Behavioral Interactions Between Coexisting Species: Song Playback Experiments with Wood Warblers

Behavioral interactions between coexisting species may reflect underlying ecological interactions or may arise from factors unrelated to ecological interactions between species. We examined behavioral interactions between two coexisting, migratory wood warblers that competitively interact on breeding territories in central Arizona, USA. The larger Orange-crowned Warbler (Vermivora celata) is aggressive toward the later-arriving Virginia’s Warbler (V. virginiae) and responds to playback of Virginia’s Warbler songs by approaching the playback speaker or by singing over Virginia’s Warbler songs. Virginia’s Warblers retreat from interactions with Orange-crowned Warblers and avoid the playback speaker when presented with Orange-crowned Warbler songs. Responses of both species to song playback of the opposite species differed from responses to conspecific songs, indicating that behavioral interactions do not result from misdirected intraspecific aggression. Behavioral responses were consistent with observed ecological interactions between the two species and suggest that asymmetrical behavioral aggression by the dominant Orange-crowned Warbler may be an important mechanism for competitive interactions involving nest sites. These results support previous studies that have used behavioral experiments to infer ecological interactions among coexisting species. While Orange-crowned Warblers may benefit from aggressively excluding Virginia’s Warblers from preferred nest sites, limited data on Virginia’s Warbler settlement patterns suggest that Virginia’s Warblers do not avoid settling on Orange-crowned Warbler territories. Similar reproductive success in sympatric vs. allopatric habitats suggests little consequence for Virginia’s Warblers settling with Orange-crowned Warblers, despite increased reproductive success of Virginia’s Warblers in sympatric habitat when Orange-crowned Warblers were experimentally removed.