Songbirds have a species number nearly equal to compared to animals, and tend to be classic models for learning mechanisms of speciation and sexual selection. Intercourse chromosomes are hotspots of both procedures, yet their history that is evolutionary in stays ambiguous. To elucidate that, we characterize feminine genomes of 11 songbird types having ZW sex chromosomes, with 5 genomes of bird-of-paradise types newly manufactured in this work. We conclude that songbird intercourse chromosomes have actually encountered at the least four steps of recombination suppression before their species radiation, creating a gradient pattern of pairwise series divergence termed ‘evolutionary strata’. Interestingly, the stratum that is latest probably emerged because of a songbird-specific rush of retrotransposon CR1-E1 elements at its boundary, or chromosome inversion regarding the W chromosome.