When I arrived today all three were on the tree, making an horrendous noise as they attacked each other. At that moment the parent bird flew from the log in the water into the top of the nest tree. One chick stayed in- or very near- the nest, watching while the other two scrabbled about higher up in the tree. Eventually one (again I am assuming it was the adventurous one who first left the nest) was chased away and climbed up to where the parent bird was sitting.
He did not get a good reception when he squawked and flapped his wings; the parent seemed to bechasing him away too. This whole episode lasted for nearly three hours,until the chick finally climbed right to the very top of the tree- on the dead branches- where he moved about for some time before flying down to the log in the water where he fished yesterday.