A merganser is a type of diving duck with a long, slender, serrated bill designed for catching and holding fish. They’re part of the genus Mergus (and closely related genera), and are built more like aquatic hunters than dabbling ducks—streamlined bodies, narrow bills, and strong legs set far back for underwater propulsion. Key points: • Diet: Mostly fish, along with aquatic insects and crustaceans. • Bill: Thin, saw-toothed edges for gripping slippery prey—earning them the nickname “sawbills.”