The fulvous whistling duck or fulvous tree duck is 45?53 cm (18?21 in) long; the male weighs 748?1,050 g (26.4?37.0 oz), and the female averages marginally lighter at 712?1,000 g (25.1?35.3 oz). It is a long-legged duck, mainly golden-brown with a darker back and an obvious blackish line down the back of its neck. It has whitish stripes on its flanks, a long grey bill and grey legs. In flight, the wings are brown above and black below, with no white markings, and a white crescent on the rump contrasts with the black tail. All plumages are fairly similar, but the female is slightly smaller and duller-plumaged than the male. The juvenile has paler underparts, and appears generally duller, especially on the flanks. There is a complete wing moult after breeding, and birds then seek the cover of dense wetland vegetation while they are flightless. Body feathers may be moulted throughout the year, although each feather is replaced only once annually. Adult birds in Asia can be confused with the similar lesser whistling duck, although that species is smaller, has a blackish crown and lacks an obvious dark stripe down the back of the neck. Juvenile fulvous whistling ducks are very like young lesser whistling ducks, but the crown colour is still a distinction. Juvenile comb ducks are bulkier than whistling ducks and have a dark cap to the head. In South America and Africa, juvenile white-faced whistling ducks are separable from fulvous by their dark crowns, barred flanks and chestnut breasts.
Habitat and Distribution
The fulvous whistling duck has a very large range extending across four continents. It breeds in lowland South America from northern Argentina to Colombia and then up to the southern US and the West Indies. It is found in a broad belt across sub-Saharan Africa and down the east of the continent to South Africa and Madagascar. The Indian subcontinent is the Asian stronghold. It undertakes seasonal movements in response to the availability of water and food. African birds move southwards in the southern summer to breed and return north in the winter, and Asian populations are highly nomadic due to the variability of rainfall. This species has strong colonising tendencies, having expanded its range in Mexico, the US and the West Indies in recent decades. Wandering birds can turn up far beyond the normal range, sometimes staying to nest, as in Morocco, Peru and Hawaii. The fulvous whistling duck is found in lowland marshes and swamps in open, flat country, and it avoids wooded areas. It is particularly attracted to wetlands with plenty of emergent vegetation, including rice fields. It is not normally a mountain species, breeding in Venezuela, for example, only up 300 m (980 ft), but the single Peruvian breeding record was at 4,080 m (13,390 ft).
The fulvous whistling duck feeds in wetlands by day or night, often in mixed flocks with relatives such as white-faced or black-bellied whistling ducks. Its food is generally plant material, including seeds, bulbs, grasses and stems, but females may include animal items such as aquatic worms, molluscs and insects as they prepare for egg-laying, which may then comprise up to 4% of their diet. Ducklings may also eat a few insects. Foraging is by picking plant items while walking or swimming, by upending, or occasionally by diving to a depth of up to 1 m (3 ft). Favoured plants include water snowflake, aquatic ragweeds, bourgou millet, shama grass, Cape blue water lily, waxy-leaf nightshade, beakrush, flatsedge and polygonums. Rice is normally a small part of the diet, and a survey in Cuban rice fields found that the plants taken were mainly weeds growing with the crop. However, in a study in Louisiana, 25% of the diet of incubating females consisted of the cereal.
Breeding coincides with the availability of water. In South America and South Africa, the main nesting period is December?February, in Nigeria it is July?December, and in North America mid-May?August. In India, the breeding season is from June to October but peaking in July and August. Fulvous whistling ducks show lifelong monogamy, although the courtship display is limited to some mutual head-dipping before mating and a short dance after copulation in which the birds raise their bodies side-by-side while treading water. Pairs may breed alone or in loose groups. In South Africa, nests may be within 50 m (160 ft) of each other, and breeding densities of up to 13.7 nests per square kilometre (35.5 per square mile) have been found in Louisiana. The nest, 19?26 cm (7.5?10.2 in) across, is made from plant leaves and stems and has little or no soft lining. It is usually built in dense vegetation and close to water, but sometimes in tree holes. In India, the use of tree holes, and even the old nests of raptors or crows, is much more common than elsewhere. Eggs are laid at roughly 24?36 hour intervals, starting before the nest is complete, resulting in some losses from the clutch. They are whitish and on average measure 53.4 x 40.7 mm (2.1 x 1.6 in) and weigh 50.4 g (1.78 oz). The clutch is usually around ten eggs, but other females sometimes lay into the nest, so 20 or more may be found on occasion. Eggs may also be added to the nests of other species, like ruddy duck. Both sexes incubate, changing over once a day, with the male often taking the greater share of this duty. The eggs hatch in about 24?29 days, The downy ducklings are grey, with paler upperparts, and a white band on the neck, and weigh 22?38 g (0.78?1.34 oz) within a day of hatching. Like all ducklings, they are precocial and leave the nest after a day or so, but the parents protect them until they fledge around nine weeks later. Eggs and duckling may be preyed on by mammals, birds and reptiles, although one parent may try to distract a potential predator with a broken-wing display while the other adult leads the ducklings away. Birds are sexually mature after one year, and the maximum known age is 6.5 years.
Calls and Songs
These are noisy birds with a clear whistling kee-wee-ooo call given on the ground or in flight. Quarrelling birds also have a harsh repeated kee. In flight, the beating wings produce a dull sound. The calls of males and females show differences in structure and an acoustic analysis on 59 captive birds demonstrated 100% accuracy in sexing when compared with molecular methods.