Block openings to lofts and vents with netting, wire screen, metal or glass. Pigeons prefer to roost on flat surfaces. Install metal, wood, or some sheathing at a 60-degree or greater angle, to make it difficult for the birds to obtain secure footing. Despite its appearance, this product evidently does not harm birds. Use flexible mesh netting to protect trees and garden vegetables from droppings.
Habitat modification can be effective.
For example, thin tree branches where birds tend to gather. Do not feed roosting birds, especially pigeons. The free handouts birds have become accustomed to in cities, parks, and yards are largely responsible for the abundance of roosting birds, especially pigeons. If feeding is eliminated, chances are good that the birds will move elsewhere. Many forms of repellents are also effective.