The Ring-necked Duck is a small to medium-sized diving duck with distinctive white bill markings and a short crest that gives its head an angular profile. The species is native to North America, but sightings outside of the continent are increasingly common. Migratory throughout its range, this duck nests at generally low densities in subarctic deltas, taiga, boreal forest, aspen parkland, and to a lesser extent, prairie regions. Its breeding range expanded east of the Great Lakes beginning in the 1930s and westward into Alaska and Yukon Territory during the 1980s.
Ring-necked Ducks winter inland along the Gulf of Mexico and southern Atlantic Coasts of the United States. Historically they were probably dispersed in small flocks (10–40 birds) across available wintering habitat, but recently they have become more concentrated (>500 birds) at some wintering sites because of habitat changes. During summer and winter, Ring-necked Ducks prefer shallow, freshwater wetlands with stable water levels and abundant emergent and submerged or floating plants. Migrants are found on shallow lakes with dense stands of emergent or submergent vegetation and on temporally flooded areas with abundant moist-soil vegetation.
Ring-necked Ducks are believed to be seasonally monogamous, but genetic studies to confirm this are lacking. Individuals pair during spring migration in Mar and Apr and persist as pairs until early incubation. They nest in flooded or floating emergent vegetation within 200 m of open-water feeding areas. Only the female provides parental care, incubating eggs and generally remaining with the young until they fledge.
This species dives for its food (in shallow water) and has a more generalized diet than do other North American diving ducks of the genus Aythya. Except possibly during breeding, diets of male and female are similar, consisting mostly of plant foods (seeds and below-ground plant parts). Generalized feeding habits probably facilitate colonization of new areas and occupancy of habitats such as bogs that have low productivity compared to wetlands used by other North American waterfowl.
Ring-necked Ducks are potentially vulnerable to intensive hunting (overharvest) and prone to ingesting spent lead shot. Population estimates are imprecise because the species is difficult to census and much of its current breeding range is not included in areas traditionally surveyed for waterfowl. Nonetheless, the continental population is considered stable or increasing. Curiously, the breeding distribution expanded and the population increased during the 1980s and early 1990s, when populations of most other North American ducks, especially prairie-nesting species, were in decline. During the 2000s, continental Ring-necked Duck populations have been stable, but higher than their long term average since 1955.
The species has been studied extensively on breeding areas in Maine (Mendall 1958), Minnesota (Hohman 1984a, CLR, CMH), and Michigan (Sarvis 1972), and at wintering sites in Florida (Jeske 1985) and South Carolina (Alexander 1980c). Generally well understood are diet, molts, body mass and composition changes in the annual cycle, nesting parameters, and nonbreeding behavior. Information is lacking, however, for fall and spring migrants and from core breeding areas in the Canadian boreal forest and wintering sites along the central Gulf Coast. In general, life history and demographic aspects are less well known for this species than for other North American Aythya (except the Greater Scaup [Aythya marila]), the Wood Duck (Aix sponsa), prairie-nesting waterfowl, and Arctic-nesting geese), but Ring-necked Ducks are better studied than seaducks and mergansers.