Abstract

Birds play very essential ecological functions such as pest control, pollination, seed dispersal as well as nutrient dynamics and they are very good indicators of the ecosystem health in a landscape. Biodiversity inventory and their conservation including ecosystem restoration at landscape level has recently emerged as a global priority for effective management planning to ensure ecosystem stability and ecological functionality. This study aims to create a baseline database of avifaunal assemblages from the recently recognized Raimona National Park in the state of Assam, India. This new protected area is located in the Bhabar belt covering 422 km² area under the Kachugaon forest division of the state. The systematic grid-based line transect method was followed from November 2020 to April 2021 and confirmed the presence of total 227 avian species from the study area among which 7 species were globally threatened. The area also harbours the suitable habitat of critically endangered White-bellied heron (Ardea insignis Hume, 1878). Extensive research and long-term monitoring will be very crucial in the near future for the inventory of more avian fauna along with their conservation in the Raimona National Park.

1. Introduction

Birds play very essential ecological functions such as pest control, pollination, seed dispersal as well as nutrient dynamics and they are very good indicators of the ecosystem health in a landscape ^{1, 2, 3}. As north eastern part of India holds unique environmental conditions and diversified habitat types due to its geographical position have helped to flourish more than 950 avian species which around 77% of the avifauna recorded from India ^{4, 5, 6}. Assam harbours a total 850 avifauna including a few doubtful species which are likely to occur in the state ^{7, 8}. But, at present our global avian diversity is under tremendous pressure of anthropogenic factors like encroachment, deforestation and over exploitation of biological resources that adversely affected the ecosystem functionalities ^{9, 10, 11, 12, 13}. Biodiversity inventory and their conservation including ecosystem restoration at landscape level has recently emerged as a global priority for effective management planning to ensure ecosystem stability and ecological functionality ^{14, 15}.

The Ripu Reserve Forest (RF) under Kachugaon forest division of Kokrajhar district in Assam was one of the best managed forests since the late 19^th century in the country ¹⁶. The area was well known for huge stretches of sal (Shorea robusta) forest, which were systematically extracted and transported by the colonial authority for making railway sleeper ^{17, 18}. This landscape is one of the Important Bird and Biodiversity Areas (IBA Site; IN-AS-37) of the country ¹⁹. The unsustainable trend of forest products extraction and exploitation in the late 20^th century resulted severe deterioration of wildlife habitats and major part of the Ripu RF on its southern side has been decimated altogether converting to agricultural land and homestead settlement ²⁰. To arrest this trend of suicidal destruction of such century old managed natural forest, a larger part (422 km²) of Ripu RF has included in the protected area network and notified as “Raimona National Park” vide Govt. Notification No. FRW.02/2021/27 dated 9^th June, 2021 for long term conservation of its wildlife and their habitats in the landscape ¹³. No detailed study on the avifauna has been conducted in the landscape yet. The main aim of this inventory survey was to create the baseline of avian fauna found in the Raimona National Park of Assam, India.

2. Materials and Methods

The survey was carried out in the Raimona National Park (NP) spanning across 422 km² area that falls under Kachugaon forest division in the north-western most part of Assam, India (Figure 1). The Indo-Bhutan International border forms the northern boundary from the Sonkosh river on the west to Saralbhanga river on the east. The Buxa Tiger Reserve (TR) of West Bengal is located on the west and the Phipsoo Wild Life Sanctuary (WLS) of Bhutan is located on the north which are contiguous with the study area.

The study area falls under typical Bhabar belt intersected by numerous water courses. The ground is gently sloping towards south with elevation varies from 85-240m above mean sea level. The soil over the bulk of Bhabar area is dry sandy loam superimposed on a bed of pebbles with only a very thin humus layer. Surface stones are fairly frequent ^{13, 21}. Climate of the study area is moist tropical monsoon type with temperature varies from 7°C to 34°C and with annual average rainfall ranges from 2000mm to 3000mm ¹⁹. Due to its unique geographical location and geology, as many as twelve different types and sub-types from the very moist sal forests, sub-Himalayan high alluvial semi-evergreen forests, moist-mixed deciduous forests, savannah forests, riparian fringing forests to khoir-sisoo forests including the wide river beds classified by Champion and Seth ²².

The study area was divided into 104 grids of size 4 km² each (2km x 2km). A total 85 sampling grids were selected randomly for the study those were accessible and representative of the entire landscape. In each grid three line transects of length 1km were laid for conducting the field survey ²³. The survey was carried out following the line transect method by a team consisting of two biologists and two local frontline staffs of forest department during day-time in two sessions i.e., in the morning (06h30-10h30) and in the afternoon (15h00-17h00) during winter and pre-monsoon season for six months from November 2020 to April 2021. Opportunistic observations were also taken into consideration so that every species sighted during the survey period had been well recorded. The birds were observed by the aid of binoculars (Vortex 8X42, Zeiss 8X42) and photographed using digital camera (Nikon Coolpix P900, Canon sx600) whenever possible. GPS data were collected with help of Garmin eTrex 30. For some shy and elusive birds call playback method was also used with help of standard sound recorders (Zoom H6). The recorded avian species were identified in field with the help of standard field guidebook ²⁴. The identifications of avian fauna were also confirmed with the help of guide book by Ali and Ripley ²⁵. Broad habitat types, migratory status and conservation status were assigned to the species’ based on the field observation ^{26, 27}.

3. Results

During the six months period of survey in winter and pre-monsoon season, a total 267 km walked in transects following the existing forest paths and animal trails in 89 sampling grids in 11 forest blocks of the study area. This survey revealed the presence of total 227 avian species belonging to 19 orders and 58 families distributed throughout different habitat types of the Raimona National Park (Table 1). Out of all the orders, Passeriformes holds around 116 species (51%) making it the dominant order in terms of species richness followed by order Accipitriformes (18 species), Piciformes (14 species), Coraciiformes (11 species), Columbiformes (9 species), Charadriiformes (9 species), Strigiformes (7 species), Cuculiformes (7 species), Bucerotiformes (5 specie), Falconiformes (5 species), Pelecaniformes (5 species), Gruiformes (5 species), Galliformes (4 species), Psittaciformes (3 species), Anseriformes (3 species), Ciconiiformes (2 species), Suliformes (2 species), Caprimulgiformes, (1 species), and Trogoniformes (1 species) (Figure 2).

Among all the recorded avian fauna, Black-crested bulbul (Rubigula flaviventris Tickell, 1833), Black drongo (Dicrurus macrocercus Vieillot, 1817) and Golden-fronted leafbird (Chloropsis aurifrons Temminck, 1829) were respectively three highly dominant species found in all the habitat types of Raimona National Park. There were total 7 globally threatened avian species found in the study area, out of which two species were critically endangered such as White-rumped vulture (Gyps bengalensis Gmelin, 1788) and Slender-billed vulture (Gyps tenuirostris Gray, 1844); five vulnerable viz., Greater spotted eagle (Clanga clanga Pallas, 1811), Great hornbill (Buceros bicornis Linn, 1758), Wreathed hornbill (Rhyticeros undulates Shaw, 1811), Rufous-necked hornbill (Aceros nipalensis Hodgson, 1829), Lesser adjutant (Leptoptilos javanicus Horsfield, 1821) as well as seven near threatened species. Amongst these, there were a total 43 migratory bird species and 184 were residential bird species as per Choudhury (2000). These includes a total 45 species of aquatic birds and 182 species of terrestrial birds as observed in the field and described by Grimmett et al. (2016) (Figure 3).

4. Discussion

This short-term inventory survey revealed the presence of total 227 species of avian fauna in the Raimona National Park of Assam which signifies the conservation importance and shows equally important like Buxa Tiger Reserve of West Bengal on its west and Phipsoo Wildlife Sanctaury of Bhutan on its north. A total 284 species of avian fauna recorded from the Buxa Tiger Reserve ²⁸ and total 177 species of avian fauna from the Phipsoo Wildlife Sanctuary ²⁹. A preliminary survey conducted between Sankosh river in the west and Aie river in the east had recorded a total 270 avian species from the area which was slightly more than our findings ³⁰. A few notable woodlands avian fauna viz., Pygmy flycatcher (Ficedula hodgsoni), Bay woodpecker (Blythipicus pyrrhotis), Short-billed minivet (Pericrocotus brevirostris), Rufous-necked laughingthrush (Pterorhinus ruficollis) and Greater adjutant (Leptoptilos dubius) were also reported to be present in this IBA site ¹⁹; but our survey couldn’t record their presence in the study area. Short survey period and detection difficulty in dense vegetation cover including some inaccessible locations or terrain like Bamba Forest block along with the northernmost part of Pekua and Polo Forest blocks may have partly resulted the slightly lower number of avian species in the study area. Extensive research and long-term monitoring will be very crucial in near future for the inventory of more avian fauna along with their conservation in the Raimona National Park.

The dominance of order Passeriformes having 116 species of avian fauna indicates the presence of heterogenous habitat types in the study area ³⁰. The avian fauna of Passeriformes are also known as songbirds because of their excellent singing abilities. The area is a home for around 30 species of predatory bird which include diurnal raptors belonging to order Accipitriformes and Falconiformes and nocturnal predatory birds of order Strigiformes. Raptors plays significant roles as apex predators of an ecosystem and their presence indicates a healthy ecosystem health ³¹. The presence of 7 globally threatened avian fauna is an indication that the area needs utmost protection for the conservation of these threatened species. The largest frugivorous forest birds such as Great Indian hornbill, Wreathed hornbill and Rufous-necked hornbill were recorded from the deep forest habitats in the study area which proves that the forest is still pristine at least in some parts but they are sensitive too to the selective logging especially their roosting and nesting trees along with other human disturbances ³². Presence of Swamp francolin (Francolinus gularis) and Bengal florican (Houbaropsis bengalensis) are also suspected to be present the grassland habitats, but we couldn’t record these birds during our survey period. The recent records of critically endangered White-bellied heron (Ardea insignis Hume, 1878) from Phipsoo Wildlife Sanctuary of Bhutan as well as from Jamduar and Pepsu area of Raimona is an important indication of the fact that the study area holds suitable habitat for this highly threatened bird species ²⁹.

5. Conclusion

The present study is the first of its kind and forms the baseline data in terms avian fauna in the Raimona National Park of Assam, India. Confirmed presence of minimum 227 avian species that includes 7 globally threatened avian fauna is very significant for the area. Extensive research and long-term monitoring in all the habitat types covering all the seasons of the year will be very crucial in near future for the inventory of more avian fauna along with their conservation in the Raimona National Park of Assam, India.

Acknowledgements

The authors take this opportunity to thank the Department of Environment and Forest-Government of Assam and Bodoland Territorial Council for their co-operation and collaboration with Wildlife Trust of India (WTI). We also acknowledge the major funding support of the International Fund for Animal Welfare-IFAW in restoration and conservation of Greater Manas landscape. We are also very thankful to CHD Forest of BTC and DFO Kachugaon Forest Division for providing necessary permission and other logistic supports during the survey period. We specially acknowledge Dr. Rahul Kaul and Dr. Samir K. Sinha for their valuable suggestions and constant support provided at all the time. We also indebted to all the Range Officers and frontline forest staffs including NGO members of Raimona National Park for their constant support and kind help during the survey. The authors are also thankful to the reviewers for their constructive comments and suggestions in improving this document.

References