The Breeding Season Diet of the Powerful Owl Ninox strenua at Brisbane, Queensland

Abstract

The diet of a pair of Powerful Owls, successfully breeding in regrowth open forest and woodland at Mt. Coot-tha, Brisbane, was assessed over two consecutive years. Diet was examined by analysing pellets and prey remains found below roosts and identifying carcasses the birds were holding. Eight mammal, sixteen bird and two insect species were recorded as prey, ranging in weight from 1 kg to 2 g. Fruit-bats, Common Ringtail Possums and Scalybreasted Lorikeets were taken most frequently. The estimated biomass of the four prey groups consumed each year was fruit-bats (46% both years), Common Ringtail Possum (25% in 1989, 29% in 1990), other arboreal marsupial species (17% and 7%) and diurnal birds (12% and 18%). There was a significant difference in biomass among prey groups each year. The frequency and biomass of prey groups in the diet did not differ significantly between the two years. There was no significant variation in the frequency of prey groups taken during the first four stages of the breeding cycle (incubation to fledgling) each year. Predation on Black and Greyheaded Fruit-bats and Scaly-breasted Lorikeets, species that are normally nomadic blossom and fruit feeders, occurred during all stages of the breeding cycle. Predation on the Common Ringtail Possum (predominantly juveniles) took place in suburbs adjacent to the study site. Hunting was observed within parkland and along forest edges.