Kirwan, G. M., Schweizer, M., & Copete, J. L. (2015).

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), 28–50. https://doi.org/10.11646/zootaxa.3904.1.2