Järvi, T., T. Radesäter, and S. Jakobsson. 1978. “Aggressive Responses of Two Hole-Nesting Passerines, Parus Major and Ficedula Hypoleuca, to the Play-Back of Sympatric Species Song”. Ornis Fennica 55 (4):154–157. https://ornisfennica.journal.fi/article/view/132989.