Like most birds, pigeons can carry fleas, ticks, or mites. It has been argued that they also carry diseases which can be transmitted to humans through direct contact with either the birds or their feces but these reports seem to be largely unsubstantiated. Their droppings however can damage the paint on your car or the finish on a building, and their highly-flammable nesting materials can clog up drains and vents.
The starling: you may think he's a handsome individual, with his iridescent blue-black plumage and his bold eye—that is, until you look up and see 3000 of his friends flocking in to roost all around you. In their huge numbers, starlings do a tremendous amount of damage.
While birds in general are beautiful to watch as they glide through the air, feed at your bird feeder or enjoy a dip in the birdbath, some birds are not actually meant to be dwelling in your backyard. Bird species that are non-native and introduced into an ecology can wreak havoc on the native species, decimating populations by destroying their eggs and killing the adults. One such non-native troublemaker is the Sparrow, also called the House Sparrow.