Round P.D.Promnun P.Pierce A.J.Sankamethawee W.Allen D.N.Fuchs J.Lwin N.Safoowong M.Mahidol University2023-07-072023-07-072023-06-07Bulletin of the British Ornithologists' Club Vol.143 No.2 (2023) , 265-27200071595https://repository.li.mahidol.ac.th/handle/20.500.14594/87742Summary . A total of 20 individual Phylloscopus warblers in the ‘Blyth's Leaf Warbler P. reguloides lineage', caught for ringing in the non-breeding season in Thailand and Myanmar, were resolved via mtDNA assay as P. reguloides (seven individuals), Claudia's Leaf Warbler P. claudiae (12) and Hartert's Leaf Warbler P. goodsoni (one). As expected, P. claudiae proved to be the most widely distributed. The occurrence of four P. claudiae on an island in the Thai Gulf, alongside large numbers of typically Sundaic wintering species on northbound migration during late March-early April, indicates that its non-breeding season range probably extends further south than previously recognised, into that subregion.Agricultural and Biological SciencesArticleSCOPUS10.25226/bboc.v143i2.2023.a112-s2.0-85162914597