These are small, compact ducks with stout, scoop-shaped bills, and long, stiff tails they often hold cocked upward. They have slightly peaked heads and fairly short, thick necks. Ruddy Ducks measure 35 to 43 centimters in length, with a wingspan of 56 to 62 centimeters. Male Ruddy Ducks have blackish caps that contrast with bright white cheeks. In summer, they have rich chestnut bodies with bright blue bills. In winter, they are dull gray-brown above and paler below with dull gray bills. Females and first-year males are brownish, somewhat like winter males but with a blurry stripe across the pale cheek patch. In flight, Ruddy Ducks show solidly dark tops of the wings. Ruddy Ducks dive to feed on aquatic invertebrates, especially midge larvae. They feed most actively at night, so you’ll often see Ruddy Ducks sleeping during the day, head tucked under a wing and tail cocked up. They nest in marshes adjacent to lakes and ponds, primarily in the Prairie Potholes region. In migration, they flock to large rivers, ponds, and lakes, and also gather in coastal estuaries, frequently mixing with other diving ducks such as Bufflehead and goldeneyes. This species is of low conservation concern.
Ruddy Ducks lay big, white, pebbly-textured eggs—the largest of all duck eggs relative to body size. Energetically expensive to produce, the eggs hatch into well-developed ducklings that require only a short period of care.
Pleistocene fossils of Ruddy Ducks, at least 11,000 years old, have been unearthed in Oregon, California, Virginia, Florida, and Illinois.
Ruddy Ducks are very aggressive toward each other and toward other species, especially during the breeding season. They are even known to chase rabbits feeding on the shore.
Though Ruddy Ducks are native to the Americas, one population became established in England after captive ducks escaped in 1952. This population grew to about 3,500 individuals by 1992, and now appears to be expanding into the Netherlands, France, Belgium, and Spain.
Source: Ruddy Duck Overview and Identification Information, All About Birds, The Cornell Lab of Ornithology