How to repel pigeons so that they don't loiter behind my windows?
Many buildings in my area have the same problem. I have seen many clever items, but the one that seems to work well is a strip of plastic with stainless nails extending up from under the plastic sill covers. These are constructed with strips of acrylic plexeglass cut to fit over the exterior window sill, then drilled every few inches all over with Stainless 3 inch nails protruding up from under the strips.   The birds will not land on the sharp points.