@Joe Nation,
They sometimes get disturbed and move on when theys ense that their not wanted. The couple that took up residence neath the WRightsville Bridge between Lancaster and York County Pa (over the Susquehanna River), got outta the way when the STate Highway guys were out there screwing around the armpits of the bridge during nesting time this year. The hawks then set up a new residence on the cliffs of Chiques Rock on the Lancaster Side. This rock is off limits by fencing because so many people have jumped to their deaths presumably unrelated to their peregrine falcon dissapointnment..