After a few days remaining in the nest box, the third and final chick fledged on Thursday.  In the late afternoon, had a nice opportunity to observe the fledgling on a lower ledge closer to Merrimack Street.  It was testing its wings and hopping along a ledge.  Not only a treat to watch from a close vantage point, but also had the chance to observe and document the black/green bicolor leg bands used on peregrines in Eastern United States.  This fledgling has black numbers (59) over green letters (BD).

More photos: http://www.pbase.com/birdshots/image/156086349

There is an international protocol in North America for colored leg bands on Peregrine Falcons. The color indicates the origin or subspecies for chicks banded in the nest. The colors in the protocol and their meaning are:

Red Captive bred
Black/red bicolor Eastern United States
Black/green bicolor Eastern United States
Blue Tundra Peregrines
Black/blue bicolor Tundra or Anatum captured off the breeding grounds or subspecies unknown
Green Peale’s Peregrines
Black Anatum Peregrines

Characters used on the Peregrine bands are letters and numbers, with one character on the top of the band and one character on the bottom of the band. Older bands may have these characters either vertical or tipped ninety degrees to the left. Newer bands have all vertical characters.

The fledglings continue to be seen in a variety of locations around the Clock Tower with one of first two fledglings remaining for a day on a nearby ledge.  The older fledgling has flown to upper ledges and even atop the weathervane at the top of the Clock Tower!