Vol. XXIX1 



1912 



J McAtee, Contents of Bird Stomachs. 463 



different elements of the food.) [A footnote in original]. In 

 recording the results of examinations a separate record is made 

 for each species and for each month. Monthly averages are based 

 on the number of stomachs collected in the month, but yearly 

 averages are determined from the monthly averages; for unless 

 the collections of stomachs were much more evenly distributed as 

 to months than they are at present, an average based directly on 

 the number of stomachs collected in the year would be misleading." 

 The results would be just so much more accurate if the abundance 

 and distribution of material warranted reduction of the time-unit 

 to a week, or better a day. The writer has proposed also, as a 

 further step toward accuracy, to reduce the disturbing effect of 

 peculiar local conditions by averaging the contents of stomachs 

 collected in one locality in the same month, and giving such aver- 

 ages (of more than a certain minimum number of stomach contents) 

 equal weights in the monthly tabulation. 



Summary. 



The principal objection to the method of reckoning the contents 

 of bird stomachs solely by the number of individual insects or 

 seeds, is that the method takes no account of size of the objects, 

 and hence conveys no idea to those unacquainted with the groups 

 concerned of the relative importance of the foot elements. 



Size has much to do with economic status — i. e., capacity for 

 good or harm — and it receives proper recognition only under the 

 percentage-by-bulk system. 



We have shown furthermore that statements as to the frequency 

 with which certain food items are taken by birds, by no means 

 indicate the importance of these items in the diet of the species. 

 Under the volumetric method however, the proportions the various 

 elements contribute to the animal's subsistence are evident at a 

 glance, and the animal's capacity for good and for harm are clearly 

 shown. 



Numerical notations in most cases greatly exaggerate the im- 



' Bull. 15. Biological Survey, 1901, pp. 14-15. 



