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 to "N. connivens". Genetic and call analysis show the Christmas boobook ("N. natalis") to be very close to the Australian populations of the southern boobook, leading Gwee and colleagues to suggest it be reclassified within this species. Gwee and colleagues found that boobook populations on larger mountainous islands were more distinct from Australian stock, while those on flatter smaller islands were much more similar, suggesting that these locations were colonised much more recently after previous populations had become extinct. Eleven subspecies of "Ninox boobook" are recognised in version 7.3 of the IOC World Bird List, published in July 2017: The