Southern boobook smallest owl on the Australian mainland, the southern boobook is long. The nominate subspecies is the largest. It has short, rounded wings and a short tail, with a compact silhouette in flight. Southern boobooks on the Australian mainland follow Bergmann's rule, in that birds from cooler and more southerly parts of the range tend to be larger. Thus, birds from the Canberra region weigh around while those from the Cape York Peninsula and Broome are around . Females tend to be a little larger and heavier than males, with males weighing and females . The southern boobook has generally dark
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