It was our third season of successfully hosting nesting Black-capped Chickadee, but it was the first time we've (potentially) witnessed a "replacement brood". All I know about the failure of the first brood is that one day in late May I woke up and realized the frenzied activity at the nest had suddenly stopped. As a matter of practice, I opened the nest box with the intention of removing the nest and repacking the box with wood shavings for the next season. But for a reason that I do not recall, I decided to postpone that chore for another day. Then on 8 June 2014, I noticed renewed activity at the nest box, and from that point forward, I decided to pay closer attention to the evolution of this brood.

I believe two chicks successfully fledged from this second brood, two days apart, approximately 16 days after hatching. 

According to (The Birds of North America - Online), the reuse of nest sites is rare, and when old cavities are used, clutch sizes are typically larger.

Our "replacement brood", however, was made up of just two chicks who occupied a tiny portion (4 sq. cm) of the entire nest cavity that measured 13 centimeters square. This, combined with the fact that six unhatched eggs came tumbling out from beneath the nest structure while I was clearing the nest box, has left me scratching my head.

Twenty-eight Images - Spanning 8 June 2014 - 26 June 2014: