According to avid birder Parag Rangnekar: "It's too early, but it could be a passage migrant, a gull-billed tern, which will travel further south of Goa." He explained, "They will be here for a few days and then will go south. The true migratory birds which spend their winter here come in October-November."
Amateur bird watchers who sighted the birds confirmed that they are gull-billed terns. Terns are amongst the first migratory birds to arrive in Goa. They are white birds, the size of crows, with pointed wings and can be sighted till the beginning of summer as they fly to and from the Chorao bird sanctuary. They always fly only in the middle of the river as they go hunting for fish to eat out into the Mormugao-Aguada bay, making for a pretty sight as they dive or dip to the surface of the water.