Tracing the origin of vagrant Siberian songbirds with stable isotopes: The case of Yellow-browed Warbler (Abrornis inornatus) in Fennoscandia

Vagrant birds are mesmerizing birdwatchers worldwide, but the nature of vagrancy and the true origin of the vagrants are poorly known. To Western Europe, the massive Siberian land mass delivers most of the vagrant songbirds, e.g. Yellow-browed Warbler (YBW) (Abrornis inornatus, formerly Phylloscopus inornatus). In this study we used stable hydrogen isotope ratios in tail feathers ( 2 Hf ) from two ringing stations in northern Fennoscandia in an attempt to link vagrant YBW to potential regions of origin. We could do this thanks to a collection of samples from nestling and breeding adult YBW in Central Siberia. Compared with the nestling samples, the Fennoscandian 2 Hf data indicated origins …