The Inside Scoop

More and more people regard birdhouses and feeders as garden accessories (or gardens as bird accessories). This is why an ever-growing number of savvy retailers are devoting valuable floor space to bird-related products: They know their customers want phlox and feeders, hostas and houses.

Birdhouses 101

Birdhouses, also known as nest boxes, have become much more specialized and function-oriented than the little structures we hammered together when we were kids. There now are houses specifically designed for bluebirds, purple martins and chickadees. To find what works best for birds, in terms of safety and security, we need to wade through a bewildering array of choices.

Nest box designs range from the whimsical and lovely to the straightforwardly functional; some are ceramic, others come coated with birdseed and some even have roofs fashioned from license plates.

Not all bird species nest in houses — only about 10 percent of our backyard birds do and they have some pretty particular requirements. Retailers can perform a real service to customers by selecting and stocking birdhouses that are built to last, designed for specific bird species and able to stand up to weather extremes. Avoid houses that are cheaply constructed, with sharp edges or protruding nails — these can actually harm birds. Metal is not a good idea (except for purple martins).

The Box To The Bird

There’s no single birdhouse that will work well for all birds. As a matter of fact — and this comes as a shock to most customers — a good birdhouse will work for only one or two species of birds. It’s the size of the entrance hole that determines which birds will use a nest box. Larger birds will take over a nest box from smaller birds, if they can fit through the entry. Staff should interview a potential birdhouse customer to learn what kind of bird(s) they want to house. Most often they’ll cite chickadees, tufted titmice or wrens, popular small birds that do nest in cavities. (If they name goldfinches or hummingbirds, an educated retailer can point out that these species won’t use a nest box, but also point out the backyard birds that do.)

Nest Box Basics

When it comes to safety and comfort, some nest boxes are better than others. Here are some things to look for:

• A good nest box is designed for a specific bird species, each of which requires a “just-my-size” entrance hole. There’s no such thing as a one-size-fits-all nest box.
• Nest boxes should not have outer perches, unless you want to attract house sparrows and European starlings. Desirable species don’t need a perch.
• The roof or a side should be hinged so the box can be checked frequently and cleaned easily.
• The roof should hang over the entrance by at least 2 inches to keep out rain and roof-perching predators.
• Nearly all nest boxes require drain holes in the floor and ventilation holes near the roof.
• Good nest boxes are made of untreated lumber like cedar and redwood or recycled plastic; if fasteners are needed, galvanized screws should be used with wood instead of nails (nails loosen easily). Avoid stapled boxes as these generally last only a single season.
• Proper insulation is important, which is why ¾-inch thick lumber or plastic are the best choices. Metal is generally not a good nest box material since it heats up in direct sunlight and can kill nestlings. (However, white-painted metal works well for purple martins.)
• Most nest boxes should be attached to a post, building or tree. And many require predator guards to protect the inhabitants. It’s not a good idea to hang nest boxes from a branch since few species will tolerate a box that sways in the wind.

Safety Is #1

Birds on nests and their hatchlings are sitting ducks, so to speak, so nearly all nest boxes require some kind of baffling to foil predators.

Poles need pole guards, either metal cylinders or cones; boxes mounted on trees require tin or aluminum flashing wrapped around the trunk below the box. A determined predator can get around almost all kinds of guard materials, but we can keep the majority of cats, raccoons and snakes out.

There’s no need to bring in nest boxes after nesting season is over. In fact, on very cold nights, a number of bird species (bluebirds, nuthatches, tree swallows and some others) will use nest boxes to huddle together to conserve body heat.

Some of the housing offered for birds falls into the “merely pretty” category. If a box isn’t actually harmful and a customer has his or her heart set on it, there’s no reason why the customer shouldn’t place a cute box in the yard. Such houses can be a decorative garden accent and the roof might become popular with birds as a place to perch.