The main competitor for the nest boxes here are Tree Swallows. The pair seen below are the main protagonists.
Just like the Eastern Bluebird, the male is the more colorful one (above) on the upper left. A closer look confirms his elegant form. As the male shifts relative to the light's direction, his back flashes a lively blue.
Through the morning, the Bluebird pair showed a preference for one of the two nest boxes in front of me. They chose the perch stick above that box with greater frequency. When the Tree Swallows soared past the box, the male would spread his wings in a display of his size. See below a typical response.
Then, the female Bluebird entered the nest box and remained for over twenty minutes. I wondered if she was laying an egg or simply establishing ownership? During that time, a female Tree Swallow made several attempts to enter. She always retreated quickly.
The male Bluebird remained very close. He even defended the perch over the second nest box.
I must admit that I am becoming very interested in seeing how this drama between the Tree Swallows and Eastern Bluebirds plays out. Yes, I am rooting for the Bluebird male. He puts on quite a show in the sunlight. If the Tree Swallows settle in the second box, it will be interesting to see the interplay. Will they work out a truce?