The Policemen of the Air 



81 



the bird. We must learn the 

 nature of its food at all times of 

 year, and then strike a fair bal- 

 ance between its good and its bad 

 deeds ; hence the absolute neces- 

 sity for the examination of the 

 contents of birds' stomachs, by 

 which means may be accurately 

 determined not only the kinds of 

 food eaten but their relative 

 quantities. This method is ex- 

 ceedingly slow and laborious, re- 

 quqires a high order of expert 

 ability, and moreover is open to 

 the very serious objection that 

 it necessitates the taking of use- 

 ful lives. So far as possible, 

 the latter objection has been min- 

 imized by utilizing the stomachs 

 of birds killed by naturalists for 

 scientific purposes. This mate- 

 rial, which otherwise would be 

 lost to economic science, renders 

 it unnecessary, except in special 

 cases to destroy birds for the 

 purpose of food examinations. 



In the above connection it 

 must not be forgotten that when 

 a thorough examination of the 

 food of a given species is once 

 made and the results published, 

 the work is done for all time. The food 

 habits of a species having been once de- 

 termined by this method, no possible ex- 

 cuse exists, so far as food investigations 

 go, for further destruction of bird life ; 

 and the more so because the contents of 

 all stomachs examined are preserved as 

 vouchers for further verification, should 

 that be deemed necessary. 



Passing to a consideration of some of 

 the practical problems presented, it might 

 seem that the relation of birds to agricul- 

 ture were simple, since the question is 

 chiefly one of food. Do birds destroy 

 crops? then of course they are injurious. 

 Do they eat insects? then of a certainty 

 they must be beneficial. But the problems 

 are not to be settled in this off-hand fash- 

 ion. In reality they are extremely com- 

 plex and are to be understood only after 

 much painstaking study. It has been 



From the Biological Survey 

 SPARROW HAWK 



Which helps the farmer by eating grasshoppers, crickets, 

 and beetles (see page 85-) 



found, for instance, that a bird may be in- 

 jurious at one time and not another. In 

 one region it may be a pest and in another 

 an unmixed blessing. Some birds — un- 

 fortunately not many — are always bene- 

 ficial. Others — fortunately not many — 

 are always and everywhere injurious. 

 But the great bulk of birds are both harm- 

 ful and beneficial by turns, according to 

 age, season of the year, the presence or 

 absence of their natural food, and a va- 

 riety of circumstances. 



the; tree; sparrows very beneftciai, 



For present purposes we may roughly 

 group the bulk of our small birds into two 

 classes — seed-eaters and insect-eaters. 

 The seed-eaters, mostly of the sparrow 

 family, have stout bodies and strong coni- 

 cal bills, expressly designed for crushing 

 seeds. Their name is legion and the 



