A review and field verification of avian diversity and habitat use in the greater Sundarbans of India, Bangladesh and their hinterland

The world-famous greater Sundarbans, the largest single block of tidal halophytic mangrove forest in the world and endangered ecosystem located in the Bengal delta, is now confined to 10,277 km2conservation areas in India (4260 km2) and Bangladesh (6017 km2) over 250 odd-islands, designated as the Natural World Heritage-cum-Ramsar Sites of ornithological importance. The Sundarbans is fringed by 11,936.26 km2 reclaimed agricultural fields/human settlements [‘Sundarbans Transition Zone’ (STZ), India and Ecologically Critical Areas (ECAs) plus Sundarbans Impact Zone (SIZ), Bangladesh]. This highly productive ecosystem provides diverse and abundant floral and faunal food resources, having high caloric concentrations, for the aves. A comprehensive study was conducted during 2019–2022 to bridge the knowledge-gaps of the avian diversity and habitat use through structural review of published and grey literature as well as field-based rapid assessment in the potential sites. 598 species, classified under 23 orders, 85 families and 277 genera, including seven extinct and about 40 old records, have been recorded in the study area. The terrestrial, arboreal and aquatic habitats are conveniently utilised by 32% resident and 68% migratory (summer and winter) birds for meeting their biological needs. 32.27% of them are commonly sighted and 67.73% rarely confronted. Considering the present biotic and abiotic threats, the rare birds are of high priority for future conservation actions.