My bride reckons this is a mopoke (Ninox novaeseelandiae).
I don't know enough about birds (the feathered variety) to argue.
He's taken up residence, camping in the tree during the day, and feeding (hopefully) on mice etc at night.
The Noisy Miners (Manorina melanocephala) aren't keen on him at all - they give him a wide berth. If he can keep them away, he can stay as long as he likes.