FORSMAN, D. Ageing and moult in western palaearctic Hawk Owls Surnia u. ulula L. Ornis Fennica, [S. l.], v. 57, n. 4, p. 173–175, 1980. Disponível em: https://ornisfennica.journal.fi/article/view/133053. Acesso em: 19 apr. 2025.