Mating Patterns and Postzygotic Barriers in a Hybrid Swarm of Two Closely Related Pigeon Species

Hybrid zones provide a valuable framework for understanding evolutionary pathways. We investigated mating patterns and reproductive barriers using captive individuals derived from a natural hybrid swarm between hill pigeons (Columba rupestris) and feral pigeons (C. livia), maintained under controlled conditions. Both parental taxa exhibited significant assortative mating. The observed mating structure suggests that morphological similarity, mate availability, social interactions, and genetic relatedness may jointly shape pairing patterns. Reproductive performance was assessed at three stages-clutch size, hatching, and fledging-across four cross types (hill pigeon, feral pigeon, within-hybrid, and heterotypic cross types). Clutch size did not differ among cross types. Hatchling and fledgling mortality in within-hybrid crosses and heterotypic crosses did not differ from that in hill pigeon conspecific crosses. Within-hybrid crosses and heterotypic crosses had higher hatchling mortality than feral pigeon conspecific crosses, and only heterotypic crosses showed higher fledgling mortality. Between parental taxa, hill pigeon conspecific crosses exhibited higher hatchling mortality than feral pigeon conspecific crosses. These results suggest asymmetric postzygotic isolation that is most evident in comparisons involving feral pigeons, with implications for reinforcement of conspecific mate choice in feral pigeons and continued directional introgression into hill pigeons.