122 TRANSACTIONS OF THE ILLINOIS 



irretrievable financial ruin of nearly our whole population. That so 

 gigantic a natural force as they seem to constitute, almost as necessary to 

 us as the light of the sun or the rains of heaven falling in their season, 

 should not have been carefully investigated long ago, in all its results and 

 relations, is certainly a surprising phenomenon. What should we say of 

 the intelligence and capacity of the mechanical engineers of America, if 

 we should learn that, notwithstanding the enormous waste of force in a 

 locomotive engine, no thorough scientific investigation by competent 

 physicists had ever even been attempted of the laws governing the trans- 

 mutation of fuel into mechanical work ? Let us hope that our agricul- 

 turists and horticulturists will require and sustain investigations into the 

 laws and forces of nature relating to their calling as precise and elaborate 

 as those made in the interest of far less important industries. This 

 investigation would well repay its trifling cost, if it should have no other 

 effect than to give us an intelligent acquaintance with the subject; but 

 we already see the way open to recommendations of practical value. 



I wish to say beforehand, however, that if any are listening to me 

 with the hope of learning from this paper whether we should destroy or 

 cherish any one bird or group of birds, they will certainly be disap- 

 pointed. I have no positive conclusion to offer. If positive assertions 

 are wanted, a plenty of them are already extant; nearly every work on 

 ornithology abounds in them. 



Many papers have been published in this country settling this exceed- 

 ingly complex and difficult question out of hand, without so much as a 

 glance at a microscope. The time has come for the hesitation and 

 uncertainty of careful and impartial study, and of a cautious balancing of 

 evidence; for the modified and guarded judgment of those who are at 

 least prepared to understand their own ignorance and to realize some of the 

 conditions of the problem. 



I will not now enter into the details of the work that has hitherto 

 been done in this country, but will only say that it all seems to me fatally 

 defective as a basis for sound opinion or definite action, for this reason, 

 if for no other, that scarcely an attempt has been made to determine 

 the relative amounts of the different elements of the food of each species. 



The fact is that birds have their preferences among the objects 

 which they will eat. With several appropriate articles of food around 

 them in equal abundance, they will, for some reason, certainly select 

 some and neglect others. These preferences have, of course, a great 

 deal to do with the value of the species, and often determine the case, 

 as we shall presently see. They can be discovered only by noting the 

 relative amounts of these different elements in the stomachs of all the 

 birds examined and averaging these ratios for each species. I do not 

 know of a single case in which this has been attempted, except in a paper 

 by Mr. Samuels, of New England, on the birds of Massachusetts, and this 

 author has contented himself with giving in percentages the relative 

 numbers of birds in which the different elements mentioned were found. 

 If five per cent, of his birds have eaten caterpillars, for example, he 

 concludes that caterpillars constitute five per cent, of the food of all, a 



