Comb duck (Sarkidiornis melanotos)
|Also known as:||black-backed goose, Knob-billed duck, knob-billed goose|
|French:||Canard à bosse|
|Size||Length: 56 - 76 cm (2) (3)|
|Weight||1.2 - 2.6 kg (4)|
The comb duck is classified as Least Concern (LC) on the IUCN Red List (1) and listed on Appendix II of CITES (5).
The goose-like comb duck gets its common name from the large, fleshy, dark grey growth or ‘comb’ on the top of the male’s black beak (6) (7), an unusual and distinctive structure which enlarges during the breeding season (4) (8). Male comb ducks are large birds, with glossy blue-black or green-black upperparts, tail and wings, white underparts and pale grey or black flanks. The top of the head and back of the neck are black, and the rest of the head is white, speckled black, with yellow tinges on the sides and on the neck during the breeding season. Narrow black bands run along the sides of the upper breast. The comb duck’s legs and feet are dark grey, and the eyes dark brown (6) (9). Females are much smaller than males, with less glossy plumage, less well-defined black breast bands, more speckling on the head, which lacks any yellowish tinge, and sometimes with brownish mottling on the underparts. Females may appear almost white, and also lack the male’s ‘comb’ (6) (7) (9). Young comb ducks are brownish, with a dark eye-stripe, and attain adult plumage in the second year (4) (6) (9).
There are two subspecies of comb duck: the Old World comb duck, Sarkidiornis melanotos melanotos, and the South American comb duck, Sarkidiornis melanotos sylvicola, which was previously treated as a separate species and is still considered a full species by some (2) (3) (4) (9) (10). South American comb ducks are distinguished from their Old World counterparts by their smaller size, smaller comb, and black rather than grey sides and flanks, which are dark grey or brown in the female (2) (3) (6) (9) (11).
The comb duck has a wide distribution across sub-Saharan Africa, Madagascar, South and Central America, and tropical Asia, including Cambodia, China, India, Japan and Vietnam. S. m. sylvicola is found throughout South America, east of the Andes, as well as in Panama and Trinidad, while S. m. melanotos is found in Africa and Asia (India to South East Asia) (2) (3) (4) (9) (10). In parts of Africa, comb ducks are partially migratory, undertaking sometimes extensive seasonal journeys in response to dry season water availability (4) (7) (9).
Swamps, rivers and lakes in open or lightly wooded areas, as well as more open grassland, marshes, floodplains, flooded forest, pastures and rice-paddies (2) (3) (4) (9) (10). Comb ducks are also often seen away from water, flying over woodland or perched in dead trees (8). Although mainly found in lowlands, they have also been reported up to elevations as high as 3,500 metres (7).
Comb ducks are usually found in single pairs or, particularly in parts of Africa, small groups (harems) during the breeding season, and in groups of up to 30 to 40 birds at other times, when they may join flocks of other wildfowl. Harems are not known in Asia (3), and the species’ social structure is poorly known in South America (2). The diet consists mainly of vegetable matter, such as aquatic vegetation, seeds of grasses and sedges, grain (including crops such as rice and corn), as well as various invertebrates, such as aquatic insect larvae and locusts (4) (10).
Comb ducks usually nest close to water, in large tree cavities, holes in the walls of isolated buildings, abandoned nests of other birds, including that of the hamerkop (Scopus umbretta), or sometimes on the ground. The nest is a rough structure built from twigs and course grass, and is lined with grass, leaves and feathers (4) (10). The breeding season is variable, but usually coincides with the rainy season (4). In some areas comb ducks are monogamous, while in others males may hold small harems of two to four females, which they defend against other males (7) (12). Between 6 and 20 eggs may be laid (4), though nests sometimes contain the eggs of more than one female (7). Incubation lasts 28 to 30 days, and is performed exclusively by the female (4) (12). Within just a day or two of hatching, the ducklings leap from the nest, which may be up to 12 metres above the ground (10), when summoned by the female (7). Fledging occurs at about ten weeks (4) (7).
Although widely distributed, and with a large population in Africa, the comb duck is scarcer and probably declining in Asia, and is considered under threat in South America (4) (9). The main threats to the comb duck include habitat destruction, overhunting and, in South America, the use of poison against foraging wildfowl in rice fields (4) (9) (10). The comb duck is also susceptible to avian influenza, so is potentially threatened by future outbreaks of this virus (10).
The comb duck is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning international trade in comb ducks should be carefully monitored and controlled (5). It is also listed under Appendix II of the Convention on Migratory Species (CMS), which aims to conserve migratory species throughout their range and lists species that would benefit from international co-operation (13), and on Annex 2 of the associated African-Eurasian Waterbird Agreement (AEWA), which calls upon parties to engage in a range of conservation actions to help protect and conserve bird species that are dependent on wetlands for at least part of their annual cycle (14). The comb duck is currently part of a satellite tracking programme aimed at improving understanding of wild duck behaviour and migratory routes in light of the spread of Highly Pathogenic Avian Influenza (HPAI) H5N1 virus (15).
For more information on the conservation of migratory waterbirds, see:
African-Eurasian Waterbird Agreement (AEWA):
For more information on the comb duck see:
BirdLife International - Comb duck:
- Incubation: the act of incubating eggs, that is, keeping them warm so that development is possible.
- Invertebrates: animals with no backbone.
- Larvae: stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Monogamous: having only one mate during a breeding season, or throughout the breeding life of a pair.
- Subspecies: a population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
IUCN Red List (December, 2008)
- Callaghan, D. (2005) South American comb duck Sarkidiornis sylvicola. In: Kear, J. (Ed.) Ducks, Geese and Swans. Oxford University Press, Oxford.
- Young, G. (2005) African comb duck Sarkidiornis melanotos. In: Kear, J. (Ed.) Ducks, Geese and Swans. Oxford University Press, Oxford.
- del Hoyo, J., Elliott, A. and Sargatal, J. (1992) Handbook of the Birds of the World. Volume 1: Ostrich to Ducks. Lynx Edicions, Barcelona.
CITES (December, 2008)
- Erritzoe, J. (1993) The Birds of CITES and How to Identify Them. The Lutterworth Press, Cambridge.
- Todd, F.S. (1996) Natural History of the Waterfowl. Ibis Publishing Company, Vista, California.
- Sinclair, I. and Davidson, I. (2006) Sasol Southern African Birds: A Photographic Guide. Struik, Cape Town.
- Ogilvie, M.A. and Young, S. (2002) Photographic Handbook: Wildfowl of the World. New Holland Publishers, London.
BirdLife International (December, 2008)
- Blake, E.R. (1977) Manual of Neotropical Birds. Volume 1: Spheniscidae (Penguins) to Laridae (Gulls and Allies). University of Chicago Press, Chicago and London.
- Batt, B.D.J., Afton, A.D., Anderson, M.G., Ankney, C.D., Johnson, D.H., Kadlec, J.A. and Krapu, G.L. (1992) Ecology and Management of Breeding Waterfowl. University of Minnesota Press, Minneapolis, MN.
Convention on the Conservation of Migratory Species of Wild Animals (December, 2008)
African-Eurasian Waterbird Agreement (December, 2008)
Wild Birds and Avian Influenza in Africa (December, 2008)