ECONOMIC RELATIONS OF O'UR BIRDS. 
Group II. 
m 
Birds whose habits, so far as they are known, make it doubtful wliether they 
are, on the whole, beneticial or injurious. 
This group is necessitated partly by conflicting evidence, partly by the ab¬ 
sence of evidence, and partly by evidence whicli seems to indicate that the de¬ 
structiveness and usefulness of the birds aa’e nearly balanced. As in the first 
group, this may be divided into three classes; 
(a) Birds ivhose relations of structure and habits ally them to Group I, but 
ivhich in the absence of data, or on account of conflicting data, cannot be placed 
there at present. 
(b) Birds ivhose knoivn beneficial and injurious results appear to balance. 
(c) Birds whose relations of structure ally them to Group HI, but which in the 
absence of data, or on account of conflicting statements, cannot be placed there 
at present. ' 
Group III. 
Biixls whose habits, so far as they are known, render them, on the whole, 
injurious. 
In this group are placed those birds whose ability to do injury appears to ex¬ 
ceed their beneficial agencies. It is divisible into two classes: 
(a) Birds ivhose known habits render them injurious at all times. 
As in the first class of Group I, it is probable that, ultimately, the members of 
this class wall all be placed in the next. 
(b) Birds which are known to be to some extent beneficial, but whose known 
injuries exceed their known services. 
How shall a bird's food account be expressed numerically in terms of debit 
and credit 9 This is at once the most difficult and the most important of all 
the questions requiring solution in order to express the specific economic rela¬ 
tions of any bird. 
Nothing can be more certain than that, after the food of a bird has been 
classified under the heads “Elements Beneficial” and “Elements Detrimental” 
to man, neither the relative volumes nor the relative weights of these two 
classes of materials can express the true economic relations of the bird. 
If we compare the corn plant-louse, the gall stage of the grape phylloxera, 
the plum-curculio, the small parasitic military microgaster, which lays its eggs 
in several kinds of cut worms, the potato-beetle and the chinch-bug, with the 
large coral-winged grasshopper, bulk for bulk, the ratios will appear about as 
follows: 
1 coral-winged grasshopper = 12,000 military microgasters, 
1 coral-winged grasshoppers 8,000 phylloxera. 
1 coral-winged grasshoppers 1,500 corn plant-lice. 
1 coral-winged grasshopper s 750 chinch bugs. 
1 coral-winged grasshopper s 60 plum curculios. 
1 coral-winged grasshopper s 7 potato-beetles. 
1 coral-winged grasshoppers 1,000 young potato-beetles. 
By a system of gauging bulk for bulk, it is evident from the table that one 
coral-winged grasshopper eaten by a bird would give it a credit which would 
offset completely the destruction of 12,000 military microgasters, a proposition 
sufficiently absurd. The same system of gauging would also count the destruc¬ 
tion of seven adult Colorado potato-beetles as the full equivalent of 1,000 very 
