Birds and Pigeons

Pigeons and birds keep attacking my condo. Their droppings are left on the balconies and the walls. Just recently a couple of birds have built their "home" inside the air vent, which has not been in use during the time that I went to Hokkaido. To scare them off, I am now using scarecrows, which are crows or owls, to deter them. They have not come back ever since but I will have to closely monitor to see if they really work.