Nest Box Dimensions

Species Box floor (inches) Box height (inches) Entrance height (inches) Entrance (inches) Placement diameter height (feet)
American Robin[1] 7×8 8 —— ——
Eastern & Western Bluebirds 5×5 8-12 6-10 1½ 4-6
Mountain Bluebird 5×5 8-12 6-10 1½ 4-6
Chickadee 4×4 8-10 6-8 1⅛ 4-15
Titmouse 4×4 10-12 6-10 1¼ 5-15
Ash-throated Flycatcher 6×6 8-12 6-10 1½ 5-15
Great Crested Flycatcher 6×6 8-12 6-10 1¾ 5-15
Phoebe[1] 6×6 6 —— —— 8-12
Brown-headed/Pygmy/
Red-breasted Nuthatch 		4×4 8-10 6-8 1¼ 5-15
White-breasted Nuthatch 4×4 8-10 6-8 1⅜ 5-15
Prothonotary Warbler 5×5 6 4-5 1⅛ 4-8
Barn Swallow[1] 6×6 6 —— —— 8-12
Purple Martin 6×6 6 1-2 2¼ 6-20
Tree and Violet-Green Swallows 5×5 6-8 4-6 1½ 5-15
Downy Woodpecker 4×4 8-10 6-8 1¼ 5-15
Hairy Woodpecker 6×6 12-15 9-12 1½ 8-20
Lewis’s Woodpecker 7×7 16-18 14-16 2½ 12-20
Northern Flicker 7×7 16-18 14-16 2½ 6-20
Pileated Woodpecker 8×8 16-24 12-20 3×4 15-25
Red-Headed Woodpecker 6×6 12-15 9-12 2 10-20
Yellow-bellied Sapsucker 5×5 12-15 9-12 1½ 10-20
Bewick’s/House Wrens 4×4 6-8 4-6 1¼ 5-10
Carolina Wren 4×4 6-8 4-6 1½ 5-10
Barn Owl 10×18 15-18 4 6 12-18
Screech-Owl and Kestrel 8×8 12-15 9-12 3 10-30
Osprey 48×48 platform
Red-tailed Hawk/Great Horned Owl 24×24 platform
Wood Duck 10×18 10-24 12-16 4 10-20

[1]Use nesting shelf, platform with three sides and an open front

Now that you have the correct dimensions for your bird house, take a look at how to make it safe: ventilation, drainage, susceptibility to predators, and ease of maintenance.

Ventilation

You should provide air vents in bird boxes. There are two ways to provide ventilation: leave gaps between the roof and sides of the box, or drill ¼ inch holes just below the roof.

Drainage

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 drilling ¼-inch holes. Nest boxes will last longer if the floors are recessed about ¼ inch.

Entrance Hole

Look for the entrance 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 duplexes or houses that have more than one entrance hole. Except for purple martins, cavity-nesting birds prefer not to share a house. While these condos look great in your yard, starlings and house sparrows are inclined to use them.

Accessibility

Bird houses should be easily accessible so you can see how your birds are doing and clean out the house. Monitor your bird houses every week and evict unwanted creatures such as house sparrows or starlings.

Be careful when you inspect your bird boxes—you may find something other than a bird inside. Don’t be surprised to see squirrels, mice, snakes or insects. Look for fleas, flies, mites, larvae and lice in the bottom of the box. If you find insects and parasites, your first reaction may be to grab the nearest can of insect spray. If you do, use only insecticides known to be safe around birds: 1 percent rotenone powder or pyrethrin spray. If wasps are a problem, coat the inside top of the box with bar soap.

Here’s how to check your nest boxes for unwanted visitors:

Watch the nest for 20-30 minutes. If you don’t see or hear any birds near the box, go over and tap on the box. If you hear bird sounds, open the top and take a quick peek inside. If everything is all right, close the box. If you see problems (parasites or predators), remove them and close the box.

A bird house with easy access makes the job simple. Most bird houses can be opened from the top, the side, the front or the bottom. Boxes that open from the top and the front provide the easiest access. Opening the box from the top is less likely to disturb nesting birds. It’s impossible to open a box from the bottom without the nest falling out. While side- and front-opening boxes are convenient for cleaning and monitoring, they have one drawback: the nestlings may jump out. If this happens, don’t panic. Pick them up and put them back in the nest. Don’t worry that the adults will reject the nestlings if you handle them. That’s a myth; most birds have a terrible sense of smell.

If you clean out your nest boxes after each brood has fledged, several pairs may use the nest throughout the summer. Some cavity-nesting birds will not nest again in a box full of old nesting material.

In the fall, after you’ve cleaned out your nest box for the last time, you can put it in storage or leave it out. Gourds and pottery last longer if you take them in for the winter. You can leave your purple martin houses up, but plug the entrance holes to discourage starlings and house sparrows.

Leaving your wood and concrete houses out provides shelter for birds, flying squirrels and other animals during winter. Each spring, thoroughly clean all houses left out for the winter.

Limiting Predator Access

Proper box depth, and roof and entrance hole design will help reduce access by predators, such as raccoons, cats, opossums, and squirrels. Sometimes all it takes is an angled roof with a three-inch overhang to discourage small mammals.

The entrance hole is the only thing between a predator and a bird house full of nestlings. By itself, the ¾-inch wall is not wide enough to keep out the arm of a raccoon or house cat. Add a predator guard (a ¾-inch thick rectangular wood block with an entrance hole cut in it) to thicken the wall and you’ll discourage sparrows, starlings, and cats.