Understanding the bird diversity patterns and habitat stratification in a freshwater ecosystem

This study documented avian species richness, abundance, and distribution across five habitat zones – open water, riparian margins, floating vegetation, emergent vegetation, and upland areas – while assessing the impact of invasive vegetation of a large freshwater wetland in Nagaon district of Assam, India. Field surveys conducted from February 2024 to March 2025, using fixed-point counts and geographic information system (GIS)-based vegetation analysis, recorded 55 bird species belonging to 15 orders, 30 families and 59 genera, with Passeriformes being the most dominant. Diversity indices showed the highest richness in riparian zones (33 species; Shannon–Wiener H′ = 2.89; Simpson 1 − D = 0.81), and the upland zone the highest H′ value (29 species; H′ = 2.95), whereas the open water zone showed the lowest diversity (7 species; H′ = 0.12; 1 − D = 0.04) as Lesser Whistling Duck dominated the open water. GIS analysis revealed the rapid spread of Eichhornia crassipes, fragmenting open water and reducing ecological heterogeneity. Findings highlight invasive species and anthropogenic pressures as major threats, underscoring the need for basin-level management to restore habitats and conserve Hanhila Beel’s biodiversity.