It's nesting time

My bluebirds never went anywhere for the winter. Bluebirds and robins just hung around here all winter and we did have some pretty cold weather. Lately I have been checking my bluebird house to see if they have started building a nest. Much to my surprise today the nest was all built. How do they do this without my ever seeing them? I cleaned out the old nest from last season and had it all ready for them to rebuild and they did. My cousin, who is an expert on bluebirds, told me they would be back. I have not seen any hummers yet, but I have a new feeder ready to put out for them. I'm anxiously awaiting the days I can sit on my patio and watch the hummers fight each other!!