Exclude pigeons from entering spaces to prevent the situation from happening in the first place. Make sure that all attic and soffit vents are properly screened to keep birds and other animals out. Some of the things to do immediately include:
Filling large openings and doors with heavy door curtains of plastic strip to discourage entry. If they do get inside, pigeons can be discouraged from roosting on ledges and light fixtures by creating sloping surfaces over the flat surface.
Sealing the edges of places where birds nest, using hardware cloth and silicon caulk or plastic bird netting. In large open structures, like barns and warehouses, close off the space above the rafters where pigeons roost and nest with industrial bird netting.