Gustavsson, C G. “A White Feathered Area on the Forehead Is More Common in Hybrids of Greylag Goose Anser Anser and Greater Canada Goose Branta Canadensis Than in the Parent Species”. Ornis Svecica 21, no. 1 (January 1, 2011): 37–44. Accessed May 25, 2024. https://journals.lub.lu.se/os/article/view/22617.