Sammalisto, L. (1956) “Secondary intergradation of the Blue-headed and Grey-headed Wagtails (Motacilla f. flava L. and Motacilla f, thunbergi Billb.) in South Finland”, Ornis Fennica, 33(1), pp. 1–19. Available at: https://ornisfennica.journal.fi/article/view/132588 (Accessed: 25December2024).