Integrated Taxonomic Information System (ITIS): Bubo ascalaphus (TSN 555406)itis.gov. Viitattu 12.5.2012. (englanniksi)
iucnredlist.org
BirdLife International: Bubo ascalaphusIUCN Red List of Threatened Species. Version 2013.2. 2012. International Union for Conservation of Nature, IUCN, Iucnredlist.org. Viitattu 16.5.2014. (englanniksi)