When you’re ready to build a birdhouse, one of the most important considerations you must make is the birdhouse hole diameter. While the floor space, entrance hole height and roof height are also important dimensions, it is the diameter of the entrance hole that will most accurately determine which birds find the house attractive.
Why Hole Diameter Matters
To make birds feel welcome at your birdhouse, the entrance size is critical. A fraction of an inch too small and your desired birdhouse residents will not fit into the house, and a fraction of an inch too large and you may find less desirable birds such as house sparrows and European starlings usurping the birdhouse. While different individuals of the same species may vary slightly in size, these basic birdhouse entrance hole dimensions can help ensure that your birdhouse attracts the types of birds you want to invite to become backyard residents.
Resizing a Birdhouse Entrance
Many birdhouse kits and novelty birdhouses come with pre-drilled entrance holes that may not match the optimum hole size for birds you want to nest in your backyard. Fortunately, it is easy to increase or decrease the size of a birdhouse hole and still use the birdhouse design you are interested in.
If a hole is much too small for your birds’ needs, use a paddle or spade drill bit to enlarge it uniformly, taking care not to crack or splinter the wood around the hole. If the hole only needs to be enlarged a small bit, a round file may be sufficient or you can use a smaller drill bit along the edges of the hole. Be sure to increase the hole size uniformly around the circumference to preserve the circular shape.
Making a birdhouse hole smaller is easier than it may seem. For simple birdhouses, you can attach a piece of balsa wood or other thin wood with an appropriately sized hole over the original entrance hole with nails or carpenter’s glue. A wooden resizer, however, may only last one nesting season, so for a more permanent solution consider using thin sheet of metal that will resist chewing and talon damage from resident birds.
Photo – Birdhouse Entrance © Mahalie Stackpole
Optimum Hole Sizes (Inches) for Common Birdhouse Nesting Species
|Ash-Throated Flycatcher||1 1/2|
|Black-Capped Chickadee||1 1/8|
|Carolina Wren||1 1/2|
|Downy Woodpecker||1 1/4|
|Eastern Bluebird||1 1/2|
|House Wren||1 1/4|
|Northern Flicker||2 1/2|
|Prothonotary Warbler||1 1/8|
|Purple Martin||2 1/2|
|Tufted Titmouse||1 1/4|
|Violet-Green Swallow||1 1/2|
|White-Breasted Nuthatch||1 1/4|