The American horned owls and the Old World eagle-owls make up the genus Bubo, at least as traditionally circumscribed. This genus, depending on definition, contains about one or two dozen species of typical owls (family Strigidae) and occurs in many parts of the world. Some of the largest living Strigiformes are in Bubo. Traditionally, only owls with ear-tufts were included here, but this is now known to be wrong.

Systematics

mtDNA cytochrome b sequence data supports the decision to consider the Snowy Owl an eagle-owl adapted to Arctic conditions and moving it into Bubo, rendering the monotypic genus Nyctea invalid.

The four fish-owls previously in the genus Ketupa were provisionally moved into Bubo as well. However, the mtDNA cytochrome b data suggests that in this case, to make Bubo monophyletic 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 2 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.

Living species

The following living owls are usually included in Bubo:

• Great Horned Owl, Bubo virginianus
• South American Great Horned Owl, Bubo virginianus nacurutu
• Magellanic Horned Owl, Bubo magellanicus
• Eurasian Eagle-owl, Bubo bubo
• Rock Eagle-owl, Bubo bengalensis
• Pharaoh Eagle-owl, Bubo ascalaphus
• Cape Eagle-owl, Bubo capensis
• Mackinder's Eagle-owl, Bubo (capensis) mackinderi
• Spotted Eagle-owl, Bubo africanus
• Greyish Eagle-owl, Bubo cinerascens
• Fraser's Eagle-owl, Bubo poensis
• Usambara Eagle-owl, Bubo vosseleri
• Spot-bellied Eagle-owl, Bubo nipalensis
• Barred Eagle-owl, Bubo sumatranus
• Shelley's Eagle-owl, Bubo shelleyi
• Verreaux's Eagle-owl, Bubo lacteus
• Dusky Eagle-owl, Bubo coromandus
• Akun Eagle-owl, Bubo leucostictus
• Philippine Eagle-owl, Bubo philippensis
• Snowy Owl, Bubo scandiacus

The fish- and fishing-owls are:

• Blakiston's Fish-owl, Ketupa blakistoni or Bubo blakistoni
• Brown Fish-owl, Ketupa zeylonensis or Bubo zeylonensis
• Tawny Fish-owl, Ketupa flavipes or Bubo flavipes
• Buffy Fish-owl, Ketupa ketupu or Bubo ketupu
• Pel's Fishing-owl, Scotopelia peli or Bubo peli
• Rufous Fishing-owl, Scotopelia ussheri or Bubo ussheri
• Vermiculated Fishing-owl, Scotopelia bouvieri or Bubo bouvieri

Fossil record

Named and distinct Bubo species are:

• Bubo florianae (Late Miocene of Csákvár, Hungary, tentatively placed here)
• Bubo binagadensis (Late Pleistocene of Binagady, Azerbaijan)
• Cuban Horned Owl, Bubo osvaldoi (Late Pleistocene of Cuba)

Some notable undescribed fossils of prehistoric horned owls, usually quite fragmentary remains, have also been recorded:

• Bubo sp. (Late Pliocene of Senèze, France)
• Bubo sp. (Late Pliocene of Rębielice Królewskie, Poland; tentatively placed here)
• Bubo sp. (Late Pleistocene of San Josecito Cavern, Mexico)

Specimen UMMP V31030, a Late Pliocene coracoid from the Rexroad Formation of Kansas (USA), cannot be conclusively assgned to either the present genus or Strix. This fossil is from a taxon similar in size to the Great Horned Owl (B. virginianus) or the Great Grey Owl (S. nebulosa).

The Pleistocene Sinclair Owl from California (Bubo sinclairi) may have been a paleosubspecies of the Great Horned Owl, while Bubo insularis 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 may well be very close to the living Eurasian Eagle-owl..

Footnotes

References

• (1970): Some birds of prey from the Upper Pliocene of Kansas. Auk 87(4): 795-797. DjVu fulltext PDF fulltext
• (1999): Owls: A guide to the owls of the world. Yale University Press, New Haven. ISBN 0300079206
• (1947): A preliminary survey of trends in avian evolution from Pleistocene to recent time. Condor 49(1): 10–13. DjVu fulltext PDF fulltext
• (1933): Handbuch der Palaeornithologie [Handbook of Paleornithology]. Gebrüder Bornträger, Berlin. [in German]
• (2002): Cenozoic Birds of the World, Part 1: Europe. Ninox Press, Prague. ISBN 80-901105-3-8 PDF fulltext
• (2003): Brown Fish Owl (Bubo zeylonensis) in Europe: past distribution and taxonomic status. Buteo 13: 61-65. PDF fulltext
• (2002): A new Ninox owl from Sumba, Indonesia. Emu 102(3): 223-231. PDF fulltext
• (1985): The fossil record of birds. In: : Avian Biology 8: 79-238. Academic Press, New York.
• (1994): New Information on the Late Pleistocene Birds from San Josecito Cave, Nuevo Leon, Mexico. Condor 96(3): 577-589. DjVu fulltext PDF fulltext