Behavioral Interactions of Red-Winged Blackbirds and Common Grackles on a Common Breeding Ground

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Abstract
The nature and effects of interspecific behavior in Red-winged Blackbirds (Agelaius phoeniceus) and Common Grackles (Quiscalus quiscula) nesting in close association in a small cattail marsh were observed at Madison, Wisconsin during the 1962 and 1963 breeding seasons. Interactions were generally initiated by Red-wings, and involved threat displays or attacks toward grackles penetrating the Red-wing territories in the marsh. Female Red-wings were aggressive to grackles only about the Red-wing nest sites. Grackles only occasionally directed displays or attacks toward Red-wings, probably because their territories comprised only small areas directly about their nests. Territores of both species were to some extent mutually exclusive. The behavioral interactions had these effects on reproductive behavior several Red-wing nests were apparently neglected and failed because of frequent participation of the incubating or brooding birds in interspecific conflicts; grackle courtship flights and nest sites were oriented with respect to Red-wing territory edges; and grackles approached the nest indirectly, through the vegetation, rather than in direct flight as in undisturbed situations. The use of species-characteristic displays in interspecific as well as intraspecific encounters indicates that each species produces a reasonably close approximation of the releasers of the threat displays of the other species.