Bluebird Predator Control
House cats and raccoons are among the most serious bluebird predators. Baffles or a greased pole are advised for use in areas where cats and raccoons are likely. A 5-inch roof overhang above the entrance hole reduces the possibility of raccoon or cat predation from above.
If raccoons or other predators are present, avoid mounting your box on a tree or fence post. Raccoons will naturally patrol fence lines and are more likely to locate the nest box.
This PVC box, while not fancy, is effective. It has an overhang on the front to prevent predators from reaching into the box from above and an extended shade guard to provide protection from the hot afternoon sun.
It is often a good idea to place a guard under the box to prevent snakes and other animals from entering the nest box. Commercial guards of several types are available or you may construct your own.