Avian assemblages in two contrasting oxbow lakes of the lower Gangetic delta, West Bengal, India: A comparative approach

A comparative study was conducted to assess the species composition, diversity and abundance of avifauna in and around two contrasting oxbow lakes from lower Gangetic delta of West Bengal, India: Purbasthali lake (PL) and Hansadanga lake (HL). Comprehensive avian surveys were carried out for one year (January 2024 to December 2024) using fixed-radius point count method, followed by some analytical approaches. PL supported a markedly richer avian assemblage, with 82 species across 23 families, compared with 45 species across 19 families in HL. Family-level dominance also differed, as Anatidae dominated PL, while Ardeidae prevailed in HL, as reflected in Relative Diversity (RD_i) values. Both lakes were dominated by carnivores, with transitional-zone species most frequent, especially in PL. Species richness and diversity were highest during post-monsoon months in both the lakes due to influx of migratory waterbirds. Winter migrants were more abundant in PL (51.2% of species) compared to HL (28.9%). Diversity indices and multivariate community analyses further demonstrated that PL, owing to its semi-lotic hydro-environmental condition, supports richer and more functionally diverse bird communities with greater migrant abundance than the closed-lentic HL. The current findings emphasize the ecological significance of semi-lotic oxbow lakes like PL as vital refuges for migratory and threatened waterbirds in the lower Gangetic delta, warranting strengthened conservation and management. In contrast, the degraded condition of closed-lentic oxbow lakes such as HL highlights the urgent need for ecological restoration and sustainable interventions to enhance their capacity to support diverse bird assemblages.