The most common type of bird houses are wren bird houses as they are cavity nesting that readily make use of man-made wren houses. Wren houses require the smallest entrance, only 1-1/8 inches which also helps keep larger birds and predators out. They should be around 8" tall with a 4"x4" base and placed 5'-10' high in a tree near an open yard. Wrens are a helpful addition to your backyard habitat as they eat many insects pests like grasshoppers, spiders and snails while providing you with endless entertainment. Enjoy these inquisitive birds bubbling chatter with loud and melodious songs.