Fig. 1

Distribution ranges and possible migration routes of the Yellow-browed Warbler (Phylloscopus inornatus). Migration routes in Asia (orange) indicated are based on the information collected in the literature [24]. The presumed route to Europe is hypothetical, it follows the areas where the species is most abundant during the autumn period between the most western breeding sites (Ural Mountains, indicated by a dotted line) and the areas where the species is regular in winter (i.e., Iberian Peninsula [26]). Breeding (light red) and non-breeding ranges (blue) are taken from BirdLife International [126]. Green dots represent the locations of YBW sightings between September and November 2018 provided by GBIF [127]. The majority of sightings are concentrated in Western Europe and south-east Asia with some exceptions in the Middle East and Central Asia. Note that the frequency of the green dots does not reflect the frequency of occurrence of the species in the correct proportion due to an observer/recorder bias. The photo shows a Yellow-browed Warbler observed on Ouessant Island, France, during 2020 fall (Photo Frédéric Veyrunes)