Anas strepera
gadwall

Anas strepera is a migratory bird. It winters from southern Mexico and Guatemala to coastal Alaska, the Atlantic, and Gulf coast regions of the United States and many areas in-between. Their summer breeding grounds range from the Atlantic coast of Canada to as far north as the western coastal regions of Alaska. Although, the largest concentration of them are found in the summer breeding grounds of the prairie pot-hole region of southern Canada and northern United States. Gadwalls can also be found in Iceland during the breeding season. They can also be found breeding in the Iceland, British Isles, Europe, and Asia (Tesky 1993, LeSchack et. al. 1997).

Gadwalls prefer marshes, sloughs, ponds, and small lakes with grasslands in both fresh and brackish water as breading habitats. They tend to be more abundant on small prairie marshes than in temporary water areas, deep marshes, and open water marshes. They generally avoid wetlands that are bordered by woodlands or thick vegetation. In the winter they prefer the brackish water marshes with abundant leafy aquatic vegetation. There are many winter populations that have made yearly migrations back to the same waterfowl refuges, reservoirs, beaver ponds, and sewage treatment plants (Johnsguard 1979, Tesky 1993, LeSchack et al. 1997).

Gadwalls can be very easy to identify in hand, but they can be very difficult to identify in the field. They are a medium-sized dabbling duck with non-distinct plumage and are most commonly misidentified in the field. The male and female gadwalls look very similar and resemble the hen mallard in drab plumage. The adult male has a gray plumage in the breeding season with distinct vermiculation on the scapular and back feathers. The head is brown and the upper and lower tail covers are black. The adult male tertials are long, and acutely pointed colored silver-gray. In basic plumage, the male Gadwall looks almost identical to the female. The adult female tertials are shorter and more bluntly pointed. The females lack the vermiculation but look very similar to the males with plumage more is more brownish on the back and buffy tan on the breast. The most distinguishing marks for both male and females are the white secondaries with black greater secondary coverts. This is very easy to see when in flight. The white speculum is the most identifying mark to recognize both sexes in the field but is only visible when in flight. The males will begin their prebasic molt after breeding with the female sometime during early to mid-summer depending on mating time and nest success. During this time they are not able to fly and are very vulnerable to predation (Bellrose 1980, Tesky 1993, LeSchack et al. 1997).

The Gadwall has to go through its juvenile plumage that may last 10 weeks until they begin their prealternate molt. The juvenile plumage of both the male and females look almost identical to the female plumage of all dabbling ducks. When the male juvenile goes through its prealternate molt, it then begins to take on the distinct male plumage with silver tipped tertials, puffy gray head, vermiculation, and rusty colored speculum (Bellrose 1980, LeSchack et al. 1997).

The courtship displays of Gadwall males can be very elaborate. The displays that the males perform range from the Head-Up-Tail-Up (male throws his head back and jerks with his tail feathers erect) to the Grunt-Whistle (male rears out of the water and slowly sinks back down while making a loud whistle). Both the male and accepting female then continues the courtship by performing other displays separately or in unison. Copulation begins with both sexes bobbing their heads up and down and touching their bills to the water horizontally with their necks extended. As the female extends her neck the male mounts her. After copulation the female bathes while the male faces her and then he bathes. There have been reported occurrences of extra-pair copulations. In the late laying and incubation season paired females unaccompanied by their mates have been chased by one to several paired males which occasionally has ended up in rape.If the nest is predated, then the female will usually make another nest and lay a second clutch. (Bellrose 1980, Tesky 1993, LeSchack et al. 1997).

Gadwalls are monogamous in their breeding behavior. Pairs of adult birds will bond in the mid to late fall, while inmature birds will pair by mid winter. Pair bonds are renewed each year. Most yearlings will mate the following breding season but studies on domestic flocks have showed that sometimes the late hatchlings were not sexually active untill their second year. The breeding season will vary but usually can occur in May and go through mid-July (Johnsguard 1979).

The male and the female will fly low over meadows and upland habitat in search of a nesting site. The female will usually choose a nest site near her natal nesting grounds. It is believed that this behavior is from the imprinting of familiar and successful nesting areas. As the male stands guard, the female will inspect an area that has suitable materials for nest building. When an area has been chosen, the female constructs a nest bowl by scraping a depression in the soil. She then lines it with leaves, grasses, and twigs from nearby material. She may then line the nest with down feathers plucked from her body.

She will lay a clutch from 7 to 13 eggs at the rate of one egg per day. The average incubation period will last 26 days with the female spending 85% of her time on the eggs. Many males will abandon the female after the clutch is laid and to a safe area where they will molt to their basic plumage.

The precocial young will hatch and be led by their mother from the vulnerable nest area to brood-rearing habitat. Since the ducklings are precocial, they obtain their own food. The female will raise the brood for no more than 10 weeks and will then abandon her young (Baldsarre et al. 1994, LeSchack et al. 1997).

Although there is no data on longevity or mean life expectancy, there was a banded Gadwall in Alaska that was recovered in Louisiana that had reached 19 years of age (Tesky 1997).

Gadwalls are gregarious, migratory waterfowl. They will leave their breeding grounds in the north from September in Alaska to the beginning up to late October in the Prairie-Pothole regions and other southern areas. Some weather event will be the trigger that will signal migration timing. The birds will fly in flocks of less than 100 individuals, but as many as 10, 000 will migrate in separate groups to the same destination arriving within hours of each other.

Although they are diurnal in their daily behavior, migrations flights usually take place at night. This is believed to avoid predation and conserve energy by flying in cooler temperatures (LeSchack et al. 1997).

Gadwalls main food sources are aquatic vegetation, aquatic invertebrates, and seeds. They are surface feeders feeding mostly on plant material growing close to the surface. They can also be found in fields feeding on grain or even in woodlands feeding on acorns. Their main diet of plant material includes leaves and stems of aquatic plants. Gadwalls will also supplement their plant diet with insects, crustaceans, amphibians, mollusks, and fish. Females will eat a protein and fat rich diet prior to mating. This provide them with extra resources for the egg laying and incubation periods. During this time, males eat more plant material than females (LeSchack et al. 1997).

Some of the plant material Gadwalls eat: pondweed (Potamogeton spp.), niad (Najas spp.), water milfoil (Myriophyllum spp.), algae (Cladophoraceae), smartweed (Polygonum spp.), bulrush (Scirpus spp.), spikerush (Eleocharis spp.), saltgrass (Distichlis spp.) and muskgrass (Chara spp.).

The Gadwall has many predators, including: humans from hunting and urban accidents, fox (Vulpes spp.), raccoons (Procyon lotor), coyotes (Canis latrans), badgers (Taxidea taxus), weasels (Mustela spp.), hawks (Accipitridae), crows (Corvus spp.), and minks (Mustela vison). (Tesky 1993).

Gadwalls are most vulnerable when females are nesting and when the males are molting from alternate to basic back to alternate plumage. Their main source of defense is to be on the water. Like all ducks, they also become very vulnerable when feeding to close to the shore in dense vegetation. This makes them subject to the quick strike of fox and coyotes (Tesky 1993, LeSchack et al. 1997).

Humans benefit from Gadwalls not as much economically as they do socially and traditionally. Hunting has been a tradition in the North America since the beginning of recorded history. The Native Americans have told of hunting waterfowl in their traditional stories. The hunting of Gadwalls as well as other waterfowl is deeply rooted in traditions of North Americans. Because of the demand by hunters to continue to harvest these birds, the U.S. fish and wildlife service monitors the populations and sets regulations on hunting of waterfowl. This system can be seen to have a positive impact on humans because of the rewards of the food source from hunting. Also money generated from the sale of hunting premits and liscenses helps to maintain and create new waterfowl refuges as well as supplies revenue to monitor populations for the next years hunting regulations (LeSchack et al. 1997).

There are no conservation plans for the Gadwall at this time. Their populations have been increasing since 1955. With the Conservation Reserve Program (CRP) under the Food Security Act of 1985, the retirement of 14 million acres of cropland in the Prairie Pothole region by 1996 has been attributed to a steady increase of many waterfowl populations including Gadwalls (Tesky 1993, LeSchack et al. 1997).