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The knob-billed duck (''Sarkidiornis melanotos''), or African comb duck, is a
duck Duck is the common name for numerous species of waterfowl in the family Anatidae. Ducks are generally smaller and shorter-necked than swans and geese, which are members of the same family. Divided among several subfamilies, they are a form ...
found in tropical wetlands in
Sub-Saharan Africa Sub-Saharan Africa is, geographically, the area and regions of the continent of Africa that lies south of the Sahara. These include West Africa, East Africa, Central Africa, and Southern Africa. Geopolitically, in addition to the List of sov ...
,
Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Afric ...
and the
Indian Subcontinent The Indian subcontinent is a physiographical region in Southern Asia. It is situated on the Indian Plate, projecting southwards into the Indian Ocean from the Himalayas. Geopolitically, it includes the countries of Bangladesh, Bhutan, In ...
from northern
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
to
Laos Laos (, ''Lāo'' )), officially the Lao People's Democratic Republic ( Lao: ສາທາລະນະລັດ ປະຊາທິປະໄຕ ປະຊາຊົນລາວ, French: République démocratique populaire lao), is a socialist s ...
and extreme southern
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
. Most taxonomic authorities split this species and the comb duck from each other. The supposed
extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
"Mauritian comb duck" is based on misidentified remains of the
Mauritius sheldgoose The Mauritius sheldgoose (''Alopochen mauritiana''), also known as the Mauritius shelduck, is an extinct species of sheldgoose that was endemic to the island of Mauritius. While geese were mentioned by visitors to Mauritius in the 17th century, ...
(''Alopochen mauritiana''); this was realized as early as 1897, but the
mistaken identity Mistaken identity is a defense in criminal law which claims the actual innocence of the criminal defendant, and attempts to undermine evidence of guilt by asserting that any eyewitness to the crime incorrectly thought that they saw the defenda ...
can still occasionally be found in recent sources.


Description and systematics

This common species is unmistakable. It is one of the largest species of duck. Length can range from , wingspan ranges from and weight from .''Sarkidiornis melanotos'' (Comb duck, Knob-billed duck)
biodiversityexplorer.org
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 Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfl ...
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 Bill(s) may refer to: Common meanings * Banknote, paper cash (especially in the United States) * Bill (law), a proposed law put before a legislature * Invoice, commercial document issued by a seller to a buyer * Bill, a bird or animal's beak Pla ...
. Young birds are dull
buff Buff or BUFF may refer to: People * Buff (surname), a list of people * Buff (nickname), a list of people * Johnny Buff, ring name of American world champion boxer John Lisky (1888–1955) * Buff Bagwell, a ring name of American professional w ...
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 The cotton pygmy goose or cotton teal (''Nettapus coromandelianus'') is a small perching duck which breeds in Asia, Southeast Asia extending south and east to Queensland where they are sometimes called white-quilled pygmy goose. They are among ...
(''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 Plumage ( "feather") is a layer of feathers that covers a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage differ between species and subspecies and may vary with age classes. Within species, ...
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.


Gallery

File:Sarkidiornis melanotos - Royal Museum for Central Africa - DSC06799.JPG, Specimens from the Royal Museum for Central Africa (female, male) File:CombDuck DSC0264.jpg, knob-billed duck at edge of lake near Jodhpur, Rajasthan, India, feeding alongside feral pigeons. File:CombDuck.jpg, Flying knob-billed duck / comb duck at
Chilika Lake Chilika Lake is a brackish water lagoon, spread over the Puri, khordha and Ganjam districts of Odisha state on the east coast of India, at the mouth of the Daya River, flowing into the Bay of Bengal, covering an area of over . It is the bigge ...
, Odisha, India Knob-billed duck (Sarkidiornis melanotos) female in flight Jojawar.jpg, female, Jojawar, India File:Male knob-billed duck in water.jpg, Male knob-billed duck at Austin Roberts Bird Sanctuary in Pretoria, South Africa File:Knob-billed Duck, Bharatpur.jpg, Knob-billed Duck (Sarkidiornis melanotos) alongside Eurasian Coot ((Fulica atra) in
Keoladeo National Park Keoladeo National Park or Keoladeo Ghana National Park (formerly known as the Bharatpur Bird Sanctuary) is a famous avifauna sanctuary in Bharatpur, Rajasthan, India, that hosts thousands of birds, especially during the winter season. Over 350 ...
,
Rajasthan Rajasthan (; lit. 'Land of Kings') is a state in northern India. It covers or 10.4 per cent of India's total geographical area. It is the largest Indian state by area and the seventh largest by population. It is on India's northwestern ...
,
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
File:Knob-billed Duck AaMSM9151.jpg, Male at
Jamnagar Jamnagar () is a city located on the western coast of India in the state of Gujarat of Saurashtra region. It is the administrative headquarters of the Jamnagar district and the fifth largest city in Gujarat. The city lies just to the south o ...
,
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
File:Knob-billed Duck Male AMSM8872.jpg, Close-up Male
Uncertainty surrounds the correct systematic placement of this species. Initially, it was placed in the
dabbling duck The Anatinae are a subfamily of the family Anatidae (swans, geese and ducks). Its surviving members are the dabbling ducks, which feed mainly at the surface rather than by diving. The other members of the Anatinae are the extinct moa-nalo, a yo ...
subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus Genus ( plural genera ) is a taxonomic rank used in the biological classifica ...
Anatinae The Anatinae are a subfamily of the family Anatidae (swans, geese and ducks). Its surviving members are the dabbling ducks, which feed mainly at the surface rather than by diving. The other members of the Anatinae are the extinct moa-nalo, a youn ...
. Later, it was assigned to the " perching ducks", a
paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...
assemblage of waterfowl most of which are intermediate between dabbling ducks and
shelduck The shelducks, most species of which are found in the genus ''Tadorna'' (except for the Radjah shelduck, which is now found in its own monotypic genus ''Radjah''), are a group of large birds in the Tadorninae subfamily of the Anatidae, the biolog ...
s. As the "perching ducks" were split up, the knob-billed duck was moved to the Tadorninae or shelduck
subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus Genus ( plural genera ) is a taxonomic rank used in the biological classifica ...
. Analysis of
mtDNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial DNA ...
sequence In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order matters. Like a set, it contains members (also called ''elements'', or ''terms''). The number of elements (possibly infinite) is called ...
s of the cytochrome ''b'' and
NADH dehydrogenase NADH dehydrogenase is an enzyme that converts nicotinamide adenine dinucleotide (NAD) from its reduced form (NADH) to its oxidized form (NAD+). Members of the NADH dehydrogenase family and analogues are commonly systematically named using the for ...
subunit Subunit may refer to: * Subunit HIV vaccine, a class of HIV vaccine *Protein subunit, a protein molecule that assembles with other protein molecules *Monomer, a molecule that may bind chemically to other molecules to form a polymer * Sub-subunit, ...
2
gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
s, however, suggests that it is a quite basal member of the Anatidae, vindicating the earliest placement. But its closest living relatives cannot be resolved to satisfaction without further study.


Ecology

It breeds in still
freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does incl ...
swamp A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...
s and
lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...
s in the
tropics The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also refer ...
. It is largely resident, apart from dispersion in the wet season. This
duck Duck is the common name for numerous species of waterfowl in the family Anatidae. Ducks are generally smaller and shorter-necked than swans and geese, which are members of the same family. Divided among several subfamilies, they are a form ...
feeds on vegetation by grazing or dabbling and to a lesser extent on small fish,
invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chorda ...
s, and seeds. It can become a problem to rice farmers. 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 The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
. It is one of the species to which the ''
Agreement on the Conservation of African-Eurasian Migratory Waterbirds The Agreement on the Conservation of African-Eurasian Migratory Waterbirds, or African-Eurasian Waterbird Agreement (AEWA) is an independent international treaty developed under the auspices of the United Nations Environment Programme's Conventio ...
'' applies.


Reproduction

African birds breed during and after the rainy season and may not breed if the rain is scanty. Knob-billed ducks nest mainly in tree holes, also in tall grass. Males may have two mates at once or up to five in succession. They defend the females and young but not the nest sites. Females lay 7 to 15 yellowish-white eggs.


References


External links


Species text in The Atlas of Southern African Birds
{{Taxonbar, from=Q426968 Sarkidiornis Birds of Sub-Saharan Africa Birds of India Birds of Southeast Asia knob-billed duck Taxa named by Thomas Pennant