Savova, Adelina, and Ralitza Berberova. “Development of Ornithological Tourism in the Kresna Gorge – Opportunity for Conservation of the Griffon Vulture (Gyps Fulvus)”. Annual of Natural Sciences Department 7 (December 30, 2022): 1–8. Accessed May 21, 2024. https://ojs.nbu.bg/index.php/ANSD/article/view/858.