The Knob-billed Duck, or African Comb Duck, is one of the larger waterfowl species in South Africa; at over 2.5kg in weight with a wingspan of 1.5m the male is considerably bigger than the female, though the large knob on its bill is his most conspicuous feature.
In South Africa, Knob-billed Ducks are found mainly in North West, Gauteng, Limpopo and Mpumalanga, marginally into the Free State and Kwazulu-Natal, with a handful of vagrants in other provinces. Furthermore they’re widely distributed over all of sub-Saharan Africa, Madagascar, India and South-east Asia. Within this range they roam widely, covering distances of over 3,500km, following the rains to recently inundated floodplains, marshes, pans, and more permanent waterbodies surrounded by woodland and savanna, at times disappearing almost completely from parts where they were still abundant just a few weeks earlier. Knob-billed Ducks are omnivores, feeding on seeds, small fruit, and a variety of aquatic animals and plants.
In the late-summer breeding season, Knob-billed Ducks are usually encountered in pairs or family groups consisting of a mature, territorial male, one or more mature females, and their ducklings, but outside of the breeding season they’re highly gregarious, coming together in flocks numbering from a few dozen into the thousands. They breed in holes in trees or large, abandoned nests, such as those of the hamerkop, always quite close to water and often using the same nest year-after-year. Clutches of 6-11 eggs are incubated by the female only for about 4 weeks, and shortly after hatching the ducklings have to jump out of their tree nest to follow their mother to water. The female is also solely responsible for caring for the ducklings, which become independent at around ten weeks old.
The IUCN considers the Knob-billed Duck to be of least concern, despite noting that its populations are in decline.