yellow bittern

This is a small species at 36 to 38 cm (14 to 15 in) in length, with a short neck and longish bill. The male is uniformly dull yellow above and buff below. The head and neck are chestnut, with a black crown.
Immature on a Typha species in Kolkata, West Bengal, India.

The female's crown, neck and breast are streaked brown, and the juvenile is like the female but heavily streaked brown below, and mottled with buff above.

Their breeding habitat is reedbeds. They nest on platforms of reeds in shrubs. 4-6 eggs are laid. They can be difficult to see, given their skulking lifestyle and reedbed habitat, but tend to fly fairly frequently, when the striking contrast between the black flight feathers and the otherwise yellowish plumage makes them unmistakable.

Yellow Bitterns feed on insects, fish and amphibians.(WIKI)