Simply. It's called a nest. Whether its a wasp, hornet or jellow jacket nest. Whether its in a tree, in the wall of a house or underground, a nest. A communal wasp or hornet's nest is called a vespiary.
Clean them once the bluebird abandons the nest; usually after the babies leave the nest. If a sparrow or other bird starts making a nest over the current bluebird nest remove the materials of the nest in process. Do not… Full Answer