Lesser Whistling Duck

The lesser whistling duck, also known as the Indian whistling duck or lesser whistling teal, is found in eastern Pakistan, India and Sri Lanka to southeast China and south through southeastern Asia to Sumatra, Borneo, Java and Bali. It gets the name "whistling" duck from the whistling sound it makes while it flies which may be due to the shape of an outermost primary feather. 

Lesser whistling ducks in Yala NP.

It is the smallest of the whistling ducks. It is chestnut brown and has chestnut upper-tail coverts unlike the creamy white upper-tail coverts in the fulvous whistling duck. I've struggled with differentiating my relatively poor photos and whether what I was seeing was the lesser or fulvous whistling duck, and decided on the former based on a number of photo comparisons. 

Lesser whistling ducks in Bundala NP.

I saw some of these ducks in early morning light in Yala National Park and later saw a couple of them in Bundala National Park.