The wrens are determined! I have hanging baskets up front with fake ferns because I can never remember to water the front. She did a brood there. Then I bought real ferns for the back, so she moved. While they were building, I kept pulling it out, I don't want to water the babies and she had it right on the surface of the soil.
So she moves to the other plant, and places the nest up in the leaves. So, I left it. I can water the plant without watering the nest. Not sure why she couldn't stay out front, she was successful there. Unless it's a 2nd pair of birds. The timing was perfect for it to be the same pair though.
Robins are nesting, and we have PRIME robin territory with the ducks and all the water. Add a compost pile, and it's worm heaven. So we seem to have 3 pair of Robin in neighboring yards, who meet and fight in our yard. Everyday they are screaming at each other and tussling around at the compost pile. There's a 4th male hanging around, haven't seen a mate for him though.
Sparrows and starlings in the dead tree off to the side, bickering and fighting nonstop... prime territory for them too with the mulberry tree and local bird feeders. The starlings try to kick the sparrows out, and they start a whole flock war. Husband wants to cut the trees down, but I wouldn't want the sparrows, starlings, and squirrels in the other tree looking for a new place on our house. Even the squirrels had to fend off the birds!
We have so many birds.. I'm not adding any houses!
Blue birds have specific nesting requirements. Try to build specifically for them to reduce the odds of someone else stealing it. They're rare because they are mild natured and also have specific nesting. They like being in the open near woods, off of a tree line. Wrens like a little more security. When you drive around the country and see bird houses on fence posts, or on stakes in a field about 4-5 ft up, those are for blue birds. Usually too low or open for other species.