Feral pigeons will nest almost exclusively on buildings & at height, accounting for why this pest has adjusted so well to cities & towns from its origins as a cliff dwelling bird. The fouling of buildings will often occur in places where they roost & nest. Chemicals in stone work react with the acidic droppings creating erosion & destruction of the surfaces. Amass of these droppings can harbour infestations of mites & insects. Pigeons carry many diseases, notably Chiamdiosis, a virus similar to influenza, and Psittacosis, similar to pneumonia and Extrinsic Allergic Alveolus’s (Pigeon Fancier’s Lung) to name but a few.