Several species of birds can become pests if they make a lot of noise, leave droppings all over your house if they frequent your roof or droppings all over your car if they make nests in your carport or garage. Pigeons have highly corrosive uric acid in their droppings, Seagulls can cause havoc around your waste collection areas and Starlings can flock in their thousands and overwhelm buildings and trees. Birds can block gutters with nests, be aggressive and attack and also carry parasites which can spread disease.