What Makes a "Good" Bird House?

Homemade or store-bought bird boxes provide a much needed place for cavity nesting birds. Cavity-nesters are birds that seek out holes in trees to lay their eggs and raise their young. Some examples are the nuthatch, brown creeper, wood duck, prothonotary warbler, bluebird, chickadee, owl, purple marten, wren, and of course the woodpecker. Woodpeckers create some of the holes in trees; other holes occur when limbs fall off trees, when insects and disease attack, or when fungi decompose what's left.

Unfortunately, many Americans have adopted a philosophy that everything growing in their yard or on their property must "look clean," and they are quick to remove any standing dead trees. This means a shortage of suitable nesting sites or "den trees" for cavity-nesters.

You can help cavity-nesters by putting up a bird house that has been specially designed for them. Each bird species is unique and has particular requirements, such as the size of the box opening or how high off the ground they will nest. It is extremely important to locate the bird house in the correct habitat for that bird, if you have your heart set on attracting a particular species. Mounting a bluebird house near any buildings or other structures, for example, will almost certainly be taken over by a house sparrow—a non-native species which competes with our native cavity-nesters. Starlings should also be discouraged. Here are more pointers:

  • The box should have ¼" holes or larger in the bottom for proper drainage.
  • No perch on the front! This just makes it easier for a predator to gain a "foothold" and raid the box.
  • There should be holes or spaces on the sides of the box near the roof for adequate ventilation
  • Construct the box with wood at least ¾" thick and preferably 1" thick to insulate nesting birds from the heat
  • The roof should overhang the front of the box a good 2" to shelter the opening from wind and rain
  • If the box is painted, it should be painted in a light color to reflect heat; clear varnish works fine
  • Check to see that the back of the box is long enough to make it easy to mount to a post
  • An excellent reference is Woodworking for Wildlife: Homes for Birds and Mammals, by Carroll L. Henderson, Minnesota Department of Natural Resources; new edition to be released in early 2009.

Graphic from BirdScope