Many people think the main problem with pigeons is the unattractive mess they leave in their wake. Pigeons also carry disease, and if they're roosting outside your window, it's best to do something about it. There are a number of solutions available on the market that vary in effectiveness and desirability. Electronic devices that emit high-pitched tones are costly and, many say, ineffective. Glues work only for short periods before they become covered with a blanket of grit and dirt.
Poisons can be needlessly cruel.
The simplest and best solution is to make the area where the pigeons roost inhospitable. Start by removing the nests and scrubbing the area. Then you can use chicken wire to cover the area. Since it's difficult and uncomfortable for pigeons to stand on the wire, they'll soon move away. Or, try guard ledges and eaves with a roost deterrent, which is a wooden, plastic or metal base overlaid with small nails, spikes or sharp wire.