107 
inant as to prejudice his conclusions. But with all its disadvan- 
tages it remains an always open field for the critical observer and 
if done by the aid of good field glass, or by the aid of the camera: 
during the feeding of young, may become fruitful of excellent 
results. 
That neither of these methods alone is sufficiently conclusive 
is evident in that neither has found perfect agreement in the 
hands of different observers. It may be well to point out in this 
connection some of the sources of error in the first as has also 
been done in the second. 
One of the first difficulties encountered in an examination of 
the stomach contents of birds is the promiscuous mixture and 
mutilated and semi-digested condition of much of the food con- 
tents which in many cases renders actual indentification largely 
impossible. ‘To estimate the number or amount of insect food 
from the fragments of a few elytra or disarticulate segments of 
legs can best only be an approximation. A further difficulty and 
one more serious to my mind than the first is the almost impossi- 
ble task of making any equitable comparison as to the relative 
importance and equivalence of beneficial or harmful elements. 
Certainly a comparison of bulk in most cases would be mani- 
festly absurd. For example, the bulk of a single blackberry 
would outmeasure a thousand plant aphids or chinch-bugs, yet 
as to economic balance of the two masses it would be glaringly 
absurd to claim equivalence. So too of cut worms or straw- 
berries, May-beetles and May cherries. ‘To presume upon an 
equivalence here, or to meet out praise or blame, as the one or the 
other element might predominate, would be hasty and uncritical. 
Again it seems to me that it 1s equally unscientific to insti- 
tute a comparison and contrast even between the so-called bene- 
ficial elements as against injurious or neutral. To class all berry 
seeds as among the beneficial is uncritical. Who will presume to 
distinguish between the seeds of the wild and cultivated berry? 
How much of the wild fruit under present conditions is to be 
claimed as of economic importance and value? <A very large 
measure of it must under the most favorable conditions go to 
waste unless used by birds or other fruit eating animals, and to 
