Is it just one section or area that is being affected? My parents had a problem with birds, they used this swirling silver thing (it hangs like a wind chime, but makes no noise). The wind will blow it and it will twirl around. I have no idea what it's called, but it has worked, as the shiny reflective surface of it have scared the birds that they used to have constantly, away. I believe it was $15 or $20 for one... I'll try to see if I can find the name of that thing.
I just found this as well, which may be better suited for your application:
http://www.biconet.com/birds/flashTape.html