Morepork though he followed Mees in treating them as a single species. Janette Norman and colleagues tested the cytochrome "b" DNA of three subspecies (as well as the powerful and rufous owls) to ascertain whether the closest relative was used in breeding with the last surviving female of the Norfolk boobook. They discovered that although the Norfolk boobook was similar in plumage to the Tasmanian boobook, it was genetically much closer to the New Zealand subspecies. In fact, the two were so close genetically that they considered whether the Norfolk boobook should be recognised as a separate taxon at all, although
Southern boobook treated Australian and New Zealand boobooks, along with several taxa from Indonesia and Papua New Guinea, as one species—"Ninox novaeseelandiae"—with 16 subspecies. In his 1968 book "Nightwatchmen of the Bush and Plain", Australian naturalist David Fleay observed that the boobooks from Tasmania more closely resembled those of New Zealand than those from mainland Australia, though he followed Mees in treating them as a single species. The southern boobook was split from the Tasmanian boobook and morepork in volume 5 of the "" in 1999, though several authors, including Australian ornithologists Les Christidis and Walter Boles, continued to treat the three