Many birdhouses found in pet stores and online are not suitable for birds.

That’s because cavity-nesting birds — those that naturally nest in tree hollows—don’t require birdhouses that mimic their natural homes. However, they do have specific housing needs.

For instance, the size of the entrance hole is crucial for enabling the appropriate bird species to enter while keeping predators and invasive bird species out.

The ideal entry-hole width for Violet-Green Swallows, Tree Swallows, and Bluebirds is 1.5 inches. For Chickadees, it ranges from 1 inch to 1.125 inches, while for House Wrens, it is 1.125 inches.

Entrances that exceed these sizes can allow predators such as American Crows and squirrels to prey on nestlings or allow invasive species such as European Starlings and House Sparrows to enter the house and build nests before our native migratory birds return to find no place to nest.

A slotted opening can also discourage English House Sparrows from entering a birdhouse while attracting Bluebirds. Google “sparrow-resistant bluebird house” to see one.

The interior space of the birdhouse is also important. If it’s too large, it can make it difficult for small birds to build a compact but cozy nest that keeps the nestlings warm. On the other hand, if the interior is too small, it can lead to overcrowding.

The interior of a birdhouse must consist of rough-milled, untreated, and unpainted wood. The inside of the front needs to be roughed or scored with horizontal scribing to enable young birds to grip the wood with their toenails for feeding and to eventually take flight. Smooth, painted, or planed interiors can trap young birds inside their houses.

Search Google for “basic songbird nest box WDFW” to discover species-specific opening sizes, birdhouse dimensions, material requirements, and tips on where to place your nest box.

Some birdhouses are made of metal, which can roast their occupants on a hot day. Others feature an asphalt-composition roof that mimics a human house’s roof. This, too, can create overheating.

The most bird-friendly birdhouses for the Olympic Peninsula are made entirely of rough milled cedar boards and assembled with galvanized screws. I learned this from Ken Wiersema, the education chair for the Olympic Peninsula Audubon Society, during a recent class he led on birdhouse construction at the Dungeness River Nature Center in Sequim.

Wiersema stated that cedar boards should be at least half an inch thick to provide adequate insulation during hot summers and particularly cold winters.

If you insist on a painted birdhouse, steer clear of those with an acrylic exterior or any paint on the inside, as birds might mistake it for food and perish, Wiersema said.

Some birdhouses, such as those for Flickers, must be large and filled halfway with wood shavings. The one I installed under the eave of my house is 19 inches tall, 9.5 inches deep, and 9 inches wide, and features a roof that extends 3 inches beyond the entrance to protect against rain and predators.

I bought the Flicker birdhouse at the Wild Birds Unlimited store in Gardiner on my way home from Wiersema’s class, where my wife and I each made a basic songbird house that will soon be added to 11 other birdhouses in our backyard.

Christie Lassen, the store’s owner for 23 years, has extensive knowledge about birdhouses. She and Wiersema emphasized that, regardless of the bird species, birdhouses should not have a perch in front of the entrance. Predators often use such perches to reach through entry holes and prey on nestlings.

Proper birdhouses also include drainage holes at the bottom for rain, ventilation holes on the sides near the top for heat, and a clean-out door for maintenance.

Lassen reminded me that some cavity-nesting birds are social butterflies, so to speak, while others are lone wolves.

“Chickadees are kind of territorial,” she said. “They like about 2 acres per mated pair. Chickadees have a social structure with dominant pairs, and flocks defend their territories from other Chickadee flocks.”

“Wrens, on the other hand, like to make multiple nests in multiple boxes in a smaller area to woo a female, and once she picks one, sometimes the male will show other females the unchosen boxes to see if he can entice a side piece,” Lassen said.

She said that Swallow boxes can be mounted back-to-back on posts 12 to 14 feet high in open areas to attract two pairs at once. If Swallows cannot see their neighbors, this may encourage more to enter your yard.

Check the inside of a nest box before installing it if it has been outside previously. Swallows are known for being messy nesters. Sometimes fleas and mites are brought in with the grasses that Swallows use to line their nests. The insects must be removed each season to help keep the baby birds healthy.

Some people enjoy assisting cavity-nesting birds by placing nest-like materials in birdhouses at the beginning of the nesting season. Wiersema warned that this can be risky. For instance, dryer lint contains plastics from synthetic fabrics and can poison baby birds.

Instead, line the bottom of the box with 100% natural cotton, which won’t become soggy and cold like dryer lint, Lassen said. Avoid synthetic cotton — “cotton balls” that contain no actual cotton whatsoever.

Birdhouse placement varies by species. It should generally face away from the wind, avoid direct sunlight, and be situated far from busy feeders or high-traffic areas. For species-specific installation instructions, Google “(name of species) birdhouse.” location.”

Deforestation increases the need for birdhouses to replace lost tree cavities. With Washington state losing 70,000 acres of forest to development each year, please install a birdhouse. Do it quickly, as our migratory birds are arriving now.

Scott Doggett is a former staff writer for the Los Angeles Times’ Outdoors section. He and his wife, Susan Englen, live in Port Townsend.