I have never observed them go into a nest box, but come spring, some of my trail boxes have evidence of Eastern Bluebirds (EABL) roosting. I would post a picture but don’t know how. EABL droppings look entirely different from HOSP droppings and if latter has been roosting, easy early season trapping opportunity. I also get a few Downy Woodpeckers using boxes to keep warm over the winter and new fronts or face plates needed for those come spring.
