The Food of Bh-(]s. 93 



of this spontaneous restoration of the unsettled balance of 

 natural forces, are, of course, worthy of the most careful 

 study. It is only by working in harmony with them that we 

 ourselves can help to readjust the disturbed order. A fuller 

 treatment of this matter may best be postponed until the 

 general discussion of results obtained by the investigation. 

 Enough has been said to show that the subject, although 

 complicated and difficult, will richly repay the study nec- 

 essary to its mastery. A full and accurate knowledge of 

 the mutual relations of the various forms of organic life of 

 a region, both normal and abnormal, is certainly quite as 

 essential to the general welfare as a knowledge of the 

 chemistry and geology of its soils, the peculiarities of its 

 meteorology, or any other part of the inorganic environ- 

 ment. 



Concerning the special subject of this paper, the knowl- 

 edge we need is such that we shall be able to afford for 

 every species a tolerably correct answer to the questions, 

 What would be the main consequences if this species were 

 exterminated? if it were reduced to half its present num- 

 bers? What if it were doubled in number? if it were 

 quadrupled? When this is known, we shall evidently be 

 able to act wisely and with the best results. That these 

 questions are not unanswerable, I shall undertake to prove 

 by answering them in substance, for several species, in 

 this paper, and by demonstrating the sufficient accuracy 

 of the answers. 



Methods. 



Three methods are possible in determining the food of 

 birds. The birds may be fed in confinement, and the kinds 

 of food apparently preferred and the amount eaten may be. 

 noted. This evidently shows only what the bird ivlll eat 

 when restrained of its liberty, of such food as may be 

 placed before it, and furnishes few data which we can use 

 with safety in making up an account of its food in free- 

 dom, when foraging for itself. The state of confinement 

 is so abnormal for a bird that on this account, also, we can 

 rarely reason from its habits in that state to its ordinary 

 habits. This method is, therefore, available only for the 

 solution of a few separate questions. A far more useful 



