Parrott, D.; McKay, H. V. Mute swan grazing on winter crops: Estimation of yield loss in oilseed rape and wheat. Mute swans occasionally eat insects, amphibians and smaller birds. J. Crop Protection. 2001, 20 (10): 913–919. doi:10.1016/s0261-2194(01)00041-2.
Wedderburn, Pete. Animals grieve just as people do. The Telegraph. 3 September 2015 [25 July 2019]. (原始内容存档于12 January 2022) (英国英语). 含有連結內容需訂閱查看的頁面 (link)
gutenberg.org
丁尼生, "The Dying Swan," The Early poems of Alfred Lord Tennyson (页面存档备份,存于互联网档案馆) (Project Gutenberg text), search on "shawm." This and other sources assert not merely that the swan sings, but that the song is beautiful.
Wedderburn, Pete. Animals grieve just as people do. The Telegraph. 3 September 2015 [25 July 2019]. (原始内容存档于12 January 2022) (英国英语). 含有連結內容需訂閱查看的頁面 (link)
丁尼生, "The Dying Swan," The Early poems of Alfred Lord Tennyson (页面存档备份,存于互联网档案馆) (Project Gutenberg text), search on "shawm." This and other sources assert not merely that the swan sings, but that the song is beautiful.