All mergansers have slender elongated serrated bills tipped with a hooked nail.
These bills are ideally suited for capturing and controlling the slippery fish that make up a large part of their diet. They are extremely agile swimmers and divers but awkward on land because their legs are set well back on their bodies. Hooded Mergansers are highly sexually dimorphic. In breeding males this hood has a large central white patch boldly bordered in black. When the hood is down, the visible white is reduced to a narrow band trailing back from the bright yellow eye.