This bird does not appear in either the Reader's Digest Complete Book of Australian Birds, or Pizzey & Knight's The Field Guide to the Birds of Australia.
General consensus seems to be that this is an Eastern Reef Heron in the Dark Morph. I'm not 100% convinced, but have no other explanation.
Distinguishing features, yellow clawed feet on short feathered legs; yellowish/slate straight, long, pointed beak; sooty black plummage, slightly lighter underwing; no discernable tail or neck.
Behaviour: Perches on rocks along the shore looking for prey of some sort. Slow flapping and gliding flying technique. Glides with wings as shown in photo.
View all photos taken: Sunday, 6th July 2008, This photo: 1:45pm