Southern boobook their upperparts. The tips of their feathers are white and fluffy, remnants of the nestlings' down. These are worn away over time, persisting longest on the head. The feathers of the head, neck and underparts are fluffier overall. Immatures in their second and third year have plumage more like adults, though their crowns are paler and more heavily streaked. On mainland Australia, it could be confused with the barking owl or the brown hawk-owl ("Ninox scutulata"), a rare vagrant to the northwest, although the southern boobook is easily distinguished by its squat posture and distinctive pale border to its face
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