BirdLife International 2004. Asio stygius. In: IUCN 2007. 2007 IUCN Red List of Threatened Species.] - Rødliste over truede arter. Hentet 5. mai 2008.
iucnredlist.org
BirdLife International 2004. Asio stygius. In: IUCN 2007. 2007 IUCN Red List of Threatened Species.] - Rødliste over truede arter. Hentet 5. mai 2008.