What can an apt. dweller do to get rid of finches (i think) which tap incessantly on the exterior walls?

It is the equivalent of hearing a pencil tapping on a desk ... alllllll aftn. It's becoming a deterrant to staying home on the wknds. I have 3 windows on this side of the bldg ... where it is occurring... although of course I can't go throw a scarecrow up or anything in that this isn't my property.