Seasonal bird diversity of an urban lake with the history of eutrophication and restoration

Long-term biodiversity monitoring studies of restored wetland ecosystems are essential for successful conservation. We studied the bird diversity of century-old Pashan Lake (18.5344°N, 73.7853°E), Pune, Maharashtra, India, after 15 years of restoration. Pashan Lake is an overwintering site for many birds and recently went through a restoration event after eutrophication. Currently, the lake receives heavy sewage water and industrial effluents through a small river Ramnadi. The lake receives heavy monsoon rainwater, and in late winter and summer, hyacinth vegetation covers the entire lake surface. We monitored bird diversity (number of species with abundance) at Pashan Lake throughout the year (June 2021-May 2022) using the point transact method during morning and evening hours. We also recorded physicochemical parameters, including water temperature, pH, dissolved oxygen, conductivity, salt, and TDS (Total Dissolved Solids). We calculated diversity indices for each season, Monsoon (June–September), winter (October-January), and summer (February-May). We recorded a total 81 bird species with the highest bird diversity in the winter season. Omnivorous and insectivorous birds dominate the fauna. Bird community recorded every month was clustered into two groups, June-November and December-May, suggesting the influence of hyacinth vegetation. Bird community was dissimilar among seasons. The study signifies the importance of long-term biodiversity monitoring studies for wetland conservation.