44 II. Bericht über das perman. intern, ornithol. Comit^. 



injurious; and many kinds which are really of great practical 

 value are killed whenever opportunity offers. For example, 

 hawks and owls collectively are almost universally regarded 

 as detrimental, while as a matter of fact several of them 

 never touch poultry but feed almost exclusively on mice 

 and grasshoppers, 



The Wholesale slaughter of small birds has been known 

 to be followed by serious increase of noxious insects. On 

 the other band, invasions of insects which threatened to 

 devastate large tracts of country have been cut nearly short 

 by the timely Services of some of our native birds. 



In view of the above facts, and many others which 

 might be cited, it is clear that a comprehensive systematic 

 investigation of the inter- relation of birds and agriculture 

 will prove of enormous value to farmers and horticulturists. 

 Such an investigation has been undertaken by the newly- 

 established branch of Economic Ornithology under the 

 Division of Entomology of the Department of Agriculture^ 

 and the assistance and co-operation of persons interested are 

 earnestly solicited. 



The food of all birds consists either of animal matter 

 or vegetable matter or both, and its comsumption must be 

 serviceable or prejudicial to the interests of mankind. There- 

 fore, according to the food they eat, all birds may be classed 

 under one of two headings — beneficial or injurious. Many 

 species are both beneficial and injurious, and it is impossible 

 to assign them to either category until the percentages of 

 their food-elements have been positively determined and the 

 sum of the good balanced against the sum of the evil. 



In a very large proportion of our small birds the food 

 varies considerably with the season , sometimes changing 

 from vegetable to animal, or from injurious to beneficial. 

 Furthermore, many birds feed their young upon substances 

 which the adults rarely or never eat; and the young on 

 leaving the nest sometimes greedily devour things which 

 are discarded as they grow older. Hence it becomes neces- 

 sary to ascertain the food of each species at different times 

 of the year, and at different ages. 



