The cubic capacity of the bird houses one sees is nearly always much too great—often several times too great. Builders seem to believe that the diameter of the nesting chamber should at least equal the total length of the bird—a theory as erroneous as it is plausible. Plate I illustrates the fact that the sitting bird normally occupies a space measuring much less from side to side than the outstretched length of the bird. Figure No. 4, Plate I, shows how much work is often made for the House Wren, while figure No. 5, on the same plate, shows how greatly this work may be reduced—with the greater inducement to the prospective occupant.
The square or rectangular door is another frequent mistake—a projection of the designer’s own plantigrade and vertical personality.
To place the entrance at or near floor level is also an error. Remember that birds close no doors against drafts, that their “beds” are laid on the floor and consist of light straws, feathers, or other flimsy materials.
Many a wren house with entrance (as it should be) too small for any English Sparrow to enter, is hung _swinging from a branch_ as a further protection against the unwanted sparrow. That is like beheading a criminal and then, “just to be on the safe side,” shooting him into the bargain! It is said that wrens do not hesitate to use these swinging nesting sites, but we have our serious doubts. We have personally seen one instance of a wren nesting in the pensile home of a Baltimore Oriole, but it is significant that in this case we failed to find any better site nearby. Some persons report success with this type of house and prefer it because of the ease of putting it up and taking it down without injury to a living tree.
Two doors, presumably entrance and exit, to a bird house of one compartment is nearly as ridiculous an innovation as the two doors said to have been provided by a famous scientist for the use of his old cat and her kittens, respectively.
[Illustration: Plate I. Nesting Sites, Natural and Artificial
1, 2, 3, A nesting woodpecker, a Chickadee, and a pair of bluebirds, respectively. Compare length of bird with diameter of nesting chamber. 4, A wren house, as frequently made, of eight to ten times the necessary cubic capacity. 5, A wren house of proper and ample size.]
