Damage to Structures
Bird droppings are easily noticeable by tell-tale white stains. These droppings are acidic and can deface and accelerate deterioration of building materials. Accumulated droppings can plug the gutters of roofs, causing water damage. The weight of droppings can threaten the collapse of ceilings. Nests can obstruct exhaust vents and may cause fires.
Damage to Livestock and Pets
Pigeons consume livestock feed and contaminate it with feces, raising the risk of disease transmission.
Damage to Landscapes
Dropping-covered sidewalks are aesthetically unpleasing. Starlings damage cultivated fruits such as grapes, peaches, blueberries, strawberries, figs, apples, and cherries. They also damage ripening corn.
Health and Safety Concerns
Droppings present the risk of disease transmission, as well as being unsightly. In particular, soils contaminated with droppings encourage the growth of the fungus responsible for causing histoplasmosis. While bird droppings provide suitable conditions to grow the fungus that causes histoplasmosis, the birds themselves do not appear to excrete the fungus. (Bat droppings, however, often host the fungus). Accumulated droppings may weaken bridges or other structures by their weight and acidic nature. Around airports, flocks of birds pose the threat of air-strike to airline safety. Pigeons may spread Newcastle disease and cryptococcosis.
The role of these species in transmitting diseases to humans is not understood as well as it is for livestock. People can reduce their risk of infection by avoiding contaminated areas or by wearing proper protection during bird control and fecal cleanup. Although rare, people in areas with active roosts can suffer bites from mites that are associated with the birds.
Pigeons are active during daylight and their presence often is noticeable and annoying to people. Aside from problems with individual birds, large flocks of these birds raise the most ire in urban areas. Problems can range from excessive noise to large quantities of excrement deposited on sidewalks, cars, and buildings. Pigeon excrement on gas station canopies can clog downspouts leading to their collapse during rainfall. The acidic nature of bird droppings also degrades marble statues and building materials, potentially threatening structural integrity.