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I decide on a design for my chickadee birdbox

I have made up my mind to install some birdhouses in the backyard to encourage chickadees to nest. I plan to build my own. In fact, I planned to build several and place them in the backyard, hoping that one would be chosen.

My next challenge is to settle on a design; there are in fact lots of different styles to choose from.

Early birdhouses in medieval Holland were fashioned from clay and shaped like flasks. They attracted birds that were human commensals like European starlings and house sparrows, and the people probably harvested the eggs for food. It wasn't till the nineteenth century that birdboxes were erected to encourage and protect birds for their own sake. The noted British taxidermist and explorer, Charles Waterton, built and installed wooden nestboxes for owls and starlings on his game preserve.

The basic wooden box design has remained most popular. The whimsical, cuckoo-clock inspired renditions aside, wooden nestboxes all have the following key features: sturdy construction, an entrance hole with a diameter determined by the species that is being attracted, a flat top roof which affords some rain protection, ventilation, and some way of getting in to the box to check the contents or clean out last year's mess.

I was familiar with the basic birdbox design. Years ago as a teenager on my Uncle's farm in the south island of New Zealand, I spent a good part of my summer holidays building dozens of wooden nestboxes to attract starlings to his pastures. Down there, the introduced European starling was considered a beneficial species since it included pasture pests in its diet. Here, of course, it gets mixed reviews and is generally thought to be a competitor of native species such as eastern bluebirds.

And then there are the "alternative" designs, like a PVC pipe design developed by biologists studying chickadees who needed an efficient design that allowed them to build a lot of boxes quickly and cheaply. The three-inch diameter thin-walled plumbing pipe is fitted with caps at each end, a circular entrance hole, and metal strapping for installation on the trunk of a tree. Ventilation holes are drilled in the bottom cap. Wood shavings are stuffed into the pipe up to just below the entrance hole; apparently chickadees like to excavate wood chips from the nest during construction.

Intrigued, I did some further reading, and uncovered a slightly more complex pipe design favoured by bluebird enthusiasts. The Gilbertson design has some special features to deter predators and competitors. The entrance hole diameter is calibrated precisely so that starlings can't get in; the depth of nest fill that is placed inside is deep enough to deter sparrows. Then in correspondence with a contact in New Zealand I learned that the PVC pipe designs had also been used with some success for riflemen, tiny forest songbirds.

The only other down side to the PVC boxes was that the plastic might emit fumes that could harm the developing embryos. But while this might result in invisible defects, it does not seem to result in deaths; the bluebird enthusiasts report successful rearing of thousands of chicks from the Gilberson nestboxes over many years, so that's good enough for me.

I settled on the simple PVC pipe design for my chickadee boxes. Although perhaps not as pleasing a design as the standard wooden boxes, the PVC version is cheaper and quicker to build. It can be painted to improve its look in the garden. If only I had known of this design when I was building the starling boxes for my Uncle's farm in New Zealand those many years ago.

Next week: In the workshop... the build

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