The process of speciation is completed with the cessation of genetic exchange.
To summarize, the particular song a male sings, and the behavioral responses of females to song and morphological signals, are not genetically inherited in a fixed manner but are determined by learning early in life.
Thus mating of females was strictly along the lines of paternal song.
We observe closely related species in sympatry and infer how they evolved from a common ancestor.
The divergence of songs in the new population away from those in the progenitor population would only be prevented if these processes were balanced by repeated immigration and subsequent breeding: song flow.
