Cavities are built only in large, old pines. Pecking a cavity in a live tree takes a long time, since the wood is very hard. The sticky sap keeps predators like snakes away from the nest cavity. Also, periodic natural fires, which historically kept the pinewoods open, have been suppressed since settlement. Periodic fire is needed to control the brushy understory and keep the pinewoods open.
Most clusters have some cavities under construction, some completed and in use, and some abandoned.