88 
The Food of Birds . 
dollars per annum, equivalent to the addition of over one 
and one-half million dollars to the permanent value of 
our property; or, if, as is in fact a most moderate esti- 
mate, we should succeed in increasing the efficiency of 
birds five per cent., we should thereby add eight and one- 
fourth million dollars to the permanent wealth of the 
State, provided, as before, that birds do not eat unduly 
of beneficial species. 
These figures will be at once rejected by most natural- 
ists as absurdly low. The young robin of Prof. Treadwell 
(a bird whose fame has extended over both hemispheres) 
required not less than sixty earthworms a day to keep it 
alive. A pair of European jays have been found, Dr. 
Brewster informs us, to feed their brood half a million 
caterpillars in a season, and to eat a million of the eggs 
in a winter. I have myself taken one hundred -and seven- 
ty-five larvae of Bibio from the stomach of a single robin, 
and the intestine probably contained as many more. 
Compared with these numbers, my two thousand four 
hundred insects a year for each bird seem certainly many 
times too few; and similar criticisms might very prob- 
ably be made on other items of the estimate. I prefer, 
however, to put these matters with a moderation which 
will command general assent, especially as we see that 
the importance of the subject does not require exaggera- 
tion. Of course the individual farmer or gardener could, 
by intelligent and careful management, if he knew just 
what to do, increase the value of his own birds far beyond 
his individual share of the above-mentioned aggregate. 
The subject has, also, a considerable scientific interest. 
Since the struggle for existence is chiefly a struggle for 
subsistence, a careful comparative account of the food of 
various competing species and genera, at different places 
and seasons and at all ages of the individual, such as has 
not heretofore been made for any class of animals, can- 
not fail to throw much light upon the details, causes and 
effects of this struggle. The flexibility of the food-habits 
of the widely ranging species, the direct effects of normal 
departures from the usual average of food elements upon 
the origin of variations and the general reactions of bir 1 ' 
