Fitness consequences of anthropogenic hybridization in wild red-legged partridge (Alectoris rufa, Phasianidae) populations

Hybridization is a widespread phenomenon, which plays crucial roles in the speciation of living beings. However, unnatural mixing of historically isolated taxa due to human-related activities has increased in recent decades, favouring levels of hybridization and introgression that can have important implications for conservation. The wild red-legged partridge (Alectoris rufa, Phasianidae) populations have recently declined and the releases of farm-reared partridges have become a widespread management strategy. The native range of the red-legged is limited to the south-west of Europe (from Italy to Portugal). This species does not breed in sympatry with the chukar partridge (A. chukar), whose range is Eurasian (from Turkey to China). However, red-legged partridges have often been hybridized with chukar partridges to increase the productivity of farmed birds, and game releases may have spread hybrid birds into the wild. In this study, we investigated the fitness (survival and breeding) differences between hybrid and “pure” red-legged partridges in a wild population located in central Spain. Incubation probability was similar in hybrids and “pure” partridges. Hybrid females laid larger clutches than “pure” ones, but hatching success did not differ between hybrid and “pure” partridges. Hybrid birds had lower survival rate than “pure” ones, mainly because of higher predation rates. Our results show that, despite lower survival, hybrid partridges breed in natural populations, so this could increase extinction risk of wild pure partridge populations, through releases of farmed hybrid birds. The consequences of continued releases could be of vital importance for the long term conservation of wild red-legged partridges.