Powerful Owl Ninox strenua Diet from Two Sites in the Australian Capital Territory

The diet of three Powerful Owls Ninox strenua in the Australian Capital Territory was studied in 2007. A pair in Namadgi National Park took five Sugar Gliders Petaurus breviceps, a Greater Glider Petauroides volans, birds and a crustacean. Among avian prey, the Bassian Thrush Zoothera lunulata is a new record for Powerful Owls. An Owl at the Botanic Gardens took 41 Sugar Gliders, 10 Common Ringtail Possums Pseudocheirus peregrinus and two juvenile Common Brushtail Possums Trichosurus vulpecula, the last apparently off the femalesâ¿¿ backs. This Owl was observed perching on prey items on 11.9% of the days it was seen: seven times on Sugar Gliders, twice on Ringtail Possums, and twice on Brushtail Possums. It was seen attacking Sugar Gliders and adult Brushtail Possums, but beak-clacking when attacking the Brushtail Possums (so apparently attacking them as competitors, not prey). It was agile while hunting. Its behaviour was affected by mobbing by diurnal birds. Geometric Mean Prey Weight (GMPW) of Powerful Owl prey (including four items from a previous Namadgi analysis) in the ACT was 176.48 g, and the prey/predator weight ratio was 0.118. GMPW calculated from a previous study in Canberra of Southern Boobooks Ninox novaseelandiae was 2.11 g, and the prey/predator weight ratio was 0.008, much lower than for Powerful Owls. Standardised Food Niche Breadth for Powerful Owls was 0.115, and for Southern Boobooks 0.325; i.e. dietary evenness and richness were much higher for Boobooks. Powerful Owls took 95.2% arboreal marsupials, whereas Boobooks took a wider range of species including a large proportion of insects.