Some species of birds are known as cavity dwellers, which means they only build their nests inside a cavity, usually a hollow inside the trunk of a tree. Manmade birdhouses (also called a nest box) provide a good simulation for a tree cavity, and have been credited for bringing the Eastern Bluebird back from the brink of extinction.Dimensioning is an important aspect of preparing a nest box for a particular species. It is desirable for the hole to be just large enough for the desired species, but too small for a larger, more aggressive cavity dweller. Studies conducted several decades ago helped determine the inside box dimensions most acceptable to each species. Like people, birds do not have any hard rules about what they will live in, but the closer a box size is to the preferred dimension, the more likely it will be to attract the desired species. Fir, pine, cedar, and plywood all make good nest box construction materials. Consider using scrap lumber or previously used wood as an environmentally sound means of recycling it. A birdhouse should never be constructed with wood which has been chemically treated to protect it against rotting. A few one-half inch holes near the top of the box on each side will provide a means for the box to ventilate by natural convection. It is also a good idea to drill some small holes in the bottom corners to allow drainage of any water that gets inside. The birdhouse should be place in a naturally shaded location, such as on the north side of a tree truck. Consider using aluminum nails if you are nailing to the side of a tree, because the nails will neither rust nor damage saw blades that may strike them later. Every birdhouse should be constructed in such a way that it can easily be opened during the month of March for removal of old nesting material and the parasites that accompany it. Use gloves while handling this material, and beware of other critter that may be hiding inside: snakes, rodents, & squirrels. Having a hinged top with a hook lock is an easy solution. A perch looks cute on a birdhouse, but contrary to popular belief birds do not need them. Cavity dwelling birds are equipped with very strong claws for hanging onto vertical surfaces. The danger of having a perch or of mounting a birdhouse on a tree immediately above a limb is that they provide a platform for cats, raccoons, opossums, rats and non-cavity dwelling birds to destroy the nest. Crow and jays cannot easily hold onto the side of a box and would be more apt to leave it undisturbed.
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Nest Box Dimensions |
| Species | Floor (inches) | Depth of Cavity at Front (inches) | Height of Center of Entry Hole (inches) | Diameter of Entry Hole (inches) | Approx. Height of Box Above Ground (feet) | Preferred habitat & box location |
| House Wren | 4 x 4 | 7 | 5 | 1 | 6 | Open fields and thickets |
| Bewick's Wren | 4 x 4 | 7 | 5 | 1-1/8 | 6 | Open fields and thickets |
| Carolina Wren | 4 x 4 | 7 | 5 | 1-3/8 | 6 | Open fields and thickets |
| Black-capped Chickadee | 4 x 4 | 8 | 6 | 1-1/8 | 5 | Open woods and edges |
| Carolina Chickadee | 4 x 4 | 8 | 6 | 1-1/8 | 5 | Open woods and edges |
| Tufted Titmouse | 4 x 4 | 8 | 6 | 1-1/4 | 5 | Open woods and edges |
| Red-brested Nuthatch | 4 x 4 | 8 | 6 | 1-1/3 | 12 | Open woods and edges |
| White-breasted Nuthatch | 4 x 4 | 9 | 7 | 1-1/4 | 12 | Open woods and edges |
| Downy Woodpecker | 4 x 4 | 10 | 8 | 1-1/4 | 12 | Forest openings and edges |
| Hairy Woodpecker | 5.5 x 5.5 | 14 | 11 | 1-3/4 | 20 | Forest openings and edges |
| Golden-fronted Woodpecker | 6 x 6 | 14 | 11 | 2 | 8 to 20 | Forest openings and edges |
| Pileated Woodpeckers | 12 x 12 | 24 | 19 | 4 | 15 to 25 | Mature forests |
| Red-headed Woodpecker | 5.5 x 5.5 | 14 | 11 | 1-3/4 | 20 | Forest openings and edges |
| Red-bellied Woodpecker | 6 x 6 | 14 | 11 | 2 | 20 | Forest openings and edges |
| Northern Flicker | 7 x 7 | 16 | 13 | 2-1/2 | 15 | Farmland, open country. Use a tree will shrubs underneath. |
| Tree Swallow | 5 x 5 | 6 | 4 | 1-1/2 | 5 | Open land near water |
| Barn Swallow | 6 x 6 | 6 | 3 sides open | 3 sides open | 8 | Open land |
| Purple Martin | 6 x 6 | 6 | 2-1/2 | 2-1/2 | 17 | Pastures, fields, golf courses |
| Eastern Phoebe | 6 x 6 | 6 | 3 sides open | 3 sides open | 8 | Wheltered ledge over water, under brideg or on building. |
| Ash-throated Flycatcher | 6 x 6 | 12 | 8 | 1-3/4 | 6 to 20 | Open, semi-arid country |
| Great Crested Flycatcher | 6 x 6 | 10 | 7.5 | 2 | 10 | Open woods and edges |
| American Robin | 7 x 7 | 8 | 3 sides open | 3 sides open | 6 | Open areas; side of house is a good place to mount box. |
| Eastern Bluebird | 5 x 5 | 9 | 7 | 1-1/2 | 4 | Open land with scattered trees |
| House Finch | 6 x 6 | 6 | 4 | 2 | 8 | Back yards and porches |
| American Kestrel | 8 x 8 | 16 | 13 | 3 | 20 | Open fields, wooded edges, farmlands |
| Barred Owls | 14 x 14 | 28 | 23 | 8 | 15 to 30 | Mature bottomland forests |
| Saw-whet Owl | 7 x 7 | 15 | 12 | 2-1/2 | 15 | Forest clearings and edges |
| Screech Owl | 8 x 8 | 16 | 13 | 3 | 12 | Farmland, orchards, woods |
| Barn Owl | 18 x 20 | 18 | 4 | 6 | 18 | Farmland; high on barn, silo, or large tree; entrance hole shoud be four inches above floor. |
| Bufflehead | 7 x 7 | 18 | 14 | 3 | 8 to 15 | Wooded lakeshores and marshes |
| Wood Duck | 10 x 10 | 21 | 16 | 4 | 5 feet over water; 15 feet over land | Wooded rivers or mashes |
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