I too have been attacked by redwing blackbirds. Some pulled hair the first time past... I did a high speed pass the second time (on my road bike) which allowed me enough distance the bird gave up the chase. My visiting cousin didn't get enough speed on one of the later passes and had a bloodied neck to show for it.

I was thinking an airhorn to sonically scare the bejeebers out of it- never tried it out though.

-Scott