Guwahati, Oct. 29: A rare sighting of wildlife and more so when the location is not its habitat requires sheer luck.

This is what happened on an overcast morning on October 24 when Gautam Bhattacharya - a nature enthusiast from Bengal - clicked pictures of the critically endangered white-bellied heron at the Maguri-Motapong wetland in Tinsukia district.

The white-bellied heron, one of the 50 rarest birds in the world, is a critically endangered species, with an estimated global population of less than 250.

"It was luck, of course, and it seems the more I challenge the limits, the more I get luckier," Bhattacharya told The Telegraph today.

On that day he was not carrying his best equipment to save the camera from rain and shot the pictures through his stand-by gear.

Bhattacharya, who works as a faculty member of the State Council of Educational Research and Training, West Bengal, was on a birding tour to the wetland, when he chanced upon the rare bird. Local guide Palash Phukan helped Bhattacharya spot the white-bellied heron.

"The sky was overcast on that day. I was just curious and asking Palash if purple-grey herons can be sighted in those waters, to which he responded in the affirmative. As if to just prove his point, we saw a distant black spot that looked like a heron...a purple one to Phukan, and an unknown one to me from such a distance," he said.

"We drew as close as we could get (about 150 feet within its reach), and gradually we were convinced by viewing through our binoculars that it was neither purple nor grey but something else," he added.

Bhattacharya just took the pictures, came back and checked the field guidebook, when he found to his utter amazement that it was the rare white-bellied heron.

"The present sighting is significant as this is the first photographic record of the species in the Brahmaputra Valley. So far, the white-bellied heron is sighted and known to breed only in Bhutan and Myanmar and some parts of Namdapha National Park in Arunachal Pradesh. We know very less about the species and there is no information on whether it migrates locally from their breeding ground to any other place in the non-breeding season. All the known habitats of the heron is in hilly areas with rivers that have sandy or stone beds... This sighting is important, as there are probably not more than 250 birds of this species left in the world and the development of a conservation and management plan for the white-bellied heron requires inclusion of all such information," Udayan Borthakur, a wildlife genetics expert who has worked on herons, told The Telegraph.

Ranjan Kumar Das, who teaches geography at Tinsukia College and is an avid bird-watcher, said this was an amazing sighting as the location was not its habitat.