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.
Position the house so its opening does not face into direct sunlight or prevailing winds. Full or partial shade will help keep the house cooler, and a more protected location will be safer. If necessary, a longer overhang above the entrance can also help provide shade and shelter. Angle the house so rain cannot easily run into the opening or through ventilation holes. Some bird house models include an angled face to ease water runoff, and a larger roof overhang can also help keep the interior of the house dry. The house could also be positioned in a more sheltered area, such as underneath the eaves of a roof or against the trunk of a large, full tree that will help protect the bird house.