Owls - protecting you from other birds

I mostly see these fake owls on the roofs of gas stations. They put them on the roof to scare away other birds. The owl is supposed to keep the others (nasty pigeons!) from hanging out and pooping everywhere. We visit this owl from time to time because my son likes to see it, we call him by his French name, Monsieur Hiboo. At one time this owl was on the roof of the neighbor's house, but they moved it to right near their front door. I guess they found that his duty on the roof was not necessary or maybe not very effective.