I'm not sure where you live and what the weather is like, but it could be a territorrial thing where he is
with his own immage. We once had a demented robbin that kept pecking at our upstairs window from sunrise to sunset, we couldn't get any sleep and finally had to put cardboard infront of the window so he couldn't see himself! Obviously that isn't an option for you, but is there some way you could keep him from seeing his reflection
? Or maybe distract him with a mirror or other object where he can see his reflection nearby on the ground or somewhere else where it doesen't matter if he makes a mess
? In any case I think he will eventually give up and go away.