Probable Pin Cushions!
It was really, really nasty out today, so I decided to head directly to the museum and catch up on work. However, I just want to note that – again, if my calculations are correct – this is day 10 for the chick(s).
If this is right, the chicks should be growing by leaps and bounds. They should be about 3-4 times their hatching size at this point and are voracious eaters. Their eyes have opened awhile ago and their keen eyesight has developed. At this point, they recognize their parents and imprinting should be taking place.
Their second coat of down should be all in and uniform by now. The outer tail feathers (rectrices) should be just breaking the skin. The flight feathers grow about 2-3mm a day, so they should be visible, though still completely enclosed in the feather sheath. You can see this stage here.
Chicago Peregrine Falcon Blog 