16 THE RELATION OF SPARROWS TO AGRICULTURE. 



would eat on another farm where the food supph' was identical. This 

 line of research might be continued until it could be foretold with 

 reasonable certaint}^ which of the different objects in the accessible 

 food supply of a locality a given bird would i^robabl}^ select. 



In recapitulation it may be stated that in the investigation of the 

 food habits of any bird the first thing to be done is to examine enough 

 stomachs to obtain a general idea of the bird's food, so that intelligent 

 field work may be done. Then the observer should go to some favor- 

 able spot, note carefully the different kinds of available food, watch 

 the birds feeding for a while, and collect stomachs for examination. 

 In this way it will be possible to ascertain what a bird will eat, what 

 it prefers, and what it will refuse. 



CLASSIFICATION OF BIRD FOOD. 



To aid in reaching final conclusions as to the economic X30sition of 

 a bird it lias been found convenient to divide the food into three cate- 

 gories according as its consumption tends to produce a (1) beneficial, 

 (2) injurious, or (3) inappreciable effect on agriculture. The bene- 

 ficial part consists chiefly of insect pests and weed seed, tlie-injurious 

 part consists largely of insect enemies of insect pests and plunder 

 from cultivated crops, and the neutral ivdrt comprises neutral insects 

 and the fruits and seeds of plants of no economic importance. The 

 relations which these three parts of the food bear to one another deter- 

 mine in large measure the economic status of a bird. 



Of course, there can be no hard and fast rule in the luatter. The 

 beneficial and injurious elements of the food are marked b}^ infinite 

 degrees of gradation, and qualit}" must be considered as well as quan- 

 tit}^ The importance of the consumption of wheat varies greatly 

 according to whether the grain is taken from the newly sown field, 

 the growing crop, the stubble, or the shock. Insects may be either 

 serious pests or insignificant in power to damage croi)s, with every 

 shade of injuriousness between these extremes. 



The abundance of a bird has also much weight in fixing its value. 

 A si)ecies must be numerous, must live among cultivated crops, and 

 must take food that has a close connection with agriculture in order 

 to produce an}^ significant effect on the farm. 



The neutral element of the food must uot be overlooked. The 

 greater its proportion the more abundant must the bird be in order 

 to produce any effect either one way or the other. With mau}^ shore 

 and woodland birds it is so large, in companson with the injurious 

 or beneficial parts, that it is likely that such birds have scarcely any 

 effect in rural economy. 



These and man}^ other like factors have to be considered in deciding 

 a bird's economic status; but for a rough general estimate it is safe 

 to assume that a bird that feeds on insects, seeds, and fruit, and is 

 abundant on a farm, will do more good than harm, and usually be 



