Ah, nature at its rawest and most brutal: bluebirds in distress

Best viewed full screen. Yesterday, looking out our window, I noticed bluebirds fluttering and swooping in front of opening in birdhouse along with quite a bit of chirping. Watched and videoed for a few minutes (above video), then realized these two had a problem. Went out to see what was wrong. While checking the birdhouse out, a face appeared in the opening. Not a bluebird; not a bird even; ---a red squirrel. It startled me so much I forgot I had a camera with me. I rang my knuckles on the side to make it exit and it did jump out, not on me thankfully. Red squirrels are about half the size of a gray squirrel therefore small enough to easily enter the small hole in birdhouse. Don't know if it found anything inside. (Last year one ate the eggs in a chicadee nest, same birdhouse, saw the r.s. enter and saw the shells on ground.) No shells this year, and the bluebirds are still going in and out of the nest today. Can't see into the nest even when I opened the door. I'll let you know what happens: whether new brood or abandonment by the bluebirds. How distressful to have a nest raider after all the time spent creating it; keeping vigil of it; and possibly having young in it. ) : (