Head bangin' birds

Bit difficult to get this on camera but these are pics of head bangin' galahs.

I've always been perplexed by the antics of Galahs. I once saw a whole flock of them fly at breakneck speed into a gum tree, miss the branches completely and tumble onto the ground all screaming blue murder. I know that the word 'galah' has become a popular euphemism for stupidity in Australia but I never knew how the bird themselves got that way. Now I think I've figured it out. They are constantly doing this really weird thing to one another. I wonder if I'm the only one who notices it. One will take grab another one with it's beak (just above the 'its' beak) and pound the wahgibbies outta it. Head banging I call it. The trees around Callington are riddled and quaking with head bangin birds. I know there must be a scienitific explanation for this. Something to do with mating I supposed. It wouldn't be unlike a galah to get 'the wrong end'. Anyway, it's a noisy practice and has to scramble the brains of one if not both birds. If anyone reading my blog can shine any light on the reasoning behind all this head bangin' galah stuff, be it truth or yarn, I'd love to hear from you.