While it is okay to paint the outside of a bird house, do not paint the interior surfaces or the inner rim of the entrance hole. Furthermore, use only environmentally safe paints, stains or varnishes on the outside and avoid any lead_based paints that can poison birds from fumes or ingestion. Choose a bird house design with the proper interior dimensions for the desired residents: Too small of a house may cause growing birds to smother, while too large of a house will not be attractive to nesting parents. Smaller birds could also become too chilled in a larger house if they are not huddled together when needed.
Tree cavities are formed by tree disease and decay and by woodpeckers. All six woodpecker species in Alaska excavate cavities for nesting and roosting. Most other cavity_nesting birds use abandoned woodpecker holes. Usually a pair of woodpeckers excavates a new hole every year. Before selecting a final nest site, a pair may start, then abandon, several holes. During fall, overwintering woodpeckers also excavate cavities for winter roosting. However, woodpeckers are only able to excavate holes in dead or decaying trees.