A. Hedenström and J. Pettersson, “Migration routes and wintering areas of Willow Warblers Phylloscopus trochilus (L.) ringed in Fennoscandia”, Ornis Fenn, vol. 64, no. 4, pp. 137–143, Dec. 1987, Accessed: Jan. 09, 2026. [Online]. Available: https://ornisfennica.journal.fi/article/view/133244