Guy M. Kirwan, Manuel Schweizer i José Luis Copete. Multiple lines of evidence confirm that Hume’s Owl Strix butleri (A. O. Hume, 1878) is two species, with description of an unnamed species (Aves: Non-Passeriformes: Strigidae). „Zootaxa”. 3904 (1), s. 28–50, 2015. DOI: 10.11646/zootaxa.3904.1.2.
iucnredlist.org
apiv3.iucnredlist.org
BirdLife International, Strix butleri, [w:] The IUCN Red List of Threatened Species 2021, wersja 2021-3 [dostęp 2021-12-19](ang.).