Ojanen, M., and M. Orell. “Method for Determining the Incubation Stage of Pied Flycathcher Ficedula Hypoleuca Eggs”. Ornis Fennica 55, no. 1 (March 31, 1978): 29–31. Accessed April 20, 2025. https://ornisfennica.journal.fi/article/view/132958.