Family : Anatidae
Text © Dr Davide Guadagnini
English translation by Mario Beltramini
The Sarkidiornis duck (Sarkidiornis melanotos Pennant, 1769), known also under the name of knob-billed duck or comb duck, is a bird belonging to the order of the Anseriforms (Anseriformes), family of the Anatids (Anatidae), genus Sarkidiornis, to which belongs as only one species the Sarkidiornis melanotos with two subspecies: Sarkidiornis melanotos melanotos and Sarkidiornis melanotos silvicola. The two subspecies are considered as two different species by some authors. The systematic classification of this species is still now uncertain and is subject of discussion.
The name of the genus sarkidiornis comes from the Greek “sarkidion”, which means “morsel of meat” and “ornis” = bird; the name therefore refers to the evident fleshy protuberance adorning the bill of the adult males of this species.
The epithet “melanotos” comes from the Greek “melas” meaning black and from “notus”, which means friend, therefore, “friend of the black”. Even though this species shows white parts of the livery and others with colourful reflections, there is no doubt that the dark and gloomy colours do characterize it starting from the black bill, the dark eye and from the peculiar fleshy grey-black protuberance of the male and then passing to the black spots of the head and of the neck to the black of the back and ending into the grey of the legs.
This unique duck has an origin and a distribution including a vast and long pan-tropical belt. It is present in the wet tropical zones of the sub-Saharan Africa and in Madagascar. It is also found in southern Asia; from Pakistan and Laos to southern China. Finally, it is also present in South America, with the subspecies Sarkidiornis melanotos silvicola, from eastern Paraguay to south-eastern Brazil to the extreme north-eastern part of Argentina; straying also in Trinidad. The South-American population has probably gotten its origin from a trans-Atlantic immigration.
This duck usually lives in the wet and woody areas even if it doesn’t spend all its time in water and has arboreal habits, it is easy to see it perched on overhanging branches (preferably dry) of trees and on elevated rocks. It may also climb vertically thanks to its robust legs and claws. They live, typically, in the grassy savannahs surrounding the lagoons, in the woody areas subjected to periodical flooding, in the floodplains, in ponds, in the rivers’ deltas and along rivers and lakes.
Although it resides mainly in the lowlands, the South American populations may live also in mountain zones at high altitudes with respect to the sea level. This species, mainly sedentary, can effect seasonal movements correlated to the availability or not of the water. The African populations are more mobile being obliged to perform displacements of even some thousands of miles. If disturbed, it gets immediately up in flight with slow, noisy and vigorous wing beats. The flocks, which during the displacements can reach the number of some hundreds of individuals, move in elongated or irregular V-formations. In some areas it is considered as dangerous because it causes damages to the cultivations (mainly of rice).
The common names of this duck (knob-billed duck, comb duck) refer to the remarkable dark grey-black caruncle shaped like a disk or a disk placed on the rear of the upper rhamphotheca of the bill which, starting from the beginning of the bill gets to surmount the bill almost entirely (but the tip) during the maximum seasonal expansion.Such a quite evident excrescence is present only in the adult males, as secondary sexual character and reaches its maximum development during the time of the courting increasing its size by 2-3 times; period during which presumably it shows the vigour and the prowess of the males ready for the reproduction.
Beyond the quite evident lump, the male easily distinguishes from the female also due to the different vocalizations, more muffled in the male, stronger and louder in the female and due to the size; the male’s one is in fact twice the size than the female’s. These ducks are 50 to 80 cm long; weigh 1 to 3 kg and have a wingspan from 115 to almost 150 cm, the whole depending on the sex and the subspecies.
This duck has a rather massive body which reminds that of a Muscovy duck (Cairina moschata) with, however, longer legs. In particular, the head and the neck remind, also in the expression of the face, those of the young (without fleshy growths) Muscovy ducks (Cairina moschata). The head and the first part of the neck have a unique colour: white more or less spotted of black which reminds the colour of the Stracciatella ice cream. In this zone, almost at the end of the head, dorsally, is present a slight crest of feathers slightly wrinkled-rippled. The black spotting is very variable and some males may have the presence of an abundant black colour becoming an almost totally black line on the apex of the head and along the rear of the first part of the neck. The neck continues into a large white chest. The white colour continues also in the ventral part of the body. The back, the wings and the tail are black, darker in the males and of a more nuanced slate colour in the females, with more intense and iridescent violet-purple-green-bronze metallic reflections in the males. The secondary, tertiary and covert feathers of the wings of the males reach the maximum of the iridescent colours and of the bright reflections. The head and the neck, in the males, may be spotted by yellowish-orange shades which can be present also on the sides and on the belly. Always in the males, two yellow-orange spots are usually present on the sides of the under-tail.
Even if the South American subspecies, Sarkidiornis melanotos silvicola, usually smaller and slightly longer than the nominal subspecies, Sarkidiornis melanotos melanotos, distributed in the Old World (Africa, Asia) distinguish also for the evident difference of colour on the sides, at times more marked in the masculine specimens. The nominal subspecies has pale grey sides in the male and sometimes whitish in the female. The South American subspecies has dark grey, black sides in the male and matt dark grey in the female which tends to be more spotted and darker. The bill is dark grey-black, the legs are grey with possible greenish suffusions, the eyes have brown, very dark iris which, also thanks to the rather big eyes, grant this species a sweet and, at the same time, a proud look.
The Sarkidiornis duck nourishes of vegetables, which it assumes grazing on the grassy banks and of the most tender parts of the aquatic plants growing in the swamps and in the lakes it frequents. It does not disdain, when it happens, to complete the diet with seeds of sedge and of other plants, invertebrates such as larvae of aquatic insects, small fishes and small aquatic animals.
In Africa the reproductive period varies mainly concentrating during the rain season or immediately after. If the season is too droughty, the broods may not happen, thus skipping the reproduction. The flocks disperse by the coming of the rains. This species is polygamous in the ideal habitats becoming monogamous in the marginal locations.
The harem is not too vast and usually one reproduction male mates with 2-4 females keeping with them a weak pair bond which normally disappears by the beginning of the spawning. In any case, usually, when the females forming the harem are more than two the couplings are not contemporaneous but take place in time sequence. Inside the harems territory, a hierarchy is in force with dominating females and females which may be tolerated even if not paired; the males having no harem gather at the margins of the territory occupied by the harems watching the same from heights in order to catch the occasions of courting or forcing to the mating possible females momentarily alone. The intruding males, once sighted by the dominating male, are actively attacked and driven put by this last one and the fights between males are quite frequent.Also when this species is kept in captivity, seen the ardour of the males, it is advisable to breed trios formed by one male and two females in suitably sized spaces. If bred in couple the male might persist in too often mating with the only one female risking to injury it or even to kill it. For nidificating, the females utilize the hollows of the trees or, occasionally, other cavities; even in uninhabited dwellings.
If needed, they can utilize also very close and intert- wined branches to be used as supporting platforms; or nests abandoned by other species of birds such as raptors and aquatic birds or, in Africa, the closed nests of the Hamerkop (Scopus umbretta).
For nidifying, the African populations take advantage of the damages done to the trees by the elephants (Loxodonta africana) because ideal cavities take form in the branches and dead trees. In South America, they frequently utilize dead palms and big branches covered by epiphytic vegetation which acts as supportive base for the nests. The feminine ducks are in strong competition during the research and the occupation of the cavities for the nests; especially in the early morning, as soon as the sun rises, during the reproductive season they inspect carefully every location climbing along the branches and controlling every nook and cranny looking for the best hollows. If the elevated cavities do not abound, this species adapts to nidify also on the ground trying to camouflage among the thickets of grassy vegetation or among the rocks, the nests are quilted by down the mother tears off from its chest. The nests may be located at a fair distance from the water. When captive, the Sarkidiornis duck reproduces utilizing artificial box nests.
The brood is formed by 7-15 roundish, yellowish cream white eggs, but it is not unusual to meet nests with an even bigger number of eggs (some tens at times) fruit of the spawning of several females into the same nest. In particular, some females which have not found a suitable place for their nest may try to spawn in already occupied nests behaving as conspecific parasites, if however the number of spawned eggs is much exceeding that of a single brood, the residing female is not able to complete the hatching. The incubation lasts 30 days about and the duckies are yellow and brown; the brown colour is present on the top of the head, runs on the back of the neck and goes on dorso-laterally along the whole body. The face is yellow, but a brown stripe crossing the eye, and all the ventral part of the body. Yellow are also some characteristic marks present on the back and along the line of the wing in the middle of the remaining brown part.
In its whole, the ducky is much similar to the one of the Muscovy duck (Cairina moschata) in the ancestral colouration, just slightly paler and yellower. After one or two days from the hatching, the ducks jump out from the nest for reaching the ground; often the mother, out from the nest, incites the young to leave the same calling them by vocalizing from the ground at the base of the tree. If it detects the presence of predators, it delays the operation or waits for the young in silence.
The young, which upon their birth weigh a few tens of grams, jump flattening and opening the small wings and the webbed feet trying to make the maximum possible resistance to the air. Once fallen on the ground, bouncing, the duckies follow closely the mother which will take them in a safe aquatic location. The broods, especially where the predation is strong, can gather in ampler groups hoping that a bigger number of young will reach the age of independence. The growth of the young is rather fast and the young are able to fly when about 2-3 months old; this s the moment when they reach the independence from the mothers which, alone, take care of the brood. The young have a less defined and darker colouration than the adult specimens.
The reproductive age will be reached when 2-3 years old. The comb duck has a not uniform distribution, in its own territories, and in spite some populations may result locally abundant, it has suffered from the excessive hunting, the habitat destruction and the treatments with insecticides done in the rice fields (especially the South American population). In Asia, the population is of only some thousands of individuals; in South America they estimate a total population of about 100.000 specimens and in Africa the population is deemed to stand between the 100.000 and the million of individuals. The Sarkidionis duck is not much diffused among the breeders who prefer more colourful species. It is, actually, an animal interesting to breed due to its calm temper, which allows its breeding along with other species, as well as for the satisfactions it can give connected with its rusticity and to the fact of reproducing it. This species should be bred in spacious aviaries, thus giving it the possibility to fly. The subspecies Sarkidiornis melanotos melanotos is more bred by the American breeders, conversely, the subspecies Sarkidiornis melanotos silvicola is more bred by the European breeders even if, unluckily, the two subspecies have been often bred in a promiscuous way.