Sasvári, L., P. Péczely, and Z. Hegyi. 2008. “Parental Testosterone and Estradiol Concentrations in the Early Nestling Period Correlate With the Age-Dependent Breeding Performance in Tawny Owls Strix Aluco”. Ornis Fennica 85 (2):46–54. https://ornisfennica.journal.fi/article/view/133704.