Osiejuk, T., K. Ratyńska, S. Dale, Øyvind Steifetten, and J. Cygan. “Ortolan Buntings Emberiza Hortulana Mimicking Other Species and Other Dialects of Own Species”. Ornis Norvegica, Vol. 27, Jan. 2004, pp. 73-79, doi:10.15845/on.v27i0.199.