Decreased fitness of restocked hybrid quails prevents fast admixture with wild European quails

Restocking with non-native species for hunting purposes is a widespread practice in some Galliformes species that may result in the introgression of maladaptive alleles into native populations. Quails farmed for restocking are produced by interbreeding domestic Japanese quails (Coturnix japonica) with European quails (Coturnix coturnix). Massive releases of these animals could represent a threat to native European quails. In this study we radio-track 16 female native European quails and 51 female farm-reared quails over four breeding seasons in a single locality. Our results show that farmed female quails attracted more wild common quail males than European quail females, probably because they produce more rally calls. Here for the first time we show empirical evidence that European quails and restocked farmed quails interbreed in the wild. Further, hybrid farmed females and European females had similar probabilities of mating, nesting success, clutch size, fertility, hatching probability and chicks' survival probability. However, female farmed quail had higher mortality than European quail females, and their nests had a higher rate of predation. These last observations could explain why the two lineages do not appear completely admixed after more than 20 years of massive restocking practices. However, our results clearly show a lack of reproductive barriers in the wild and that introgression may not be completely prevented. An immediate ban of the release of non-native quails is necessary to preserve their genetic integrity. Thus, banning restocking with Japanese quail or hybrids is necessary to prevent the progressive introduction of maladaptive alleles into the European quail populations.