This genus contains 20 species that are found in many parts of the world. Some of the largest living Strigiformes are in Bubo. Traditionally, only owls with ear-tufts were included in this genus, but that is no longer the case.
Systematics of which species to include among the horned owls is in an upheaval at present. While Mitochondrial DNA (mtDNA) cytochrome bsequence data favors the decision by some to regard the snowy owl as an eagle-owl adapted to Arctic conditions, moving it into Bubo, this is not accepted by all authorities, many still preferring Nyctea.
Likewise disagreement exists over the decision by some to move the four fish-owls previously in the genus Ketupa provisionally into Bubo as well, which introduces a good bit of confusion. While the mtDNA cytochrome b data suggests that in this case, to make Bubomonophyletic the Scotopelia fishing owls would also need to be included there. On the other hand, the genus then becomes quite large and ill-defined, and Bubo in the expanded sense seems to consist of two distinct clades. Thus, the fish and fishing owls can alternatively be united in Ketupa if some aberrant eagle-owls - at least the barred, spot-bellied and Usambara eagle-owls, perhaps also Fraser's eagle-owl and maybe others - are moved into that genus too. As some enigmatic eagle-owls remain essentially unstudied and others - e.g. Verreaux's eagle-owl - are of unresolved relationships, more research is needed.
The Sinclair owl (Bubo sinclairi) from Late Pleistocene California may have been a paleosubspecies of the great horned owl, while the roughly contemporary Bubo insularis of the central and eastern Mediterranean has been considered a junior synonym of a brown fish owl paleosubspecies. Additional paleosubspecies are discussed on the appropriate species page.
Several presumed Bubo fossils have turned out to be from different birds. The Late Eocene/Early Oligocene eared owls "Bubo" incertus and "Bubo" arvernensis are now placed in the fossil barn-owl genera Nocturnavis and Necrobyas, respectively. "Bubo" leptosteus is now recognized as primitive owl in the genus Minerva (formerly Protostrix). "Bubo" poirreiri from the Late Oligocene or Early Miocene of Saint-Gérard-le-Puy in France, is now placed in Mioglaux.
On the other hand, the supposed fossil heron"Ardea" lignitum from the Late Pliocene of Plaue-Rippersroda (Germany) was apparently an owl and close to Bubo or more probably actually belongs here. Given its age - about 2 million years ago or so - it is usually included in the Eurasian eagle-owl today.
Interactions with humans
Because of their nocturnal habits, most owls do not directly interact with humans. However, in 2015, an eagle owl in Purmerend, Netherlands, attacked some fifty humans before it was caught by a hired falconer.
^Possibly a junior synonym of Ketupa, if that is a valid genus: Pavia (1999), Mlíkovský (2002, 2003).