If you’re thinking about building a bird house, it’s important to think about what types of birds you are looking to provide housing for. That decision will impact two additional key decisions: the size of the house and the size of the hole that birds access the house through.
The variation ultimately isn’t very wide for most songbirds, which don’t need much room to sneak into a bird house, but if you’re looking to build a house for ducks or screech owls, for example, you’ll need to make your entry a little bit larger.
Most songbirds will need an entryway between just over an inch and just under two inches in diameter. Let’s take a look at the requirements for some of the most common bird house users.
Key Takeaways
- Match entry size to bird type: Different birds need different entry hole sizes for their houses. For example, bluebirds need holes from 1 1/2 to 1 9/16 inches, while larger birds like woodpeckers and ducks need larger ones.
- Control invasive species: Using the right-sized entry hole can help keep out unwanted birds like house sparrows and European starlings, which can outcompete native birds for nest space.
- Follow recommendations: Stick to specific guidelines for each bird species to ensure your bird house is both effective and safe. For instance, the North American Bluebird Society has detailed recommendations for bluebird house entry sizes.
Bird House Entry Size
Bluebirds
Bluebirds are one of the most popular birds for which bird houses are built. It doesn’t take going too far back into most birders’ memory banks to remember a time when bluebird populations were in serious trouble, with habitat decreasing and available nesting space dwindling due to invasive cavity nesters like house sparrows and European starlings.
Fortunately, Eastern bluebird populations in particular are on the recovery path, although mountain bluebirds haven’t been so fortunate thus far.
If you want to be part of these species’ continued survival and own property with a suitable habitat where bluebirds may nest, the North American Bluebird Society recommends the following hole sizes:
- Eastern bluebird: 1 1/2-inch round hole, a 1 3/8 x 2 1/4-inch vertical oval hole or 1⅛-inch horizontal slot entrance
- Western bluebird and mountain bluebird: 1 9/16-inch round opening or 1 3/16-inch slot entrance.
Keep in mind that the bigger you make the hole, the higher the chance that European starlings could sneak into houses not meant for them. These invaders require an entry of at least 1 9/16 inches, according to the Cornell Lab of Ornithology’s NestWatch.
Wrens and Chickadees
North America’s most common and widespread wren is the house wren. Of all native songbird species, they’re probably the one for which you could get away with the smallest bird house entry.
- You could still put up a bird house with a 1 1/2-inch hole and see what birds show up as long as you don’t mind these other native birds.
Keep in mind that bigger cavities exceeding 1 ½ inches may allow entry to starlings, an unwanted native species that competes with beloved native birds for housing. House sparrows, another invasive cavity stealer, can sneak into smaller holes, but you could exclude them by dropping down even lower to a 1 1/8 or 1 1/16-inch hole that’s only big enough for a wren or black-capped chickadee.
Other wren species may require a bigger nest box entry.
Nuthatches and Titmice
Nuthatches and titmice are just bigger than chickadees and wrens, so you’ll need a slightly bigger hole. You probably can’t exclude house sparrows with size if you’re looking to include nuthatches or titmice — though you can remove them other ways. Removing or destroying house sparrow nests is a personal choice.
”It is the responsibility of every bluebird landlord to ensure that no house sparrows fledge from their boxes. It is better to have no nestbox than to have one that fledges house sparrows,” says the Bluebird Society, referencing that these birds may harass or attack native birds in competition for nest sites.
- Back to bird house hole sizes, nuthatches and titmice aren’t as big as bluebirds and could fit into a hole of 1 1/4 or 1 1/3 inches, but a 1 1/2-inch hole for bluebirds will allow a wider range of songbirds to utilize the bird house.
Tree Swallows
Tree swallows are not quite as big as bluebirds, but they often utilize the same holes, as they share similar habitat. If you walk through an open field with nest boxes in the eastern United States, you may find that bluebirds aren’t the only blue birds using the homes provided by land managers.
You can make your bird house hole about 1 1/2 inches for tree swallows, the same as you would for eastern bluebirds.
Woodpeckers
Woodpeckers are known for drilling their own holes in trees to nest in, but they may also use a bird house.
Downy woodpeckers, the smallest North American woodpecker, are of similar size to other songbirds already discussed and could sneak into a bird house the size of a titmouse or nuthatch, but the rest are going to need bigger holes.
- Northern flickers, red-headed woodpeckers, and hairy woodpeckers will require holes of at least two inches or more. Northern flickers need an entrance hole of 2 1/2 inches, for example, according to the Wildlife Center of Virginia, which also suggests a 3-inch nest box for American kestrels, North America’s smallest falcon.
Size for Ducks and Owls
While they may seem too large to nest in tree cavities, there are a number of ducks that you can also host with a nest box. The most popular among them is probably the common and widespread wood duck, though goldeneyes, buffleheads, and two merganser species will also potentially utilize nest boxes.
Hooded mergansers are similar in size to wood ducks, but the larger common merganser will require an even bigger entryway.
- Ducks Unlimited suggests a 4 1/2 by 3 1/2-inch oval hole for wood ducks and a 4 1/2 by 5-inch entry for common mergansers.
Screech owls will require a similar size nest hole as American kestrels, at three inches.
What Other Species Use Nest Boxes?
Other wrens like Bewick’s and Carolina wrens, flycatchers like the great crested flycatcher, and purple martins are among the other birds that may utilize human-provided nest boxes.
If you have another cavity-nesting bird near you that you’re hoping to attract, do some additional research about that species to learn not just bird house size or entrance hole size, but also the type of habitat needed to support that species.
Happy birding!