Aix sponsa

Quiet inland waters near woodland, such as wooded swamps, flooded forest, greentree reservoirs, ponds, marshes, and along streams. Winters on both freshwater and brackish marshes, ponds, streams, and estuaries (AOU 1983, Dugger and Fredrickson 1992).

Nests in holes in large trees in forested wetlands, and in bird boxes, usually within 0.5 km of water and near forest canopy openings, sometimes 1 km or more from water. Prefers cavities with an entrance size of at least 9 cm, an interior basal area of at least 258 sq cm, and a height of 2 m or more above ground (Dugger and Fredrickson 1992). Elms and maples are important habitat components in most areas because they provide protein-rich samaras in spring and suitable nest cavities. Often returns to same nesting area, sometimes same nest box, in successive years. If nest destroyed, moves to new site to renest. After young leave nest, female may led them up to several km to suitable habitat (food and cover). Shallowly flooded habitat with good understory cover is important cover for broods. Commonly lays eggs in nests of conspecifics.

During migration, sometime forms roosting flocks of 100 or more; in winter, smaller groups of less than 30 are more common (Dugger and Fredrickson 1992).

High annual mortality rate (commonly 50% in adults, higher in young of year). Common predators of young include mink, raccoon, snapping turtle, bullfrog, largemouth bass, and other large predatory fishes. Summer home ranges of of fledged broods were 0-12.8 kilometers along a river (Stewart 1958). Home ranges of breeding males in Minnesota averaged 202 ha and those of unpaired males, 526 ha (Gilmer 1971).

Upon arrival in breeding areas, migratory females forage intensively and built up nutrient reserves prior to nesting. Nests are initiated as early as late January in the south, early March in the Midwest, and mid-March to early April in the north. Clutch size is 9-15 (usually 10-12), but more than one female may contribute eggs to a nest, resulting in nests with many more eggs (commonly up to 30 for successful nests in nest boxes). Often two broods per year are raised in the south, occasionally in the north. Incubation lasts 27-37 days, by female. Females with broods commonly move a kilometer or more from the nest site soon after hatching. Most juvenile mortality occurs during the first few weeks after hatching. Young first fly at about 9 weeks, abandoned by parent at 1-2 months. Yearlings may breed but often unsuccessfully or not at all. Most of the above information is from Dugger and Fredrickson 1992).