Appropriateness of size considerations are vital to bird house success. First to attract the right birds and distract the wrong ones. Next to ensure that the parents and nestlings are safe from predators. And finally correct temperature and ventilation.

How elaborate you make your bird house depends on your personal sense of aesthetics. For the most part, all the birds care about is their safety and the right dimensions: box height, depth and floor, diameter of entrance hole, and height of hole above the box floor.

Nesting Box Dimensions

Minimize the Chance of Predator Access

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 bird house 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.

Refer to the above chart, keeping in mind that birds make their own choices, without regard for charts. So don’t be surprised when you find tenants you never expected in a house you intended for someone else.

Ventilation, Temperature and Drainage

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

Without air vents, boxes 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.

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 by drilling 1/4 inch holes in the box floor. Nest boxes will last longer if the floors are recessed about 1/4 of an inch.

Entrance Hole Sizes

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

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Part of being a responsible bird house landlord is your willingness to look after your wild tenants. If you monitor your bird houses every week and evict unwanted creatures such as house sparrows, starlings, rodents, snakes, and insects, you’ll have much more success in the long run.

For your own safety, please be careful when you inspect those wild bird houses. You may find something other than a bird inside! Don’t be surprised to see squirrels, a mouse, a snake, or a nest of bees or wasps. As for insects, inspect the house for fleas, mites, larvae, and lice on the bottom panel.

If you find insects or parasites try to temper your first reaction to grab the nearest can of insect spray. If you use insect spray use only insecticides known to be safe around birds. An easy check is the label on the can; 1% rotenone powder or pyrethrin spray are known to be safe for wild birds. If wasps persist over time it will help to coat the inside top of the box with bar soap.

Here’s how to check your nesting boxes or bird houses:

Watch the nest for awhile. If you don’t see or hear any birds, go over and tap on the box. If you hear bird sounds, open the top and take a quick peek inside. If everything’s okay, close the box. If you see problems (parasites or predators), remove them and close the box.

This is one time when a bird house with easy access comes in handy! 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. On the other hand, it’s absolutely impossible to open a box from the bottom without the nest falling out. Side and front opening boxes are convenient for cleaning and monitoring but they have one major drawback: the nestlings may jump out.

If this happens, don’t panic. Just 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 an urban legend, old wive’s tale or myth. Most birds have a terrible sense of smell.

If you clean out your nesting box after each brood has fledged, several pairs may use the nest throughout the summer. Many cavity nesting birds will not nest again in a box full of old nesting however so a good cleaning says “We’re open for business!”

In the fall, after you’ve cleaned out your houses for the last time, you can put them in storage or leave them out. Gourds and pottery nests will last longer if you take them in for the winter. You can leave your purple martin houses up, but be sure to plug the entrance holes to discourage starlings and house sparrows habitating the bird house before the martins return.

Leaving your wood and concrete houses out provides shelter for birds during the harsh months as well as flying squirrels.

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Nesting materials can also be hung in a wire cage. These cages are especially popular in the spring when birds will come and choose those that are suitable for them. Try thin strips of clothing or rags, small twigs, wool, and even feathers.

There are more than two dozen birds in the USA and Canada that are happy to nest in bird houses. The most important measurement in any nesting box and the birds it attracts is the diameter of the entrance hole. An inch and a half is small enough to deter starlings. Starlings and house sparrows have been known to kill many baby birds as well as adults sitting on the nest.

Nesting birds have problems with other predators as well. The easiest way to discourage predatory cats, snakes, raccoons, and chipmunks is to mount the nesting box on a metal pole, or pick up a metal predator guard for wood post mounts.

Here are a few of the most common, and preferred, wild birds that you can help in your neighborhood:

Bluebirds – If you put up a bluebird house near an open field, orchard, park, cemetery, or golf course, you’ll have a very good chance of attracting a pair of nesting bluebirds. These beautiful and beneficial birds prefer nest boxes on a tree stump or wooden fence post, elevated to between three and five feet high. Bluebirds will also nest in the old nesting holes of woodpeckers so if a dead or dying tree isn’t posing any troubles and you see a woodpecker hole in the trunk you might like to leave it standing – at least until autumn.

Robins – Robins are our largest birds of the thrush family. They prefer to build their nest in the crotch of a tree or a nesting platform. These birds like to nest six feet or higher up in a shaded area. We get them under the overhang of our hay shed and front porch. Creating “mud puddles” nearby assists robins in the spring, as they use mud to line their nests.

Chickadees, Nuthatches, and Titmice These smaller birds share the same food, feeders, and habitats. If you put a properly designed nest box in a wooded yard, at least one pair is sure to check it out and one may stay to grace you with babies that return year after year! Chickadee nesting boxes are perfect at 6′ elevation. Nuthatches can be between 5-6′ elevation. You can hang them from limbs or secure them to tree trunks. The entrance hole should be 1-1/8″ to attract chickadees yet exclude house sparrows. Encourage these birds to stay in your yard by continuing to fill your suet and peanut feeders through the summer and keep a bird bath or dripper going at all times for them.

Brown Creepers and Prothonotary Warblers – Brown creepers generally like to nest behind the curved bark of tree trunks. If your yard or garden is heavily wooded, slab bark houses will appeal to creepers. Prothonotary warblers also prefer slab bark houses, but they will only nest in boxes positioned over water.

Wrens – Wrens don’t seem to be very picky about where they nest and are a beautiful wild bird to watch rear their young. Try nest boxes with a 1″ x 2″ horizontal slot (larger for the Carolina wren) instead of the standard circle shape entrance as these rectangular openings are easier for the wrens to use. Wrens are notorious for filling up any conceivable nest cavity with twigs, regardless of whether they end up using the nest or not. Since male house wrens build several nests for the female to choose from, hang several nest boxes at eye level on partly sunlit tree limbs. Wrens have always been one of my personal favorites because they are not ‘put off’ by humans being near their homes so they can be poisitioned quite close to the house and are perfect for smaller lots.

Tree and Violet-green Swallows – Beautiful white-bellied birds with iridescent blue-green backs and wing, are a joy to have nearby. They’re also beneficial as they are insect eaters. Tree swallows prefer nest boxes attached to dead trees. Space the boxes seven feet apart, the ideal setting is on the edge of a field near a lake, pond, or river. The gorgeous violet-green swallows from the west, nest in forested mountains. Nesting boxes placed on large trees in a semi-open woodland attracts them.

Barn Swallows and Phoebes – Barn swallows and phoebes are another easy and beneficial bird to attract. It’s their nesting behavior, not their plumage or song, that you’ll fall in love with over and over again. These birds tend to nest where you’d rather not have them: on a ledge right over your front door or at the far entrance to the barn. To avoid a mess by your door, offer the birds a nesting shelf nearby where it’s more convenient and you may get lucky if they prefer it. These birds are not bothered by human activity nearby.

Purple Martins – Many people want martins because, it’s been said, each bird can eat 2,000 mosquitoes a day. While it’s true that Purple Martins eat flying insects, don’t expect purple martins to wipe out your mosquito population. Martins actually prefer dragonflies, which are far more benefical for mosquito control as they prey on mosquito larvae. Don’t cross martins off your list because they don’t live up to their mosquito killing reputation though, these gregarious wild birds from the swallow family put on quite a show for human observers! Martins prefer to nest on the edge of a pond or river, surrounded by a field or lawn. As they nest in groups, the houses you may purchase for a colony are often the most elaborate. Look for a house with a minimum of four large rooms, 6 or more inches on all sides, with a 2 1/2″ entrance hole. You might also like to check out bird house gourds as purple martins seem to prefer these.

Flycatchers – The Great Crested Flycatcher and its western cousin, the Ash-Throated Flycatcher, are common in wooded suburbs. Their natural nesting sites are abandoned woodpecker holes (see note on dead or dying trees above). Flycatchers may nest in a bird house if it’s elevated about ten feet up, in a tree in an orchard, or at the edge of a field or stream.

Woodpeckers – Beautiful and funny wild birds that are easily attracted with suet feeders. However, only the flicker and the red-bellied woodpeckers are likely to use a nesting box to rear their young. These birds prefer a box with roughened interior and a floor covered with a two-inch layer of wood chips or coarse sawdust. Flickers are especially attracted to nest boxes filled with sawdust, which they “excavate” to suit themselves. For best results, place the box in direct sunlight.

Owls – Owls seldom build their own nests. The Great horned Owl and the Long-Eared Owls prefer abandoned crow and hawk nests. Other owls (barred, barn, saw-whet, boreal and screech) will nest in tree cavities and bird houses though. Barn owls are best known for selecting nesting sites near farms. Where trees are sparse, these birds will nest in church steeples, silos, and hay mows. If you live near a farm or a golf course, try fastening a nest box about 15 feet up on a tree trunk to see if you can attract them onto your property (they’re great to keep the rodent population down!). Screech owls prefer abandoned woodpecker holes at the edge of a field or neglected orchard. They will readily take to a nesting box if you line it with an inch or two of wood shavings. If you clean the box out in late spring after the young owls have fledged, you may attract a second tenant–a kestrel. Trees isolated from larger tracts of woods have less chance of squirrels taking over, and often ruining the nesting box.

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