Song Divergence in Passerines

Song is important for mate choice among passerines because males use song to attract mates and females determine mate quality based on song. Therefore, song is likely a reproductive isolating mechanism between populations or species. We can examine the differences in song between hybridizing and non-hybridizing species to better understand speciation. We compared song parameters for 23 pairs of closely related hybridizing and non-hybridizing sympatric passerine species. We predicted that hybridizing species pairs would have more similar songs than non-hybridizing species pairs. Hypervolumes were constructed, from song parameters, for each species and we quantified the differences between pairs as the distance between centroids of the hypervolumes. We found a non-significant trend where hybridizing species had greater differences in songs than non-hybridizing species, which is not what we predicted. Most pairs of hybridizing and non-hybridizing species had the same range of song differences. Hybridizing species pairs with the greatest song differences were Eastern and Western meadowlarks, Golden-winged and Blue-winged warbles, and Grace's and Black-throated Gray warblers. Non-hybridizing species pairs with the smallest song differences were Bay-breasted and Blackburnian warblers, Northern and Louisiana waterthrushes, and Pyrrhuloxias and Northern Cardinals. Song has an influence on reproductive isolation for certain species, but across passerines it might not be a good predictor for reproductive isolation. Environmental niche divergence might be a better predictor for reproductive isolation across passerines than song.