How can I persuade a large flock of starlings to roost elsewhere? I estimate over 2000 birds.

How can I persuade a large flock of starlings to roost elsewhere? There is a very large flock of 2000-3000 starlings who, every evening roost in a row of trees and bushes next door to our house. The trees are covered in droppings and there is a bad smell as you walk past. The trees are in the middle of a town, even though the fields and rural hedgerows are under a mile away. Also ours cars and roof windows are covered in bird droppings. Is it a council issue, or something my neighbours and I need to resolve?  I am a nature lover and a member of the RSPB, so want to resolve this without harming the birds.