Hedenström, A., Åke Lindström, and J. Pettersson. “Interrupted Moult of Adult Willow Warblers Phylloscopus Trochilus During Autumn Migration through Sweden”. Ornis Svecica, vol. 5, no. 2, Apr. 1995, pp. 69-74, doi:10.34080/os.v5.23006.