Are Iberian Chiffchaffs Phylloscopus (collybita) brehmii long-distance migrants? An analysis of flight-related morphology

Capsule Iberian Chiffchaffs Phylloscopus (collybita) brehmii are genetically, morphologically and bioacoustically different from European Chiffchaffs (P [c.] collybita). Aim To examine the difference in migratory pattern between brehmii and collybita. Methods We inferred variation in distance of migration between brehmii and collybita by analysing differences in flight-related morphology (wing-length, wing shape and tail-length) between individuals breeding or wintering in the Iberian Peninsula. Results Controlling for body size and allometry of feather dimensions, birds captured in spring had more pointed wings (more concave wing shapes and pointed wing tips) and a shorter tail than birds caught in winter, although no spring-to-winter difference was found for wing-length. Conclusion Iberian breeders appear better suited to long-distance migration (their traits are likely to give a higher speed and a lower energy consumption during long non-stop flights) than wintering individuals, which strongly supports the hypothesis that brehmii move south of the Sahara in autumn and are substituted by central European collybita populations in winter. This different migration pattern of brehmii and collybita has important implications for the maintenance of differentiation in their contact zone, because selection against hybrids with maladaptive, intermediate migratory behaviours might contribute to reproductive isolation