A common breeding duck in the north-central United States and prairie Canada, Blue-winged Teal are early migrants for wintering habitats largely south of the United States. Like other small dabbling ducks that breed in North America, they pair in late winter or as they initiate northern migration in spring. As with most ducks, females tend to return to breeding and natal regions more than males, although the species shows considerably greater dispersal overall than most other dabbling ducks, being rather opportunistic and sometimes breeding in abundance outside their typical range.
Upon arrival on breeding areas, a female selects a territory that her mate strongly defends until late incubation. Females generally nest in upland vegetation; eggs are laid daily and nest visits get progressively longer, but nocturnal incubation of early season nests may not begin until the fourth or fifth night after the termination of laying during cold periods. Nest failure, due primarily to mammalian predation, often exceeds 90%; renesting, however, is surprisingly rare given the short life span. Ducklings hatch in synchrony and spend less than a day in the nest, following the female to shallow wetlands. In the course of the 36–40 days required to reach flight stage, the brood often makes overland treks with the adult female to other wetlands. Most young fledge in late July or early August.
Females molt after their brood is nearly full grown, although females with nests that hatch late due to renesting often abandon their half-grown young to initiate the annual wing molt. Females rarely undertake a molt migration. Males typically initiate the wing molt ahead of females because males are not involved in incubation or brood care. Adult males also begin southern migration well ahead of females and juveniles and are often abundant in Gulf Coast marshes by mid-August.
The population status of the Blue-winged Teal mirrors wetland conditions on the prairie breeding grounds. Populations dropped to a 40-year low in 1990 after several dry years, but in the decade following numbers more than doubled. This suggests that long-term wetland degradation on the prairies had not irreversibly damaged teal breeding habitat. Like other prairie-nesting ducks, the local productivity of a population is strongly influenced by nest success and probably brood survival.
Blue-winged Teal limit foraging to aquatic areas where the majority of their diet is plant matter, particularly seeds. Only during the period just before and during egg-laying do adult females consume large amounts of aquatic invertebrates, mainly insect larva and snails, to meet the heightened protein requirements for egg production. Like many other waterfowl, females store fat prior to nesting and then use this energy to form eggs and help meet the demands of incubation.
Their abundance as breeding ducks in the United States and southern Canadian prairies have made Blue-winged Teal the focus of many studies of nesting biology (Bennett 1938c, Sowls 1955, Glover 1956, Dane 1966), behavior (McKinney 1970, Miller 1976, Stewart and Titman 1980, Lokemoen et al. 1990a), nest success (Klett et al. 1988, McKinnon and Duncan 1999), incubation (Feldheim 1997, Loos 1999), food habits (Swanson et al. 1974b, Swanson and Meyer 1977, Manley et al. 1992), and postbreeding ecology (Oring 1964a, DuBowy 1985b, DuBowy 1985d). Studies of wintering ecology (Thompson and Baldassarre 1991, Thompson and Baldassarre 1992) are scarce because of their neotropical wintering sites. Likewise, studies of survival rates are few because of sparse band recoveries from North American hunters. Abundance and tolerance for disturbances at the nest make the Blue-winged Teal an excellent subject for experimental studies of parental investment (Armstrong and Robertson 1988), reproductive output (Rohwer 1984, Rohwer 1985a, Arnold et al. 1987), or incubation (Feldheim 1997).