Eggs hatch within a 24 hour period, so they may begin on Day 0 and complete on Day 1.

Between days 5 and 8 the eyes will open. Feathers begin to break out of the tracts.

Day 11 or later the feathers appear more developed.

By Day 14 it is advisable to only open the box if you have a plexiglass shield to prevent the birds from jumping or flying out.

These photos take us to Day 16, when bluebirds are fully feathered. However, they may not fledge at this time. See an explanation below Day 16.

AFTER DAY 16, by Margaret MacKenzie:

Nestlings don’t leave the nest box until 18 to 21 days for Mountain Bluebirds in our area and even up to 23 days for Western Bluebird. We have often seen this, as we go to check out a box that we are sure the nestlings should have fledged, but they are still there and are more than 21 days old. Occasionally bluebirds do fledge earlier than 18 days. During Heavy periods of smoke in our area or very hot weather we have seen nestlings leave boxes at around 15 days.