I have recently also replaced my Gilbertson with a slightly larger version (6 instead of 4 inches in diameter and homemade), and it looks like I made the switch just in time.

There has been lots of Bluebird activity today, both are taking turns bringing things in and out (even though he looks to be a bit more excited than her, even making the nest shaping "shuffle"). I added the needles to make the transition for them easier and the box less "new". The larger box is supposed to help them raising stronger and healthier chicks, providing more room to exercise the wings and also better air flow during hot times.

They are very entertaining to watch and I am excited to see what happens next.