Hakala, A., K. Huhtala, A. Kaikusalo, E. Pulliainen, and S. Sulkava. “Diet of Finnish Snowy Owls Nyctea Scandiaca”. Ornis Fennica, vol. 83, no. 2, July 2006, pp. 59–65, https://ornisfennica.journal.fi/article/view/133655.