I investigated recognition of individual neighbors' songs in a migratory species with large repertoires, the Red-eyed Vireo (Vireo olivaceous). To test for abilities to recognize individual neighbors, I measured responses to playbacks of neighbors' songs from appropriate and inappropriate boundaries in two different years. Because the responses to the two types of playbacks were not statistically different in either year, I concluded that Red-eyed Vireos have difficulty recognizing their

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... rs by song. If recognition of neighbors serves to reduce energy expended in territorial defense during the breeding season, a large repertoire could be costly to male Red-eyed Vireos.