462 McAtee, Contents of Bird Stomachs. [q^' 



depended almost entirely on this .... method of investigation, 

 because it is evidently the most profitable and reliable, and be- 

 cause the method of cursory observation having been resorted to 

 heretofore, most of the recorded facts are due to it. So far as one 

 method could correct the deficiencies of the other, it was desirable 

 that this more tedious and laborious but more fruitful one should 

 be given greater prominence." (pp. 87-88). 



The volumetric method of stomach analysis has twice received 

 official sanction by the Biological Survey. In 1895 Professor W. B. 

 Barrows wrote that " In the case of a bird which eats insects only 

 it might be possible to use the numerical method with some ac- 

 curacy; yet even then much would have to be left to individual 

 judgment in estimating how many small insects were equivalent 

 to one large one, or how many harmful insects would be necessary 

 to offset the consumption of a given number of beneficial insects. 

 Moreover, only under the most favorable circumstances would it 

 be possible to determine just how many individuals of each kind 

 were represented in the stomach contents, for, even if swallowed 

 whole, so soon as digestion begins the individual insects become 

 dismembered, crushed and broken, and within a short time only 

 the hardest parts, such as heads, wing covers, legs, and jaws, remain 

 in recognizable condition. 



" It has seemed best, therefore, in attempting to determine the 

 proportions of the various food substances in Crow stomachs, to 

 depend upon the method of equal masses or bulks, which method 

 is adopted in the present bulletin. In most cases the number of 

 individual seeds, insects, or other animals has been recorded also, 

 but these numbers have not been considered in determining per- 

 centages." ^ 



In 1901 Dr. Sylvester D. Judd in describing the process of 

 stomach examination said: " After each element in a bird's stomach 

 has been identified and placed in a separate pile, the percentages of 

 the different elements are estimated by volume. (Of course it 

 must be understood that mathematical exactness is not attainable 

 in these examinations ; but every possible means is taken to reduce 

 the error to a minimum, and with a sufficient number of stomachs 

 a very correct idea may be obtained of the proportions of the 



1 Bull. 6, Biological Survey, 1895, pp. 28-29. 



