The wrens were quite loud today. It sounds like they are just singing out of joy, announcing their arrival. The reality is that the male arrived several weeks ago in a stealth-like fashion.
I checked my bird house a couple weeks ago and saw that a couple of twigs had been left. Wild Bird Watching.com (http://www.wild-bird-watching.com/House-Wren.html) says that the male wren arrives around the first of May, and places sticks at various potential nesting sites. After pairing with a mate, the male then takes the female around to all of the nesting sites he has begun building.
The female wren selects the one she likes, throws out his sticks and rebuilds the nest, adding soft materials before she lays her eggs.
I left the twigs alone, knowing that for several years the wrens always settle on my wren house that overlooks a shade garden with hostas and ferns. Nearby there are various shrubs where all sorts of insects can be found.
Once I am sure that the wrens have settled in, I might clean out the bluebird house in case a bluebird still wants to build a nest in the house I am providing them. Then again, a few twigs in the bluebird house might help attract a bluebird