Bluebirds & Brown-headed Nuthatch (1 Viewer)

We have bluebirds in one of our nestboxes, now with young ones. A couple of days ago, I noticed a brown-headed nuthatch at the box, looking around in all directions and then 'peeking' into the nestbox. He keeps coming back with what looks like food in his beak but always looking around before putting his head into the opening. A couple of times he has entered into the box completely. When the male or female bluebird appears, the nuthatch flies away, sometimes chased by the bluebirds.

Does anyone know what is happening? Does the nuthatch feed to bluebird young ones? Or does the nuthatch have young ones in the box, too?

I'm surrounded by these Nuthatches and have never seen their involvement with the chickadees or Bluebirds in their nest boxes so I can't tell you what's going on. As far as I know Nuthatches don't use nest boxes. At least I've never seen it in the 20 years I've been watching and counting the Nuthatches.

Please let us know what transpires with this.