Why you should put up a birdhouse

One of the nicer ideas that humanity has come up with over the years is that of birdhouses. We construct little boxes that suit the nesting needs of various birds, perhaps add a few decorative touches to give it a homey feeling in our human eyes and then hang it up in a tree to encourage more birds to make babies. The whole activity feels both thoughtfully altruistic and benignly self-interested: adding more birds to our lives adds to the pleasures of our existence, but it does so through helping other creatures.

Let’s start with the basics — how do these things work? Birdhouses, also known as nest or nesting boxes, have one primary purpose. Birds don’t live in them all year-round the way that people live in our houses, but instead use them just for nesting during spring. You put out an empty box, imitating the natural or woodpecker-excavated tree cavities that certain birds usually look for, and they do the rest: Birds will bring in their preferred nesting material, lay eggs and raise their young. In fall, you clean out the nest box and wait to see who moves in next year.

Not all birds use nest boxes — just the relative minority of “cavity-nesting” species. Most birds construct open cup nests, so you won’t see finches, jays, robins, hummingbirds, doves or most sparrows moving into your birdhouse. But there are still several potential occupants in our area. For a general purpose nest box with a 1 1/2-inch or 1 9/16-inch entrance hole (which you may see described as a “bluebird box”), typical occupants include titmice, wrens, chickadees, bluebirds, tree swallows and violet-green swallows.

Those six species probably represent the big six of Marin’s most likely cavity-nesting birds. But they don’t exhaust the possibilities. In woodland habitats, you could also attract the smaller woodpeckers, nuthatches or ash-throated flycatchers. A larger, specialty box could attract northern flickers or screech owls in woodland habitats (or kestrels in open country), and a much larger box could attract barn owls in a variety of more open habitats.

Some people have had disappointing experiences with nest boxes. Maybe no one moved in, or maybe a nest failed or was abandoned. Wild birds are not always predictable, but there are definitely things you can do to maximize the odds of successful nesting.

This starts with features of the physical box itself. The first, mandatory item is to have an appropriately sized box and entrance hole: One common misstep is to purchase an excessively small decorative birdhouse. Entrance holes should be at least 1 ¼ inches and 1 ½ or 1 9/16 inches to attract a wide variety of potential users. Some other features that enhance the odds of success are adequate ventilation and no dark-colored paints (to prevent overheating), a predator guard around the entrance (to block jays and crows) and construction that allows for an annual cleanout.

Birdhouse placement is also important if you want your box to be accepted. Here there are three main things to keep in mind: stability, height and seclusion. Almost all birds prefer a solidly mounted box to one that’s loose and swaying. In general, placing a box 6 feet or more above the ground will feel safer and more inviting than if it is mounted at a low height. Finally, keep in mind that birds are looking for a safe and quiet nursery to raise their children. This means you want to avoid placing it in areas of high human activity and in areas of high bird activity (don’t mount your nest box right next to your bird feeders). If you meet all of these considerations, a variety of locations can work: a tree trunk, the side of a building or a free-standing pole are all possible options.

Famous conservationist Aldo Leopold once counted birdhouses as he drove past 100 different farmsteads. Finding that only 12 had installed these basic accessories of a joyful existence, he asked, “Did the owners of the other 88 have so much pleasure already that they needed no more?” If you’re on the fence about adding a birdhouse, ask yourself the same question: Do you have so much pleasure already that you need no more?

Jack Gedney’s On the Wing runs every other Monday. He is a co-owner of Wild Birds Unlimited in Novato and author of “The Private Lives of Public Birds.” You can reach him at jack@natureinnovato.com.