Territorial responses of male Bermuda White-eyed Vireos (Vireo griseus subsp. bermudianus) reflect phylogenetic similarity of intruders and acoustic similarity of their songs

For signal divergence to drive speciation, receivers should perceive structural differences in divergent signals; similar-structured signals from closer relatives are expected to elicit stronger responses than dissimilar signals from distant relatives. Two mechanisms can affect receiver responses to passerine song: (1) sympatric song familiarity and (2) an innate auditory template used to assess acoustic similarity. We examined the role of acoustic similarity by comparing behavioral responses of male Bermuda White-eyed Vireos (Vireo griseus bermudianus) to playback of the songs of allopatric species from across the family Vireonidae. Phylogenetic distance between the focal and stimulus species predicted response strength. Males uttered fewer vocalizations, had fewer speaker flyovers, and remained farther from the speaker during playback of the songs of more distantly related vireos. We then tested whether structural similarity of playback songs, as defined by three phylogenetically conserved song traits, explained these relationships. As predicted, males uttered fewer vocalizations, had fewer speaker flyovers, and remained farther from the speaker in response to more dissimilar songs. Collectively, our results suggest that male Bermuda Vireos perceive and respond to interspecies variation in the phylogenetically conserved song traits of allopatric species of vireos. This suggests that song divergence, and the ability to distinguish divergent songs, reinforces reproductive isolation and competitor exclusion.