Our slotted-entrance Bluebird house is designed to keep out treacherous House Sparrows. (Keeping the Bluebird’s nemesis, the non-native English House Sparrow, out of your nest box is critical. Please see our resource House Sparrows: Deadly Foreign Invaders to find out more.)
The design is based on research by the University of Kentucky. Bluebirds will accept the slot entrance, while House Sparrows tend to prefer standard circular holes and deeper boxes.
So, Sparrows generally reject this type of shallow box which will make your monitoring easier. But, just in case, an enclosed wooden insert can be adjusted to reduce depth even more. We’ve seen this box in action and it works!
Come in and see it for yourself!