Harteman Wildfowl, presented by Jan Harteman
Mareca strepera (del Hoyo and Collar 2014) was previously placed in the genus Anas.
The gadwall is a common and widespread duck of the family Anatidae.
The gadwall was first described by Linnaeus in 1758 in his Systema naturae, under its current scientific name. DNA studies have shown that it is a sister species with the falcated duck, and that these two are closely related to the wigeons.
There are two subspecies described:
The gadwall breeds in the northern areas of Europe and Asia, and central North America. In North America, its breeding range lies along the Saint Lawrence River, through the Great Lakes, Alberta,Saskatchewan, the Dakotas, south to Kansas, west to California, and along coastal Pacific Canada and southern coastal Alaska. The range of this bird appears to be expanding into eastern North America. This dabbling duck is strongly migratory, and winters farther south than its breeding range, from coastalAlaska, south into Central America, and east into Idaho, Kansas, Ohio, Virginia, and then south all the way into Central America. Its conservation status is Least Concern.
In Great 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 to Great Britain, with continental birds staying to breed in Scotland. It has been reported in the River Avon in Hampshire and Wiltshire. In Ireland a small breeding population has recently become established, centred on Wexford in the south and Lough Neagh in the north.
The gadwall is a bird of open wetlands, such as prairie or steppe lakes, wet grassland or marshes with dense fringing vegetation, and usually feeds by dabbling for plant food with head submerged. 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. This is a fairly quiet species; the male has a hoarse whistling call, and the female has a Mallard-like quack. The young birds are fed insects at first; adults also eat some molluscs and insects during the nesting season. The gadwall is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies.
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend is not known, but the population is not believed to be decreasing sufficiently rapidly to approach the thresholds under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern (IUCN, 2012).
The species is threatened by pollution (Kear 2005b) and disturbance from recreational use of freshwater wetlands (Kear 2005b, Pease et al. 2005). It also suffers mortality as a result of lead shot ingestion (Spain) (Mondain-Monval et al. 2002) and nest predation by American mink Neovison vison (Europe) (Opermanis et al. 2001). The species is susceptible to avian influenza, so may be threatened by future outbreaks (Melville and Shortridge 2006). The species is hunted throughout most of its range (Kear 2005b) both for recreation (Bregnballe et al. 2006, Shortridge et al. 2006) and commercial uses (Balmaki and Barati 2006), but is rarely taken in large numbers except where it is particularly abundant (Kear 2005b). The eggs of this species used to be (and possibly still are) harvested in Iceland (Gudmundsson 1979).
Above: adult drake Gadwall
Above: juvenile female Gadwall