Sarkidiornis melanotos (Comb duck, Knob-billed duck) 

Knobbeleend [Afrikaans]; Nkuva [Kwangali]; Pura [Shona]; Patu ra nhova [Tsonga]; Legôu, Sefalabogôgô [Tswana]; Knobbeleend, Pronkeend [Dutch]; Canard à bosse [French]; Höckerente [German]; Pato-de-carúncula [Portuguese]

Life > Eukaryotes > Opisthokonta > Metazoa (animals) > Bilateria > Deuterostomia > Chordata > Craniata > Vertebrata (vertebrates)  > Gnathostomata (jawed vertebrates) > Teleostomi (teleost fish) > Osteichthyes (bony fish) > Class: Sarcopterygii (lobe-finned fish) > Stegocephalia (terrestrial vertebrates) > Tetrapoda (four-legged vertebrates) > Reptiliomorpha > Amniota > Reptilia (reptiles) > Romeriida > Diapsida > Archosauromorpha > Archosauria > Dinosauria (dinosaurs) > Saurischia > Theropoda (bipedal predatory dinosaurs) > Coelurosauria > Maniraptora > Aves (birds) > Order: Anseriformes > Family: Anatidae

Comb duck female. [photo Callie de Wet ©]

Comb duck male. [photo Callie de Wet ©]

The comb duck is so called because the male has a round knob on top of the bill, which is particularly prominent in the breeding season (the word comb can mean the comb you use for your hair but also has a number of meanings relating to a crest). These large distinctive ducks are blue-black on the back, white on the front, and the head is white overlaid by black speckles. In the breeding season, males hold territories to which they often attract more than one female (polygynous). Females usually nest inside holes of trees. Comb ducks have a wide distribution including parts of Asia, South America and Africa. They prefer pans, lakes or rivers surrounded by woodland. 

Records

Distribution and habitat

Has a wide distribution covering southern Asia (Pakistan to S China), tropical South America and sub-Saharan Africa. Widespread within Sub-Saharan Africa but absent from semi-arid and arid regions. Within southern Africa, its distribution basically follows the distribution of mature woodlands because it prefers pans,  lakes or rivers bordered by woodland. Its habitat preferences are therefore directly opposite to those of the South African Shelduck, which likes water bodies without trees around them. Not surprisingly, their distributions within South Africa are almost directly opposite of one another, with only a few areas of overlap (e.g. in Namibia).  

Movements

Moves extensively round Sub-Saharan Africa, as recorded by ringing of these birds. Nearly 10% of ringing recoveries were > 2000 km from where they were originally ringed. Many birds ringed in southern Africa have been recovered north of the equator. 

Predators and parasites

• Predators:
  • Panthera pardus (Leopard): rare
  • Haliaeetus vocifer (African fish-eagle): regular predator of ducklings.
• Ectoparasites (parasites on the outside of the body)
  • Hexapoda (insects) 
    • Malophaga (lice) > feather lice
      • Holomenopon leucoxanthum
      • Anaticola asymmetricus
      • Anatoecus icterodes
      • Anatoecus dentatus
      • Trinoton straeleni
    • Diptera (flies) > Hippoboscidae
      • Ornithoctona laticornis
  • Arachnida (arachnids) > Acarina (ticks and mites) 
    • feather mites
      • Freyana anatina
      • Freyana largifolia
      • Bdellorhynchus psalidrus
    • nasal mites
      • Speleognathus womersleyi
      • Rhinonyssus rhinolethrum
• Pathogens
  • Mycobacterium causing avian tuberculosis (recorded in captivity)
  • aspergillosus

Food

The following food items have been recorded in its diet:

• Foraging in the water
  • Plant matter 
    • Potamogeton crispus (Wavy-leaved pondweed): at one site recorded as 99.9% of the diet. 
    • Nymphaea nouchali (Blue water lily): fruits
    • Nymphoides indica (Small yellow water lily): seeds
    • Cyperus esculentus (Nut grass): rhizomes
    • Jungle rice: leaves
    • Vossia cuspidata (Hippo grass)
  • Aquatic insects: form a minor component of the diet (c 0.1%)
• Foraging on land
  • crop residues in cultivated fields of:
    • wheat
    • groundnuts
  • seeds and fruits of grasses and herbs
    • Brachiaria xantholeuca (Signal grass)
    • Echinochloa colona (Jungle rice)
    • Digitaria ciliaris (Tropical finger grass)
    • Sorghum verticilliflorum var. latiglume (Johnson grass)
    • Sacciolepis africana (Swamp hood grass)
    • Aeschynomene fluitans (knuckle-beans)
    • Aeschynomene nilotica (knuckle-beans)
    • Ambrosia artemisifolia (Ragweed)
  • insects
    • termite alates

Breeding

• In good habitats, males are capable of keeping a harem of females, but in poorer habitats, they tend to be monogamous (one female only). Males are also sometimes serially polygynous where they form a bond with one female at a time, moving on to the next one once she has laid the eggs.  
• Usually nest in a cavity of a tree, 4-12 m above the ground, but also known to nest on old Hamerkop nests and on a rotten palm stump.  Can also nest in clumps of sedges or among rocks. The nest is usually near water but can be up to 2 km away. Females compete for nest sites, resorting to fighting one another if necessary. The nest itself consists of a bowl of down.
• Breeding season is from September to April
• The female usually lays 8-11 eggs (probably one egg per day) and on completion of the clutch, incubates them for 28-30 days before they hatch. Clutches of up to 20 are probably due to more than one female laying in the nest. When the female leaves the nest to feed, she covers the eggs with down, which keeps them warm. 
• Ducklings have very sharp claws and are able to climb vertical wooden surfaces. They jump from the nest when the female calls them from below the nest. Only the female looks after the young although the male is in the vicinity to drive off intruding males. By 65-70 days, the young have fully developed flight feathers. 

Threats

No significant threats; in fact the population has expanded as a result of the building of dams.

References

• Hockey PAR, Dean WRJ and Ryan PG (eds) 2005. Roberts - Birds of southern Africa, VIIth ed. The Trustees of the John Voelcker Bird Book Fund, Cape Town.