This is a great photo. The cockatoo looks most outraged!
Presumably they managed to drive this one away (from your other photos of cockatoo harassing lace monitor), which is pretty impressive. Was it just one bird or were several involved?
There were several in the trees screaming loudly, but this one in particular got in close and was quite aggressive. While in the tree the monitor seemed to ignore it and searched several tree hollows while I watched. At one point he was in a hollow for so long I thought he was going to stay there to avoid the ruckus, but as I started to leave he re-emerged and went on to a few other hollows. Once he left the tree and came onto the ground this particular cocky then kept flying at him (quite close) and tormenting the lizard. You can see in one of the other photos he has lifted his tail of the ground which they do when they are running and feel threatened.