality, hydrological
variability, and migration dynamics as major drivers of shorebird and waterbird assemblages (Jagadeesan
& Pandiyan 2021; Ma et al. 2021).
Community
characteristics
The wetland-associated bird
community of the Bajali landscape exhibited distinct
patterns in species occurrence, migratory status, conservation status, and
feeding guild composition (Table 2), reflecting the ecological heterogeneity
and seasonal resource availability of the wetland ecosystem.
Based on the frequency of
occurrence, the avifaunal community was dominated by common species, comprising
24 species (54.55%), followed by uncommon species (13 species; 29.55%), locally
common species (6 species; 13.64%), and a single rare species (1 species; 2.27%).
The predominance of common species suggests that the study wetlands provide
relatively stable environmental conditions capable of supporting persistent
populations of several wetland-associated birds throughout the annual cycle.
Conversely, the limited representation of rare species may reflect
species-specific habitat preferences, naturally low population densities, or
seasonal occurrence within the study area.
Analysis of migratory status
showed that resident species constituted the major component of the wetland
bird assemblage, accounting for 65.91% (29 species) of the total recorded
species, whereas winter visitors comprised the remaining 34.09% (15 species).
The dominance of resident species indicates that the wetlands provide suitable
breeding, nesting, and foraging habitats throughout the year. In contrast, the
substantial contribution of winter migratory species demonstrates the seasonal
importance of these wetlands as feeding and resting habitats along regional
migratory routes. Similar dominance of resident species accompanied by a
pronounced winter influx of migratory waterbirds has
been documented from other wetland ecosystems across India (Verma
2008; Nair & Krishna 2013; Kar & Debata
2019), highlighting the importance of maintaining habitat quality for both
resident and migratory populations.
Assessment of conservation status
based on the IUCN Red List revealed that the majority of recorded species were
classified as ‘Least Concern’ (42 species; 95.46%), whereas only two species
(4.54%), namely the Lesser Adjutant Leptoptilos
javanicus and the Asian Woollyneck
Ciconia episcopus,
were categorized as ‘Near Threatened’. Although these threatened species represented
only a small proportion of the recorded avifauna, their regular occurrence
emphasizes the conservation value of the Bajali
wetlands in supporting species of global conservation concern. The presence of
Near Threatened waterbirds further highlights the
need for continued monitoring and effective habitat management to ensure the
long-term persistence of these vulnerable populations.
The wetland-associated bird
assemblage was also differentiated according to feeding guilds. Carnivorous
species predominated, accounting for 29 species (65.91%), followed by omnivorous
species (10 species; 22.72%), insectivorous species (4 species; 9.09%), and a
single piscivorous species (1 species; 2.27%). The predominance of carnivorous
birds reflects the high availability of aquatic prey, including fishes,
amphibians, molluscs, crustaceans, and aquatic
invertebrates, within the wetland ecosystem. Such trophic composition is
characteristic of productive freshwater wetlands, where abundant food resources
support a diverse assemblage of higher trophic-level waterbirds.
Collectively, these community
characteristics demonstrate that the wetlands of the Bajali
landscape support a structurally diverse avian assemblage composed
predominantly of resident and common species, while simultaneously functioning
as important seasonal habitats for migratory waterbirds
and species of conservation concern. The coexistence of multiple feeding guilds
further indicates that these wetlands provide a wide range of ecological
resources capable of sustaining diverse functional groups throughout the year,
thereby emphasizing their ecological significance within the regional wetland
network.
Seasonal
variation in diversity indices
The diversity indices revealed
pronounced seasonal variation in the structure, composition, and stability of
the wetland-associated bird community (Table 4). Observed species richness (Taxa_S) was highest during autumn and winter (44 species
each), followed by summer (42 species), whereas the monsoon recorded the lowest
richness (29 species). The higher richness during autumn and winter coincided
with the arrival of migratory waterbirds and the
availability of favourable habitat conditions
following the monsoon. In contrast, the reduced richness during the monsoon is
likely attributable to extensive flooding, increased water depth,
breeding-related behavioural changes, and lower
detectability of birds within dense emergent vegetation. Similar seasonal
fluctuations have been widely reported in freshwater wetlands, where hydrological
regimes strongly regulate habitat availability and bird community composition (Saygili et al. 2011; Kumar & Sharma 2019).
Patterns of species diversity
further supported these seasonal differences. The Shannon–Wiener diversity
index (H′) reached its highest value during autumn (3.655), followed closely by
winter (3.654) and summer (3.426), while the lowest value was recorded during
the monsoon (3.080). Likewise, Simpson’s diversity index (1−D) was highest
during autumn (0.971), followed by winter (0.9708) and summer (0.9595), whereas
the monsoon exhibited the lowest diversity (0.9448). Conversely, Simpson’s
dominance index (D) showed an inverse trend, attaining its highest value during
the monsoon (0.05524) and lowest value during autumn (0.02905). The concurrence
of high Shannon and Simpson diversity together with low dominance during autumn
and winter indicates a comparatively balanced community in which individuals
were more evenly distributed among species. Conversely, increased dominance
during the monsoon suggests that only a few species contributed
disproportionately to total abundance, resulting in a comparatively simplified
community structure under seasonally constrained environmental conditions.
Similar seasonal responses of diversity indices have been reported in wetland
bird communities where hydrological fluctuations influence habitat quality and
resource availability (Azizoglu et al. 2023).
Species evenness also varied
considerably among seasons. Pielou’s evenness (J’)
was highest during autumn (0.8791), followed by winter (0.8777) and monsoon
(0.7505), while the lowest value occurred during summer (0.7320). Greater
evenness during autumn and winter indicates a more equitable distribution of
individuals among species, suggesting relatively balanced resource utilization
and reduced numerical dominance. In contrast, the lower evenness observed
during summer and the monsoon reflects greater dominance by a limited number of
abundant species, likely resulting from seasonal variation in habitat
conditions and resource availability.
The richness estimators showed
remarkable consistency in describing seasonal community structure. Menhinick’s index reached its highest value during autumn
(0.9685), while Margalef’s richness index was also
greatest during autumn (5.634), followed by winter (5.409). Similarly, Fisher’s
alpha attained its maximum value during autumn (7.900) and remained
comparatively high during winter (7.393). The agreement among these independent
richness estimators provides robust evidence that post-monsoon and winter
conditions supported the greatest true species richness within the study
wetlands. These periods are characterized by stabilized hydrological
conditions, increased habitat heterogeneity, and enhanced availability of
aquatic food resources, thereby creating favourable
conditions for both resident and migratory waterbirds.
The Berger–Parker dominance index
further reinforced these seasonal patterns. The lowest dominance was recorded
during autumn (0.05329), whereas comparatively higher values were observed
during summer (0.09009) and the monsoon (0.08997). Lower Berger-Parker values
indicate that no single species overwhelmingly dominated the assemblage,
reflecting a more heterogeneous and balanced bird community during the
post-monsoon period. In contrast, increased dominance during summer and the
monsoon suggests that environmental conditions favoured
relatively few adaptable species, thereby reducing overall community
heterogeneity.
The seasonal patterns observed in
the diversity indices were further supported by the Q–Q plot (Image 4),
which demonstrated that bird abundance data generally conformed to normality
assumptions across seasons, with only minor deviations at the lower and upper
quantiles. Winter and autumn communities exhibited comparatively stable
distributional patterns, whereas the steeper gradient observed during the
monsoon reflected greater variability in abundance and the influence of a few
highly dominant species. These results indicate that seasonal hydrological
conditions not only influence species richness and diversity but also affect
the overall distributional characteristics of wetland bird assemblages.
Collectively, the diversity
analyses demonstrate that the wetland bird community of the Bajali
landscape undergoes substantial seasonal reorganization in response to
hydrological fluctuations and habitat dynamics. The post-monsoon and winter
seasons supported the highest levels of species richness, diversity, and
community evenness, primarily owing to improved habitat conditions, greater
habitat heterogeneity, enhanced food availability, and the seasonal influx of
migratory waterbirds. In contrast, extensive
monsoonal inundation reduced habitat suitability for several species, resulting
in lower species richness, increased dominance, and a comparatively simplified
community structure. These findings are consistent with previous studies
demonstrating that seasonal hydrology, water-level fluctuations, habitat
quality and heterogeneity, prey availability, and migration dynamics are the
principal ecological drivers shaping the diversity, abundance, and community
organization of wetland-associated birds across freshwater and coastal wetland
ecosystems (Colwell & Dodd 2017; Kumar & Sharma 2018, 2019; Kumar 2019;
Ellis et al. 2021; Jagadeesan & Pandiyan 2021; Kularatne 2021; Ma
et al. 2021; Rashiba
et al. 2022; Byju et al. 2025a,b). Overall, these
findings highlight the ecological importance of maintaining natural
hydrological regimes, habitat heterogeneity, and wetland integrity to sustain
diverse resident and migratory wetland bird communities.
CONCLUSION
This study provides the first comprehensive
baseline assessment of the diversity, seasonal dynamics, and community
structure of wetland-associated birds in the wetlands of Bajali
District, Assam, thereby addressing an important knowledge gap for the lower
Brahmaputra floodplain. The documented assemblage of resident and migratory
species demonstrates that these wetlands function as ecologically important
habitats that support breeding, foraging, and seasonal refuge for a diverse
avifaunal community. The marked seasonal variation in species richness,
abundance, and community composition confirms that hydrological regimes,
habitat heterogeneity, and seasonal resource availability are the principal
ecological drivers shaping wetland bird assemblages in the region.
The regular occurrence of the ‘Near Threatened’
Lesser Adjutant and Asian Woollyneck further
highlights the conservation significance of these wetlands and underscores the
need to maintain habitat quality amid increasing anthropogenic pressures.
Protecting shallow wetlands, marshes, seasonally exposed mudflats, and riparian
habitats will be essential for sustaining both resident populations and winter
migratory birds that depend on these ecosystems.
Beyond providing the first
checklist for Bajali District, this study establishes
an important ecological benchmark against which future changes in wetland bird
communities can be evaluated. Continued long-term monitoring, combined with
habitat restoration, regulation of wetland degradation, and community-based
conservation initiatives, will be crucial for safeguarding the ecological
integrity of these wetlands under ongoing land-use change and climate
variability. The findings presented here provide a scientific foundation for
future biodiversity assessments, conservation planning, and sustainable wetland
management in the lower Brahmaputra valley.
Table 1. The geographic coordinates, elevation, and habitat characteristics of the five bird
survey sites.
|
|
Survey sites |
Coordinates |
Habitat type and vegetation
characteristics |
Elevation (in m) |
|
|
Latitude (oN) |
Longitude (oE)
|
||||
|
1 |
Site-1 |
26.5071 |
91.1876 |
Grass embankments of village
ponds with standing freshwater and emergent aquatic vegetation |
44 |
|
2 |
Site-2 |
26.5055 |
91.2272 |
Marshlands with extensive
reedbeds fringing permanent wetlands |
47 |
|
3 |
Site-3 |
26.5481 |
91.1671 |
Damp grasslands interspersed
with cultivated paddy fields |
49 |
|
4 |
Site-4 |
26.5287 |
91.1625 |
Seasonally flooded grasslands
associated with rice-growing areas |
47 |
|
5 |
Site-5 |
26.5310 |
91.1500 |
Riverbank habitats with
riparian vegetation |
45 |
Table 2. Checklist of wetland-associated
bird species recorded in Bajali District, Assam, with taxonomic details, local names, habitat, feeding guilds, abundance, phenology, and conservation status.
|
|
Family |
English name |
Scientific name |
Local name/ Assamese name |
IUCN Red List status |
IWPA |
Habitat location |
Feeding habits/ Feeding guilds |
Abundance status |
Phenological status |
|
1 |
Ardeidae |
Little Egret |
Egretta garzetta (Linnaeus, 1766) |
টেটেৰী বগ |
LC |
Schedule II |
WE, OW, T |
CA |
COM |
R |
|
2 |
Grey Heron |
Ardea cinerea (Linnaeus, 1758) |
হালখেদা |
LC |
Schedule II |
WE |
CA |
COM |
R |
|
|
3 |
Indian Pond Heron |
Ardeola grayii (Sykes, 1832). |
কণামুচৰি |
LC |
Schedule II |
WE |
CA |
COM |
R |
|
|
4 |
Yellow Bittern |
Ixobrychus sinensis (Gmelin, 1789). |
হালধি কণা/ হালধীয়া বগুলা |
LC |
Schedule II |
WE |
CA |
UNCOM |
R |
|
|
5 |
Great Egret |
Ardea alba (Linnaeus, 1758) |
বৰ বগ |
LC |
Schedule II |
OW, WE, T |
CA |
COM |
R |
|
|
6 |
Cattle Egret |
Bubulcus ibis (Linnaeus, 1758) |
গো বগ |
LC |
Schedule II |
WE |
CA |
COM |
R |
|
|
7 |
Purple Heron |
Ardea purpurea (Linnaeus, 1766) |
আজান |
LC |
Schedule II |
OW, WE |
CA |
UNCOM |
R |
|
|
8 |
Medium Egret |
Ardea intermedia (Wagler, 1829.) |
মাজু বগ |
LC |
Schedule II |
OW, WE |
CA |
COM |
R |
|
|
9 |
Cinnamon Bittern |
Ixobrychus cinnamomeus (Gmelin, 1789). |
ইটাগুড়ীয়া |
LC |
Schedule II |
WE |
CA |
LOC COM |
R |
|
|
10 |
Black- crowned Night Heron |
Nycticorax nycticorax (Linnaeus, 1758) |
ৱাক চৰাই |
LC |
Schedule II |
WE |
CA |
UNCOM |
R |
|
|
11 |
Scolopacidae |
Common Sandpiper |
Actitis hypoleucos (Linnaeus, 1758). |
বালি খোঁচৰা |
LC |
Schedule II |
WE |
CA |
COM |
WM |
|
12 |
Marsh Sandpiper |
Tringa stagnatilis (Bechstein, 1803) |
বোকাপানী খোঁচৰা / পিতনিৰ বালি খোঁচৰা |
LC |
Schedule II |
OW, WE |
CA |
UNCOM |
WM |
|
|
13 |
Common Greenshank |
Tringa nebularia (Gunnerus, 1767). |
পাত ঠেঙী |
LC |
Schedule I |
OW, WE |
CA |
UNCOM |
WM |
|
|
14 |
Green Sandpiper |
Tringa ochropus (Linnaeus, 1758) |
বালি বগুৱা/ সেউজীয়া বালি খোঁচৰা |
LC |
Schedule II |
WE |
CA |
RARE |
WM |
|
|
15 |
Common Snipe |
Gallinago gallinago (Linnaeus, 1758) |
চেৰেকা চৰাই / বালিটোকা |
LC |
Schedule II |
WE |
CA |
UNCOM |
WM |
|
|
16 |
Spotted Redshank |
Tringa erythropus (Pallas, 1764). |
ফুটুকী ৰঙা বালি খোঁচৰা |
LC |
Schedule II |
OW, WE |
CA |
UNCOM |
WM |
|
|
17 |
Temminck's Stint |
Calidris temminckii (Leisler, 1812) |
|
LC |
Schedule II |
OW, WE |
CA |
UNCOM |
WM |
|
|
18 |
Charadriidae |
Pacific Golden Plover |
Pluvialis fulva (Gmelin, 1789) |
সোণালী লৰিয়লি |
LC |
Schedule I |
OW, WE |
OM |
UNCOM |
WM |
|
19 |
Grey-headed Lapwing |
Vanellus cinereus (Blyth, 1842). |
দলঘোঁৰা |
LC |
Schedule II |
WE |
INSEC |
COM |
WM |
|
|
20 |
Red-wattled
Lapwing |
Vanellus indicus (Boddaert, 1783) |
বালিঘোঁৰা / টিটিহুট |
LC |
Schedule II |
WE |
OM |
COM |
R |
|
|
21 |
Little Ringed Plover |
Charadrius dubius (Scopoli, 1786. ) |
সৰু লৰিয়লি |
LC |
Schedule II |
WE |
CA |
UNCOM |
R |
|
|
22 |
Rallidae |
White-breasted Waterhen |
Amaurornis phoenicurus (Pennant, 1769). |
ডাউক |
LC |
Schedule II |
WE |
OM |
COM |
R |
|
23 |
Watercock |
Gallicrex cinerea (Gmelin, 1789) |
পানী কুকুৰা |
LC |
Schedule II |
WE |
OM |
UNCOM |
R |
|
|
24 |
Grey-headed Swamphen |
Porphyrio poliocephalus (Latham, 1801). |
কাম চৰাই |
NE |
Schedule II |
WE |
OM |
COM |
R |
|
|
25 |
Common Moorhen |
Gallinula chloropus (Linnaeus, 1758). |
দেশী কোৰা ঢেকৰ |
LC |
Schedule II |
WE |
OM |
COM |
R |
|
|
26 |
Ciconiidae |
Asian Openbill |
Anastomus oscitans (Boddaert, 1783). |
শামুক ভঙা |
LC |
Schedule II |
WE |
CA |
COM |
R |
|
27 |
Lesser Adjutant Stork |
Leptoptilos javanicus (Horsfield, 1821). |
বৰটোকোলা/ হদং |
NT |
Schedule I |
WE |
CA |
LOC COM |
R |
|
|
28 |
Asian Woollyneck
|
Ciconia episcopus (Boddaert, 1783). |
কনুৱা চৰাই |
NT |
Schedule IV |
WE |
CA |
LOC COM |
R |
|
|
29 |
Jacanidae |
Bronze-winged Jacana |
Metopidius indicus (Latham, 1790). |
দলপুঙা |
LC |
Schedule II |
WE |
OM |
COM |
R |
|
30 |
Pheasant-tailed Jacana |
Hydrophasianus chirurgus (Scopoli, 1786). |
দলম'ৰা/ জলময়ূৰ |
LC |
Schedule II |
WE |
OM |
COM |
R |
|
|
31 |
Threskiornithidae |
Black-headed Ibis |
Threskiornis melanocephalus (Latham, 1790). |
আঁকুহী বগ |
LC |
Schedule II |
WE |
CA |
COM |
WM |
|
32 |
Glossy Ibis |
Plegadis falcinellus (Linnaeus, 1766). |
ইটাগুড়ীয়া আঁকুহী বগ |
LC |
Schedule II |
WE |
CA |
LOC COM |
WM |
|
|
33 |
Motacillidae |
White Wagtail |
Motacilla alba (Linnaeus, 1758) |
বগা বালিমাহী/ খঞ্জন |
LC |
Schedule II |
WE |
INSEC |
COM |
WM |
|
34 |
Citrine Wagtail |
Motacilla citreola (Pallas, 1776) |
হালধিমূৰীয়া বালিমাহী |
LC |
Schedule II |
WE, WA |
INSEC |
COM |
WM |
|
|
35 |
Alcedinidae |
Stork-billed Kingfisher |
Pelargopsis capensis (Linnaeus, 1766) |
বৰটোকোলাঠুঁটীয়া মাছৰোকা |
LC |
Schedule II |
T |
CA |
LOC COM |
R |
|
36 |
White-throated Kingfisher |
Halcyon smyrnensis (Linnaeus, 1758) |
বগাবুকুৱা মাছৰোকা |
LC |
Schedule II |
T |
CA |
COM |
R |
|
|
37 |
Common Kingfisher |
Alcedo atthis (Linnaeus, 1758) |
সাধাৰণ মাছৰোকা |
LC |
Schedule II |
T |
CA |
COM |
R |
|
|
38 |
Pied Kingfisher |
Ceryle rudis (Linnaeus, 1758) |
পখৰা মাছৰোকা |
LC |
Schedule II |
T |
CA |
COM |
R |
|
|
39 |
Phalacrocoracidae |
Little Cormorant |
Phalacrocorax niger (Vieillot, 1817) |
পানী কাউৰী |
LC |
Schedule II |
OW |
CA |
COM |
R |
|
40 |
Anhingidae |
Oriental Darter |
Anhinga melanogaster (Pennant, 1769) |
মণিয়ৰি |
LC |
Schedule II |
OW, WE, T |
CA |
LOC COM |
R |
|
41 |
Glareolidae |
Small Pratincole |
Glareola lacteal (Temminck, 1820) |
তিতিয়লী |
LC |
Schedule II |
OW |
INSEC |
UNCOM |
R |
|
42 |
Anatidae |
Lesser Whistling Duck |
Dendrocygna javanica (Horsfield, 1821) |
শৰালি হাঁহ |
LC |
Schedule II |
OW |
OM |
COM |
R |
|
43 |
Ruddy Shelduck |
Tadorna ferruginea (Pallas, 1764) |
চাকৈ-চকোৱা |
LC |
Schedule II |
OW |
OM |
COM |
WM |
|
|
44 |
Pandionidae |
Osprey |
Pandion haliaetus (Linnaeus, 1758) |
চিল কুৰুৱা |
LC |
Schedule I |
OA, WA |
Pisc |
UNCOM |
WM |
OA—Open Area | OW—Open Water |
WE—Water Edge | T—Trees | WA—Water Associated | COM—Common | UNCOM—Uncommon |
LOC COM—Locally common | CA—Carnivorous | INSEC—Insectivorous | OM—Omnivorous |
Pisc—Piscivorous | R—Resident | WM—Winter Migrant |
LC—Least Concern | NT—Near Threatened.
Table 3. Seasonal abundance of wetland-associated bird families and
their relative diversity in the Bajali District, Assam.
|
Name of the family |
Number of species observed |
Relative diversity (%) |
Seasons with no of individuals
observed |
|||
|
Summer (pre-monsoon) |
Monsoon |
Autumn (post monsoon) |
Winter |
|||
|
Ardeidae |
10 |
22.72 |
758 |
981 |
505 |
657 |
|
Scolopacidae |
7 |
15.90 |
91 |
0 |
290 |
415 |
|
Charadriidae |
4 |
9.09 |
179 |
184 |
273 |
259 |
|
Rallidae |
4 |
9.09 |
168 |
446 |
222 |
230 |
|
Ciconiidae |
3 |
6.81 |
168 |
238 |
110 |
195 |
|
Jacanidae |
2 |
4.54 |
96 |
161 |
62 |
100 |
|
Threskiornithidae |
2 |
4.54 |
113 |
0 |
100 |
201 |
|
Motacillidae |
2 |
4.54 |
32 |
0 |
92 |
121 |
|
Alcedinidae |
4 |
9.09 |
126 |
177 |
144 |
204 |
|
Phalacrocoracidae |
1 |
2.27 |
102 |
152 |
62 |
121 |
|
Anhingidae |
1 |
2.27 |
36 |
48 |
32 |
46 |
|
Glareolidae |
1 |
2.27 |
4 |
0 |
34 |
41 |
|
Anatidae |
2 |
4.54 |
124 |
214 |
126 |
211 |
|
Pandionidae |
1 |
2.27 |
12 |
0 |
12 |
34 |
|
Total |
44 |
|
2009 |
2601 |
2064 |
2835 |
Table 4. Seasonal variation in diversity indices of the wetland-associated
bird community in the study area.
|
Indices |
Summer (pre-monsoon) |
Monsoon |
Autumn (post-monsoon) |
Winter |
|
Taxa_S |
42 |
29 |
44 |
44 |
|
Individuals |
2009 |
2601 |
2064 |
2835 |
|
Dominance_D |
0.0405 |
0.05524 |
0.02905 |
0.0292 |
|
Simpson_ 1-D |
0.9595 |
0.9448 |
0.971 |
0.9708 |
|
Shannon_H |
3.426 |
3.08 |
3.655 |
3.654 |
|
Evenness_e H/S |
0.732 |
0.7505 |
0.8791 |
0.8777 |
|
Menhinick |
0.937 |
0.5686 |
0.9685 |
0.8264 |
|
Margalef |
5.391 |
3.561 |
5.634 |
5.409 |
|
Fisher_alpha |
7.509 |
4.57 |
7.9 |
7.393 |
|
Berger-Parker |
0.09009 |
0.08997 |
0.05329 |
0.06561 |
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