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.
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.
The following living owls are usually included in Bubo:
The fish- and fishing-owls are:
Some notable undescribed fossils of prehistoric horned owls, usually quite fragmentary remains, have also been recorded:
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..
Diet-tissue discrimination factors of carbon and nitrogen stable isotopes in blood of Snowy Owl (Bubo scandiacus).(Report)
Apr 03, 2012; Introduction Naturally occurring stable isotopes of carbon ([sup.13]C, [sup.12]C) and nitrogen ([sup.15]N, [sup.14]N) are present...