Hybridization between two insectivorous bird species and the effect on prey-handling efficiency

Gene flow between closely related species is not always impeded by hybrid inviability or sterility but may be limited by behavioural or ecological factors. European common redstarts, Phoenicurus phoenicurus, and black redstarts, P. ochruros, are insectivorous passerine bird species which regularly interbreed in the wild and produce viable and fertile progeny. Yet, the isolation barriers, which prevent extensive gene flow between these distinct species, are unknown. I studied prey-handling time and efficiency in both species and the F₁-hybrids in captivity. All birds changed prey-handling mode from a single pick to more complex behaviour with increasing prey length and their handling time was a positive function of prey length. Common redstarts tended to handle their prey quicker than black redstarts. Hybrids appeared to be intermediate. However, individual differences were significant, but group membership was not. Handling efficiency decreased with increasing prey length and was determined by individual and family effects. Hybrid females handled their prey as efficient as hybrid males. Small differences in beak morphology could not explain individual differences in prey-handling behaviour. The results of this study suggest that prey-handling in F₁-hybrids is not a postzygotic barrier which prevent gene flow between common and black redstarts in the wild.