The Green-winged teal is the smallest North American dabbling duck. The breeding male has grey flanks and back, with a yellow rear end and a white-edged green speculum, obvious in flight or at rest. It has a chestnut head with a green eye patch. The female is light brown, with plumage much like a female mallard. In non-breeding (eclipse) plumage, the drake looks more like the female.
Green-winged teal breed from the Aleutian Islands, northern Alaska, Mackenzie River delta, northern Saskatchewan, Manitoba, Ontario, Quebec, and Labrador south to central California, central Nebraska, central Kansas, southern Minnesota, Wisconsin, Ontario, Quebec, Newfoundland, and the Maritime Provinces. These birds are migratory and winter from southern Alaska and southern British Columbia east to New Brunswick and Nova Scotia and south to Central America. They also winter in Hawaii. Green-winged teal inhabit sheltered wetlands, such as taiga bogs, inland lakes, marshes, ponds, pools, and shallow streams with dense emergent and aquatic vegetation. These birds also inhabit arctic tundra and semidesert communities and avoid treeless or brushless habitats. They winter in both freshwater or brackish marshes, ponds, streams, and estuaries and nest in grasses, sedge meadows, or on dry hillsides having brush or aspen cover.
Green-winged teal are highly gregarious; outside of the breeding season, they form large flocks and are often found resting on mudbanks or stumps, or perching on low limbs of dead trees. They feed by day and prefer to seek food on mudflats. Where mudflats are lacking, the birds will occur in shallow marshes or temporarily flooded agricultural lands. Green-winged teal usually feed by dabbling on the water surface for plant food or grazing on the ground. They will occasionally dive to get their food and to avoid predators. Green-winged teal are among the earliest spring migrants. They arrive on nesting areas almost as soon as the snow melts. Green-winged teal are very noisy birds; the males communicate with clear whistles, whereas the females have a feeble 'quack'.
Green-winged teal are herbivores (granivores, folivores). They usually eat vegetative matter consisting of seeds, stems, and leaves of aquatic and emergent vegetation. They will occasionally eat insects, mollusks, and crustaceans and during spring months, may gorge on maggots of decaying fish that are found around ponds.
Green-winged teal are serially monogamous and form new pairs each breeding season; however, some males may exhibit polygynous behavior and mate with more than one female. In North Dakota, Green-winged teal generally begin nesting in late April. In the Northwest Territories, they begin nesting between late May and early July. At Minto Lakes, Alaska, their breeding season starts in early June and in late July. These ducks nest in depressions on dry ground located at the base of shrubs, under a log, or in dense grass. The nests are usually located 2 to 300 ft (0.61 to 91.44 m) from water. The female lays 5 to 16 eggs and incubates them alone for 21-23 days. The males leave females at the start of incubation and congregate on safe waters to molt. Females molt on breeding grounds. The ducklings hatch precocial (fully-developed) and leave the nest a few hours after hatching. They often fledge 34 to 35 days after birth or usually before 6 weeks of age and become reproductively mature in their first winter.
Although the Green-winged teal is widespread and common. However, it is highly vulnerable to hunting pressure being a very popular species taken by hunters each year in the U.S.
According to Partners in Flight, the North American breeding population of the Green-winged teal is 6,700,000 breeding birds.