Habitat loss has driven some species away from former nesting areas. The right house can bring birds back.

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The world of birdhouses is divided into two parts: cute, decorative, often whimsical creations that appeal to humans; and functional nesting boxes that the birds will actually use.

Candi Meyer wrestles with that dichotomy regularly as manager of Wild Birds Unlimited in Sacramento, Calif. She stocks some people-pleasing painted birdhouses, but she makes sure they actually will meet the needs of their hoped-for occupants.

Western bluebirds, wrens, titmice, nuthatches, woodpeckers, tree swallows and other house-hunting species will flock to plain, unfinished wood boxes — as long as they have the right location and dimensions.

“They’ve got to be functional,” Meyer said. “But (all kinds of birdhouses) get people interested in helping birds and get the boxes out there for them.”

Why provide birdhouses? Habitat loss has driven some species away from former nesting areas. The right house can bring birds back home.

The Stone Lakes National Wildlife Reserve near Elk Grove, Calif., has scores of well-used birdhouses to attract a range of species, from tree swallows to barn owls. The boxes are mostly perched on posts.

“Every one of the boxes gets used,” said ranger Amy Hopperstad. “We have a lot of cavity nesters, but not a lot of trees. … If you put a box up, they’ll find it.”

The entry hole’s size and the box’s location are crucial, Hopperstad added. “If the hole is too big, it invites predators; rats and possums take the eggs. If the box is placed too low, snakes will get inside. Too big a hole also invites other (species of) birds to raid the nest. It’s a bird-eat-bird world out there.”

Nationwide, a lot of effort has gone into fostering bluebirds, which had vanished in some states. California’s Western bluebird prefers to make its home in native oaks and depends on mistletoe berries to survive the winter. (In summer, it eats mostly bugs.)

But as cities have grown, oaks have disappeared, depriving bluebirds of their favorite homes.

“Habitat loss is the single greatest threat to our birds,” said Adam Roberts, executive vice president of the conservation group Born Free USA. “You can help offset some of these threats by creating habitats in your backyard and community — and get the whole family involved.”

Birds’ needs are straightforward: food, water and shelter. Bird feeders and birdbaths help provide the first two.

Birdhouses cater to a different clientele than backyard feeders. They provide shelter to cavity-nesting species, which for the most part eat insects and berries instead of seed. Because they draw different kinds of birds, houses add to backyard diversity.

Nesting boxes also make a great project for kids. The houses are easy to build or set up and maintain.

Not surprisingly, bluebird nesting boxes are the best sellers at Wild Birds Unlimited. “Western bluebirds — that’s what everyone wants to see,” Meyer said. “There’s such a push to put bluebird boxes out there. Nuthatches will also use the same style box.”

Bluebirds prefer wide-open spaces with room to spot insects in mowed grass, their favorite hunting grounds, she said. “They like golf courses and school yards, without much tree cover. They like lawn.”

Wrens are the easiest to please; they don’t mind people. But for their home, they need a small entry hole — only 1 ¼ inches across — to keep uninvited guests out.

When choosing a location, put some distance between the birdhouse and the bird feeder or bath. There’s too much feathered traffic around feeders and baths for young families to feel comfortable.

“It’s just like raising your own kids,” Meyer said. “You don’t want to live next door to McDonald’s. You need some peace and quiet.”

What do birds want in a house?

Avian experts have spent decades researching that simple question — with a view to what makes the birds feel welcome, not necessarily what makes the prettiest backyard ornament.

Here is their advice:

— Location, location, location. In most cases, place the birdhouse 5 feet or more off the ground and at least 20 feet from feeders or birdbaths. Put it atop a pole or post, or attach it to a tree trunk. (PVC pipe can make a good pole; it discourages climbing cats and other critters.)

Choose a spot without a lot of foot traffic so the young family can have some privacy. Fences usually won’t work; cats, raccoons, rodents and other predators have too easy access. Wrens will use hanging boxes, but most birds prefer their homes to feel stable and securely anchored. If possible, have the entry face east, away from prevailing winds. Be patient with a new home — it may take more than one season for birds to find their house.

— Aged wood. Most cavity-nesting birds prefer weathered natural wood; it mimics tree trunks where they would otherwise nest. Use lumber at least 3/4-inch thick to help insulate the box from hot or cold weather. Rough, raw wood on the inside of the box gives babies a foothold to scramble up to the opening, so don’t paint or smooth the interior. A few square inches of wire mesh or recessed grooves below the doorway also are helpful to baby birds trying to climb up.

— Cozy space. Think of a hollow tree; that pocket is snug and deep. Cavity-nesting birds like their houses that way, too; 5 by 5 inches at the bottom is an ideal dimension for most species, with a depth of 5 to 6 inches below the entry and an overall height of 10 to 12 inches. Robins like an open-faced box — almost like a shelf — with no front wall.

— Single occupancy. While martins like apartment complexes, other birds are territorial about their nests. They want a home of their own without noisy neighbors.

— The right-size entry. Different-size holes attract different kinds of birds. They want an entry large enough to get in, but small enough to keep larger birds or predators out. Most songbirds think a 1 ½-inch hole is just right. Wrens want a 1 ¼-inch hole. A ring of wood around the entry discourages critters from reaching inside.

— Slanted roof. That allows rainwater to run off easily. Make sure it extends over the entry.

— That weathered look. Often, birds won’t use a new house until it shows some age. Weathering also softens up the wood, making it easier for young ones to grab hold, so leave the house up year-round. A painted, decorated birdhouse may be cute, but unvarnished cedar, pine or redwood will get more use.

If you paint your birdhouse, birds aren’t picky about color, but stay away from black or dark colors that absorb heat. Use nontoxic stains or varnishes.

— A few extras. Proper ventilation and drainage are important to a happy feathered home. Make some slits or small holes just below the roof’s eaves to let air in. Add some small drainage holes in the floor, at the corners or along the walls. A flip-top roof or side panel makes it easier to open the box for cleaning.

— No perch necessary. Most cavity-nesting birds can cling to the outside of the box without aid, especially if it’s natural wood. Perches actually help other birds or predators who may harass the nesters.

— Nesting materials. Most songbirds won’t reuse a nest the following year (although they have no problem reusing a house), which means they need new stuff each spring. Among favorite materials to line a new nest: moss, twigs, feathers, pine needles, shredded bark, soft grasses, yarn scraps, small pieces of fabric and hair (human, dog or horse). Author and bird-watcher Kate Rowinski stuffs a suet-style feeder with such treasures and hangs it in a sheltered location, such as under an eave, near her nesting boxes to make it easier for the birds to redecorate.

— Maintenance: Once a year, take the box down and clean it out. Remove the old nest. Scrub with a stiff brush and a mild bleach solution to kill mites or other parasites.

(Contact Debbie Arrington at darrington@sacbee.com)