Lord Howe boobook than both the New Zealand and Norfolk Island subspecies. The Lord Howe boobook was restricted to Lord Howe Island where it inhabited the native forests as well as occurring around the settlements. Exactly when the Lord Howe boobook became extinct is uncertain. Boobook calls were apparently heard on the island until the 1950s, but during the 1920s boobooks from near Sydney in eastern Australia had been introduced, along with barn owls and masked owls, in an unsuccessful effort to control the black rats that had overrun the island. The rats had been accidentally introduced in June 1918 with the grounding
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