[3] Based on patterns of speciation in other endemic montane bird species of the same region, it may potentially have to be split into two distinct species; if so, the name Otus brookii would be restricted to just the Bornean population.

[5] Taking into account speciation patterns within Otus and general phylogeographic patterns of montane birds on Borneo and Sumatra, both subspecies likely represent two distinct species; taxonomic studies will be required to confirm or deny this claim.

[4] O. b. solokensis has a comparatively large range, being distributed throughout the length of the Barisan Mountains.

[1] Due to its secretive nature, it had not been sighted since its description by Richard Bowdler Sharpe in 1892.

[7] O.b.solokensis has an explosive "owh" or "owh-owh" barking call lasting about a half-second and repeated irregularly.