Hanski, I. K. and Tiainen, J. (1991) “Morphological variation in sympatric and allopatric populations of European Willow Warblers and Chiffchaffs”, Ornis Fennica, 68(1), pp. 1–16. Available at: https://ornisfennica.journal.fi/article/view/133310 (Accessed: 16May2024).