This is very evident with young I have observed feeding with their parents. This also makes for easy sexing in the nest. The crest of both sexes is unique to the Australian Cockatoo in that they curve forward. Feet are fleshy and grey in coloration. These birds use their feet extensively to hold their food.
Bills are greyish white.
Their bills form a large part of the bird's head and is very strong as evidenced by their feeding habits, i.e. the seed pods they break up. If ever you have the opportunity to handle one of these birds, investigate this head bill construction for yourself. The Gang-Gang voice is like no other bird I know of. It is a raspy screech, often described like someone removing a cork from a bottle - not including the pop at the end. They have a curious little growling voice when in close contact with each other, e.g. when preening each other or just close on the perch.