The gadwall is 47–58 cm (19–23 in) long with a 78–85 cm (31–33 in) wingspan.[10] The male is slightly larger than the female, weighing on average 990 g (35 oz) against her 850 g (30 oz).[11] The breeding male is patterned grey, with a black rear end, light chestnut wings, and a brilliant whitespeculum, obvious in flight or at rest.[12] In non-breeding (eclipse) plumage, the drake looks more like the female, but retains the male wing pattern, and is usually greyer above and has less orange on the bill.[11]
The female is light brown, with plumage much like a femalemallard. It can be distinguished from that species by the dark orange-edged bill, smaller size, the whitespeculum, and white belly.[12] Both sexes go through two moults annually, following a juvenile moult.[10]
The gadwall is a quieter duck, except during itscourtship display. Females give a call similar to thequack of a female mallard but higher-pitched, transcribed asgag-ag-ag-ag. Males give a grunt, transcribed asmep, and a whistle.[11]
InGreat Britain, the gadwall is a scarce-breeding bird and winter visitor, though its population has increased in recent years. It is likely that its expansion was partly through introduction, mainly to England, and partly through colonization by continental birds staying to breed inScotland. In Ireland a small breeding population has recently become established, centred onCounty Wexford in the south andLough Neagh in the north.[13] The Gadwall is also seen in some parts ofSouth Asia, particularly the southern part of India.[14]
The gadwall is a bird of open wetlands, such asprairie orsteppe lakes, wet grassland or marshes with dense fringing vegetation, and usually feeds by dabbling for plant food with head submerged. They can also dive underwater for food, more proficiently than other dabbling ducks, and may also steal food from diving birds such as coots.[15] It nests on the ground, often some distance from water. It is not as gregarious as some dabbling ducks outside the breeding season and tends to form only small flocks.
Gadwalls are monogamous and may start breeding after their first year. Pair formation begins during fall migration or on breeding grounds, but has also been reported to occur in August when males are still in eclipse plumage. Gadwalls are generally quiet, except during courtship. The male utters amep call during a display known as theburp, where he raises his head pointing his bill towards a female.[16] Thegrunt-whistle is similar to that of mallards, where the male rears his outstretched head with the bill dipped into water, displacing a stream of water droplets towards a nearby female as the bill is raised against the chest. During this display the male makes a loud whistle call followed by a lowburp.[17] Paired males may follow other females in flight displays.[15][18]
During nesting season, the female lays a clutch of 7–12 eggs with each of them measuring 4.9–6 cm (1.9–2.4 in) in length and 3.4–4.4 cm (1.3–1.7 in) in width. Incubation lasts for 24–27 days and the nestlings leave after around 1–2 days. A gadwall can only raise one brood a season[2]
Currently, the gadwall is listed asleast concern in theIUCN Red List of Threatened Species.[1] The gadwall is one of the species to which theAgreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies. Populations have increased approximately 2.5% over the course of 49 years (from 1966 to 2010), and continue to grow. Gadwalls are one of the most hunted duck species (3rd to themallard andgreen-winged teal), with 1.7 million shot each year.[19]
Because of the efforts of the United States and Canadian groupsDucks Unlimited,Delta Waterfowl Foundation and other private conservation groups, the species continues to be sustainably hunted there.[2]
^"gadwall".Merriam-Webster. Retrieved24 August 2011.
^abcdFloyd, T. (2008).Smithsonian Field Guide to the Birds of North America. New York: HarperCollins.
^abcMadge, Steve; Burn, Hilary (1988).Wildfowl: An Identification Guide to the Ducks, Geese and Swans of the World. Christopher Helm. pp. 200–202.ISBN0-7470-2201-1.
^abcdDunn, J.; Alderfer, J. (2006).National Geographic Field Guide to the Birds of North America (5th ed.).
^Crabtree, Robert L.; Broome, Linda S.; Wolfe, Michael L. (1989). "Effects of Habitat Characteristics on Gadwall Nest Predation and Nest-Site Selection".The Journal of Wildlife Management.53 (1):129–137.doi:10.2307/3801319.ISSN0022-541X.JSTOR3801319.
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