Adjacent nesting home ranges of four radio-tagged Southern Boobooks (Ninox novaeseelandiae) were studied in a Canberra, Australia, woodland over 418 observation nights during four breeding seasons. Spatial locations and bouts of territorial calling (“boobook calls”) were recorded during each observation night. Home ranges and core areas were computed from the spatial locations using minimum convex polygons and characteristic hull polygons. Home-range sizes varied by individual owl, between breeding seasons, and by estimation method, ranging from 18.1 to 205.8 ha. Core-area estimates varied from 0.2 ha to 19.6 ha, indicating intensive use of core areas within much larger home ranges. Overall, about 26% of the boobooks' vocalizations occurred within core areas and about 56% within the home range but outside the core area, often near the border shared with the adjacent pair. Approximately 21% of boobook calls were observed on or outside home-range boundaries, which suggested that owls actively defended areas larger than their core areas.