In order to accommodate the wide range of bird preferences, there exists a large variety of birdhouse designs, each with a carefully chosen opening diameter, cavity size (both floor space and box height), depth, and material. Wrens and chickadees tend to prefer the smallest houses with the smallest openings. Opening sizes of about 7/8” to 1 1/8” are typical in wren/chickadee houses and quite often they can be hung, rather than fix-mounted. With a somewhat larger opening size (about 1½”) are houses designed for bluebirds. Bluebird houses tend to be larger and taller than wren/chickadee houses and need to be mounted. These two house sizes are the most commonly seen. Some of the larger houses you may see include woodpecker and flicker houses, screech owl houses and wood duck houses.