Nest Boxes for Birds

Materials
You can buy a bird house through special mail order suppliers, your local Audubon Society or local garden and nursery stores. Or you can build one following the guidelines and plans under "Fun Projects for Urban Wildlife". Whether you buy it or build it, here are some important things to keep in mind.

Wood is the best material to use for bird houses. It’s a good insulator, it’s available and easy to use, and it blends in well with the landscape. Three-quarter inch boards are the easiest to work with. Soft wood, such as cedar, is fine for both smaller and larger boxes. If you use plywood, make sure it is exterior grade. A well-constructed and maintained house can last 10 years.

Use galvanized nails to build houses if necessary, but remember that they loosen up as wood expands and contracts in extreme weather conditions. Nest boxes made with outdoor wood screws are more sturdy and last longer.

Design

Entrance Hole
Design and construction of a bird house need to be bird specific. The most important part of the bird house is the entrance hole. If the hole is too small, the desired bird won’t be able to enter. If it’s too big (and this is more likely) undesirable wildlife – like non-native sparrows and starlings can get in and harm or evict the intended bird.

As a rule, house sparrows can’t enter a nest box if the entrance hole is less than 11/8 inches in diameter. Starlings can’t enter if the hole is less than 11/2 inches in diameter. The entrance hole sizes in this publication are designed to exclude these birds wherever possible.

Roof
Roofs need to be built with enough of a slant to shed water. The top front edge of the roof should overhang at least 2 inches to protect the entrance from driving rain or snow, and to keep cats from reaching in from above.

Provide a hinged side or roof so houses can be easily checked and cleaned out each year. (Annual cleaning reduces the possibility of spreading parasites and diseases from year to year.) Hinges should be rust-proof. Duck and owl box roofs kept shut with a hook and eye can be opened by raccoons. It’s much easier to use paired roofing nails with large heads or duplex nails on the side of the roof and the upper edge of a side. Wiring these nails together will keep the bird house shut and raccoon-proof (See Fun Projects).

• DO NOT use wood treated with preservative.
• DO NOT paint, stain or treat box with creosote.
• DO NOT use tin cans, milk cartons or metal for nests. Metals quickly heat up to lethal temperatures on warm spring and summer days, overheating the eggs and killing the birds.

Sides and Seams
Natural tree cavities have rough interior surfaces that give young birds traction, especially when climbing out of the nest. A bird house can mimic this rough surface below the entrance holes with grooves or a roughed-up surface that can be gripped by the bird's feet.

Don't screw the sides to the top of the floorboard. The sides of a bird house should enclose the floorboard. This keeps rain from seeping into the crack between sides and floor and then into the nest. Placing the floorboard 1/2 inch above the bottom of the sides also keeps moisture from seeping in from below.

All seams that won't be open should be water tight. Caulk any wide gaps.

Ventilation Holes
At least two 1/4-inch holes should be drilled near the top of the right and left sides of all bird boxes to let air circulate. This is especially important for small nest boxes located in hot areas. Drainage holes are also important. Drill at least four 1/4-inch drain holes in the floor of the house. This will help drain moisture that manages to get inside.