Two bluebirds showed up on our yard today.  These are the first two we have seen this year, even though in years past, bluebirds had  been more plentiful in our neighborhood.  I almost didn't recognize them at first, because I first saw the blue back of one of them as it sat on one of our shepherd's hooks.  They seemed quite interested in the Gilbertson nesting box that we have; unfortunately, the tree swallows are already living there.  the birds stayed in the backyard for several minutes, sitting on top of the Gilbertson box, and sitting on top of the shed which is only a few feet away from the nesting box, looking at it.  At one point, one of the bluebirds even looked inside the nesting box but saw that it was already occupied.  Having seen the bluebirds, I put up another birdhouse on our bird-feeding station, hoping that perhaps the bluebirds will come back and use that birdhouse instead.  We had tried to buy another Gilbertson nesting box at the local bird store, but they are currently out of them.