Gadwall (Anas strepera)
by Wanda Gorsuch

Common Names: gray duck, gray mallard

With their drab plumage, it is not unusual to mistake a gadwall for a hen mallard at a distance.  However, any flock that looks like it is entirely made up of hen mallards is more likely to be gadwalls in disguise.

Identification

A medium sized dabbling duck, gadwalls lack any brilliant colorization.  Though drab, on closer examination their coloring could be considered eye-catching. 

Drakes are a gray brown with a white abdomen and black rump and undertail coverts.  They sport a white speculum that distinguishes them in flight from other ducks, along with a bit of black and chestnut on their wings.  Their head and neck are a lighter gray brown than the body and wings.  Other distinguishing features include a slate blue bill and yellow legs.

At a quick glance, gadwall hens resemble other brown female ducks, except they have a distinctive orange yellow bill with gray black spots and a white speculum.  Hens are a buffy tan as opposed to the males gray brown with little difference in shading between the head, neck and body.  They have little, if any, chestnut color, unlike the drakes.

Distribution

In breeding season, gadwalls are found centered in western North America.  Greatest densities can be found in the Dakota’s and Prairie Provinces.  During the winter months, gadwalls can be found from southern Alaska (west), southern Ontario (east) and south to south Mexico.  Highest numbers are found along the Atlantic, Pacific and Gulf coasts and in the southern US.

Habitat

Gadwalls inhabit mixed prairie, parkland, shortgrass prairie, tallgrass prairie and sub-Arctic deltas during breeding season.  Seasonal and semi-permanent wetlands with a 1:1 vegetation:water ratio make up an important part of preferred breeding habitat.  In winter months, gadwall will use reservoirs, beaver ponds, farm ponds, coastal fresh and brackish marshes.  Gadwalls are primarily found in lakes and inland marshes with lot’s of leafy aquatic vegetation.  They can also be found on rivers and in scrub-shrub habitat.

Food

Gadwalls eat submerged aquatic plants such as pondweed, widgeon grass, water milfoil and algae. They also eat seeds from pondweeds, smartweed, bulrush and spike rush.  In breeding season they eat an increased amount of invertebrates including crustaceans and midges.  It is thought that in the winter invertebrates are only incidentally eaten.

Reproduction

Pairs are generally formed during fall migration.  In the spring, gadwall are one of the latest nesting dabbling ducks with nesting starting around mid to late May.  Gadwall like to nest in tall, emergent vegetation near water and prefer islands. 

The hen builds her nest by scraping a shallow bowl in the soil and than extending her head to pick up twigs, leaves and branches from around the area, tucking them against her body with a sideways movement.  After the nest is completed, one egg a day is laid between 5:00am and 7:00am until there are 7 – 12 eggs.  Drakes will generally accompany hens to the nest site until laying is finished.  Only hens incubate the eggs and care for the brood.

Incubation starts during laying and increases as laying progresses and is completed.  Females will spend 85% of their time incubating and taking daily recesses that last a total of 220 minutes.  Eggs are incubated for about 26 days. 

Ducklings hatch out generally in less than 24 hours.  Hen and ducklings will leave the nest 24-36 hours after hatching and go to water.  Ducklings are able to feed themselves from the time of hatching.  Hens will brood ducklings for up to 14 days after hatch.

Conservation and Management

Since 1955, gadwall numbers have been increasing.  In the US, it stands third behind mallard and green-winged teal as the most harvested duck.  However, as other waterfowl, gadwall are sensitive to continuously decreasing habitat and variable water conditions.

Sources of Information

Bellrose, F.C.  1976.  Ducks, geese and swans of North America, 2nd edition. Stackpole Books, Pennsylvania.

Johnsgard, P.A.  1978.  Ducks, geese, and swans of the world. University of Nebraska Press, Nebraska.

Leschack, C.R., S.K. McKnight, and G.R. Hepp.  1997.  Gadwall (Anas strepera). In The Birds of North America, No. 283 (A. Poole and F. Gill, Eds.). Philadelphia: The Academy of Natural Sciences; Washington, D.C.: The American Ornithologists’ Union.