The onset of courtship among immature blue-winged teal often starts in late January or early February. Chronology of nesting can vary from year to year as a result of weather conditions.
Clutch size can also vary with the age of the hen.
Adult drakes depart the breeding grounds well before adult hens and immatures. The northern regions experience a steady decline in blue-winged teal populations from early September until early November. Blue-winged teal in central migration areas tend to remain through September, then diminish rapidly during October, with small numbers remaining until December. Blue-winged teal are surface feeders and prefer to feed on mud flats, in fields, or in shallow water where there is floating and shallowly submerged vegetation plus abundant small aquatic animal life. During one study, about half of the nest failures of blue-winged teal were caused by mammals.