If you’ve been thinking about building your own wild bird nesting boxes for the Spring season, this article may help you determine appropriate sizes for the birds you hope to attract.
Appropriateness of size considerations are vital to bird house success. First to attract the right birds and distract the wrong ones. Next to ensure that the parents and nestlings are safe from predators. And finally correct temperature and ventilation.
How elaborate you make your bird house depends on your personal sense of aesthetics. For the most part, all the birds care about is their safety and the right dimensions: box height, depth and floor, diameter of entrance hole, and height of hole above the box floor.
Nesting Box Dimensions
| Species | Box floor height |
Box height |
Entrance diameter |
Entrance height |
Placement |
| Eastern, Western and Mountain Bluebird | 5×5" | 8-12" | 6-10" | 1-1/2" | 4-6" |
| Chickadees | 4×4 | 8-10 | 6-8 | 1 1/8 | 4-15 |
| White-breasted Nuthatch | 4×4 | 8-10 | 6-8 | 1 3/8 | 5-15 |
| Purple Martin | 6×6 | 6 | 1-2 | 2-1/4 | 6-20 |
| Tree and Violet-Green Swallows | 5×5 | 6-8 | 4-6 | 1 1/2 | 5-15 |
Minimize the Chance of Predator Access
Proper box depth, roof, and entrance hole design will help minimize predator (raccoons, cats, opossums, and red squirrels) access. Sometimes all it takes is an angled roof with a three-inch overhang to discourage mammals.
The entrance hole is the only thing between a predator and a bird house full of nestlings. By itself, the 3/4″ wall isn’t wide enough to keep out the arm of a raccoon or house cat.
Add a predator guard a 3/4 inch thick rectangular wood block, to thicken the wall, and you’ll discourage sparrows, starlings, and cats.
Refer to the above chart, keeping in mind that birds make their own choices, without regard for charts. So don’t be surprised when you find tenants you never expected in a house you intended for someone else.
Ventilation, Temperature and Drainage
Now that you have the correct dimensions for your bird house, take a look at how to make it safe: ventilation, drainage, susceptibly to predators, and ease of maintenance.
Without air vents, boxes can turn into bird ovens. There are two ways to provide ventilation: leave gaps between the roof and sides of the box, or drill 1/4″ holes just below the roof.
Water becomes a problem when it sits in the bottom of a bird house. A roof with sufficient slope and overhang offers some protection. Drilling the entrance hole on an upward slant may also help keep the water out.
Regardless of design, driving rain will get in through the entrance hole. You can assure proper drainage by cutting away the corners of the box floor and by drilling 1/4 inch holes in the box floor. Nest boxes will last longer if the floors are recessed about 1/4 of an inch.
Entrance Hole Sizes
Look for the entrance hole (and exit) hole on the front panel near the top. A rough surface both inside and out makes it easier for the adults to get into the box and, when it’s time, for the nestlings to climb out.
If your box is made of finished wood, add a couple of grooves outside below the hole. Open the front panel and add grooves, cleats, or wire mesh to the inside.
Never put up a bird house with a perch below the entrance hole. Perches offer starlings, house sparrows, and other predators a convenient place to wait for lunch.
Don’t be tempted by those beautiful duplexes or houses that have more than one entrance hole. With the exception of purple martins, cavity-nesting birds prefer not to share a house. While these condos look great in your yard, starlings and house sparrows are the only birds inclined to use them.
Filed in: Bird Houses, Wild Birds
Search by: bird house, predator, purple martins
