Comb Duck

About

The Comb Duck, also known as the Knob-billed Duck, is a large perching duck found in tropical wetlands in Sub-Saharan Africa, Madagascar, and South Asia. Males are distinctive for the large, fleshy, black knob on their bill, especially prominent during the breeding season. They are primarily herbivorous, feeding on seeds, grasses, and aquatic vegetation.

Size & lifespan

Length

56-76 cm (22-30 in)

Wingspan

116-145 cm (46-57 in)

Weight

1.2-2.9 kg (2.6-6.4 lbs)

Lifespan

Up to 10-15 years in the wild

Diet

Herbivore (primarily seeds, grasses, aquatic vegetation, some insects)

Physical characteristics

Plumage

Adults have a glossy blue-black cap and hindneck, extending down the back. The face, neck, and underparts are white, often with a yellowish or buff wash. The flanks are grey, and the back and wings are iridescent blue-black. Some individuals, particularly in the African subspecies, may show dark mottling or spotting on the flanks and breast. The tail is black.

Beak shape

Large, broad, and flattened. Males possess a prominent, fleshy, black, erectile knob on the culmen, which is much reduced or absent in females.

Eye color

Dark brown

Leg color

Dark grey to black

Distinguishing features

The most distinctive feature is the large, black, fleshy knob on the male's bill. In flight, they show large white wing patches on the upperwing coverts, contrasting with the dark flight feathers. The overall large size and upright posture are also characteristic.

Juvenile appearance

Juveniles are duller than adults, with a brownish-grey cap and back, and less distinct white underparts. The bill knob is absent in young males.

Seasonal changes

The male's bill knob is most prominent and swollen during the breeding season, shrinking outside of this period. Plumage generally remains consistent year-round, though iridescence may appear more vibrant in breeding plumage.

Sexual dimorphism

Males are significantly larger than females and possess the prominent black knob on the bill, which is absent or very small in females. Females are generally duller in plumage, with less iridescence.

How to identify

1. 1

   Male's Bill Knob

   Look for the distinctive large, black, fleshy knob on the male's bill, especially prominent during the breeding season. This is the most reliable field mark for males.

2. 2

   Plumage Pattern

   Observe the glossy blue-black cap and back contrasting with the clean white face, neck, and underparts. Note the grey flanks and iridescent sheen on the back and wings.

3. 3

   In-flight Markings

   When flying, look for the large, conspicuous white patches on the upperwing coverts, which stand out against the dark flight feathers.

4. 4

   Size and Posture

   Note its relatively large size for a duck and its often upright posture when standing or perching in trees.

5. 5

   Habitat

   Search in tropical freshwater wetlands, particularly those with emergent vegetation and scattered trees for perching.

Habitat & range

Biomes

Tropical and subtropical wetlands, including freshwater lakes, swamps, marshes, rivers, and flooded grasslands.

Geographic range

Sub-Saharan Africa, Madagascar, and South Asia (India, Sri Lanka, Bangladesh, Myanmar, Thailand, Cambodia, Laos, Vietnam, southern China).

Elevation range

Typically found from sea level up to 1,500 meters (4,900 feet), occasionally higher.

Preferred environments

Prefers shallow, well-vegetated freshwater bodies, often with emergent vegetation and scattered trees for perching. Also found in rice paddies and other agricultural wetlands.

Behavior

Activity time

Diurnal, most active during early morning and late afternoon.

Feeding habits

Primarily grazes on aquatic vegetation, seeds, and grasses. They dabble and up-end in shallow water, but also graze on land. Occasionally consumes insects, small fish, and invertebrates, especially during the breeding season.

Social behavior

Typically seen in pairs or small family groups, but can form larger flocks of up to several hundred individuals outside the breeding season, especially at favored feeding or roosting sites.

Flight pattern

Strong, direct flight with relatively slow wingbeats. The white wing patches are very conspicuous in flight. Often flies in small flocks.

Migration pattern

Generally resident in many parts of its range, but can be locally nomadic or migratory in response to rainfall and water availability. African populations may undertake seasonal movements, while Asian populations are largely sedentary.

Territoriality

Males can be territorial during the breeding season, defending nesting sites and mates. Outside of breeding, they are more gregarious.

Breeding & reproduction

Breeding season

Varies geographically, typically coinciding with the rainy season. In Africa, often July-December; in Asia, June-September.

Nesting habits

Nests are typically built in tree hollows, often high above the ground, or in dense vegetation near water. They may also use old nests of other large birds. The nest is a simple scrape lined with grass and down.

Clutch size

7-15 eggs, sometimes up to 20 in communal nests.

Egg description

Creamy white to pale yellowish-buff, smooth, and unspotted. Oval to elliptical in shape.

Incubation period

28-30 days

Fledging period

Approximately 70 days, but young can fly earlier.

Parental care

Primarily the female incubates the eggs and cares for the ducklings. Males may guard the territory but generally do not participate in incubation or direct chick rearing.

Where to find

Field tips

1. Scan Water Bodies. Carefully scan the edges of wetlands, especially areas with dense vegetation or floating plants where they might be feeding.
2. Look Up. Don't forget to look in trees near water, as Comb Ducks frequently perch on branches, unlike many other duck species.
3. Observe Flocks. Outside the breeding season, they may gather in larger flocks, making them easier to spot. Look for groups dabbling or grazing.
4. Listen for Calls. While generally quiet, listen for the soft quacks of females or the low grunts of males, especially if disturbed.

Similar species

Quick facts

Distinguishing Feature:

Male's prominent bill knob

Habitat:

Tropical freshwater wetlands

Diet:

Mainly vegetarian

Flight Markings:

Conspicuous white wing patches

Nesting:

Often in tree hollows

Fun facts

• The Comb Duck is one of the few duck species that regularly perches in trees, often at considerable heights.
• Despite its name, it is not a true 'comb' duck in the sense of having a comb-like structure, but rather a fleshy knob on the bill.
• The species was formerly split into two subspecies, African Comb Duck (S. m. melanotos) and American Comb Duck (S. m. sylvicola), but the American population is now recognized as a distinct species, the American Comb Duck (Sarkidiornis sylvicola).
• Males are known to be polygynous, often mating with multiple females and defending a territory that encompasses several nests.

Scientific classification

Kingdom

Animalia

Phylum

Chordata

Class

Aves

Order

Anseriformes

Family

Anatidae

Genus

Sarkidiornis

Species

Sarkidiornis melanotos

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