We love swallows, but in the barns where their droppings were a problem we stretched small gauge netting below the roof. It stops them getting in to the beams to roost. Obviously only do this before the swallows arrive. Worked for us.
Hi, No damage except to trees, lost 4 apples and two ash trees but we've had so much rain, local flooding and the ground is sodden. Worrying about where I'll turn out the lambs at the beginning of March.