knob billed duck

The Knob-billed Duck has distinctive appearance with the fleshy knob of the male. This species has wide range, shared by two subspecies, but the race “sylvicola” is now considered as full species under the name Comb Duck.The adult male of the nominate race has blackish upperparts, wing-coverts and secondary flight feathers with green, bluish-purple and bronze gloss. The rump is grey. The underparts are white, except the greyish flanks and some narrow black bars on breast sides. The undertail-coverts are white, often tinged yellow.Head and neck are white with black speckles. Crown and nape appear almost black, due to concentration of black spots.It has prominent, fleshy, blackish knob at base of the upper mandible. The bill is black. The eyes are dark brown. Legs and webbed feet are blackish.In breeding plumage, the knob is much larger, and the sides of head and neck are washed yellowish-buff. The female is similar but smaller and duller than male, and she lacks the fleshy knob. Her plumage is less glossy. The juvenile is brownish with dark brown crown and upperparts, and scaled underparts.

The Knob-billed Duck frequents wet areas such as swamps, rivers and lakes with scattered trees. It may occur in more open lowlands and grasslands in tropical regions.

The Knob-billed Duck feeds on aquatic plants and invertebrates when wading in shallow water. It also takes small fish. On land, it grazes and takes terrestrial insects. This duck spends most of its time resting on bank or islet during the day, and feeds mainly in the early morning and the late evening.

The Knob-billed Duck is usually silent but it may occasionally utter some low croaking sounds. During the breeding period, it gives whistles and grunts during the displays or when fighting against rivals. The female gives quacks and grunts. A hoarse, whistled sound can be heard during the flight.

The knob-billed duck (Sarkidiornis melanotos) or African comb duck is a duck found in tropical wetlands in Sub-Saharan Africa Madagascar and south Asia from Pakistan to Laos and extreme southern China. Most taxonomic authorities split this species and the comb duck from each other. The supposed extinct "Mauritian comb duck" is based on misidentified remains of the Mauritian shelduck (Alopochen mauritianus) this was realized as early as 1897 but the mistaken identity can still occasionally be found in recent sources. This common species is unmistakable. It is one of the largest species of duck. Length can range from 56 to 76 cm (22 to 30 in) wingspan ranges from 116 to 145 cm (46 to 57 in) and weight from 1.03 to 2.9 kg (2.3 to 6.4 lb). 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 much 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 upperparts top of the head and eyestripe. Knob-billed ducks are generally larger in size when compared to comb ducks and flanks are usually lighter (light grey in females sometimes whitish). Immature knob-billed ducks look like a large greyish 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. 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.