Droll Yankees NBBB100 12-Inch Nest Box for Bluebirds with Bird Design Exaggerated roof overhang - keeps rain and sun out, keeping eggs and birds dry and temperature stable Unique entry hole replicates a natural tree cavity Side door - easy access for monitoring and cleaning Ventilation - under eaves and in the floor for proper air flow Kerfs on inside front - help fledglings climb out of the box