by John Hughes
Gadwalls (Mareca strepera) are medium sized dabbling ducks. Males are 19-22 inches in length with females being slightly smaller at 18-20 inches. Most people can pick out a male Gadwall fairly easily in a mixed flock of ducks. When asked to describe a Gadwall, what you most often hear is the gray duck with a black rump. While this is a good description of a male Gadwall at a distance, upon closer inspection the male has intricate markings of gray, black and white feathers on its chest and flanks with a chestnut hue on the upper wings. It has a slate gray bill, yellow legs, a black-bordered white speculum and a white belly. As with other sexually dimorphic ducks, females are brownish overall but can be distinguished from other female ducks with similar coloration by an orange bill with a dark longitudinal midsection and dark lateral spots and a white speculum.
I remember the first time I viewed a male Gadwall through a spotting scope and was blown away at how beautiful it was. The genus name Mareca is from the Brazilian-Portuguese word Marreco meaning small duck. I was disappointed to find that the word Gadwall, while having been in use since the mid seventeenth century, was of unknown origin. Linnaeus first described the Gadwall in his Systema naturae in 1758. Perhaps one of our readers can help me out with the origin of the word.
Gadwalls are widely distributed throughout the world. In North America, breeding populations can be in the north-central U.S. and Prairie Provinces of Canada. Gadwalls are found year round in western Montana where open water exists during the winter months. In eastern Montana, Gadwalls migrate south for the winter. They tend to prefer wetlands and are found at most wildlife refuges or waterfowl production areas but make use of sewage treatment plant ponds, stock tanks and other human made bodies of water. Migration begins in September and October for non-resident birds. Short distances are covered, usually at night with frequent stops along the way. North American populations winter in the southern U.S. and coastal Mexico with the largest concentrations along the southern gulf states of the U.S., with the largest populations found in Louisiana and Texas.
A Gadwall’s diet consists mainly of submerged aquatic vegetation, seeds and aquatic insects. They prefer shallow to deep wetlands where they feed over beds of aquatic vegetation on the surface to a depth of about 11 inches by submerging their heads or tipping up. Gadwalls tend to feed in deeper water than most dabblers and are known to steal food (kleptoparasitize) diving American Coots. They will feed during the day and night and spend over 60% of their time feeding during the winter.
Gadwalls are monogamous with pair bonding occurring during fall migration. Ninety-seven percent are paired up by November. Breeding is initiated during May in Montana. Typically there is only one clutch per season unless there is nest failure and time to lay another clutch. The pair will fly low over potential nest sites seeking spots with dense, tall grasses, forbs or shrubs that afford adequate cover to conceal the nest. Nest density is greatest on islands but Gadwall will also nest in fields, meadows and on dikes. The distance from water can vary anywhere from one-tenth mile to 1.5 miles from water. The male stands guard while the female determines the suitability of the site. Females have been known to use the same site for multiple years indicating the female may direct the male in the location of a nest site. Nests are created by scooping out a depression and pulling sticks and grasses around her body and finishing with down feathers in the middle plucked from the females brood patch area. Seven to twelve oval, whitish to greenish eggs are laid at a rate of one per day. The male guards the female during egg laying but leaves once all the eggs are laid. The female is responsible for incubation and care of the young. The female relies on fat reserves during this period. She also consumes more invertebrates during this period for protein. Incubation lasts about 26 days with the female spending 85% of her time on the nest. The chicks are precocial at birth and leave the nest within 24-36 hours after hatching. Brooding begins at hatching and last for about 14 days. The hen will lead the young to a brood-rearing area, which usually consists of tall emergent aquatic vegetation.
The chicks acquire their own food consisting of aquatic invertebrates in the beginning and transitioning to aquatic plants. The female abandons the brood at about 10 weeks. Flight is achieved approximately 50 days after hatching.
The Gadwall is listed as a species of least concern. Its populations and range have been increasing for the last 30 years. In the 1960s through the mid 1980s populations were low due to habitat destruction and drought. Between 1986 and 1996 populations are reported to have increased by 129% due to improved wetland conditions. This has enabled Gadwalls to expand their breeding range into formerly unoccupied areas in northwestern U.S. and eastern Canada. While this species is doing well, it should not be lost on anyone that the increase in their population was due to conservation efforts to set aside and improve wetland conditions. With an uncertainty in future climatic conditions, it is very important to continue to protect and improve our wetland habitats.
What’s that gray duck with a black rump? Why, it’s a Gadwall of course. Enjoy picking them out at great distances with just those characteristics. And if anyone knows the etymology of the word Gadwall, please let me know.