A compact diving duck with a distinctive head shape—a sloping forehead and peaked rear crown. The crown flattens when they are diving. In flight, Ring-necked Ducks appear large-headed with a thin neck and a short, round body. They measure 39 to 46 centimeters in length with a wingspan of 62 to 63 centimeters. Males are bold black-and-gray ducks with a dark head, black back, and gray sides with a white hash mark on the chest. Females are rich brown with a contrastingly pale cheek, a white patch near the bill, and a whitish eyering. Adult males have a prominent white ring on the bill. Ring-necked Ducks are often in small flocks and pairs, diving to feed on mollusks, invertebrates, and submerged aquatic vegetation. Sometimes they flock with scaup; other times you may see them with dabbling ducks. Look for Ring-necked Ducks on smaller bodies of water than other diving ducks. In winter and on migration, this can include beaver ponds, small lakes, marshes, cattle ponds, or even flooded agricultural fields across North America. Ring-necked Ducks breed in freshwater marshes, bogs, and other shallow, often acidic wetlands. This species is of low conservation concern.
This bird’s common name (and its scientific name "collaris," too) refer to the Ring-necked Duck's hard-to-see chestnut collar on its black neck. It’s not a good field mark to use for identifying the bird, but it jumped out to the nineteenth century biologists that described the species using dead specimens.
Ring-necked Ducks on their breeding grounds occasionally get attacked by the much larger Common Loon, the Red-necked Grebe, and even the much smaller Pied-billed Grebe.
Source: Ring-necked Duck Overview and Identification Information, All About Birds, The Cornell Lab of Ornithology