Footnote

a Birds are divided into eight main visual categories: (1) swimmers—ducks and ducklike birds, (2) aerialists—gulls and gull-like birds, (3) long-legged waders—herons and cranes, (4) smaller waders—plover and sandpipers, (5) fowllike birds—grouse and quail, (6) birds of prey—hawks, eagles, and owls, (7) passerine (perching) birds, and (8) nonpasserine land birds.—A Field Guide to the Birds East of the Rockies, by Roger Tory Peterson.