Herons must eat large numbers of fish to survive  Ttherefore, according to naturalists, when many herons nest near each other in a marsh, large numbers of fish must be available to them
But many herons successfully nest in the Pahargaon marsh, and that marsh has been nearly empty of fish for many years
The Pahargaon marsh has been growing saltier over the years, killing off much of the vegetation that the fish needed to eat.