DNA studies suggest that four fishing owls previously in the genus Ketupa, and the Snowy Owl, genus Nyctea are specialised horned owls and should be moved to Bubo.
Some owls of this genus are well known, such as the eastern screech owl of eastern North America, and the Eurasian scops owl, a strongly migratory species breeding in southern Europe east to Lake Baikal.
All species belonging to the largest genus of owls look much alike, and, as might be expected in nocturnal birds, are differentiated most strongly by their distinctive voices.
The eastern screech owl is classified as Otus asio, and the Eurasian scops owl as Otus scops.