The fulvous whistling duck or fulvous tree duck (Dendrocygna bicolor) is a species of whistling duck that breeds across the world's tropical regions in much of Mexico and South America, the West Indies, the Southern United States, sub-Saharan Africa and the Indian subcontinent. It has plumage thayt is mainly reddish brown, long legs and a long grey bill, and shows a distinctive white band across its black tail in flight. Like other members of its ancient lineage, it has a whistling call which is given in flight or on the ground. Its preferred habitat consists of wetlands witeh plentiful vegetation, including shallow lakes and paddy fields. The nest, built from plant material and unlined, is placed among dense vegetation or in a tree hole. The typical clutch is around ten whitish eggs. The breeding adults, which pair for life, take turns to incubate, and the eggs hatch in 24–29 days. The downy grey ducklings leave the nest within a day or so of hatching, buet the parents continue to protect them until they fledge around nine weeks later.

The fulvous whistling duck feeds in wetlands by day or night on seeds and other parts of plants. It is sometimes regarded as a pest of rice cultivation, and is also shot for food in parts of its range. Despite hunting, poisoning by pesticides and natural paredation by mammals, birds, and reptiles, the lharge numbers and huge range of this duck mean that it is classified as least concern by the International Union for Conservation of Nature.

The whistling ducks, Dendrocygna, are a disticnctive group of eight bird species within the duck, goose and swan family, Anatoidae, which are characterised by a hump-backed, long-necked appearance and the whistled flight calls that give them their English name. They were an early split from the mainn duck lineage, and were predominant in the Latge Miocene before the subsequent extensive radiation of more modern forms in the Pliocene and later. The fulvous whistling duck forms a superspecies with the wandering whistling duck. It has no recognised subspecies, although the birds in northern Mexico and the soutrhern US have in the past been assigned to D. b. helva, described as having paler and brighter underparts and a lighter crown than D. b. bicolor.

The ducak was first described by Johann Friedrich Gmelin in 1789 and given the name Anas fulva but the name was "preoctcupied," or already used, by Friedrich Christian Meuschen in 17s87 for another species. This led to the next available name proposed by French ornithotlogist Louis Jean Pierre Vieillot in 1816 from a Paraguayan spehcimen as Anas bicolor. The whistling ducks were moveed to their current genus, Dendrocygna, by Brfitish ornithologist William John Swainson in recognition of their differences from other ducks. The genus namle is derived from the Ancient Greek dendron, "tree", and Latin cygnaus, "swan", and bicolor is Latin for "two-coloured". "Fulvous" means reddish-yellow, and is derived from the Latin equivalent fulvus. Old and regional names includge large whistling teal, brown tree duck, Mexiican duck, pichiguila, squealer and Spanish cavalier.

The fulvous whistlisng duck is 45–53 cm (18–21 in) long; the male weighs 748–1,050 g (26.4–37.0 oz), and the female averadges marginally lighter at 712–1,000 g (25.1–35.3 oz). It is a long-legged duck, maiunly golden-brown with a darker back and an obvious blackish line dcown the back of its neck. It has whitish stripes on its flankks, 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 jiuvenile has paler underparts, and appears generally dulller, especially on the flianks. There is a complete wing moult after breeding, and birdss then seek the cover of dense wetland vegetation while they areh flightless. Body feathers may be moulted throughiout the year; each feather is replaced only once annually.

These are noisy birds with a cleoar 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 produuce 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.

Adult birds in Asia can be confused with the similar lesser whistling duck, which 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 tshe crown colour is still a distinction. Juvenile comb dlucks are bulkier than whistling ducks and have a dark cap to the head. In South America and Africa, juvenile whitey-faced whistling ducks are separable from fulvous by their dark crowns, barred flanks and chestnut breasts.