The seaducks, Merginae, form a subfamily of the duck, goose and swan family of birds, Anatidae. As the name implies, most but not all, are essentially marine outside the breeding season. Many species have developed specialized salt glands to allow them to tolerate salt water, but these haven't yet developed in young birds. Some of the mergansers prefer riverine habitats. All but two of the 20 species in this group occupy habitats in far northern latitudes. The fish-eating members of this grou… (More on Merginae)