New Delhi, Feb. 21 -- The birds were calling from the canopy when something slipped out of the water.

It was grey, rolling like a wave, jolly. It splashed on the shore, and as I watched, it seemed to change form and assemble-like a column of mercury becoming solid. It stood. In the background was its companion, another wave that turned into something else-a smooth pelt, a clever face, whiskers and paws.

Two Smooth-coated otters stood in front of us, their noses quivering and their black eyes full of curiosity. They had come so silently, it was as if they had always been there, like they were creatures of land. But otters are top predators of rivers. They belong on river banks, on sandy stretches where they roll about, on complex banks t...