ECONOMIC RELATIONS OF OUR BIRDS.


young beetles of the same species, while, as a matter of fact, the destruction
of
seven very young beetles should be counted a greater service than the destruc-
tion of an equal number of adult forms, since not only is the food required
to
mature the young beetles saved, but the possibility of a deposition of seven
thousand eggs (it is estimated that one female may lay one thousand eggs),
is
effectually precluded.
The fragmentary condition, also, of the contents of a bird's stomach renders
any purely quantitative system of gauging as fruitful of false values as
does the
inequality of size and weight among insects. A single maxilla, a bit of elytron,
or a sm all wing would count for almost nothing in the account by such a
sys-
tem, while each is positive proof of the d -struction of a whole insect of
some
kind, no matter how small the fragment may be.
But when insects are estimated bulk for bulk with grains, weed seeds and
fruits, the diversion from true relations reaches the maximum.
A peck of plums and a peck of curculios, a peck of wheat and a peck of
chinch-bugs, or a peck of corn and a peck of cut-worms, are manifestly not
to
be considered as equivalent values on opposite sides of any account.
Even in those cases where the individuals are nearly equal in bulk and weight,
there is often little justice in offsetting one with the other, for then
no account
will be taken of the relative service or injury of the two species, or of
the dif-
ferent rates of reproduction.
In view of the fact that we have no standard of insect values, and that,
in
the present state of progress of entomological science, a satisfactory one
can
hardly be furnished, the simplest and, I believe, all things considered,
the most
reliable method of exhibiting the results of observations on the food of
birds, as
well as one which will leave the materials accumulated in the most available
form for subsequent more critical examination, is to exhibit the number of
indi-
vidual forms of life which a bird can be proved to have eaten in as systematic
a form and as specifically as possible. In the tables which follow under
the
various families of birds, an effort has been made to do this. The second
table
in each case exhibits the details as far as they could be shown in the space
allowed, and the first table exhibits the same facts brought together under
the
heads " Elements Beneficial," " Elements Detrimental,"
and " Elements whose
Economic Relations are Unknown." There are two general tables introducing
the body of the report which exhibit the same results for all of the birds
examined, brought together under the families to which they belong.


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