At 5:10ish, one bird (Cowboy by size) was sitting on the smoke stack. Kate was sitting on the J on JBRC building.
I went and did a errand and came back to check on them at 5:30. Kate was still on the same spot - Cowboy had moved over to the rooftop of the Buhler building just over her head. Cowboy then took off to the north and disappeared over the main hospital building, Kate followed a minute later. I go home north over the Arlington street bridge, pass the Federal Lab building. One of the birds was sitting on the Lab building, took off across Arlington and disappeared further north. I got stopped by a red light on the south side of the bridge. As I was sitting there, all of sudden the pigeons on the railway cars all took off at once. I didn't see the falcons again, but I am guessing, some birdie was looking for supper.
My daughter and I have spotted what looked to be a falcon on the Federal Lab building in the last 2 weeks on 3 other occasions, just didn't think that it could be our peregrine.