452 McAtee, Contents of Bird Stomachs. [bet. 



F. H. King, who is thus quoted by Wilcox, further asks : ^ 



" How shall a bird's food account be expressed numerically in terms 

 of debit and credit? This is at once the most difficult and the most 

 important of all the questions requiring solution in order to express 

 the specific economic relations of any bird. 



" Nothing can be more certain than that, after the food of a bird 

 has been classified under the heads "Elements Beneficial" and 

 "Elements Detrimental" to man, neither the relative volumes nor 

 the relative weights of these two classes of material can express the 

 true economical relations of the bird. (p. 398.) 



"A peck of plums and a peck of curculios, a peck of wheat and 

 a peck of chinch-bugs, or a peck of corn and a peck of cutworms, 

 are manifestly not to be considered as equivalent values on opposite 

 sides of any account." (p. 399.) 



And Mason says as above noted "Comparative bulks of food, 

 if expressed merely as percentages, are of absolutel^^ no value what- 

 ever, and cannot give any idea as to the true economic ratio of the 

 food of the bird in question." 



First it should be stated that these gentlemen have no occasion 

 to be so emphatic; their criticisms are wide of the mark for no 

 one claims that percentages do express economic values. They are 

 simply convenient handles to facts and they must be interpreted. 



This point is well brought out by the arguments Wilcox advanced 

 in proposing his hybrid system. He says: 



" Having seen from the start that the ratios of the different food 

 materials could not justly be estimated according to bulk, and 

 having seen also that a system based upon the number of insects, 

 plant fruits, etc., found in the stomachs examined would be almost 

 equally likely to introduce error, and that it would be a system 

 particularly difficult to carry out in consequence of the fragmentary 

 condition of the food, I decided to combine these two systems of 

 computing the proportions in a way which seemed to me to repre- 

 sent justly all the elements of food. It would be approximately 

 true to say that I have estimated the proportion of animal food 

 according to the number of the individuals, and vegetable food 

 according to bulk. But all fruits which have a definite number of 



» Trans. Wis. State Agricultural Society, Vol. XXIV, 1886. 



