This Kentucky style, slot entrance bluebird bird house is designed to thwart sparrows. According to research at the University of Kentucky, bluebirds prefer a slot entrance to the standard circular hole -- sparrows prefer the opposite. In addition, sparrows don't like a shallow box and bluebirds don't seem to mind. This box is only 5" deep but if sparrows still continue to be a problem, a wooden insert is included to reduce the depth even more. Sparrows rarely use the 3-1/2" depth, but bluebirds will still occupy it. RANGE: Breeds east of the Rockies from southeastern Canada to Gulf of Mexico. Winters in southern part of breeding range and Mexico. Measures approximately 10" h x 6" w x 8 1/2" d. Made in Maine from eastern white pine.