A census of the endangered river dolphin has been planned in the Sunderbans forest in West Bengal, wildlife officials said. The census has been scheduled for December.

Once abundantly available in the Ganges [Images] and its tributaries at the confluence of the Bay of Bengal, river dolphins have come to be a threatened species after rampant hunting and pollution of rivers.

Not much is known about these dolphins, and the census will not only be a headcount of this species, but also a study of their habitat, behaviour and related issues.

According to West Bengal wildlife official Atanu Raha, the month of December had been chosen because the rivers remain calm and spotting the shy, elusive dolphins is a trifle easier at that time.

The Sunderbans, a maze of rivers and small islands, better known for being the world's largest tiger habitat, are also home to various species of wildlife, including the sweet water dolphin and the estuarine crocodile.

This kind of dolphin is also found in the neighbouring state of Orissa. "We are getting experts from Orissa to help our personnel carry out the census," Raha said.

Groups of enumerators will set out in mechanised boats in the three major rivers of the Sunderbans -- Matla, Muriganga and Thakuran -- and their tributaries and look for the dolphins, which are spotted bobbing in and out of the water in groups.

The study will also look at the effects of environmental change on dolphin life -- the Gangetic and Irrawady variety. The second kind is also found in Burma, Malaysia and Indonesia.