Audubon Entities BG900 Natural Screw on Bird Guardian (Discontinued by Manufacturer) The newest bird guardian features a natural look attractive to birds and homeowners alike Patented, tested and approved by naturalists, this one-of-a-kind product is constructed of strong durable plastic made to last year after year The bird guardian was designed for all cavity-nesting backyard birds Each year scientific studies and tests continue to prove this product superior in the battle to save our endangered backyard songbirds The bird guardian fits birdhouse openings from 1-inch through 1-1/2-inch