Eastern bluebirds nest in cavities (holes). These holes may be in old trees, old fence posts, etc. They take readily to nest boxes erected in the proper habitat. The male Eastern Bluebird displays at his nest cavity to attract a female. He brings nest material to the hole, goes in and out, and waves his wings while perched above it. That is pretty much his contribution to nest building; only the female Eastern Bluebird builds the nest and incubates the eggs.
Eastern Bluebirds typically have more than one successful brood per year. Young produced in early nests usually leave their parents in summer, but young from later nests frequently stay with their parents over the winter.
The best place to see Bluebirds in Reading is at the Bare Meadow Conservation land off of Pearl St. Two years ago, a pair raised 3 broods (families)! I observed 1 male bird there this spring.
Photos from All About Birds.