Knob-billed duck (Sarkidiornis melanotos), or comb duck
These ducks with a knob shaped bill(male) were photographed at Koonthankulam bird sanctuary in Tamilnadu state of India. I went there on 22nd October, 2015. The best time to visit Koonthankulam is most probably from January to March. There were very few birds at the time of my visit but managed to get some lovely pictures here.