The comb duck or American comb duck (''Sarkidiornis sylvicola''), is an unusual

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 t ...

, found in tropical wetlands in continental

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

south to the

Paraguay River The Paraguay River (Río Paraguay in Spanish, Rio Paraguai in Portuguese, Ysyry Paraguái in Guarani) is a major river in south-central South America, running through Brazil, Bolivia, Paraguay and Argentina. It flows about from its headwaters in ...

region in eastern

Paraguay Paraguay (; ), officially the Republic of Paraguay ( es, República del Paraguay, links=no; gn, Tavakuairetã Paraguái, links=si), is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to th ...

, southeastern

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

and extreme northeastern

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

, and as a

vagrant Vagrancy is the condition of homelessness without regular employment or income. Vagrants (also known as bums, vagabonds, rogues, tramps or drifters) usually live in poverty and support themselves by begging, scavenging, petty theft, temporar ...

Trinidad Trinidad is the larger and more populous of the two major islands of Trinidad and Tobago. The island lies off the northeastern coast of Venezuela and sits on the continental shelf of South America. It is often referred to as the southernmos ...

. Most taxonomic authorities split this species and the

knob-billed duck The knob-billed duck (''Sarkidiornis melanotos''), or African comb duck, is a duck found in tropical wetlands in Sub-Saharan Africa, Madagascar and the Indian Subcontinent from northern India to Laos and extreme southern China. Most taxonomic au ...

from each other. The comb duck is generally smaller in size when compared to the knob-billed duck, and flanks are darker (black in males, medium grey in females).

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 Plac ...

. If seen at a distance, immature comb ducks can also be mistaken for a

fulvous whistling duck The fulvous whistling duck or fulvous tree duck (''Dendrocygna bicolor'') is a species of whistling duck that breeds across the world's tropical regions in much of Mexico and South America, the West Indies, the southern United States, sub-Sahar ...

(''Dendrocygna bicolor''). 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. 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. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

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 duck The term perching ducks is used colloquially to mean any species of ducks distinguished by their readiness to perch high in trees Until the late 20th century, perching ducks meant ''Cairinini'', a tribe of ducks in the duck, goose and swan family ...

s", a

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

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 biologi ...

s. As the "perching ducks" were split up, the comb duck was moved to the

Tadorninae The Tadorninae is the shelduck-sheldgoose subfamily of the Anatidae, the biological family that includes the ducks and most duck-like waterfowl such as the geese and swans. This group is largely tropical or Southern Hemisphere in distribution, w ...

or shelduck

. 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 calle ...

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 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 ba ...

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 include ...

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 referred to ...

. It is largely resident, apart from dispersion in the wet season. This

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 chordate ...

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.

Reproduction

Comb ducks nest mainly in tree holes, also in tall grass. They line their nests with reeds, grass, or feathers, but not down. 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 seven to 15 yellowish-white eggs. Several females may lay in a single "dump nest" containing up to 50 eggs.

References

{{Taxonbar, from=Q3473539 Sarkidiornis Taxa named by Hermann von Ihering Taxa named by Rodolpho von Ihering Birds described in 1907