Shorebird abundance and nutritional quality of intertidal biofilm at a tropical estuarine system, Muttukadu Backwaters, India

Despite global recognition of intertidal biofilm as a key dietary component for small-sized shorebirds, the trophic relationship between biofilm and shorebirds remains poorly understood in tropical regions. We address this gap by investigating seasonal and annual variation in biofilm composition and shorebird abundance at Muttukadu Backwaters, India, on the Central Asian Flyway, 2021–2025, four times per year, during the non-breeding period of shorebirds (Sep–Mar). We sampled biofilm and water using standard procedures and counted small-bodied shorebirds using direct visual observation and block counts. Annual mean concentration of biochemical constituents of intertidal biofilm remained consistent across years but seasonal fluctuations were observed within each migratory cycle. Small-bodied shorebirds (nine species) had consistently low abundance during the months of September and November, followed by an increase in abundance in January and a decline in March. High shorebird abundance at Muttukadu Backwaters coincided with times when biofilm was high in carbohydrate, protein, lipid, nitrate, and chlorophyll a, but low in nitrite, phosphate, and calcium. Our study suggests a potentially pivotal role of biochemical constituents of biofilm in influencing shorebird use of tropical stopover and non-breeding sites. To strengthen conservation strategies for migratory shorebirds and improve management of intertidal mudflats, future research should examine the factors driving biofilm composition in tropical backwaters along the Central Asian Flyway.