Safe shelter or death trap? How to give backyard birds a better chance at survival

The author builds a new nest box out of scrap wood for nuthatches in the garage of his home in San Francisco. Mike Coren/The Washington Post
Eastern bluebird numbers have been recovering since a push to save them by building habitats for them to nest. Global breeding population now stands at 23 million. Getty Images/iStockphoto

I wanted to build a first-class home. Small enough to be cozy, but big enough to raise a family. I needed an ideal location, near a wooded area, with a natural supermarket nearby. And the design should be simple, crafted entirely out of wood. While I was worried about the cost, I needn’t have been. I finished building mine for about $5 in materials in an afternoon.

Soon, I hope, my new home will host a family of pygmy nuthatches, tiny songbirds with slate gray wings and a high-pitched call reminiscent of squeezing a rubber ducky.

Humans are known for destroying the habitat of our wild neighbors. But we can excel at creating it. My new birdhouse is just one example. After decades studying their avian subjects, ornithologists have designed structures catering to the needs of hundreds of species ranging from box homes for barn owls to simple baskets for mourning doves tucked into tree branches.

Birds, as you might have heard, are in trouble. North America’s birds have seen a staggering loss of 3 billion breeding adults, or nearly 30% of the population, over the last half-century, according to eBird, a crowdsourced database of bird observations managed by the Cornell Lab of Ornithology.

Humans have stripped the landscape of large, dead trees where cavity-nesting birds make their homes. That’s left many birds homeless in habitats otherwise suitable for them. While finding shelter is not birds’ only challenge — pesticides, introduced predators, habitat loss and glass collisions rank highly — more and better homes can slow losses and help declining populations rebound.

“Nest boxes are especially important in habitat where lots of trees are missing,” says Jack Dumbacher, curator of ornithology at the California Academy of Sciences. “Most urban and suburban areas could definitely use them.”

But things can go wrong. Nest boxes and structures designed poorly can entice predators, overheat baby birds or encourage overcrowding. That leads to birds ignoring and abandoning potential homes or, worse, entering death traps.

Here’s a guide to creating first-class bird accommodations.

What is a nest box?

Nest boxes or birdhouses re-create habitats provided by cavities in dead trees for nesting, roosting and perching. Not all birds need nest boxes. In North America, only about 85 species, less than half of those typically living in natural forests, use cavities. But for many, these shelters can be essential to their survival.

Hundreds of other bird species that don’t nest in cavities can still use structures of some kind, from shelves mounted on the side of your house to raised platforms hundreds of feet up for birds of prey.

The poster child for the birdhouse success are Eastern bluebirds, a species similar to robins except with blue plumage and rusty-colored throats. By the mid-20th century, populations of this songbird were on the decline across the country, crowded out by European starlings and house sparrows, aggressive introduced species. But campaigns to build nest boxes in the 1960s, often designed to deter the larger European starling with slightly smaller openings, eased this competition. Ever since, Eastern bluebird numbers have been recovering, and the global breeding population now stands at 23 million.

Today, if you erect a box for bluebirds in the morning, the birds may fly into it the same day, says Robyn Bailey, who manages research and education for the Cornell lab’s NestWatch program.

But mimicking natural habitats — tree tops or hollows that can take more than a century to develop — is not always easy. Even minute differences — as little as one-eight of an inch in the width of the entrance hole, less than the thickness of two quarters — can spell the difference between excluding one species and welcoming another.

Materials also matter. Early designs were sometimes made from plastic, chemically treated wood or other harmful materials. Some can overheat, while others offer easy access to pests or predators such as feral cats, snakes and mammals. At worst, these become “ecological traps,” structures that attract species with the promise of a safe home to nest, but ultimately harm animals’ survival.

Dumbacher recalls one row of evenly spaced, exposed Eastern bluebird nest boxes along a farmer’s fence line that became easy pickings for a bear. The animal wiped out the entire row. He recommends not placing nest boxes too close together, and offering more natural camouflage.

Doing it right doesn’t have to be hard — if you know how. Luckily, there’s NestWatch.

The bird monitoring program uses volunteers to track more than 282,000 nests, offering ornithologists essential information about where birds lay their eggs and how successful they are at raising their young. It also offers a tool for you to find the right home for the right bird in your neighborhood, even offering blueprints so you can become a master architect for the avian world.

How to build a nest box

I started with a virtual tour of the idealized birdhouse’s features, such as a sloped roof, recessed floors, drainage and ventilation holes, and entrances protected against predators. Then I fired up NestWatch’s interactive tool, adding my ZIP code and local landscape, to generate a list of suitable birds and their ideal housing.

I started simple. I chose one of my favorite birds, the mourning dove, whose melodic triplet, coo-oo, coo-oo, coo-oo, is the soundtrack of my childhood. The species, also called turtle doves, are on a mysterious decline, but they’re easy to host.

Using this blueprint, I cut out a simple wire-mesh circle from hardware cloth (available in any hardware store), then snipped out a pie-shaped piece. By bringing the ends together, I formed a cone serving as a nesting basket. To finish the home, a male dove brings twigs, pine needles and grass stems to the female, who weaves a flimsy nest out of the materials. Parents spend about a month incubating the eggs and feed the hatchlings before they fly off on their own.

I placed it in the crotch of a tree branch, securing it with wire (though doves will nest amid foliage, gutters, eaves or on the ground). If I wanted to invite them to nest on the walls of my house, then I could attach this nest shelf, beloved by robins and swallows as well.

But I had grander visions. For my next project, I chose a classic nest box: A wooden enclosure with four walls and a roof that can host a variety of species. Using a single four-foot piece of scrap lumber left over from a remodel, I sawed and nailed six pieces to make an 11-by-8-inch redwood palace. The entrance hole, precisely one inch in diameter, can welcome wrens, chickadees, titmice or nuthatches, but exclude larger house sparrows, a competitor European species.

I plan to mount this on a pole for extra protection, although any live or dead tree will do, and install bird-friendly glass films or markings to avoid bird strikes. (You can read about the finer points of birdhouse placement and predator protection here).


How hard was it to build a nest box? Pretty easy. The whole process took a bit over an hour.

How much did it cost? Around $5. Everything I used was either in my garage or borrowed. Tool libraries are also excellent. If you buy everything you need new, it can get pricey. But if you team up with neighbors and divide the costs, the project can be a cheap weekend adventure, especially for kids.

What’s next? I wish I had built my bird starter homes years earlier. But with most species just starting to nest this spring, it’s perfect timing to build out an avian real estate empire.

First, I’ll see who moves into my two existing homes, join NestWatch to contribute my findings and perhaps even install a camera to watch generations of birds hatch.

Having furnished shelter, I’ll focus on food. In many places, birds suffer from a dearth of edible plants and insects. Climate change is making plants bloom and fruit earlier, shifting the timing of the food supply and potentially hurting migrating and late-nesting birds.

My ongoing tidy wildlands project, converting a portion of my yard into a riot of native plants, should help attract bugs and stock the buffet. Raising a single brood of chicks can require 9,000 caterpillars.

If I still need more projects, I’ll graduate to advanced bird architecture: the spacious accommodations of a barn owl.

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