Hydrogen isotopes reveal contrasting patterns of broad‐scale connectivity among three Phylloscopus taxa during post‐breeding migration

Understanding migratory connectivity is fundamental to interpreting range dynamics and determining the drivers of population change. Stable hydrogen isotope ratios can be used to infer the provenance of individual migrants due to predictable broad‐scale spatial trends. We compare hydrogen isotopes (δ 2 H) among and within three Phylloscopus taxa occurring in Britain during post‐breeding migration to characterize patterns of connectivity. δ 2 H values of nominate Common Chiffchaffs Phylloscopus collybita were significantly higher than, and did not overlap with, those of Siberian Chiffchaffs P. c. tristis or Yellow‐browed Warblers P. inornatus . We found no evidence of a difference between the latter two taxa. There was a significant negative relationship between wing length and δ 2 H in the nominate Common Chiffchaffs. A negative but weakly supported trend between wing length and δ 2 H was also found in Yellow‐browed Warblers with no relationship found in Siberian Chiffchaffs. Our results suggest broad geographical structuring within nominate Common Chiffchaffs passing through Britain but weak evidence for this in Yellow‐browed Warblers and Siberian Chiffchaffs. The origins of Yellow‐browed Warblers and Siberian Chiffchaffs are probably largely overlapping and unlikely to be confined to the western range edge.