1. Bird Life International, . Accessed 13 May 2019.
2. J. Zalles and K. Bildstein, Raptor Watch: a global directory of raptor migration sites (Birdlife International, Cambridge (RU), 2000).
3. B. Michev, S. Peev, and T. Michev, “Birds of open waters off the Bulgarian Black Sea coast,” in Acta Zool. Bulg, 66.4 (2014), pp. 485–492.
4. A. Prostov, “Studies on the Ornithofauna of Bulgaria,” in Bull. Inst. Zool, vol. 15 (1964), pp. 5–68. [in Bulgarian]
5. D. Königstedt and D. Robel, “To the Avifauna of Bulgaria - An Addendum,” in Beitr. Vogelkd, 24.5 (1978). [in German]