If you erect bird nesting boxes, invariably there will come a time when a woodpecker, gray, or flying squirrel takes it upon itself to enlarge the entrance hole on one of your bird boxes. When this happens the perpetrator might enlarge a 1.5-inch entrance hole to one that is now is 3-4 inches in diameter.
Whenever a bird or mammal remodels the entrance hole in a nesting box, the structure is often destroyed or, at the very least, puts any bird that tries to nest in the box at risk.
A bigger hole allows larger birds to nest in the box. Most boxes erected in Georgia are designed to help alleviate the eastern bluebird’s housing shortage. A box equipped with a 1.5-inch hole, prevents larger, more aggressive European starlings from nesting in the box. Without such protection, bluebird numbers would plummet.
A larger hole also allows nest predators such domestic cats, raccoons, and even opossums to reach into a box and snatch out nesting adults, their eggs, and young.
I have found that one of the best ways thwart unsolicited attempts to alter the size of entrance holes is to equip nesting boxes with a simple, inexpensive device called a hole guard.
The hole guard is nothing more than a piece of metal that is attached around the entrance to a nest box. They are available in various sizes. For example, if you want to encourage birds the size of a bluebird or smaller, install a hole guard featuring a 1.5-inch opening. Likewise, if your goal is to encourage smaller birds, such as Carolina chickadees to nest in your boxes cut a one-inch entrance hole in your box and protect it with a one-inch hole guard.
Believe me these simple devices work. In fact, they are so effective, I will not erect a new box without one.
In all the years that I have used them, I have seen a hole guard fail only once. In that case, the hole guard actually worked, however, an unknown critter almost totally destroyed the entire box. In spite of this all out attack, the hole guard remained in place.
Hole guards can be purchased are stores that specialize in birds. If you try one, you will not be disappointed.