Designed to invite the bluebirds in, keep the sparrows out.This Kentucky style, slot entrance bluebird 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. Habitat: Enjoys open woodlands, fields and farmlands with scattered trees. Range: Breeds east of the Rockies from southeastern Canada to Gulf of Mexico. Winters in southern part of breeding range and Mexico.