Preferential settling at sites with higher conspecific density does not protect Yellow Warblers (Setophaga petechia) from brood parasitism

Conspecific attraction has been found in many songbird species, but the benefit of settling near conspecifics is generally unknown. Previous research indicates that Yellow Warblers (Setophaga petechia) use conspecific cues to select breeding habitat, and cluster territories more closely around experimental playbacks mimicking high conspecific density. We were interested if Yellow Warblers at sites treated with playback of high conspecific density would be more likely to detect and aggressively interact with Brown-headed Cowbirds (Molothrus ater), a brood parasite that often reduces the reproductive success of warblers. We found that at sites treated with playbacks of high conspecific density, more Yellow Warblers approached and alarm-called toward models of Brown-headed Cowbirds early in the season. There were fewer cowbirds at high-density treatments, but overall brood parasitism rates did not vary across density treatments.