Though Chatterjee didn't get to document the beautiful paradise flycatcher, he got the grizzly photograph of a decapitated head of an iora that had been killed by a sling shot instead. Chatterjee saw poachers down two egrets with practised ease, stuff then into nylon bags and saunter away as though they were out on a cavalier hunting spree.

Most birdwatchers arrive at Piyali Island - 75 km from Kolkata - early, spend the day sighting or photographing before leaving around 2.30-3pm to make the return journey.

Chatterjee, too, followed the routine but on June 21, he and Argha Adhikari decided to go to the island around dusk to get a better opportunity to click the paradise flycatcher and other rare and uncommon birds like the brown-winged kingfisher, collared kingfisher, scarlet-back flowerpecker, changeable hawk eagle, small minivet and other migratory bird species.

"Since Piyali is not inhabited like some of the other islands in the Sunderbans, it is extremely rich in avifauna. The island draws a large variety of bird species - common, uncommon and rare. Naturally, it is a hotspot for birdwatchers. Usually, dozens of birdwatchers roam the island during the day. Since we did not want to add to the crowd, we went in the evening to pick our spots," explained Chatterjee.

The duo began clicking photographs to the north of the island that had a large bird count before Chatterjee decided to venture to the south. He had walked about a kilometre, wondering why there were so few birds to the south when he chanced upon three men, two of whom were aiming at birds with slingshots (gulti). Their aim was deadly. Two little egrets dropped dead. The third man stepped forward with a nylon bag and stuffed the fresh kills into it.

As he turned around, he spotted Chatterjee and momentarily froze. That was enough to alert the two marksmen. One of them picked up another bag that was full of birds they had hunted and began calmly heading towards a boat perched on the bank of Piyali river.

"They were not afraid to have been caught in the act. Instead, they appeared nonchalant and even conversed aloud amongst themselves about how unsafe these parts were for strangers to venture at this hour and how those who did not heed warnings got killed and buried in the ground. It was around 3.30-4pm at the time and the island was deserted. Since Argha was busy clicking at the other end, way beyond earshot, I felt vulnerable. But I also realized that since they did not know me, I could also pass off as someone who wasn't bothered about hunting and get them to converse with me," Chatterjee recounted.

Initially suspicious, one of the men began talking after Chatterjee - who is also the honorary conservation officer at the Calcutta Snake Park - showed them photographs of rare snakes that he had earlier taken. "We have killed the birds to eat. Our target was to get 12-14 open bill stork. But we didn't get them. So we had to kill many small birds," he said, pointing to the two bags - one packed to the brim and other only half full.

The half-empty bag contained 30 birds - three yellow-feet green pigeons, 11 spotted doves, three collared doves, three night herons, seven little egrets, two white collared kingfisher and an iora whose head had been severed during the kill. Chatterjee reckons the other bag would have contained at least 50 birds. "I could see the forest office across the river, barely 200 ft from where we stood, but could not do anything," he rued.

Expressing dismay over the poaching activities, West Bengal Wildlife Board member Dipak Mitra said such wanton killing of birds was unprecedented. "There have been instances of a couple of birds being shot, but not in such large numbers. It just goes to show that the poachers have no fear. If they get away with it, they will get even bolder and next target animals," said Mitra.

Principal Chief Conservator of Forests (Wildlife) N C Bahuguna promised prompt action in the incident. "I have already instructed the divisional forest officer to show the photographs around, find the names of the persons involved in the killings and submit the chargesheet. There will be no laxity in dealing with the culprits," he said.