3 New ones in the air

When I went out to take the mealworms to the feeder this morning the adult Bluebirds did not appear in the trees as they usually do. They did not “dive-bomb” me as I approached the nestbox. So I opened it gently and found the 3 little ones gone.
They must have left yesterday as the nest was clear, no fecal sacs, no worms or bug, just empty. I will clean the box and see if the try for another nest, like Carol’s birds, but I am not counting on it at this late date.