^'"^Oif^"'^] McAtee, Contents of Bird Stomachs. 451 



In striking contrast to the diversity of opinion about a numerical 

 system is the consistent application of the volumetric method, 

 by at least 9 American food analysts. Dr. G. Rorig of Germany 

 prefers the related but more technical and difficult method of 

 ascertaining proportions by weight. 



Some of Wilcox's objections to the percentage-by-bulk system 

 are stated in the following quotation.^ 



"How to estimate the relative proportions of the various food 

 matters found in the stomachs examined is a very important but 

 rather difficult question. Upon a slight consideration it becomes 

 evident that we cannot base our proportions upon the relative 

 bulk of different materials. To illustrate, suppose we place on one 

 side of the equation a blackberry and on the other enough chinch 

 bugs to equal the bulk of the berry. It would obviously be very 

 absurd to assume that the one counterbalances the other. Mr. 

 King. . . .has considered this difficulty in the following words: 



" If we compare the corn plant-louse, the gall stage of the grape 

 phylloxera, the plum curculio, the small parasitic military micro- 

 gaster, which lay its eggs in several kinds of cutworms, the potato 

 beetle and the chinch bug with the large coral-winged grasshopper 

 bulk for bulk, the ratios will appear about as follows : 



1 Coral-winged grasshopper = 12,000 military microgasters. 



3,000 phylloxera. 

 1,500 corn plant-lice. 

 750 chinch bugs. 

 60 plum curculios. 

 7 potato beetles. 

 1,000 young potato beetles. 



" By a system of gauging bulk for bulk it is evident from the table 

 that one coral-winged grasshopper eaten by a bird would give it a 

 credit which would offset completely the destruction of 12,000 mili- 

 tary microgasters, a proposition sufficiently absurd." 



We may remark that Wilcox's own system of estimating the 

 proportions of animal food according to the number of individuals, 

 violates every intent of this precept, as it also gives all individuals 

 equal weight. 



1 Wilcox, E. v. Bui. 43, Ohio Agric. Exp. Sta., Sept., 1892, pp. 118-119. 



