Here are some measurements for boxes for other bird species:

Be sure to buy, build, and erect nest boxes that can be cleaned out easily. These should have some sort of hinge and latch to allow humans--but not predators--to open the box for inspection.
If you live in the woods, you probably won't get Eastern Bluebirds in your nest boxes. Bluebirds prefer open areas, so your nestbox occupants will likely be other species of birds--or perhaps Southern Flying Squirrels (right)
Given a choice, face a bluebird nest box toward the east so morning sun warms the box and dries out dew. (Face it west and you run the risk of prevailing winds blowing rain into the opening.) However, if the nestbox is on the edge of a field, ignore the compass direction and face the opening toward the field.
At the end of the breeding season (about 1 September for most cavity-nesting species), many bluebird fanciers clean out all nest boxes with a wire brush. You can use a mild solution of bleach to sanitize the box. (See note below about cleaning out after fledging occurs.)
Do NOT take down nest boxes during the winter. They often are used as out-of-the-weather roosting boxes by bluebirds, nuthatches, woodpeckers, and other bird species.
Not later than 14 February (HINT: Valentines Day), check nest boxes and re-clean them if necessary. Bluebirds may spend all winter peeking into boxes and preparing for the spring mating season. Established breeding pairs may be on eggs by early April.
Bluebirds typically use straw, grass, and/or pine needles to build a nest that, when completed, will have an unlined depression or "cup" in which the eggs will be laid. Other bird species use different materials, such as: Mosses, animal fur, and plant down (chickadees & nuthatches); leaves and sticks (wrens); pine-seed husks, bark strips, and cotton (nuthatches); and wood chips (woodpeckers).
Nestboxes for woodpeckers (and perhaps nuthatches) should include woodchips in the bottom. These species, which typically excavate their own cavities, seem more at home in a box with a little "construction debris." Cedar chips may help deter nest parasites.
ALL cavity-nesting birds in the United States are protected by law, except for on-native House Sparrows and European Starlings.
Remember that suitable nesting cavities are relatively scarce in nature. Thus, one should welcome ANY protected bird that nests in one of your boxes. It's hard to rationalize why one should remove wrens or Carolina Chickadees (right) just because one would RATHER have bluebirds. Plus, such actions are against state and federal laws.
If Tree Swallows compete with Eastern Bluebirds for a nestbox, try mounting TWO boxes back to back. The bluebirds often occupy one box and the swallow pair the other.
Cavity nesters lay one egg a day until the clutch is complete. Bluebirds usually lay 3-6 eggs. Incubation usually does not begin until the last egg in the clutch is laid; this allows for a synchronous hatch so that all chicks are the same age. For a given female, first clutches in a particular year usually have more eggs than later ones.
Bluebird eggs, which are pale blue (right)--rarely pure white--take about 13-15 days to hatch.
Try not to disturb an incubating bluebird female during the first 3-4 days of incubation. Chances are higher she will desert during this period.
Baby songbirds, including bluebirds, are born naked, blind, and helpless. They are unable to thermoregulate (maintain their own body temperatures) for several days after hatch. Thus, try not to disturb a brooding female for a week after hatch date. NEVER check a nest box on days that are cold, windy, and/or rainy, and NEVER check a box after mid-afternoon. If you spook a female too close to nightfall, she may stay off the nest.
If a clutch of bluebird eggs doesn't hatch after three weeks, remove the nest and eggs to stimulate re-nesting. Likewise, if chicks die in a nest, discard everything and sanitize the box with a mild solution of bleach.
Nestling bluebirds leave the nest about two weeks after hatch date. Thus, it's best not to open the box after about Day 11, lest premature fledging occur.
Once baby bluebirds have successfully fledged, folks often remove the nest and brush out the box, but there is disagreement about whether this is a good practice. Some researchers report that nest removal may stimulate re-nesting; if nothing else, they say it gets rid of accumulated nest parasites (mites, blowflies, lice, etc.) that might adversely affect later broods. Other investigators report that bluebirds prefer nest boxes in which a nest from the previous season remains in the box, and that leaving the nest does not cause an increase in parasites the following year. Some even speculate that the old nest may harbor beneficial wasps that parasitize blowfly larvae that can kill nestlings.
Many folks like to encourage bluebirds by putting out feeding trays with mealworms. These protein-rich beetle larvae (right) can be raised fairly easily on dried oatmeal but otherwise are available from pet shops and mail-order sources.
No matter how good your habitat or how well-constructed a nest box, there's no guarantee it will attract a tenant. Some folks put up a box and find it occupied the same day, while others go years before a pair of birds moves in. If a box goes unused for several breeding seasons in a row, you probably should move it.
You can put up more than one nest box in a small area, but they'll probably end up being occupied by different species. Boxes intended for Eastern Bluebirds should be at least 100 yards apart.
Consider starting a Bluebird Trail. If you live where there is appropriate habitat, talk to local farmers about putting up nest boxes along their fence rows. When you decide to create a trail, however, be sure to monitor it and keep your boxes in good shape.

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