It could be a mating ritual.

I looked out my front window this afternoon and saw a flock of cockatoos in my yard doing something really weird, I have a big umbrella tree and it's been dropping the long thick stems because it's winter and the birds were picking them up in the beaks, flattening out their wings and rocking their heads up and down like banging the sticks into the ground. What were they doing? Ive never seen them do that before.