Monday, January 3, 2011

Knob billed Duck (Comb Duck)

Photograph taken at Thol wild life sanctuary- Ahmedabad

Knob-billed Duck
(Sarkidiornis melanotos)

  • Description: This common species is unmistakable. Adults have a white head freckled with dark spots, and a pure white neck and underparts. The upperparts are glossy blue-black upperparts, with bluish and greenish iridescence especially prominent on the secondaries (lower arm feathers). The male is larger than the female, and has a large black knob on the bill. Young birds are dull buff below and on the face and neck, with dull brown upper parts, top of the head and eye stripe. The adults are unmistakable. Immature Knob-billed Ducks look like a large grayish female of the Cotton Pygmy Goose (Nettapus coromandelicus) and may be difficult to tell apart if no other birds are around to compare size and hue. If seen at a distance, they can also be mistaken for a Fulvous Whistling - Duck. However, Knob-billed Ducks in immature plumage are rarely seen without adults nearby and thus they are usually easily identified too. The Knob-billed Duck is silent except for a low croak when flushed.

  • Distribution: It breeds in still freshwater swamps and lakes in the tropics. It is largely resident, apart from dispersion in the wet season. Knob-billed Ducks often perch in trees. They are typically seen in flocks, small in the wet season, up to 100 in the dry season. Sometimes they separate according to sex. The Knob-billed Duck is declining in numbers locally, but due to its wide range it is not considered globally threatened by the IUCN.

  • Diet: Konb-Billed Ducks feeds on vegetation by grazing or dabbling and to a lesser extent on small fish, invertebrates, and seeds. It can become a problem to rice farmers.