Sánchez-Alonso, C., X. Ruiz, G. Blanco, and I. Torre. 1996. “An Analysis of the Diet of Red-Billed Chough Pyrrhocorax Pyrrhocorax Nestlings in NE Spain, Using Neck Ligatures”. Ornis Fennica 73 (4):179–185. https://ornisfennica.journal.fi/article/view/133451.