Geographic probability distribution of the most probable place of origin of an assigned migrant (upper panel) and an assigned local bat (lower panel). The color scale indicates the level of certainty of correct assignment (expressed as P-value). Bats for which a local status could be excluded using an α = 5% threshold were assigned a migrant status. Bats for which a local origin could not be excluded were assigned a local status, i.e., originating from the sampling location Prieros, Brandenburg, Germany (~ 40 km Southeast of Berlin, indicated on the maps by the blue star). Isoclines (regions of similar δ²HP values) follow latitude closely and thus resolve animal movements from East to West poorly. However, there is substantial evidence for migration happening along an axis from Northeast to Southwest, making it unlikely that bats carrying the ”local” isotopic fingerprint are actually migrants stemming from more Eastern regions on the same latitude (e.g., as suggested in the lower panel)