EVER WONDER ABOUT nest boxes–about which design is best, or where you should place them in the garden to attract bluebirds, perhaps, or some other species? Ellen Blackstone of BirdNote, the daily public-radio show, will once again be our guide for exploring what’s going on as we look skyward, in Part 6 of our ongoing series.

Before we get started, the BirdNote backstory: In 2002, the then-executive director of Seattle Audubon heard a short public-radio show called StarDate. “We could do that with birds,” she thought. In 2005 the idea became a two-minute daily public-radio show. I recently asked BirdNote to help answer the recent questions you’d asked me.

Parts of Ellen’s answers below are in 2-minute audio clips to stream (all in the green links–or you can read the transcripts at those links if you prefer):

what birds like to nest in

Q. Though we think of a basket- or cup-shaped twiggy thing as a nest, different birds see different spaces as the ideal “nest.” Tell us about the range of choices.

A. Birds raise their families in all kinds of different places–from a rock cliff or the ledge of a skyscraper, to a simple indentation on a beach, a woven bag (made by orioles, bushtits, and others), a cup nest, a gourd, an old shoe (those pesky wrens!), a hole in a tree, and more.

Probably the fiercest competition is for a cavity, a simple hole in a tree. The migratory birds that return to their territories first beat the others to that valuable commodity. More on that fascinating topic is here.

But there’s a way that we can help. Nestboxes! Build them. Buy them. Make them out of wood or old logs or even tin cans. Check out this clever use by the Hendricksons of Leavenworth, Washington–recycled coffee cans that delighted their swallows.

sizes and shapes of birdhouses

Q. But what nestbox shape and size is the best? I see a confusing range in the garden center and catalogs.

A. First, determine what sort of bird you want to attract. Building plans and finished nestboxes are available not just for sweet little songbirds, but also for Northern flickers, screech-owls, and even wood ducks. Today, we’ll focus mainly on the smaller birds.

The “perfect nestbox” is one that will allow native birds in and keep nonnative birds, such as European starlings and house sparrows, out. It has much to do with the size of the hole, although placement makes a difference, too. And just as with birdfeeding and birdbaths, if you decide to invite the birds in, you need to take responsibility for maintaining the box, cleaning it once a year, etc.

Look for–or construct–a nestbox that’s plain wood, none of that fancy stuff. Birds prefer their nest sites to be inconspicuous. If the birdhouse comes with a cute little dowel perch, remove it. The nesting birds don’t need the perch. And it just makes it easier for a house sparrow to land and go after the eggs or young.

Now, here’s the complicated part: you need to determine the size of the entrance hole. And that depends on the bird you want to attract. (Sialis.org—sialis is Latin the species name of the Eastern bluebird, Sialia sialis–has a guide for determining specifications for nestboxes for many species.)

A smaller hole, around 1-1/4 to 1-3/8 inches, will keep out sparrows and starlings, while allowing in nuthatches and chickadees. You’ll need to experiment to see what works best for “your” birds. And if you have a nestbox with a hole that’s too big, you could add an adapter (see the top photo of the Western bluebird pair), although some birds are averse to such additions.

Don’t trust that just because a nestbox is for sale somewhere, that it’s actually appropriate for birds. Many are too small–with too little interior volume–to accommodate an avian family. Most birds won’t nest in them, so you’ll be wasting your time and money. Do your homework! (If you see birhhouses that are pretty but not technically ideal for desirable species, you can always close up the hole and use them for pure garden ornament rather than housing.)

Make sure your nestbox has a rough interior. When it’s time to fledge, many young songbirds leave the nestbox gradually over a few days. They poke their heads out, and stretch their wings during the day. Then they tuck back in at night. With the rough interior, the young birds can climb up, venture out, and return, all part of their natural fledging process.

where to site my nestboxes?

Q. Where is the ideal spot for a nestbox in my yard or garden?

A. Place the box where it’s out of reach of any predator–raccoon, squirrel, snake. A tree generally isn’t the best place, due to those tree-climbing nest-raiders. You’ll soon learn if you need to add a baffle [photo below of an example of a baffle].

Rita Shultz, whose story appears in this BirdNote show, found that Vicks VapoRub is a great deterrent for snakes. (You rub it on the base of the pole on which the nestbox rests, not close to the hole.)

And where specifically to place it? Open fields are good for bluebirds and tree swallows. (House sparrows don’t like being far from cover, so they’ll be less interested in such a spot.) Spots that are too close to water are more likely to attract raccoons. Always aim the nest-hole away from the mid-day sun.

Improvise! Mark Borden of Whidbey Island, WA, put his vinyl horse fence posts to work as cavities for swallows. Win-win, for both the swallows that have a place to nest and a steady diet of horseflies–and for the horses. Learn about his clever solution.

Numbers of Eastern, Western, and mountain bluebirds have increased, thanks in great measure to the “bluebird trails” set up by friends of these birds. A rural mail carrier in Virginia went on a campaign to help bluebirds along her route, for instance. Violet-green and tree swallows also happily take up residence in nestboxes. Chickadees and nuthatches and wrens, too, although not all nestbox landlords are happy having vociferous wrens as tenants.

Purple martins have come back in many places where people have hung nesting gourds. Choose the species you wish to attract, then educate yourself online about what works best for that bird.

And a final note: One of the best possible sources of cavities for many of these birds is a wildlife snag–a dead tree, left to stand and rot (obviously not where it is posing any danger to your home or yourself). Russell Link, who wrote “Landscaping for Wildlife,” says that one of his top 10 favorite plants is a dead or dying tree!  So if you don’t want to spend time and energy building or maintaining a nestbox, at least leave a snag for those cavity-nesters. Hear what he has to say.

more, more, more details

Q. Where can we look for more information?

A. Cornell and Audubon, among others, have great tips on attracting birds to your yard, including nest boxes. Cornell offers plans for boxes for various species; Audubon has one for a screech owl, even.

And as mentioned, there are specific dimensions and placements for different species—and organizations for different species, which can help you learn more. For example the North American Bluebird Society  or the Purple Martin Conservation Association, etc.

how to get birdnote

THE NEXT INSTALLMENT of my series in collaboration with BirdNote, providing answers from among the 150-plus questions you asked me recently, will be a month from now. If you have questions you’d like us consider, ask them in the comments below.

You may find answers to other bird questions in the BirdNote show archives, or on their FieldNotes blog.

Meantime, listen to BirdNote’s latest podcast anytime on the player below, or by visiting their website. Subscribe to the podcast or RSS, free. More than 100 public radio stations playing BirdNote are listed here; if you like what you hear, why not ask your local station why they don’t carry it?

In case you missed installment 1 of this series, we tackled How do birds make themselves at home—even in winter? Week 2 was about birds on the move: the miracle of hummingbird migration, and on flying in formation. Week 3: on daring behavior, such as when a mob of small birds chase after a bigger one, or a woodpecker drums on my house. Week 4: whether birds mate for life, and how long they live. Week 5: What senses birds of prey use to hunt.

(Photo of Western bluebird pair at nestbox by Tom Grey. Baffle photo by Rita Schultz.)