Data from: Complex migration and breeding strategies in an elusive bird species illuminated by genetic and isotopic markers

Unlike the annual bi-directional movements of over 200 bird species within the Palaearctic–Afrotropical region, irregular movements such as irruptive migration with a low degree of philopatry are reported for a variety of species depending on highly seasonal and unpredictable resources. These flexible movements allow for itinerant breeding – consecutive breeding attempts in two or more geographically different regions during the same annual reproductive cycle. In order to illuminate migratory and breeding strategies of the erratic wetland species Baillon's crake Zapornia pusilla across the W-Palaearctic–Afrotropical region, we used a set of six DNA microsatellites as well as δ2Hf values of individuals sampled at one African and four European breeding sites. We investigated the degree of genetic population structure within and among different sites and assigned individuals’ feathers of unknown origin to their probable moulting (hence breeding) site using a likelihood approach. We found three genetic clusters, differentiating into one ‘European’ and two ‘African’ populations. Connectivity between the sampling sites was probable as genetic ‘African’ individuals were found in breeding conditions in Europe and vice versa. Likewise, assigned moulting locations based on δ2H isoscapes suggested trans-continental movements as well as moulting and possibly breeding by the same individual both in African and European breeding grounds. Both isotopic and genetic data reveal the Baillon's crake pursue a complex migration and breeding strategy, allowing as well for irruptive movements and itinerant breeding across the W-Palaearctic–Afrotropical region. However, a better knowledge about the species’ distribution as well as a more comprehensive data set, including samples from the southern and eastern boundaries of the distribution area would be necessary to improve the spatial resolution to the precision required to unambiguously infer migration directions and extent of exchange between African and European breeding grounds.