The bluebird box behind the Carriage House and Geology Museum has been pretty quiet since it was put up a couple of years ago. There was a wren nest there, late one year.
So I was surprised, and glad, to see a bluebird pair checking it out. They may choose a better spot (I've seen investigation before, too), but it's the time of year that boxes are being investigated. We have 12 or so boxes here at the Garden, most of which are used actively, and support several broods a year.
Here's a photo of a bluebird dad and fledgling that I took near the Hayden Conference Center several seasons ago.