A feast and famine ecosystem
Nal Sarovar is a vast, shallow depression of about 120 square kilometers located west of Ahmedabad. This natural lake shows seasonal extremes. In the dry summer months, large portions of it evaporate, leaving behind cracked mudflats and reducing the inundated area to around 60 square kilometers. The water that remains becomes increasingly saline. This is the season of famine.
The arrival of the monsoon from July to September dramatically transforms the landscape. Rainwater from the surrounding districts floods the basin, which can expand to 350 square kilometers in years with heavy rainfall. This influx of freshwater reduces the salinity and, importantly, carries nutrients from the catchment area into the lake. The combination of shallow, sunlit water and a fresh supply of nitrates and nitrites triggers a massive bloom of phytoplankton. The lake's 48 recorded species of algae form the base of a suddenly productive food web, turning the famine into a feast. This immense pulse of primary productivity is the engine that powers the entire wetland for the months to come.
An avian metropolis
Life does not stop with algae. Zooplankton graze on the phytoplankton, and in turn become food for fish and aquatic insects. This abundance attracts an enormous number of birds. More than 210 species have been recorded at Nal Sarovar, with winter populations historically averaging 174,000 individuals. Migratory birds begin arriving in October from as far away as Siberia and Central Asia, using the lake as an wintering site on the Central Asian Flyway.
The shallow waters, which rarely exceed two meters in depth, are ideal for wading birds. Huge flocks of Greater Flamingos (Phoenicopterus roseus) and Lesser Flamingos (Phoeniconaias minor) filter the water for food. They are joined by Dalmatian Pelicans (Pelecanus crispus), Sarus Cranes (Grus antigone), and numerous species of ducks, geese, and storks. The timing of their arrival is remarkably synchronized with the post-monsoon peak in food availability. Local communities have long observed that the arrival of specific species, such as the Jacobin cuckoo (Clamator jacobinus), traditionally heralds the coming rains, a piece of ecological knowledge that connects the birds' migratory patterns to the subcontinent's most important climatic event.