From Massbird:

Someone asked recently how to report a banded bird, a question that I have noticed is asked quite frequently. Perhaps we should keep the information in a telephone book or somewhere where it can be available when the occasion arises? Bird bands may be reported by calling the U.S. Fish and Wildlife Service Bird Banding Laboratory toll free at 1-800-327-BAND. The report becomes part of the national bird banding database and the caller receives information on the banded individual. The recovery of banded birds, either from retrapping by banders or reports from others who find banded birds as roadkills, harvested waterfowl, or however found, has provided much of what we know about bird migration, longevity of birds in the wild, migratory routes, etc.  Please do report banded birds when you come upon them, which will not be often.  The one exception to this request is sightings of banded Rock Doves, or "pigeons". Pigeon fanciers who raise homing pigeons have told me that they do not want to continue breeding pigeons that do not "home" quickly, so when a banded pigeon turns up in a chicken yard or at someone's bird feeder they no longer have any interest in that individual.

-- Sean T Noonan (sean@stnphotography.com), June 25, 2002