I have the same situation, except with two nests in boxes that are about 25 feet apart. This is the first year I have seen this behavior. They started building in one box, but after only one day a HOSP pair decided to take over the box, so the bluebirds moved to the other box. Then an even stranger thing happened. After two days, (and NO nest building) the HOSP pair just decided to leave! I have never seen this happen before, and I don't know why they moved on. (Maybe they could read my mind that a trap was in their future??) But I think this is the reason the bluebirds are building in both boxes - to try to control the territory. It will be interesting to see which box they choose.

Lisa - thanks for the play-by-play. Your little Hussy sounds like such a character! Congrats on the five new blues!

yes my box is baffled and the nest is not messed up at all.I wonder if I had a visit from a HOWR while I was gone.I know one baby was hatching the day we left.I think you must be right though,something happened to that last nesting.I had no problem with HOWR all summer,so I had not put on a wren guard.If thats what it was,I guess I am glad I was not here.I just looked out and Daddy is on top of the box.Guess I will just have to wait and see when this batch hatches,cause I have no idea when the eggs were layed.Time will tell,I'll keep you posted....Jane

Karen no problem. You put it on after first egg. Any box would do. In fact it's a big joke about the cheese-its but I love them and since it worked so well the first time about 4 or 5 years ago I won't use anything else! LOL What happened is I had blues and eggs in a box way in the back of my yard (first nest of the year) and all of a sudden I heard that dreaded sound. I had planned to make one out of wood with sides on it but hadn't got around to it yet. They came the earliest I'd ever seen that year and my husband is a carpenter so of course we always have wood around but hardly ever have any tools around here. I had to leave that day and so I had to come up with something quick. All I had was duct tape and that was my biggest box. I have had the same one last 2 nestings with no problem but I put a lot of tape on the inside of all the corners and those front corners too. I just screw it to the sides of the top of the box like you would with the mono fishing line for hosps and maybe tape the top and sides down to the box or you can tack it on with finish nails driven part way in and just bend them over or use thumbtacks. Make sure you have at least 2 1/2" of clearance so they can get in. I completely cover the hole so mine come down pretty far but I haven't had any casualties since I started using these. Karen just make sure they can figure it out. Sometime young birds will have a problem with this BUT eventually they always find their way in. The couple this year was not very bright. I had to take it off the second morning so she could lay her next egg and I put it right back on when she was done. She got it the third day. My Tres have been vigilant enough to not need one but one lady on Bet's site has used a guard with Tres successfully. I just think it kind of goes against their grain. You know the way they look out of the hole for each other and change places so fast. You know what I'd do with those wrens? I'd take a piece of cardboard and tack it to the front of the box covering the hole and run some duct tape down the outside corners so it looks like the guard from the front. I do this with empty boxes in my yard to try to teach them when they see this it means no entry just in case you have a persistent bird it may help next year. Hope it helps Cathy