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Nov 12 2011

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Knob-billed Duck (Sarkidiornis melanotos)

Knob-billed Duck

[order] ANSERIFORMES | [family] Anatidae | [latin] Sarkidiornis melanotos | [authority] Pennant, 1769 | [UK] Knob-billed Duck | [FR] Canard-a-bosse bronze | [DE] Glanzente | [ES] Pato Crestudo (Arg, Bo) | [NL] Knobbeleend

Subspecies

Monotypic species

Genus

The Knob-billed Duck and Comb Duck is the only known species of the genus Sarkidiornis. 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. Uncertainty surrounds the correct systematic placement of this species. Initially, it was placed in the dabbling duck subfamily Anatinae. Later, it was assigned to the “perching ducks”, a paraphyletic assemblage of waterfowl most of which are intermediate between dabbling ducks and shelducks. As the “perching ducks” were split up, the Knob-billed Duck was moved to the Tadorninae or shelduck subfamily.. In addition, Some taxonomists separate the two subspecies into distinct species.

Physical charateristics

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


wingspan min.: 116 cm wingspan max.: 145 cm
size min.: 56 cm size max.: 76 cm
incubation min.: 28 days incubation max.: 30 days
fledging min.: 65 days fledging max.: 75 days
broods: 1   eggs min.: 7  
      eggs max.: 15  

Range

Africa, Oriental Region : widespread

Habitat

This species inhabits grassy ponds or lakes in savanna, open woodlands along large rivers and lakes, swamps, marshes, floodplains, river deltas, flooded forest, pastures and rice-paddies and occasionally sandbars and mudflats.

Reproduction

The species nests close to water, building rough structures of twigs and coarse grass1 in large hollow tree cavities, between 7 and 12 m high, or in holes in the walls of isolated buildings (or other cavities with a floor diameter of c.200 mm). It may also use the abandoned nests of other bird species, such as Hamerkop Scopus umbretta or nest on the ground in the shelter of tall grass or on tree stumps. When the species is tree nesting, the same cavity may be used from year to year. Males may have two mates at once or up to five in succession. They defend the females and young but not the nest sites. Unmated males perch in trees and wait for opportunities to mate. Females lay 7 to 15 yellowish-white eggs. Several females may lay in a single “dump nest” containing up to 50 eggs
to year. The eggs are incubated for about a month; the young fledge after another 10 weeks.

Feeding habits

Its diet consists largely of vegetable matter, including the seeds of grasses and sedges, the soft parts of aquatic plants (e.g. water-lilies), agricultural grain (e.g. rice, corn, oats, wheat and groundnuts) as well as aquatic insect larvae and locusts.

Video Knob-billed Duck

copyright: Brooke Clibbon


Conservation

This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The species is threatened by hunting (e.g. in Madagascar), habitat destruction (e.g. from deforestation), and indiscriminate use of poison in rice-fields. The species has declined in the Senegal Delta following the damming of the Senegal River (which has resulted in habitat degradation and loss from vegetation overgrowth, desertification processes and land conversion to agriculture). This species is also susceptible to avian influenza, so is potentially threatened by future outbreaks of the virus.
Knob-billed Duck status Least Concern

Migration

This species is an intra-African migrant undertaking poorly-understood seasonal movements in relation to water availability. It breeds during the wet season in single pairs or small groups (harems), and outside of the breeding season usually occurs in small parties of up to 30-40 individuals. Large flocks also gather in the dry (non-breeding) season on suitable waters4, but these break up and disperse to breeding grounds at the onset of the rains.

Distribution map

Knob-billed Duck distribution range map

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