My first attempt at building a nest box for bluebirds was pretty crude: cardboard painted with shellac, and a hole cut out with a pair of scissors. I also remember that a house wren nested in the box. So while it was crude, it worked. Then again, house wrens will nest in almost anything. But I was only five years old, and this small success was great for my ego.

I didn't build another birdhouse until about 10 years later. My family and I were living in the country at the time, about 25 miles west of Philadelphia. One spring morning I looked out the bedroom window and saw a pair of eastern bluebirds perched on a telephone line near our house. During the intervening years I had seen some real birdhouses -- ones made of wood, with perfectly circular entrance holes and wooden roofs covered with shingles. Cardboard was a thing of the past.

In those days there were few books on how to build birdhouses; there was no Internet; and the nearest library was miles away. The birds were there, however, and I thought that they might nest in my yard if I could get a house up in time. So with a handsaw and some thin plywood that I found under my father's workbench, I set about my task. I watched the bluebirds closely with my father's old Navy binoculars, estimating their size and how big the box should be to attract them.

I don't remember the exact dimensions of the box, but I do remember that I painted it with a bright-white enamel and nailed it to a dying maple in the front yard. The next morning the bluebirds were at the box, and the following day the female began buildng a nest in it. She laid eggs, incubation went smoothly, and five young hatched. About halfway through the nestling stage, though, starlings found the box, and because the hole was too large, they were able to reach in and extract the young. I found the featherless nestlings scattered about the yard, still alive but suffering from hypothermia. I gathered them up, warmed them under a lightbulb until they recovered, and put them back into the nest box. Even though the young birds had been out of the nest for some time, the adults immediately began feeding them again. All five young fledged successfully.

That experience provided my first important lesson in birdhouse building. A nest box that is badly designed or that uses the wrong materials can be a death trap for young birds, or even for incubating adults. The white color may have attracted the starlings, and the big entrance hole placed low on the box allowed them easy access to the nest. Because I had put the box in a tree, climbing predators could reach it as well. The bluebirds in my yard tried two more times to nest in that box, but they failed because of its poor design and location. Beginning in the 1950s, bluebird populations declined dramatically in the eastern United States, in part because of the scarcity of suitable nesting sites due to habitat destruction; competition from introduced, non-native house sparrows and starlings; increased use of pesticides on lawns, gardens, and farms; and several severe ice storms in the late 1950s. To see a bluebird in the mid-'60s was a notable event, one worth mentioning as an unusual bird sighting at an Audubon chapter meeting. The turnaround for the species came when people began to take an interest in its plight, and large-scale nest-box programs were started. In those first years, however, there were many failures, similar to my own as a boy.

It is safe to say that an intense interest by humans has been the most significant factor in the recovery of the eastern bluebird. Thousands of hours have gone into thinking about the design of nest boxes, what types of materials to use in building them, and where to place them.

To say that nest-box design is fairly straightforward and agreed upon by all would be a gross misstatement. Designs have proliferated like weeds in the spring, and many are advocated and advertised without adequate experimentation and research. Improper entrance-hole sizes and shapes, various internal and external configurations, and other design flaws can place the birds at risk to predators, provide inadequate room for the development of nestlings, and subject the mating birds and their eggs and nestlings to hostile weather conditions. The individual most responsible for the recovery of the eastern bluebird in my old neighborhood of southeastern Pennsylvania is Warren H. Lauder, who has devoted the past 38 years to analyzing bluebird boxes and trying to design the best one. Forty years ago bluebirds were essentially nonexistent in Lauder's area. It took him three years to find his first bluebird, and when that bird found a mate, he had his first pair. The birds nested successfully in one of Lauder's boxes, and so began their rebound.

Lauder's work was not without the occasional failure. The first pair's second nesting attempt failed when all the young died of heat prostration. Lauder, who was a senior editor for technical journals at the DuPont Company, in Newark, Delaware, sought out a co-worker who was an expert in ventilation. Together they designed a system that ventilates the box only in hot weather, thus protecting the young birds during cool weather. Lauder placed a dark asphalt shingle on the roof, and during hot summer days the warm roof heated the upper portions of the interior of the box. As the warm air rose and flowed out of strategically placed ventilation holes, cooler air was sucked in from the bottom, thus lowering the interior temperature. Lauder experienced no further heat-related mortality. During his years of observation, Lauder changed his design to correct other flaws. He lengthened the roof overhang to protect the birds from the elements and to deter predators. He cut additional ventilation holes for greater air circulation and put the entrance hole higher on the front of the box to further deter predators. He found that wood at least three-fourths of an inch thick gives greater insulation from cold and heat. He extended the side panels below the bottom of the box and caulked the roof joint on the back of the box to keep the nest and its contents dry during heavy rains. He made the floor five inches square -- adequate room for young birds to develop. Two nails and a screw hold the front to the rest of the box -- an arrangement that allows easy access to the interior for cleaning, observing the contents, and banding the young. The exterior of the box needs no paint; a natural finish is best and most attractive. The placement of the box in the proper habitat is also a key factor in its success. Open fields, meadows, and lawns are more attractive to bluebirds than are wooded areas, which are likely to attract competitors such as house wrens. Boxes mounted on trees, as opposed to those on baffled metal poles, increase the chance of predation. Tree branches also provide perches from which starlings and other competitors can launch attacks on the bluebirds.

Lauder believes that some of the new designs in nest boxes ignore the features of nest holes found in nature. For instance, open-topped boxes, designed to dissuade house sparrows and other competitors, let rain saturate the nest. Lauder's research shows that when given a choice, bluebirds will shun these boxes for the roofed variety. He found that boxes with narrow V-shaped interiors, also designed to deter house sparrows, provide inadequate room for young bluebirds to develop. Elliptical entrance holes were also supposed to deter house sparrows, but Lauder determined that they allow increased predation. The best chance for success in attracting bluebirds is to use common sense and to keep these considerations in mind: protection from heat stress, protection from inclement weather, the proper-size entrance hole and interior dimensions, predator deterrents, placement in proper habitat, and height above the ground. The bluebird's preferred natural nesting sites are in tree cavities and abandoned woodpecker nest holes. Lauder's box design takes those basic features into account and adds many safeguards. In fact, his nest box is probably safer than a natural site.

To learn how to make your own birdbox click here!

Jesse Grantham directs the National Audubon Society's Mississippi State Office.