I spotted the baby bluebirds peeking out of the nest box yesterday evening. Today they are 15 days old. They generally fledge at 17-18 days.

It has been hot for a couple of days, almost 90 degrees and sunny. Maybe they just wanted a breath of cooler evening air!

Here are daily photos on Sialis.org of bluebirds from Eggs to Empty Nest. More info: Development.

Day 14: no unfeathered areas visible. Wings are longer. Capable of weak, short-distance flight. Bird can right itself and make short shuffling movements backwards and forwards.
Day 15: completely feathered. Nestlings huddle together, preen, exercise, stand on edge of nest and look out of nest cavity.
Day 16: able to hop well by day 16. During final days in nest, nestlings flap wings vigorously.

Fledging (leaving the nest): Typically 17-18. May leave as early as 12 (premature) and stay as long as 19-21 days. May be latest for early broods. If the box is empty in this time frame, the nest is flattened, and there is some fecal material (white) on the walls, it usually means fledging was successful. Occasionally a runt will fledge one or even two days later than the others. Insect availability may speed up or delay fledging.