I found a completed nest in one of my boxes that looks to be a bluebird nest but haven't seen the bird. The nest was built in a day but four days later I have no eggs. Is it likely to have a delay like this between nesting and eggs. If mama never returns, should I leave the nest and expect another bird to use it? Since my titmouse and bluebirds have both fledged I now have three other boxes available for nesting so there is no urgency to clean this box.