| Fulvous whistling duck | |
|---|---|
 | |
| Adult at theLake Apopka, Florida | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Anseriformes |
| Family: | Anatidae |
| Genus: | Dendrocygna |
| Species: | D. bicolor |
| Binomial name | |
| Dendrocygna bicolor (Vieillot, 1816) | |
 | |
Approximate breeding range | |
Thefulvous whistling duck orfulvous tree duck (Dendrocygna bicolor) is a species ofwhistling duck that breeds across the world's tropical regions in much ofMexico andSouth America, theWest Indies, the southernUnited States,sub-Saharan Africa and theIndian subcontinent. It hasplumage that 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 preferredhabitat consists ofwetlands with plentiful vegetation, including shallow lakes andpaddy fields.The nest, built from plant material and unlined, is placed among dense vegetation or in a tree hole. The typicalclutch 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, but the parents continue to protect them until theyfledge 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 bypesticides and natural predation by mammals, birds, and reptiles, the large numbers and huge range of this duck mean that it is classified asleast concern by theInternational Union for Conservation of Nature.
Thewhistling ducks,Dendrocygna, are a distinctive group of eight bird species within the duck, goose and swan family,Anatidae, which are characterised by a hump-backed, long-necked appearance and the whistled flight calls that give them their English name.[2] They were an early split from the main duck lineage,[3] and were predominant in theLate Miocene before the subsequent extensive radiation of more modern forms in thePliocene and later.[4] The fulvous whistling duck forms asuperspecies with thewandering whistling duck. It has no recognisedsubspecies, although the birds in northern Mexico and the southern US have in the past been assigned toD. b. helva,[5] described as having paler and brighter underparts and a lighter crown thanD. b. bicolor.[6]
The duck was first described byJohann Friedrich Gmelin in 1789 and given the nameAnas fulva but the name was "preoccupied", or already used, byFriedrich Christian Meuschen in 1787 for another species.[7][a] This led to the next available name proposed by FrenchornithologistLouis Pierre Vieillot in 1816 from a Paraguayan specimen asAnas bicolor.[9][b] The whistling ducks were moved to their current genus,Dendrocygna, by BritishornithologistWilliam Swainson in recognition of their differences from other ducks.[10] The genus name is derived from the Ancient Greekdendron, "tree", and Latincygnus, "swan",[11] and bicolor is Latin for "two-coloured".[12] "Fulvous" means reddish-yellow, and is derived from the Latin equivalentfulvus.[13] Old and regional names include large whistling teal,[5] brown tree duck,Mexican duck, pichiguila, squealer and Spanish cavalier.[14]
The fulvous whistling 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).[5] The wingspan ranges from 85 to 93 cm.[15]
It is a long-legged duck, mainly different shades of brown; head, neck and breast are particularly richbuff (fulvous) with a darker back.[16] The mantle is more darker shade of brown with buff-tipped feathers, the flight feathers and tail are dark brown, and a dark brown to black stripe runs through the center of the crown down the back of the neck to the base of the mantle. 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.[17][18] 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.[5] There is a complete wingmoult after breeding, and birds then seek the cover of dense wetland vegetation while they are flightless. Body feathers may be moulted throughout the year; each feather is replaced only once annually.[19]
These are noisybirds with a clear whistlingkee-wee-ooo call given on the ground or in flight, frequently heard at night.[16] Quarrelling birds also have a harsh repeatedkee. In flight, the beating wings produce a dull sound.[20] 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.[21]
| Songs and calls |
Adult birds in Asia can be confused with the similarlesser 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 the crown colour is still a distinction. Juvenilecomb ducks are bulkier than whistling ducks and have a dark cap to the head. In South America and Africa, juvenilewhite-faced whistling ducks are separable from fulvous by their dark crowns, barred flanks and chestnut breasts.[20]
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 theWest Indies. It is found in a broad belt acrosssub-Saharan Africa and down the east of the continent toSouth Africa andMadagascar. TheIndian subcontinent is the Asian stronghold.[20] It undertakes seasonalmovements 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.[20] This species has strong colonising tendencies, having expanded its range in Mexico, the US and the West Indies in recent decades with northerly range expansions into California in late 19th century and rice-growing regions of the U.S. Gulf Coastal Plain in the early to mid-20th century, given its affinity for rice-growing areas.[20][16] Breeding in the northern American region is restricted to the Gulf Coastal Plain of Texas and Louisiana and localities in southern California and south- and east-central Florida.[16] Observations of the bird outside the nesting season, especially since the 1950s have been recorded in temperate regions as far north as the Mississippi River Basin, eastern Great Lakes region, and along the Pacific and Atlantic Coasts right up to southern Canada.[16] Wandering birds can turn up far beyond the normal range, sometimes staying to nest, as in Morocco, Peru and Hawaii.[5]
The fulvous whistling duck is found in lowland marshes and swamps in open, rice fields, flat country, and it avoids wooded areas. It is not normally a mountain species, breeding in Venezuela, for example, only up 300 m (980 ft),[18] but the single Peruvian breeding record was at 4,080 m (13,390 ft).[5]
This species is usually found in small groups, but substantial flocks can form at favoured sites. It walks well, without waddling, and normally feeds by upending, though it can dive if necessary.[20] It does not often perch in trees, unlike other whistling ducks. It flies at low altitude with slow wingbeats and trailing feet, in loose flocks rather than tight formation. It feeds during the day and at night in fairly large flocks, often with other whistling duck species, but rests or sleeps in smaller groups in the middle of the day.[19] They are noisy and display their aggression towards other individuals by throwing back their heads. Before taking off in alarm, they often shake their head sideways.[22]
Severalarthropod parasites have been recorded on this duck, includingchewing mites of the familiesPhilopteridae andMenoponidae,[23][24]feather mites and skinmites. Internalhelminth parasites includeroundworms,tapeworms andflukes. In a survey in Florida, all 30 ducks tested carried at least two helminth species; none had blood parasites. Only one duck had no mites or lice.[25]
Breeding coincides with the availability of water. In South America and South Africa, the main nesting period is December–February, inNigeria it is July–December, and in North America mid-May–August.[5] In India, the breeding season is from June to October but peaking in July and August.[26] Fulvous whistling ducks show lifelongmonogamy; 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.[19]
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 inLouisiana. 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 on the ground (unlike theBlack-bellied whistling duck), in marsh vegetation, and in artificial habitats such as shallowly-flooded rice fields, in dense vegetation and close to water,[5][16][18] but sometimes in tree holes. In India, the use of tree holes, and even the old nests ofraptors orcrows, is much more common than elsewhere.[20] Eggs are laid at roughly 24- to 36-hour intervals, starting before the nest is complete, resulting in some losses from theclutch. They are whitish and on average measure 53.4 mm × 40.7 mm (2.10 in × 1.60 in) and weigh 50.4 g (1.78 oz).[19] The clutch is usually around ten eggs, but other femalessometimes lay into the nest, so 20 or more may be found on occasion.[5] Eggs may also be added to the nests of other species, likeruddy duck.[27]
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,[5] The downy ducklings are grey, with paler upperparts,[19] and a white band on the neck,[14] and weigh 22–38 g (0.78–1.34 oz) within a day of hatching. Like all ducklings, they areprecocial and leave the nest after a day or so, but the parents protect them until theyfledge around nine weeks later.[5] Eggs and duckling may be preyed on by mammals, birds and reptiles; one parent may try to distract a potential predator with a broken-wing display while the other adult leads the ducklings away.[19] Birds are sexually mature after one year, and the maximum known age is 6.5 years.[5]
In South Africa, a few records of hybridization with thewhite-faced whistling duck have been noted in the wild;[28][29] in most parts of southernAfrica, the two species breed at different times,bicolor during the dry season (April to September) andviduata during the rains (October to March).[30] Hybridization in captivity is more frequent but limited to other species in the genusDendrocygna.[31][32]
The fulvous whistling duck feeds in wetlands by day or night, often inmixed flocks with relatives such as white-faced orblack-bellied whistling ducks. Its food is generally plant material, including seeds, bulbs, grasses and stems, but females may include animal items such asaquatic 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 (3.3 ft). Favoured plants includewater snowflake, aquaticragweeds,bourgou millet,shama grass,Cape blue water lily,waxy-leaf nightshade,beakrush,flatsedge andpolygonums. 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 cereal.[5]
TheInternational Union for Conservation of Nature (IUCN) estimates the population of the fulvous whistling duck to be from 1.3 to 1.5 million individuals around the world.[1] This may be an underestimate since regional assessments suggest 1 million birds in the Americas, 1.1 million in Africa and at least 20,000 in South Asia for a grand total of 2.12 million ducks around the world.[19] The population appears to be declining, but the decrease is not rapid enough to trigger the vulnerability criteria for extinction. The large numbers and huge breeding range mean that this duck is classified by the IUCN as being ofLeast Concern.[1] It is one of the species to which theAgreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies.[33]
The fulvous whistling duck has expanded its range in the West Indies, and into the southern US.[20] A series of invasions from South America and reaching the eastern US commenced around 1948, fueled by rice cultivation, and breeding was recorded in Cuba in 1964,[19] and Florida in 1965. Some Florida birds still winter in Cuba.[34] In Africa, it bred on theCape Peninsula between 1940 and the 1960s. A survey of eighteen species which had colonised the area in recent decades found that most were wetland species that had used irrigated farmland as "stepping stones" across the arid country separating the peninsula from the breeding main range. However, the status of the two whistling duck species featured in the research is dubious since they are popular ornamental species, so their origin is unclear.[35]
Outside North America it is subject to hunting for food or because of its liking for rice, and persecution means that it is now rare in Madagascar. Pesticides used on rice fields may also have an adverse impact,[5] causing liver and breast muscle damage even at sub-lethal levels.[36]
