For those of you wondering exactly what I'm looking for, the coloured bands are on the chick's left legs, and they can spin around. Preening is a great time to catch band numbers because the birds stand up, twist, poop as part of the process all of which moves their leg feathers out of the way for band viewing ... and on the male chicks, I'm looking for the top number as they both have Y as the bottom digit.
Don't worry, won't monopolixe the cam for this all day, just on-off ...