When it comes to building and placing birdhouses, one of the most important considerations is the hole size. The diameter of the entrance hole is a key factor in determining which species of birds will be attracted to and able to enter and nest in your birdhouse. Selecting the appropriate hole size can make all the difference in whether or not your birdhouse is successful in hosting nesting birds.

Why Hole Size Matters

The hole size on a birdhouse serves multiple important purposes:

It regulates which species can fit through and nest. Birds can only use holes that are appropriately sized for their bodies. Hole sizes that are too small will exclude birds that can’t fit through. Ones that are too large may allow predators or larger, aggressive birds access.
It helps deter predators. The right sized hole can prevent larger animals from entering a birdhouse and preying on eggs, nestlings or adult birds.
It provides insulation and climate control. A hole size that is well matched to the nesting bird helps contain warmth and maintain a stable microclimate inside the box.
It prevents overcrowding. A properly sized entrance hole limits the number of adult birds that can enter and reduces competition over the nest site.
It allows a secure grip for fledglings. The diameter needs to be small enough for young birds to grasp the edge as they prepare for their first flight.

For these reasons, taking the time to drill a hole that matches the target species is an important step in creating an appealing and functional birdhouse.

Common Hole Sizes by Species

The optimal hole diameter depends entirely on the species of bird you intend to attract. Here are some of the most common hole sizes used for popular backyard birds:

1 – 1 1⁄4 inches – Chickadees, Nuthatches, Titmice

Species suited for this size include: Black-capped Chickadee, Tufted Titmouse, White-breasted Nuthatch.
1 – 1 1/4 inches is the best size to use if you want to attract small songbirds like chickadees and nuthatches.
Make sure the interior floor space appropriately matches the hole size (see floor dimensions below).
Be sure to monitor for European Starlings, as they may also attempt to enter a hole of this size. Installing a restricting plate around the hole can help prevent starlings.

1 1⁄2 inches – Eastern & Mountain Bluebirds

The Eastern Bluebird and Mountain Bluebird arecavity nesters that will readily accept a 1 1⁄2 inch opening.
Monitoring may be needed with this size to ensure European Starlings do not take over the birdhouse. Starling-resistant features can help.
A 1 1⁄2 inch hole works well for bluebirds in areas where they are the target species. House Sparrows may also attempt to enter holes of this size.

1 1⁄2 – 2 inches – Tree Swallows, Violet-green Swallows, House Wrens

This is an ideal hole diameter for Tree Swallows, Violet-green Swallows, and House Wrens.
Tree Swallows and Violet-green Swallows are highly social swallow species that nest in cavities and boxes near water. They will readily accept birdhouses with 1 1⁄2 – 2 inch openings.
House Wrens will also utilize a hole of this size. They are very active foragers that consume large quantities of insects.
Monitor boxes with 1 1⁄2 – 2 inch holes for European Starlings that may compete for nesting sites. Using starling-deterrent features can be beneficial.

2 1⁄2 – 2 3⁄4 inches – Northern Flickers, Red-Bellied Woodpeckers, Downy Woodpeckers

Woodpeckers such as Northern Flickers, Red-bellied Woodpeckers, and Downy Woodpeckers prefer a larger hole size from 2 1⁄2 – 2 3⁄4 inches.
A 2 1⁄2 inch hole is ideal for Northern Flickers, whereas Red-bellieds and Downy Woodpeckers do well with 2 3⁄4 inches.
Woodpeckers will excavate their own openings in time, so providing them with a starter hole in this size range helps attract them more quickly to a nest box.
Woodpeckers are less likely to nest in boxes designed for smaller birds because of the hole size limitations.

Larger Holes – American Kestrels, Barn Owls, Geese, Ducks

Even larger holes are necessary for species such as American Kestrels, Barn Owls, Wood Ducks, Common Goldeneyes, Hooded Mergansers, and geese.
Entry holes for American Kestrels typically range from 3 – 3 1⁄2 inches as these small falcons are cavity nesters. They favor holes just large enough for them to swoop directly into.
Barn Owls use extremely large cavities and will accept birdhouse openings 6 – 9 inches wide. Platform perches and use of predator guards are also recommended for Barn Owl boxes.
Wood ducks and Common Goldeneyes utilize birdhouses with a racetrack entrance about 3 x 4 inches up top.
A hole about 4 inches wide works well for Hooded Mergansers. Additional reinforcement provides needed sturdiness.
Goose nest boxes also require a 4 inch opening but need extra durability and strength.

In summary, sizing the entrance hole properly for the desired bird species is an essential step in creating an effective birdhouse. Follow the recommended diameters carefully, and monitor for any unwanted visitors. Adjustments to the hole may be needed over time depending on your experience and observations. Proper hole sizing paired with suitable interior space and other features will lead to greater success attracting specific nesting birds.

How to Choose the Right Hole Size

When deciding on hole size for your birdhouse, consider the species of birds you want to attract, the sizes of those birds, and whether other animals are likely to inhabit the area. Follow these tips:

Identify your target bird species and research recommended hole sizes specific to each species. This ensures the hole will accommodate them.
Consider the average weight and heights of adult birds to make sure they can comfortably fit through the hole. Measure width at the wings and body.
Avoid very large holes that expose birds and eggs to predators. Openings should be snug for the species.
If multiple target species are similar in size, choose a hole size acceptable for all. For example 1 1⁄4 inches works for chickadees, titmice, nuthatches.
In public areas, smaller holes discourage European Starlings which are aggressive cavity invaders. Monitoring for starlings is important.
Wooden restrictor plates or collars placed around the entrance can further deter larger, unwanted birds.
Allow fledglings room to exit but not excess space around their bodies. The hole provides them needed support.
Clean holes with clean cuts using a utility knife, hole saw drill bit, or wood auger bit in a drill. No splinters.
Take the biology of species and nest site competition levels into account depending on your location.

Proper birdhouse hole dimensions make a big difference in attracting desired nesting species. Consult bird guides, research your local birds’ sizes, observe bird behavior, and use appropriate hole diameters. Sizing the entrance hole thoughtfully helps create an enticing cavity for your backyard birds.

Floor Space Dimensions Based on Hole Size

In addition to entrance hole diameter, an appropriately sized interior floor is also vital in birdhouses. The dimensions should match the birds using it.

For 1 – 1 1⁄4 inch holes, provide:

Floor Dimensions – 4 x 4 inches
Cavity Depth – 6 – 8 inches

This interior space works well for Black-capped Chickadees, Tufted Titmice, White-breasted Nuthatches and other small songbirds. It provides sufficient room for their nests and movement in and out of the entry hole without being too large.

For 1 1⁄2 inch holes, provide:

Floor Dimensions – 5 x 5 inches
Cavity Depth – 8 – 12 inches

Eastern & Mountain Bluebirds require slightly larger floor space than smaller songbirds. This gives them adequate room for their nests and for maneuvering in and out of the hole.

For 1 1⁄2 – 2 inch holes, provide:

Floor Dimensions – 6 x 6 inches
Cavity Depth – 6 – 12 inches

Tree Swallows, Violet-green Swallows, and House Wrens can utilize cavities with the above dimensions. Allowing enough interior room for nests and entering and exiting the hole is key.

For 2 1⁄2 – 2 3⁄4 inch holes, provide:

Floor Dimensions – 7 x 7 inches
Cavity Depth – 16 – 18 inches

Northern Flickers, Red-bellied Woodpeckers, and Downy Woodpeckers need larger floor spaces than other backyard birds. Nesting materials fill more space, and the birds are larger bodied.

For Larger Birds:

Follow specific recommendations for the species.
Larger dimensions are needed for American Kestrels, wood ducks, geese, and other birds using holes over 3 inches wide. Consult bird books and online references for details.

Matching the floor area and cavity depth to the bird utilizing the entrance hole is critical. Floor space that is too small will deter birds, while that too large makes them feel exposed. Follow guidelines to ensure appropriate fit.

Locating the Entrance Hole

Proper placement of the entrance hole matters too for birdhouses. Consider the following recommendations:

Position the hole centered near the top of one of the birdhouse’s sides, unless a back entry is needed.
Face the hole away from prevailing winds, and angle it downwards slightly to deflect precipitation.
Make sure the hole aligns properly with the designated floor space inside.
Allow adequate space above the hole for ease of entry and exit.
For hanging boxes, the hole can be located higher. Leave room for perching and entering.
Avoid situating the hole near feeder perches which may aid predators.
East or southeast facing holes provide early sun. North or northeast give more shade.
For trail or walkway boxes, face holes away to minimize disturbances.
Enable clear entry and exit flight pathways free of obstacles like branches.
Prevent unused holes by plugging them or making covers. Blocking unused holes reduces drafts and predation.

Take the hole position into careful consideration for optimal use by nesting birds. Ensure the location allows straight forward access in and out of the cavity. This contributes to birdhouse success.

Hole Shape Options

The majority of birdhouse entrance holes are round or oval. However, there are some creative shape options to consider:

Crescent Moon Shape

Works well for nest boxes targeting Eastern Bluebirds.
The tapered shape deters larger European Starlings from entering.
Cut a 1 1⁄2 inch tall by 2 3⁄4 inch wide crescent moon using a jigsaw or bandsaw.

Rectangle Shape

Instead of a circular hole, a horizontal rectangle about 1 x 2 inches can be used.
Allows chickadees easier entry and exit without contorting their short tails.
Decreases likelihood of starlings attempting to gain entrance.

Half-Circle Arch Shape

Cut a half circle that joins the floor and front wall of the nest box.
Works for woodpeckers which need extra space due to their long tail feathers.
Provides shelter and tail support as they enter and exit the cavity.

Creative Shapes

Customized shapes like diamonds, stars, hearts or others may be cut.
Can serve an aesthetic purpose while still appropriately fitting target species.
Use durable, smooth wood 1 – 2 inches thick to maintain hole integrity over time.

While a basic round hole is most common, hole shapes can be tailored to certain species. Consider branching out beyond a circle if other shapes offer improved benefits.

Perches at Birdhouse Holes

Sometimes external perches may be present around the entrance holes of birdhouses. Evaluate including a perch based on these factors:

Advantages

Perches provide a landing spot for birds coming and going from the cavity, especially helpful for inspecting sites.
They offer a place for male birds to sing from to attract mates and declare the nest site.
Can enable juveniles to develop flight skills while safely remaining close to the entrance.
Extra space for adults to keep watch for intruders trying to enter their box.

Disadvantages

Predators like squirrels and cats may take advantage of the perch as an access point.
Species such as chickadees prefer not to have perches which may allow easier nest predation.
Perches directly around the hole may facilitate stakeouts by aggressive birds.
Fledglings may prematurely venture out of the cavity onto the perch before fully ready.

Tips on Perches

Only include perches if targeting open-cavity nesters that utilize them naturally like Eastern Bluebirds.
Position perches a few inches below or to the side of holes, not directly surrounding it.
Flat, thin, roughened wooden edges or plastic shelf brackets work well to discourage predators.
Ensure drainage so perches don’t pool water and increase chances of disease.
Monitor use. Remove perches if issues develop with problematic animals utilizing them.

Take the natural history and needs of the target species into account when deciding on entrance hole perches. Monitor for unwanted impacts and adjust as needed.

Restrictor Plates and Predator Guards

Using metal or wooden plates with smaller center holes around the entrance hole of a birdhouse can help deter larger birds while still allowing desired species access.

Benefits Include:

Discourage European Starlings from entering and taking over nest sites.
Prevent larger aggressive species from displacing smaller native birds.
Stop small predators like squirrels and raccoons from accessing nests.
Funnel birds through the center hole to reduce fighting at the opening.
Allow monitoring of nest by providing a peeking spot.

Tips for Proper Use:

Size the center hole appropriately for targeted nesting species.
Ensure the plate fully surrounds the entrance hole like a picture frame.
Attach plates snugly to the birdhouse with wood screws to prevent prying off.
For starling deterrence, center holes should be 1 – 1 1⁄4 inches.
Metal guards are more durable. Plastic can work too.
Check that plates don’t impede the open/close swinging of the front birdhouse panel during monitoring.

Used properly, restrictor plates reinforce correct hole sizes. They act as physical barriers keeping unwanted species out while allowing desired birds to access the nest box. Being selective helps achieve nesting success.

Nest Box Placement for Birdhouse Success

Just like a new home for a person, the location of a birdhouse significantly contributes to its appeal and functionality for nesting birds. Careful placement relative to trees, buildings, feeders and other features can entice target species and lead to greater occupancy and reproductive success. Consider the following ideal placement tips:

Height Recommendations

Mounting a birdhouse at the proper height helps attract birds and protects them:

Install birdhouses for smaller species like chickadees and titmice 5 to 8 feet high.
Larger songbirds like Robins and Phoebes do well at heights of 6 to 10 feet.
For Bluebirds, Tree Swallows, House Wrens and other cavity nesters, mount boxes 5 to 15 feet up.
Woodpeckers, owls and Wood Ducks need higher boxes usually 15 to 30 feet up.
Place nests for water birds over water at optimal depths and distances from shore.
In wooded areas, go higher to discourage predators. More clearance in open areas.
Measure heights conservatively based on average snow depths in your region in winter.
Ensure heights allow easy access for cleaning and monitoring nest boxes.
Use gradually sloped mounting poles and predator guards to limit climbing access.

Proper birdhouse height keeps contents safer while allowing the adult birds easy, natural access. Follow guidelines for your target species.

Favorable Locations and Habitats

Certain spots around a property tend to be more favorable for attracting birds to utilize nesting boxes:

Trees – Mount boxes on mature, shade trees without many low branching limbs which allow predators to access boxes more easily. dead trees provide good cover. Oak, maple and birch work well. Face cavity away from prevailing winds and sun.

Buildings – Barns, garages, sheds and houses make excellent spots to erect birdhouses, often with added protection. Install below overhanging eaves for added shelter. Face hole away from windows with high activity levels.

Fence Posts – Existing fence posts along property boundaries work nicely for mounting single birdhouses. Space multiple boxes at least 25-30 feet apart.

Water – Nest boxes near ponds, lakes, rivers or streams appeal to species like wood ducks, flycatchers and swallows that feed over water. Place boxes in adjacent trees pointing back towards water.

Fields & Meadows – For birds like Bluebirds and Tree Swallows, locate nest boxes within or along edge of open fields. Site boxes on wooden posts or isolated trees. Avoid busy areas.

Place nest boxes in natural habitats fitting to the preferred surroundings of the target species. This greatly increases chances of discovery and occupancy.

Distance from Buildings and Feeding Areas

When situating birdhouses near buildings, keep these spacing guidelines in mind:

Position nest boxes 10 to 30 feet away from buildings, but still in view. Provides a happy medium offering visibility but avoiding too much disturbance.
Face the entrance hole perpendicular or angled away from doors, windows and high traffic areas. This minimizes endangering nesting birds.
Do not place boxes directly above pathways frequently used by people, pets or machinery.
Mount boxes on the sides of buildings rather than under eaves to help

Birdhouse Hole Sizes