^°'i9if ^"^1 McAtee, Contents of Bird Stomachs. 453 



seeds have been estimated upon a numerical basis. It is evident 

 that this would have been very difficult or even impossible in the 

 case of blackberries or raspberries in which the number of seeds is 

 so variable. 



"It may be objected that the computation of the vegetable 

 food on one basis and of the animal food upon another basis is a 

 fruitful source of error. But I have exercised all care and diligence 

 to avoid every possibility of error, and, in fact, an estimation of 

 the relative proportions of the several kinds of food would not make 

 the vegetal part appear larger than it really is, since a raspberry 

 or blackberry is no greater in bulk than an earthworm or May 

 beetle. It may as well be admitted that, in the present state of 

 knowledge, only an approximation to the truth can be attained 

 in a statement of the relative proportion of the various food mate- 

 rials in a bird diet. 



"But even after we have tabulated the numerous articles of food 

 in their differing proportions in a more or less satisfactory manner, 

 the task is by no means completed. In order that we may decide 

 whether the robin is on the whole a benefit or an injury to farmers 

 and gardeners, we must first determine the economic relations of 

 the various species of plants and animals upon which the robin 

 feeds." 



It is very evident that interpretation of economic values is the 

 most important point in presenting the results of stomach examina- 

 tion. Whether such results are expressed by the numerical or by 

 the percentage system, the figures in themselves are powerless to 

 convey an impression of economic values. Hence the assertions 

 of Mason, King and others are no more a criticism of the percentage- 

 by-bulk system than they are of the numerical system. For 

 instance King's dictum that "a peck of corn and a peck of cut- 

 worms are manifestly not to be considered as equivalent values on 

 opposite sides of any account," applies just as well to his own nu- 

 merical accounts. Does it mean anything definite to say that 10 

 individuals of a certain species of bird have consumed 20 beneficial 

 insects and 35 injurious ones? Do these figures tell us whether 

 the insects in question are large or small? Whether they are 



1 Bull. 43, Ohio Agric. Exp. Sta., Sept., 1892. pp. 119-120. 



