I too had this problem , I got a ladder , went up and put loads of plastic tie wraps on it facing upwards with the tails still on, it meant the birds didn't like to even try to land on it anymore, to use an old phrase " they don't like it up 'em captain manering" lol
You posted this before zingo. A simple child's windmill could be attached up there, or, as tufty says - some tie wraps or something similar. Failing that - move the aerial?