[Illustration: Illustrated capital A]
Although there are a number of points which should be considered in the
proper designing and placing of a bird house, there is one simple idea
which practically covers the whole subject. Every species of our small
native birds that nests in a bird house nested originally in a hollow
tree, by preference in a hollow of one unvarying type--the burrow made
by a woodpecker. Thus we need only know what the burrow of a woodpecker
is like and we have automatically solved in a general way the questions
of material; size and shape of entrance; diameter, depth and form of
cavity; height above ground; and situation. The nature of nesting
material and its whereabouts should play absolutely no part in human
plans for the prospective tenants. "Unfurnished" rooms are the only kind
for which birds are looking.
There is solid ground for assuming a woodpecker's burrow to be the ideal
pattern for a bird house. The woodpecker, whatever its species, free to
excavate any form of chamber that it might wish, invariably uses _one_
type of burrow. The birds which by preference habitually adopt for their
own use the woodpecker's abandoned home have likewise thus placed their
own age-old stamp of approval on that type. It is logical to assume,
therefore, that the artificial bird house should follow at least the
general plan of that long-tried and preeminently successful nesting
site. Since a theory may be plausible while yet utterly untenable in
actual application, it remains to add that abundance of experience in
building and placing bird houses all goes to prove the foregoing basic
principle soundly correct in practice. With or without benefit of the
plans and specifications in such a bulletin as this, a person who takes
his cue from a woodpecker will not go far wrong. In planning a bird
house, we must continually hark back to the idea of the woodpecker's
burrow--or rather, we should never quite lose sight of it.
_Some Current Notions Corrected_
Attention should be called to some common misconceptions. The colony
bird house, or any bird house with more than one compartment, is always
a mistake unless it has been designed for Purple Martins. Yet certain
firms have for years been advertising "wren houses" of four or more
chambers. One who knows this pugnacious little bird tries in vain to
imagine two pairs of wrens living peaceably under one small roof! Every
bird house should consist of one, and only one, chamber--with the single
exception of a house intended for the Purple Martin, which nests in
colonies.
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.]
Overcrowding is a prevalent fault. On an area insufficient properly to
harbor two pairs of wrens or bluebirds there will often be a half-dozen
or more bird houses. Tree Swallows are social birds and will occupy
boxes placed near to one another, but ordinarily, birds, especially
those of the same species, do not build near each other. It is a large
town lot which will properly accommodate more than one pair of nesting
wrens. Even the demure bluebirds do not like to build within a stone's
throw of each other. While the martin colony may number upward of a
dozen pairs in the same house, there may not be other martins within a
mile. There is many a small village whose single martin house
accommodates all the martins to be found within a radius of several
miles.
The size of entrance seems often to be a stumbling block. One sees wren
houses with perfect bluebird entrances, and bluebird houses with
doorways best suited to wrens or chickadees or, at the other extreme, to
doves!
Although arguments, supported by some experience, have been advanced for
larger entrances, we nevertheless suggest entrances of nearly minimum
size--a suggestion based on personal experience and long familiarity
with the preferences shown by the species concerned. Apparently John
Burroughs was first to point out that when birds hesitate to enter a
small opening it is evidently because their bodies, completely filling
the entrance, render the cavity totally dark and therefore alarming. Cut
a few small auger holes to admit light, and the bird enters the now
somewhat less mysterious chamber. The holes also provide needed
ventilation, but they should be small and well above the entrance-level,
for drafts must be avoided. The entrance to the house for wren,
chickadee, or Tree Swallow should be, since it easily may be, too small
to admit English Sparrows. It is not possible to exclude English
Sparrows from houses of other birds in that way.
Finally, the mistake is often made of providing simply _a_ bird house
instead of a _martin_ house, a _wren_ house, a _bluebird_ house, or a
house for some other definite species. The result is that such houses
usually go unoccupied or else are promptly claimed by the first English
Sparrows that spy them. Any bird house will suit the English Sparrow if
only he can get into it, and he usually can get into _a_ bird house. So
avoid type _a_--the too common variety.