I had a similar problem when visiting unoccupied equipment buildings, the birds had set up home on signs and stuff, and would dive bomb your head, hitting you with beak and claws. Tried wearing a climbing helmet but the sods wouldn't give up and would then go for your neck. So I took a tennis racket with me. One hovered over me, missed with the first swipe but got him with the backhand, twatted him clear across the road into the bushes on the other side. After a couple of mins he got back up dazed and went back to his nest. From then on they left me alone, but I heard they still attacked anyone else who went to the site.
A year later, different site, same problem, multiple offenders. Took my trusty slazenger, wallop, got the bastard first go, watched him bounce off a tree and slide to the turf. He too got back up and flew off (to my relief). His mates cottoned on and gave me a wide berth. Who'd ave thunk the pea brains learn so quickly. Mind you, at another location, same problem but I never got to try the "treatment" as an eagle sat atop the light pole swooped on the lucky punter as he sat over the door, and proceeded to eat him leaving blood all over the door frame.