Bustnes, J. O., and K. E. Erikstad. “The Diets of Sympatric Wintering Populations of Common Eider Somateria Mollissima and King Eider S. Spectabilis in Northern Norway”. Ornis Fennica, vol. 65, no. 4, Dec. 1988, pp. 163–168, https://ornisfennica.journal.fi/article/view/133269.