Southern boobook taxa (southern plus Tasmanian boobooks and moreporks) as a single species. Examining both morphological and genetic (cytochrome b) characters in 2008, German biologist Michael Wink and colleagues concluded that the southern boobook is distinct from the morepork and Tasmanian boobook (which they proposed to be raised to species status as "Ninox leucopsis"), and that it is instead the sister taxon to the barking owl ("N. connivens"). A 2017 study by Singapore-based biologist Chyi Yin Gwee and colleagues analysing both multi-locus DNA and boobook calls confirmed a sister relationship of "N. n. novaeseelandiae" and "N." ("n.") "leucopsis" and their close relationship
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