Birdhouse Specifications

As you are building your birdhouse, consider that different birdhouse dimensions attract different types of birds. Construction materials, ventilation, drainage, entrance hole, accessibility, and predator access will also influence how habitable a birdhouse is. Birds will choose houses they find comfortable and that will keep them safe from predators such as cats, raccoons, snakes, and other birds. Refer to the following chart, keeping in mind that birds make their own choices, without regard for charts.

Species___________Floor (in)__Height (in)__Entrance Height (in)__Entrance Diameter (in)
Robin.................................7x8...............8..................................................................
Bluebird.............................5x5...............8........................6................................1 1/2
Chickadee..........................4x4.............8-10...................6-8..............................1 1/8
Tufted Titmouse................4x4.............8-10...................6-8..............................1 1/4
Great Crested Flycatcher....6x6.............8-12..................6-10.............................1 3/4
Eastern Phoebe..................6x6...............6..................................................................
Red-Breasted Nuthatch.....4x4.............8-10....................6-8..............................1 1/4
White-Breasted Nuthatch..4x4.............8-10....................6-8..............................1 3/8
Prothonotary Warbler.......5x5................6......................4-5..............................1 1/8
Barn Swallow.....................6x6................6................................................................
Purple Martin....................6x6................6.......................1-2..............................2 1/4
Tree Swallow.....................5x5..............6-8.....................4-6...............................1 1/2
Downy Woodpecker..........4x4.............8-10....................6-8..............................1 1/4
Hairy Woodpecker............6x6.............12-15..................9-12..............................1 1/2
Pileated Woodpecker........8x8.............16-24.................12-20.............................3x4
Red-Headed Woodpecker..6x6............12-15...................9-12................................2
Northern Flicker...............7x7.............16-18..................14-16............................2 1/2
Yellow-Bellied Sapsucker..5x5.............12-15...................9-12.............................1 1/2
House Wren......................4x4...............6-8.....................4-6..............................1 1/4
Carolina Wren...................4x4..............6-8......................4-6..............................1 1/2
Barn Owl.........................10x18............15-18.....................4...................................6
Eastern Screech Owl and
American Kestrel..............8x8..............12-15...................9-12................................3

Materials - Wood is durable, has good insulating qualities, and it breathes. Gourds are also breathable and make great bird houses. Because they sway in the wind, gourds are less likely to be taken over by house sparrows and starlings. Pottery, concrete, and plastic houses are durable and breathable, but must be secured tightly so they will not fall to the ground and shatter in high winds. Resist the temptation to put a metal roof on your bird house, the metal is more likely to attract predators.

Ventilation - Without air vents, birdhouses can turn into bird ovens. There are two ways to provide ventilation: leave gaps between the roof and sides of the box, or drill 1/4" 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. You can assure proper drainage by cutting away the corners of the box floor and by drilling 1/4 inch holes in the box floor. Nest boxes will last longer if the floors are recessed about 1/4 inch.

Entrance Hole - Place the entrance (and exit) 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 for them to grab onto.

Accessibility - Birdhouses should be easily accessible so you can see how your birds are doing and when the time comes, to clean out the house. Boxes that open from the top and the front provide the easiest access and are less likely to disturb nesting birds. While side- and front-opening boxes are convenient for cleaning and monitoring, they have one drawback: the nestlings may jump out.

Limiting Predator Access - Never put up a birdhouse with a perch below the entrance hole. Perches offer starlings, house sparrows, and other predators a convenient place to wait for lunch. Proper box depth, roof, and entrance hole design will help minimize predator (raccoons, cats, opossums, and red squirrels) access. Sometimes all it takes is an angled roof with a three-inch overhang to discourage mammals. The entrance hole is the only thing between a predator and a birdhouse full of nestlings. By itself, the 3/4" wall isn't wide enough to keep out the arm of a raccoon or house cat. Add a predator guard a 3/4 inch thick rectangular wood block, to thicken the wall, and you'll discourage sparrows, starlings, and cats.

For more information, visit the US National Fish & wildlife Service webpage: http://library.fws.gov/Bird_Publications/house.html#5aDESIGN