Bluebirds Touring Their Own Stomping Grounds?

On Sunday afternoon I was doing some yard work when I glanced toward the east side of my house where I keep one of my three bluebird houses.  A bluebird was perched on the house staring into the hole.  It left and perched in my cherry bush and another bluebird flew out of the cherry bush and it looked into the hole of the bluebird house.  A movement of blue caught my eye and I saw another bluebird in my garden.  It picked up a potato vine that I had just pulled out of the soil and flew off with it.  Carrying nesting material is a sign of breeding behavior.  Between the nearest oak, cherry bush, black spruce and the bluebird house, I saw a total of eight bluebirds.  Each of them took turns peering into the hole of the bluebird house.  It was a bluebird reunion!  I've never seen that many bluebirds congregating together before.  Were they confused by the nice weather into thinking it was time to start nesting again?  Or were they headed south in a group and just stopping by to see the old home place one more time before heading to Texas or Mexico?  I tried to get closer with my camera and they all took off.  The bluebird extravaganza was over; fleeing but awesome.