Temporal changes in diversity and abundance of wintering birds in the Gavkhuni international wetland, Isfahan Province, Iran

Wetlands serve as critical habitats for migratory birds, providing vital resources for foraging, resting, and breeding. This study assessed the diversity and abundance of wintering aquatic and wader birds in the Zayandeh-Rud–Gavkhuni basin over five years (2020–2024). A total of 12,219 individuals from 57 species and 17 families were recorded. The Anatidae family, particularly Anas platyrhynchos, dominated the counts, reflecting its reliance on shallow foraging habitats. Biodiversity indices highlighted significant temporal variations. The Shannon-Wiener diversity index (H') and Simpson diversity index (λ) revealed the highest diversity levels in 2023 (H' = 3.248; λ = 0.953) and 2024, alongside a consistently increasing trend in species evenness, culminating in a Pielou evenness index of 0.946 in 2024. Despite these positive trends, the findings also exposed ecological vulnerabilities. Species like Phoenicopterus roseus have shown significant decline due to habitat degradation, reduced water inflow, and declining populations of Artemia-their main food source. These are attributed to the changed hydrological regime of the Zayandeh-Rud Dam and the prolonged drought conditions which have reduced wetland water levels and quality. Comparative analysis with previous studies reflected the resilience of Gavkhuni Wetland, with a higher species diversity and abundance than during the previous periods of droughts; however, annual fluctuations in the bird population varied between 352 individuals in 2023 and 6,367 in 2022, which reflected the sensitivity of this wetland to environmental stressors. This study emphasizes the importance of biodiversity monitoring as a tool for understanding ecological dynamics and informing conservation strategies. Reducing human-induced pressures and maintaining environmental flows would allow the wetland to continue as an important refuge for migratory avian species, thus supporting regional and global biodiversity conservation efforts.