You think you have problems? Some time ago parts of my town had an infestation of Buzzards.. Vultures. Big guys. Think of a cup of oatmeal, add some charcoal, bits and pieces of long dead critters, all of that on sidewalks and cars and even people who loitered on their way to somewhere.
Town tried cannons, loud music, cursing, were talking about hiring a witch to get rid of them, and some folks thought of shooting them and/or cutting down trees. Others suggested fire hoses. Finally they felt unloved, left and went somewhere else..
I just got some cat repellant because there's 3 neighborhood toms who come to my front screen door where my altered tom sits inside in the sun light, then they back up and pee like a fire hose on my screen. The repellant is mostly pepper of some hot variety, you might try that in a spray. Just be sure YOU are protected while doing this, then run inside while it dries. It won't hurt the birds but maybe they won't like it. Just a suggestion.
You might want to also talk to someone in the county farm advice office. They have some pretty smart folks there.