I noticed the birds were making a different sound from what I was used to hearing, when they were circling the boxes.
Then, with the morning sun behind them showing a blue iridescence, and there is no white coloring above the eye as in the violet-green swallow, this must be a tree swallow.
Have the tree swallows been mixed in with the violet-greens all the time?
Walked down to the open field last night where the nest boxes are, the majority of the swallows seem to be the violet-greens for sure. Did notice the barn swallow flying with them again.
Looks like the nest boxes have attracted the tree swallows into the little valley here, where they were not noticed before!
Anna's hummer in backyard, browsing the red salvia flowers