I'm sorry to be light hearted, but I really did read your question wrongly. I read it as 'Mad Cow'.
When I was working at the local primary school we had your problem with a crow who all day long banged at the windows like you describe, much to the delight of the children because it disrupted the lessons. It happened to me with a Jackdaw, but we think he was probably someone's pet Jackdaw, because he also used to walk in the back door to find us!! Also we had a mad Jay one year that attacked us in our gardens! Eventually, he went away, but it was quite frightening.
Can you phone up the RSPB and ask their advice. They might be able to help.