For anyone in the future looking - while I understand your quandary, you certainly did the best thing for your home and your health. Often birds have mites. Being on a wreath on your front door, chances are the mites would have made their way into your home. My understanding is they are extremely difficult to be rid of (minus a match). Our family found out the hard way about mites. Bird had nested in our primary door wreath when we were away on vacation. We just used an alternate door so as to not disturb them. Thought it would be interesting with the kiddos to keep an eye on how things work. A few days after they hatched, I kept noticing a black smudge on the inside of the door. I'd wipe it off, another would show up. I finally looked really close and saw the smudge was moving! MITES. Birds nest had to be moved immediately! We put it in the closest tree (about 40' away) lt turned out fine as momma found her lil ones. They took flight within a couple weeks, it seems like.

It is the most amazing thing if you get box you can open and see the babies or handle them each day to see the startling amount of growth/changes every single day! Our boxes are right under the power line and the parents will sit on the line and watch us and sometimes chirp, but they are a- ok with their babies being handled as long as you don't let them get chilled and are gentle. I learned the hard way to stop trying to hold them after 12 days when i made one batch fledge early. Kept trying to put them back in, but it was too late and the parents really got mad about that. I don't think we've ever had a nest that went much beyond 16 days though, so it's interesting that they are supposed to stay in 21 days. I don't even open the box after day 12. Yes, predators love blues (any baby bird). When you figure out where you want to put a house, make sure cats, coons or snakes can't get to it. Grease the pole or use a baffle or mount the box in such a way that nothing can get in. BTW, the big boxes sell very reasonably priced cedar blue houses- like $12 last i looked. You may very well get some competition from titmice or chickadees- they all like the same size, so you could get multiples and hang them (titmice are the fiercest mamas- they won't budge and will hunker down and hiss at you!). Blues happily nest close to the others but won't nest close to their own kind. And they love to have a choice of boxes. Some years i've had 3 out of my 4 boxes full. The only ones you may want to evict if the get into the box would be the alien house finches. Knock on wood, i've never had it be a problem, but have head from others that it can be.

This is not in my house but I’m posting here b/c the one in my house looks like this. I had no battery left on my phone to photograph ours but it looks very similar and perched on the upper trim of a window. I think it’s recent but we only noticed it as we were driving away. We’ll remove it next time. Hubs is aggravated b/c house was recently painted and those nests leave a mess once removed. The location is High, so he’ll need grab a ladder, climb, clean, yada yada. Not as easy as flicking off a light fixture.

Not 100% sure about birds moving eggs but, I would think, highly unlikely. More plausible is they were on some critters menu.