I saw this male Eastern Bluebird picking up nesting material from the ground. I see it standing on top of the nestbox. It went inside the nestbox with the stuff, pulling it all in. I thought, what an industrious little fella until I learned what he was actually doing.
The only thing he does with respects to nest building is perform a "nest demonstration display" to attract the female. He does this by bringing nest material to the hole (as pictured) and then goes in and out and waves his wings while perched above it. That is pretty much his contribution to nest building as only the female Eastern Bluebird builds the nest and incubates the eggs. --- Info from Cornell All About Birds website