The Ultimate Bluebird House is made with brass hinged doors on both sides. Each box has a solid copper predator protector surrounding the entry hole so animals and birds cannot enlarge the entrance.  There is a nest lift in the bottom of each house that helps keep the nest high and dry while also helping to control parasites and other nesting problems.  Each Ultimate Bluebird House uses zinc chromate plated screws that provide a sturdier and longer lasting house than one assembled with nails.