We have had a flock of 12 Eastern Bluebirds visiting our "Bobolink Farm" property, here, in southern NH. They roam around then go to each of our bird houses and go inside, then land on the roof and just explore them. Our friends have called to say they are seeing bluebirds also.
This is typical behavior of bluebirds in fall. It does not mean they are nesting in the houses now. They're just exploring them so they know about potential nesting sites next spring. Sometimes bluebirds may also roost at night in the boxes during the fall or winter, if they're here. Bluebirds may or may not winter in New England, depending on the weather and available food resources. They mainly eat berries in winter.
It's encouraging for us to see bluebirds, since this past season was a disaster for bluebird nesting here. Last spring we had a pair of bluebirds that were thinking about nesting, then the terrible April cold weather and snowstorms arrived and the bluebirds disappeared and did not return.
So there is hope some of these roaming bluebirds may return next spring to nest here.