KAMPE-PERSSON, H. Variation in bill colour among Greylag Geese Anser anser breeding in south-west Scania. Ornis Svecica, Lund, Sweden, v. 13, n. 2–3, p. 63–66, 2003. DOI: 10.34080/os.v13.22808. Disponível em: https://journals.lub.lu.se/os/article/view/22808. Acesso em: 22 may. 2022.