WIENS (1965), in a study of the behavioral interactions of Redwinged Blackbirds (Agelaius phoeniceus) and Common Grackles (Quiscalus quiscula) on a small cattail (Typha latifolia) marsh in Madison, Wisconsin, points out that the cattail habitat is typical for Red-wings and unusual for grackles, and that a potentially competitive situation exists in a marsh where the two species nest together. The emphasis of his study was on behavioral interactions and the effect of these interactions on reproduction. The purpose of the present investigation is to consider other parameters, namely food and feeding behavior, which may be very important in the relationships of Red-wings and grackles breeding on this cattail marsh. Indeed, as expressed by Orians and Collier (1963: 457), Ecological compatibility, the prime requirement for sympatry, . . . is strongly influenced by such behavioral attributes as feeding behavior which vary remarkably in morphologically similar In addition, selected breeding biology data are presented from the years following Wiens' study to elucidate further the relationships of Red-wings and grackles on this marsh. For extensive discussion of the breeding biology and displays of Redwings see Beer and Tibbitts (1950) and Nero (1956). Peterson and Young (1950) and Ficken (1963) give corresponding discussions of grackles, and Wiens (1965) compares the two species.