Had a nice opportunity to observe the chicks from a distance under late afternoon overcast skies.  They are playful and flapping thier wings in anticipation of fledging soon.  According to Birds of North America, at 35 days, while mostly feathered, large conspicuous patches of down around legs, under wings, and on crown. At 40 days, almost fully feathered with traces of down on crown and under wings and outer several remiges; rectrices not fully grown but bird capable of weak flight.  With this in mind, these chicks looks close to the 40 day mark and weak flight along the rooftop happens nest!