I disturbed what appeared to me to be either a Nankeen Night Heron, or a Yellow Bittern, or an Australasian Bittern from nearby pool. It flew up into a low-lying branch. I had a good view of it, though did not take a camera, so no picture. It was being dive-bombed by the willy wagtails and mudlarks. Reported the sighting to Birdlife Australia.